JP2006109624A - Drive device for brushless dc motor - Google Patents

Abstract

To reduce the size and cost of a brushless DC motor drive device.
A snubber capacitor connected in parallel with an inverter has a function as a smoothing capacitor, and when the position cannot be detected by a position detecting means, the position is estimated and the inverter is operated. As a result, even when position detection is impossible, the position can be estimated and commutation according to position detection can be performed, so that stable operation can be performed. The drive device of the brushless DC motor 14 can be reduced in size and cost.
[Selection] Figure 1

Description

  The present invention relates to a brushless DC motor driving apparatus mounted on a compressor of a refrigerating and air-conditioning system such as a refrigerator or an air conditioner.

  Conventionally, a brushless DC motor driving device mounted on a compressor or the like in this type of refrigerating and air-conditioning system generally includes a rectifier circuit having a sufficiently large smoothing capacitor and an inverter, and eliminates a position detection sensor and induces it. It is driven by detecting the position from voltage or motor current. This is because it was extremely difficult to attach the position sensor in a high-temperature atmosphere such as a compressor, a refrigerant atmosphere, or an oil atmosphere.

  In recent years, in order to reduce the size of this drive device, efforts have been made to significantly reduce the capacity of the smoothing capacitor of the rectifier circuit (see, for example, Patent Document 1).

  FIG. 8 is a block diagram of a conventional brushless DC motor driving apparatus described in Patent Document 1. In FIG.

  A conventional brushless DC motor driving apparatus uses a single-phase AC power source 1 as a power source. The input side of the diode full-wave rectifier circuit 2 is connected to the single-phase AC power source 1, and the output side is connected to the smoothing capacitor 3. The smoothing capacitor 3 has a sufficiently small capacity, and is a conventional capacitor having a capacity of about 1/100.

  The PWM (pulse width modulation) inverter 4 has six switching elements (including diodes in the reverse direction) connected in a three-phase bridge. The input side is connected to both ends of the smoothing capacitor 3.

  The motor 5 provided with the three-phase winding is connected to the output side of the PWM inverter 4 and is driven thereby.

The control circuit 6 receives the information such as the voltage v of the single-phase AC power source 1, the direct current portion idc, the output currents ia, ib, ic of the PWM inverter 4, and the position information θ from the position detection sensor 7 as an optimum drive. The gate of the PWM inverter 4 is driven so that
JP 2002-51589 A

  However, in the conventional configuration, no consideration is given to a power supply method for controlling the gate of the inverter. For example, a power supply circuit is provided in parallel with the PWM inverter 4 from both ends of the smoothing capacitor 3, and a power supply for gate control is provided. When supplying, the smoothing capacitor 3 requires a capacity of about 1 μF / 1 W (about 10 μF for a 10 W output power supply). Further, about 140 V is applied to both ends of the smoothing capacitor 3 when AC 100 V is input.

  Generally, an electrolytic capacitor having a high capacity, a high withstand voltage, and a relatively low cost is used as the smoothing capacitor 3. However, since the allowable ripple current value is reduced depending on the capacity of the electrolytic capacitor, a large output motor for a compressor or the like. In driving, the ripple current exceeds the allowable value and cannot be used, and a film capacitor or the like needs to be selected. In addition, the film capacitor of about 10 μF has a problem that the cost is high and it is difficult to reduce the size of the device due to the increase in size of the capacitor.

  Further, in the above-described conventional configuration, the position detection sensor 7 having an encoder or a hall element can detect the position even if the DC voltage is lowered, but the position detection sensor is attached like a compressor. It cannot be used for purposes that cannot be used. Generally known methods for driving a brushless DC motor without the position detection sensor 7 include a method for detecting the induced voltage of the motor and a method for detecting the rotational position from the motor current.

  However, this position detection is possible when the smoothing capacitor 3 is sufficiently large and the ripple voltage is small. At this time, the induced voltage and the motor current are stabilized, so that a sufficiently stable position can be detected. However, if the capacity of the smoothing capacitor 3 is significantly reduced as in this conventional example, the ripple of the input voltage of the inverter 4 is greatly increased. Especially, when the voltage is low, the induced voltage cannot be detected, or since the voltage is low, the motor current necessary for position detection cannot be passed.

  As a result, position detection when the DC voltage is low becomes impossible, and the commutation is greatly out of timing, causing a reduction in efficiency and in the worst case a large current flows, causing the motor to stop or malfunction Had the problem of causing

  The present invention solves the above-described conventional problems. Even when there is a large ripple voltage with a significantly reduced capacity of the smoothing capacitor, the current can be stabilized without the efficiency reduction without the position detection sensor, and the motor can be driven stably. The object is to provide a drive device for a brushless DC motor at a small size and at a low cost.

  In order to achieve the above object, a brushless DC motor driving apparatus according to the present invention provides a snubber capacitor of an inverter circuit with a function as a smoothing capacitor after rectification by a first rectifier circuit, and via a second rectifier circuit. A small-capacity smoothing capacitor is provided and input to the power supply for the control circuit.

  This eliminates the need for expensive and large parts such as a film capacitor for the smoothing capacitor.

  In the brushless DC motor driving apparatus of the present invention, the function of a smoothing capacitor for inverter input is provided in the snubber capacitor of the inverter, so that the number of parts of the device can be reduced and the cost can be reduced.

  Further, the power supply of the control circuit is connected to a smoothing capacitor having a small capacity via a second rectifier circuit different from the inverter input, and connected in parallel with the smoothing capacitor. Since a large ripple current due to capacitor charging / discharging does not occur, a capacitor having a low allowable ripple current can be used, and the cost of the apparatus can be reduced.

  In addition, since the position is estimated when the position detection unit cannot detect the position and the inverter is operated, the position is estimated even when position detection is impossible. Since commutation can be performed accordingly, stable operation is possible.

  In addition, when the brushless DC motor is driven, the DC input voltage ripple content to the inverter is set to 90% or more. Here, a very small capacity and small capacitor can be used, so the drive device can be greatly reduced in size. it can.

  In addition, when the position cannot be detected, it is estimated that the position changes every predetermined time. When the position cannot be detected, the motor operates with inertia (moment of inertia). Therefore, stable operation can be realized and motor stoppage can be prevented.

  In addition, when the output voltage of the first rectifier circuit is equal to or lower than a predetermined voltage, it is determined that position detection is impossible, and a portion where position detection cannot be performed is accurately determined. Therefore, more stable operation can be performed.

  In addition, if the compressor that constitutes the refrigeration and air conditioning system is driven, it is possible to realize a small-capacitance capacitor in applications where the position detection sensor cannot be attached. Miniaturization can be realized.

  Further, since the reciprocating compressor has a large inertia, even when a voltage having a ripple content of 90% or more is input to the inverter, a stable cooling performance can be obtained without cooling failure due to the refrigeration system being stopped.

  In addition, when the refrigerant used in the cooling system is R600A, which has a low refrigeration capacity, the motor inertia increases as a result of the increase in the piston of the compressor. Highly stable operation is possible.

  The invention of the brushless DC motor driving device according to claim 1 includes an AC power supply, a first rectifier circuit that rectifies an input of the AC power supply, an inverter connected to the first rectifier circuit, and the inverter in parallel. A connected snubber capacitor; a brushless DC motor driven by the inverter; a position detecting means for detecting a rotational position of a rotor of the brushless DC motor from an induced voltage or a motor current of the brushless DC motor; and the position detecting means. And a control means for controlling the inverter to drive the brushless DC motor based on the rotor position information obtained from the controller, and the snubber capacitor for smoothing the output voltage of the first rectifier circuit By being configured to function also as a capacitor, the number of parts of the device can be reduced and the cost can be reduced.

  The brushless DC motor drive device according to claim 2 is an AC power supply, a first rectifier circuit and a second rectifier circuit for rectifying an input of the AC power supply, an inverter connected to the first rectifier circuit, A snubber capacitor connected in parallel with the inverter, a brushless DC motor driven by the inverter, and a rotational position of a rotor of the brushless DC motor is detected from an induced voltage or a motor current of the brushless DC motor. Based on position information for operation, rotor position information obtained from the position detection means, control means for controlling the inverter to drive the brushless DC motor, and rectification by the second rectifier circuit A smoothing circuit for smoothing the voltage, and a direct current connected in parallel with the smoothing circuit and smoothed by the smoothing circuit A power supply circuit for converting the voltage into a DC low voltage, and the power supply circuit is configured to supply power to the control means. The power supply for the control circuit is different from the input to the inverter. Supply from a smoothing capacitor via a second rectifier circuit.

  The smoothing capacitor does not generate a large ripple current due to capacitor charging / discharging when the motor is driven, and a capacitor with low allowable ripple current, such as a low-cost electrolytic capacitor, can be used. Cost can be reduced. In addition, when the brushless DC motor stops suddenly due to a step-out, etc., the regenerative energy generated can be absorbed by the smoothing circuit connected via the second rectifier circuit, so that an overvoltage higher than the withstand voltage is applied to the snubber capacitor. And failure of the apparatus can be prevented. Also, since the power supply circuit that supplies power to the inverter control means is connected from both ends of the smoothing circuit, when regeneration occurs, the regenerative energy absorbed by the smoothing circuit is consumed by the power supply circuit, so regeneration occurs again. When it is done, regenerative energy can be absorbed stably. In addition, since the input voltage to the power supply circuit is supplied from the smoothing circuit, there is no need to add a separate rectifier circuit and smoothing circuit for the power supply circuit, realizing a significant reduction in cost and downsizing of the device. it can.

  According to a third aspect of the present invention, there is provided a brushless DC motor driving device according to the first or second aspect, wherein when the position cannot be detected by the position detecting means, the position is estimated. By operating the inverter, the position is estimated when the position detection means cannot detect the position and the inverter is operated. When the position cannot be detected, the position is estimated. Since commutation according to position detection can be performed, stable operation is possible.

  According to a fourth aspect of the present invention, there is provided a brushless DC motor driving device comprising: the first rectifier circuit according to any one of the first to third aspects; By setting the ripple content ratio to 90% or more, it is possible to use a very small-capacity and small-sized capacitor, so that the drive device can be significantly reduced in size.

  The invention of the brushless DC motor drive device according to claim 5 is the invention according to any one of claims 1 to 4, wherein a predetermined time is determined based on a detection time when position detection is possible. The time is set and estimation is performed on the assumption that the position changes every predetermined time when the position cannot be detected. In a state where the position cannot be detected, the motor operates with inertia (moment of inertia). Therefore, stable operation can be realized and motor stop can be prevented.

  According to a sixth aspect of the present invention, there is provided the brushless DC motor drive device according to any one of the first to fifth aspects, wherein the output voltage of the first rectifier circuit is equal to or lower than a predetermined voltage. In this case, since it is determined that the position cannot be detected, it is possible to accurately determine a portion where the position cannot be detected, and a more stable operation can be performed.

  A brushless DC motor driving device according to a seventh aspect of the present invention is the brushless DC motor according to any one of the first to sixth aspects, wherein the brushless DC motor is refrigerated and air-conditioned together with a condenser, a decompressor, and an evaporator. Drives the compressor that makes up the system, and can realize a small-capacitance capacitor for applications that cannot be equipped with position detection sensors. .

  The invention of the brushless DC motor driving device according to claim 8 is such that the compressor in the invention according to claim 7 has a reciprocating configuration, whereby the motor inertia is increased and the ripple content is 90% or more. Even when the voltage is input to the inverter, stable cooling performance can be obtained without cooling failure due to stoppage of the refrigeration system or the like.

  The invention of the brushless DC motor drive device according to claim 9 is such that the refrigerant of the refrigeration air conditioning system in the invention of claim 7 or claim 8 is R600A, and as the refrigerant of the refrigeration air conditioning system, When using R600A with low refrigeration capacity, the piston of the compressor becomes large, resulting in an increase in motor inertia, which is less susceptible to motor rotation due to the ripple of the inverter input voltage, and more stable in speed. realizable.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the same reference numerals are given to the same configurations as those of the conventional technology or the embodiments described above, and detailed description thereof will be omitted. In addition, this invention is not limited by this embodiment.

(Embodiment 1)
FIG. 1 is a block diagram of a brushless DC motor driving apparatus according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the compressor according to the first embodiment.

  In FIG. 1, an AC power supply 10 is a general commercial power supply, and is 100 V 60 Hz or 60 Hz in Japan. In the first rectifier circuit 11, four diodes are bridge-connected, and an input from the AC power supply 10 is converted into a DC voltage.

  The inverter 12 has a three-phase bridge connection of six circuits each including a switch element and a diode connected in the opposite direction to the switch element. In the first embodiment, an IGBT is used as the switch element, but a power element such as a transistor or FET may be used. When an FET is used as the switch element, a diode connected in the opposite direction to the switch element uses a parasitic diode between the source and drain.

  A snubber capacitor 13 is inserted in parallel with the inverter 12, and a film capacitor having a small capacity of 0.01 μF to 1 μF is generally used. The insertion position of the snubber capacitor 13 is arranged so that the wiring distance to the inverter 12 is as close as possible. Furthermore, the wiring distance between the inverter 12 and the first rectifier circuit 11 is as close as possible, so that the distance between the snubber capacitor 13 and the first rectifier circuit 11 is close, and the snubber capacitor 13 serves as a smoothing capacitor. Will come to have.

  The brushless DC motor 14 is driven by the three-phase output from the inverter 12. The stator 15 of the brushless DC motor 14 is provided with a three-phase star-connected winding. This winding method may be concentrated winding or distributed winding. The rotor 16 is provided with a permanent magnet. The arrangement method may be a surface magnet type (SPM) or an embedded type (IPM), and the material of the permanent magnet may be rare earth or ferrite. Absent.

  In FIG. 2, oil 18 is stored in a sealed container 17 and a refrigerant 19 of R600a is sealed, and the brushless DC motor 14 and the compression element 20 driven thereby are elastically supported by a spring or the like. The compression element 20 includes a crankshaft 23 composed of a main shaft portion 21 and an eccentric shaft portion 22 to which the rotor 16 is fixed, a cylinder 25 that supports the main shaft portion 21 of the crankshaft 23 and has a compression chamber 24. Since the reciprocating type compressor machine 28 is configured by including a piston 26 that reciprocates in the compression chamber 24 and a connecting means 27 that connects the eccentric shaft portion 22 and the piston 26, a rotary configuration and a scroll configuration are provided. Compared with this compressor, the compressor has a large motor inertia.

  Furthermore, in the first embodiment, R600A is used as the refrigerant. For example, since the refrigerating capacity is low compared to the refrigerant such as R134A, the volume of the cylinder 25 of the compressor is set to ensure the same refrigerating capacity. As a result of the increase in the piston 26, the motor inertia is further increased.

  The discharge gas compressed by the compressor 28 constitutes a refrigeration air-conditioning system that returns to the suction of the compressor 28 through the condenser 29, the decompressor 30, and the evaporator 31. At this time, the condenser 29 dissipates heat and the evaporator 31 absorbs heat, so that cooling and heating can be performed. If necessary, the heat exchange may be further promoted by using a blower or the like for the condenser 29 or the evaporator 31.

  The control unit 32 includes a position detection unit 33, a position estimation unit 34, a voltage detection unit 35, a switching unit 36, and a commutation unit 37, and is operated by a power supply supplied from a power supply circuit 38.

  The position detection means 33 detects the relative rotational position of the rotor 16 of the brushless DC motor 14 from the induced voltage of the brushless DC motor 14 or the motor current. In the first embodiment, a method for detecting the rotational position of the rotor 16 from the induced voltage will be described. The inverter 12 is a 120-degree energization method rectangular wave drive, and in this method, a phase that is not always energized is generated. The zero cross point of the induced voltage generated in the non-energized phase is detected, and the relative position of the rotor is detected.

  When the position detecting unit 33 normally detects the rotor position, the position estimating unit 34 measures the time of the detection timing. Then, position estimation is performed based on this timing time, and motor drive output is performed.

  The voltage detection means 35 detects the output voltage of the first rectifier circuit 11, that is, the input voltage of the inverter 12, and compares the voltage value with a predetermined value set in advance.

  The switching unit 36 selects one of the position detection unit 33 and the position estimation unit 34 from the output of the voltage detection unit 35 and outputs the selected one to the commutation unit 37. The commutation means 37 controls ON / OFF of the IGBT of the inverter 12 by the output from the switching means.

  The power supply circuit 38 connects a circuit in which a second rectifier circuit 39 formed of a diode and a smoothing circuit 40 having a smoothing capacitor having a relatively small capacity are connected in series with the first rectifier circuit 11, and thereby a smoothing circuit. A low voltage power supply (usually in the range of 3V to 24V) to be supplied to the control means 32 is generated with the voltage at both ends of 40 as an input.

  The operation of the brushless DC motor driving apparatus configured as described above will be described.

  Although the AC power supply 10 is full-wave rectified by the first rectifier circuit 11, the voltage input to the inverter 12 has a large ripple because the capacity of the snubber capacitor 13 also serving as a smoothing capacitor is very small. It becomes a waveform. The smoothing circuit 40 smoothes the output of the first rectifier circuit 11, but the voltage across the smoothing capacitor of the smoothing circuit 40 is higher than the output voltage of the first rectifier circuit 11 because it passes through the second rectifier circuit 39. Even when the load of the brushless DC motor 14 is large and the input voltage to the inverter 12 is large, the smoothing circuit 40 is connected via the second rectifier circuit 39, so that the smoothing capacitor is charged. Charge release can be prevented. Therefore, the voltage applied to both ends of the smoothing circuit 40 becomes a constant voltage that is slightly smoothed. As a result, a stable DC voltage can be supplied to the power supply circuit 38.

  FIG. 3 is a characteristic diagram showing voltage values across the snubber capacitor 13 and the smoothing circuit 40 of the first embodiment.

  Here, the withstand voltage of the used snubber capacitor 13 and the smoothing capacitor of the smoothing circuit 40 is set to 450V. Here, if the brushless DC motor 14 suddenly stops due to out-of-step or the like and regeneration is generated, if only the snubber capacitor 13 is present, the voltage across the snubber capacitor 13 as shown in the voltage waveform a of FIG. Suddenly rises, exceeds the withstand voltage 450V and becomes overvoltage, and the device may break down.

  On the other hand, in the first embodiment, since the smoothing circuit 40 is connected in parallel with the inverter 12 via the second rectifier circuit 39, the smoothing capacitor of the smoothing circuit 40 absorbs the energy generated by the regeneration. Therefore, as shown in the voltage waveform b in FIG. 3, the voltage increase due to the regenerative power can be suppressed below the withstand voltage of the capacitor.

  Further, since both ends of the smoothing circuit 40 are connected to a power supply circuit 38 for supplying power to the control means 32, the electric charge charged by the energy due to regeneration is consumed by the power supply circuit 38 and the control means 32, and is smoothed. As shown by the voltage waveform c in FIG. 3, the voltage across the circuit 40 recovers to a normal level (about 140 V in the first embodiment). Therefore, even if regeneration occurs again, the smoothing circuit 40 can absorb the regenerative energy again, so that the withstand voltage of the smoothing capacitor and the snubber capacitor 13 is not exceeded.

  Since the position detection means 33 detects the relative rotational position of the rotor 16 of the brushless DC motor 14 from the induced voltage or the motor current, when the output voltage of the first rectifier circuit 11 is low, a predetermined voltage or A sufficient current cannot be secured, and it becomes impossible to detect the position of the rotor.

  On the other hand, the position estimation means 34 always detects the position detection timing of the position detection means 33, and if no position detection signal is input, the position estimation means 34 estimates that there is position detection at the same timing as the previous position detection timing. , Output a signal.

  If the output voltage of the first rectifier circuit 11 (ie, the inverter input voltage) detected by the voltage detection means 35 is higher than a predetermined voltage value set in advance (50 V in the first embodiment), the switching means 36 detects the position. The signal of the means 33 is selected and output to the commutation means 37.

  Although not shown here, the voltage detection means 35 always detects the output voltage of the first rectifier circuit 11 (that is, the input voltage of the inverter 12), performs feedforward control to the PWM control duty of the output, and the inverter 12 The output voltage or current is controlled to be constant.

  That is, when the output voltage of the first rectifier circuit 11 (that is, the input voltage of the inverter 12) is high with respect to the basic duty obtained by the speed control, the duty is reduced, and when the output voltage is low, the output is reduced. The voltage or current is adjusted, and the brushless DC motor 14 is smoothly driven.

  Next, the input voltage waveform of the inverter 12 will be described with reference to FIGS.

  In FIG. 1, since a smoothing capacitor is not inserted in the output of the first rectifier circuit 11, the full-wave rectified voltage of the AC power supply is input to the input of the inverter 12, but the snubber capacitor 13 is smoothed. As a result of also serving as a capacitor, a voltage slightly smoothed by the snubber capacitor 13 is input to the inverter input.

  FIG. 4 is a timing chart showing the input voltage waveform of the inverter according to the first embodiment. The vertical axis represents voltage, and the horizontal axis represents time. The AC power supply 10 is an AC power supply of AC 100 V and 50 Hz.

  A is a state when the brushless DC motor 14 is stopped, that is, when the load current is very small (when almost no current flows), the charge of the snubber capacitor 13 is hardly used, and the voltage drop is small. . However, the load current referred to here is an output current of the first rectifier circuit 11 and indicates an input current to the inverter 12 and an input current to the power supply circuit 38. The average voltage at this time is about 132 V, and the ripple content is about 23%. In addition, a ripple voltage and a ripple content rate shall be defined as (Equation 1) and (Equation 2).

次にブラシレスＤＣモータ１４が低負荷状態で駆動し、インバータ１２に流れる負荷電流が発生すると、スナバコンデンサ１３の充電電荷が使われ、Ｂに示すように瞬時最低電圧が低下する。但し、電源電圧から決まる瞬時最高電圧は１４１Ｖで変わらない。Ｂに示す場合、瞬時最低電圧は４０Ｖであるため、平均電圧は約１１２Ｖとなり、リプル電圧は１０１Ｖ、リプル含有率は９０％となる。

Next, when the brushless DC motor 14 is driven in a low load state and a load current flowing through the inverter 12 is generated, the charge charged in the snubber capacitor 13 is used, and the instantaneous minimum voltage decreases as shown in B. However, the instantaneous maximum voltage determined from the power supply voltage is 141 V and does not change. In the case of B, since the instantaneous minimum voltage is 40V, the average voltage is about 112V, the ripple voltage is 101V, and the ripple content is 90%.

  Further, when the load of the brushless DC motor 14 is increased to increase the load current flowing through the inverter 12, almost no charge charge is stored in the snubber capacitor 13, and the instantaneous minimum voltage is reduced to 0V as indicated by C. However, since the instantaneous maximum voltage determined from the power supply voltage is constant at 141 V, the average voltage is 100 V, the ripple voltage is 141 V, and the ripple content is 141%. As the load current increases, the input voltage of the inverter 12 increases the AC voltage. It approaches a wave rectified waveform.

  Next, the relationship between the load current, the instantaneous minimum voltage, and the ripple content will be described in more detail with reference to FIG. FIG. 5 is a characteristic diagram showing the load current, instantaneous minimum voltage, and ripple content in the first embodiment.

  In FIG. 5, the horizontal axis represents the load current, and the vertical axis represents the instantaneous minimum current and the ripple content. The solid line indicates the instantaneous minimum voltage characteristic, and the broken line indicates the ripple content characteristic.

  In the case of the current waveform indicated by A described in FIG. 4, the load current is 0.01 A, the instantaneous minimum voltage is 111 V, and the ripple content is about 23%. In the case of the current waveform shown in B, the load current (the sum of the input current of the control circuit 38 and the input current of the inverter 12) is about 0.18 A, the instantaneous minimum voltage is 40 V, and the ripple content is 90%. is there. In the case of the current waveform shown in C, the load current is 0.35 A, the instantaneous minimum voltage OV, and the ripple content rate is 141%. When the load current is 0.35 A or more, neither the instantaneous minimum voltage nor the ripple content is changed.

  In the first embodiment, when the brushless DC motor 14 is stably driven in the actual use range of the apparatus, the snubber capacitor 13 is selected such that the ripple content is always 90% or more. .

  In the first embodiment, as described above, the position cannot be detected at 50 V or less, and as a result, when the brushless DC motor 14 is being driven, a timing at which the position cannot be detected occurs.

  Next, the operation in FIG. 1 will be described in more detail with reference to FIGS. FIG. 6 is a flowchart showing the operation in the first embodiment.

  First, in STEP 1, the voltage detection means 35 detects the DC voltage Vdc. The DC voltage Vdc referred to here is the input voltage of the inverter 12. Next, in STEP2, the voltage is compared with a predetermined voltage 50V at which position detection cannot be performed. If it is less than 50V, the process proceeds to STEP3.

  In STEP 3, the switching unit 36 selects and switches the position estimation unit 34. The position estimating means 34 determines whether or not the position detection signal has passed a certain time since the previous change, as shown in STEP 4. This fixed time is a time determined in advance by position detection, and the time varies depending on the rotational speed.

  If the predetermined time has not passed, the process passes as it is and the processing is completed. If the predetermined time has elapsed, the process proceeds to STEP 5 and performs an operation (commutation) of switching the switching element of the inverter 12 by the commutation means 37, assuming that the position has been detected.

  If it is determined in STEP2 that the result of comparison with the predetermined voltage 50V at which position detection cannot be performed is 50V or more, the process proceeds to STEP6. In STEP 6, the switching unit 36 selects and switches the position detection unit 33. The position detection means 33 determines whether or not the position detection signal has changed from the previous change, as shown in STEP 7.

  If the state has not changed in STEP 7, it passes and the process is completed. If the state has changed, the process proceeds to STEP 8, and the operation of switching the switching element of the inverter 12 by the commutation means 37 (commutation) is performed on the assumption that the position has been detected.

  By repeating these operations within a predetermined time, the voltage detecting means 35 can always detect the state of the DC voltage, and the signal between the position detecting means 33 and the position estimating means 34 can be switched by the switching means 36 according to the state. The commutation operation can be performed even when the DC voltage is low and the position cannot be detected, and the brushless DC motor can be continuously driven stably.

  The case where the operation described above is performed will be further described with reference to FIGS. FIG. 7 is a timing chart showing waveforms at various parts in the first embodiment.

  In FIG. 7, (A) is a DC voltage, which is an input voltage of the inverter 12. (B) is voltage detection and is an output signal of the voltage detection means 35. The voltage detection means 35 outputs a result of comparing the direct current voltage of (A) with a predetermined voltage (50 V in the first embodiment). If it is 50 V or more, the High level is set, and if it is less than 50 V, the Low level is set. Output a signal. FIG. 7 shows a case where the DC voltage is 50 V or less at times T6 and T7.

  (C) is position detection, and shows the output of the position detection means 33. (D) is position estimation, and shows the output of the position estimation means 34. When the DC voltage is 50 V or higher, position detection is possible, and position detection can be performed in a normal state during the time periods T1 to T5 and T8 to T12 in FIG.

  On the other hand, since the DC voltage is less than 50 V at times T6 and T7 in FIG. 7, no position detection signal is output from the position detection means 33. Moreover, even if it comes out, there is a high possibility that the timing is not exactly matched and an unreliable signal is generated.

  Therefore, at time T6 and T7, the signal of the position estimation means 34 is used for commutation. The position estimation means measures the time from the previous commutation timing T5, and performs commutation after a predetermined time has elapsed from time T6 when a predetermined time has elapsed. Similarly, at time T7, commutation is performed after a predetermined time has elapsed from time T6. The predetermined time mentioned here is a predetermined time by measuring a time during which position detection is normally performed, for example, a time between time T4 and T5.

  As described above, the switching means 36 selects and outputs the output of the position detection means 33 at times T1 to T5 and times T8 to T12. At times T6 and T7, the switching means 36 selects and outputs the output of the position estimating means 34. The output of the switching means 36 is input to the commutation means 37, and the commutation means 37 turns on / off the six switching elements of the inverter 12 as shown in (E) to (J) of FIG. In FIG. 7, the High level is ON and the Low level is OFF.

  As an example of the output waveform of the inverter 12, FIG. The maximum output voltage is regulated by the DC voltage, and the envelope of the U-phase voltage (shown by a broken line) matches the DC voltage of (A).

  As described above, since the duty of the PWM control is changed according to the voltage level of the DC voltage, as shown in FIG. 7K, the duty is increased at a low voltage (for example, between time T5 and T6), and the voltage At high places (for example, between questions T11 to T12), the duty is lowered. This prevents current instability due to voltage fluctuations.

  In the first embodiment, the voltage detection means 35 that directly detects the voltage level is used. However, it may be one that detects timing such as zero crossing and estimates the voltage level according to time.

  Further, the position detection means 33 and the position estimation means 34 are switched by the DC voltage, but a method of automatically switching to the position estimation means 34 when no position detection signal is output may be used.

  In the first embodiment, the position detection means 33 detects the position in real time. However, the position detection means averaged overall (for example, the timing difference between the overall position detection and commutation is averaged). You may use the method of viewing).

  Further, in the first embodiment, the power supply destination of the power supply circuit 38 is only the control means 32, but for other additions such as a blower provided to promote heat exchange of the condenser 29 and the evaporator 31. It does not matter as a configuration to supply.

  As described above, the brushless DC motor driving apparatus according to the present invention can reduce the number of parts and reduce the cost, and can achieve a significant reduction in size. Furthermore, since stable driving can be realized, the present invention can be applied not only to a compressor driving device but also to all devices using brushless DC motors such as household appliances.

1 is a block diagram of a brushless DC motor driving apparatus according to Embodiment 1 of the present invention. Sectional drawing of the compressor using the brushless DC motor in the same embodiment The characteristic figure which shows the voltage value of the both ends of the snubber capacitor and smoothing circuit of the drive device of the brushless DC motor of the embodiment Timing chart showing the input voltage waveform of the inverter of the brushless DC motor driving apparatus of the embodiment Characteristic diagram showing load current, instantaneous minimum voltage and ripple content of the brushless DC motor drive device of the same embodiment The flowchart which shows operation | movement of the drive device of the brushless DC motor of the embodiment Timing chart showing waveforms of respective portions of the brushless DC motor driving apparatus of the same embodiment Block diagram of a conventional brushless DC motor drive device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 AC power supply 11 1st rectifier circuit 12 Inverter 13 Snubber capacitor 14 Brushless DC motor 16 Rotor 19 Refrigerant R600A
28 Compressor 29 Condenser 30 Decompressor 31 Evaporator 32 Control means 33 Position detection means 34 Position estimation means 36 Switching means 38 Power supply circuit 39 Second rectifier circuit 40 Smoothing circuit

Claims (9)

  An AC power source, a first rectifier circuit that rectifies the input of the AC power source, an inverter connected to the first rectifier circuit, a snubber capacitor connected in parallel with the inverter, and a brushless DC motor driven by the inverter The brushless DC motor based on position detection means for detecting the rotational position of the rotor of the brushless DC motor from the induced voltage or motor current of the brushless DC motor, and position information of the rotor obtained from the position detection means. A drive unit for a brushless DC motor configured to control the inverter to drive the inverter, and the snubber capacitor also functions as a smoothing capacitor that smoothes the output voltage of the first rectifier circuit .   An AC power source, a first rectifier circuit and a second rectifier circuit that rectify the input of the AC power source, an inverter connected to the first rectifier circuit, a snubber capacitor connected in parallel with the inverter, and the inverter driven Brushless DC motor, position detecting means for detecting the rotational position of the rotor of the brushless DC motor from the induced voltage or motor current of the brushless DC motor, and operating the inverter, and the rotor obtained from the position detecting means Based on the positional information, a control means for controlling the inverter to drive the brushless DC motor, a smoothing circuit for smoothing the voltage rectified by the second rectifier circuit, and a parallel connection to the smoothing circuit. A power supply circuit that converts a DC high voltage smoothed by the smoothing circuit into a DC low voltage, and the power supply circuit Brushless DC motor driving device configured so as to supply power to said control means.   3. The brushless DC motor driving device according to claim 1, wherein when the position cannot be detected by the position detecting means, the position is estimated and the inverter is operated. .   4. The brushless DC motor according to claim 1, wherein the first rectifier circuit has an output DC voltage ripple content of 90% or more in an actually used output range. 5. Drive device.   A predetermined time is determined based on a detection time when the position can be detected, and estimation is performed on the assumption that the position is switched every predetermined time when the position cannot be detected. The drive device of the brushless DC motor according to any one of claims 1 to 4.   The brushless according to any one of claims 1 to 5, wherein when the output voltage of the first rectifier circuit is equal to or lower than a predetermined voltage, it is determined that the position cannot be detected. DC motor drive device.   The brushless DC motor according to any one of claims 1 to 6, wherein the brushless DC motor drives a compressor constituting a refrigeration air conditioning system together with a condenser, a decompressor, and an evaporator. Drive device.   The brushless DC motor driving apparatus according to claim 7, wherein the compressor has a reciprocating configuration.   The brushless DC motor driving apparatus according to claim 7 or 8, wherein the refrigerant of the refrigeration air conditioning system is R600A.

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