WO2010143274A1 - Dc voltage converter - Google Patents

Abstract

Auxiliary switching elements (Q3, Q4) that generate auxiliary currents (Irp, Irp#) that do not directly contribute to DC voltage conversion are provided to reduce the switching loss by primary switching elements (Q1, Q2) used for DC voltage conversion. An auxiliary switch turnoff instruction is normally generated after auxiliary current disappears. A driver (156) determines whether a turnoff instruction produced by control signals (S3, S4) is a normal turnoff instruction or an abnormal turnoff instruction and, if the turnoff instruction is an abnormal turnoff instruction, lowers the gate driving speed of the auxiliary switching elements compared with the case of a normal turnoff instruction.

Description

DC voltage converter

The present invention relates to a DC voltage converter, and more particularly, to an auxiliary switching that generates an auxiliary current that does not directly contribute to DC voltage conversion in order to reduce switching loss of a main switching element for DC voltage conversion. The present invention relates to switching control of a DC voltage converter including an element.

By repeating the on-off operation of the power semiconductor switching element (hereinafter simply referred to as "switching element"), the low voltage is achieved by combining the operation of storing the electromagnetic energy in the inductor and the operation of releasing the electromagnetic energy stored in the inductor. A configuration of a so-called step-up chopper type DC voltage converter (DC-DC converter) for boosting the output voltage of a power supply is known.

In this type of DC-DC converter, an inductor is required as a circuit element, but there is a trade-off relationship between the increase in switching frequency to miniaturize the inductor and the increase in switching loss due to the increase in frequency. . Therefore, application of so-called soft switching such as zero current switching or zero voltage switching has been advanced so that switching loss can be suppressed even when the power semiconductor switching element is turned on and off at high frequency.

For example, Japanese Unexamined Patent Application Publication No. 2005-261059 (Patent Document 1) describes a circuit configuration in which an auxiliary circuit for realizing soft switching is provided in the configuration of a current bi-directional converter having a boosting function and a control method thereof. ing. The auxiliary circuit is configured to have a circuit element group for generating an auxiliary current that does not directly contribute to the direct current voltage conversion to realize soft switching.

Also, as general techniques for reducing switching loss, Japanese Patent Application Laid-Open Nos. 10-023743 (Patent Document 2), Japanese Patent Application Laid-Open Nos. 2005-198406 (Patent Document 3), and Japanese Patent Application Laid-Open Nos. 10-075124 (Patent Document 2) Patent Document 4) describes a configuration in which the drive speed of the control electrode (gate), that is, the switching speed is controlled by switching of the gate resistance.

Japanese Patent Laid-Open No. 2005-261059 Japanese Patent Application Laid-Open No. 10-023743 JP 2005-198406 A Japanese Patent Application Laid-Open No. 10-075164

In the current bidirectional converter described in Patent Document 1, in order to reduce the voltage between terminals (collector-emitter voltage) at the time of switching of the main transistor (Q1, Q2) that directly performs direct-current voltage conversion, An auxiliary current path is formed by turning on the auxiliary transistors (Q3, Q4) in the circuit.

However, in the configuration of Patent Document 1, the auxiliary current passes through the inductor (Lr) in the auxiliary circuit. Therefore, when the auxiliary transistor is turned off while the auxiliary current is flowing, the energy stored in the inductor may generate an overvoltage between the collector and the emitter of the turned off auxiliary transistor. That is, due to the energy stored in the inductor, a surge-like overvoltage exceeding the withstand voltage of the auxiliary transistor may be generated between the collector and the emitter, and the transistor may be damaged.

Usually, the occurrence of the above overvoltage can be avoided by appropriately controlling the off timing of the auxiliary transistor (Q3, Q4). However, during an emergency stop where it is necessary to forcibly turn off each switching element (transistor) due to the occurrence of a short circuit current or the like, the turn-off instruction of the auxiliary transistor may be issued despite the auxiliary current remaining. . The same possibility exists when turn-off is instructed by an erroneous signal such as noise.

The present invention has been made to solve such problems, and an object of the present invention is to reduce the switching loss of the main switching element for DC voltage conversion. In a DC voltage converter provided with an auxiliary switching element generating an auxiliary current not contributing directly, protection of the switching element for generating the auxiliary current is achieved.

A direct current voltage converter according to the present invention is a direct current voltage converter for performing direct current voltage conversion between a low voltage power supply and a power supply wiring, and includes a main inductor, first and second main switching elements, and first and second main switching elements. And an auxiliary resonance circuit provided corresponding to at least one of the first and second main switching elements, a control circuit, and a drive circuit. The main inductor is connected between the low voltage power supply and the first node. The first main switching element is connected between the power supply line and the first node. The first main rectifier element is connected in antiparallel with the first main switching element. The second main switching element is connected between the reference voltage line and the first node. The second main rectifier element is connected in antiparallel with the second main switching element. The auxiliary resonant circuit includes a capacitor connected in parallel with at least one main switching element, an auxiliary switching element and an auxiliary inductor connected in series connected in parallel with the capacitor, and a current when the auxiliary switching element is on And an auxiliary rectifying element connected in series with the auxiliary switching element to block current in the opposite direction. Each main switching element and the auxiliary switching element are turned on or off in response to the voltage or current of the respective control electrode. The control circuit is configured to generate a control signal instructing on / off of each main switching element and the auxiliary switching element. The drive circuit is configured to drive the voltage or current of the control electrode of each main switching element and the auxiliary switching element in response to the control signal. The drive circuit includes a drive selection circuit and a first drive unit. The drive selection circuit is configured to determine whether the turn-off indication of the auxiliary switching element by the control signal is a normal turn-off indication or an abnormal turn-off indication. The first drive unit drives the control electrode of the auxiliary switching element at a first speed in response to the control signal in the normal turn-off instruction, and responds to the control signal in the abnormal turn-off instruction. Thus, the control electrode of the auxiliary switching element is configured to be driven at a second speed lower than the first speed.

According to the DC voltage converter, when there is a command to turn off the auxiliary switching element for flowing the auxiliary current (partial resonance current) for reducing the loss of the main switching element for DC voltage conversion, In the case of an abnormal turn-off instruction that may have been issued during energization, the drive speed of the control electrode is reduced as compared to the normal turn-off instruction. Therefore, even when the auxiliary switching element is turned off by the abnormal turn-off command during energization, the rise of the voltage across the terminals due to the turn-off can be moderated by reducing the turn-off speed. . As a result, the auxiliary switching element can be reliably prevented from being damaged when the voltage between the terminals exceeds the withstand voltage.

Preferably, an identification signal to be turned on at the time of an emergency stop of the auxiliary switching element is input to the drive selection circuit. The drive selection circuit determines that the turn-off instruction when the identification signal is turned on is an abnormal turn-off instruction, while determines that the turn-off instruction when the identification signal is turned off is a normal turn-off instruction.

In this way, the turn-off command for an emergency stop generated regardless of whether the auxiliary switching element is energized can be determined as an abnormal turn-off command. This can prevent the auxiliary switching element from being damaged due to the occurrence of an overvoltage at turn-off.

Also preferably, the DC voltage converter further includes a current detector for detecting a passing current of the auxiliary switching element. The drive selection circuit determines that the turn-off instruction at the time of current detection by the current detector is a normal turn-off instruction, while determines that the turn-off instruction at the time of no current detection by the current detector is an abnormal turn-off instruction. .

In this way, based on the output of the current detector, it is possible to reliably distinguish the abnormal turn-off instruction for reducing the drive speed of the control electrode from the normal turn-off instruction. This can prevent the auxiliary switching element from being damaged due to the occurrence of an overvoltage at turn-off.

More preferably, the drive circuit further includes a second drive unit. The second drive unit is responsive to the control signal when instructed to turn on the auxiliary switching element, and the control electrode of the auxiliary switching element has a third speed higher than any of the first and second speeds. Configured to drive on.

In this way, it is possible to reduce the switching loss by increasing the drive speed of the control electrode at the time of turn-on without concern about the occurrence of an overvoltage.

Alternatively and preferably, the drive circuit further includes an over voltage protection circuit. The overvoltage protection circuit drives the control electrode to forcibly turn on the auxiliary switching element when the voltage between the first and second terminals of the auxiliary switching element in the off state becomes higher than a predetermined voltage. Configured to

In this way, when the voltage across the auxiliary switching element in the off state rises above the predetermined voltage, the control electrode can be driven to turn on the auxiliary switching element forcibly. As a result, it can be reliably prevented that the voltage between the terminals of the auxiliary switching element exceeds the withstand voltage and is broken.

A DC voltage converter according to another configuration of the present invention is a DC voltage converter for performing DC voltage conversion between a low voltage power supply and a power supply wiring, comprising: a main inductor; first and second main switching elements; And an auxiliary resonance circuit provided corresponding to at least one of the first and second main switching elements, a control circuit, and a drive circuit. The main inductor is connected between the low voltage power supply and the first node. The first main switching element is connected between the power supply line and the first node. The first main rectifier element is connected in antiparallel with the first main switching element. The second main switching element is connected between the reference voltage line and the first node. The second main rectifier element is connected in antiparallel with the second main switching element. The auxiliary resonant circuit includes a capacitor connected in parallel with at least one main switching element, an auxiliary switching element and an auxiliary inductor connected in series connected in parallel with the capacitor, and a current when the auxiliary switching element is on And an auxiliary rectifying element connected in series with the auxiliary switching element to block current in the opposite direction. Each main switching element and the auxiliary switching element are turned on or off in response to the voltage or current of the respective control electrode. The control circuit is configured to instruct on / off of each main switching element and the auxiliary switching element. The drive circuit is configured to drive the voltage or current of the control electrode of each main switching element and the auxiliary switching element in response to the control signal. Furthermore, the drive circuit includes an over voltage protection circuit. The overvoltage protection circuit drives the control electrode to forcibly turn on the auxiliary switching element when the voltage between the first and second terminals of the auxiliary switching element in the off state becomes higher than a predetermined voltage. Configured to

According to the DC voltage converter, in the auxiliary switching element for flowing the auxiliary current (partial resonance current) for reducing the loss of the main switching element for DC voltage conversion, the voltage between terminals in the OFF state is higher than the predetermined voltage Ascending, the control electrode can be driven to forcibly turn on the auxiliary switching element. As a result, it can be reliably prevented that the voltage between the terminals of the auxiliary switching element exceeds the withstand voltage and is broken.

Preferably, the over voltage protection circuit comprises a voltage comparator for comparing the voltage between terminals with a predetermined voltage, and for driving the control electrode to turn on the auxiliary switching element in response to the output of the voltage comparator. And a gate circuit. More preferably, the gate circuit is further configured to drive the control electrode to turn on the auxiliary switching element in response to the control signal when turn-off of the auxiliary switching element is instructed.

Also preferably, the overvoltage protection circuit comprises a zener diode. The Zener diode is electrically connected between one of the first terminal and the second terminal of the auxiliary switching element, which is a high voltage when the auxiliary switching element is off, and the control electrode of the auxiliary switching element. Be done. The breakdown voltage of the zener diode is equal to a predetermined voltage, and the zener diode is connected in the forward direction from the control electrode to one of the terminals.

In this way, the overvoltage protection circuit can be configured with a simple configuration.

According to the present invention, in the DC voltage converter including the auxiliary switching element for generating the auxiliary current not directly contributing to the DC voltage conversion, in order to reduce the switching loss of the main switching element for the DC voltage conversion, It is possible to protect the switching element for generating the auxiliary current.

FIG. 1 is a circuit diagram showing a circuit configuration of a DC-DC converter according to an embodiment of the present invention. FIG. 6 is a waveform diagram for explaining the operation when the auxiliary resonance circuit of the DC-DC converter shown in FIG. 1 is operated. It is a wave form diagram explaining the restrictions of the turn-off timing of the auxiliary switching element in FIG. FIG. 7 is a waveform diagram for explaining the turn-off behavior of the auxiliary switching element at the time of abnormal turn-off in the DC-DC converter according to the embodiment of the present invention. It is a circuit diagram explaining the comparative example of the gate drive composition of an auxiliary switching element. FIG. 6 is a circuit diagram illustrating a comparative example of the gate drive configuration of the auxiliary switching element in the DC-DC converter according to the embodiment of the present invention. FIG. 5 is a circuit diagram showing a first configuration example of an overvoltage protection circuit for protecting an auxiliary switching element in an off state from overvoltage. It is a circuit diagram showing the 2nd example of composition of an overvoltage protection circuit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding portions in the drawings will be denoted by the same reference numerals, and the description thereof will not be repeated in principle.

FIG. 1 is a circuit diagram showing a circuit configuration of a DC-DC converter 100 according to an embodiment of the present invention.

Referring to FIG. 1, DC-DC converter 100 according to the embodiment includes a main converter circuit 110 and an auxiliary resonant circuit 120.

The main converter circuit 110 outputs a voltage Vo obtained by boosting a voltage Vi corresponding to the output voltage of the battery BAT, which is a "low voltage power supply", between the power supply line PL and the reference voltage line GL connected to the load 200. The voltage Vo between the line PL and the reference voltage line GL can be stepped down to the voltage Vi to charge the low-voltage power supply, so that it has a configuration of a so-called non-insulated current bidirectional (buck-boost) converter.

As load 200, an AC motor driven via, for example, an inverter circuit is applied. Then, application to a hybrid vehicle traveling by engine output and / or motor output, an electric vehicle traveling only by motor output, etc. is mentioned as a typical application example of the DC-DC converter according to the embodiment of the present invention. In this case, for example, the output voltage (voltage Vi) of the low voltage power supply (battery BAT) is about 200 V, while the voltage Vo to be supplied to the load 200 is about 500 V.

Main converter circuit 110 includes a capacitor C0, an inductor L1 as a “main inductor”, switching elements Q1 and Q2 as a “main switching element”, and diodes D1 and D2 as a “main rectifying element”.

Capacitor C0 is connected between the positive electrode terminal and the negative electrode terminal of battery BAT to smooth voltage Vi. Inductor L1 is connected between the positive electrode terminal of battery BAT and node N1 (first node).

Although IGBTs (Insulated Gate Bipolar Transistors) are illustrated as switching elements Q1 and Q2 in the present embodiment, switching elements capable of controlling turn-on and turn-off by drive control of control electrodes (gates or bases) may be used. It is possible to apply voltage-driven switching elements (MOS-FETs and the like), current-driven switching elements (bipolar transistors and the like), and various switching elements.

Main switching element Q1 is connected between power supply line PL and node N1. The collector of the main switching element Q1, which is an IGBT, is connected to the power supply wiring PL, while the emitter is connected to the node N1. Further, main switching element Q2 is connected between reference voltage line GL and node N1. The collector of main switching element Q2 is connected to node N1, while the emitter is connected to reference voltage line GL. Furthermore, on / off of the main switching elements Q1, Q2 is controlled by voltage driving of the control electrode (gate) by the driver 156. The diodes D1 and D2 are connected in antiparallel to the switching elements Q1 and Q2.

Auxiliary resonant circuit 120 includes capacitors C1 and C2 connected in parallel to main switching elements Q1 and Q2, inductors L2 and L3 connected in series between nodes N1 and N2, and power supply line PL and node N2, respectively. It includes switching element Q3 and diode D3 connected in series, and diode D4 and switching element Q4 connected in series between node N2 and reference voltage line GL.

The switching elements Q 3 and Q 4 are provided as “auxiliary switching elements”, and the on / off thereof is controlled by voltage driving of the control electrode (gate) by the driver 156. Diodes D3 and D4 as "auxiliary rectifying elements" are connected in such a polarity as to block current in the opposite direction to auxiliary currents Irp # and Irp generated when auxiliary switching elements Q3 and Q4 are turned on.

The inductor L2 is electromagnetically coupled to the inductor L1 so that an electromotive force is induced in a reverse polarity to a terminal on the node N1 side of the inductor L1 and a terminal on the node N1 side of the inductor L2. The electromagnetic coupling is realized, for example, by configuring a transformer with the inductor L1 and the inductor L2.

As understood from FIG. 1, the configuration and operation of the main converter circuit 110 and the auxiliary resonant circuit 120 which constitute the DC-DC converter 100 are the same as those of the above-mentioned Patent Document 1.

Therefore, in the main converter circuit 110, basically, the main switching elements Q1 and Q2 are controlled by the control circuit 150 to be alternately turned on and off. In operation, on / off control (duty control) of main switching element Q2 may be executed after fixing main switching element Q1 off when operating as a boost converter, and when operating as a step-down converter, main may be performed. It is also possible to execute on / off control (duty control) of the main switching element Q1 after fixing the switching element Q2 off.

Then, at the time of boosting operation where main converter circuit 110 boosts voltage Vi from battery BAT to voltage Vo to power supply wiring PL, the electromagnetic energy accumulated in main inductor L1 due to conduction of main switching element Q2 is converted to the main switching element It operates to supply power supply line PL via Q1 and anti-parallel diode D1. Further, at the time of the step-down operation of stepping down the voltage Vo of the power supply line PL to the voltage Vi to the battery BAT, the main converter circuit 110 reduces the electromagnetic energy stored in the main inductor L1 by the conduction of the main switching element Q1 to the main switching element Q2. And an antiparallel diode D2 to supply the low voltage power supply BAT.

Control circuit 150 includes a duty control unit 152 and a timing control unit 154. The control circuit 150 comprehensively shows control elements of the DC-DC converter 100, and for the duty control unit 152 and the timing control unit 154 corresponding to each control function part, software processing by execution of a predetermined program, Also, it can be realized by any of hardware processing by dedicated electronic circuit construction. Further, the driver 156 is usually constructed by an electronic circuit (hardware).

The duty control unit 152 controls the duty ratio of the main switching elements Q1 and Q2 based on the voltage command value Vor of the voltage Vo or the voltage Vi and the detected values of the voltage Vi and the voltage Vo. The duty ratio is generally indicated by the ratio of the on period of the main switching element Q1 and / or the main switching element Q2 to a predetermined switching period. For example, in the step-up operation, the command duty of the main switching element Q2 is set, and in the step-down operation, the command duty of the main switching element Q1 is set.

Timing control unit 154 generates pulse-like control signals S1 to S4 for controlling on / off of switching elements Q1 to Q4 according to the command duty from duty control unit 152. For example, control signals S1 to S4 are set to logic high level (hereinafter, also referred to as H level) in the on period of switching elements Q1 to Q4, while logic low level (hereinafter referred to as L) is set in each off period. (Also called a level).

The driver 156 drives the gate voltages Vg1 to Vg4 of the switching elements Q1 to Q4 in accordance with the control signals S1 to S4 from the timing control unit 154. The configuration of the driver 156 will be described in detail later.

Next, with reference to FIG. 2, the DC-DC converter 100 when the auxiliary resonant circuit is operated will be described in detail. In FIG. 2, the boosting operation of the DC-DC converter 100 will be described.

Referring to FIG. 2, main switching elements Q1 and Q2 are complementarily turned on and off. For example, in timing control unit 154 (FIG. 1), a DC voltage according to the command duty from duty control unit 152, and a carrier wave (triangular wave or sawtooth wave) of a predetermined frequency corresponding to the switching frequency of main switching elements Q1 and Q2. A pulse signal that defines on / off of the main switching elements Q1 and Q2 can be generated based on the voltage comparison of

Here, when the main switching elements Q1 and Q2 are turned off, an increase in collector-emitter voltage is suppressed by the capacitors C1 and C2 connected in parallel to the main switching elements Q1 and Q2, so zero voltage switching can be applied. In addition, since the diode D1 normally conducts by commutation in response to the off period of the main switching element Q2 during boosting operation, the switching element Q1 is turned on by zero voltage switching in a state where a slight voltage is applied to the collector / emitter. can do.

Therefore, in the step-up operation, it is necessary to take measures against the turn-on loss of the main switching element Q2, and the auxiliary resonant circuit 120 applies zero voltage switching to turn on the main switching element Q2.

As shown in FIG. 2, in the step-up operation, after the main switching device Q1 is turned off, the auxiliary switching device Q4 is turned on to generate the auxiliary current Irp (FIG. 1) in the auxiliary resonant circuit 120. As a result, the conduction of the diode D2 can turn on the main switching element Q2 with a slight voltage applied between the collector and the emitter, so that power loss due to application of soft switching (zero voltage switching) can be reduced. It can control.

As described above, at the time of the boosting operation, the switching loss of the main switching element Q1 is low both at turn on and off, so the auxiliary switching element Q3 in the auxiliary resonant circuit 120 may be fixed in the off state. Alternatively, the main switching element Q1 may be turned on and off with the turning on and off of the auxiliary switching element Q3.

Although not illustrated, during step-down operation of DC-DC converter 100, switching elements Q1 and Q2 which are main switching elements are complementarily turned on and off, while in auxiliary resonance circuit 120, auxiliary switching element Q3 is main switching Prior to the turn-off of element Q1, it is turned on for a certain period of time to generate auxiliary current Irp # (FIG. 1). The auxiliary switching element Q4 may be fixed in the off state, and may be controlled to be turned on prior to the turning on of the main switching element Q2.

The auxiliary resonant circuit 120 shown in FIG. 1 includes a switching element Q4 for generating an auxiliary current Irp for soft switching of the switching element Q2 in the step-up operation, and a soft switching of the switching element Q1 in the step-down operation. Although both of switching element Q3 for generating auxiliary current Irp # are provided, auxiliary resonant circuit 120 may be configured to generate an auxiliary current for only one of switching elements Q1 and Q2. It is possible.

As an example, in the case of the configuration corresponding to the soft switching of only switching element Q2, the arrangement of switching element Q3 and diode D3 can be omitted to disconnect node N2 and power supply wiring PL.

Here, restrictions on the turn-off timing of the auxiliary switching elements Q3 and Q4 will be described with reference to FIG. In FIG. 3, the auxiliary switching element Q4 will be described as an example.

Referring to FIG. 3, when auxiliary switching element Q4 is turned on at time t0, collector-emitter voltage V4ce, that is, the voltage between terminals of switching element Q4 is reduced, and auxiliary current (partial resonance current) Irp is generated. Do.

The auxiliary current Irp decreases toward zero after reaching its peak value due to the resonance phenomenon between the inductors L2 and L3 and the capacitor C2. Then, since the current in the reverse direction is blocked by the diode D4, after Irp = 0 at time t2, the current does not flow in the negative direction and disappears.

The auxiliary switching element Q4 is normally turned off at a timing after the auxiliary current Irp disappears. Therefore, the control signal S4 is set to transition from L level to H level at time t1 and to transition from H level to L level at time t3 after time t2.

Here, when an emergency stop is instructed by the occurrence of a short circuit current inside DC-DC converter 100, or when a malfunction due to noise or the like occurs, that is, auxiliary current Irp flows before time t2. It is assumed that the control signal S4 has changed to L level while

In this case, when the auxiliary switching element Q4 is turned off in response to the reduction of the gate voltage Vg4, which is the voltage of the control electrode driven by the control signal S4, the energy stored in the inductor L3 causes the collector The inter-emitter voltage V4ce rapidly rises to generate a large surge voltage. If V4ce exceeds withstand voltage Vmax due to this voltage rise, there is a possibility that auxiliary switching element Q4 may be damaged.

Therefore, in the DC-DC converter according to the present embodiment, as shown in FIG. 4, the auxiliary switching element is protected by reducing the switching speed against the abnormal turn-off command shown in FIG.

FIG. 4 further shows the waveform of the gate voltage Vg4 in addition to FIG. Similarly to FIG. 3, the control signal S4 instructs turn-on by transitioning from L level to H level at time t0, and instructs turn-off by transitioning from H level to L level at time t1. That is, a turn-off command is issued at an abnormal timing at which the auxiliary current Irp flows.

At the time of turn-on command, gate voltage Vg4 is rapidly driven. In response to the rise of the gate voltage Vg4, the turn-on speed of the auxiliary switching element Q4 is also relatively high.

On the other hand, at the time of turn-off, gate voltage Vg4 is driven gently. For this reason, the turn-on speed of the auxiliary switching element Q4 is low, and there is a time margin for absorbing the energy stored in the inductor L3. For this reason, the rise of the collector-emitter voltage V4ce accompanying turn-on becomes gradual, and the surge voltage also decreases. As a result, the auxiliary switching element Q4 can be protected by preventing V4ce from exceeding the withstand voltage Vmax.

A similar problem occurs when the auxiliary switching element Q3 is turned off when the auxiliary current Irp # is flowing.

Next, with reference to FIGS. 5 and 6, the drive configuration of the auxiliary switching element for realizing the turn-off operation shown in FIG. 4 will be described.

FIG. 5 shows a gate drive configuration of the auxiliary switching element as a comparative example of the embodiment of the present invention.

FIG. 5 shows the configuration of the portion of driver 156 shown in FIG. 1 related to the driving of auxiliary switching element Q4 (or Q3). Hereinafter, although the drive configuration of the auxiliary switching element Q4 will be described, a point that it is possible to apply the same configuration to the auxiliary switching element Q3 will be confirmed and described.

Referring to FIG. 5, auxiliary switching element Q4 includes a gate 201 which is a "control electrode", and a collector 202 and an emitter 203 corresponding to "first terminal" and "second terminal".

Gate 201 is electrically connected to voltage source 205 through drive switch 210 and gate resistor 220. The voltage source 205 supplies a power supply voltage VH (also referred to as an on voltage VH) corresponding to a gate voltage for turning on the auxiliary switching element Q4. The auxiliary switching element Q3 is turned off when the difference between the gate voltage and the emitter voltage is smaller than a predetermined value. The gate voltage at this time is also referred to as an off voltage VL.

Furthermore, the gate 201 is connected to the emitter 203 through the drive switch 215 and the gate resistor 225.

The drive switch 210 is turned on when the control signal S4 becomes H level. When the drive switch 210 is turned on, the gate voltage is driven to the on voltage VH. The driving speed at this time depends on the resistance value R0 of the gate resistor 220.

On the other hand, the drive switch 215 is turned on when the control signal S4 becomes L level. When the drive switch 215 is turned on, the gate 201 is driven to the off voltage VL. The driving speed at this time depends on the resistance value R1 of the gate resistor 225.

The resistance value R0 of the gate resistor 220 is designed to be smaller than the resistance value R1 of the gate resistor 225. Therefore, while increasing the driving speed of the gate 201 at turn-on, the driving speed of the gate 201 decreases according to the resistance value R1 of the gate resistor 225 at turn-off. As a result, as shown in FIG. 4, the auxiliary switching element Q4 can be protected from breakage even when the turn off is abnormal at the timing when the auxiliary current Irp exists.

However, according to the drive configuration of FIG. 5, since the drive speed of the gate 201 at the turn-off time of the auxiliary switching element is uniformly reduced, the turn-off speed is also reduced for a normal turn-off command. However, at the time of normal turn-off, since the auxiliary current Irp is turned off and then turned off, the switching loss does not increase even if the turn-off speed decreases. Also, by optimizing the resistance value R0, the turn-on speed can be set independently of the turn-off speed so that the switching loss at turn-on does not increase.

However, if the turn-off speed is uniformly reduced, the assistance may be performed when increasing the frequency of the DC-DC converter 100 or when the duty ratio of the main switching elements Q1 and Q2 approaches 0 (%) or 100 (%). Before the switching element Q4 (Q3) is completely turned off, the main switching element Q2 (Q1) may cause a malfunction to be turned on. Conversely, if the turn-off speed of the auxiliary switching element Q4 (Q3) is uniformly reduced, the variable range of the duty ratio of the main switching elements Q1 and Q2 and the switching frequency may be restricted.

FIG. 6 shows the drive configuration of the control electrode of the auxiliary switching element in the DC-DC converter according to the present embodiment.

In the gate drive configuration of the auxiliary switching element shown in FIG. 6, a drive switch 217 and a gate resistor 227 are further provided for gate drive at turn-off, as compared with the configuration of FIG. Drive switch 217 and gate resistor 227 are connected in parallel with drive switch 215 and gate resistor 225 between gate 201 and emitter 203. Here, the resistance value R2 of the gate resistor 227 is smaller than the resistance value R1 of the gate resistor 225 and larger than the resistance value R0 of the gate resistor 220. That is, it is a relation of R0 <R2 <R1.

Furthermore, a drive selection circuit 155 for selectively turning on the drive switches 210, 215, and 217 is provided. The configuration of the other parts is the same as that of FIG.

The drive selection circuit 155 turns on the drive switch 210 when the control signal S4 is at the H level. When control signal S4 is at the L level, drive select circuit 155 determines whether the turn-off instruction is normal or not, and one of drive switches 215 and 217 is set according to the determination result. Selectively turn on.

For example, the drive selection circuit 155 receives an identification signal Fem that is turned on when an emergency stop command for the auxiliary switching element occurs. When the control signal S4 becomes L level when the identification signal Fem is on, the drive selection circuit 155 determines that the turn-off instruction is abnormal and turns on the drive switch 215. On the other hand, when the control signal S4 becomes L level when the identification signal Fem is turned off, the drive selection circuit 155 determines that it is a normal turn-off instruction, and turns on the drive switch 217.

Thus, for an abnormal turn-off instruction, the turn-off speed can be reduced by the gate resistance 225 (resistance value R1) as shown in FIG. On the other hand, for a normal turn-off instruction, the gate resistance 227 (resistance value R2) can make the turn-off speed higher than at an abnormal turn-off. Therefore, the auxiliary switching element can be protected after solving the problems when the turn-off speed described in FIG. 5 is significantly reduced uniformly.

Alternatively, the drive selection circuit 155 may select one of the drive switches 215 and 217 based on the output of the current detector 207 that detects the passing current of the auxiliary switching element Q4. The current detector 207 may be provided as a separate current sensor outside the auxiliary switching element Q4, and may be realized by the current detection function of the modularized switching element.

When the control signal S4 becomes L level at the time of current detection by the current detector 207 (detection current value> 0), the drive selection circuit 155 determines that the turn-off instruction is abnormal and turns on the drive switch 215. On the other hand, when the control signal S4 becomes L level when the current detector 207 detects no current (detection current value = 0), the drive selection circuit 155 determines that it is a normal turn-off instruction and turns on the drive switch 217. .

Also in this case, the auxiliary switching element can be protected against the turn-off while the auxiliary switching element Q4 is energized, and the problems when the turn-off speed is uniformly reduced can be solved.

As described above, according to the DC-DC converter according to the embodiment of the present invention, the auxiliary switching elements Q3 and Q4 for reducing the loss of the main switching elements Q1 and Q2 for DC voltage conversion are auxiliary switching elements In the case of an abnormal turn-off instruction that may have been issued during the power-on, the driving speed of the gate 201 (control electrode) is reduced as compared with the normal turn-off instruction. Therefore, even when the auxiliary switching element is turned off during energization, the rise of the collector-emitter voltage Vce (voltage between terminals) at the time of turn-off can be moderated by reducing the turn-off speed. As a result, the auxiliary switching elements Q3 and Q4 can be reliably prevented from being damaged when the voltage between the terminals exceeds the withstand voltage.

In the embodiment, the driver 156 corresponds to a "drive circuit". Further, the drive switches 215 and 217 and the gate resistors 225 and 227 constitute a “first drive unit” for switching the turn-off speed. Furthermore, the drive switch 210 and the gate resistor 220 constitute a “second drive unit” whose drive speed is higher than that of the “first drive unit”.

Moreover, although the example of a structure which switches the drive speed of a gate (control electrode) was demonstrated in FIG. 6 by switching gate resistance, the structure for switching a drive speed can apply any well-known thing. .

In the above, the overvoltage prevention at the time of turning off the auxiliary switching element in the on state has been described. Next, a circuit configuration for protecting the auxiliary switching element in the off state from an overvoltage will be described with reference to FIGS. 7 and 8. Although the configuration of the overvoltage preventing circuit applied to the auxiliary switching element Q4 will be described below as well, the point that it is possible to apply the same overvoltage preventing circuit to the auxiliary switching element Q3 is also confirmed. Do.

FIG. 7 shows a first configuration example of the overvoltage protection circuit.
Referring to FIG. 7, overvoltage protection circuit 300 includes a voltage divider 305 formed of resistance elements 306 and 307, a voltage source 310 outputting a predetermined voltage V1, a voltage comparator 320, and a gate circuit 330. .

The resistive elements 306 and 307 constituting the voltage divider 305 are connected in series between the collector 202 and the emitter 203 of the auxiliary switching element Q4. The voltage divider 305 outputs a voltage Vd obtained by dividing the collector-emitter voltage Vce (inter-terminal voltage) according to a voltage division ratio determined by the resistance values of the resistance elements 306 and 307.

The divided voltage Vd from the voltage divider 305 and the predetermined voltage V1 output from the voltage source 310 are input to the voltage comparator 320. The voltage comparator 320 sets the output voltage to the H level when Vd> V1, and sets the output voltage to the L level when Vd ≦ V1. The predetermined voltage V1 is set to V1 = V0 × (Vd / Vce) with respect to the predetermined voltage V0 (V <Vmax) determined to have a margin with respect to the withstand voltage Vmax.

The gate circuit 330 is configured as a logic gate that sets the on voltage VH to the H level and the off voltage VL to the L level. The output node of the gate circuit 330 is electrically connected to the gate 201 of the auxiliary switching element Q4 via the gate resistor 220.

When the output voltage of voltage comparator 320 attains the H level, gate circuit 330 drives the output node with on voltage VH. Thus, the gate 201 is driven to the on voltage VH via the gate resistor 220.

Furthermore, the gate circuit 330 may be configured to output a logical sum operation result between the control signal S4 and the output of the voltage comparator 320. Thus, when Vce ≦ V0, the output voltage of voltage comparator 320 attains the L level, and therefore the output node of gate circuit 330 is driven to one of on voltage VH and off voltage VL according to control signal S4. Ru. That is, the auxiliary switching element Q4 can be turned on / off according to the control signal S4.

Thus, the overvoltage prevention circuit 300 shown in FIG. 7 forcibly forces the gate voltage of the auxiliary switching element to the on voltage VH when the voltage Vce between the terminals of the auxiliary switching element Q4 in the off state rises above the predetermined voltage V0. It can be driven and turned on. Therefore, it can be reliably prevented that a high voltage exceeding the withstand voltage is applied between the terminals of the auxiliary switching element.

It is also possible to use the overvoltage prevention circuit 300 shown in FIG. 7 in combination with the drive configuration shown in FIG. Specifically, on / off of the drive switch 210 can be controlled according to the output of the overvoltage prevention circuit 300.

A second configuration example of the overvoltage protection circuit is shown in FIG.
Referring to FIG. 8, overvoltage prevention circuit 300 # includes a Zener diode 340 and a resistance element 350 connected in series between gate 201 and collector 202. The zener diode 340 is connected with the direction from the gate 201 to the collector 202 as a forward direction. The reverse breakdown voltage of the zener diode 340 corresponds to the above-mentioned predetermined voltage V0.

The drive switches 210 and 215 are selectively turned on according to the control signal S4. Thereby, the auxiliary switching element Q4 is turned on / off in response to the control signal S4. Furthermore, when an overvoltage occurs between the terminals of the auxiliary switching element Q4 in the off state (between the collector and the emitter), the zener diode 340 conducts to drive the gate 201 to the turn-on voltage. Thus, the switching element Q4 can be forcibly turned on, and the voltage between terminals (collector-emitter voltage Vce) is reduced. That is, by preventing the voltage between terminals from exceeding the withstand voltage in advance, the auxiliary switching element Q4 can be prevented from being broken.

It is also possible to use overvoltage protection circuit 300 # shown in FIG. 8 in combination with the drive configuration shown in FIG. Specifically, overvoltage prevention circuit 300 # can be connected between gate 201 and collector 202 of auxiliary switching element Q3 (Q4).

Although an IGBT is illustrated as a semiconductor switching element in the present embodiment, the drive configuration and overvoltage of the auxiliary switching element according to the present invention can be applied to other voltage driven elements such as a power MOS (Metal Oxide Semiconductor) transistor. The prevention circuit can be applied. Further, as with the gate voltage drive speed in the present embodiment, by controlling the current drive speed of the control electrode (base), a DC voltage in which the auxiliary switching element is constituted by a current drive type element such as a power bipolar transistor. The drive configuration of the auxiliary switching element according to the present invention can also be applied to the converter. The overvoltage protection circuit according to the present invention is also applicable to current driven switching elements.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims.

The present invention is applied to a DC voltage converter provided with an auxiliary power semiconductor switching element that generates an auxiliary current that does not directly contribute to DC voltage conversion in order to reduce the switching loss of the main power semiconductor switching element. can do.

Reference Signs List 100 DC-DC converter, 110 main converter circuit, 120 auxiliary resonance circuit, 150 control circuit, 152 duty control unit, 154 timing control unit, 155 drive selection circuit, 156 driver, 200 load, 201 gate, 202 collector, 203 emitter, 205 voltage source, 207 current detector, 210, 215, 217 drive switch, 220, 225, 227 gate resistance, 300, 300 # over voltage protection circuit, 305 voltage divider, 306, 307 resistance element, 310 voltage source, 320 voltage comparison , 330 gate circuit, 340 zener diode, 350 resistor element, BAT low voltage power supply, C0 capacitor, C1, C2 capacitor (auxiliary resonant circuit), D1, D2 reverse parallel diode (main rectifying element ), D3, D4 diode (auxiliary rectifier element), Fem identification signal (emergency stop), GL reference voltage wiring, Irp, Irp # auxiliary current (partial resonant current), L1 inductor (main inductor), L2, L3 inductor (aux Resonant circuit), N1 and N2 nodes, PL power supply wiring, Q1 and Q2 power semiconductor switching devices (main switching devices), Q3 and Q4 power semiconductor switching devices (auxiliary switching devices), R0, R1 and R2 resistance value, S1 ~ S4 Control signal, Vg1 ~ Vg4 gate voltage, VH power supply voltage (on voltage), VL off voltage, Vmax breakdown voltage, Vo output voltage, Vor voltage command value.

Claims (9)

A DC voltage converter for performing DC voltage conversion between a low voltage power supply (BAT) and a power supply wiring (PL), comprising:
A main inductor connected between the low voltage power supply and a first node (N1);
A first main switching element (Q1) connected between the power supply line and the first node;
A first main rectifier element (D1) connected in antiparallel to the first main switching element;
A second main switching element (Q2) connected between the reference voltage line (GL) and the first node;
A second main rectifier (D2) connected in anti-parallel to the second main switching device;
An auxiliary resonant circuit (120) provided corresponding to at least one of the first and second main switching elements;
The auxiliary resonant circuit is
Capacitors (C1, C2) connected in parallel with the at least one main switching element;
A series connected auxiliary switching element (Q3, Q4) and an auxiliary inductor (L2, L3) connected in parallel to the capacitor;
An auxiliary rectifying element (D3, D4) connected in series with the auxiliary switching element to block a current in a direction reverse to the current when the auxiliary switching element is on,
Each said main switching element and said auxiliary switching element are turned on or off in response to the voltage or current of the respective control electrode,
The DC voltage converter
A control circuit (150) configured to generate control signals (S1 to S4) instructing on / off of each of the main switching element and the auxiliary switching element;
A driving circuit (156) for driving a voltage or a current of control electrodes (201) of each of the main switching elements and the auxiliary switching elements in response to the control signal;
The drive circuit is
A drive selection circuit configured to determine whether a turn-off instruction of the auxiliary switching element (Q3, Q4) by the control signal (S3, S4) is a normal turn-off instruction or an abnormal turn-off instruction 155),
When the normal turn-off instruction is performed, the control electrode of the auxiliary switching element is driven at a first speed in response to the control signal, while when the abnormal turn-off instruction is performed, the control signal is responsive to the control signal. And d) a first drive unit (215, 217, 225, 227) configured to drive a control electrode of the auxiliary switching element at a second speed lower than the first speed. The drive selection circuit (155) receives an identification signal (Fem) which is turned on at the emergency stop of the auxiliary switching element (Q3, Q4),
The drive selection circuit (155) determines that the turn-off instruction when the identification signal is turned on is the abnormal turn-off instruction, while the drive selection circuit (155) determines that the turn-off instruction when the identification signal is turned off is normal. The DC voltage converter according to claim 1, which is determined to be a turn-off instruction. It further comprises a current detector (207) for detecting a passing current of the auxiliary switching element (Q3, Q4),
The drive selection circuit (155) determines that the turn-off instruction at the time of current detection by the current detector is the normal turn-off instruction, while the drive selection circuit (155) determines the non-turn-off instruction at the time of current non-detection by the current detector. The DC voltage converter according to claim 1, which is determined to be a normal turn-off instruction. The drive circuit is
When it is instructed to turn on the auxiliary switching element (Q3, Q4), in response to the control signal, the control electrode (201) of the auxiliary switching element is operated at any of the first and second speeds. A DC voltage converter according to any of the preceding claims, further comprising a second drive unit (210, 220) configured to drive at a high third speed. The drive circuit (156)
When the inter-terminal voltage (Vce) between the first and second terminals (202, 203) of the auxiliary switching element (Q3, Q4) in the off state becomes higher than a predetermined voltage (V0), the auxiliary switching element The DC voltage converter according to claim 1, further comprising an overvoltage prevention circuit (300, 300 #) for driving said control electrode (201) to forcibly turn on A DC voltage converter for performing DC voltage conversion between a low voltage power supply (BAT) and a power supply wiring (PL), comprising:
A main inductor connected between the low voltage power supply and a first node (N1);
A first main switching element (Q1) connected between the power supply line and the first node;
A first main rectifier element (D1) connected in antiparallel to the first main switching element;
A second main switching element (Q2) connected between the reference voltage line (GL) and the first node;
A second main rectifier (D2) connected in anti-parallel to the second main switching device;
An auxiliary resonant circuit (120) provided corresponding to at least one of the first and second main switching elements;
The auxiliary resonant circuit is
Capacitors (C1, C2) connected in parallel with the at least one main switching element;
A series connected auxiliary switching element (Q3, Q4) and an auxiliary inductor (L2, L3) connected in parallel to the capacitor;
An auxiliary rectifying element (D3, D4) connected in series with the auxiliary switching element to block a current in a direction reverse to the current when the auxiliary switching element is on,
Each said main switching element and said auxiliary switching element are turned on or off in response to the voltage or current of the respective control electrode,
The DC voltage converter
A control circuit (150) configured to generate a control signal instructing on / off of each of said main switching element and said auxiliary switching element;
A driving circuit (156) for driving a voltage or a current of control electrodes (201) of each of the main switching elements and the auxiliary switching elements in response to the control signal;
The drive circuit is
When the voltage (Vce) between the first and second terminals (202, 203) of the auxiliary switching element in the off state becomes higher than a predetermined voltage (V0), the auxiliary switching element is forcibly turned on. A DC voltage converter including an overvoltage prevention circuit (300, 300 #) for driving the control electrode to cause The overvoltage protection circuit (300) is
A voltage comparator (320) for comparing the inter-terminal voltage (Vce) with a predetermined voltage (V0);
The direct current according to claim 5 or 6, further comprising: a gate circuit (330) for driving said control electrode to turn on said auxiliary switching element in response to the output of said voltage comparator. Voltage converter. The gate circuit (330) further controls the auxiliary switching element to turn on in response to the control signal (S3, S4) when the auxiliary switching element (Q3, Q4) is instructed to turn off. The direct current voltage converter according to claim 7, which drives an electrode. The overvoltage prevention circuit (300 #)
One of the first terminal (202) and the second terminal (203) of the auxiliary switching element, which is a high voltage when the auxiliary switching element is turned off (202); Having a Zener diode (202) electrically connected to the control electrode (201);
The breakdown voltage of the zener diode is equal to the predetermined voltage (V0), and the zener diode is connected in a forward direction from the control electrode toward the one terminal. The DC voltage converter according to claim 6.

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