JP2013090350A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion apparatus which restrains noise generated by the vibration of currents flowing in a reflux diode.SOLUTION: The power conversion apparatus comprises: a power conversion circuit, having a plurality of switching elements Q1 to Q6 and reflux diodes D1 to D6, which switches on/off of the plurality of switching elements Q1 to Q6 to convert input power and outputs the converted power to a load; a drive circuit 20 which drives the plurality of switching elements Q1 to Q6; and control means of controlling the power conversion circuit and the drive circuit 20. When a supply current supplied from the power conversion circuit to the load is near 0 amperes, the control means lowers a switching speed at which the switching elements Q1 to Q6 are turned on, so that it is lower than a switching speed applied in cases when the supply current is not near 0 amperes.

Description

  The present invention relates to a power conversion device.

  It has 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 to convert the supplied DC power into AC power and convert it to a generator motor. An AC / DC conversion circuit for supplying power and a control circuit for intermittently controlling the semiconductor switching element are provided, and the control circuit drives the semiconductor switching element through a gate resistor having a maximum resistance value when the generator motor is started. There is known a vehicular generator motor control device that delays a state transition between an ON state and an OFF state of the vehicle and suppresses switching noise within an allowable level range (Patent Document 1).

JP 2005-65460 A

In the above-described conventional vehicle 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 insufficient to suppress noise.

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

According to the present invention, when the supply current supplied from the power conversion circuit to the load is in the vicinity of 0 amperes, the switching speed when the switching element is turned on is lower than the switching speed in the case where the supply current is not in the vicinity of 0 amperes. This solves the above problem.

  According to the present invention, when the switching element is turned on, the rate of change of the recovery current flowing through the freewheeling diode is suppressed. Therefore, when the supply current to the load is near 0 ampere, the current is generated by the freewheeling diode current. The effect that the noise which carries out can be suppressed is produced.

1 is a block diagram of a motor control system including a power conversion device according to an embodiment of the present invention. FIG. 2 is a circuit diagram of the drive circuit in FIG. 1. It is a block diagram of the control circuit of FIG. FIG. 2 is a circuit diagram of a portion corresponding to a U phase of the inverter of FIG. 1. 4b is a graph showing the time characteristics of the current flowing through the diode of FIG. 4a. 2 is a graph showing di / dt characteristics with respect to supply current in the inverter of FIG. 1. 2 is a graph showing collector current characteristics and collector-emitter voltage characteristics in the inverter of FIG. 1. It is a block diagram of the control circuit which concerns on the modification of this invention. It is a block diagram of the control circuit which concerns on the modification of this invention. It is a circuit diagram of the drive circuit of the power converter device which concerns on other embodiment of this invention. It is a graph which shows the characteristic of the gate voltage with respect to the electric current designation value in the power converter device which concerns on other embodiment of this invention. It is a circuit diagram of the drive circuit of the power converter device which concerns on other embodiment of this invention. It is a circuit diagram of the drive circuit of the power converter device which concerns on other embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<< First Embodiment >>

  FIG. 1 is a block diagram showing a motor control system including a power converter according to an embodiment of the present invention. 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, and 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 opened and closed by the 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 includes a plurality of switching elements (insulated gate bipolar transistors IGBTs) Q1 to Q6 and a rectifying element that is connected in parallel to the switching elements Q1 to Q6 and in which a current flows in a direction opposite to the current direction of the switching elements Q1 to Q6. (Reflux diodes) D1 to D6 are provided, and the DC power of the battery 1 is converted into AC power and supplied 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. . The same switching element is used for each switching element Q1-Q6, for example, an insulated gate bipolar transistor (IGBT) is used. 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, switching elements Q5 and Q6 are connected in series, and between the switching elements Q1 and Q2 and the U phase of the motor 3, switching element 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. Switching elements Q 1, Q 3, Q 5 are electrically connected to the positive electrode side of battery 1, and switching elements Q 2, Q 4, Q 6 are electrically connected to the negative electrode side of battery 1. The switching of the switching elements Q1 to Q6 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 switching. Provided in each phase between the connection point of the elements Q5 and Q6 and the motor 3, and outputs a detection current signal to the control circuit 30.

  The drive circuit 20 transmits a gate signal to each of the switching elements Q1 to Q6 to drive on and off of each of the switching elements Q1 to Q6. The drive circuit 20 receives the signal from the voltage sensor 15, converts the signal into 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. The specific configuration of the drive circuit 20 will be described later.

The control circuit 30 controls the switching elements Q <b> 1 to Q <b> 6 via the drive circuit 20 and controls the operation of the motor 3. The control circuit 30 is a signal indicating a torque command value (T ^* ) transmitted from the vehicle controller 5, a signal from the rotor position sensor 6, a feedback signal transmitted from the current sensor 16, and a signal from the voltage sensor 7. Is generated, a PWM (pulse width modulation) signal is generated, and the signal is transmitted to the drive circuit 20. Then, the drive circuit 20 turns on and off the switching elements Q1 to Q6 at a predetermined timing based on the pulse width modulation signal. The specific configuration of the control circuit 30 will be described later.

The vehicle controller 5 includes a central processing unit (CPU), a read-on memory (ROM), and a random access memory (RAM), and is a control unit that controls the entire vehicle according to the present embodiment. The value (T ^* ) is calculated, and the torque command value (T ^* ) is output 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 12 is a sensor such as a resolver or an encoder, is provided in the motor 3, detects the position of the rotor of the motor 3, and outputs the position of the rotor to the motor controller 9.

  Next, the configuration of the drive circuit 20 will be described with reference to FIG. FIG. 2 shows a circuit diagram of the gate power supply unit and the drive unit of the drive circuit 20. In FIG. 2, the circuit of the drive circuit 20 connected to the semiconductor module 11 is shown, but the circuit of the drive circuit 20 connected to the semiconductor module 12 and the semiconductor module 13 has the same configuration, and thus the description thereof is omitted. To do.

  The drive circuit 20 includes 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 21, and is a drive power supply circuit that drives the switching elements Q1 to Q6. The gate power source includes a power source IC 211 that controls power supplied from the primary side power source, an 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, and a voltage 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 221 compares the detection voltage signal input to the FB terminal with the reference voltage, controls the ON / OFF duty ratio of the FET 1, and makes the output voltage of the winding of the flyback transformer 212 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 power supplies of the switching elements Q2, Q4, and Q6 take the N-side DC power supply line as the same reference power supply, and the power supplies 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, and is a current path that flows through a series circuit of the resistors R1 and R2 connected to the primary winding side of the flyback transformer 212. By switching the input voltage to the FB terminal of the power supply IC 221, the gate voltage of the switching elements Q1 to Q6 is adjusted. The voltage switching unit 213 has a series circuit of an FET 2 and a resistor R3, and 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 (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 signal output from the control circuit 30, and applies a gate voltage between the gate and emitter of the switching elements Q1 and Q2 via the gate resistors Rg1 and Rg2, respectively. Then, the switching elements Q1, Q2 are switched 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. FIG. 3 is a block diagram of the control circuit 30. As shown in FIG. 3, 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 A calculation unit 36, a rotation number 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. With reference to the detected voltage (V _dc ), the map is referred to, and the dq axis current command values (I _d ^* , I _q ^* ) indicating the target value of the alternating current supplied from the inverter 1 to the motor 3 are calculated. . The map outputs a current command value in order to output a dq axis current command value (I _d ^* , I _q ^* ) using the torque command value (T ^* ), angular frequency (ω), and voltage (V _dc ) as indices. It is stored in the calculation unit 31 in advance, and is associated with the input so as to output an optimal command value that minimizes the loss of the inverter 1 and the loss of the motor 3. Here, the dq axis represents a component of the rotating coordinate system.

The current controller 32 receives the dq-axis current command value (I _d ^* , I _q ^* ), the dq-axis current (I _d , I _q ), which is the output of the three-phase dq converter 35, as input, and the dq-axis current (I _d, dq axis current command value ^{_{I q) (I d *,}} dq -axis voltage command value to match the ^{_{I q *) (V d *}} , V q *) is calculated and outputs.

The dq three-phase conversion unit 33 receives the dq axis voltage command value (V _d ^* , V _q ^* ) and the phase detection value (θ) of the phase calculation unit 36 as inputs, and receives the dq axis voltage command value (V _{d of the} rotating coordinate system _). ^*, to convert the _V ^{q *)} u fixed coordinate system, v, voltage command values of the w-axis ^_(V u ^_*, V v _*, the _V ^{w *).} The dq three-phase conversion unit 33 outputs the converted voltage command values (V _u ^* , V _v ^* , V _w ^* ) to the PWM signal generation unit 34.

The PWM signal generation unit 34 generates a PWM signal for switching control of the switching elements Q1 to Q6 based on the detection voltage (V _dc ) and the voltage command value (V _u ^* , V _v ^* , V _w ^* ), Output to the drive circuit 20.

The three-phase dq conversion unit 35 is a control unit that performs three-phase to two-phase conversion. The phase current (I _u , I _v , I _w ) detected by the current sensor 16 and the phase detection value (θ ) As an input, the phase current (I _u , I _v , I _w ) in the fixed coordinate system is converted into the phase current (I _d , I _q ) in the rotating coordinate system. The three-phase dq conversion unit 35 outputs the converted phase currents (I _d , I _q ) 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 of the rotor of the motor 3, and the dq three-phase conversion unit 33, three-phase dq conversion Output to the unit 35 and the rotational speed calculation unit 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 to switch the gate voltages of the switching elements Q1 to Q6 based on the dq axis current command values (I _d ^* , I _q ^* ) output from the current command value calculation unit 31. The gate power supply voltage switching signal corresponding to the determination result is transmitted 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 switching elements Q1 and Q2 and diodes D1 and D2, which are U-phase portions, for explaining the current path of the return current. FIG. 4b is a graph showing the time characteristic of the reflux current.

As shown in FIG. 4a, when a return current (If) flows from the motor 3 to the inverter 1 and a current (If) flows through the diode D1, the switching element Q2 is turned on, and the current flows through the diode D1. The reflux current flows out to the switching element D1. At this time, due to the accumulation of carriers in the diode D1, a current flows in the reverse direction of the diode D1, and then converges to zero. As shown in Figure 4b, in a state in which the return current (If) is flowing through the diode D1, when turning on the switching element Q1 at time t _0, and the vibration after becoming zero at time t1, converges to zero . This oscillating current is the recovery current.

  By the way, when the power conversion device of this example is mounted on, for example, a vehicle and the maximum drive current value of the motor 3 is set to about 600 A and the motor 3 is driven, the current supplied from the inverter 1 to the motor 3 is around 0 A ( It was confirmed by the present invention that noise caused by the recovery current is generated when the current value is sufficiently smaller than the maximum drive current value, which is about 30 A or less in this case. And since the said noise interferes with the radio etc. which were mounted in the vehicle, it was necessary to suppress the said noise. Moreover, in the semiconductor module, since it is calculated | required to suppress the heat_generation | fever of switching element Q1-Q6, it is also necessary to suppress the loss of the power modules 11-13.

  The present invention sets a plurality of switching speeds when turning on the switching elements Q1 to Q6 as follows, and when the supply current supplied from the inverter 1 to the motor 3 is in the vicinity of 0 amperes, the switching element Q1 The switching speed for turning on 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 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 in the vicinity of 0 amperes, and the dq axis current command value (I _d ^* , I) output from the current designation value calculation unit 31. _q ^* ) is used.

The voltage switching determination unit 38 compares the dq-axis current command value (I _d ^* , I _q ^* ) output from the current specified value calculation unit 31 with a preset current threshold, and according to the comparison result. Then, on (H) and off (L) waveforms of the power supply voltage switching signal are generated. When the supply current is in the vicinity of 0 ampere, the oscillation of the recovery current becomes large and noise is generated thereby. 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 the present example, the allowable magnitude of noise radiated by the recovery current oscillation is measured in advance, and the change in the recovery current relative to the supply current is within the allowable range. After evaluating the rate (di / dt), 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). Further, since the supply current has a correlation with the dq-axis current command values (I _d ^* , I _q ^* ), the control circuit 30 does not necessarily detect the supply current directly, but the supply current is close to 0 amperes. 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 (I _d ^* , I _q ^* ) is lower than the current threshold, the voltage switching determination unit 38 determines that the supply current to the motor 3 is near 0 amperes, and the gate power supply A voltage switching signal (L) is transmitted to the drive circuit 20. The drive circuit 20 reduces the gate voltage of the switching elements Q1 to Q6 based on the gate power supply voltage switching signal (L). When the switching circuit Q1 to Q6 is turned on by the PWM signal, the driving circuit 20 turns on the switching elements Q1 to Q6 with a low gate voltage. Therefore, the switching speed of the switching elements Q1 to Q6 decreases, and the return current The recovery current change rate (di / dt) in the diodes D1 to D6 where the current flows can be suppressed to a limit change rate (di / dt_max) or less.

On the other hand, when the dq-axis current command value (I _d ^* , I _q ^* ) 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 the gate power supply A voltage switching signal (H) is transmitted to the drive circuit 20. Based on the gate power supply voltage switching signal (H), the drive circuit 20 changes the gate voltage of the switching elements Q1 to Q6 to a normal gate voltage, in other words, a gate higher than the gate voltage when the supply current is near 0 amperes. Set to voltage. When the switching circuit Q1 to Q6 is turned on by the PWM signal, the driving circuit 20 turns on the switching elements Q1 to Q6 with a normal gate voltage. Therefore, the switching speed of the switching elements Q1 to Q6 is the same as that during normal control. It becomes speed. That is, if the gate voltage is lowered to decrease the switching speed of the switching elements Q1 to Q6, the loss of the switching elements Q1 to Q6 increases, so that the gate voltage is always kept low regardless of the magnitude of the supply current. Then, 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 to suppress the loss of the switching elements Q1 to Q6.

  Next, the relationship between the gate voltage and the rate of change (di / dt) corresponding to the switching speed will be described with reference to FIG. FIG. 6 shows time characteristics of the collector current (Ic) and the collector-emitter voltage (Vce). Graph a shows Ic when the gate voltage is lowered, and graph b shows Ic when the gate voltage is normal. Graph c shows Vce when the gate voltage is lowered, and graph d shows Vce when the gate voltage is normal.

  When the gate voltage is lowered, the time for charging the input capacitance between the gates and the emitters of the switching elements Q1 to Q6 becomes longer. Therefore, as shown in graphs a and b, 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, d (Ic) / dt of the collector current (Ic) is also reduced. Similarly for Vce, as shown in graphs c and d, Vce when the gate voltage is lowered changes more slowly than Vce when the gate voltage is normal. Therefore, d (Vce) / dt of the gate-emitter voltage (Vce) is also reduced.

  Thereby, by decreasing the gate voltage, it is possible to suppress the rate of change of Ic (d (Ic) / dt) and d (Vce) / dt of Vce. Since the change rate of Ic (d (Ic) / dt) and d (Vce) / dt of Vce are equivalent to the change rate of the recovery current of the diodes D1 to D6, the supply current is 0 amperes. When it is in the vicinity, noise can be reduced by lowering the gate voltage and lowering 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 near 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 near 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 near 0 amperes. Noise generated by current vibration can be suppressed. Further, in this example, when the supply current is not in the vicinity of 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 in the vicinity of 0 amperes based on the specified current value calculated by the current command value calculation unit 31. Thereby, it is possible to compare the current threshold value with the supply current using the specified current value to determine whether or not the supply current is near 0 amperes.

  In this example, the control circuit 30 reduces the switching speed by reducing the gate voltage 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 (I _d ^* , I _q ^* ) with the current command value and the corresponding current threshold, and determines whether the supply current is near 0 amperes. Whether or not the supply current is in the vicinity of 0 amperes may be determined based on the detection current of the current sensor 16. 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.

Further, 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 (I _d , I _q ) that is the output of the three-phase dq converter 35. May be. FIG. 7 is a block diagram of the control circuit 30 of the power conversion device according to the modification of the present invention. The voltage switching determination unit 38 extracts a motor current component (Ia) from the dq-axis current (I _d , I _q ), compares the motor current component (Ia) with a current threshold value, and the supply current is near 0 amperes. The gate voltage is reduced 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 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 are equivalent to the “freewheeling diode” of the present invention, the motor 3 is equivalent to the “load”, the control circuit 30 is equivalent to “control means”, and the circuit included in the inverter 1 is “ It corresponds to a “power conversion circuit”, and the specified current value calculation unit 31 corresponds to “command value calculation means”.

<< Second Embodiment >>
FIG. 9 is a circuit diagram of a drive circuit 20 of a power conversion device according to another 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 uses the dq-axis current command value (I _d ^* , I _q ^* ) output from the current specified value calculation unit 31 as the gate power supply voltage command value to the drive circuit 20. Output. As shown in FIG. 9, dq axis current command values (I _d ^* , I _q ^* ), which are gate power supply voltage command values from the control circuit 30, are input to the power supply IC 211. The power supply IC 211 has a dq-axis current command value (I _d ^* , I _q ^* ) that is equal to or less than a predetermined threshold (I _ds ^* ) and a dq-axis current command value (I _d ^* , I _q ^* ) is close to zero. The FET 1 is controlled so that the gate voltage becomes lower.

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 (I _d ^* , I _q ^* ) is higher than a predetermined current threshold value (I _ds ^* ), the drive circuit 20 Gate voltage (V _g1 ). In addition, when the dq-axis current command value (I _d ^* , I _q ^* ) is equal to or less than the current threshold value (I _ds ^* ), the gate voltage increases as the dq-axis current command value (I _d ^* , I _q ^* ) approaches zero. Decreases linearly, and the drive circuit 20 decreases the gate voltage so as to approach a gate voltage (V _g2 ) lower than the gate voltage (V _g1 ).

  As described above, in this example, the drive circuit 20 decreases the switching speed as the supply current is closer to 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 in the vicinity of 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 a drive circuit 20 of a power conversion device according to another 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 gate power supply unit 21, a drive unit 22, and a gate power supply unit 23. The gate power supply unit 21 includes a voltage switching unit 213 that is a circuit for lowering the gate voltage based on a gate power supply voltage switching signal, and is electrically connected to the switching element Q2 of the lower arm circuit. On the other hand, the gate power supply unit 23 does not have 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, and 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, so that the upper arm circuit The gate voltages of the switching elements Q1, Q3, and Q5 included in are not reduced.

  As described above, in this example, when the supply current supplied to the motor 3 is in the vicinity of 0 amperes, the gate voltage of one switching element Q2, Q4, Q6 among the switching elements Q1-Q6 connected in series. 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 can be suppressed. Moreover, since the control which increases a loss is limited in part to switching elements Q1-Q6, the loss in the power modules 11-13 can be suppressed.

<< 4th Embodiment >>
FIG. 12 is a circuit diagram of a drive circuit 20 of a power conversion device according to another 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 configuration other than this is the same as that of the first embodiment described above, the description of the first to third embodiments is incorporated as appropriate.

  The control circuit 30 transmits a gate resistance switching signal 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 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 (H) when the supply current is near 0 amperes, and transmits a gate resistance switching signal (L) when the supply current is not near 0 amperes. .

  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 elements Q1 and 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 transmitted from the control circuit 30. Resistor circuits in which resistors Rg1 and Rg2 and resistors Rg1 'and Rg2' for setting the gate resistance are connected in parallel are connected to the gate terminals of the switching elements Q1 and 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 (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, thereby causing the resistors Rg1, Rg2, and the resistors Rg1 ′, Rg2 ′. Into a parallel circuit. On the other hand, when the driving circuit 20 receives the gate resistance switching signal (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 current paths of the resistors Rg1 ′ and Rg2 ′. 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. Thereby, this example reduces the switching speed of switching element Q1-Q6 by making gate resistance high.

  As described above, the present example includes a resistance circuit for setting a plurality of gate resistances, which is formed by the switching element 225, the resistances Rg1 and Rg2, and the resistances Rg1 ′ and Rg2 ′. Switching speed is reduced by switching. Thereby, when the supply current is in the vicinity of 0 amperes, noise generated by the oscillation of the recovery current can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... Inverter Q1-Q6 ... Switching element D1-D6 ... Diode 11, 12, 13 ... Power module 14 ... Capacitor 15 ... Voltage sensor 16 ... Current sensor 20 ... Drive circuit 21, 23 ... Gate power supply part 211 ... Power supply IC
212 ... Flyback transformer 213 ... Voltage switching unit 22 ... Drive unit 221 ... Drive IC
222 ... Push-pull circuit 223 ... Insulating element 224, 225 ... Switching element 30 ... Control circuit 31 ... Current command value calculation unit 32 ... Current control unit 33 ... dq 3-phase conversion unit 34 ... PWM signal generation unit 35 ... 3-phase dq conversion unit 36 ... Phase calculation unit 37 ... Rotational speed calculation unit 38 ... Voltage switching determination unit

Claims (9)

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;
Control means for controlling the power conversion circuit and the drive circuit,
The control means 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. The power converter characterized by the above-mentioned. The control means 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 means 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. Based on the rotational speed of the motor that is 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 Further comprising command value calculating means for calculating a value,
The control means includes
3. The power converter according to claim 1, wherein it is determined whether or not the supply current is in the vicinity of 0 amperes based on a current designation value calculated by the command value calculation unit. The control means 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 rotational 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 for setting a plurality of gate resistances of the switching elements;
The control means includes
The power converter according to claim 1, wherein the switching element speed is decreased by controlling the resistance circuit and switching to a circuit that increases 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 means includes
The power conversion device according to claim 1, wherein the switching speed is reduced by lowering 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.

Images