JP2007209098A - Inverter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter device that can prevent the overheating and the breakage of a MOSFET when a reverse voltage application circuit is failed, and is improved in safety. <P>SOLUTION: When a backflow current flows into the MOSFET in each series circuit of a switching circuit 1, a reverse voltage is applied to the MOSFET from a reverse voltage application circuit prior to the turning-on of the other switching element of the same series circuit as of the MOSFET for suppressing a reverse recovery current in the MOSFET. When the reverse voltage application circuit is failed as inoperable, a frequency is reduced in the generation of the reverse recovery current in the MOSFET. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter device for driving a motor, for example.

  An inverter device for driving a load including an inductive component, for example, a brushless DC motor, includes a plurality of series circuits of two switching elements on the upstream side and the downstream side in the voltage application direction. The interconnection point of the downstream switching element is connected to each phase winding of the brushless DC motor. Each switching element has a free wheel diode (also referred to as a parasitic diode).

  Recently, many IGBTs and MOSFETs have been adopted as switching elements. When a MOSFET is used, there is a merit that high-frequency switching is possible because the on / off speed of the MOSFET is fast, and it is frequently used when driving a motor with a small output such as a fan motor because the loss at low voltage output is small. Is done.

  However, in MOSFET, there is a problem that reverse recovery characteristics of a free-wheeling diode made on the same element in the process of manufacturing the element are poor. In recent years, super junction MOSFETs have been developed that have low on-state resistance and excellent switching characteristics. However, in this super junction MOSFET, the reverse recovery characteristics of the freewheeling diode formed on the device become worse. ing.

  If the reverse recovery characteristic of the freewheeling diode is poor, the following problems occur. That is, when the MOSFET is turned off, the forward current (also called the reflux current) flows to the MOSFET's freewheeling diode due to the energy stored in the inductive load. In this state, the other switching element of the same series circuit is turned on. When a DC voltage is applied to the MOSFET, a large reverse recovery current (also referred to as a spike current) due to the charge stored in the freewheeling diode flows through the freewheeling diode. This reverse recovery current results in a large power loss. In addition, most of the power loss is generated when the other switching element paired with the MOSFET is turned on, and when this is increased, the other switching element is destroyed by the heat.

  For this reason, it is very difficult to employ a MOSFET for an inverter through which a large current flows, for example, to drive a compressor motor of an air conditioner.

Therefore, conventionally, a reverse voltage application circuit that applies a reverse voltage to the MOSFET prior to turning on the other switching element is provided, and the reverse recovery current flowing to the freewheeling diode is prevented by applying the reverse voltage, thereby reducing power loss. There is something to plan (for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-327585

  When the reverse voltage application circuit as described above is adopted, the power loss due to the reverse recovery current can be greatly suppressed, so that a MOSFET can be adopted as a switching element for a large output motor for driving a compressor motor or the like. If a failure (opening failure) occurs due to breakdown or deterioration of characteristics in the voltage application circuit, reverse recovery current in the freewheeling diode cannot be prevented, and in the worst case, the switching element overheats and breaks down. End up.

  Although the reverse voltage circuit is a simple electric / electronic circuit configuration such as a diode or a capacitor, it is unlikely that a failure will occur. However, a switching element is used to control the timing and period of reverse voltage application. Since this switching element part becomes an electrically movable part, the possibility that a failure will occur in this part is the highest. And it is considered that most of the failure of this circuit finally leads to an open (open) failure.

  In addition, when a failure occurs, it is possible to prevent the switching element from being destroyed by stopping the operation of the inverter device, but the load on the inverter device is an air conditioner, refrigerator compressor, water supply pump, large-scale ventilation in the factory. In the case of a fan or the like, it is desirable to continue the operation within a range where the failure does not expand any more.

  In view of the above circumstances, the present invention provides an inverter device capable of continuing operation while preventing overheating and destruction of a switching element even when a failure occurs in which a reverse voltage application circuit does not operate. With the goal.

  The inverter device of the invention according to claim 1 includes a plurality of series circuits of two switching elements using at least one of MOSFETs having a freewheeling diode, and an interconnection point of each switching element of these series circuits is connected to a load. First control means for sequentially switching energization to the load by a switching circuit and a switching element upstream of at least one of the series circuits and a switching element downstream of at least one other series circuit And, prior to turning on the other switching element of the same series circuit as the MOSFET, a reverse voltage application circuit for applying a reverse voltage to the MOSFET, and a failure detection means for detecting a malfunction of the reverse voltage application circuit, When a failure is detected by this failure detection means, the number of times the MOSFET is switched is And it includes a second control means for reducing a normally, the.

  According to the inverter device of the present invention, when the reverse voltage application circuit fails, the frequency of the reverse recovery current in the MOSFET is reduced. Thereby, a certain amount of continuous operation is possible while preventing overheating and destruction of the switching element.

[1] A first embodiment of the present invention will be described below with reference to the drawings.
In FIG. 1, M is a brushless DC motor (load) used as a compressor motor of an air conditioner, and includes a stator having three phase windings Lu, Lv, Lw connected in a star shape, and a rotor having a permanent magnet. It is configured. The rotor rotates due to the interaction between the magnetic field generated by the current flowing through the phase windings Lu, Lv, and Lw and the magnetic field generated by the permanent magnet.

  The brushless DC motor M is accommodated in the compressor 20 as a power source. During cooling, the refrigerant discharged from the compressor 20 flows to the outdoor heat exchanger 22 via the four-way valve 21 as shown by the solid line arrow in the figure, and the refrigerant passing through the outdoor heat exchanger 22 passes through the expansion valve 23. It flows to the indoor heat exchanger 24. Then, the refrigerant that has passed through the indoor heat exchanger 24 is sucked into the compressor 20 through the four-way valve 21. Thereby, the outdoor heat exchanger 22 functions as a condenser, and the indoor heat exchanger 24 functions as an evaporator. At the time of heating, the four-way valve 21 is switched, whereby the refrigerant flows in the direction indicated by the broken-line arrow, and the indoor heat exchanger 24 functions as a condenser and the outdoor heat exchanger 22 functions as an evaporator.

  The brushless DC motor M is connected to the inverter device of the present invention. The inverter device includes a switching circuit 1 that receives an output (for example, DC 280 V) of a DC power source 30 rectified from a commercial AC power source and performs energization to the phase windings Lu, Lv, and Lw and switching of the energization. It is comprised by the control part 10 which controls drive.

  The switching circuit 1 has a series circuit of low-loss power MOSFETs (superjunction MOSFETs, etc.) for three phases U, V, and W as upstream and downstream switching elements along a DC voltage application direction. MOSFET 2u is provided upstream of the phase, MOSFET 3u is provided downstream of the U phase, MOSFET 2v is provided upstream of the V phase, MOSFET 3v is provided downstream of the V phase, MOSFET 2w is provided upstream of the W phase, and MOSFET 3w is provided downstream of the W phase. . The free-wheeling diodes Du +, Dv +, and Dw + are connected in reverse parallel to the MOSFETs 2u, 2v, and 2w, respectively. The free-wheeling diodes Du−, Dv−, and Dw− are connected in reverse parallel to the MOSFETs 3u, 3v, and 3w, respectively. These free-wheeling diodes are built in corresponding MOSFETs (element bodies) as parasitic diodes.

  The unconnected ends of the phase windings Lu, Lv, and Lw are respectively connected to an interconnection point between the MOSFETs 2u and 3u, an interconnection point between the MOSFETs 2v and 3v, and an interconnection point between the MOSFETs 2w and 3w.

  In addition, the switching circuit 1 has a downstream current when a forward current (return current) flows through the freewheeling diodes Du +, Dv +, and Dw + by the energy stored in the phase windings Lu, Lv, and Lw that are inductive loads. In order to suppress the reverse recovery current Irr flowing through the free-wheeling diodes Du +, Dv +, and Dw + when the MOSFETs 3u, 3v, and 3w are turned on, the free-wheeling diodes Du + and Dv + of the MOSFETs 2u, 2v, and 2w are turned on before the MOSFETs 3u, 3v, and 3w are turned on. , Dw + are provided with reverse voltage application circuits 4u, 4v, 4w.

  Similarly, reverse-side voltage application circuits 5u, 5v, and 5w are provided in the downstream MOSFETs 3u, 3v, and 3w, respectively.

  The reverse voltage application circuit 4 u applies a voltage (for example, 15 V) of the DC power supply 40 to the reverse voltage application capacitor 42 via the resistor 41, and uses the voltage of the reverse voltage application capacitor 42 as the drain of the reverse voltage application MOSFET 43. A reverse voltage is applied to the MOSFET 2u between the sources and via the diode 44. Further, the reverse voltage application circuit 4 u has a pulse generation circuit 45 and a gate drive circuit 46 for driving the reverse voltage application MOSFET 43. The pulse generation circuit 45 generates a pulse signal for applying a reverse voltage in response to a command from the control unit 10. The gate drive circuit 46 outputs a one-shot pulse signal for turning on the reverse voltage application MOSFET 43 based on the pulse signal generated by the pulse generation circuit 45. This output is supplied to the gate of the reverse voltage application MOSFET 43.

  The other reverse voltage application circuits 4v and 4w and the reverse voltage application circuit 5u have the same configuration as the reverse voltage application circuit 4u. Therefore, the description is omitted. The reverse voltage application circuits 5v and 5w are the same as the reverse voltage application circuit 4u, except that the reverse voltage application circuits 5v and 5w are different from the other in that a direct current voltage is taken from the direct current power source 40 of the reverse voltage application circuit 5u.

  On the other hand, a current detection resistor 11u is inserted downstream of the MOSFET 3u in the series circuit of the MOSFET 2u and the MOSFET 3u. A current detection resistor 11v is inserted downstream of the MOSFET 3v in the series circuit of the MOSFET 2v and the MOSFET 3v. A current detection resistor 11w is inserted downstream of the MOSFET 3w in the series circuit of the MOSFET 2w and the MOSFET 3w. A voltage of a level corresponding to the current flowing through the MOSFETs 3u, 3v, 3w is generated in these resistors 11u, 11v, 11w. Then, voltages generated in the resistors 11u, 11v, and 11w are supplied to the control unit 10.

  The controller 10 detects the current flowing through each phase winding of the brushless DC motor M from the voltage generated in the resistors 11u, 11v, and 11w, and estimates the rotational speed of the rotor of the brushless DC motor M from the detected current. Drives each MOSFET and each reverse voltage application circuit of the switching circuit 1 at a predetermined timing based on the rotational speed. As a main function, the upstream side of at least one of the series circuits of each MOSFET in the switching circuit 1 First control means for sequentially switching energization of each phase winding by the MOSFET on the downstream side of the MOSFET and another at least one series circuit, and failure detection means for detecting a failure of each reverse voltage application circuit in the switching circuit 1 When a failure is detected by this failure detection means, a reverse recovery current flows through each MOSFET. And a second control means for reducing the frequency that. Specifically, in order to reduce the frequency at which the reverse recovery current flows, the second control means executes control for reducing the number of switching times of each MOSFET than usual. The principal part of this control part 10 is shown in FIG.

  In FIG. 2, reference numeral 50 denotes a reference signal generation unit having a three-phase sine wave signal generation unit 51, a waveform shaping unit 52, and a selection unit 53. The three-phase sine wave signal generator 51 generates three-phase sine wave signals whose phases are different from each other by 120 degrees. The waveform shaping unit 52 performs two-phase modulation based on the interphase voltage (voltage difference) of the three-phase sine wave by shaping the waveform based on the three-phase sine wave signal generated by the three-phase sine wave signal generation unit 51. Signal, that is, a three-phase wave signal having a voltage waveform whose phase is fixed at a zero level over a predetermined period (period having a phase of 120 degrees). The selection unit 53 responds to a command from a selection control unit 74 described later among the three-phase sine wave signal generated by the three-phase sine wave signal generation unit 51 and the two-phase modulation signal generated by the waveform shaping unit 52. Any one of them is output as the reference signals Eu, Ev, Ew. The reference signal Eu is supplied to the PWM basic signal Vu generator 55, the reference signal Ev is supplied to the PWM basic signal Vv generator 56, and the reference signal Ew is supplied to the PWM basic signal Vw generator 57, respectively.

  A triangular wave signal generator 54 generates a triangular wave signal (also called a carrier signal) Eo having a predetermined frequency and voltage level. The triangular wave signal Eo is supplied to the PWM basic signal Vu generator 55, the PWM basic signal Vv generator 56, and the PWM basic signal Vw generator 57.

  The PWM basic signal Vu generation unit 55, the PWM basic signal Vv generation unit 56, and the PWM basic signal Vw generation unit 57 are output from the reference signals Eu, Ev, Ew output from the reference signal generation unit 50 and the triangular wave signal generation unit 54. The PWM basic signals Vu, Vv, Vw for switching for each MOSFET are generated by voltage comparison with the triangular wave signal Eo.

  FIG. 3 shows an example of waveforms of the reference signal Eu, the triangular wave signal Eo, and the PWM basic signal Vu when the three-phase sine wave signal generated by the three-phase sine wave signal generation unit 51 is selectively output as the reference signal Eu. Yes. FIG. 4 shows an example of waveforms of the reference signal Eu, the triangular wave signal Eo, and the PWM basic signal Vu when the two-phase modulation signal generated by the waveform shaping unit 52 is selectively output as the reference signal Eu.

  The PWM basic signal Vu generated by the PWM basic signal Vu generating unit 55 is supplied as an upper element drive signal to the upstream side MOSFET 2u and the reverse voltage applying circuit 4u via the delay unit 61, and the inverting circuit 62 and the delay circuit. A lower element drive signal is supplied to the downstream side MOSFET 3u and the reverse voltage application circuit 5u via 63.

  The PWM basic signal Vv generated by the PWM basic signal Vv generator 56 is supplied as an upper element drive signal to the upstream MOSFET 2v and the reverse voltage application circuit 4v via the delay unit 64, and also includes the inverting circuit 62 and the delay circuit. The lower element drive signal is supplied to the downstream side MOSFET 3v and the reverse voltage application circuit 5v through 63.

  The PWM basic signal Vv generated by the PWM basic signal Vv generation unit 57 is supplied as an upper element drive signal to the upstream side MOSFET 2w and the reverse voltage application circuit 4w via the delay unit 67, as well as the inverting circuit 68 and the delay circuit. 69 is supplied as a lower element drive signal to the downstream side MOSFET 3w and the reverse voltage application circuit 5w via 69.

  FIG. 5 shows an example of the reference signal Eu, the triangular wave signal Eo, the PWM basic signal Vu, the upper element driving signal, the lower element driving signal, the inverted signal, the pulse signal generated by the reverse voltage application circuit 5u, and the one-shot pulse signal. Yes. FIG. 5 shows a signal waveform of low level driving (Low Active). When the upper element driving signal, the lower element driving signal, and the one-shot pulse signal are low level, the MOSFET is turned on, and when it is high level. The MOSFET is turned off.

  The delay unit 61 causes the upper element drive signal to fall to a low level after a predetermined time t1 from the fall of the PWM basic signal Vu to a low level. The inverting circuit 62 inverts the high level and low level of the PWM basic signal Vu. The delay unit 63 lowers the lower element drive signal to a low level after a predetermined time t1 from the rising of the PWM basic signal Vu to a high level. The pulse generation circuit 45 of the reverse voltage application circuit 5u falls to the low level of the PWM basic signal Vu, that is, falls after a certain time t2 from the rise of the lower element (3u) drive signal, and the lower element (3u) drive signal. A pulse signal having a waveform rising after a certain time t2 from the falling of the signal is generated. Further, the pulse generation circuit 45 generates a one-shot pulse signal having a waveform that falls to a low level in synchronization with the fall of the generated pulse signal to a low level and rises to a high level after a certain time t3 from the fall. Output. This one-shot pulse signal becomes the gate drive signal of the gate drive circuit 46, and turns on the reverse voltage application MOSFET 43 of the reverse voltage application circuit 5u.

  There are conditions of t1> t2 and t3> (t1-t2) in the fixed times t1, t2, and t3. Among these, the fixed time t1 is a dead time for preventing the upstream-side MOSFET 2u and the downstream-side MOSFET 3u from being simultaneously turned on (the series circuit is short-circuited) in the same series circuit. The fixed time t2 is for setting the generation timing of the one-shot pulse signal in the period from when the downstream side MOSFET 3u is turned off to when the upstream side MOSFET 2u is turned on. Therefore, the fixed time t3 is a period including the timing when the upstream MOSFET 2u is turned on. That is, the reverse voltage application circuits 4 and 5 of the MOSFETs 2 and 3 are turned on after the corresponding MOSFET is turned off, and turned off after the MOSFET paired with the MOSFET is turned on.

  On the other hand, the voltage generated in the resistors 11u, 11v, and 11w is supplied to the current detector 70. The current detection unit 70 detects the current flowing through each MOSFET, that is, the current flowing through each phase winding of the brushless DC motor M, from the voltages generated in the resistors 11u, 11v, and 11w. This detection result is supplied to the three-phase sine wave signal generation unit 51 of the reference signal generation unit 50 and also to the failure detection unit 71. The three-phase sine wave signal generation unit 51 estimates the rotational speed of the rotor of the brushless DC motor M from the detection result of the current detection unit 70, and the frequencies of the three-phase sine wave signals Eu, Ev, Ew according to the estimated rotational speed. To change. The failure detection unit 71 detects a failure of the reverse voltage application circuits 4u, 5u, 4v, 5v, 4w, and 5w in the switching circuit 1, and is excessive from the current flowing through each MOSFET detected by the current detection unit 70. Generation of the reverse recovery current Irr is detected, and it is determined whether or not the reverse voltage application circuits 4u, 5u, 4v, 5v, 4w, and 5w are malfunctions. The determination result is supplied to the selection control unit 54. The selection control unit 54 controls the selection unit 53 of the reference signal generation unit 50. When the determination result of the failure detection unit 71 indicates no failure, the selection control unit 54 outputs the three-phase sine wave signal from the three-phase sine wave signal generation unit 51. The two-phase modulation signal from the waveform shaping unit 52 is selectively output when the determination result of the failure detection unit 71 is faulty. The reverse recovery current Irr is generated when the reverse voltage application circuit is operating normally when the reverse voltage application circuit is operating normally, and is generated when the paired MOSFET is turned on when the reverse voltage application circuit is not operating. Since the timing is different and the magnitude of the current is also different, detection is possible using either one of these two conditions or a combination of both.

Next, the operation will be described with reference to FIGS.
So-called three-phase modulation is performed by voltage comparison between the reference signals Eu, Ev, Ew of the three-phase sine wave (FIG. 3) and the triangular wave signal Eo. The frequencies of the reference signals Eu, Ev, Ew change in proportion to the rotation speed of the brushless DC motor M. By this voltage comparison, an upper element drive signal for turning on and off the upstream side MOSFETs 2u, 2v, and 2w, and a lower element drive for turning on and off the downstream side MOSFETs 3u, 3v, and 3w of another series circuit, respectively. A signal is created.

  By the upper element drive signal and the lower element drive signal created by this three-phase modulation, the upstream MOSFET of at least one series circuit of each series circuit in the switching circuit 1 is turned on and off to turn on at least one other series. Multiple-phase energization in which the downstream MOSFET of the circuit is turned on is sequentially switched. By switching the multiphase energization, three interphase voltages are generated, and the interphase voltages are applied to the phase windings Lu, Lv, and Lw of the brushless DC motor M. Thereby, a sinusoidal current flows through Lu, Lv, and Lw, and the brushless DC motor M operates.

  By the way, it is assumed that a current based on the energy stored in one of the phase windings flows in the forward direction through the free-wheeling diode Du + of the upstream MOSFET 2u. When this forward current so-called return current flows, the reverse voltage application MOSFET 43 of the reverse voltage application circuit 4u is turned on prior to turning on the downstream side MOSFET 3u, and the voltage stored in the reverse voltage application capacitor 42 is reduced. The reverse voltage is applied to the freewheeling diode Du + of the MOSFET 2u. The reverse voltage application period starts after the MOSFET 3u is turned off and is a fixed time t3 including the ON timing of the MOSFET 2u.

  When a voltage is applied from the reverse voltage application circuit 4u to the MOSFET 2u in a state where the return current flows, a reverse recovery current Irr flows through the return diode Du + of the MOSFET 2u. In this case, the reverse voltage applied to the MOSFET 2u is a voltage based on the DC power supply 40 in the reverse voltage application circuit 4u and is much lower than the voltage of the DC power supply 30 (for example, DC 280V). Even if the reverse recovery current Irr flows through the diode Du +, the value of the reverse recovery current Irr is extremely small.

  Note that the period during which the reverse recovery current Irr flows is longer than when the voltage of the DC power supply 30 (for example, 280 V) is applied. However, since the integrated power value of the freewheeling diode Du + of the MOSFET 2u is a product of the power consumption and the time, even if the period of the reverse recovery current Irr is long, if the value of the reverse recovery current Irr is very small, the integrated power is Significantly lower. Therefore, the power loss in the free-wheeling diode Du + of the MOSFET 2u can be greatly reduced, and the efficiency can be improved.

  Here, if an inoperative failure that opens in each reverse voltage application circuit occurs, the reverse recovery current Irr cannot be suppressed, and the temperature of the MOSFET corresponding to the failed reverse voltage application circuit rises greatly. In this case, the failure detection unit 71 determines that any one of the reverse voltage application circuits has a failure.

  When it is determined that there is a failure, the two-phase modulation signal shown in FIG. 4 is selectively output as the reference signals Eu, Ev, Ew. Then, by performing so-called two-phase modulation based on voltage comparison between the reference signals Eu, Ev, Ew of the two-phase modulation signal and the triangular wave signal Eo, the number of switching times of each MOSFET is almost the same as usual (during three-phase modulation). Decrease to 2/3. Along with this, the frequency of the reverse recovery current Irr flowing through each MOSFET is reduced. By reducing the frequency of the reverse recovery current Irr flowing through each MOSFET, the temperature rise of the MOSFET corresponding to the failed reverse voltage application circuit is suppressed, and overheating and destruction of the MOSFET can be prevented. Along with this change in the modulation method, there are some problems such as efficiency reduction and waveform distortion, but since no fatal problem occurs, the operation can be continued as it is.

[2] A second embodiment will be described.
The principal part of the control part 10 is shown in FIG. That is, a frequency control unit 75 is employed instead of the selection control unit 74 of the first embodiment. The frequency control unit 75 controls the frequency of the triangular wave signal Eo generated by the triangular wave signal generation unit 54, and the frequency of the triangular wave signal Eo is determined in advance when the determination result in the failure detection unit 71 indicates no failure. The predetermined frequency fs is set, and when the determination result is a failure, the frequency of the triangular wave signal Eo is set to a frequency lower by Δf than the predetermined frequency fs.
Other configurations are the same as those of the first embodiment. The operation is shown in the flowchart of FIG.
When it is determined that there is a failure, the frequency of the triangular wave signal Eo is set to a frequency lower by Δf than the normal frequency fs. Thus, the frequency of the triangular wave signal Eo is reduced, so that the number of switching times of each MOSFET is reduced more than usual. Along with this, the frequency of the reverse recovery current Irr flowing through each MOSFET is reduced.

[3] A third embodiment will be described.
The principal part of the control part 10 is shown in FIG. That is, instead of the selection control unit 74 of the first embodiment, a frequency control unit 75 is adopted, and a current estimation unit 72 that estimates the magnitude of the current flowing through the MOSFET from the detection current of the current detection unit 70 is newly provided. In addition, the estimation result of the current estimation unit 72 is supplied to the frequency control unit 75.

The frequency control unit 75 sets the frequency of the triangular wave signal Eo to a predetermined frequency fs that is set in advance when the determination result in the failure detection unit 71 indicates no failure, and the frequency of the triangular wave signal Eo when the determination result indicates that there is a failure. Is set to a frequency lower than the predetermined frequency fs and according to the current estimation result of the current estimation unit 72. The other configuration is the same as that of the first embodiment, and the operation is shown in the flowchart of FIG.
If it is determined that there is a failure, the frequency of the triangular wave signal Eo is set to a frequency that is lower than the predetermined frequency fs during normal operation and that corresponds to the current estimation result of the current estimation unit 72. That is, the greater the current estimated by the current / temperature estimation unit 72, the greater the reduction in the frequency of the triangular wave signal Eo under the judgment that the temperature rise of the MOSFET is greater.

  By reducing the frequency of the triangular wave signal Eo, the switching frequency of each MOSFET is reduced more than usual, and overheating and destruction of the MOSFET can be prevented.

[4] A fourth embodiment will be described. In the fourth embodiment, in addition to the control of any of the first, second, and third embodiments described above, the current flowing through the MOSFET is adjusted by adjusting the motor vector control when the reverse voltage application circuit fails. To reduce.
The configuration of the reference signal generation unit 50 in the control unit 10 is shown in FIG. 11, and the outline of the operation is shown in the flowchart of FIG. The reference signal generator 50 estimates the rotational speed of the rotor of the brushless DC motor M from the phase winding current detected by the current detector 70, and calculates the difference between the estimated rotational speed ωest and the externally set rotational speed ωref. The current control value Iqref corresponding to the obtained difference is obtained by the PI control unit, and another current control value Idref is obtained from the current control value Iqref. The reference signal generation unit 50 passes the current control values Iqref and Idref through the Iq limiting unit and the Id limiting unit, and further passes through the PI control unit, thereby obtaining the voltage control values Vq and Vd, and the voltage control value Vq , Vd, a three-phase sine wave signal having a voltage level corresponding to Vd is output as reference signals Eu, Ev, Ew. The Iq restriction unit and the Id restriction unit turn on the Iq restriction and the Id restriction when a failure is detected by the failure detection unit 71. With this restriction ON, the voltages of the reference signals Eu, Ev, Ew are set to a level lower than the normal level. As a result, the on / off duty of each MOSFET decreases, and accordingly, the current flowing through each MOSFET decreases, and the reverse recovery current decreases accordingly.
Other configurations are the same as those of the first embodiment.

  As a modification, as shown in the flowchart of FIG. 13, the control of the first embodiment, the control of the third embodiment, and the control of the fourth embodiment may be combined. The temperature rise of the MOSFET corresponding to the failed reverse voltage application circuit is reliably suppressed, and the MOSFET can be prevented from overheating and destruction.

[5] A fifth embodiment will be described.
In each of the above embodiments, the failure is detected from the current, and the control amount such as the number of switching is changed according to the current of each MOSFET. However, the temperature of each MOSFET is indirectly detected, and the failure is detected. While using for a detection, it is good also as a structure which changes a control amount.

  That is, in FIG. 14, 80 is a circuit board on which the switching circuit 1 is mounted. A frame 81 is erected on the circuit board 80, and the MOSFETs 2 u, 3 u, 2 v, 3 v, 2 w, and 3 w are in close contact with the heat sink (fined heat sink) 83 on the back surface via three holding members 82. So that it is held. These MOSFETs are connected to the circuit board 80 by wiring. A temperature sensor 84 that detects the temperature of the heat sink 83 is attached to the heat sink 83 near the MOSFET. Although there is only one temperature sensor 84, each MOSFET is located close to each other and is attached in close contact with a heat sink 83 with good thermal conductivity, so if any one of the MOSFETs rises in temperature, Can be detected.

  When this configuration is applied to the first embodiment, the detection temperature of the temperature sensor 84 is input to the failure detection unit 71 in FIG. 2 instead of the detection result of the current detection unit 70, and the detection temperature is equal to or higher than a predetermined value. If it is less than a predetermined value, it is determined to be normal.

  Further, when applied to the third embodiment of FIG. 9, the detected temperature of the temperature sensor 84 is input to the failure detection unit 71 instead of the detection result of the current detection unit 70, and the temperature estimation is performed instead of the current estimation unit 72. Parts are provided. This temperature estimation part is detected by the temperature sensor 84 and estimates the temperature of the MOSFET element from the heat sink temperature. When it is determined that there is a failure, the frequency width of the triangular wave signal Eo is increased as the frequency of the triangular wave signal Eo is lower than the normal frequency fs and the estimated temperature is higher. Similarly, the present invention can be applied to the second and fifth embodiments.

  In addition, failure detection is detected by current, and the change of the control amount (switching circuit) is controlled based on the estimated temperature of the element, or conversely, the failure is detected by temperature. It is also possible to control based on the estimated current value, and various combinations are conceivable.

  [6] In each of the above embodiments, MOSFETs are all used as switching elements in the switching circuit 1. However, the MOSFETs only need to be used in at least one of the series circuits in the switching circuit 1, and the remaining switching elements are other switching elements. It is possible to use.

The figure which shows the structure of 1st Embodiment of this invention, and the structure of a refrigerating cycle. The block diagram which shows the structure of the principal part of the control part in 1st Embodiment. The figure which shows the waveform of the three-phase sine wave signal in 1st Embodiment, a triangular wave signal, and a PWM basic signal. The figure which shows the waveform of the signal for a two-phase modulation in 1st Embodiment, a triangular wave signal, and a PWM basic signal. The figure which shows the honorific waveform of each part in each embodiment. The flowchart for demonstrating the effect | action of 1st Embodiment. The block diagram which shows the structure of the principal part of the control part in 2nd Embodiment. The flowchart for demonstrating the effect | action of 2nd Embodiment. The block diagram which shows the structure of the principal part of the control part in 3rd Embodiment. The flowchart for demonstrating the effect | action of 3rd Embodiment. The block diagram which shows the structure of the principal part of the control part in 4th Embodiment. The flowchart for demonstrating the effect | action of 4th Embodiment. The flowchart for demonstrating the effect | action of the modification of 4th Embodiment. The figure which shows the attachment state of the temperature sensor in 5th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Switching circuit, 2u, 2v, 2w ... Upstream side MOSFET (switching element), 3u, 3v, 3w ... Downstream side MOSFET (switching element), 4u, 4v, 4w ... Reverse voltage application circuit, 5u, 5v, 5w ... reverse voltage application circuit, Du +, Dv +, Dw +, Du-, Dv-, Dw -... freewheeling diode, 10 ... control unit, 30 ... DC power supply, 42 ... reverse voltage application capacitor, 43 ... reverse voltage application MOSFET 50 ... reference signal generator 51 ... three-phase sine wave signal generator 52 ... waveform shaping unit 53 ... selection unit 54 ... triangular wave signal generator 55 ... PWM basic signal Vu generator 56 ... PWM basic signal Vv generator, 57 ... PWM basic signal Vw generator, 70 ... current detector, 71 ... failure detector, 72 ... current / temperature estimator, 73 ... failure determiner, 74 ... selection controller, 7 ... frequency control unit, 80 ... circuit board, 84 ... temperature sensor, M ... brushless DC motor, Lu, Lv, Lw ... phase winding

Claims (5)

A switching circuit in which a plurality of series circuits of two switching elements each using a MOSFET having a free-wheeling diode are used, and an interconnection point of each switching element of these series circuits is connected to a load;
First control means for sequentially switching energization to the load by a switching element upstream of at least one of the series circuits and a switching element downstream of another at least one of the series circuits;
Prior to turning on the other switching element of the same series circuit as the MOSFET, a reverse voltage application circuit for applying a reverse voltage to the MOSFET,
Failure detection means for detecting a malfunction of the reverse voltage application circuit; and
A second control means for reducing the number of switchings of the MOSFET from a normal level when a failure is detected by the failure detection means;
An inverter device comprising: The first control means is capable of generating a three-phase sine wave signal and a two-phase modulation signal, and outputs either one of the generated three-phase sine wave signal or two-phase modulation signal as a reference signal. And a basic signal generation unit that generates a basic signal for switching with respect to each of the switching elements by voltage comparison between the reference signal output from the reference signal generation unit and the triangular wave signal,
The second control unit outputs the three-phase sine wave signal from the reference signal generation unit when no failure is detected by the failure detection unit, and generates the reference signal when a failure is detected by the failure detection unit. Output the two-phase modulation signal from the unit,
The inverter device according to claim 1. The first control means generates a three-phase sine wave signal, outputs the generated three-phase sine wave signal as a reference signal, a reference signal and a triangular wave signal output from the reference signal generation unit, A basic signal generation unit that generates a basic signal for switching for each of the switching elements by voltage comparison of
The second control means sets the frequency of the triangular wave signal to a predetermined frequency when no failure is detected by the failure detecting means, and the triangular wave signal when a failure is detected by the failure detecting means. Is set to a frequency lower than the predetermined frequency,
The inverter device according to claim 1. The failure detection means includes: estimation means for estimating a current flowing through each switching element or a temperature of each switching element; and whether the reverse voltage application circuit is a malfunction that does not operate according to an estimation result of the estimation means. Determination means for determining whether or not
The inverter device according to any one of claims 1 to 3, wherein The first control means generates a three-phase sine wave signal, outputs the generated three-phase sine wave signal as a reference signal, a reference signal and a triangular wave signal output from the reference signal generation unit, A basic signal generation unit that generates a basic signal for switching for each of the switching elements by voltage comparison of
The second control unit sets the voltage of the reference signal to a normal level when no failure is detected by the failure detection unit, and sets the voltage of the reference signal when the failure is detected by the failure detection unit. Set to a lower level,
The inverter device according to claim 1.

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