JP5627316B2 - Power conversion device and control circuit for semiconductor switching element - Google Patents

Description

The present invention relates to a power conversion device and a control circuit for a semiconductor switching element .

In a power converter using a semiconductor switching element, it is necessary to increase the switching speed in order to reduce the loss of the switching element. On the other hand, when the switching speed is increased, problems such as destruction of the element due to a surge voltage when the switching element is turned on or turned off and generation of electromagnetic noise due to a surge current often occur.

  As a solution to such a problem, a method of switching the value of the gate resistance inserted between the gate drive voltage source and the gate terminal at the time of switching or adjusting the gate drive current has been proposed. As an example of such an invention, there is a drive circuit that adjusts a gate drive parameter in accordance with a collector voltage in the “gate drive circuit of a voltage-driven element”. The configuration will be described below with reference to FIG.

In FIG. 6, the gate terminal G of the IGBT Q1 includes a first gate charge charging circuit including a resistor (R3) and an NPN transistor (Q3), and a second gate charge generated by the resistor (R1) and the NPN transistor (Q2). Connected to the charging circuit.

  When the gate signal (VG) rises, the NPN transistor (Q3) is turned on, and the gate current (Ig0) flows to the gate (G) terminal of the IGBT (Q1) via the resistor (R3). At the same time, the NPN transistor (Q2) is also turned on, and the gate current (Ig1) flows to the gate (G) terminal of the IGBT (Q1) via the resistor (R1).

  As a result, when the gate-emitter voltage Vge of the IGBT (Q1) rises and reaches the turn-on voltage threshold, the IGBT (Q1) starts the turn-on operation, and the collector current (Ic) flows and the IGBT (Q1) The collector-emitter voltage (Vce) begins to drop.

  At this time, as the collector-emitter voltage (Vce), a negative time variation (dVce / dt) is generated, and the capacitor (C1) is negatively directed toward the collector terminal (C) of the IGBT (Q1). The differential current (Idiff) proportional to the time change amount (dVce / dt) of the current flows out. Since the differential current (Idiff) serves to reduce the base current (Ib) of the NPN transistor (Q2), the gate current (Ig1) also starts to decrease.

  As a result, when the second gate charge charging circuit is set to have a dominant influence on the charge rate of the gate charge of the IGBT (Q1), the collector-emitter voltage (Vce) of the IGBT (Q1). The time change amount (dVce / dt) of the IGBT (Q1) is suppressed to a small value, and the collector current (Ic) flowing through the collector (C) of the IGBT (Q1) is also suppressed to a small flat value without increasing rapidly.

  Thus, feedback control is performed so that the collector voltage change rate of the IGBT Q1 becomes a constant value.

JP 2008-86068 A

However, in the conventional invention, an adverse effect occurs because the current proportional to the time variation dVce / dt of the collector-emitter voltage Vce of the IGBT Q1 is directly subtracted from the base current of the transistor Q2 of the gate drive circuit. The Vce of the IGBT Q1 depends on not only the switching operation of the Q1 itself but also the operation of the flywheel diode connected in parallel, the DC power supply voltage, and the like, and includes many noise components. Further, it is known that the noise component is included in a higher frequency range than the waveform of Vce to be observed. However, the time change amount of Vce is a differential operation, and is the same as passing through a kind of high-pass filter in which the gain becomes higher in the high frequency region when considered in the frequency region. For this reason, dVce / dt contains a large amount of noise components, and if current Idiff proportional to dVce / dt is used for control as it is in the invention of Patent Document 1, there is a risk of malfunction due to noise. It will increase. For this reason, there is a problem that the risk of malfunction due to noise is great.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a stable and highly reliable gate drive circuit and a power converter using the same.

In order to solve the above-described problem, a power conversion device according to the present invention is a power conversion device including a plurality of semiconductor switching elements, and a control circuit that controls a control electrode included in each of the semiconductor switching elements constituting the power conversion device. A voltage detecting means for generating a first voltage signal proportional to a voltage applied between the main electrodes of the semiconductor switching element, and a low-frequency signal of the first voltage signal is extracted to obtain a second voltage signal. It has a resulting low-pass filter and a subtraction means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal, the semiconductor in response to the third voltage signal The voltage applied to the control electrode of the switching element is adjusted.
The semiconductor switching element control circuit according to the present invention includes a semiconductor switching element.
In a control circuit for a semiconductor switching element for controlling a control electrode having the semiconductor switch, the semiconductor switch
Voltage detection that generates a first voltage signal proportional to the voltage applied across the main electrodes of the etching element
Means and a low pass for extracting a low frequency signal of the first voltage signal and generating a second voltage signal
The difference between the filter and the first voltage signal and the second voltage signal is the third voltage signal.
Subtracting means to obtain, the semiconductor switching element of the semiconductor switching element according to the third voltage signal
The voltage applied to the control electrode is adjusted.

According to the present invention, a power conversion has a gate driving circuit of the stable and reliable devices and semi
A control circuit for the conductor switching element can be provided.

Configuration diagram for explaining the first embodiment Waveform diagram for explaining the operation of the first embodiment Circuit diagram for explaining the first embodiment Configuration diagram for explaining a second embodiment Configuration diagram for explaining a third embodiment Structure diagram explaining the prior art

Hereinafter, embodiments of a power conversion device according to the present invention will be described with reference to the drawings.

(First embodiment)
First, Embodiment 1 will be described with reference to FIG. In FIG. 1, an IGBT 10 is driven, and a flywheel diode (FWD) 11 entering in parallel is energized when a current flows in the reverse direction. The collector-emitter voltage (Vce) of the IGBT 10 is divided by the voltage divider 21 and then supplied to the input terminal of the low-pass filter (LPF) 22 and one input terminal of the subtractor 23. Vce filtered by the LPF 22 is supplied to the other input terminal of the subtractor 23. The output of the subtracter 23 is connected to one input terminal of the subtractor 24, and the other input terminal of the subtracter 24 is connected to the output of the on-gate voltage source 26. The gate signal 25 is connected to the input terminals of the on-gate voltage source 26 and the off-gate voltage source 27, and the output of the off-gate voltage source 27 and the output of the subtractor 24 are combined and connected via the gate resistor 12 to the IGBT. 10 gate terminals.

  The operation of the first embodiment of the present invention shown in FIG. 1 having such a configuration will be described with reference to the waveform diagram of FIG. In FIG. 2, an on-gate voltage source 26 and an off-gate voltage source 27 generate positive and negative voltage pulses in response to the gate signal 25, respectively. On the other hand, Vce decreases at a switching speed determined by the gate resistance 12 when the gate voltage of the IGBT 10 exceeds a certain threshold value, and increases when the gate voltage falls below the threshold value. Since the output of the LPF 22 is obtained by extracting the low frequency portion of the Vce waveform, when viewed in the time domain waveform, it becomes a dull waveform with a reduced rate of time change. The subtracter 23 obtains a signal obtained by subtracting the low frequency signal extracted by the LPF 22 from the divided voltage signal of Vce. That is, the high frequency component in the divided Vce signal is output from the subtracter 23. When viewed in the time domain, the output waveform of the subtracter 23 has a portion with a large time change rate corresponding to the high frequency component of the original Vce waveform. Further, by subtracting the output of the subtractor 23 from the on-gate signal by the subtracter 24, the level of the rising portion of the on-gate signal is reduced when the time conversion rate of Vce is large, and the on-gate signal is reduced when the time change rate of Vce is small The level of the rising part of becomes larger.

  With such an operation, the first embodiment of the present invention shown in FIG. 1 uses an LPF and a subtractor circuit that filter noise components contained in a high frequency region without using a differentiating circuit that is likely to be affected by noise. And has a function of adjusting the time conversion rate of Vce to a desired value.

  FIG. 3 shows an example in which the first embodiment of the present invention shown in FIG. 1 is configured by an actual circuit. The LPF, the subtractor, etc. are all easily configured by an operational amplifier (OP amplifier). Each of the on-gate voltage source 26 and the off-gate voltage source 27 is composed of a transistor and a fixed voltage source, but these can be replaced by elements or integrated circuits having similar functions such as MOSFETs and OP amplifiers. Needless to say.

(Second Embodiment)
In the first embodiment of the present invention, the voltage applied to the gate electrode of the switching element is controlled via the gate resistance. On the other hand, the gate electrode can be driven by the control current source without going through the gate resistance. In a voltage controlled element such as an IGBT, switching is controlled by a voltage applied to the gate, but the switching speed itself is controlled not by the voltage but by the gate current at the time of switching transient. Therefore, in the second embodiment of the present invention shown in FIG. 4, the switching speed is controlled by a current source.

  In FIG. 4, the gate terminal of the IGBT 10 is connected to the outputs of the on-gate current source 30 and the off-gate current source 31. Since the input of the on-gate current source 30 is connected to the output of the subtractor 24, when the IGBT 10 is turned on, the time change rate of Vce becomes a desired value, as in the first embodiment of the present invention. Thus, feedback control is performed. On the other hand, the gate signal 25 is connected to the input of the off-gate current source 31, and when an off-gate command is issued, a constant current is drawn from the gate electrode by the off-gate current source 31, and the IGBT 10 is turned off. The voltage at the gate terminal is connected to the on-gate voltage detector 32 and the off-gate voltage detector 33 to monitor the gate voltage at turn-on and turn-off, respectively. When the gate voltage reaches a voltage defined as a steady on state, the on gate voltage detector 32 detects this and stops the operation of the on gate current source 30. Similarly, at the time of turn-off, the off-gate voltage detector 33 detects that the gate voltage has reached a voltage defined as a steady off state, and stops the operation of the off-gate current source 31.

(Third embodiment)
In the embodiments of the present invention thus far, the time change rate of Vce is controlled by continuously changing the gate drive voltage and current. However, there are some applications where it is sufficient to change the Vce time change rate stepwise. A third embodiment of the present invention shown in FIG. 5 shows a gate drive circuit suitable for such an application. In FIG. 5, the output of the subtractor 23 is input to the comparator 40, and the output of the comparator 40 takes the logical value true or false depending on whether or not the time conversion rate of Vce is below a certain value. Here, it is assumed that two gate drive circuits controlled by the gate signal 25, a high-speed gate drive circuit 41 and a low-speed gate drive circuit 43 are provided. These gate drive circuits are provided with an enable input for controlling whether to drive the output. The enable input of the high-speed gate drive circuit 41 is the output of the comparator 40, and the enable input of the low-speed gate drive circuit 43 is the NOT logic. 42 to the output of the comparator 40. By adopting such a configuration, when the time change rate of Vce is large, the output of the comparator 40 is false, and when the low speed gate drive circuit 43 is operated and the time change rate of Vce is small, the output of the comparator output 40 is true. Thus, the high-speed gate drive circuit 41 operates. This makes it possible to adjust the time change rate of Vce to a desired value range.

  Here, the switching is performed in two stages of the high-speed gate driving circuit 41 and the low-speed gate driving circuit 43. However, if the number of driving circuits is increased and a large number of comparators are prepared, switching of switching speed is adjusted in any number of stages. It becomes possible. Furthermore, since the gate driving circuit is a circuit for supplying a gate current to the IGBT 10, it is also possible to operate two gate driving circuits at the same time. In this case, a plurality of gate driving circuits may be operated simultaneously to increase the switching speed, and only one gate driving circuit may be operated to decrease the switching speed.

10 ... IGBT
11 ... FWD
12 ... Gate resistance 21 ... Voltage detector 22 ... LPF
23 ... Subtractor 24 ... Subtractor 25 ... Gate signal 26 ... On-gate voltage source 27 ... Off-gate voltage source 30 ... On-gate current source 31 ... Off-gate current source 32 ... On-gate voltage detector 33 ... Off-gate voltage detector 40 ... Comparator 41 ... High speed Gate drive circuit 42 ... NOT logic 43 ... Low speed gate drive circuit

Claims (8)

In a power conversion device constituted by a plurality of semiconductor switching elements,
A control circuit for controlling the control electrodes of the each of the semiconductor switching elements constituting the power converter,
Voltage detecting means for generating a first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal;
Subtracting means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal ;
A power conversion device that adjusts a voltage applied to the control electrode of the semiconductor switching element in accordance with the third voltage signal . In a power conversion device constituted by a plurality of semiconductor switching elements,
A control circuit for controlling the control electrodes of the each of the semiconductor switching elements constituting the power converter,
Voltage detecting means for generating a first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal;
Subtracting means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal;
A power converter that adjusts a current flowing into a control electrode of the semiconductor switching element according to a third voltage signal . In a power conversion device constituted by a plurality of semiconductor switching elements,
A control circuit for controlling the control electrodes of the each of the semiconductor switching elements constituting the power converter,
Voltage detecting means for generating a first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal;
Subtracting means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal;
Two gate drive circuits, a first gate drive circuit and a second gate drive circuit connected to the control electrode,
One of the first gate driving circuit and the second gate driving circuit is operated in accordance with the third voltage signal . The control circuit switches between a mode in which only the first gate driving circuit is operated and a mode in which the first and second gate driving circuits are simultaneously operated in accordance with the third voltage signal. The power conversion device according to claim 3 . In a power conversion device constituted by a plurality of semiconductor switching elements,
A control circuit for controlling the control electrodes of the each of the semiconductor switching elements constituting the power converter,
Voltage detecting means for generating a first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal;
Subtracting means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal;
A power conversion device comprising a plurality of gate drive circuits connected to the control electrode and selectively operating one of the gate drive circuits according to the third voltage signal . In a power conversion device constituted by a plurality of semiconductor switching elements,
A control circuit for controlling the control electrodes of the each of the semiconductor switching elements constituting the power converter,
Voltage detecting means for generating a first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal;
Subtracting means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal;
A gate voltage source for applying a voltage to the control electrode, and a gate resistor connected between the gate voltage source and the control electrode,
A power conversion device that adjusts a voltage of the gate voltage source in accordance with the third voltage signal . Control circuit of a semiconductor switching element for controlling a control electrode of the semiconductor switching element
On the road
A first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
Voltage detection means to generate,
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal
And
A subtractor that obtains a difference between the first voltage signal and the second voltage signal as a third voltage signal.
Having a step,
A voltage applied to the control electrode of the semiconductor switching element in response to the third voltage signal.
A control circuit for a semiconductor switching element, wherein the pressure is adjusted. Control circuit of a semiconductor switching element for controlling a control electrode of the semiconductor switching element
On the road
A first voltage signal proportional to the voltage applied between the main electrodes of the semiconductor switching element;
Voltage detection means to generate,
A low-pass filter that extracts a low-frequency signal of the first voltage signal and generates a second voltage signal
And
Subtracting means for obtaining a difference between the first voltage signal and the second voltage signal as a third voltage signal;
Have
Adjust the current flowing into the control electrode of the semiconductor switching element according to the third voltage signal
A control circuit for a semiconductor switching element.