WO2013054741A1 - Power converter and method for controlling power converter - Google Patents

Abstract

A power converter is provided with a power converter circuit, a drive circuit (20), and a control circuit (30). The power converter circuit has a plurality of switching elements (Q1-Q6) and reflux diodes (D1-D6); and, by switching on and off the plurality of switching elements (Q1-Q6), converts inputted power and outputs to a load. The drive circuit (20) drives the plurality of switching elements (Q1-Q6). The control circuit (30) controls the power converter circuit and the drive circuit (20). When a supply current supplied from the power converter circuit to the load is approximately 0 A, the control circuit (30) causes the switching speed when turning on the switching elements (Q1-Q6) to be lower than the switching speed when the supply current is not approximately 0 A.

Description

Power converter and control method of power converter

The present invention relates to a power conversion device and a control method thereof.

2. Description of the Related Art A vehicular generator / motor control device is known that includes a power conversion circuit that converts DC power supplied from a DC power source into AC power and supplies power to the generator motor, and a control circuit that controls the power conversion circuit (Patent Literature). 1). The AC / DC converter circuit includes a plurality of bridge-connected diodes and a semiconductor switching element connected in parallel to each diode, and is arranged between the DC power supply and the generator motor. The control circuit controls an on state and an off state of the semiconductor switching element. The control circuit drives the semiconductor switching element through a gate resistor having a maximum resistance value when starting the engine of the generator motor. Thereby, the state transition between the ON state and the OFF state of the switching element is delayed, and the switching noise is suppressed to the allowable level range.

JP 2005-65460 A

In the above-described vehicular generator motor control device, the switching noise is suppressed by slowing the change in the current flowing through the switching element by delaying the state transition between the ON state and the OFF state of the switching element. It was not enough to suppress.

The noise generated by the switching operation of the switching element includes not only noise generated by a change in the current flowing through the switching element but also noise generated by vibration of the current flowing through the return diode connected in parallel to the switching element.

The power conversion device according to the first aspect of the present invention includes a plurality of switching elements and a plurality of freewheeling diodes connected in parallel to the plurality of switching, respectively, and by switching on and off the plurality of switching elements, A power conversion circuit that converts input power and outputs it to a load, a drive circuit that drives a plurality of switching elements, and a control circuit that controls the power conversion circuit and the drive circuit are provided. The control circuit lowers the switching speed when turning on the switching element when the supply current supplied from the power conversion circuit to the load is near 0 ampere than the switching speed when the supply current is not near 0 ampere. .

A control method for a power conversion device according to a second aspect of the present invention includes a plurality of switching elements and a plurality of free-wheeling diodes connected in parallel to the plurality of switchings, and switches on and off the plurality of switching elements. Thus, a method for controlling a power conversion device including a power conversion circuit that converts input power and outputs the converted power to a load when the supply current supplied from the power conversion circuit to the load is in the vicinity of 0 amperes. The switching speed when turning on the switching element is made lower than the switching speed when the supply current is not near 0 amperes.

FIG. 1 is a block diagram showing a motor control system including a power conversion device according to the first embodiment of the present invention. FIG. 2 is a circuit diagram showing the drive circuit 20 of FIG. FIG. 3 is a block diagram showing the control circuit 30 of FIG. FIG. 4a is a circuit diagram of a portion corresponding to the U phase of the inverter of FIG. FIG. 4b is a graph showing the time characteristic of the current If flowing through the diode D1 of FIG. 4a. FIG. 5 is a graph showing the characteristics of the change rate (di / dt) of the recovery current with respect to the output current of the inverter 1 of FIG. FIG. 6 is a graph showing the collector current characteristic and the collector-emitter voltage characteristic in the inverter 1 of FIG. FIG. 7 is a block diagram showing a control circuit 30 according to a first modification of the first embodiment of the present invention. FIG. 8 is a block diagram showing a control circuit 30 according to a second modification of the first embodiment of the present invention. FIG. 9 is a circuit diagram showing a drive circuit 20 of the power conversion device according to the second embodiment of the present invention. FIG. 10 is a graph showing characteristics of the gate voltage with respect to the current command value in the power conversion device according to the second embodiment of the present invention. FIG. 11 is a circuit diagram showing a drive circuit 20 of the power conversion device according to the third embodiment of the present invention. FIG. 12 is a circuit diagram showing a drive circuit 20 of the power conversion device according to the fourth embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< First Embodiment >>
With reference to FIG. 1, a motor control system including a power converter according to a first embodiment of the present invention will be described. Although detailed illustration is omitted, the electric vehicle of this example is a vehicle that travels using a three-phase AC power permanent magnet motor 3 as a travel drive source. The motor 3 is coupled to the axle of the electric vehicle. Hereinafter, an electric vehicle will be described as an example. However, the present invention can also be applied to a hybrid vehicle (HEV), and the present invention can also be applied to a power conversion device of a device other than a vehicle.

The motor control system of this example includes an inverter 1, a battery 2 that is a power source of the motor 3, the above-described three-phase AC motor 3, a relay 4, a vehicle controller 5, and a rotor position sensor 6.

The battery 2 is connected to the inverter 1 via the relay 4. The battery 2 is mounted with a secondary battery such as a lithium ion battery, for example. The relay 4 is driven to open and close by a vehicle controller 5 in conjunction with an ON / OFF operation of a key switch (not shown) of the vehicle. When the key switch (not shown) is on, the relay 4 is closed, and when the key switch (not shown) is off, the relay 4 is opened.

The inverter 1 has, for example, a plurality of switching elements Q1 to Q6 and rectifying elements (for example, freewheeling diodes) D1 to D6. The free-wheeling diodes D1 to D6 are connected in parallel to the switching elements Q1 to Q6, and a current flows in a direction opposite to the current direction of the switching elements Q1 to Q6. The inverter 1 converts the DC power of the battery 1 into AC power and supplies it to the motor 3. In this example, three pairs of circuits in which two switching elements are connected in series are connected in parallel to the battery 1, and each pair of switching elements is electrically connected to the three-phase input portion of the motor 3. . For each switching element Q1 to Q6, the same switching element is used, for example, an insulated gate bipolar transistor (IGBT). The switching elements Q1 and Q2 and the diodes D1 and D2 are modularized as the power module 11, and similarly, the switching elements Q3 and Q4 and the diodes D3 and D4 are the power module 12, and the switching elements Q5 and Q6 and the diode D5, D6 is modularized as a power module 13.

In the example shown in FIG. 1, switching elements Q1 and Q2, switching elements Q3 and Q4, and switching elements Q5 and Q6 are connected in series. The switching elements Q1 and Q2 are connected to the U phase of the motor 3, the switching elements Q3 and Q4 are connected to the V phase of the motor 3, and the switching elements Q5 and Q6 are connected to the W phase of the motor 3. The switching elements Q1, Q3, Q5 are electrically connected to the positive electrode side of the battery 1. The switching elements Q2, Q4, Q6 are electrically connected to the negative electrode side of the battery 1. Switching of each of the switching elements Q1 to Q6 between the on state and the off state is controlled by the control circuit 30 via the drive circuit 20.

The inverter 1 includes power modules 11 to 13, a capacitor 14, a voltage sensor 15, a current sensor 16, a drive circuit 20, and a control circuit 30. The capacitor 14 and the voltage sensor 15 are connected between the relay 2 and the switching elements Q1 to Q6. The capacitor 14 is provided to smooth the DC power supplied from the battery 1. The voltage sensor 15 is a sensor that detects the voltage between the P-side and N-side DC power supply lines by detecting the voltage of the capacitor 14. The current sensor 16 is a sensor that detects each phase current (Iu, Iv, Iw) supplied from the inverter 1 to the motor 3, and includes a connection point between the switching elements Q1, Q2, a connection point between the switching elements Q3, Q4, and Provided in each phase between the connection point of the switching elements Q5 and Q6 and the motor 3, and outputs a detection current signal to the control circuit 30.

The driving circuit 20 transmits a gate signal to each of the switching elements Q1 to Q6, and drives each of the switching elements Q1 to Q6 to be turned on and off. The drive circuit 20 receives the signal from the voltage sensor 15, converts the signal to a waveform level that can be recognized by the control circuit 30, and transmits the signal to the control circuit 30 as a signal indicating the voltage of the capacitor 14 (DC voltage signal). . The specific configuration of the drive circuit 20 will be described later.

The control circuit 30 controls the switching elements Q1 to Q6 via the drive circuit 20 to control the operation of the motor 3. The control circuit 30 transmits a signal indicating a torque command value (T *) transmitted from the vehicle controller 5, a signal indicating the rotor position (φ) of the motor 6 from the rotor position sensor 6, and a current sensor 16. A feedback signal indicating a detected current and a signal from the voltage sensor 7 are read to generate a pulse width modulation signal (PWM signal) PS, and the PWM signal PS is transmitted to the drive circuit 20. Then, the drive circuit 20 switches the on / off states of the switching elements Q1 to Q6 at a predetermined timing based on the PWM signal PS. The specific configuration of the control circuit 30 will be described later.

The vehicle controller 5 includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM), and controls the entire vehicle of this example. The vehicle controller 5 calculates a torque command value (T ^* ) based on an accelerator signal or the like, and outputs the torque command value (T ^* ) to the control circuit 30. Further, the vehicle controller 5 outputs a start request command based on driving of the vehicle and a stop request command based on stopping of the vehicle to the control circuit 30. Further, the vehicle controller 5 transmits the opening / closing information of the relay 4 to the control circuit 30.

The rotor position sensor 6 is composed of a sensor such as a resolver or an encoder, and is provided in the motor 3 to detect the position (φ) of the rotor of the motor 3 and output it to the motor controller.

Next, the configuration of the drive circuit 20 will be described with reference to FIG. FIG. 2 shows a portion of the drive circuit 20 connected to the power module 11. Since the portions of the drive circuit 20 connected to the power module 12 and the power module 13 have the same configuration, illustration and description thereof are omitted.

The drive circuit 20 has a gate power supply unit 21 and a drive unit 22. The gate power supply unit 21 is a circuit that supplies power to the drive unit 22 that is insulated from the gate power supply unit 21, and is a drive power supply circuit that drives the switching elements Q1 to Q6. The gate power supply unit 21 includes a power supply IC 211 that controls power supplied from the primary-side power supply, a FET 1 (field effect transistor), a flyback transformer 212, and a voltage switching unit 213. The gate power supply unit 21 is composed of a flyback converter. A detection voltage signal obtained by dividing the voltage from the voltage detection winding of the flyback transformer 212 by the resistors R1 and R2 is input to the FB (feedback) terminal of the power supply control IC 211. The power supply IC 211 compares the detection voltage signal input to the FB terminal with a reference voltage. The power supply IC 211 controls the on / off duty ratio of the FET 1 so that the output voltage of the winding of the flyback transformer 212 is constant. The flyback transformer 212 insulates the main circuit side of the inverter 1 from the primary power supply side of the drive circuit 20. The switching elements Q2, Q4, Q6 are supplied with the N-side DC power supply line as the same reference power supply. The power sources of the switching elements Q1, Q3, and Q5 are respectively taken from insulated windings.

The voltage switching unit 213 is a circuit for switching the gate voltages of the switching elements Q1 to Q6. The voltage switching unit 213 switches a current path that flows through the series circuit of the resistor R1 and the resistor R2, which is connected to the primary winding side of the flyback transformer 212. As a result, the input voltage to the FB terminal of the power supply IC 211 is switched, and the voltage switching unit 213 adjusts the gate voltages of the switching elements Q1 to Q6. The voltage switching unit 213 has a series circuit of an FET 2 and a resistor R3. The series circuit is connected in parallel to the resistor R2. The voltage switching unit 213 turns off the FET 2 by the gate power supply voltage switching signal GVT (L) transmitted from the control circuit 30. When the FET 2 is turned off, the voltage input to the FB terminal of the power supply IC 211 increases, and the gate voltages of the switching elements Q1 to Q6 decrease.

The drive unit 22 includes a drive IC 221 and a push-pull circuit 222. The driver IC 221 controls the push-pull circuit 222 based on the PWM signals PS _Q1 and PS _Q2 output from the control circuit 30. The drive unit 22 applies a gate voltage between the gate and emitter of the switching elements Q1 and Q2 via the gate resistors Rg1 and Rg2, respectively, to switch the switching elements Q1 and Q2 on and off. The input sides of the plurality of push-pull circuits 222 are connected to a plurality of transformers included in the flyback transformer 212, respectively, and the output sides are connected to switching elements Q1 and Q2 via gate resistors R1 and R2, respectively. The drive unit 22 is insulated from the control circuit 30 by a photocoupler or the like.

Next, the configuration of the control circuit 30 will be described with reference to FIG. The control circuit 30 includes a current command value calculation unit 31, a current control unit 32, a dq three-phase conversion unit 33, a PWM signal generation unit 34, a three-phase dq conversion unit 35, a phase calculation unit 36, and a rotation speed. A calculation unit 37 and a voltage switching determination unit 28 are provided.

The current command value calculation unit 31 includes the torque command value (T ^* ), the angular frequency (rotation speed) (ω) of the motor 3 calculated by the rotation speed calculation unit 37, and the capacitor 5 detected by the voltage sensor 15. The dq-axis current command values (Id ^* , Iq ^* ) are calculated with reference to the map using the detected voltage (Vdc) of. The dq axis current command values (Id ^* , Iq ^* ) indicate the target value of the alternating current supplied from the inverter 1 to the motor 3. The map shows the relationship between the torque command value (T ^* ), the angular frequency (ω), and the voltage (Vdc) and the dq-axis current command values (Id ^* , Iq ^* ). Stored. Torque command value ^(T *), the angular frequency (omega), and to the input of the voltage (Vdc), loss and optimum dq-axis current command value to minimize the losses of the motor 3 of the inverter 1 ^(Id *, Iq ^* ) is associated. Here, the dq axis represents a component of the rotating coordinate system.

The dq axis current command value (Id ^* , Iq ^* ) and the dq axis current (Id, Iq) output from the three-phase dq converter 35 are input to the current controller 32. The current controller 32 calculates and outputs the dq axis voltage command values (Vd ^* , Vq ^* ) so that the dq axis currents (Id, Iq) coincide with the dq axis current command values (Id ^* , Iq ^* ). .

The dq three-phase conversion unit 33 receives the dq axis voltage command values (Vd ^* , Vq ^* ) and the phase detection value (θ) of the phase calculation unit 36. The dq three-phase conversion unit 33 converts the dq axis voltage command value (Vd ^* , Vq ^* ) of the rotating coordinate system into the u, v, w axis voltage command values (Vu ^* , Vv ^* , Vw ^* ) of the fixed coordinate system. The converted voltage command values (Vu ^* , Vv ^* , Vw ^* ) are output to the PWM signal generator 34.

The PWM signal generation unit 34 generates a PWM signal PS for switching control of the switching elements Q1 to Q6 based on the detection voltage (Vdc) and the voltage command values (Vu ^* , Vv ^* , Vw ^* ), and the drive circuit 20 Output to.

The three-phase dq conversion unit 35 is a control unit that performs three-phase to two-phase conversion. The phase current (Iu, Iv, Iw) detected by the current sensor 16 and the phase detection value (θ) of the phase calculation unit 36 are input. Is done. The three-phase dq converter 35 converts the phase current (Iu, Iv, Iw) in the fixed coordinate system into the phase current (Id, Iq) in the rotating coordinate system. The three-phase dq conversion unit 35 outputs the converted phase currents (Id, Iq) of the rotating coordinate system to the current control unit 32.

The phase calculation unit 36 calculates the phase (θ) of the rotor based on the signal transmitted from the rotor position sensor 6 and indicating the position (φ) of the rotor of the motor 3, and the dq three-phase conversion units 33, 3 It outputs to the phase dq conversion part 35 and the rotation speed calculating part 37. The rotation speed calculation unit 37 calculates the rotation speed (electrical angular velocity) (ω) by differentiating the phase (θ) and outputs it to the current command value calculation unit 31.

The voltage switching determination unit 38 determines whether or not to switch the gate voltages of the switching elements Q1 to Q6 based on the dq-axis current command values (Id ^* , Iq ^* ) output from the current command value calculation unit 31. The voltage switching determination unit 38 transmits a gate power supply voltage switching signal GVT corresponding to the determination result to the voltage switching unit 213. The specific control contents of the voltage switching determination unit 38 will be described later.

Here, the recovery current flowing through the diodes D1 to D6 will be described with reference to FIGS. 4a and 4b. FIG. 4a is a circuit diagram of the switching elements Q1 and Q2 and the diodes D1 and D2 for explaining the current path of the return current. FIG. 4b is a graph showing the time characteristics of the return current flowing through the diode D1.

As shown in FIG. 4a, a reflux current (If) flows from the motor 3 toward the inverter 1, and a circulating current (If) flows through the diode D1. In the state shown in FIG. 4a, when the switching element Q2 is turned on, the return current flowing in the diode D1 flows out to the switching element Q2. At this time, due to the accumulation of carriers in the diode D1, a reverse current flows through the diode D1, and then converges to zero. As shown in FIG. 4b, when the switching element Q2 is turned on at time t0 in a state where the return current (If) is flowing through the diode D1, the current flowing through the diode D1 becomes zero after time t1. To converge to zero. The oscillating current is the recovery current RC.

By the way, when the power converter of this example is mounted on a vehicle, for example, the maximum drive current value of the motor 3 is about 600 amperes and the motor 3 is driven, the current supplied from the inverter 1 to the motor 3 is 0 amperes. It has been confirmed by the present inventor that noise caused by the recovery current RC occurs in the vicinity. And since the said noise interferes with the radio etc. which were mounted in the vehicle, it was necessary to suppress the said noise. Further, since the power modules 11, 12, and 13 are required to suppress the heat generation of the switching elements Q1 to Q6, it is also necessary to suppress the loss of the power modules 11 to 13. Note that “near 0 amperes” is a current value sufficiently small with respect to the maximum driving current value (about 600 amperes), and here indicates about 30 amperes or less.

The inverter 1 according to the embodiment sets a plurality of switching speeds when turning on the switching elements Q1 to Q6 as follows, and the supply current supplied from the inverter 1 to the motor 3 is in the vicinity of 0 amperes. The switching speed when turning on the switching elements Q1 to Q6 is set lower than the switching speed when the supply current is not near 0 amperes.

Next, the control contents of the control circuit 30 will be described with reference to FIGS. 1 to 3 and FIG. FIG. 5 is a graph showing the characteristics of the change rate (di / dt) of the recovery current with respect to the output current (supply current) of the inverter 1. The control circuit 30 determines whether or not the supply current supplied from the inverter 1 to the motor 3 is near 0 amperes, and the dq axis current command values (Id ^* , Iq ^*) output from the current command value calculation unit 31 ^. ) Is used.

The voltage switching determination unit 38 compares the dq-axis current command value (Id ^* , Iq ^* ) output from the current command value calculation unit 31 with a preset current threshold value, and determines the gate according to the comparison result. On (H) and off (L) waveforms of the power supply voltage switching signal GVT are generated. When the supply current is in the vicinity of 0 ampere, the recovery current RC oscillates greatly, thereby generating noise. For this reason, in this example, the current threshold is set according to the recovery current change rate (di / dt). That is, in a device such as a vehicle equipped with the power conversion device of this example, the allowable magnitude of noise radiated by the recovery current vibration is measured in advance, and the recovery current relative to the supply current is set so as to fall within the allowable noise range. The rate of change (di / dt) is evaluated. Then, a current threshold is determined at the design stage.

As shown in FIG. 5, the characteristics of the recovery current change rate (di / dt) with respect to the supply current from the inverter 1 to the motor 3 are evaluated in advance. Therefore, the recovery current limit change rate (di / dt_max) that falls within the allowable noise range is determined, and the supply current corresponding to the limit change rate is set to the reference value (Ith). The supply current has a correlation with the dq axis current command value (Id ^* , Iq ^* ). For this reason, the control circuit 30 does not necessarily determine whether or not the supply current is in the vicinity of 0 amperes after directly detecting the supply current, and the threshold value of the current command value corresponding to the reference value (Ith). Is stored in the voltage switching determination unit 38 as a current threshold value.

Then, when the dq-axis current command value (Id ^* , Iq ^* ) is lower than the current threshold, the voltage switching determination unit 38 determines that the supply current to the motor 3 is in the vicinity of 0 amperes, and switches the gate power supply voltage. A signal GVT (L) is transmitted to the drive circuit 20. The drive circuit 20 reduces the gate voltages of the switching elements Q1 to Q6 based on the gate power supply voltage switching signal GVT (L). The switching elements Q1 to Q6 are turned on with a low gate voltage when turned on by the PWM signal PS. For this reason, the switching speed of the switching elements Q1 to Q6 is reduced, and the change rate (di / dt) of the recovery current in the diodes D1 to D6 in which the return current flows is suppressed to be equal to or less than the limit change rate (di / dt_max). be able to.

On the other hand, when the dq-axis current command value (Id ^* , Iq ^* ) is higher than the current threshold, the voltage switching determination unit 38 determines that the supply current to the motor 3 is not near 0 amperes, and switches the gate power supply voltage. The signal GVT (H) is transmitted to the drive circuit 20. Based on the gate power supply voltage switching signal GVT (H), the drive circuit 20 sets the gate voltage of the switching elements Q1 to Q6 to be higher than the normal gate voltage, in other words, the gate voltage when the supply current is near 0 amperes. Set to gate voltage. Since the switching elements Q1 to Q6 are turned on with a normal gate voltage when turned on by the PWM signal PS, the switching speed of the switching elements Q1 to Q6 becomes the speed during normal control. That is, if the gate voltage is lowered to decrease the switching speed of switching elements Q1 to Q6, the loss of switching elements Q1 to Q6 increases. For this reason, regardless of the magnitude of the supply current, if the gate voltage is always kept low, the heat generation from the switching elements Q1 to Q6 increases. Therefore, in this example, when it is determined that the supply current to the motor 3 is not near 0 amperes, the gate voltage is returned to the normal time, and the loss of the switching elements Q1 to Q6 is suppressed.

Next, the relationship between the gate voltage, the collector current (Ic) corresponding to the switching speed, and the time change rate of the collector-emitter voltage (Vce) will be described with reference to FIG. FIG. 6 shows the time characteristics of the collector current (Ic) and the collector-emitter voltage (Vce). Graph ga is Ic when the gate voltage is lowered, graph gb is Ic when the gate voltage is normal, graph gc is Vce when the gate voltage is lowered, and graph gd is when the gate voltage is normal. Vce is shown.

When the gate voltage is lowered, the time required to charge the input capacitance between the gates and the emitters of the switching elements Q1 to Q6 becomes longer. Therefore, as shown in the graph ga and the graph gb, Ic when the gate voltage is lowered is Compared with Ic when the gate voltage is set to normal, the current flows more slowly. Therefore, the time change rate d (Ic) / dt of the collector current (Ic) is also reduced. Similarly for Vce, as shown in graphs gc and gd, Vce when the gate voltage is lowered changes more slowly than Vce when the gate voltage is normal. For this reason, the time change rate d (Vce) / dt of the gate-emitter voltage (Vce) is also reduced.

Thereby, by decreasing the gate voltage, the time change rate of Ic (d (Ic) / dt) and the time change rate of Vce d (Vce) / dt can be suppressed. The time change rate of Ic (d (Ic) / dt) and the time change rate of Vce d (Vce) / dt are equivalent to the change rates of the recovery currents of the diodes D1 to D6. Therefore, in this example, when the supply current is in the vicinity of 0 amperes, the noise can be reduced by lowering the gate voltage to lower the switching speed of the switching elements Q1 to Q6.

As described above, in this example, when the supply current supplied from the inverter 1 to the motor 3 is in the vicinity of 0 amperes, the control circuit 30 determines the switching speed when turning on the switching elements Q1 to Q6 as the supply current. Is lower than the switching speed when it is not near 0 amperes. As a result, when the supply current is close to 0 amperes, the switching elements Q1 to Q6 are turned on to suppress the rate of change of the recovery current flowing through the diodes D1 to D6, and the recovery is performed when the supply current is close to 0 amperes. Noise generated by current vibration can be suppressed. Further, in this example, when the supply current is not near 0 amperes, the switching speed is returned to the normal speed, so that the loss in the power modules 11 to 13 including the switching elements Q1 to Q6 can be suppressed. it can.

In this example, the control circuit 30 compares the supply current with the current threshold corresponding to the limit change rate of the recovery current flowing through the diodes D1 to D6 by turning on the switching elements Q1 to Q6, and the supply current is the current. If it is lower than the threshold, it is determined that the supply current is in the vicinity of 0 amperes, and the switching speed is reduced. Thereby, when the supply current is in the vicinity of 0 amperes, noise generated by the oscillation of the recovery current can be suppressed.

In this example, the control circuit 30 determines whether or not the supply current is near 0 amperes based on the current command value calculated by the current command value calculation unit 31. Thereby, using the current command value, the current threshold value and the supply current can be compared to determine whether or not the supply current is in the vicinity of 0 amperes.

In this example, the control circuit 30 reduces the switching speed by reducing the gate voltages of the switching elements Q1 to Q6. Thereby, when the supply current is in the vicinity of 0 amperes, noise generated by the oscillation of the recovery current can be suppressed.

In this example, the voltage switching determination unit 38 compares the dq-axis current command value (Id ^* , Iq ^* ) with the current command value and the corresponding current threshold value to determine whether or not the supply current is near 0 amperes. However, based on the detection current of the current sensor 16, it may be determined whether or not the supply current is near 0 amperes. That is, the current threshold value is set in advance to a threshold value corresponding to the current supplied to the motor 3 instead of the current command value as described above, and the control circuit 30 compares the detected current of the current sensor 16 with the current threshold value. When the detected current is lower than the current threshold, it is determined that the supply current is in the vicinity of 0 amperes. Thus, it is possible to determine whether or not the supply current is in the vicinity of 0 amperes using the detection value of the current sensor 16.

In this example, as shown in FIG. 7, it is determined whether or not the supply current is in the vicinity of 0 amperes based on the dq axis current (Id, Iq) that is the output of the three-phase dq converter 35. Good. FIG. 7 is a block diagram of the control circuit 30 of the power conversion device according to the first modification of the present invention. The voltage switching determination unit 38 extracts the motor current component (Ia) from the dq axis current (Id, Iq), compares the motor current component (Ia) with the current threshold value, and the supply current is near 0 amperes. Whether or not, and the gate voltage is lowered according to the determination result. The current threshold value is set to a threshold value corresponding to the motor current component (Ia).

Further, in this example, as shown in FIG. 8, based on the torque command value (T ^* ) input from the outside of the inverter 1 and the angular frequency (ω) of the motor 3, whether or not the supply current is near 0 amperes. It may be determined. FIG. 8 is a block diagram of the control circuit 30 of the power conversion device according to the second modification of the present invention. The voltage switching determination unit 38 is preset with a torque and angular frequency range in which the supply current to the motor 3 is near zero. The voltage switching determination unit 38 receives the torque command value (T ^* ) and the angular frequency (ω) of the motor 3 as inputs, and the torque command value (T ^* ) and the angular frequency (ω) of the motor 3 are within the ranges. In some cases, it is determined that the supply current is in the vicinity of 0 amperes, and the gate voltage is reduced according to the determination result. Thus, it is possible to determine whether or not the supply current is in the vicinity of 0 amperes using the torque command value and the rotation speed of the motor 3.

The diodes D1 to D6 correspond to the “return diode” of the present invention, the motor 3 corresponds to the “load”, the circuit included in the inverter 1 corresponds to the “power conversion circuit”, and the current command value is calculated. The unit 31 corresponds to a “command value calculation unit”.

<< Second Embodiment >>
FIG. 9 is a circuit diagram of the drive circuit 20 of the power conversion device according to the second embodiment of the invention. In this example, the configuration of a part of the drive circuit 20 and the control circuit 30 is different from the first embodiment described above. Since the other configuration is the same as that of the first embodiment described above, the description thereof is incorporated.

Unlike the first embodiment, the control circuit 30 directly outputs the dq-axis current command values (Id ^* , Iq ^* ) output from the current command value calculation unit 31 to the drive circuit 20 as the gate power supply voltage command value. . As shown in FIG. 9, dq axis current command values (Id ^* , Iq ^* ), which are gate power supply voltage command values from the control circuit 30, are input to the power supply IC 211. In the power supply IC 211, the dq-axis current command value (Id ^* , Iq ^* ) is equal to or less than a predetermined threshold value (Ids ^* ), and the dq-axis current command value (Id ^* , Iq ^* ) is closer to zero. The FET 1 is controlled to be low.

FIG. 10 is a graph showing characteristics of the gate voltage with respect to the current command value. That is, as shown in FIG. 10, when the dq-axis current command value (Id ^* , Iq ^* ) is higher than a predetermined current threshold value (Ids ^* ), the drive circuit 20 changes the gate voltage to the normal gate voltage. (Vg1). In addition, when the dq-axis current command value (Id ^* , Iq ^* ) is equal to or smaller than the current threshold value (Ids ^* ), the drive circuit 20 increases the gate voltage (Id) as the dq-axis current command value (Id ^* , Iq ^* ) approaches zero. The gate voltage is linearly lowered so as to approach a lower gate voltage (Vg2) than Vg1).

As described above, in this example, the drive circuit 20 decreases the switching speed as the supply current is near 0 ampere. Thereby, when the supply current is in the vicinity of 0 amperes, noise generated by the oscillation of the recovery current can be suppressed. Further, in this example, when the supply current is not near 0 amperes, the switching speed is returned to the normal speed, so that the loss in the power modules 11 to 13 including the switching elements Q1 to Q6 can be suppressed. it can.

<< Third Embodiment >>
FIG. 11 is a circuit diagram of the drive circuit 20 of the power conversion device according to the third embodiment of the invention. In this example, the configuration of a part of the drive circuit 20 is different from the first embodiment described above. Since the configuration other than this is the same as that of the first embodiment described above, the descriptions of the first embodiment and the second embodiment are incorporated as appropriate.

As shown in FIG. 11, the drive circuit 20 includes a first gate power supply unit 21, a drive unit 22, and a second gate power supply unit 23. The first gate power supply unit 21 includes a voltage switching unit 213 that reduces the gate voltage based on the gate power supply voltage switching signal GVT, and is electrically connected to the switching element Q2 of the lower arm circuit. On the other hand, the second gate power supply unit 23 does not have a circuit corresponding to the voltage switching unit 213, and is electrically connected to the switching element Q1 of the upper arm circuit. That is, the drive circuit 20 of this example reduces the gate voltage of the switching elements Q2, Q4, Q6 included in the lower arm circuit in the power conversion circuit of the inverter 1 based on the gate power supply voltage switching signal GVT, so that the upper arm The gate voltage of the switching elements Q1, Q3, Q5 included in the circuit is not lowered.

As described above, in this example, when the supply current supplied to the motor 3 is in the vicinity of 0 amperes, among the switching elements Q1 to Q6 connected in series, the gate voltage of one switching element Q2, Q4, Q6 And the gate voltage of the other switching element Q1, Q3, Q5 is not lowered. Thereby, when the supply current is in the vicinity of 0 amperes, noise generated by the oscillation of the recovery current RC can be suppressed. Further, since the control for increasing the loss is limited in part to the switching elements Q1 to Q6, the loss in the power modules 11 to 13 can be suppressed.

<< 4th Embodiment >>
FIG. 12 is a circuit diagram of the drive circuit 20 of the power conversion device according to the fourth embodiment of the invention. In this example, the configuration of a part of the drive circuit 20 and the control circuit 30 is different from the first embodiment described above. Since the other configuration is the same as that of the first embodiment described above, the descriptions of the first to third embodiments are incorporated as appropriate.

The control circuit 30 transmits a gate resistance switching signal GRS to the drive circuit 20 based on the determination result of whether or not the supply current to the motor 3 is near 0 amperes. The gate resistance switching signal GRS is a control signal for switching the gate resistance of the switching elements Q1 to Q6. The control circuit 30 transmits a gate resistance switching signal GRS (H: high level) when the supply current is in the vicinity of 0 amperes, and when the supply current is not in the vicinity of 0 amperes, the gate resistance switching signal GRS ( L: low level).

The driving circuit 20 includes a driving IC 221, a push-pull circuit 222, an insulating element 223, and switching elements 224 and 225 corresponding to the switching element Q1 and the switching element Q2. The insulating element 223 is an element for insulating the power supply portion of the drive circuit 20 and the control circuit 30 with a photocoupler or the like. The insulating element 223 controls the switching element 224 and the switching element 225 based on the gate resistance switching signal GRS transmitted from the control circuit 30. Resistor circuits in which resistors Rg1, Rg2 and resistors Rg1 ', Rg2' for setting the gate resistance are connected in parallel are connected to the gate terminals of the switching elements Q1, Q2, respectively. A switching element 225 is connected to one end of each of the resistors Rg1 'and Rg2', and the resistance value of the resistor circuit changes depending on whether the switching element 225 is turned on or off. That is, in the resistor circuit, if the resistors Rg1 and Rg2 and the resistors Rg1 'and Rg2' are a parallel circuit, the gate resistance is low, and if only the resistors Rg1 and Rg2 are conductive, the gate resistance is high.

When the driving circuit 20 receives the gate resistance switching signal GRS (L) transmitted from the control circuit 30 by the insulating element 223, the driving circuit 20 controls the switching element 224 and the switching element 225 to thereby control the resistors Rg1, Rg2, and the resistors Rg1 ′, Rg2. Form a resistance circuit with 'connected in parallel. On the other hand, when the driving circuit 20 receives the gate resistance switching signal GRS (H) transmitted from the control circuit 30 by the insulating element 223, the driving circuit 20 controls the switching element 224 and the switching element 225, and the current of the resistors Rg1 ′ and Rg2 ′. The path is blocked, and the resistance circuit of the resistors Rg1, Rg1 ′, Rg2, and Rg2 ′ is used as a conduction circuit of the resistors Rg1 and Rg2. Thus, for example, when Rg1 = Rg1 ′ and Rg2 = Rg2 ′, when the supply current is in the vicinity of 0 amperes, the gate resistance is doubled compared to the case in which the supply current is not in the vicinity of 0 amperes. As a result, the switching speed decreases. Thus, in this example, the switching speed of the switching elements Q1 to Q6 is decreased by increasing the gate resistance.

As described above, the drive circuit 20 includes a resistor circuit for setting a plurality of gate resistors, which is formed by the switching element 225, the resistors Rg1 and Rg2, and the resistors Rg1 'and Rg2'. The control circuit 30 controls the resistance circuit to increase the gate resistance, thereby reducing the switching speed. Thereby, when the supply current is in the vicinity of 0 amperes, noise generated by the oscillation of the recovery current can be suppressed.

The entire contents of Japanese Patent Application No. 2011-225533 (filing date: October 13, 2011) are incorporated herein by reference.

As mentioned above, although the content of the present invention has been described according to the embodiments, the present invention is not limited to these descriptions, and it is obvious to those skilled in the art that various modifications and improvements are possible.

According to the present invention, when the switching elements Q1 to Q6 are turned on, the rate of change of the recovery current flowing through the freewheeling diodes D1 to D6 is suppressed, so that when the supply current to the load is near 0 amperes, the freewheeling diode Noise generated by vibration of the currents D1 to D6 can be suppressed. Therefore, the present invention has industrial applicability.

DESCRIPTION OF SYMBOLS 1 ... Inverter Q1-Q6 ... Switching element D1-D6 ... Diode 20 ... Drive circuit 30 ... Control circuit 31 ... Current command value calculation part

Claims (10)

It has a plurality of switching elements and a plurality of free-wheeling diodes connected in parallel to the plurality of switching, and converts the input power by switching on and off of the plurality of switching elements and outputs it to the load A power conversion circuit;
A drive circuit for driving the plurality of switching elements;
A control circuit for controlling the power conversion circuit and the drive circuit,
The control circuit includes:
When the supply current supplied from the power conversion circuit to the load is in the vicinity of 0 amperes, the switching speed when turning on the switching element is lower than the switching speed in the case where the supply current is not in the vicinity of 0 amperes. A power converter characterized by that. The control circuit includes:
By comparing the supply current with a current threshold value corresponding to a limit change rate of a recovery current flowing in the return diode by turning on the switching element,
The power converter according to claim 1, wherein when the supply current is lower than the current threshold, it is determined that the supply current is in the vicinity of 0 amperes. A current sensor connected between the power conversion circuit and the load;
The control circuit includes:
The power converter according to claim 1 or 2, wherein it is determined whether or not the supply current is in the vicinity of 0 amperes based on a detection current detected by the current sensor. The control circuit includes:
Based on the rotation speed of the motor as the load, the voltage of the power source connected to the power conversion circuit, and the torque command value input from the outside, the current command of the alternating current output from the power conversion circuit to the load A command value calculation unit for calculating a value;
The control circuit includes:
The power conversion device according to claim 1 or 2, wherein it is determined whether or not the supply current is in the vicinity of 0 amperes based on the current command value calculated by the command value calculation unit. The control circuit includes:
2. The method according to claim 1, wherein it is determined whether or not the supply current is in the vicinity of 0 amperes based on a rotation speed of the motor as the load and a torque command value input from the outside. Power converter. The drive circuit is
Including a resistance circuit capable of setting a plurality of gate resistances of the switching elements;
The control circuit includes:
The power conversion device according to any one of claims 1 to 5, wherein the switching speed is reduced by controlling the resistance circuit and increasing the gate resistance. The drive circuit is
Applying a gate voltage between the gate and emitter of the switching element to turn on the switching element;
The control circuit includes:
The power conversion device according to any one of claims 1 to 5, wherein the switching speed is reduced by reducing the gate voltage. The drive circuit is
The power conversion device according to any one of claims 1 to 7, wherein the switching speed is decreased as the supply current is closer to 0 ampere. The power conversion circuit includes:
A series circuit in which the plurality of switching elements are connected in series between a plurality of power supply lines;
The drive circuit is
The power converter according to any one of claims 1 to 8, wherein a gate voltage of at least one of the plurality of switching elements is lowered. It has a plurality of switching elements and a plurality of free-wheeling diodes connected in parallel to the plurality of switching, and converts the input power by switching on and off of the plurality of switching elements and outputs it to the load A control method for a power conversion device comprising: a power conversion circuit; and a drive circuit that drives the plurality of switching elements,
When the supply current supplied from the power conversion circuit to the load is in the vicinity of 0 amperes, the switching speed when turning on the switching element is lower than the switching speed in the case where the supply current is not in the vicinity of 0 amperes. A method for controlling a power conversion device.

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