JP2017017871A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device which can reduce a loss and a surge current at the turn-off of first and second main switching elements.SOLUTION: When a switching element S1 is turned off at step-up operation, a switch Sa3 is turned on to thereby make a current of a reactor L1 flow to the output terminal side of a switching power supply 4 through a switch Sa3, a capacitor Ca1 and a diode Da1, so as to discharge an electric charge. On completion of discharging the capacitor Ca1, the Sa3 is turned off, and the switching elements Sa1 and Sa2 are turned on, to thereby make a part of the current, flowing to the output terminal side through the parasitic diode of the switching element S2, flow to a reactor La1 also. Next, after the switching element S1 is the turned on, simultaneously or thereafter, the switching elements Sa1 and Sa2 are turned off, and the switch Sa3 is turned on, to charge the capacitor Ca1 by the current of the reactor La1. During the above time, a switch Sa4 is maintained to be an off state.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power converter that includes a series circuit composed of first and second main switching elements connected to a main inductor at a common connection point, converts the input power by switching them, and outputs the converted power.

  For example, many drive systems used in main machines of electric vehicles and hybrid vehicles include a bidirectional DC-DC converter that is a power converter between a battery and an inverter circuit that is a motor drive circuit. In general, the bidirectional DC-DC converter is composed of many passive elements such as a smoothing capacitor and a reactor, so that the circuit size becomes large and presses the arrangement space in the vehicle. In order to avoid an increase in circuit size, it is conceivable to set the switching frequency high. In this case, however, there is a problem in that the switching loss increases and the efficiency decreases.

  For example, Patent Document 1 discloses a technique in which an auxiliary circuit including a snubber capacitor is added to a bidirectional DC-DC converter, and soft switching is performed when a switching element constituting the main circuit is turned off. By this soft switching, the turn-off loss of the main circuit is reduced and the efficiency is improved.

Japanese Patent Laying-Open No. 2015-8622

  However, the configuration of Patent Document 1 has a problem in that a surge current is generated because the charging charge of the snubber capacitor is discharged through the switching element when the switching element is turned on.

  This invention is made | formed in view of the said situation, The objective is providing the power converter device which can suppress a surge current, without suppressing the reduction effect of the turn-off loss of a 1st and 2nd main switching element. It is in.

  According to the power conversion device of the first aspect, the first series circuit includes the first and second main switching elements connected between the high potential side terminal and the low potential side terminal. One end of the main inductor is connected to the positive terminal of the DC power supply, and the other end is connected to a common connection point of the first series circuit. The second series circuit connected in parallel to this comprises a first diode, a first capacitor, first and second switches, a second capacitor, and a second diode.

  The third series circuit includes a first auxiliary switching element and a third diode connected in parallel to the series part from the first diode to the second capacitor in the second series circuit. The fourth series circuit includes a fourth diode and a second auxiliary switching element connected in parallel to the series part from the first capacitor to the second diode in the second series circuit.

  The auxiliary inductor is connected between the common connection point of the third series circuit and the common connection point of the fourth series circuit, the cathode of the first diode is connected in common with one end of the second main switching element, and the second diode Is connected in common with one end of the first main switching element. The anode of the third diode is connected in common with the cathode of the second diode, and the cathode of the fourth diode is connected in common with the anode of the first diode.

  According to this configuration, when the power conversion device performs a step-up operation or a step-down operation of the DC power supply voltage, the first or second switch is turned off by turning off one of the first or second switches when the main switching element is turned on. It is possible to prevent the electric charge charged in the two capacitors from being discharged. Thereby, generation | occurrence | production of the surge current at the time of turn-on of a main switching element can be suppressed, and the fall of efficiency can be suppressed.

  According to the power conversion device of the second aspect, when the voltage of the DC power supply is boosted, the second switch is always turned off, and the first switch turns on at least the first and second auxiliary switching elements. Then, after the auxiliary inductor is energized, the first main switching element is turned on when it is turned on. As a result, the first capacitor is charged with a current flowing by the magnetic energy accumulated in the auxiliary reactor.

  Further, the first switch is turned on when the second main switching element is turned off, and the current flowing through the main inductor is commutated to the first switch, the first capacitor, and the first diode. Therefore, similarly to Patent Document 1, it is possible to reduce the loss when the first main switching element is turned off.

  According to the power conversion device of the third aspect, when the voltage of the DC power supply is stepped down, the first switch is always turned off, and the second switch turns on at least the first and second auxiliary switching elements. After energizing the auxiliary inductor, the second main switching element is turned on when it is turned on. As a result, the second capacitor is charged with a current flowing by the magnetic energy accumulated in the auxiliary reactor.

  In addition, the second switch is turned on when the second main switching element is turned off, and the current flowing through the main inductor is commutated to the second diode, the second capacitor, and the second switch. Therefore, similarly to Patent Document 1, it is possible to reduce the loss when the second main switching element is turned off.

The figure which is 1st Embodiment and shows the circuit structure of a switching power supply device Timing chart of boost operation The figure which shows the circuit current which flows into the period M4 in the timing chart of FIG. The figure which shows the circuit current which flows in the same period M5 Step-down timing chart The figure which shows the circuit current which flows into the period M4 in the timing chart of FIG. The figure which shows the circuit current which flows in the same period M5 The figure which is a 2nd embodiment and shows the case where a switching power supply device is applied to the drive power supply of the inverter circuit which drives the drive motor of an electric vehicle

(First embodiment)
As shown in FIG. 1, an input side capacitor C <b> 1 is connected to both ends of the DC power source 1. For example, the first and second main switching elements S1 and S2, which are N-channel MOSFETs, are connected in series, and constitute a first series circuit. The drain of the switching element S2 corresponds to a high potential side terminal, and the source of the switching element S1 corresponds to a low potential side terminal. A reactor L1 is connected between the positive terminal of the DC power supply 1 and the source of the switching element S2. Reactor L1 corresponds to a main inductor.

  The first series circuit includes a second series circuit including a first diode Da1 in the reverse direction, a first capacitor Ca1, a first and second switch Sa3 and Sa4, a second capacitor Ca2, and a second diode Da2 in the reverse direction. Connected in parallel. Capacitors Ca1 and Ca2 are both snubber capacitors. The common connection point of the switches Sa3 and Sa4 is connected to the source of the switching element S2. These switches Sa3 and Sa4 are analog switches formed by combining, for example, semiconductor switching elements, and are configured as switch circuits capable of conducting in both directions.

  Between the cathode of the diode Da1 and the cathode of the diode Da2, a third series circuit of a first auxiliary switching element Sa1 made of, for example, an N-channel MOSFET and a third diode Da3 in the reverse direction is connected. Further, a fourth diode Da4 in the reverse direction and a fourth series circuit of a second auxiliary switching element Sa2 made of, for example, an N-channel MOSFET are connected between the anode of the diode Da1 and the ground. A reactor La1 is connected between the source of the switching element Sa1 and the drain of the switching element Sa2. Reactor La1 corresponds to an auxiliary inductor. Further, the output side capacitor C2 is connected in parallel to the first series circuit.

  In the above, the switching elements S1 and S2 and the reactor L1 constitute the bidirectional chopper 2, and the circuit element group excluding the remaining capacitors C1 and C2 constitutes the loss reduction circuit 3. And the switching power supply device 4 corresponded to a power converter device is comprised including these.

Next, the operation of this embodiment will be described. As shown in FIG. 2, the operation period when the switching power supply device 4 performs the boosting operation is divided into six periods M1 to M6, and each period will be described below.
<Boosting operation; Period M1>
This is a period during which the switching element S1 side is on, and the switches Sa1 to Sa4 are all off. As a result, the reactor L1 is energized to accumulate magnetic energy.

<Period M2>
The switching element S1 is turned off and the switch Sa3 is turned on. Then, the current of the reactor L1 flows to the output terminal side of the switching power supply device 4 through the switch Sa3, the capacitor Ca1, and the diode Da1. At this time, the electric charge charged in the capacitor Ca1 is discharged, and the change in the drain-source voltage of the switching element S1 is moderated (see FIG. 2B). Thereby, the switching loss at the time of turn-off is reduced.

<Period M3>
The switch Sa3 is turned off. When the discharge of the capacitor Ca1 is finished, the current of the reactor L1 flows to the output terminal side via the parasitic diode of the switching element S2.
<Period M4>
As shown in FIG. 3, the switching elements Sa1 and Sa2 are turned on, and a part of the current flowing through the parasitic diode is also passed to the reactor La1.

<Period M6>
As shown in FIG. 4, after the switching element S1 is turned on (M5), the switching elements Sa1 and Sa2 are turned off and the first switch Sa3 is turned on. In this case, the period during which the switching elements Sa1 and Sa2 are turned on is, for example, a predetermined period. Then, the current of the reactor La1 flows along the path of the diodes Da2 and Da3 → the reactor La1 → the diode Da4 → the capacitor Ca1 → the switch Sa3, and the terminal voltage of the capacitor Ca1 is the output voltage V2 of the switching power supply 4 (shown in FIG. 2). Charge until. If magnetic energy remains in the reactor La1 when charging is completed, current flows to the output terminal side via the diode Da1. Then, it returns to the period M1.

  Here, since the switch Sa4 is turned off when the switching element S1 is turned on in M5, no current flows through the capacitor Ca2 via the diode Da2. Therefore, the surge current is prevented from flowing when the switching element S1 is turned on.

Next, as shown in FIG. 5, the operation when the switching power supply device 4 performs the step-down operation will be described in the same manner as described above.
<Step-down operation; Period M1>
This is a period during which the switching element S2 side is on, and the switches Sa1 to Sa4 are all off. As a result, the reactor L1 is energized in reverse polarity from the output terminal side, and magnetic energy is accumulated.

<Period M2>
The switching element S2 is turned off and the switch Sa4 is turned on. Then, the current of the reactor L1 flows to the DC power supply 1 side through the path of ground → diode Da2 → capacitor Ca2 → switch Sa4 → reactor L1. At this time, the electric charge charged in the capacitor Ca2 is discharged, and the change in the drain-source voltage of the switching element S2 is moderated. Thereby, the switching loss at the time of turn-off is reduced.

<Period M3>
The switch Sa4 is turned off. When the discharge of the capacitor Ca2 ends, the current of the reactor L1 flows to the DC power supply 1 side via the parasitic diode of the switching element S1.
<Period M4>
As shown in FIG. 6, the switching elements Sa1 and Sa2 are turned on to energize the reactor La1.

<Period M6>
As shown in FIG. 7, after the switching element S2 is turned on (M5), the switching elements Sa1 and Sa2 are turned off and the switch Sa4 is turned on. Also in this case, the period during which the switching elements Sa1 and Sa2 are turned on is, for example, a predetermined period. Then, the current of the reactor La1 flows through the path of the diode Da4 and Da1, the switching element S2, the switch Sa4, the capacitor Ca2, and the diode Da3, and the terminal voltage of the capacitor Ca2 is the output voltage V2 of the switching power supply device 4 (shown in FIG. 5). Charge until). If magnetic energy remains in the reactor La1 when charging is completed, the current flows to the input terminal side via the reactor L1. Then, it returns to the period M1.

  Here, since the switch Sa3 is turned off when the switching element S2 is turned on in M5, no current flows through the capacitor Ca1 via the diode Da1. Therefore, the surge current is prevented from flowing when the switching element S2 is turned on.

  As described above, according to the present embodiment, when the switching element S1 is turned off in the step-up operation, the switch Sa3 is turned on, and the current of the reactor L1 is supplied to the switching power supply device 4 via the switch Sa3, the capacitor Ca1 and the diode Da1. It flows to the output terminal side, and the charge of the capacitor Ca1 is discharged. Thereby, the change of the drain-source voltage of switching element S1 becomes loose, and the switching loss at the time of turn-off can be reduced.

  When the discharge of the capacitor Ca1 is completed, the switching elements Sa1 and Sa2 are turned on and the switch Sa3 is turned off, and a part of the current flowing to the output terminal side is also passed to the reactor La1 via the parasitic diode of the switching element S2. Then, at the same time as or after the switching element S1 is turned on, the switching elements Sa1 and Sa2 are turned off and the switch Sa3 is turned on to charge the capacitor Ca1 with the current of the reactor La1.

  Further, when the switch Sa4 is turned on and the switching element S2 is turned off in the step-down operation, the current of the reactor L1 is caused to flow to the DC power supply 1 side via the diode Da2, the capacitor Ca2, and the switch Sa4, and the charge of the capacitor Ca2 is charged. Discharge. Thereby, the change of the drain-source voltage of the switching element S2 becomes gentle, and the switching loss at the time of turn-off is reduced.

And after discharge of capacitor | condenser Ca2 is complete | finished, switching element Sa1 and Sa2 are turned ON, switch Sa4 is turned OFF, and it supplies with electricity to reactor La1. Then, at the same time as or after the switching element S2 is turned on, the switching elements Sa1 and Sa2 are turned off and the switch Sa4 is turned on to charge the capacitor Ca2 with the current of the reactor La1.
Therefore, when turning off both of the switching elements S1 and S2 with a simple circuit configuration using only one floating power source (a power source that is not constantly connected to the reference potential point) composed of the capacitors Ca1 and Ca2. Loss can be reduced.

  Further, since the capacitors Ca1 and Ca2 are always charged by the current flowing through the reactor La1, the charging operation is lossless if the loss due to the energization of the switches Sa1 and Sa2 and the loss of the diodes Da1 to Da4 are ignored. The efficiency of the power supply device 4 can be further improved. Further, if the period during which the switching elements Sa1 and Sa2 are turned on is controlled to be minimal so that a minimum current sufficient to charge the capacitors Ca1 and Ca2 is accumulated in La1, the current flowing through the switching elements Sa1 and Sa2 The loss that occurs can be reduced as much as possible.

  In addition, during the step-up operation, after the switching element S1 is turned on at M5, only the switch Sa3 is turned on and the switch Sa4 is kept off to prevent the generation of surge current. Therefore, the turn-on loss of the switching element S1 can also be reduced. Further, during the step-down operation, after the switching element S2 is turned on at M5, the generation of the surge current can be prevented by turning on only the switch Sa4 and keeping the switch Sa3 off. Therefore, also in this case, the turn-on loss of the switching element S2 can be reduced.

  In the boosting operation, the switch Sa3 may be always turned on, but the loss of the drive circuit that drives the switch Sa3 can be reduced by turning it on only for a necessary period as described above. Similarly, the switch Sa4 may be always turned on during the step-down operation, but by turning it on only for a necessary period, the loss of the drive circuit that drives the switch Sa4 can be reduced.

(Second Embodiment)
Hereinafter, the same parts as those of the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different parts will be described. As shown in FIG. 8, the second embodiment shows a case where the switching power supply device 4 of the first embodiment is applied to supply driving power to the inverter circuit 11. The inverter circuit 11 is configured by connecting six IGBTs (Insulated Gate Bipolar Transistors) Q1 to Q6 in a three-phase bridge, and a free wheel diode is connected between the collectors and emitters of the IGBTs Q1 to Q6. Yes. Each phase output terminal of the inverter circuit 11 is connected to one end of each phase stator winding of the motor 12. The motor 12 is, for example, a driving motor for an electric vehicle.

  The high potential side terminal 13 (+) and the low potential side terminal 13 (−) of the inverter circuit 11 are connected to the output terminal of the switching power supply device 4. The step-up operation and step-down operation of the switching power supply device 4 are the same as in the first embodiment, and the switching power supply device 4 boosts the voltage of the DC power supply 1 as necessary and supplies it to the inverter circuit 11. Further, during the regenerative operation, the generated voltage of the motor 12 is converted into direct current through the inverter 11, and the direct current voltage is reduced as necessary to charge the direct current power source 1.

The present invention is not limited to the embodiments described above or shown in the drawings, and the following modifications or expansions are possible.
You may use IGBT which provided the freewheel diode in switching element S1 and S2.
In the second embodiment, the motor to be driven by the inverter circuit 11 is not limited to a driving motor for an electric vehicle.

  DESCRIPTION OF SYMBOLS 1 DC power supply, 2 Bidirectional chopper, 3 Loss reduction circuit, 4 Switching power supply device, S1 1st main switching element, S2 2nd main switching element, L1 and La1 reactor, Da1 and Da2 1st and 2nd diode, Ca1 and Ca2 first and second capacitors, Sa1 and Sa2 first and second auxiliary switches, Sa3 and Sa4 first and second switches.

Claims (4)

A first series circuit composed of first and second main switching elements (S1, S2) and connected between the high potential side terminal and the low potential side terminal;
A main inductor (L1) having one end connected to the positive terminal of the DC power supply and the other end connected to a common connection point of the first series circuit;
The first diode (Da1), the first capacitor (Ca1), the first and second switches (Sa3, Sa4), the second capacitor (Ca2), and the second diode (Da2) are connected in parallel to the first series circuit. A second series circuit comprising:
A third series circuit composed of a first auxiliary switching element (Sa1) and a third diode (Da3) connected in parallel to the series part from the first diode to the second capacitor in the second series circuit;
A fourth series circuit composed of a fourth diode (Da4) and a third auxiliary switching element (Sa2) connected in parallel to the series part from the first capacitor to the second diode in the second series circuit;
An auxiliary inductor (La1) connected between a common connection point of the third series circuit and a common connection point of the fourth series circuit;
A cathode of the first diode is connected in common with one end of the second main switching element;
An anode of the second diode is connected in common with one end of the first main switching element;
An anode of the third diode is connected in common with a cathode of the second diode;
The cathode of the fourth diode is connected in common with the anode of the first diode. When boosting the voltage of the DC power supply,
Always turn off the second switch,
The first switch is turned on when the first main switching element is turned on after at least the first and second auxiliary switching elements are turned on to energize the auxiliary inductor, and the auxiliary switch is turned on. Control to charge the first capacitor (Ca1) with a current flowing by magnetic energy accumulated in the reactor,
The first switch is turned on when the first main switching element is turned off, and the current flowing through the main inductor is transferred to the first switch, the first capacitor, and the first diode. The power converter according to claim 1, wherein the power converter is controlled to flow. When stepping down the voltage of the DC power supply,
Always turn off the first switch,
The second switch is turned on at least when the second main switching element is turned on after at least the first and second auxiliary switching elements are turned on to energize the auxiliary inductor. Control to charge the second capacitor with a current flowing by magnetic energy stored in the reactor,
Further, the second switch is turned on when the second main switching element is turned off, and the current flowing through the main inductor is commutated to the second diode, the second capacitor, and the second switch. The power conversion device according to claim 1, wherein control is performed so that   4. The power conversion according to claim 1, wherein each of the first switch and the second switch is configured as a bidirectionally conductive switch using a semiconductor switching element. 5. apparatus.

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