JP3052792B2 - Inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for driving an electric motor, and is suitable for an electric vehicle or the like in which a power supply voltage fluctuates.

[0002]

2. Description of the Related Art FIG. 1 shows a motor drive system for an electric vehicle as an inverter device for driving a motor. In FIG. 1, 1 is a DC power supply, 2a, 2b, 2c, 2d,
2e, 2f are MOS input type semiconductor switching elements to which the DC power supply 1 is connected, 3a, 3b, 3c, 3d, 3
e and 3f are MOS input type semiconductor switching elements 2a
2f, a three-phase motor, 4a and 5b are current sensors for detecting U-phase and W-phase inverter output currents, and 6 is a signal from the current sensors 5a and 5b. Is a controller, 8 is an accelerator sensor provided in the accelerator of the vehicle, and 9a, 9b, 9c, 9d, 9e, 9f are gate drive circuits having the same circuit configuration.

The controller 7 drives the gate drive circuits 9a to 9f so that the three-phase motor 4 outputs a predetermined torque according to the accelerator signal of the accelerator sensor 8, and changes the energized state of the semiconductor switching elements 2a to 2f. By controlling the switching, the current path from the DC power supply 1 to the three-phase motor 4 is switched.

[0004] In the motor drive system having the above configuration, the circuit configuration of the conventional gate drive circuits 9a to 9f is shown in FIG. 5 with the gate drive circuit 9a as a representative. FIG.
, 10 is a DC power supply, 11 is a photocoupler, 1
2, 13, 14 are transistors, 15 to 18 are resistors, 1
9 is a turn-on gate resistance, 20 is a turn-off gate resistance, and 21 is a gate resistance.

Next, the operation of the conventional gate drive circuit 9a will be described. First, a case where the MOS input type semiconductor switching element 2a is turned on will be described. When the controller 7 drives the primary diode of the photocoupler 11, the secondary phototransistor of the photocoupler 11 is turned on, and the transistor 12 is turned off to prevent the base current from flowing through the transistor 12. When the transistor 12 is turned off, a base current flows to the transistor 13 through the resistor 18, so that the transistor 13 is turned on. When the transistor 13 is turned on,
The gate of the MOS input type semiconductor switching element 2a is charged through the resistors 19 and 21, and when the gate voltage exceeds a predetermined potential (threshold voltage), the MOS input type semiconductor switching element 2a is turned on.

Next, when the MOS input type semiconductor switching element 2a is turned off, when the controller 7 stops driving the primary diode of the photocoupler 11, the secondary phototransistor of the photocoupler 11 is turned off. A base current flows through the transistor 12 through the resistors 15 and 16, and the transistor 12 is turned on. When the transistor 12 is turned on, the base current supplied to the transistor 13 through the resistor 18 does not flow, so that the transistor 13 is turned off. At the same time, the base current flows to the transistor 14 through the transistor 12, so that the transistor 14 is turned on. When the transistor 14 is turned on, the MOS through the resistors 20 and 21
When the gate of the input-type semiconductor switching element 2a is discharged and the gate voltage falls below a predetermined potential (threshold voltage), the MOS-input-type semiconductor switching element 2a is turned off.

Next, switching characteristics of the MOS input type semiconductor switching element will be described. First, the turn-on switching characteristics will be described with reference to FIGS. In FIG. 6, reference numeral 22 denotes the stray inductance of the wiring, and reference numeral 23 denotes the inductance of the load. In FIG. 6, consider the operation when the MOS input type semiconductor switching element 2d is turned off while the load current IL is flowing in the direction of arrow (1) while the MOS input type semiconductor switching element 2d is on. .

[0008] MOS input type semiconductor switching element 2
When d is turned off, the load current IL flowing through the semiconductor switching element 2d is commutated to the diode 3a by the load inductance 23 and flows in the direction of the arrow (2). Next, when the MOS input type semiconductor switching element 2d is turned on again, as shown by an arrow (3), the DC power supply 1, the floating inductance 22, the diode 3a, and M
The circuit is instantaneously short-circuited through a circuit including the OS input type semiconductor switching element 2d. Although the other wiring portions actually have inductance, they are omitted for the sake of simplicity.

The reverse recovery current flows in the reverse direction of the diode 3a, and the diode 3a recovers the reverse characteristic. However, when the reverse recovery current is attenuated rapidly, the surge voltage caused by the floating inductance 22 causes the MOS input type semiconductor switching element. 2a and the diode 3a. This reverse recovery current can be identified by observing the forward current I of the diode 3a. When the MOS input type semiconductor switching element 2d is turned on at time t1, the current i becomes I
L decreases from the magnitude of L to zero, and then suddenly becomes zero after a reverse recovery current flows. At this time, a large surge voltage VD is applied to the MOS input type semiconductor switching element 2a or the diode 3a by the floating inductance 22. Is done.

This surge voltage VD is obtained by converting the DC power supply voltage to V
B, if the stray inductance 22 is L, VD = L
di / dt + VB. If the surge voltage VD is not suppressed below the rated voltage VS of the MOS input type semiconductor switching element, the element itself will break down withstand voltage. Therefore, it is necessary to reduce the surge voltage VD.

In order to reduce the surge voltage VD, the surge voltage VD is reduced by either reducing the DC power supply voltage VB, decreasing the magnitude of L of the floating inductance 22, or decreasing di / dt. However, if the DC power supply voltage VB is reduced, the power supplied to the load is limited, and the reduction of the L of the stray inductance 22 is limited from the viewpoint of wiring. Is effective.

One of the methods for reducing di / dt is to design the recovery time of a diode to be short. Further, a soft recovery diode for gradually attenuating the recovery current has been developed, but there is a limit, and the waveform A in FIG. 7 is a case where the MOS input type semiconductor switching element 2d is rapidly turned on. The current rises quickly and the surge voltage VD also has a large value, which exceeds the rated VS of the MOS input type semiconductor switching element. On the other hand, the waveform B is a case where the MOS input type semiconductor switching element 2a is slowly turned on, the value of the reverse current i and the value of di / dt are small, and the surge voltage VD is also low.

At this time, the turn-on time of the MOS input type semiconductor switching element 2d depends on the charging time of the gate. To increase the turn-on time of the MOS input type semiconductor switching element, the gate of the circuit shown in FIG. Resistance 1
It is sufficient to increase the resistance values of the gates 9 and 21 to lengthen the gate charging time. However, in order to suppress di / dt, increasing the resistance values of the turn-on gate resistors 19 and 21 to decrease the switching speed of the MOS input type semiconductor switching element as described above increases switching loss. As a result, there is a problem that the loss of the inverter device increases.

Next, the turn-off switching characteristics of the MOS input type semiconductor switching element will be described with reference to FIGS. When the load current in FIG. 6 is switched from (1) to (2), the current flowing in the MOS input type semiconductor switching element 2d changes from IL to 0, and thus both ends of the MOS input type semiconductor switching element 2d. Is applied with a surge voltage VC. Surge voltage VC
Is represented by VC = L · di / dt + VB. In order to suppress the surge voltage VC to be equal to or lower than the rated VS of the MOS input type semiconductor switching element as in the case of the turn-on switching characteristics, only di / dt can be suppressed. The turn-off time of the semiconductor switching element 2d depends on the discharge time of the gate. To increase the turn-off time of the MOS input type semiconductor switching element, the resistance values of the gate resistors 20 and 21 of the circuit shown in FIG. Then, the gate discharge time may be extended. However, also with respect to the loss aspect of the inverter device, similarly to the turn-on switching characteristic, there is a problem in that decreasing the turn-off switching speed of the MOS input type semiconductor switching element increases the switching loss.

[0015]

The surge voltage applied to a MOS input type semiconductor switching element is L · di / d
Since it is represented by t + VB, in a general-purpose inverter device supplied with electric power from a commercial power supply, it is only necessary to pay attention to the term L · di / dt, considering that the DC power supply voltage VB is substantially constant. However, in a vehicle equipped with a battery such as an electric vehicle, the DC power supply voltage VB is used when the battery is charged or when the vehicle is regenerated when a long steep downhill is regenerated.
Rise, and conversely, during acceleration, the DC power supply voltage VB fluctuates greatly so that the DC power supply voltage VB decreases.

That is, as described above, the DC power supply voltage VB
When the DC voltage increases, the switching speed is reduced in order to suppress the surge voltage in consideration of L · di / dt + VB. However, when the DC power supply voltage is low, the switching speed is increased to increase the surge voltage. However, since the absolute value of the surge voltage is small, the switching loss can be reduced without causing the breakdown voltage of the MOS input type semiconductor switching element.

According to the present invention, in a motor drive system such as an electric vehicle in which the DC power supply voltage of the inverter device fluctuates, the switching speed of the MOS input type semiconductor switching element constituting the inverter device is appropriately adjusted according to the DC power supply voltage. The control is intended to reduce the switch loss of the inverter device.

[0018]

According to the present invention, claim 1 is:
A DC power supply, a plurality of sets of voltage-driven semiconductor switching elements connected in series to the DC power supply, a feedback diode connected in anti-parallel to each output terminal of the semiconductor switching element, and turning on each of the semiconductor switching elements. A control circuit for performing off-control, and an inverter device for controlling the energization of a load connected to each series connection point of the semiconductor switching elements, wherein in the control circuit, voltage detection means for detecting a voltage of the DC power supply; And a switching speed changing means for changing a switching speed of the semiconductor switching element according to the voltage of the DC power supply detected by the voltage detecting means.

According to a second aspect of the present invention, in the first aspect, the semiconductor switching element is a MOS input type transistor, and the switching speed changing means connects the switching means to at least one of the plurality of gate resistors in parallel. The switching means is controlled in accordance with the voltage of the DC power supply to vary the charging / discharging impedance of the gate of the MOS input type semiconductor switching element, thereby charging / discharging the gate of the MOS input type semiconductor switching element. The technical means is to control the switching time of the MOS input type semiconductor switching element by controlling the time.

According to a third aspect of the present invention, in the first and second aspects, the semiconductor switching element is a MOS input type transistor, and the voltage detecting means controls charging and discharging of each gate of the plurality of sets of the MOS input type transistors. The technical means is to have each in the gate drive circuit to perform.
4. A gate drive circuit according to claim 1, wherein said semiconductor switching element is a MOS input type transistor, and said voltage detection means charges and discharges a gate of each of said plurality of sets of MOS input type transistors. A technical means is provided outside and transmits to all of the gate drive circuits whether the voltage of the DC power supply is higher or lower than a predetermined voltage.

[0021]

According to the present invention, the switching speed of a semiconductor switching element is controlled by detecting the voltage of a DC power supply by voltage detecting means and controlling the charge / discharge time of the gate of the semiconductor switching element in accordance with the voltage. Variable. Thus, when the voltage of the DC power supply is high, the switching speed of the semiconductor switching element is reduced, and the L · di / dt component of the surge voltage applied to the semiconductor switching element due to the load inductance is reduced. It does not affect the switching element. On the other hand, when the voltage of the DC power supply is low, the switching speed of the semiconductor switching element increases, and the L · di / dt component of the surge voltage applied to the semiconductor switching element due to the load inductance increases. Since the voltage itself is in a low state, the absolute value of the surge voltage is reduced, and a surge voltage exceeding the breakdown voltage is not applied to the semiconductor switching element. Further, at this time, the switching time is shortened, so that the switching loss is reduced.

[0022]

According to the present invention, as described above, the switching speed of the semiconductor switching element is changed according to the voltage of the DC power supply. Therefore, when the voltage of the DC power supply is high, the surge voltage can be reduced. When the voltage of the DC power supply is low, the switching loss can be reduced.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an inverter device according to the present invention will be described based on an embodiment of a motor drive system for an electric vehicle shown in FIG. The characteristic configuration of the present invention is applied to the gate drive circuits 9a to 9f of the motor drive system shown in FIG. 1, and the circuit configuration of the gate drive circuit 9 according to the embodiment of the present invention is shown in FIG. In FIG. 2, reference numeral 24 denotes a known voltage detection circuit constituted by a differential amplifier circuit using an operational amplifier, which detects the voltage of the DC power supply 1 in the motor drive system. 25a is a comparator, 25b is an output transistor in the comparator 25a, 26 is a reference voltage source, 27 and 28 are transistors, and 29 is a P-type MOSFET.
T and 30 are N-type MOSFETs, 31 to 45 are resistors, 46
Is a diode, and 47 is a photocoupler. Note that FIG.
In FIG. 5, components denoted by the same reference numerals as those in FIG. 5 indicate the same configuration.

Next, the gate drive circuit 9 having the above configuration
Will be described. If the voltage of the DC power supply 1 in the motor drive system is equal to or higher than a predetermined voltage, the output transistor 25b in the comparator 25a is turned off, and a base current flows through the transistor 27 through the resistors 33 and 35. Turn on.
When the transistor 27 is turned on, a base current is supplied to the transistor 28, so that the transistor 28 is turned on. When the transistor 27 is turned on, an N-type MOS
Since the gate of the FET 30 is discharged, the N-type MOSFET
T30 turns off. Further, since the transistor 28 is turned on, the gate of the P-type MOSFET 29 is charged, so that the P-type MOSFET 29 is turned off. At this time,
The charging resistance of the gate of the MOS input type semiconductor switching element is a series resistance of the resistances 44, 19, and 21, and the discharging resistance of the gate is a series resistance of the resistances 21, 20, and 45.

Conversely, if the DC power supply voltage of the inverter device is equal to or lower than a predetermined voltage, the output transistor 25b in the comparator 25a is turned on, so that no base current is supplied to the transistor 27 and the transistor 27 is turned off. Become. When the transistor 27 is turned off, the base current is not supplied to the transistor 28, so that the transistor 28 is turned off. Here, when the transistor 27 is turned off, the base current of the transistor 28 flows through the resistors 37, 42, and 43, so that the diode 46 is turned on.
8 prevents reverse turning on by mistake. When the transistor 28 is turned off, the gate of the P-type MOSFET 29 is negatively biased with respect to the source, so that the P-type MOSFET 29 is turned on. Transistor 2
7 is turned off, so that N
The N-type MOSFET 30 is turned on because the gate of the type MOSFET 30 is positively biased with respect to the source.

MOSFET of several A (ampere) class
Is turned on, the ON resistance becomes several tens of milliohms. At this time, the charge resistance of the gate of the MOS input type semiconductor switching element is almost a series resistance of the resistances 19 and 21, and the discharge resistance of the gate is the resistance 21 and 20 series resistance. Therefore, when the voltage of the DC power supply 1 in the motor drive system becomes equal to or lower than a predetermined voltage, the charge and discharge of the gate of the MOS input type semiconductor switching element become faster, and the charge and discharge time becomes shorter. As a result, the surge voltage L · di / dt generated when the MOS input type semiconductor switching element is turned off and turned on increases,
Since the voltage of the DC power supply 1 is low, the absolute value of the surge voltage is low, so that the switching loss can be reduced without causing the breakdown voltage of the MOS input type semiconductor switching element.

FIG. 3 shows a surge voltage waveform applied to the MOS input type semiconductor switching element and a current waveform flowing through the MOS input type semiconductor switching element when the gate drive circuit of this embodiment is used. In the figure, (A) shows the case where the voltage VB of the DC power supply 1 of the motor drive system is high, and (B) and (C) show the cases where it is low. (A),
(B) shows the case where the control of the present invention is performed, and (C) shows the case of the conventional technique without the control. Note that VMAX
Is the withstand voltage rating of the MOS input type semiconductor switching element.

In FIG. 3, VB1> VB2,
Comparing (A) and (B), when the voltage VB of the DC power supply 1 of the motor drive system is low (B), the switching speed increases (di / dt increases).
However, the surge voltage level is VMAX for both (A) and (B).
Comparing (B) and (C) below, in the case of (B), the switching time is short and the level of the surge voltage is high, but the level of the breakdown voltage of the MOS input type semiconductor switching element is high. VMAX has not been reached.
Also, since the switching time is shortened, it can be seen that the switching loss is reduced as compared with the case without control.

FIG. 4 shows a gate drive circuit according to a second embodiment of the present invention. In FIG. 4, reference numeral 47 denotes a photocoupler.
In the second embodiment, a voltage detecting means for detecting the voltage of the DC power supply 1 is provided in the controller 7, and the voltage of the DC power supply 1 is equal to or higher than a predetermined voltage from the controller 7 to the photocoupler 47 of each of the gate drive circuits 9a to 9f. Since the following signal is transmitted, the voltage detection circuit of each gate drive circuit can be omitted.

In each of the above embodiments, the gate drive circuit for a single power supply has been described, but a gate drive circuit for a dual power supply may be used. Although the bipolar transistors are used as 13, 14, 27, and 28, other switching means such as FETs may be used. Further, although a photocoupler is used as an interface between the controller 7 and the gate drive circuit, other insulating means such as a pulse transformer may be used. In addition, although the speed-up of the turn-on and the turn-off is performed at the same time, they may be performed separately. Further, the switching speed is divided into two stages of high speed and low speed. However, the switching speed may be divided into more than two stages, and the number of stages may be set separately for turn-on and turn-off. Further, although a voltage detection circuit is used as the DC power supply voltage detecting means, other insulating means such as an isolation amplifier may be used.

As described above, according to the present invention, in an inverter device in which the power supply voltage fluctuates, the switching speed of the MOS input type semiconductor switching element constituting the inverter device is appropriately controlled according to the power supply voltage. The switching loss of the inverter device can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a motor drive system of an electric vehicle according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a gate drive circuit of the motor drive system according to the first embodiment.

FIG. 3 is a waveform chart showing the operation of the first embodiment.

FIG. 4 is a circuit diagram showing a gate drive circuit of a motor drive system according to a second embodiment.

FIG. 5 is a circuit diagram showing a gate drive circuit as a conventional technique.

FIG. 6 is a partial circuit diagram for explaining the operation of a gate drive circuit as a conventional technique.

FIG. 7 is a waveform diagram for explaining the operation of a gate drive circuit as a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC power supply 2a-2f MOS input type semiconductor switching element 3a-3f Diode (feedback diode) 4 Three-phase motor 7 Controller 9 Gate drive circuit (control circuit, switching speed change means) 24 Voltage detection circuit (voltage detection means)

Claims (4)

(57) [Claims] A DC power supply; a plurality of voltage-driven semiconductor switching elements connected in series to the DC power supply; a feedback diode connected in anti-parallel to each output terminal of the semiconductor switching element; A control circuit for controlling on / off of the semiconductor switching element; and an inverter device for controlling energization of a load connected to each series connection point of the semiconductor switching element, wherein the control circuit detects a voltage of the DC power supply. An inverter device, comprising: a voltage detecting unit that performs switching; and a switching speed changing unit that changes a switching speed of the semiconductor switching element according to a voltage of the DC power supply detected by the voltage detecting unit. 2. The semiconductor switching device according to claim 1, wherein the semiconductor switching element is a MOS.
An input-type transistor, wherein the switching speed changing means connects a switch means to at least one of the plurality of gate resistors in parallel, and controls the switch means according to a voltage of the DC power supply; MO
By varying the charging / discharging impedance of the gate of the S-input type semiconductor switching element and controlling the charging / discharging time of the gate of the MOS-input type semiconductor switching element,
2. The inverter device according to claim 1, wherein a switching time of the MOS input type semiconductor switching element is controlled. 3. The semiconductor switching device according to claim 1, wherein the semiconductor switching element is a MOS.
The inverter according to claim 1 or 2, wherein the inverter is an input transistor, and the voltage detection means is provided in a gate drive circuit that charges and discharges each gate of the plurality of sets of MOS input transistors. apparatus. 4. The semiconductor switching device according to claim 1, wherein the semiconductor switching element is a MOS.
An input type transistor, wherein the voltage detecting means is provided outside a gate drive circuit for charging / discharging the gates of each of the plurality of sets of MOS input type transistors, and whether the voltage of the DC power supply is equal to or higher than a predetermined voltage, 3. The transmission to all of the gate drive circuits.
3. The inverter device according to claim 1.