JP6033737B2 - Inverter control device - Google Patents

Description

  The present invention relates to an inverter control device used for driving and controlling a load such as an electric motor.

As a conventional inverter device, the one described in Patent Document 1 is known. In this conventional inverter device, a power circuit of an inverter in which a voltage-driven semiconductor switching element (a MOS input type power transistor in the embodiment) and a feedback diode are connected in antiparallel is controlled on and off by a control circuit. Has been. Thereby, energization control is performed on the load connected to each series connection point of the power element.
The control circuit detects a recovery current flowing in a feedback diode connected in reverse parallel to the other power element connected in series when one of the power elements connected in series shifts to turn-on, and the recovery current becomes substantially maximum. Use a slow turn-on speed until this point, and a fast turn-on speed after reaching this point.

More specifically, when the gate voltage of the power element becomes a threshold value and the recovery current peaks, the potential Vge between the gate and the emitter drops temporarily due to the Miller effect (see FIG. 6 of Patent Document 1). By utilizing this fact, the peak detection circuit of the conventional inverter device detects a drop in the potential Vge between the gate and the emitter in order to detect the peak time of the recovery current.
When the drop in the potential Vge is detected, the gate voltage is increased quickly by increasing the gate charging current from the gate voltage that has been slowly increased at the beginning. Try to reduce.
Thus, it aims at suppressing the surge voltage which arises at the time of recovery | restoration reliably, and operating an inverter with high efficiency.

Japanese Patent No. 3379562

  However, in the above conventional inverter control device, in order to detect the approximate peak of the potential Vge, it is detected that the potential Vge between the gate and the emitter has dropped. Thus, when the gate voltage is increased after the potential decrease is detected, there is a problem in that the circuit has an operation delay time, so that the effect of reducing the switching loss is small.

  That is, the loss is a value obtained by multiplying the collector-emitter potential Vce by the current Ice flowing between the collector-emitter, so that it is slow to operate after detecting that the gate voltage has dropped, and the loss is reduced. The effect of reducing will be reduced.

  The present invention has been made paying attention to the above-mentioned problem, and its purpose is to provide a feedback diode connected in reverse parallel to the other power element connected in series when one power element of the inverter circuit is turned on. An object of the present invention is to provide an inverter control device that can detect the peak of a recovery current that flows more accurately and reduce the switching loss of a power element as compared with a conventional device.

For this purpose, the inverter control device according to the present invention is:
In an inverter device comprising a chopper circuit in which a power element and a feedback diode are connected in parallel, and controlling the power element on and off,
A gate current increasing switch for increasing the gate charging current of the power element;
A gate voltage detector for detecting that the voltage of the gate of the power element has become a predetermined voltage;
While the gate voltage at the gate voltage detecting unit is detecting that said the predetermined voltage or more, can you turn off the gate current increase the switch section, the gate voltage is said predetermined after to the OFF and gate current increase the switch part controlling means for turning on the gate current increase the switch portion at the time when lowered to the voltage,
It is provided with.

Preferably, the predetermined voltage is a threshold value of the power element.
It is characterized by that.

Preferably, the gate voltage detection unit is
It has an open collector at the output, connected to the positive input a constant voltage corresponding to the threshold power of the power element, and composed of a comparator that connects the gate of the power element to the negative input.
It is characterized by that.

Also preferably, the gate current increase switch unit control means,
While applying a drive signal via a resistor to the gate of the gate current increase switch unit,
The output of the comparator is connected to the gate of the element that constitutes the gate current increase switch unit.
It is characterized by that.

In the inverter control device of the present invention, the reverse recovery current flowing through the feedback diode is reduced while minimizing the switching loss when the power element is turned on, and the noise caused by this current is reduced in cost. Can be reduced.

  In addition, since the predetermined voltage is used as the threshold value of the power element, the timing at which the reverse recovery current flows can be accurately and reliably predicted.

  The gate voltage detector has an open collector at the output, a constant voltage equivalent to the threshold power of the power element is connected to the positive input, and a comparator that connects the gate of the power element to the negative input. With this configuration, it is possible to detect the timing when the gate voltage becomes a threshold value.

  Further, the gate current increase switch unit control means applies a drive signal to the gate of the gate current increase switch unit through a resistor, and outputs the output of the comparator to the element constituting the gate current increase switch unit. Since it is configured to be connected to the gate, the gate voltage of the gate current increasing switch unit can be controlled with a simple configuration.

It is a circuit diagram with the inverter control apparatus and inverter which concern on Example 1 of this invention. It is a figure which shows each time change of the gate voltage Ve of IGBT1a, collector voltage Vce, and collector current Ic when switching is slow. It is a figure which shows each time change of gate voltage Ve of IGBT1a, collector voltage Vce, and collector current Ic when switching is early. It is a figure which shows the time chart explaining operation | movement of the inverter control apparatus of Example 1. FIG. It is the figure which compared and showed the waveform of the gate voltage Vge and the collector current Ic when the second MOSFET is continuously turned on and when it is turned off halfway. It is the figure which compared and showed the waveform of the gate voltage Vge and the collector current Ic of the case where the 2nd MOSFET is turned off halfway and it is made to turn off as it is, and the case where it turns off halfway and returns to on.

  Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings.

First, the overall configuration of the inverter control device according to the first embodiment will be described.
In this embodiment, the inverter control device of the first embodiment is used to control an inverter that drives and controls an electric motor for driving a vehicle of an electric vehicle, for example, and is connected to an inverter 1 as shown in FIG. , A gate drive circuit 2, a gate current increase switch unit 3, a comparator 4, and a resistor R4.

As is well known, the inverter 1 is composed of a plurality of sets (for example, three sets) based on a bidirectional chopper combining a step-up chopper circuit and a step-down chopper circuit each composed of a parallel circuit of a power element and a feedback diode. The electric motor (not shown) is driven and controlled by changing the DC power to AC power.
Here, as shown in FIG. 1, only a pair of chopper circuits, an insulated gate bipolar transistor (IGBT) 1a, and a feedback diode 1b connected in reverse direction at both ends are depicted. Since the other sets have the same configuration as the above, their illustration and description are omitted.
The IGBT 1a corresponds to the power element of the present invention.

  The gate drive circuit 2 includes a pulse command unit 21 constituted by an IC so as to generate a pulse command composed of both a high signal and a low signal for turning on and off the IGBT 1a, and two signals that are turned on / off in response to the pulse command signal. It has MOS field effect transistors, that is, an on-MOSFET 5 and an off-MOSFET 6 and a gate-off MOSFET 9 for turning off the IGBT 1a. The on-MOSFET 5 and the gate-off MOSFET 9 are P-channel type, and the off-MOSFET 6 is N-channel type.

  Examples of the pulse command section 21 include “Electric Vehicle Engineering” (edited by Yukihiro Hamada and Seiji Ogasawara, Hiroto Funato, Teruyoshi Mihara, Takashi Deguchi, co-authored by Yasuyuki Hatsuda, published by Morikita Publishing Company on December 30, 2010) The command signal is generated as described in FIG. 6.5 on page 133.

  The on MOSFET 5 has a gate connected to the pulse command unit 21, a drain connected to the power source, and a source connected to the drain of the off MOSFET 6 and the resistor R4. When a low signal (negative voltage) is applied to the gate, the turn-on MOSFET 5 is turned on and conduction between the drain and source is established, but when a high signal (positive voltage) is applied to the gate, the turn-on MOSFET 5 is turned off. And shut off drain to source.

On the other hand, the off MOSFET 6 has a gate connected to the pulse command unit 21, a drain connected to the source of the on MOSFET 5 and the resistor R4, and a grounded source. When a high signal is applied to the gate, the off MOSFET 6 is turned on and conduction between the drain and the source is conducted. However, when a low signal is applied to the gate, the off MOSFET 6 is turned off and the drain to the source is shut off. To do.
Note that feedback diodes 10 and 11 are connected in antiparallel between the drain and source of the on MOSFET 5 and the off MOSFET 6, respectively.

The gate-off MOSFET 9 includes a gate connected to the source of the on-MOSFET 5 and the drain of the off-MOSFET 6, the first MOSFET 7 of the gate current increasing switch unit 3 via the resistor R 2, and the second MOSFET of the gate current increasing switch unit 3. The source of 8 has a drain connected to the gate of IGBT 1a via resistor R6 and resistor R5, and via resistor R6, and a grounded source.
When a low signal is applied to the gate of the gate-off MOSFET 9, the MOSFET 9 is turned on and the drain-source is conducted and grounded, but when a high signal is applied to the gate, the gate-off MOSFET 9 is turned off. Shut off the drain to source.
A parasitic diode 14 is connected in antiparallel between the drain and source of the gate-off MOSFET 9.

The gate current increase switch unit 3 is for amplifying the gate current of the IGBT 1a, and includes a first gate current increase switch unit 3a and a second gate current increase switch unit 3b.
The first gate current increase switch unit 3a has an N channel having a gate connected to the source of the MOSFET 5 for turning on via a resistor R3, a drain connected to a power source, and a source connected to the IGBT 1a via a resistor R6. A first MOSFET 7 of a type, and a parasitic diode 12 connected in reverse parallel between the drain and source.

  The second gate current increase switch unit 3b has an N channel having a gate connected to the source of the MOSFET 5 for turning on via the resistor R4, a drain connected to the power supply, and a source connected to the gate of the IGBT 1a via the resistor R5. A second MOSFET 8 of the type, and a parasitic diode 13 connected in reverse parallel between the drain and source.

  In any of the first MOSFET 7 and the second MOSFET 8, when a high signal is applied to the gate, they are turned on to conduct between the drain and the source, but when a low signal is applied to the gate, They turn off and block the drain-source.

The output of the comparator 4 has an open collector, is connected to the source of the on-MOSFET 5 and the drain of the off-MOSFET 6 via the resistor R4, and is connected to the gate of the second MOSFET 8. The positive input is connected to the constant voltage unit 15, and the negative input is connected to the gate of the IGBT 1a via the resistor R1 and grounded via the capacitor C1.
Here, the constant voltage unit 15 outputs a predetermined voltage to the plus input of the comparator 4, that is, a voltage at which the input voltage to the minus input corresponds to the threshold voltage of the gate of the IGBT 1a.

The operation of the inverter control apparatus of the first embodiment configured as described above will be described below, but before that, the concept of switching loss and countermeasures will be described.
The inverter is composed of a bi-directional chopper circuit as upper and lower arms. When the power element of one arm is turned off, the load current is commutated to the feedback diode of the other arm.
Next, when the power element is turned on again, the power source (battery) is instantaneously transmitted through the circuit including the parasitic inductance, the feedback diode, and the power element until the feedback diode discharges carriers and reversely recovers. A short circuit occurs.

In this case, since the reverse recovery current immediately flows through the feedback diode, the feedback diode recovers the reverse characteristics. However, if the reverse recovery current decays rapidly, a surge voltage due to wiring inductance rises and is applied to the feedback diode and the power element of the other arm.
That is, when the gate voltage Vge exceeds the threshold of the IGBT 1a, after overshooting it, the gate voltage Vge gradually decreases and the collector current also gradually decreases. The gate voltage Vge decreases when a reverse recovery current starts to flow through the diode 1b.

FIG. 2 shows temporal changes in the gate voltage Ve, collector voltage Vce, and collector current Ic of the IGBT 1a when switching is slow, and FIG. 3 shows when switching is fast.
If the peak voltage of the gate voltage Vge (the range enclosed by circles in the figure) is high, that is, if the rise time is short, the reverse recovery current increases. To reduce this, the gate voltage Vge must be suppressed. .
Therefore, although there is a method of gradually increasing the gate voltage of the power element to reduce the peak value of the reverse current by suppressing the overshoot amount, in this case, the region where the on-resistance of the power element is large is taken over time. Therefore, the switching loss increases.

Therefore, in order to reduce the switching loss of IGNBT1a, there is a method of increasing the gate current in the region where the on-voltage of the power element is large and passing it quickly, but this best timing should be immediately after the reverse recovery current. desirable.
For this reason, I want to detect immediately before the reverse recovery current, but the gate voltage at the timing immediately before this greatly exceeded the threshold of IGBT1a (when the collector current starts to flow to the emitter, that is, the gate voltage when IGBT1a is turned on) Value.
Therefore, in order to detect the immediately preceding timing, a voltage value for determination in comparison with the detection voltage is set large. However, the peak of the voltage exceeding the threshold value may be lowered depending on the current value of the inductor. In such a case, the detected gate voltage may not reach the voltage value to be compared. In such a case, the operation for controlling the gate charging current cannot be performed, but the switching loss is small because the collector current is low.

  In addition, since the operation of controlling the gate charging current after detecting the decrease in the potential Vge between the gate and the emitter of the IGBT 1a is started as in the above conventional device, there is a response delay of the IGBT 1a. However, it is too late to reduce the loss sufficiently. This will be described later in detail in comparison with the present embodiment.

In FIG. 4, the time chart of the operation | movement of the inverter control apparatus of Example 1 is shown.
As shown in FIGS. 1 and 4, in order to turn on the IGBT 1 a from the off state, a low signal is applied from the pulse command unit 21 to the on MOSFET 5 and the off MOSFET 6.
Then, the on MOSFET 5 is turned on and the off MOSFET 6 is turned off.
As a result, the gate-off MOSFET 9 is turned off because the voltage between the source of the on-MOSFET 5 and the drain of the off-MOSFET 6 is high and applied to the gate of the gate-off MOSFET 9.

When the on MOSFET 5 is turned on, a current from the power source flows from the drain to the source. This current is applied to the gate of the first MOSFET 7 through the resistor R3 to turn on the first MOSFET 7, and is also applied to the gate of the second MOSFET 8 through the resistor R4 to turn on the second MOSFET 8.
Therefore, as a result of the first MOSFET 7 and the second MOSFET 8 being simultaneously turned on at time t1 in FIG. 2, the drive current flows into the gate of the IGBT 1a through these MOSFETs 7 and 8 and the resistors R6 and R5, respectively. Vge and collector current increase.

When the gate voltage Vge increases and the gate voltage Vge exceeds the IGBT 1a threshold at time t2, the voltage generated by applying the gate drive current to the negative input of the comparator 5 via the resistor R1 and the positive input The constant voltage (predetermined voltage) of the connected constant voltage unit is compared, and the negative input voltage becomes larger than the positive input predetermined voltage. As a result, the comparator 4 switches from the previous high output to the low output.
By this switching, the gate current of the second MOSFET 8 is grounded via the comparator 4, the second MOSFET 8 is turned off, and the current application to the gate of the IGVBT 1a is stopped.
However, in the first MOSFET 7, the current supplied from the power supply via the on MOSFET 5 is suppressed from flowing into the comparator 4 due to the presence of the large resistor R4, and the rest flows into the gate, keeping the first MOSFET 7 on. .

Therefore, since the gate current applied to the gate of the IGBT 1a from the source of the second MOSFET 8 is eliminated, the current applied to the gate of the IGBT 1a is only through the first MOSFET 7, and the magnitude thereof is reduced.
As a result, the rise of the gate voltage Vge is moderated, the reverse recovery current of the diode 1b is suppressed from increasing, and the noise is also suppressed to a low level.

When the reverse recovery current starts flowing after time t2, the gate voltage Vge starts to decrease.
When the gate voltage Vge drops to the threshold voltage, the comparator 4 inverts the output and outputs a high signal. Then, the second MOSFET 8 is turned on again, and the drain and the source become conductive, and the gate current applied to the gate of the IGBT 1a is increased correspondingly. As a result, the switching loss is reduced by quickly passing through a region where the switching loss increases.
In the case of the conventional device, since the gate current is increased by detecting the drop after the peak of the gate voltage, there is a delay in the operation of the circuit, and the amount of reduction in the switching loss is reduced. .

As the second MOSFET 8 is turned on, the drop in the gate voltage Vge and the collector current Ic from time t3 stops halfway and then rises.
When the gate voltage Vge becomes larger than the threshold voltage at time t4, the second MOSFET 8 is turned off, but the first MOSFET 7 is turned on and current flows into the gate of the IGBT 1a, so that the gate voltage Vge and the collector current Ic rise gently. To go.

On the other hand, in order to turn off the IGBT 1a, a high signal is applied from the pulse command unit 21 to the on MOSFET 5 and the off MOSFET 6. Then, the on MOSFET 5 is turned off and the off MOSFET 6 is turned off.
As a result, no current is applied from the ON MOSFET 5 to the gates of the first MOSFET 7 and the second MOSFET 8. Further, the off MOSFET 6 is turned on, and the gates of the first MOSFET 7 and the second MOSFET 8 are grounded via the off MOSFET 6. Therefore, the first MOSFET 7 and the second MOSFET 8 are turned off.
On the other hand, as a result of grounding between the on MOSFET 7 and the off MOSFET 8, the gate of the gate off MOSFET 9 connected thereto is also grounded, and the gate off MOSFET 9 is turned on.
Therefore, the gate of the IGBT 1a is grounded via the resistors R6, R2 and the gate-off MOSFET 9, so that the IGBT 1a is turned off.

Here, the effect of the on / off control of the second MOSFET 8 in the inverter control apparatus of the first embodiment will be described.
FIG. 5 shows a case where the second MOSFET 8 is continuously turned on when it is turned on at time t1, and continues to be turned on without being turned off even if the gate voltage Vge becomes lower than the threshold voltage at time t2 (indicated by a one-dot chain line). FIG. 6 is a time chart of the case of 1 (indicated by a solid line; the transition to time t2 is turned off), and a diagram comparing the waveforms of the gate voltage Vge and the collector current Ic at that time.
As can be seen from this figure, in the former case, there is a concern that the peak values of the gate voltage Vge and the collect current Ic are increased, the reverse recovery current is increased, and the noise is increased. However, since the switching loss region passes slightly faster, the switching loss becomes slightly better.
Therefore, in order to reduce the reverse recovery current and reduce the noise, it is desirable to turn off the second MOSFET 8 at time t2 when the gate voltage Vge becomes the threshold voltage, as in the first embodiment.

FIG. 6 shows the case where the second MOSFET 8 is turned on at time t1 and turned off at time t2, and then turned off even when the gate voltage Vge becomes lower than the threshold voltage at time t3 (indicated by a one-dot chain line). ), And in the case of Example 1 (shown by a solid line. The signal is turned off at time t2 and turned on again at time t3), and the waveforms of the gate voltage Vge and the collector current Ic at that time are compared. FIG.
As can be seen from this figure, after the gate voltage Vge exceeds the threshold voltage, in any case, the gate voltage Vge rises gently, and the peak values of both the gate voltage Vge and the collector current Ic are pushed small. Noise can be reduced.
However, in the region where the switching loss occurs after time t2, in the former case, the gate voltage Vge only rises gently, so the collector voltage Vce also rises gradually, resulting in switching loss (= collector voltage Vce × collector current Ic). ) Is larger than the latter case.
Therefore, after time t2, the switching loss can be reduced by turning on the second MOSFET 8 and passing the switching loss region quickly.

As described above, the inverter control device of Embodiment 1 has the following effects.
In other words, the comparator 4 detects that the gate voltage Vge of the IGBT 1a has become a predetermined voltage, and the second MOSFET 8 is kept off while detecting that the gate voltage Vge is equal to or higher than the predetermined voltage. Therefore, it is possible to increase the gate charging current faster than in the case of the conventional device, further reducing the switching loss of the IGBT 1a, and reducing the through current of the feedback diode 1b to reduce noise. Will be able to.

  In addition, since the comparator 4 detects that the gate voltage Vge has reached the threshold value, even when the peak of the gate voltage Vge has become lower due to the current value of the inductor, the timing at which the gate voltage is desired to be known reliably and accurately can be quickly determined. Can be detected.

Further, since the comparator 4 is turned on when the gate voltage Vge becomes equal to or lower than the threshold value after the second MOSFET 8 is turned off, the switching loss can be reduced to achieve a low-cost configuration.
Further, since the second MOSFET 8 is controlled by the comparator 4 and the resistor R4, an inexpensive configuration is sufficient.

  As described above, the present invention has been described based on the above-described embodiments. However, the present invention is not limited to the above-described embodiments, and even when there is a design change or the like without departing from the gist of the present invention, it is included in the present invention.

For example, the power element is not limited to IGBT, and may be, for example, a MOSFET or another element.
Further, the gate voltage detection unit and the gate current increase switch control means may be configured differently from the embodiment.
Further, the comparator 4 may be turned off by either the first MOSFET 7 or the second MOSFET 8.
Moreover, the inverter control apparatus of this invention is not restricted to the application to the electric motor of an electric vehicle, It can apply also to the apparatus of another field | area.

1 Inverter
1a IGBT (power element)
1b Feedback diode
2 Gate drive circuit
21 Pulse command section
3 Gate current increase switch
3a 1st gate current increase switch part
3b Second gate current increase switch part
4 Comparator (Gate voltage detection part, gate current increase switch part control means)
5 MOSFET for ON
6 Off MOSFET
7 1st MOSFET (Gate current increase switch part)
8 Second MOSFET (Gate current increase switch)
9 Gate-off MOSFET
10, 11 Feedback diode
12, 13, 14 Parasitic diode
15 Constant voltage section
C1 capacitor
R1 to R10 resistance (R4: Gate current increase switch control means)

Claims (4)

In an inverter device comprising a chopper circuit in which a power element and a feedback diode are connected in parallel, and controlling the power element on and off,
A gate current increase switch for increasing the gate charge current of the power element;
A gate voltage detector for detecting that the voltage of the gate of the power element has become a predetermined voltage;
While the gate voltage at the gate voltage detecting unit is detecting that said the predetermined voltage or more, can you turn off the gate current increase the switch section, the gate voltage is said predetermined after to the OFF and gate current increase the switch part controlling means for turning on the gate current increase the switch portion at the time when lowered to the voltage,
An inverter control device comprising: The inverter control device according to claim 1 ,
The predetermined voltage is a threshold value of the power element;
An inverter control device characterized by that. In the inverter control device according to claim 1 or 2,
The gate voltage detector is
The output has an open collector, and a positive input is connected to a constant voltage corresponding to the threshold power of the power element, and the comparator is configured to connect the gate of the power element to the negative input.
An inverter control device characterized by that. In the inverter control device according to claim 3,
The gate current increase switch unit control means includes:
While applying a drive signal through a resistor to the gate of the gate current increase switch unit,
The output of the comparator is connected to the gate of an element that constitutes the gate current increase switch unit.
An inverter control device characterized by that.

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