JP6384316B2 - Power converter and control method of power converter - Google Patents

Description

  The present invention relates to a power conversion device that converts direct current power into alternating current power, and a control method for the power conversion device, and more particularly to a technique for discharging power stored in a smoothing capacitor.

  For example, a power conversion device such as an inverter device provided in an electric vehicle includes a smoothing capacitor. In such a power converter, it is necessary to discharge the electric power accumulated in the smoothing capacitor when the vehicle is stopped or an accident occurs. As a conventional example of a discharging method for a smoothing capacitor, for example, one disclosed in Japanese Patent No. 5375052 (Patent Document 1) is known.

  In Patent Document 1, an upper IGBT (insulated gate bipolar transistor) and a lower IGBT provided in an inverter device are alternately turned on to allow a current to flow through a diode connected in parallel to each IGBT, thereby It has been shown to dissipate the power stored in the capacitor.

  At this time, the switching frequency of each IGBT needs to be higher than the switching frequency during load driving. For this reason, the electric power output from the drive circuit for driving each IGBT increases, resulting in an increase in the circuit scale of the drive circuit.

Japanese Patent No. 5375052

  As described above, in the related art disclosed in Patent Document 1, when the electric power stored in the smoothing capacitor is discharged, it is necessary to set the driving frequency of each IGBT higher than that during load driving. As a result, the circuit scale of the drive circuit for driving the IGBT increases.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to discharge the electric power stored in the smoothing capacitor without increasing the circuit scale. It is providing the power converter device and the control method of a power converter device.

  In order to achieve the above object, the invention relating to the power conversion device of the present application includes a plurality of power modules each composed of a pair of an upper switching element and a lower switching element, and each switching element is provided with respect to its conduction direction. The rectifying elements are connected so that the opposite direction is the forward direction. The drive circuit that controls the drive voltage supplied to the control input of each switching element to turn the switching element on and off is provided. The drive circuit is configured to switch the upper switching element and the lower switching element when the smoothing capacitor is discharged. The elements are turned on alternately, and the driving frequency of each switching element is set higher than the driving frequency at the time of load driving, and the driving voltage supplied to the control input of each switching element is higher than the driving voltage at the time of load driving. Set low.

  The invention relating to the control method of the power conversion device of the present application alternately turns on and off each upper switching element for generating an AC voltage and each lower switching element when a discharge operation signal is given. A step of changing the driving frequency of each switching element to a frequency higher than the driving frequency at the time of load driving, and the electric power stored in the smoothing capacitor to the rectifying element connected in parallel to each switching element When the driving frequency of each switching element is set higher than the driving frequency of the load, the voltage supplied to the control input of each switching element is set to be higher than the voltage supplied to the control input when driving the load. And a step of setting it low.

  According to the present invention, when the smoothing capacitor is discharged, the voltage supplied to the control input of the switching element is reduced, so that the electric power stored in the smoothing capacitor can be discharged without increasing the circuit scale.

It is a circuit diagram which shows the structure of the power converter device which concerns on embodiment of this invention, and its peripheral device. FIG. 2 is a circuit diagram illustrating a detailed configuration of the drive circuit illustrated in FIG. 1 according to the first embodiment of the present invention. 4 is a timing chart showing ON / OFF timing of each transistor during smoothing capacitor discharge according to the embodiment of the present invention. It is a flowchart which shows the process sequence at the time of smoothing capacitor discharge of the power converter device which concerns on 1st Embodiment of this invention. FIG. 4 is a circuit diagram showing a detailed configuration of a drive circuit shown in FIG. 1 according to a second embodiment of the present invention. FIG. 10 is a characteristic diagram illustrating a relationship between a duty ratio and a gate power supply voltage according to the second embodiment of the present invention. FIG. 4 is a circuit diagram illustrating a detailed configuration of a drive circuit illustrated in FIG. 1 according to a third embodiment of the present invention. FIG. 10 is a characteristic diagram illustrating a relationship between a current flowing through a shunt resistor (resistor R8) and an upper limit value of a duty ratio according to the third embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an inverter device 2 (power conversion device) and peripheral devices thereof according to an embodiment of the present invention. As shown in FIG. 1, the inverter device 2 according to the present embodiment is mounted on an electric vehicle, for example, and converts DC power charged in a high voltage battery 1 into three-phase AC power having a predetermined frequency. Phase AC power is supplied to the motor 3 (load), and the motor 3 is rotated.

  The inverter device 2 includes a smoothing capacitor C1 that smoothes the DC power output from the high-voltage battery 1, a switching element group including six switching elements Tr1 to Tr6 (IGBT in this example), and each switching element Tr1 to A drive circuit 10 that controls driving of the Tr 6 and a control circuit 11 that outputs a control signal to the drive circuit 10 are provided. In this embodiment, the inverter device 2 that outputs three-phase AC power will be described as an example, but the present invention is not limited to three phases.

  The pair of switching elements Tr1 and Tr2 are connected in series to form a U-phase power module 13U. One end of the switching element Tr1 is connected to the plus side of the high voltage battery 1, and one end of the switching element Tr2 is connected to the minus side of the high voltage battery 1. That is, the switching element Tr1 is a U-phase upper arm (upper switching element), and the switching element Tr2 is a U-phase lower arm (lower switching element). The gates of the switching elements Tr1 and Tr2 are connected to the drive circuit 10, and on / off is controlled based on the drive signal output from the drive circuit 10.

  A diode D1 (rectifier element) is provided in parallel with the switching element Tr1, and a diode D2 is provided in parallel with the switching element Tr2. At this time, as shown in the drawing, the diodes D1 and D2 are connected such that the opposite direction to the conduction direction of the switching elements Tr1 and Tr2 is the forward direction.

  Similarly, the pair of switching elements Tr3 and Tr4 are connected in series to form a V-phase power module 13V. One end of the switching element Tr3 is connected to the plus side of the high voltage battery 1, and one end of the switching element Tr4 is connected to the minus side of the high voltage battery 1. That is, the switching element Tr3 is a V-phase upper arm (upper switching element), and the switching element Tr4 is a V-phase lower arm (lower switching element).

  A diode D3 is provided in parallel with the switching element Tr3, and a diode D4 is provided in parallel with the switching element Tr4. The connection direction of the diodes D3 and D4 is the same as that of the U phase described above.

  Further, the pair of switching elements Tr5 and Tr6 are connected in series to constitute a W-phase power module 13W. One end of the switching element Tr5 is connected to the plus side of the high voltage battery 1, and one end of the switching element Tr6 is connected to the minus side of the high voltage battery 1. That is, the switching element Tr5 is a W-phase upper arm (upper switching element), and the switching element Tr6 is a W-phase lower arm (lower switching element).

  A diode D5 is provided in parallel with the switching element Tr5, and a diode D6 is provided in parallel with the switching element Tr6. The connection direction of the diodes D5 and D6 is the same as in the case of the U phase described above.

  A relay 7 is provided between the high voltage battery 1 and the inverter device 2. The relay 7 is turned on when the inverter device 2 is driven, and the relay 7 is turned off when the inverter device 2 is stopped.

  Each of the U-phase, V-phase, and W-phase electric wires of the motor 3 is provided with current sensors 5U, 5V, and 5W, and current data detected by these current sensors 5U, 5V, and 5W is controlled by a control circuit. 11 is transmitted. In the present embodiment, an example in which three current sensors 5U, 5V, and 5W are provided will be described, but two current sensors may be provided.

  The control circuit 11 is connected to the vehicle controller 12 and outputs a PWM signal output command to the drive circuit 10 based on a torque command output from the vehicle controller 12. A resolver 4 is attached to the motor 3, and rotation speed data detected by the resolver 4 is output to the control circuit 11. The control circuit 11 can be configured as an integrated computer including a central processing unit (CPU) and storage means such as a RAM, a ROM, and a hard disk.

  Based on the output command output from the control circuit 11, the drive circuit 10 outputs a drive signal to the control inputs (gates in the case of IGBT) of the switching elements Tr1 to Tr6. In addition, when the smoothing capacitor C1 is discharged, the drive circuit 10 alternately turns on the upper switching elements Tr1, Tr3, Tr5 and the lower switching elements Tr2, Tr4, Tr6 of the power modules 13U, 13V, 13W. Furthermore, the driving frequency of each of the switching elements Tr1 to Tr6 is set to be higher than the frequency at the time of driving the load. In addition, the drive voltage supplied to the control inputs (gates) of the switching elements Tr1 to Tr6 is set lower than the drive voltage during load driving. By doing so, the electric power stored in the smoothing capacitor C1 is consumed in a short time, and the voltage of the smoothing capacitor C1 is lowered. The voltage across the smoothing capacitor C1 is detected, and the discharge is stopped when the detected voltage value becomes a predetermined voltage or less. Alternatively, the discharge is stopped when a predetermined time has elapsed since the discharge was started. That is, the drive circuit 10 has a function of controlling the drive voltage supplied to the control inputs of the switching elements Tr1 to Tr6 to switch the switching elements Tr1 to Tr6 on and off.

  FIG. 2 is a circuit diagram showing a detailed configuration of the drive circuit 10. As shown in FIG. 2, the drive circuit 10 includes a gate power supply unit and a drive unit for each of the U-phase, V-phase, and W-phase power modules 13U, 13V, and 13W. FIG. 2 shows a gate power supply unit 21 and a drive unit 22 for driving the U-phase power module 13U. Since the V phase and the W phase have the same configuration, the description is omitted.

  The gate power supply unit 21 mainly includes a power supply IC 23 (power supply circuit) that controls a DC voltage output from a DC power supply (Vb +, Vb−), a flyback transformer 24, and a voltage switching unit 25 (first voltage switching circuit). ). The power supply IC 23 outputs a PWM drive signal to the gate of the MOSFET (Q1; electronic switch), thereby PWM-controlling the MOSFET (Q1) with a desired duty ratio, and supplying it to the primary coil L1 of the flyback transformer 24. Generate voltage.

  Secondary coils L2 and L3 are provided on the secondary side of the flyback transformer 24, and secondary voltages proportional to the voltage applied to the primary coil L1 are generated in the secondary coils L2 and L3. To do. The voltages generated in the secondary coils L2 and L3 are rectified and smoothed by a diode and a capacitor and output to the drive unit 22. Further, a voltage detection coil L4 is provided on the primary side of the flyback transformer 24, and a voltage proportional to the voltage applied to the primary side coil L1 is generated in the voltage detection coil L4.

  The voltage generated in the voltage detection coil L4 is rectified and smoothed by a diode and a capacitor, and further divided by resistors R1 (first resistor) and R2 (second resistor). It is supplied to the feedback terminal (FB). Therefore, the power supply IC 23 adjusts the duty ratio when the MOSFET (Q1) is PWM-controlled based on the voltage (feedback voltage) acquired at the feedback terminal (FB), so that the secondary side coils L2 and L3 have desired values. The voltage can be controlled so as to be supplied.

  A voltage switching unit 25 is provided between the connection point P1 of the resistors R1 and R2 and the negative power supply terminal (Vb−). The voltage switching unit 25 includes a resistor R3 and an FET (Q2). Yes. The FET (Q2) is turned on when the load is driven, and turned off when a discharge operation signal for discharging the smoothing capacitor C1 is given. In other words, the voltage at the connection point P1 is set to be relatively higher during capacitor discharge to which a discharge operation signal is applied than during load driving. Detailed operation of the voltage switching unit 25 will be described later.

  The drive unit 22 includes two drive ICs 26 and 27 (switching element drive units) and two push-pull circuits 28 and 29. The push-pull circuit 28 has a circuit in which two transistors are connected in series, and a DC voltage obtained by rectifying an AC voltage generated in the secondary coil L2 is supplied to both ends. The output voltage of the push-pull circuit 28 is supplied to the gate of the upper switching element Tr1 of the U-phase power module 13U. Similarly, the push-pull circuit 29 has a series connection circuit of two transistors, and a DC voltage obtained by rectifying an AC voltage generated in the secondary coil L3 is supplied to both ends. Further, the output voltage of the push-pull circuit 29 is supplied to the gate of the lower switching element Tr2 of the U-phase power module 13U.

  The drive IC 26 is supplied with the PWM signal of the switching element Tr1 output from the control circuit 11, and drives and controls the push-pull circuit 28 based on the PWM signal. Similarly, the drive IC 27 is supplied with the PWM signal of the switching element Tr2 output from the control circuit 11, and drives and controls the push-pull circuit 29 based on the PWM signal.

  Hereinafter, an effect | action of the power converter device which concerns on this embodiment comprised as mentioned above is demonstrated. First, an operation at the time of driving a load, that is, an operation when driving each of the switching elements Tr1 to Tr6 as an inverter will be described. When the motor 3 shown in FIG. 1 is rotationally driven, the power modules 13U, 13V, and 13W of the inverter device 2 are driven, and electrical angle control, which is a well-known control method, is performed, whereby the U phase, V A three-phase AC voltage is generated in the phase and the W phase. By supplying this three-phase AC voltage to the motor 3, the motor 3 can be driven to rotate. At this time, electric power corresponding to the capacitance of the smoothing capacitor C1 is stored in the smoothing capacitor C1 shown in FIG.

  Next, a processing procedure when discharging the electric power stored in the smoothing capacitor C1 will be described with reference to a flowchart shown in FIG. When the ignition of the vehicle is turned off, or when the vehicle detects a collision signal, it is necessary to discharge the electric power stored in the smoothing capacitor C1. In the present embodiment, the driving of the driving circuit 10 is controlled under the control of the control circuit 11, and the smoothing capacitor C1 is discharged.

  First, in step ST1 of FIG. 4, the control circuit 11 determines whether or not a discharge operation signal is given. When the discharge operation signal is given (YES in step ST1), in step ST2, the control circuit 11 causes the upper switching elements Tr1, Tr3, Tr5 of the power modules 13U, 13V, 13W and the lower switching element Tr2 to be used. , Tr4 and Tr6 are alternately switched on and off with a predetermined dead time. For example, as shown in FIG. 3, the upper switching elements Tr1, Tr3, Tr5 are turned on for a time t1, and then all are turned off, and then the dead time t2 is turned off, and then the lower switching elements Tr2, Tr4, Tr6 are turned on for a time. Only a dead time t2 when only t1 is turned on and all are turned off again. Then, this operation is repeated.

  Simultaneously with the processing of step ST2, in step ST3, the control circuit 11 increases the switching frequency of each of the switching elements Tr1 to Tr6. For example, the switching frequency at the time of discharge is set to f2 (> f1) with respect to the switching frequency f1 at the time of load driving that outputs electric power for driving the motor 3. At the same time, in step ST4, the control circuit 11 reduces the gate voltages of the switching elements Tr1 to Tr6.

  In step ST5, the electric power stored in the smoothing capacitor C1 is consumed by flowing the electric power stored in the smoothing capacitor C1 through the diodes D1 to D6 provided to the switching elements Tr1 to Tr6. To do. As a result, the electric power stored in the smoothing capacitor C1 can be discharged.

  In step ST6, it is determined whether or not a predetermined time has elapsed since the discharge process was executed. If the predetermined time has elapsed (YES in step ST6), the discharge process is terminated.

  Here, in the process of step ST3, since it is necessary to discharge quickly, the frequency at which each switching element Tr1 to Tr6 is switched on and off is set to each switching element at the time of load driving (at the time of driving the motor 3). It is set higher than the frequency of Tr1 to Tr6. That is, the drive ICs 26 and 27 shown in FIG. 2 relatively increase the frequency f2 when the smoothing capacitor C1 is discharged when the load drive frequency is f1. That is, f2> f1.

Here, when the drive power of the IGBTs constituting the switching elements Tr1 to Tr6 is P [W], the following expression (1) is established.
P = Qg · Vg · fsw + (Vg2 / R) (1)
However, Qg is a gate charge amount, Vg is a gate voltage, fsw is a switching frequency, and R is a resistance.

  As can be understood from the above equation (1), when the switching frequency fsw of the IGBT is increased, the drive power P increases. Therefore, as described above, when the frequency f2 at the time of discharging the smoothing capacitor C1 is set to be relatively high with respect to the frequency f1 at the time of driving the load, the driving power P increases, and the driving circuit 10 has a large scale. Problem that leads to higher cost and higher cost. In the present embodiment, an increase in the driving power P caused by increasing the switching frequency fsw is suppressed by reducing the gate voltage Vg.

  Details will be described below. As described above, the voltage Vp1 at the connection point P1 of the resistors R1 and R2 shown in FIG. 2 is divided by the resistor R1 and the parallel combined resistor of the resistors R2 and R3 (third resistor) during load driving. It is a pressed voltage. The power supply IC 23 sets the duty ratio of the MOSFET (Q1) based on this voltage, and executes PWM control.

  Here, when a discharge operation signal is given from the vehicle controller 12, the gate voltage of the FET (Q2) is switched from “H” to “L”, and thereby the resistor R3 is cut off. Therefore, the voltage Vp1 at the connection point P1 is switched to a voltage divided by the resistors R1 and R2. More specifically, the voltage Vp1 at the connection point P1 is relatively higher during discharge than during load driving.

  For this reason, the duty ratio of the MOSFET (Q1) is controlled so that the voltage supplied to the feedback terminal (FB) of the power supply IC 23 shown in FIG. 2 increases and the voltage supplied to the primary coil L1 decreases. . As a result, the voltage generated in the secondary coils L2 and L3 decreases, the voltage supplied to the push-pull circuits 28 and 29 decreases, and consequently the voltage supplied to the gates of the switching elements Tr1 and Tr2. That is, since the gate voltage Vg in the above-described equation (1) decreases, an increase in the driving power P accompanying an increase in the switching frequency fsw can be suppressed.

  Thus, in the power conversion device according to the present embodiment, when discharging the power stored in the smoothing capacitor C1 when the ignition is off or when a collision occurs, the upper side of each power module 13U, 13V, 13W The switching elements Tr1, Tr3, Tr5 and the lower switching elements Tr2, Tr4, Tr6 are alternately turned on and off with a predetermined dead time. At this time, the frequency at the time of switching on and off needs to be higher than the switching frequency at the time of driving the load, and the driving power increases. In order to suppress this, the control input of each switching element Tr1 to Tr6 The drive voltage supplied to is reduced. That is, the driving voltage is changed to a driving voltage lower than the driving voltage at the time of driving the load. Therefore, an increase in the driving power of the switching element can be suppressed, and as a result, an increase in the size and cost of the device can be prevented.

  Further, the drive circuit 10 includes a voltage switching unit 25, and when a discharge operation signal for discharging the smoothing capacitor C1 is given, the feedback voltage supplied to the feedback terminal (FB) of the power supply IC 23 is increased. Let That is, the voltage switching unit 25 has a function as a first voltage switching circuit that increases the feedback voltage output from the voltage detection coil L4. And by raising the feedback voltage, the voltage generated on the secondary side of the flyback transformer 24 can be reduced, and the drive power of each of the switching elements Tr1 to Tr6 is prevented from increasing. Therefore, driving power can be reduced with a simple configuration.

  Further, as shown in FIG. 2, the voltage switching unit 25 includes an FET (Q2) and a resistor R3. When a discharge operation signal is given, the connection is made by turning off the FET (Q2). The voltage Vp1 at the point P1 is increased. Therefore, many parts are not required, and no high-power element is used, so that the scale of the apparatus can be suppressed and the cost can be suppressed.

  Here, in order to drive the motor 3 during load driving, in addition to the displacement current of the switching elements Tr1 to Tr6, a current to be supplied to the motor 3 (an extremely large current compared to the displacement current) is added. It is necessary to reduce the loss generated in Tr6 as much as possible. Therefore, it is necessary to set the gate voltage of each switching element Tr1 to Tr6 high. On the other hand, since no current flows through the motor 3 when the smoothing capacitor C1 is discharged, there is no problem even if the drive voltages of the switching elements Tr1 to Tr6 are reduced.

[Description of Second Embodiment]
Next, the power converter device which concerns on 2nd Embodiment of this invention is demonstrated. FIG. 5 is a circuit diagram showing a configuration of a drive circuit 10a used in the power conversion device according to the second embodiment. The drive circuit 10a according to the second embodiment is different from the drive circuit 10 shown in FIG. 2 in the voltage switching unit 25a connected to the power supply IC 23. That is, while the voltage switching unit 25 is used in FIG. 2, the voltage switching unit 25a (second voltage switching circuit) is used in the second embodiment. Further, the terminals provided in the power supply IC 23 are different. Since the other configuration is the same as that of the first embodiment described above, the same reference numerals are given and description of the configuration is omitted.

  As shown in FIG. 5, the power supply IC 23 includes an upper limit setting terminal (S) for setting an upper limit value of the duty ratio of the PWM control. Then, the power supply IC 23 sets an upper limit value of the duty ratio when the FET (Q1) is PWM-controlled according to the voltage input from the upper limit setting terminal (S). Specifically, the higher the voltage input from the upper limit setting terminal (S), the higher the upper limit of the duty ratio. In the second embodiment, when the discharge operation signal is given, the voltage supplied to the upper limit setting terminal (S) is reduced with respect to the load driving time, thereby suppressing the upper limit value of the duty ratio. The voltage output to the secondary side coils L2, L3 is reduced. Details will be described below.

  The voltage switching unit 25a includes four resistors R4 (fourth resistor), R5 (fifth resistor), R6 (sixth resistor), R7, and FET (Q3). The resistors R4 and R5 are connected in series, one end of which is connected to the terminal (VREF) of the power supply IC and the other end is connected to the minus terminal (Vb−). The terminal (VREF) outputs a preset reference voltage. The connection point P2 between the resistors R4 and R5 is connected to the minus terminal (Vb−) via the resistor R6 and the FET (Q3). The discharge operation signal is supplied to the gate of the FET (Q3) through the resistor R7. When the load is driven to drive the motor 3, the discharge operation signal is set to “L” and the FET (Q3) is turned off. On the other hand, when discharging the smoothing capacitor C1, the discharge operation signal is set to “H”, and the FET (Q3) is turned on. That is, the voltage Vp2 at the connection point P2 is lower when the smoothing capacitor C1 is discharged than when the load is driven.

  The discharge operation signals “L” and “H” are opposite to those in the first embodiment described above. That is, in the first embodiment, the discharge operation signal is “L” during discharge, whereas in the second embodiment, the discharge operation signal is “H” during discharge.

  As a result, when the smoothing capacitor C1 is discharged, the maximum value of the duty ratio is reduced, and the duty ratio when the FET (Q1) is PWM-controlled is limited. As a result, the voltage supplied to the primary coil L1 Decreases. As a result, the voltage supplied to the gates of the switching elements Tr1 to Tr6 constituting the power modules 13U, 13V, and 13W can be relatively reduced as compared with the load driving. Specifically, as shown in FIG. 6, when the upper limit of the duty ratio is switched from 0.5 (50%) to 0.4 (40%), for example, the gate voltage decreases from 16V to 12V.

  As described above, in the power conversion device according to the second embodiment, the upper limit of the duty ratio output from the power supply IC 23 is set by the voltage switching unit 25a (second voltage switching circuit) provided in the drive circuit 10a. The voltage supplied to the upper limit setting terminal (S) is changed. Specifically, the upper limit of the duty ratio is reduced when the smoothing capacitor C1 is discharged. Therefore, when the smoothing capacitor C1 is discharged, the gate voltage supplied to the gates of the switching elements Tr1 to Tr6 can be reduced, and the driving power of the switching elements Tr1 to Tr6 can be reduced with a simple configuration. .

  Further, as shown in FIG. 5, the voltage switching unit 25a includes an FET (Q3) and resistors R4, R5, R6, and R7. When a discharge operation signal is given, the FET (Q3) is turned on. Thus, the voltage Vp2 at the connection point P2 is reduced. Therefore, many parts are not required, and no high-power element is used, so that the scale of the apparatus can be suppressed and the cost can be suppressed.

[Description of Third Embodiment]
Next, the power converter device which concerns on 3rd Embodiment of this invention is demonstrated. FIG. 7 is a circuit diagram showing a configuration of a drive circuit 10b used in the power conversion device according to the third embodiment. The drive circuit 10b according to the third embodiment is different from the drive circuit 10a according to the second embodiment shown in FIG. 5 in the voltage switching unit 25b connected to the power supply IC 23. That is, while the voltage switching unit 25a is used in FIG. 5, the voltage switching unit 25b is used in the third embodiment. Since other configurations are the same as those of the second embodiment described above, the same reference numerals are given and description of the configurations is omitted.

  As shown in FIG. 7, the voltage switching unit 25b according to the third embodiment is arranged between the FET (Q1) and the negative voltage (Vb−), in contrast to the voltage switching unit 25a shown in FIG. And a resistor R8 (shunt resistor), and a series connection circuit of the resistor R9 and the capacitor C2. That is, a resistor R8 as a shunt resistor is provided in a current path flowing through the FET (Q1; electronic switch). The resistor R8 has a function as a current detection unit. One end of the resistor R9 is connected to a connection point P3 between the FET (Q1) and the resistor R8, and one end of the capacitor C2 is connected to a negative voltage (Vb−). The connection point between the resistor R9 and the capacitor C2 is connected to the resistor R7. The other configuration is the same as that of the voltage switching unit 25a shown in FIG.

  Next, the effect | action of the power converter device which concerns on 3rd Embodiment is demonstrated. When the power supply to the motor 3 by the inverter device 2 shown in FIG. 1 is stopped and discharging of the smoothing capacitor C1 is started, the switching frequency of each of the switching elements Tr1 to Tr6 is increased by the control of the control circuit 11. . For example, it rises from 5 [KHz] to 15 [KHz]. Along with this, in order to increase the voltage generated in the secondary side coils L2 and L3 of the flyback transformer 24 shown in FIG. 7, the duty ratio of the FET (Q1) increases, and consequently the current flowing through the resistor R8 increases. . When the voltage at the connection point P3 rises and exceeds a predetermined voltage, the transistor (Q3) is switched from off to on. As a result, the upper limit of the duty ratio of PWM control by the power supply IC 23 is reduced, and the voltage supplied to the gates of the switching elements Tr1 to Tr6 can be reduced.

  FIG. 8 is a characteristic diagram showing the relationship between the current flowing through the resistor R8 and the upper limit value of the duty ratio. As can be understood from the characteristic diagram of FIG. 8, during normal operation, the current flowing through the resistor R8 is a low value, so the upper limit value of the duty ratio is a constant value (for example, 0.5). During the discharging operation, the current flowing through the resistor R8 increases as the switching frequency of each of the switching elements Tr1 to Tr6 increases. As the current increases, the upper limit value of the duty ratio decreases linearly. Therefore, during the discharge operation, the upper limit value of the duty ratio is relatively lowered (for example, 0.4) as compared with the normal operation, and the voltage supplied to the gates of the switching elements Tr1 to Tr6 can be reduced. .

  In this way, in the power conversion device according to the third embodiment, the voltage switching unit 25b (third voltage switching circuit) provided in the drive circuit 10b detects the current flowing through the MOSFET (Q1), and the magnitude of this current Based on this, the voltage supplied to the upper limit setting terminal (S) for setting the upper limit of the duty ratio output from the power supply IC 23 is changed. Specifically, when the current flowing through the MOSFET (Q1) exceeds a preset threshold current, the voltage supplied to the upper limit setting terminal (S) is reduced. Therefore, when the smoothing capacitor C1 is discharged, the driving frequency of each of the switching elements Tr1 to Tr6 increases, and accordingly, the current flowing through the MOSFET (Q1) increases and exceeds the threshold current, so that the upper limit setting terminal (S) The supplied voltage is reduced. As a result, the gate voltage supplied to the gates of the switching elements Tr1 to Tr6 can be reduced, and the driving power of the switching elements Tr1 to Tr6 can be reduced with a simple configuration. In addition, the gate voltage of each of the switching elements Tr1 to Tr6 can be reduced in a self-contained manner without requiring a discharge operation signal output from the outside, and controllability can be improved.

  Further, as shown in FIG. 7, the voltage switching unit 25b includes an FET (Q3), resistors R4 to R9, and a capacitor C2. When a discharge operation signal is given, the FET (Q3) is turned on. As a result, the voltage Vp2 at the connection point P2 is lowered. Therefore, many parts are not required, and no high-power element is used, so that the scale of the apparatus can be suppressed and the cost can be suppressed.

  As mentioned above, although the power converter device of this invention and the control method of the power converter device were demonstrated based on embodiment of illustration, this invention is not limited to this, The structure of each part is arbitrary having the same function It can be replaced with that of the configuration.

DESCRIPTION OF SYMBOLS 1 High voltage battery 2 Inverter apparatus 3 Motor 4 Resolver 5U, 5V, 5W Current sensor 7 Relay 10, 10a, 10b Drive circuit 11 Control circuit 12 Vehicle controller 13U U-phase power module 13V V-phase power module 13W W-phase power module 21 Gate Power supply unit 22 Drive unit 23 Power supply IC
24 Flyback transformer 25, 25a, 25b Voltage switching unit 26, 27 Drive IC
28, 29 Push-pull circuit C1 Smoothing capacitor D1-D6 Diode (rectifier element)
L1 Primary coil L2, L3 Secondary coil L4 Voltage detection coil

Claims (8)

In a power converter that converts DC power output from a DC power source into AC power and supplies it to a load,
A smoothing capacitor for smoothing the DC power;
A switching element group comprising a plurality of power modules composed of a pair of an upper switching element and a lower switching element;
A rectifying element that is arranged in parallel with each switching element included in the switching element group, and is connected so that a direction opposite to a conduction direction of the switching element is a forward direction;
A drive circuit that controls a drive voltage supplied to a control input of each switching element included in the switching element group and switches the switching element on and off, and
The driving circuit alternately turns on the upper switching element and the lower switching element of each power module when discharging the smoothing capacitor, and further sets the driving frequency of each switching element to be higher than the driving frequency during load driving. A power conversion device having a high frequency and a driving voltage supplied to a control input of each of the switching elements is set lower than a driving voltage at the time of load driving. The drive circuit is
A switching element driving unit that outputs a driving signal to be supplied to a control input of each switching element;
An electronic switch;
PWM control of the electronic switch generates a desired voltage, outputs the generated voltage to the switching element drive unit, acquires a voltage according to the generated voltage as a feedback voltage, and based on the feedback voltage A power supply circuit for changing the duty ratio of the PWM control,
A first voltage switching circuit for raising the feedback voltage when a discharge operation signal for discharging the smoothing capacitor is given;
The power converter according to claim 1, further comprising: The first voltage switching circuit uses, as the feedback voltage, a voltage Vp1 obtained by dividing the generated voltage by a first resistor and a parallel combined resistor of a second resistor and a third resistor,
The power converter according to claim 2, wherein when the discharge operation signal is given, the voltage Vp1 is increased by cutting off the third resistor. The drive circuit is
A switching element driving unit that outputs a driving signal to be supplied to a control input of each switching element;
An electronic switch,
PWM control of the electronic switch generates a desired voltage, outputs the generated voltage to the switching element driving unit, and according to the voltage supplied to the upper limit setting terminal for setting the upper limit value of the duty ratio A power supply circuit for setting an upper limit of the duty ratio,
A second voltage switching circuit for lowering a voltage supplied to the upper limit setting terminal when a discharge operation signal for discharging the smoothing capacitor is given;
The power converter according to claim 1, further comprising: When the smoothing capacitor is not discharged, the second voltage switching circuit supplies a voltage Vp2 obtained by dividing a preset reference voltage by a fourth resistor and a fifth resistor to the upper limit setting terminal. ,
5. The power converter according to claim 4, wherein when the discharge operation signal is given, the voltage Vp <b> 2 is lowered by connecting a sixth resistor in parallel with the fifth resistor. . The drive circuit is
A switching element driving unit that outputs a driving signal to be supplied to a control input of each switching element;
An electronic switch,
PWM control of the electronic switch generates a desired voltage, outputs the generated voltage to the switching element driving unit, and according to the voltage supplied to the upper limit setting terminal for setting the upper limit value of the duty ratio A power supply circuit for setting an upper limit of the duty ratio,
A current detector for detecting a current flowing through the electronic switch;
A third voltage switching circuit for reducing a voltage supplied to the upper limit setting terminal when a current detected by the current detection unit exceeds a preset threshold current;
The power converter according to claim 1, further comprising: The current detection unit includes a shunt resistor provided in a current path flowing through the electronic switch,
When the smoothing capacitor is not discharged, the third voltage switching circuit supplies a voltage Vp2 obtained by dividing a preset reference voltage by a fourth resistor and a fifth resistor to the upper limit setting terminal. ,
The voltage Vp2 is reduced by connecting a sixth resistor in parallel to the fifth resistor when a voltage generated in the shunt resistor exceeds a predetermined voltage. Power converter. In a control method of a power converter that converts DC power output from a DC power source into AC power and supplies it to a load,
When a discharge operation signal for discharging a smoothing capacitor for smoothing the DC power is given, each upper switching element and each lower switching element of a plurality of power modules for generating an AC voltage are alternated. To turn on and off,
Changing the driving frequency of each switching element to a frequency higher than the driving frequency during load driving;
Flowing the electric power stored in the smoothing capacitor through a rectifying element connected in parallel to each of the switching elements;
In addition,
When the driving frequency of each switching element is higher than the driving frequency when driving the load, the voltage supplied to the control input of each switching element is set to be higher than the voltage supplied to the control input when driving the load. A method for controlling a power converter, comprising a step of setting the power converter to a lower value.

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