JP2006180606A - Controller for voltage driving element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently reduce the power loss of the entire system. <P>SOLUTION: In case that the output collector current of a voltage driving element is smaller than a specified current value and that the carrier frequency at the time of PWM-controlling the voltage driving element is lower than specified frequency, this controller judges that the amount of reduction of stationary loss being caused by increasing the gate voltage from first gate voltage to second gate voltage is larger than the increment of the driving power of the voltage driving element, and applies the second gate voltage to the gate terminal of the voltage driving element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a voltage driving element whose on / off operation is controlled by a voltage.

  Conventionally, in a control device for a voltage driving element such as an IGBT, a technique for changing a gate voltage according to the magnitude of a load current is known in order to reduce steady loss (see Patent Document 1).

JP 2004-15884 A

  However, the steady loss not only changes depending on the load current, but also changes depending on the driving frequency and temperature when driving the voltage driving element, so in the conventional technique of changing the gate voltage based only on the load current. However, there is a problem that power loss cannot always be reduced.

  In the control device for a voltage driving element according to the present invention, the condition that the amount of reduction in steady loss by increasing the gate voltage from the first gate voltage to the second gate voltage is greater than the amount of increase in driving power of the voltage driving element is satisfied. If it is determined whether the condition is satisfied, a second gate voltage is applied to the gate terminal of the voltage driving element.

  According to the voltage driving element control apparatus of the present invention, there is a condition that the reduction amount of the steady loss by increasing the gate voltage from the first gate voltage to the second gate voltage is larger than the driving power increase amount of the voltage driving element. When established, the second gate voltage is applied to the gate terminal of the voltage driving element, so that the loss of the entire apparatus can be reduced appropriately.

  Below, the example which controls IGBT which is a voltage drive element with the control apparatus of the voltage drive element in one Embodiment is demonstrated. FIG. 1 shows a circuit for one phase of a three-phase AC inverter using an IGBT. This three-phase AC inverter is used mounted on an electric vehicle, for example. In this inverter circuit, two IGBTs 1a and 1b are connected in series between the reference potential Vs and the load power supply VB, and the load L1 is turned on / off alternately by PWM control. Can output an alternating current Io. Diodes D1, D2 are connected in antiparallel to the IGBTs 1a, 1b, respectively.

  The gate terminals of the IGBTs 1a and 1b are connected to the output terminals of the drive circuits 101 and 102 via gate resistors R1 and R2, respectively. The drive circuit 101 includes a push-pull circuit including an NPN transistor 2a and a PNP transistor 3a. Similarly, the drive circuit 102 includes a push-pull circuit including an NPN transistor 2b and a PNP transistor 3b. The power supplies VN and VP of the drive circuits 101 and 102 are insulated from each other and are supplied by the power supply circuit 103. In addition, ND and PD, which are control signals output from the control device 110, are isolated and transmitted to the drive circuits 101 and 102 via the photocouplers 108 and 109.

  The power supply circuit 103 is a circuit that generates power supplies VN and VP that are insulated from the control power supply Vcc, and is a flyback converter in the present embodiment. That is, the power supply circuit 103 is configured to transmit the energy stored when the primary winding of the transformer L2 is energized to the secondary side when the transformer L2 is cut off. In addition to the transformer L2, the backflow prevention diodes D3 and D4 and the smoothing capacitor C1 , C2, a transistor Q3 for turning on / off the energization of the primary side winding, a power supply control circuit 104 for PWM driving the transistor Q3, and a feedback circuit for monitoring the output voltage and notifying the power supply control circuit 104.

  The feedback circuit includes resistors R5 to R7 that divide the output voltage, a shunt regulator 105 that sinks current when the divided voltage exceeds a predetermined voltage, a photocoupler 106 that is turned on / off by the current that the shunt regulator 105 sinks, In addition, a limiting resistor R8 that limits the energization current of the photocoupler 106 is provided. When the current notification signal OC output from the control device 110 is at a high level (Hi level), the photocoupler 107 is turned on, and both ends of the resistor R7 are short-circuited. When the resistor R7 is short-circuited, the feedback voltage notified to the power supply control circuit 104 is varied, and the voltages of the power supplies VP and VN are reduced. On the other hand, when the current notification signal OC is at a low level (Lo level), the photocoupler 107 is turned off, so that the resistor R7 is not short-circuited. The voltages of the power supplies VP and VN when the resistor R7 is not short-circuited are smaller than when the resistor R7 is short-circuited.

  As described later, control device 110 determines the signal level of current notification signal OC based on the magnitude of output collector current of IGBTs 1a and 1b and the magnitude of carrier frequency fc when PWM controlling IGBTs 1a and 1b. By switching, the magnitude of the gate voltage applied to the gate terminals of the IGBTs 1a and 1b is changed. Here, the gate voltage when the current notification signal OC is at a low level is VG1, and the gate voltage when the current notification signal OC is at a high level is VG2 (> VG1).

Here, the power loss of the IGBT that is turned on / off by the PWM control is represented by the sum of the steady loss and the switching loss. The switching loss Psw and steady loss Psat per IGBT of the three-phase inverter are expressed by equations (1) and (2), respectively.
Psw = 1 / π × Esw × fc (1)
Psat = Icp × Vce × {1/8 + (D × cos θ / 3 / π)} (2)
Here, Esw is a loss per switching pulse, and fc is a PWM drive frequency (carrier frequency). Icp represents the peak value of the collector current of the IGBT, Vce represents the collector-emitter voltage of the IGBT, D represents the modulation factor, and cos θ represents the power factor.

  From equation (2), it can be seen that the steady loss of the IGBT depends on the values of the collector current Ic and the collector-emitter voltage Vce of the IGBT. FIG. 2 is a diagram showing the relationship between the collector current Ic and the collector-emitter voltage Vce, and shows the relationship when the gate voltages VG1 and VG2 are applied to the normal temperature IGBT, respectively. As shown in FIG. 2, when the comparison is made with the same output collector current Ic, the collector-emitter voltage Vce decreases as the gate voltage increases. Therefore, from equation (2), the steady loss Psat decreases as the gate voltage increases. Further, as the collector current Ic increases, the steady loss difference between the gate voltages VG1 and VG2 increases.

  FIG. 3 is a diagram showing Ic-Vce characteristics when the IGBT voltage is different when the gate voltage is VG2. The dotted line in FIG. 3 shows the Ic-Vce characteristic when the temperature of the IGBT is low, and the solid line shows the Ic-Vce characteristic when the temperature of the IGBT is high. From FIG. 3, it can be seen that when the collector current Ic is equal to or less than Ic1, the collector-emitter voltage Vce decreases as the temperature rises when compared with the same collector current.

  FIG. 4 is a diagram showing Ic-Vce characteristics when the gate voltage is different when the temperature of the IGBT is high. As shown in FIG. 4, when the collector current Ic is equal to or less than Ic1, the difference in the collector-emitter voltage Vce between the gate voltages VG1 and VG2 becomes small.

  From the above, when the collector current Ic is equal to or less than the predetermined current value Ic1, the collector-emitter voltage Vce decreases and the ratio depending on the gate voltage decreases when the IGBT becomes high temperature.

  FIG. 5 shows the switching loss and steady-state loss of the IGBT with respect to the carrier frequency of the three-phase inverter. The collector current Ic is not more than the predetermined current value Ic1 shown in FIGS. FIG. 5 shows that when the carrier frequency fc is lowered, the switching loss Psw is reduced, whereas the steady loss Psat is increased. The reason why the steady loss Psat increases as the carrier frequency fc decreases will be described. In the region where the carrier frequency fc is high, that is, in the region where the IGBT switching loss Psw is large, the total power loss of the IGBT becomes large, so that the temperature of the IGBT rises. For this reason, as described with reference to FIG. 3, the collector-emitter voltage Vce when the IGBT is at a high temperature is smaller than that at room temperature (low temperature), so that the steady loss Psat is small.

  On the other hand, in the region where the carrier frequency fc is low, that is, in the region where the switching loss Psw of the IGBT is small, the total power loss of the IGBT is small, so that the temperature rise of the IGBT is relatively small. As described with reference to FIG. 3, when the temperature of the IGBT is low, the collector-emitter voltage Vce is larger than when the temperature is high, and the steady loss Psat is larger.

  Further, when the carrier frequency fc is low (when the temperature of the IGBT is low), the influence of the emitter-collector voltage Vce on the gate voltage increases, so that the higher gate voltage (VG2) as shown in FIG. However, the steady loss Psat is smaller than that in the case where the gate voltage is low (VG1).

  The control device 110 drives the control signals ND and PD by PWM so that the electric motor (three-phase AC motor) connected to the inverter operates stably, and supplies a current to the load L1. When controlling the current Io flowing through the load L1, the higher the carrier frequency, the higher the resolution, so that the motor can be stably operated. In a steady state, the carrier frequency is often kept high.

  However, when the inverter is mounted on an electric vehicle and used, the electric motor may become extremely low. When the current Io is passed while the motor is rotating at an extremely low speed or stopped, the time during which the current is passed through the IGBT of each phase becomes longer, so that the power loss of the IGBT increases and the temperature of the IGBT rises. For this reason, when the rotation speed of the motor is lowered, it is necessary to reduce the carrier frequency to reduce the switching loss of the IGBT (see FIG. 6) and to suppress the temperature rise of the IGBT.

  As described with reference to FIG. 5, the influence of the gate voltage related to the magnitude of the steady loss Psat is greater when the carrier frequency fc is higher (fc1) than when the carrier frequency fc is higher (fc1). Therefore, when the carrier frequency is low, the steady loss Psat can be reduced by increasing the gate voltage from VG1 to VG2.

  On the other hand, when the gate voltage is increased from VG1 to VG2, the power consumption (drive power) of the power supply circuit 103 for driving the IGBT also increases. FIG. 6 shows the gate voltage dependence of the driving power Pdrv with respect to the carrier frequency fc during inverter operation. As shown in FIG. 6, as the carrier frequency fc increases, the difference ΔPdrv between the driving power Pdrv when the gate voltage is set to VG1 and the driving power Pdrv when the gate voltage is set to VG2 increases.

  That is, when the gate voltage is increased from VG1 to VG2, the steady loss Psat is reduced, but the drive power Pdrv is increased. In this case, the magnitude relationship changes between the difference ΔPsat of the steady loss Psat and the difference ΔPdrv of the driving power of the IGBT depending on the combination of the current Io supplied from the inverter to the load L1 and the carrier frequency fc. Therefore, in the voltage drive element control device according to the embodiment, the gate voltage applied to the gate terminal of the IGBT is changed based on the carrier frequency fc and the current command value Ia for flowing the current Io to the load L1. .

  FIG. 7 is a flowchart showing the procedure of the gate voltage changing process performed by the control device 110. In step S10, it is determined whether or not the current command value Ia for setting the current supplied to the load L1 to Io is smaller than a predetermined determination current Ia1. This determination current Ia1 is at the same level as the predetermined collector current Ic1 (reference) shown in FIGS. If it determines with the electric current command value Ia being smaller than the determination electric current Ia1, it will progress to step S20, and if it determines with it being more than the determination electric current 1a1, it will progress to step S30.

  In step 20, it is determined whether the carrier frequency fc is lower than a predetermined frequency fc1. The predetermined frequency fc1 is a carrier frequency when the drive power increase ΔPdrv when the gate voltage increases and the steady loss reduction ΔPsat of the IGBT when the gate voltage increases are equal. If it is determined that the carrier frequency fc is lower than the predetermined frequency fc1, the process proceeds to step S30. If it is determined that the carrier frequency fc is equal to or higher than the predetermined frequency fc1, the process proceeds to step S40.

  In step S30, in order to set the gate voltage to VG2, a high (Hi) level current notification signal OC is output. On the other hand, in step S40, in order to set the gate voltage to VG1, a low level current notification signal OC is output.

The contents of processing performed by the voltage driving element control device according to the embodiment will be summarized.
(1) When the control current command value Ia to the IGBT is equal to or greater than the predetermined determination current Ia1, that is, when the output collector current of the IGBT is equal to or greater than the predetermined current Ic1, in order to reduce the steady loss, the gate terminal of the IGBT Is increased from VG1 to VG2 (see FIG. 2).
(2) When the control current command value Ia to the IGBT is smaller than the predetermined determination current Ia1, that is, when the collector current of the IGBT is smaller than the predetermined current Ic1, the effect of reducing the steady loss by increasing the gate voltage is Since the power consumption of the drive circuit is increased by increasing the gate voltage, it is preferable not to increase the gate voltage. However, depending on the carrier frequency at the time of PWM control of the IGBT, the steady loss reduction amount ΔPsat by increasing the gate voltage becomes larger than the IGBT driving power increase amount ΔPdrv, so the gate voltage is increased according to the carrier frequency. . That is, when the carrier frequency fc is lower than the predetermined frequency fc1, the steady loss reduction amount ΔPsat becomes larger than the IGBT drive power increase amount ΔPdrv, and thus the gate voltage is increased from VG1 to VG2. On the other hand, when the carrier frequency fc is equal to or higher than the predetermined frequency fc1, the IGBT drive power increase amount ΔPdrv by increasing the gate voltage is larger than the steady loss reduction amount ΔPsat, so the gate voltage is set to VG1.

  As described above, according to the control device for a voltage driving element in one embodiment, the amount of reduction in steady loss caused by increasing the gate voltage of the IGBT from the first gate voltage VG1 to the second gate voltage VG2 It is determined whether or not a condition for increasing the driving power increase amount of the IGBT due to the increase is satisfied. If the condition is satisfied, the second gate voltage VG2 is applied to the gate terminal of the IGBT and the condition is satisfied. If it is determined that it is not, the first gate voltage VG1 is applied. In particular, since it is determined whether the condition is satisfied based on the magnitude of the output collector current of the IGBT and the magnitude of the carrier frequency when the IGBT is PWM-controlled, the steady loss caused by increasing the gate voltage Therefore, it is possible to properly determine whether or not the reduction amount is larger than the drive power increase amount of the IGBT, and the loss of the entire system can be appropriately reduced.

  In the conventional apparatus that changes the gate voltage based only on the output collector current of the IGBT, the gate voltage is changed even when the output collector current is smaller than the predetermined current Ic1 and the carrier frequency fc is lower than the predetermined frequency fc1. However, according to the control device for a voltage driving element in one embodiment, when the output collector current is smaller than the predetermined current Ic1 and the carrier frequency fc is lower than the predetermined frequency fc1, the gate voltage is reduced. By increasing to VG2, the loss of the entire system can be reduced.

  The present invention is not limited to the embodiment described above. For example, whether or not the condition that the steady loss reduction amount by increasing the IGBT gate voltage is larger than the IGBT drive power increase amount is satisfied is determined by the magnitude of the output collector current of the IGBT and the magnitude of the carrier frequency fc. Judgment based on. As described above, when the carrier frequency is high, the temperature of the IGBT is high, and when the carrier frequency is low, the temperature of the IGBT is low. Therefore, the above condition can be determined based on the magnitude of the output collector current of the IGBT and the temperature of the IGBT. FIG. 8 is a flowchart showing the contents of control for changing the gate voltage of the IGBT based on the magnitude of the output collector current of the IGBT and the temperature of the IGBT. The difference from the flowchart shown in FIG. 8 is the processing in step S100. That is, in step S100, it is determined whether or not the temperature of the IGBT is lower than a predetermined temperature. When it is determined that the temperature of the IGBT is lower than the predetermined temperature, the process proceeds to step S30, and the gate voltage applied to the gate terminal of the IGBT is increased to VT2. On the other hand, if it is determined that the temperature of the IGBT is equal to or higher than the predetermined temperature, the process proceeds to step S40, and the gate voltage VG1 is applied to the gate terminal of the IGBT. The temperature of the IGBT may be detected by providing a temperature sensor (not shown).

  Further, the above condition may be determined based on factors other than the magnitude of the output collector current of the IGBT and the magnitude of the carrier frequency fc (the temperature of the IGBT). FIG. 9 is a flowchart showing the control contents for changing the gate voltage based on the steady loss reduction amount ΔPsat and the drive power increase amount ΔPd by increasing the gate voltage. As already described, when the steady loss reduction amount ΔPsat is larger than the driving power increase amount ΔPd, the gate voltage is set to VG2 larger than VG1, and when the steady loss reduction amount ΔPsat is equal to or less than the driving power increase amount ΔPd. The gate voltage is VG1.

  Although the IGBT has been described as the voltage driving element, the present invention can also be applied to other voltage driving elements such as a MOS-FET.

  The correspondence between the constituent elements of the claims and the constituent elements of the embodiment is as follows. That is, the control device 110 constitutes a determination unit and a control unit. In addition, the above description is an example to the last, and when interpreting invention, it is not limited to the correspondence of the component of said embodiment and the component of this invention at all.

The figure which shows the circuit for 1 phase of the 3-phase alternating current inverter using IGBT The figure which shows the relationship between the collector current Ic at the time of normal temperature, and the collector-emitter voltage Vce when the gate voltage applied to IGBT is different. The figure which shows Ic-Vce characteristic when the temperature of IGBT differs when gate voltage is VG2. The figure which shows the Ic-Vce characteristic when the gate voltage differs when the temperature of the IGBT is high. The figure which shows the switching loss and stationary loss of IGBT with respect to the carrier frequency of a three-phase inverter The figure which shows the gate voltage dependence of the drive electric power Pdrv with respect to the carrier frequency fc at the time of inverter operation | movement. The flowchart which shows the procedure of the gate voltage change process performed by a control apparatus. The flowchart which shows the control content which changes the gate voltage of IGBT based on the magnitude | size of the output collector current of IGBT, and the temperature of IGBT. A flowchart showing control contents for changing the gate voltage based on the steady loss reduction amount ΔPsat by increasing the gate voltage and the drive power increase amount ΔPd.

Explanation of symbols

100: Inverter circuits 1a, 1b ... IBDT
D1-D4 ... Diodes R1-R12 ... Resistor L1 ... Load L2 ... Transformer C1, C2 ... Smoothing capacitors 101, 102 ... Drive circuit 103 ... Power supply circuit 104 ... Power supply control circuit 105 ... Shunt regulators 106-109 ... Photocoupler 110 ... Control apparatus

Claims (9)

The amount of steady loss reduction by increasing the gate voltage of the voltage driving element from the first gate voltage to the second gate voltage increases the gate voltage from the first gate voltage to the second gate voltage. Determining means for determining whether or not a condition that is greater than the amount of increase in driving power of the voltage driving element is satisfied;
It is determined by the determination means that a condition is satisfied that a reduction amount of the steady loss by increasing a gate voltage from the first gate voltage to the second gate voltage is greater than an increase amount of driving power of the voltage driving element. And a control means for applying the second gate voltage to the gate terminal of the voltage driving element and applying the first gate voltage when it is determined that the condition is not satisfied. A control device for a voltage driving element. In the control apparatus of the voltage drive element of Claim 1,
The determination means determines whether the condition is satisfied based on the magnitude of the output collector current of the voltage driving element and the magnitude of the carrier frequency when the voltage driving element is PWM-controlled. A control device for a voltage driving element. In the control apparatus of the voltage drive element according to claim 2,
The determination means determines that the condition is satisfied when the output collector current of the voltage driving element is smaller than a predetermined current value and the carrier frequency is smaller than the predetermined frequency. Control device. In the control apparatus of the voltage drive element of Claim 2 or 3,
The determination means determines that the condition is not satisfied when the output collector current of the voltage driving element is smaller than a predetermined current value and the carrier frequency is equal to or higher than the predetermined frequency. Device control device. In the control apparatus of the voltage drive element of Claim 1,
The determination device determines whether or not the condition is satisfied based on the magnitude of the output collector current of the voltage driving element and the temperature of the voltage driving element. In the control apparatus of the voltage drive element of Claim 5,
The determination unit determines that the condition is satisfied when an output collector current of the voltage driving element is smaller than a predetermined current value and a temperature of the voltage driving element is lower than a predetermined temperature. Drive device control device. In the control apparatus of the voltage drive element of Claim 5 or 6,
The determination means determines that the condition is not satisfied when the output collector current of the voltage driving element is smaller than a predetermined current value and the temperature of the voltage driving element is equal to or higher than a predetermined temperature. Control device for voltage driving element. In the control apparatus of the voltage drive element in any one of Claims 1-7,
The control device for a voltage driving element, wherein the determination means determines that the condition is satisfied when an output collector current of the voltage driving element is equal to or greater than a predetermined current value. In the control apparatus of the voltage drive element in any one of Claims 1-8,
The voltage drive element control device according to claim 1, wherein the voltage drive element is an IGBT.

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