JP2011142794A - Power conversion system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein, if a power switching element Swp on the high-potential side is turned on, under a situation where a current is flowing in a freewheel diode Fwn, connected reverse parallel with a power switching element Swn on the low potential side, a surge is generated due to the recovery current of the freewheel diode Fwn. <P>SOLUTION: When the power switching element Swp on the high-potential side is turned on, the power switching element Swn on the low-potential side is also kept in an on state, to thereby perform shoot-through control in which both power switching elements are turned on. Thereafter, when the current flowing in the power switching element Swn at the low-potential side becomes zero and then starts to flow in the opposite direction, the power switching element Swn on the low-potential side is turned off. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a series connection of a high potential side switching element for connecting the first inductor to the positive electrode side of a DC power supply and a low potential side switching element for connecting the first inductor to the negative electrode side of the DC power supply. The present invention relates to a power conversion system including a body.

  As this type of power conversion system, for example, as seen in Patent Document 1 below, an electric path including an inductor and an electric path not including an inductor are provided between an upper arm of an inverter and a DC power source. A device having a switching element in each path has also been proposed. According to this, with the switching elements of the pair of electric paths turned off, the switching element to be turned on is changed from the switching element (low potential side switching element) of the lower arm to the switching element (high potential side switching) of the upper arm. Switching to the element) enables zero voltage switching. Further, by turning on the switching element of the electric path including the inductor prior to the turning-on operation of the switching element of the electric path not including the inductor, the ON operation of the switching element of the electric path not including the inductor is switched to zero current. It is described that it can be.

Japanese National Patent Publication No. 11-506599

  However, in the above case, for example, if the switching element of the upper arm is turned on while the current flows through the diode connected in reverse parallel to the switching element of the lower arm, a large surge is generated due to the recovery current of the diode. Such problems arise.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a high-potential side switching element for connecting the first inductor to the positive electrode side of a DC power supply, and the first inductor to the DC power supply. An object of the present invention is to provide a power conversion system capable of suitably suppressing a surge when switching the switching state of a low potential side switching element for connection to the negative electrode side of the power source.

  Hereinafter, means for solving the above-described problems and the operation and effect thereof will be described.

  The invention according to claim 1 is a high potential side switching element for connecting the first inductor to the positive electrode side of the DC power supply, and a low potential side switching element for connecting the first inductor to the negative electrode side of the DC power supply. In a power conversion system comprising a series connection body, a free wheel diode is connected in reverse parallel to one of the high potential side switching element and the low potential side switching element, and among the pair of terminals of the DC power supply A second inductor connected between the terminal connected to the first inductor by the other switching element connected in series to the one switching element and the other switching element, and the other switching element turned on When switching to the shoot through control means for turning both on, and the chute -After the both are turned on by the control means, the one switching element is switched after the time when the total current flowing through the one switching element and the freewheel diode connected in reverse parallel to the switching element becomes zero. And an off operation means for performing an off operation.

  In the above invention, since the shoot-through control means is provided, it is possible to suitably suppress or avoid a current flowing through the free wheel diode and a recovery current flowing through the free wheel diode. For this reason, it is possible to suppress a change in current when the other switching element is turned on or one of the switching elements is turned off.

  According to a second aspect of the present invention, in the first aspect of the invention, the off-operation means turns off the one switching element after the total current becomes zero.

  In the above invention, the current flowing through the second inductor is larger than the current flowing through the first inductor at the time when one of the switching elements is turned off. When one switching element is turned off, the current flowing through the other switching element gradually decreases from the current flowing through the second inductor to the current flowing through the first inductor. The gradual decrease speed at this time can be adjusted by the switching speed at which one of the switching elements is switched from the on state to the off state.

  According to a third aspect of the invention, there is provided the loop circuit according to the second aspect of the invention, further comprising a loop circuit that bypasses the one switching element and connects both ends of the second inductor. Rectification means is provided that allows the current flowing in the second inductor to flow in when one of the switching elements is turned off and regulates the current in the direction opposite to the current.

  If one of the switching elements is turned off after the absolute value of the total current becomes zero, at this time, the current flowing through the second inductor is larger than the current flowing through the first inductor. In the above invention, by providing the loop circuit, when one of the switching elements is turned off, a difference current between the current flowing through the second inductor and the current flowing through the first inductor is supplied to the loop circuit. It can flow.

  According to a fourth aspect of the invention, in the third aspect of the invention, the loop circuit includes the DC power source.

  In the said invention, since a loop circuit is provided with DC power supply, it becomes possible to collect | recover the electric energy which flows through a loop circuit in DC power supply.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein a capacitor is connected in parallel to both ends of the series connection body or to both ends of the one switching element. And

  In the above invention, the rate of voltage increase between the input terminal and the output terminal when one switching element is turned off can be controlled by the capacitance of the capacitor.

  A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects, wherein an electrode side connected to the first inductor by the other switching element of the pair of electrodes of the DC power supply is provided. A first electric path connected to the other switching element and provided with the second inductor; first opening / closing means for opening and closing the first electric path; and the other switching of the pair of electrodes of the DC power supply A second electric path connecting the electrode side connected to the first inductor by the element and the other switching element and not having the second inductor, and a second opening / closing means for opening and closing the second electric path; Are further provided.

  In the above invention, after the second inductor suppresses a sudden increase in the current flowing through the series connection body during shoot-through control, the first opening / closing means is opened and the second opening / closing means is closed. By doing so, the inductance between a direct-current power supply and a serial connection body can be reduced.

  A seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, a free wheel diode is connected in antiparallel to each of the first opening / closing means and the second opening / closing means.

  The invention according to claim 8 is the invention according to claim 7, wherein a free wheel diode is connected in antiparallel to the other switching element, and the first switching element is connected to the first switching element by the other switching element. The second inductor is connected to the electrode side connected to the inductor via the first opening / closing means, and the first inductor is connected to the first switching element among the terminals of the DC power supply. Prior to switching the switching element for energy storage that opens and closes between the terminal and the first opening / closing means and the second inductor and the one switching element to the ON state, the first opening / closing means is opened. Further, by turning on the energy storage switching element with the second opening / closing means closed, the other switch can be turned on. An energy storage processing means for performing a process of flowing a current flowing in at least one of the chucking element and a free wheel diode connected in reverse to the second inductor to the second inductor; the second opening / closing means; and a free wheel connected in reverse parallel thereto And a means for opening the second opening / closing means after the time when the total current flowing through the diode becomes zero.

  In the above invention, when the energy storage switching element is turned on, a current flowing through at least one of the other switching element and a free wheel diode connected in reverse parallel to the second switching element is caused to flow through the second inductor, The total current flowing through the freewheeling diode connected in reverse parallel to this can be reduced as the current flowing through the second inductor increases. Then, after the time when the total current flowing through the second opening / closing means and the freewheel diode connected in reverse parallel thereto becomes zero, the second opening / closing means is opened to be connected in reverse parallel to the second opening / closing means. It is possible to avoid a recovery current from flowing through the freewheeling diode.

  The invention according to claim 9 is the first shoot-through control means in the invention according to claim 8, wherein when the other switching element is switched to the on state, the shoot-through control means for turning both of them on is the first shoot-through control means. After the energy storage switching element is turned on by the energy storage processing means, the second shoot-through control means for turning both one of the switching elements on when the one switching element is turned on, and the second chute After the both are turned on by the through control means, the total current flowing through the means for turning off the energy storage switching element and the other switching element and the freewheel diode connected in reverse parallel thereto becomes zero. After that time, the other switching element is turned off. And further comprising a stage.

  In the above invention, after the time when the total current flowing through the other switching element and the freewheel diode connected in reverse parallel thereto becomes zero, the other switching element is turned off. Even if it is flowing, the voltage applied to the freewheeling diode when the forward current becomes zero can be made zero. For this reason, it can avoid suitably that a recovery current flows into this free wheel diode.

The invention according to claim 10 is a high potential side switching element for connecting the first inductor to the positive electrode side of the DC power source, and a low potential side switching element for connecting the first inductor to the negative electrode side of the DC power source. In a power conversion system comprising a series connection with
A free wheel diode is connected in reverse parallel to the other switching element connected in series to one of the high potential side switching element and the low potential side switching element, and connected to the first inductor by the other switching element. A second inductor connected between the terminal to be connected and the other switching element, and the second inductor from the second inductor side connected to the first inductor by the other switching element The first inductor is connected between the free wheel diode whose forward direction is the direction toward the electrode, the free wheel diode and the second inductor, and the one switching element among the terminals of the DC power supply. Switching for energy storage that opens and closes to the side terminal An electrode connected to the first inductor by the other switching element of the pair of electrodes of the DC power source and the first inductor, and opens and closes an electrical path that does not include the second inductor And switching the energy storage switching element in a state in which the switching means is closed prior to switching the one switching element to the ON state. By operating, an energy storage processing means for performing a process of flowing a current flowing through at least one of the other switching element and a free wheel diode connected in reverse parallel thereto to the second inductor, an opening / closing means and a reverse thereof When the total current flowing through the freewheeling diodes connected in parallel becomes zero Characterized in that it comprises a opening operation means for opening operation of the switching means in the following.

  In the above invention, when the energy storage switching element is turned on, a current flowing through at least one of the other switching element and a free wheel diode connected in reverse parallel thereto is caused to flow to the second inductor, thereby opening and closing means and The total current flowing through the freewheeling diodes connected in reverse parallel can be reduced as the current flowing through the second inductor increases. Then, after the time when the total current flowing through the switching means and the free wheel diode connected in reverse parallel thereto becomes zero, the recovery current is supplied to the free wheel diode connected in reverse parallel to the switching means by opening the switching means. Can be prevented from flowing.

  According to an eleventh aspect of the present invention, in the invention according to the tenth aspect, after the energy storage switching element is turned on by the energy storage processing means, the one switching element is switched to the on state. Control means for turning on, means for turning off the energy storage switching element after both are turned on by the control means, the other switching element, and a freewheel diode connected in reverse parallel thereto And a means for turning off the other switching element after the time point when the total current flowing through becomes zero.

  In the above invention, after the time when the total current flowing through the other switching element and the freewheel diode connected in reverse parallel thereto becomes zero, the other switching element is turned off. Even if it is flowing, the voltage applied to the freewheeling diode when the forward current becomes zero can be made zero. For this reason, it can avoid suitably that a recovery current flows into this free wheel diode.

  According to a twelfth aspect of the present invention, in the invention of the ninth or eleventh aspect, the energy storage switching element and the second inductor are connected rather than a free wheel diode connected in reverse parallel to the one switching element. The free wheel diode is characterized in that the rate of change of the recovery current is smaller.

  In the above invention, when the total current flowing through the other switching element and the freewheel diode connected in reverse parallel thereto becomes zero, the current of the freewheel diode becomes zero, and a high voltage is applied to the current. Current flows. However, since the rate of change is small, surge can be suppressed.

  A thirteenth aspect of the invention is the invention according to any one of the eighth to twelfth aspects, wherein the opening operation means includes an opening / closing means connected between the second inductor and the other switching element. The opening / closing means is turned off after the total current flowing through the freewheel diodes connected in reverse parallel becomes zero.

  In the above invention, it is possible to reliably avoid a current from flowing through the freewheeling diode when the opening / closing means is turned off.

  A fourteenth aspect of the present invention is the invention according to any one of the first to thirteenth aspects of the present invention, wherein the pair of switching elements are configured such that an electric current flows between the pair of terminals by switching the input terminal and the output terminal. It is allowed to flow in the direction.

  In the said invention, it can avoid suitably that an electric current flows into a freewheel diode by shoot through control.

1 is a system configuration diagram according to a first embodiment. FIG. The time chart which shows the operation method of the power converter circuit concerning the embodiment. The time chart which shows the operation method of the conventional power converter circuit. The time chart which shows the simulation result of the effect of the said embodiment. The time chart which shows the simulation result of the effect of a prior art. The system block diagram concerning 2nd Embodiment. The system block diagram concerning 3rd Embodiment. The system block diagram concerning 4th Embodiment. The time chart which shows the operation method of the power converter circuit concerning the embodiment. The time chart which shows the simulation result of the effect of the embodiment.

(First embodiment)
Hereinafter, a first embodiment in which a power conversion system according to the present invention is applied to a system including an inverter connected to an electric motor will be described with reference to the drawings.

  The illustrated electric motor 10 is a three-phase rotating machine, and specifically may be a synchronous machine, for example. The electric motor 10 is connected to the battery 12 via the inverter IV. Here, the inverter IV is configured by connecting in parallel three serially connected bodies of a power switching element Swp on the high potential side and a power switching element Swn on the low potential side. And the connection point of each of these series connection bodies is connected to each phase of the electric motor 10, respectively. Between the input / output terminals (between the drain and source) of the high potential side power switching element Swp and the low potential side power switching element Swn, there is a high potential side freewheel diode Fwp and a low potential side freewheel diode. The cathode and anode of Fwn are connected.

  A main switch Swm, a sub switch Sws, and an input side inductor L are connected between the power switching element Swp on the high potential side of the inverter IV and the positive electrode of the battery 12. A diode D whose forward direction is the direction from the negative electrode side to the connection point side is connected between the connection point between the sub switch Sws and the input-side inductor L and the negative electrode of the battery 12.

  The control device 20 controls the operation signals gup, gvp, gwp for operating the power switching element Swp for each of the U phase, the V phase, and the W phase of the inverter IV based on detection values of various sensors (not shown), Operation signals gun, gvn, and gwn for operating the switching element Swn are generated and output. Thereby, the switching elements Swp and Swn are operated by the control device 20. Further, the control device 20 outputs operation signals gm and gs to the main switch Swm and the sub switch Sws, respectively. Accordingly, the main switch Swm and the sub switch Sws are operated by the control device 20.

  The power switching elements Swp and Swn, the main switch Swm, and the sub switch Sws are all N-channel super junction MOS field effect transistors. A body diode is formed in these. That is, for example, a free wheel diode Fwp is connected in reverse parallel to the high potential side power switching element Swp, and a free wheel diode Fwn is connected in reverse parallel to the power switching element Swn on the low potential side.

  The super junction MOS field effect transistor has a very high rate of decrease after the recovery current of the body diode has changed from increasing to decreasing. For this reason, a surge due to a change in the recovery current may be particularly large. Therefore, in this embodiment, this problem is dealt with by the switching operation shown in FIG.

  FIG. 2 shows a switching operation method according to the present embodiment. Specifically, FIG. 2A shows the transition of the operation mode of the sub switch Sws, FIG. 2B shows the transition of the operation mode of the main switch Swm, and FIG. FIG. 2D shows the transition of the operation mode of the low-potential side power switching element Swn in phase with the power switching element Swp of FIG. 2C. FIG. 2 (e) shows the transition of the current iL flowing through the input-side inductor L (see FIG. 1 for the sign), and FIG. 2 (f) shows the current flowing through the sub switch Sws etc. (including the body diode). FIG. 2G shows the transition of the current im that flows through the main switch Swm and the like (including the body diode). Further, FIG. 2 (h) shows the transition of the current ip flowing through the power switching element Swp on the high potential side and the like (including the body diode: see FIG. 1 for the sign), and FIG. 2 (i) shows the low potential side. FIG. 2 (j) shows the transition of the current in flowing through the power switching element Swn and the like (including the body diode; reference numeral: see FIG. 1), FIG. 2 (j) shows the transition of the current flowing through the diode D, and FIG. FIG. 2 shows the transition of the voltage V1 at the connection point between the sub switch Sws and the input-side inductor L, and FIG. 2L shows the transition of the voltage V2 between the power switching elements Swp and Swn. In the following, it is assumed that a current flows from the inverter IV to the electric motor 10 in the target phase.

  As illustrated, the period T0 is a period in which the high-potential side power switching element Swp is in an off state and the low-potential side power switching element Swn is in an on state. Here, in the period T1, when the high-potential side power switching element Swp is switched to the ON state, the low-potential side power switching element Swn is intentionally maintained in the ON state in the present embodiment. Thereby, also in the period T1, a current flows through the electric motor 10 via the power switching element Swn on the low potential side, and no current flows through the free wheel diode Fwn. This is because the amount of voltage drop when a current flows through the body diode (Fwn) is larger than the amount of voltage drop when a current flows through the power switching element Swn. Thus, by performing control (shoot-through control) to turn on both of the power switching elements Swp and Swn, the dead time period is eliminated, and thus a situation in which current flows through the body diode is avoided.

  In the period T1 during which the shoot-through control is performed, the increase rate of the current flowing through the high-potential-side power switching element Swp is limited by the input-side inductor L, and therefore gradually increases. That is, in the ON state of both of the power switching elements Swp and Swn, which should normally be avoided until the dead time is provided, since the input-side inductor L is provided, the current flowing through these power switching elements Swp and Swn increases rapidly. Thus, an excessive current that causes a decrease in reliability does not flow. Here, the current ip flowing through the high-potential-side power switching element Swp is equal to the current flowing through the input-side inductor L and the current is flowing through the sub-switch Sws, and the increasing speed thereof indicates the inductance of the input-side inductor L as “L”. And the input voltage VDC, “VDC / L”. As this current increases, the absolute value of the current flowing through the power switching element Swn on the low potential side decreases. That is, the current flows through the power switching element Swn on the low potential side due to the force to continue to flow the phase current due to the output side inductor (the inductor of the electric motor 10). It is covered by the current flowing through the power switching element Swp. For this reason, the absolute value of the current flowing through the power switching element Swn on the low potential side decreases.

  Then, after the absolute value of the current flowing through the low-potential-side power switching element Swn becomes zero (after the current flow direction is reversed), the low-potential-side power switching element Swn is turned off, so that the period T2 Migrate to In this case, the current flowing through the power switching element Swp on the high potential side decreases to the same amount of current as the phase current. On the other hand, the current flowing through the power switching element Swn on the low potential side decreases to zero. These reduction speeds are controlled by the switching speed (gate discharge speed) of the power switching element Swn from the on state to the off state. Here, the current flowing in the power switching element Swn immediately before the power switching element Swn on the low potential side is turned off is an amount obtained by subtracting the phase current from the current flowing in the input side inductor L. Since this current is flowing through the input-side inductor L, it cannot be rapidly reduced to zero even when the power switching element Swn is switched to the off state, and the body diode of the main switch Swm, the sub switch Sws, and A loop circuit including the input side inductor L flows. For this reason, in the period T2, the current flowing through the input-side inductor L and the current flowing through the sub switch Sws are not reduced. In addition, by shifting to the period T2, the voltage V2 at the connection point of the power switching elements Swp and Swn rises to the input voltage VDC.

  Thereafter, the main switch Swm is turned on to shift to the period T3. As a result, the current flowing through the body diode of the main switch Swm flows between the input terminal and the output terminal of the main switch Swm. Here, the main switch Swm is turned on after the low-potential-side power switching element Swn is switched to the off state.

  Thereafter, the sub switch Sws is turned off to shift to the period T4. As a result, the current flowing through the sub switch Sws becomes zero. The decreasing speed of the current flowing through the sub switch Sws is controlled by the speed at which the sub switch Sws is turned off (gate discharge speed). However, even if the current flowing through the sub switch Sws becomes zero, the current flowing through the input-side inductor L does not become zero in synchronization with this. The current flowing through the input side inductor L is output to the electric motor 10 via the high potential side power switching element Swp. However, this current decreases as determined by the voltage VDC of the battery 12 and the inductance of the input-side inductor L. For this reason, since the current flowing through the input-side inductor L is smaller than the phase current, the current from the battery 12 is output to the electric motor 10 via the main switch Swm and the high-potential side power switching element Swp. Note that, in a period in which the current flowing through the input-side inductor L is larger than the phase current, the excess flows through a loop circuit including the main switch Swm, the battery 12, the diode D, and the input-side inductor L.

  Then, when the current flowing through the input-side inductor L becomes zero and the diode D is turned off, the period shifts to the period T5. In the period T5, the voltage V1 at the connection point between the sub switch Sws and the input-side inductor L rises to the voltage VDC of the battery 12.

  Thereafter, the main switch Swm and the high-potential side power switching element Swp are turned off to shift to the period T6.

  FIG. 3 shows a comparison target with the switching operation of the present embodiment. Here, a case is shown in which the shoot-through control is not performed and the high-potential side power switching element Swp and the low-potential side power switching element Swn are alternately turned on. In this case, after the power switching element Swn on the low potential side is switched to the off state, a current flows through the free wheel diode Fwn connected in reverse parallel thereto. This current decreases as the current flowing through the power switching element Swp on the high potential side increases and becomes zero. As a result, a recovery current flows through the freewheel diode Fwn, and this current increases and then rapidly decreases to zero. This rate of decrease is unique to the device and cannot be controlled. In particular, when a super junction MOS field effect transistor is used as the power switching element Swn, it is known that the recovery rate of the recovery current of the body diode is large. For this reason, surge tends to increase.

  FIG. 4 shows a simulation result about the effect of the present embodiment, and FIG. 5 shows a simulation result of the comparison target.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) When switching the power switching element Swp on the high potential side to the on state, shoot-through control is performed to turn on both the power switching element Swn on the low potential side and the power switching element Swp on the high potential side. Further, after the total current flowing through the low potential side power switching element Swn and the free wheel diode Fwn became zero, the low potential side power switching element Swn was turned off. In other words, the low potential side power switching element Swn is turned off after the current flowing through the high potential side power switching element Swp matches the current flowing through the input side inductor L. As a result, it is possible to preferably avoid a current from flowing through the freewheeling diode Fwn on the low potential side, and thus a surge due to the recovery current can be preferably avoided.

  (2) A diode D having a forward direction from the negative electrode side of the battery 12 to the connection point side of the sub switch Sws and the input side inductor L is provided. As a result, when the power switching element Swn on the low potential side is turned off, the difference current between the current flowing through the input-side inductor L and the phase current can be passed through the loop circuit including the diode D, The battery 12 can be recovered.

  (3) The main switch Swm, the sub switch Sws, and the input-side inductor L are connected in parallel between the positive electrode of the battery 12 and the power switching element Swp on the high potential side. As a result, after the current flowing through the power switching elements Swp and Swn during the shoot-through control is suppressed by the input-side inductor L and the like, the main switch Swm is turned on to turn on the battery 12 and the power switching element Swp. , Swn can be reduced.

  (4) A MOS field effect transistor is used as the power switching element Swn. As a result, the input terminal and the output terminal are interchanged to allow current to flow bidirectionally between the pair of terminals. Therefore, it is preferable to prevent current from flowing through the freewheel diode Fwn by shoot-through control. be able to.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 6 shows a system configuration according to the present embodiment. In FIG. 6, members corresponding to those shown in FIG. 1 are given the same reference numerals for convenience.

  As shown in the figure, in this embodiment, a capacitor Cp is provided in parallel with a series connection body of a power switching element Swp on the high potential side and a power switching element Swn on the low potential side. Thereby, after the shoot-through control, when the power switching element Swn on the low potential side is turned off, the rising speed of the voltage between the input terminal and the output terminal can be controlled by the capacitance of the capacitor Cp.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 7 shows a system configuration according to the present embodiment. In FIG. 7, members corresponding to those shown in FIG. 1 are given the same reference numerals for convenience.

  As shown in the figure, also in the present embodiment, the first sub switch Sws1, the first input side inductor L1, and the first main switch Swm1 are provided between the power switching element Swp on the high potential side and the positive electrode of the battery 12. Connect in parallel. However, in the present embodiment, the second sub switch Sws2, the second input side inductor L2, and the second main switch Swm2 are further connected in parallel between the low potential side power switching element Swn and the negative electrode of the battery 12. To do.

  Here, the second sub switch Sws2 and the second input side inductor L2 and the second main switch Swm2 are recovery current countermeasure means for the freewheel diode Fwp connected in reverse parallel to the high potential side power switching element Swp. . That is, when the phase current is input to the inverter IV side, when the power switching element Swn on the low potential side is turned on, the second sub switch Sws2 is turned on to perform shoot-through control. As a result, the current flowing through the high-potential side power switching element Swp before the shoot-through control gradually decreases as the current flowing through the second input-side inductor L2 gradually increases. Then, after the total current flowing through the power switching element Swp on the high potential side and the freewheel diode Fwp connected in reverse parallel thereto becomes zero, the power switching element Swp on the high potential side is turned off. Thereby, the situation where a recovery current flows can be suitably suppressed about the free wheel diode Fwp connected in antiparallel to the power switching element Swp on the high potential side.

(Fourth embodiment)
Hereinafter, the fourth embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 8 shows a system configuration according to the present embodiment. In FIG. 8, members corresponding to those shown in FIG. 1 are given the same reference numerals for the sake of convenience.

  As illustrated, in the present embodiment, an energy storage switching element Swe is provided between the sub-switch Sws and the input-side inductor L and the negative electrode of the inverter IV. The energy storage switching element Swe is an N-channel power MOS field effect transistor, and the diode D is a parasitic diode. The energy storage switching element Swe is a recovery current countermeasure means for the freewheel diode Fwp connected in reverse parallel to the high potential side switching element Swp, and is the main during the regenerative operation of the motor 10 (during driving as a generator). It is also a recovery current countermeasure means of a diode connected in reverse parallel to the switch Swm. In the present embodiment, as the sub-switch Sws, a switch having a smaller decrease rate after the recovery current is changed from increase to decrease is selected as compared with the super junction MOS field effect transistor. At this time, the ON resistance (voltage drop amount) is not prevented from becoming larger than that of the super junction MOS field effect transistor. This is because the energization frequency of the sub switch Sws is lower than that of the power switching elements Swp, Swn, etc., so that the increase in conduction loss can be ignored.

  FIG. 9 shows a switching operation method according to the present embodiment. Specifically, FIG. 9A shows the transition of the operation mode of the sub switch Sws, FIG. 9B shows the transition of the operation mode of the energy storage switching element Swe, and FIG. 9C shows the main mode. FIG. 9D shows the transition of the operation mode of the switch Swm, FIG. 9D shows the transition of the operation mode of the switching element Swp on the high potential side, and FIG. 9E shows the power switching device of FIG. The transition of the operation mode of the switching element Swn on the low potential side in phase with Swp is shown. FIG. 9F shows the transition of the current iL flowing through the input-side inductor L. FIG. 9G shows the transition of the current is flowing through the sub switch Sws (including the body diode). h) shows the transition of the current ie flowing through the energy storage switching element Swe (including the body diode), and FIG. 9 (i) shows the transition of the current im flowing through the main switch Swm (including the body diode). Further, FIG. 9 (j) shows the transition of the current ip flowing through the power switching element Swp on the high potential side (including the body diode), and FIG. 2 (k) shows the power switching element Swn on the low potential side ( 2 (l) shows the transition of the voltage V1 at the connection point between the sub switch Sws and the input side inductor L, and FIG. 2 (m) shows the power switching. The transition of the voltage V2 between the elements Swp and Swn is shown. In the following, it is assumed that a current flows from the motor 10 to the inverter IV in the target phase during the regenerative operation of the motor 10.

  As illustrated, the period T0 is a period in which the high-potential side power switching element Swp is in the on state and the low potential side power switching element Swn is in the off state. During this period, a current flows to the battery 12 via the high potential side power switching element Swp and the main switch Swm. Here, the period T1 is shifted to by turning on the energy storage switching element Swe. As a result, the absolute value of the current flowing to the main switch Swm gradually decreases, and the absolute value of the current flowing through the input-side inductor L and the energy storage switching element Swe increases gradually. These gradually decreasing speed and gradually increasing speed are “VDC / L” when the inductance of the input-side inductor L is “L” and the input voltage VDC is used. Then, when the current flowing through the main switch Swm is reversed from negative to positive and becomes a predetermined value, the main switch Swm is turned off, and the period shifts to the period T2. Here, even in a period in which the current flowing through the main switch Swm is negative, no current flows through the body diode, so no recovery occurs. The current flowing through the main switch Swm can be controlled by the switching speed of the main switch Swm to the off state.

  When the period T2 starts, a portion of the current flowing through the input-side inductor L and the energy storage switching element Swe that exceeds the phase current flows through the low-potential-side freewheel diode Fwn. For this reason, the voltage V2 between the power switching elements Swp and Swn becomes zero (more specifically, the voltage V2 is lower than the negative potential of the battery 12 by the forward voltage drop amount of the freewheel diode Fwn). At this time, since a current also flows through the power switching element Swp on the high potential side, the voltage at the connection point between the power switching element Swp and the main switch Swm becomes zero.

  Here, while the high-potential side power switching element Swp is in the on state, the low-potential side power switching element Swn is switched to the on state to shift to the period T3. Here, since the voltage applied to the input side inductor L is substantially zero, the current iL flowing through the input side inductor L and the current flowing through the energy storage switching element Swe do not change.

  Next, the energy storage switching element Swe is turned off to shift to the period T4. As a result, the current flowing through the input-side inductor L flows through the body diode of the sub switch Sws and the battery 12 to the negative terminal of the inverter IV and the power switching elements Swn and Swp. At this time, since the input voltage VDC is applied to the input-side inductor L, the absolute value of the current flowing through the power switching elements Swn and Swp changes at a speed of “VDC / L”. As a result, the current flowing through the power switching element Swp on the high potential side is gradually reduced to zero. Incidentally, at this time, a recovery current can flow through the body diode of the sub switch Sws. However, as described above, the sub switch Sws can reduce the surge because the rate of decrease after the recovery current changes from increasing to decreasing is small.

  Then, when the current flowing through the high-potential side power switching element Swp becomes zero, the high-potential side power switching element Swp is switched to the OFF state, thereby shifting to the period T5. Furthermore, by switching the power switching element Swn on the low potential side to the off state, the period shifts to the period T6.

  After that, the main switch Swm and the high-potential side power switching element Swp are turned on to shift to the period T0.

  Thus, in the present embodiment, it is possible to avoid a surge due to recovery of the high-potential-side freewheel diode Fwp and the body diode of the main switch Swm.

  In FIG. 10, the simulation result about the effect of this embodiment is shown in comparison with the prior art (when the main switch Swm is not turned on in the period T1). As shown in the figure, in this embodiment, it is possible to reduce a surge when the current of the main switch Swm (including the body diode) becomes zero.

  According to the embodiment described in detail above, the following effects can be obtained.

  (5) With the energy storage switching element Swe and the main switch Swm turned on, the main switch Swm was turned off after the total current flowing through the main switch Swm and its body diode became zero. Thereby, it is possible to avoid a recovery current from flowing through the body diode of the main switch Swm.

  (6) When switching the power switching element Swn on the low potential side to the on state, both the power switching elements Swp and Swn are turned on, and then the energy storage switching element Swe is turned off, and the power switching element Swp and The power switching element Swp was turned off after the time when the total current flowing through the body diode became zero. As a result, no current flows through the body diode, and even if it flows, a high voltage is not applied to the body diode, so that a recovery current can be suitably avoided.

  (7) As the free wheel diode (body diode) connected in reverse parallel to the sub switch Sws, the one having a smaller recovery current change rate than the free wheel diode Fwp was used. Thereby, it is possible to reduce a surge when a recovery current flows through the body diode of the sub switch Sws.

(Other embodiments)
Each of the above embodiments may be modified as follows.
<About power switching elements Swp and Swn>
The power switching elements Swp and Swn are not limited to super junction MOS field effect transistors, and may be arbitrary field effect transistors. Here, not only the N channel but also the P channel may be used.

  In addition, the input terminal and the output terminal are interchanged so that the bidirectional current from one of the pair of terminals to the other and the other to the other is not limited to the one, for example, an insulated gate bipolar transistor (IGBT). Alternatively, only one direction of current may be allowed. In this case, it is desirable to connect the free wheel diode in reverse parallel to the IGBT. When this configuration is applied to the first embodiment, the current flowing through the freewheeling diode connected in antiparallel to the low potential side power switching element Swn by switching the high potential side power switching element Swp to the on state. It is desirable that the current is once caused to flow through the low-potential side power switching element Swn by turning off the low-potential side power switching element Swn after the time when the voltage gradually decreases to zero.

In the fourth embodiment, when an IGBT is used as the power switching elements Swp and Swn, a current flows through the free wheel diode Fwp over the periods T0 to T4. However, if the power switching element Swp is kept on until the time when this current becomes zero, the voltage applied to the freewheel diode Fwp when the forward current of the freewheel diode Fwp becomes zero is set to zero. Recovery current does not flow. For this reason, since there is no need to use a diode having a slow recovery current change rate, it is possible to select a free wheel diode Fwp having a small forward voltage drop, thereby reducing loss. it can.
<Main switch Swm and sub switch Sws>
The main switch Swm according to the first to fourth embodiments is not limited to a super junction MOS field effect transistor, and may be any field effect transistor. Here, not only the N channel but also the P channel may be used. An IGBT may be used. In the case where the IGBT is used in the fourth embodiment, it is desirable to turn off the main switch Swm after the time when the total current flowing through the main switch Swm and the freewheel diode connected in reverse parallel thereto becomes zero. As a result, the applied voltage of the free wheel diode at the time when the current stops flowing to the free wheel diode can be made zero, so that it is possible to preferably avoid the recovery current from flowing to the free wheel diode.

  The sub switch Sws according to the first to third embodiments is not limited to a super junction MOS field effect transistor, and may be any field effect transistor. Here, not only the N channel but also the P channel may be used. An IGBT may be used.

In the fourth embodiment, an IGBT or the like may be used.
<Recovery measures for both freewheel diodes Fwp and Fwn>
The configuration for performing recovery measures for both the freewheel diodes Fwp and Fwn is not limited to the configuration exemplified in the third and fourth embodiments. For example, in the configuration shown in FIG. 7, the first input-side inductor L1, the first main switch Swm1, and the first sub switch Sws1 may be deleted, and the energy storage switching element Swe may be provided instead of the diode D. .
<About loop circuit>
When switching both the high-potential side and low-potential side power switching elements Swp and Swn from the on-state to the one-on state by shoot-through control, an excess of the current flowing through the input-side inductor L The loop circuit through which the minute) flows is not limited to the one provided with the battery 12. For example, in FIG. 1, a diode that is parallel to the input-side inductor L and has a forward direction from a terminal side connected to the main switch Swm to a terminal side connected to the sub switch Sws is provided. It may be a circuit.

Further, the rectifying means provided in the loop circuit is not limited to a diode, and may be a switching element such as a thyristor or a transistor. In this case, the switching element may be operated so that the current flows only during the period in which the current flows in the diode D in each of the above embodiments.
<About power conversion circuit>
The power conversion circuit is not limited to an inverter connected to a three-phase rotating machine. For example, a DC power source (battery) is connected to a series connection body of a high-potential side power switching element Swp and a low-potential side power switching element Swn. The step-down converter may be connected in parallel, and the first inductor and the capacitor are connected in parallel to the connection point of the series connection body and the negative electrode of the DC power supply. Note that in this case, the first inductor is a component of the power conversion circuit.

However, the output voltage is not limited to the input voltage or less, and may be a step-up / down chopper circuit, for example. For example, a DC power source is connected in parallel to the low potential side power switching element Swn via the first inductor, and a second inductor is provided between the high potential side switching element and the output terminal. Also good. A capacitor is provided at a pair of output terminals of the step-up / down chopper circuit.
<Snubber capacitor>
As a snubber capacitor, it is not restricted to what is connected in parallel to the serial connection body of a high potential side switching element and a low potential side switching element. For example, in the first embodiment, it may be connected in parallel to the switching element to be turned off after the shoot-through control, such as being connected in parallel to the low-potential-side power switching element Swn.
<Others>
In the first to third embodiments, the timing for turning on the sub switch Sws (Sws1, Sws2) may not be the same as the timing for turning on the power switching element Swp (Swp, Swn). It may be after that.

  In the third embodiment, the first input-side inductor L1, the first main switch Swm1, and the first sub switch Sws may be deleted. This is a configuration different from that of the first embodiment in the arm to which the recovery current countermeasure is applied.

  In each of the above embodiments, an input-side inductor, a main switch, and a sub switch may be provided for each phase.

  -Also in the said 1st-3rd embodiment, it is not restricted to what makes the electric motor 10 carry out a power running operation, You may carry out a regenerative operation.

  In the fourth embodiment, instead of causing the electric motor 10 to be regenerated, a power running operation may be performed.

  DESCRIPTION OF SYMBOLS 10 ... Electric motor (one embodiment of 1st inductor), 12 ... Battery, 20 ... Control apparatus, IV ... Inverter.

Claims (14)

Electric power comprising a series connection body of a high potential side switching element for connecting the first inductor to the positive electrode side of the DC power source and a low potential side switching element for connecting the first inductor to the negative electrode side of the DC power source In the conversion system,
A free wheel diode is connected in reverse parallel to one of the high potential side switching element and the low potential side switching element,
A second inductor connected between the terminal connected to the first inductor by the other switching element connected in series to the one switching element of the pair of terminals of the DC power supply and the other switching element; ,
When switching the other switching element to the on state, shoot-through control means for turning both on,
After the both are turned on by the shoot-through control means, the one switching element after the time when the total current flowing through the one switching element and the freewheel diode connected in reverse parallel to the switching element becomes zero A power conversion system comprising: an off operation means for turning off the element.   2. The power conversion system according to claim 1, wherein the off-operation unit turns off the one switching element after the total current becomes zero. A loop circuit that bypasses the one switching element and connects both ends of the second inductor;
The loop circuit allows the current flowing in the second inductor to flow in by turning off the one switching element by the off operation means, and regulates a current in a direction opposite to the current. The power conversion system according to claim 2, further comprising a rectifier that performs the operation.   The power conversion system according to claim 3, wherein the loop circuit includes the DC power supply.   5. The power conversion system according to claim 1, wherein capacitors are connected in parallel to both ends of the series connection body or to both ends of the one switching element. A first electrical path that connects the electrode side connected to the first inductor by the other switching element of the pair of electrodes of the DC power source and the other switching element and includes the second inductor;
First opening and closing means for opening and closing the first electrical path;
A second electrical path connecting the electrode side connected to the first inductor by the other switching element of the pair of electrodes of the DC power supply and the other switching element and not including the second inductor;
Second opening and closing means for opening and closing the second electric path;
The power conversion system according to any one of claims 1 to 5, further comprising:   The power conversion system according to claim 6, wherein a free wheel diode is connected in antiparallel to each of the first opening / closing means and the second opening / closing means. A freewheel diode is connected in antiparallel to the other switching element,
The second inductor is connected through the first opening / closing means to the electrode side connected to the first inductor by the other switching element of the pair of electrodes of the DC power supply,
An energy storage switching element that opens and closes between a terminal connected to the first inductor by the one switching element among the terminals of the DC power supply and between the first switching means and the second inductor;
Prior to switching the one switching element to the on state, the energy storage switching element is turned on with the first opening / closing means opened and the second opening / closing means closed. Energy storage processing means for performing a process of flowing a current flowing through at least one of the switching element and at least one of the free wheel diodes connected in reverse parallel thereto to the second inductor;
The opening / closing means for opening the second opening / closing means after the time when the total current flowing through the second opening / closing means and the freewheel diode connected in reverse parallel thereto becomes zero. The described power conversion system. When switching the other switching element to the on state, the shoot-through control means for turning both on is the first shoot-through control means,
After the energy storage switching element is turned on by the energy storage processing means, when the one switching element is switched to the on state, the second shoot-through control means for turning on both of the switching elements;
Means for turning off the energy storage switching element after both of the two are turned on by the second shoot-through control means;
9. The apparatus according to claim 8, further comprising means for turning off the other switching element after a time when a total current flowing through the other switching element and a freewheel diode connected in reverse parallel thereto becomes zero. The described power conversion system. Electric power comprising a series connection body of a high potential side switching element for connecting the first inductor to the positive electrode side of the DC power source and a low potential side switching element for connecting the first inductor to the negative electrode side of the DC power source In the conversion system,
A free wheel diode is connected in antiparallel to the other switching element connected in series to one of the high potential side switching element and the low potential side switching element,
A second inductor connected between the terminal connected to the first inductor by the other switching element and the other switching element;
A freewheeling diode having a forward direction from the second inductor side to the electrode side connected to the first inductor by the other switching element of the pair of electrodes of the DC power supply;
An energy storage switching element that opens and closes between the free wheel diode and the second inductor, and a terminal connected to the first inductor by the one switching element among the terminals of the DC power supply;
Opening / closing means for opening and closing an electrical path that is connected to the first inductor by the other switching element of the pair of electrodes of the DC power source and the first inductor and does not include the second inductor. When,
A freewheeling diode connected in reverse parallel to the switching means;
Prior to switching the one switching element to the on state, the energy storage switching element is turned on in a state in which the opening / closing means is closed, so that the other switching element and the free connected in reverse parallel thereto are connected. Energy storage processing means for performing a process of flowing a current flowing through at least one of the wheel diodes through the second inductor;
A power conversion system comprising: an opening / closing means for opening / closing the opening / closing means after a time point when a total current flowing through the opening / closing means and a freewheel diode connected in reverse parallel thereto becomes zero. After the energy storage switching element is turned on by the energy storage processing means, when the one switching element is switched to the on state, the control means for turning on both of the switching elements;
Means for turning off the energy storage switching element after both are turned on by the control means;
The apparatus further comprises means for turning off the other switching element after the time when the total current flowing through the other switching element and the freewheel diode connected in reverse parallel thereto becomes zero. The described power conversion system.   The free wheel diode connected between the energy storage switching element and the second inductor has a smaller change rate of the recovery current than the free wheel diode connected in reverse parallel to the one switching element. The power conversion system according to claim 9 or 11.   The opening operation means operates to turn off the opening / closing means after the total current flowing through the opening / closing means connected between the second inductor and the other switching element and the free wheel diode connected in reverse parallel thereto becomes zero. The power conversion system according to any one of claims 8 to 12, wherein:   The pair of switching elements allow a current to flow bidirectionally between the pair of terminals by switching between the input terminal and the output terminal. The power conversion system according to item.

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