JP2009171639A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion device which can suppress the heat generation of switching elements, can suppress a loss caused by the heat generation, and can use a cooling means which is low in cooling performance compared with a conventional means. <P>SOLUTION: A series circuit composed of first and second switching elements S1, S2, and a series circuit composed of third and fourth switching elements S3, S4 are connected in parallel with each other, and a reverse-parallel diode is connected to each switching elements S1 to S4. Input terminals are connected to a connecting point of the switching elements S1, S2 and a connecting point of the switching elements S3, S4 via coils. When an alternate current input from a power supply is converted into a direct current, the switching elements S1 to S4 are controlled by a control device so that a period T1 for simultaneously switching the switching elements S1, S4 and a period T2 for simultaneously switching the switching elements S2, S3 are alternated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device having a function of converting alternating current into direct current.

  Conventionally, as an uninterruptible power supply, as shown in FIG. 7, a power transformer 54 in which an alternating current is input to the primary side from an external commercial AC power source 51 and a load 52 and a bidirectional inverter 53 are connected to the secondary side. And a configuration in which a battery 55 is connected to the bidirectional inverter 53 (see, for example, Patent Document 1). The power transformer 54 normally supplies alternating current to the load 52 using commercial alternating current as a power source and charges the battery 55 via the bidirectional inverter 53. In the event of a power failure, alternating current is supplied from the battery 55 to the power transformer 54 via the bidirectional inverter 53, and power is supplied to the load 52. The bidirectional inverter 53 includes a low-pass filter 53a that blocks high-frequency components and a bridge circuit that includes four switching elements Q1, Q2, Q3, and Q4. An FET is used as a switching element. When the bidirectional inverter 53 operates as a charger, the switching elements Q1 and Q2 are set to an off state, and the switching unit Q3 and Q4 are switched by the control unit 56, whereby the current paths a and b shown in FIG. A current flows to charge the battery 55. 7 indicates the case where the direction of the AC voltage from the power transformer 54 is positive, and the current path b illustrated by the two-dot chain line in FIG. 7 indicates the AC path from the power transformer 54. The case where the voltage direction is negative is shown.

In order to reduce fuel consumption and reduce exhaust gas, so-called hybrid vehicles in which driving wheels are driven by motors at the start and low speed ranges and driving wheels are driven by engines at medium and high speed ranges have been put into practical use. However, in recent years, so-called plug-in hybrid vehicles that can charge a battery with a household power supply (system power supply) have been considered in order to further reduce the environmental load. For example, when the battery can be charged with midnight power and the distance that can be driven in the electric vehicle mode by the motor is increased, the ratio of using electricity to gasoline etc. increases, so carbon dioxide emissions compared to general hybrid vehicles Reduction and air pollution prevention effects can be expected. In addition, the power generation cost of the system power supply is lower than that of generating electricity individually, and if it is charged using midnight power with a low charge, the fuel cost can be reduced. Also in this case, a bidirectional inverter is provided for charging the battery and for supplying electric power charged in the battery to the motor as an alternating current.
JP 2003-143772 A

  In the conventional bidirectional inverter, when AC input is converted to DC, the switching elements Q1 and Q2 constituting the upper arm of the inverter are held in the off state, and only the lower arm switching elements Q3 and Q4 operate. For this reason, the time during which current flows through two of the four switching elements increases, heat generation increases, and loss increases. Therefore, there is a problem that a cooling means having a high cooling capacity, for example, a large fan is required for air cooling, and the apparatus is also increased in size.

  The present invention has been made in view of the above problems, and an object thereof is to suppress a heat generation amount of a switching element and a loss due to heat generation in a power conversion device having a function of converting alternating current into direct current. In addition, an object of the present invention is to provide a power conversion device that can use a cooling means having a cooling function lower than that in the conventional case when supplying the same power.

  In order to achieve the above object, an invention according to claim 1 is a power conversion device including a conversion unit that is connected to an AC power source and converts AC input from the AC power source into DC. A series circuit of the first switching element and the second switching element and a series circuit of the third switching element and the fourth switching element are connected in parallel, and a diode is connected in antiparallel to each switching element. A bridge circuit is provided. The bridge circuit includes an input terminal connected via a coil to a connection point between the first switching element and the second switching element and a connection point between the third switching element and the fourth switching element. . A first output terminal having an anode connected to a connection point between the first switching element and the third switching element of the bridge circuit via a diode on the connection point side; the second switching element; And a second output terminal connected to a connection point with the fourth switching element. Furthermore, when the alternating current input from the alternating current power source is converted into direct current, the first switching element and the fourth switching element are simultaneously switched, and the second switching element and the third switching element are simultaneously switched. And a control means for controlling each of the switching elements so as to alternate with each other. Here, each diode connected in antiparallel to each switching element is not limited to an independent component, and may be a parasitic diode of the switching element.

  The bridge circuit functions as a boost converter by outputting the energy stored in the coil when each switching element is switched. In the configuration in which the first switching element and the third switching element are held in the OFF state and the second switching element and the fourth switching element are switched, the switching is repeated with a current flowing through one switching element. The heating of the switching element increases. And in order to suppress heat_generation | fever, the cooling means which has a big cooling capacity is needed, and an apparatus enlarges. However, in this invention, the state in which the first switching element and the fourth switching element are simultaneously switched and the state in which the second switching element and the third switching element are simultaneously switched are repeated. And the current path in the ON state of the two switching elements is branched, the magnitude of the current flowing through one switching element is reduced, and the heat generation of the switching elements is suppressed. Therefore, when the same electric power is supplied, the cooling can be performed by a cooling means having a cooling capacity smaller than that in the conventional case, and the apparatus can be downsized.

  According to a second aspect of the present invention, in the first aspect of the present invention, a fifth switching element is connected in antiparallel with the diode connected to the first output terminal, and the control means includes the output terminal. Are connected to a DC power source, each switching element constituting the conversion unit is controlled to convert the DC supplied from the DC power source into an AC and output it to the input terminal. In the present invention, the current converter can be used as a bidirectional inverter, and the bidirectional inverter can be miniaturized.

  According to the present invention, in a power conversion device having a function of converting alternating current into direct current, heat generation of the switching element is suppressed, loss due to heat generation is suppressed, and when the same electric power is supplied, the power conversion device is compared with the conventional case. Thus, a cooling means having a low cooling function can be used.

(First embodiment)
A first embodiment of the present invention will be described below with reference to FIGS.
As shown in FIG. 1, the power conversion device 11 includes a conversion unit 13 that is connected to an AC power supply 12 and converts AC input from the AC power supply 12 into DC, that is, an inverter. In this embodiment, a system power supply is used as the AC power supply 12. The converter 13 includes a series circuit of the first switching element S1 and the second switching element S2 and a series circuit of the third switching element S3 and the fourth switching element S4 connected in parallel to form a bridge circuit. Diodes D1 to D4 are connected in antiparallel to the switching elements S1 to S4, respectively. In this embodiment, insulated gate bipolar transistors (IGBTs) are used as the switching elements S1 to S4, and diodes D1 to D4 are connected in antiparallel between the collectors and emitters of the switching elements S1 to S4. .

  A connection point between the emitter of the first switching element S1 and the collector of the second switching element S2 is connected to the input terminal 15a via the coil 14a. A connection point between the emitter of the third switching element S3 and the collector of the fourth switching element S4 is connected to the input terminal 15b via the coil 14b.

  A connection point between the collector of the first switching element S1 and the collector of the third switching element S3 is connected to the first output terminal 16a via the diode D5. The diode D5 is connected such that the anode is on the connection point side between the first switching element S1 and the third switching element S3. A connection point between the emitter of the second switching element S2 and the emitter of the fourth switching element is connected to the second output terminal 16b. Both output terminals 16a and 16b are connected to a charger 17 for charging the battery E.

  The control device 18 as a control means for controlling the switching elements S1 to S4 outputs a control signal to the gates of the switching elements S1 to S4. The control device 18 includes a microcomputer (not shown) and controls the switching elements S1 to S4 based on a program memory stored in the memory of the microcomputer. When charging battery E, control device 18 controls switching elements S1 to S4 so that the phase of the alternating current is the same as the phase of the alternating voltage.

  The control device 18 converts the alternating current input from the alternating current power supply 12 into direct current, the period T1 during which the first switching element S1 and the fourth switching element S4 are simultaneously switched, and the second switching element S2 and the third switching element. The switching elements S1 to S4 are controlled so that the periods T2 during which S3 is simultaneously switched are alternated.

Next, the operation of the power conversion device 11 configured as described above will be described.
When converting the AC voltage input from the system power source which is the AC power source 12 into a DC voltage that can be charged by the battery E, that is, when charging the battery E with the system power source, the switching elements S1 to S4 are controlled by the control device. Switching control is performed so that the supplied AC voltage is converted into a DC voltage by a control signal from 18, and the converted DC voltage is supplied to the charger 17. At that time, each of the switching elements S1 to S4 is controlled so that the two coils 14a and 14b function as coils of the booster circuit, and the phase of the supplied AC current is the same as the phase of the AC voltage. Be controlled.

  Specifically, as shown in FIG. 2A, the period T2 in which the second switching element S2 and the third switching element S3 are simultaneously switched, and the first switching element S1 and the fourth switching element S4 are simultaneously switched. The period T1 is controlled so as to be repeated at a predetermined cycle (a cycle corresponding to the frequency of the system power supply).

  When the direction of the current input from the AC power supply 12 is in a state of returning from the AC power supply 12 to the converter 13 through the coil 14b and returning to the AC power supply 12 through the coil 14a, as shown in FIG. The first and fourth switching elements S1, S4 are maintained in the OFF state, and the second and third switching elements S2, S3 are switched simultaneously. When the second and third switching elements S2 and S3 are turned on, the current supplied from the AC power source 12 is a path of the coil 14b → the second switching element S2 → the diode D4 → the coil 14a → and the coil 14b → The electric energy is accumulated in the coils 14a and 14b through the path of the diode D1 → the third switching element S3 → the coil 14a →. From this state, when the second and third switching elements S2 and S3 are turned off, the energy stored in the coils 14a and 14b is applied and the coil 14b → the diode D1 as shown in FIG. 3B. → Current flows in the order of charger 17 → diode D4 → coil 14a →.

  On the other hand, when the first, third, and fourth switching elements S1, S3, and S4 are maintained in the OFF state and only the second switching element S2 is switched as in the prior art, as shown in FIG. The current path becomes one. That is, when the second switching element S2 is turned on, the current supplied from the AC power source 12 flows along a path of the coil 14b → second switching element S2 → diode D4 → coil 14a →, and electric energy is supplied to the coils 14a and 14b. Is accumulated. In this state, when the second switching element S2 is turned off, the energy accumulated in the coils 14a and 14b is applied, and as shown in FIG. 3D, the coil 14b → the diode D1 → the charger 17 → A current flows so that the diode D4 → the coil 14a →.

  Further, as shown in FIG. 4A, the direction of the current input from the AC power source 12 is a state in which the AC power source 12 passes through the coil 14a toward the converter 13 and returns to the AC power source 12 through the coil 14b. In this case, the second and third switching elements S2 and S3 are maintained in the off state, and the first and fourth switching elements S1 and S4 are simultaneously switched. When the first and fourth switching elements S1 and S4 are turned on, the current supplied from the AC power source 12 is a path of the coil 14a → the diode D3 → the first switching element S1 → the coil 14b →, and the coil 14a → The electric current is accumulated in the coils 14a and 14b through the path of the fourth switching element S4 → the diode D2 → the coil 14b →. When the first and fourth switching elements S1 and S4 are turned off from that state, the energy stored in the coils 14a and 14b is applied and the coil 14a → the diode D3 → as shown in FIG. A current flows in the order of charger 17 → diode D2 → coil 14b →.

  On the other hand, when the first, second, and third switching elements S1, S2, and S3 are maintained in the OFF state and only the fourth switching element S4 is switched as in the prior art, as shown in FIG. The current path becomes one. That is, when the fourth switching element S4 is turned on, the current supplied from the AC power supply 12 flows along a path of the coil 14a → the fourth switching element S4 → the diode D2 → the coil 14b →, and the electric energy is supplied to the coils 14a and 14b. Is accumulated. From this state, when the switching element S4 is turned off, the energy accumulated in the coils 14a and 14b is applied and the coil 14a → the diode D3 → the charger 17 → the diode D2 as shown in FIG. 5B. The current flows so as to be the coil 14b →.

  That is, in the prior art, as shown in FIG. 2B, the second switching element S2 is controlled to be turned on / off during a period T2 that is half of one cycle of the alternating current input from the alternating current power supply 12, and the remaining half In the period T1, the fourth switching element S4 is controlled to be turned on and off, and each current flows through only one switching element. On the other hand, in this embodiment, as shown in FIG. 2A, the second and third switching elements S2 and S3 are simultaneously turned on and off during a period T2 that is half of one cycle of the alternating current input from the alternating current power supply 12. The first and fourth switching elements S1 and S4 are simultaneously turned on and off in the remaining half period T1. That is, in this embodiment, even though the switching times of the switching elements S1 to S4 are the same, the current path is branched into two paths, and the current flowing through the switching elements S1 to S4 is small (almost halved). As a result, heat generation as a whole of the conversion unit 13 is suppressed.

  Further, when the second and third switching elements S2 and S3 are turned on, the current is charged so as to charge the parasitic capacitances of the diode D5, the diode D1, and the diode D4 from the charger 17 side in a state where the diode D1 and the diode D4 are in parallel. Flows. That is, the parasitic capacitance is charged in a state where the diode D1 and the diode D5 are in two series and in a state where the diode D4 and the diode D5 are in two series. Compared with the case where the diode D5 does not exist, the charging time is longer. Is reduced, and the on-loss of the second and third switching elements S2 and S3 is reduced. Further, when the first and fourth switching elements S1 and S4 are turned on, the current is charged so as to charge the parasitic capacitances of the diode D5, the diode D2, and the diode D3 from the charger 17 side with the diode D2 and the diode D3 in parallel. Flows. That is, the parasitic capacitance is charged in a state where the diode D2 and the diode D5 are in two series and in a state where the diode D3 and the diode D5 are in two series, as compared with the case where the diode D5 does not exist as described above. As a result, the charging time is shortened and the on-loss of the first and fourth switching elements S1 and S4 is reduced.

According to this embodiment, the following effects can be obtained.
(1) In the power converter 11, the series circuit of the first switching element S1 and the second switching element S2 and the series circuit of the third switching element S3 and the fourth switching element S4 are connected in parallel, and each switching A conversion unit 13 is provided in which diodes D1 to D4 are connected in antiparallel to the elements S1 to S4, respectively. The input terminals 15a and 15b are connected to the connection point between the first switching element S1 and the second switching element S2 and the connection point between the third switching element S3 and the fourth switching element S4 via the coils 14a and 14b, respectively. Has been. When the alternating current input from the alternating current power source 12 is converted into direct current, the first switching element S1 and the fourth switching element S4 are simultaneously switched, and the second switching element S2 and the third switching element S3 are simultaneously switched. A control device 18 that controls each of the switching elements S1 to S4 is provided so as to alternate with the periods T2. Therefore, when each switching element S1 to S4 is turned on, there are two current paths, the current flowing through each switching element S1 to S4 in the on state is reduced, heat generation is suppressed, and when the same power is supplied, Compared to the above, cooling is possible with a cooling means having a small cooling capacity, and the apparatus can be miniaturized. In addition, compared to a configuration in which only a specific switching element is turned on, the life of the switching element that is turned on is prolonged, and the life of the apparatus is also prolonged.

  (2) In the power converter 11, the first output terminal 16a is connected to the connection point between the first switching element S1 and the third switching element S3 via the diode D5 whose anode is on the connection point side. A second output terminal 16b is connected to a connection point between the switching element S2 and the fourth switching element S4. Therefore, when the second and third switching elements S2 and S3 are turned on, the diode D1 and the diode D5 are in a two-series state and the diode D4 and the diode D5 are in a two-series state. A current flows to charge the parasitic capacitance of D5. Further, when the first and fourth switching elements S1 and S4 are turned on, the diodes D2, D3 and D3 are connected in two series, and the diodes D3 and D5 are connected in two series. A current flows to charge the parasitic capacitance of D5. Therefore, when the switching elements S1 to S4 are turned on, the charging time of the parasitic capacitances of the diodes D1, D2, D3, D4, and D5 is shortened and the recovery time is shortened, compared with the case where the diode D5 is not present. The ON loss of S1 to S4 is reduced.

  (3) As each of the switching elements S1 to S4, an insulated gate bipolar transistor (IGBT) is used. Therefore, even when the current flowing through each of the switching elements S1 to S4 is large (for example, 100 A or more), the durability of the switching elements S1 to S4 is improved.

(Second Embodiment)
Next, an embodiment in which the present invention is embodied in a bidirectional inverter of a plug-in hybrid vehicle will be described with reference to FIG. In addition, the same part as 1st Embodiment attaches | subjects the same code | symbol, and abbreviate | omits detailed description.

  A capacitor 20 is connected between a connection point between the coil 14a and the input terminal 15a and a connection point between the coil 14b and the input terminal 15b. The coils 14a and 14b and the capacitor 20 constitute a smoothing filter. The coils 14 a and 14 b are connected to the system power supply connection portion 21. The system power supply connection unit 21 includes a plug 22 that can be connected to an outlet of the system power supply and an outlet 23 as an adapter that can be connected to a plug of home appliances. Plug 22 and outlet 23 are connected to input terminals 15a and 15b via switches 24 and 25, respectively. Each of the switches 24 and 25 is constituted by a relay contact c. When the relay is on, the switches 24 and 25 are held in a state where the plug 22 can be energized with the converter 13 and the outlet 23 is converted when the relay is off. It is comprised so that the part 13 may be hold | maintained in the state which can be supplied with electricity.

  An insulation transmission unit 26 is connected between the battery E as a DC power source and the conversion unit 13. The insulation transmission unit 26 includes a transformer (not shown) and an H bridge circuit (not shown) connected to the primary side and the secondary side of the transformer. And the insulation transmission part 26 has the function which each switching element of an H bridge circuit is controlled by the control apparatus 18, converts the direct current of the battery E into the direct current of the use voltage of household appliances, and supplies it to the conversion part 13, and a system power supply The battery E is charged with the current supplied from the converter and converted into direct current by the converter 13.

  A fifth switching element S5 is connected in antiparallel with the diode D5. An IGBT is used as the fifth switching element S5. The fifth switching element S5 is controlled by the control device 18. And when the conversion part 13 converts the direct current supplied from the battery E through the insulation transmission part 26 into alternating current, and outputs it to the outlet 23, it is hold | maintained in an ON state and the conversion part 13 is supplied from a system power supply. When the alternating current to be converted into direct current is output to the insulation transmission unit 26, control is performed so as to be maintained in the off state.

  In this embodiment, when the system power is supplied from the plug 22 to the conversion unit 13 to charge the battery E, the switching elements S1 to S4 are controlled in the same manner as in the first embodiment.

  On the other hand, when an electric product connected to the outlet 23 is driven using the battery E as a power source, direct current is supplied from the output terminals 16a and 16b to the conversion unit 13 using the battery E as a power source. And each switching element S1-S4 converts the direct current supplied to the conversion part 13 from the output terminals 16a and 16b into alternating current, and the alternating voltage of predetermined voltage and predetermined frequency (for example, 100V, 60Hz) is supplied from the outlet 23. As can be obtained, switching control is performed by a control signal from the control device 18. Specifically, the switching elements S1, S4 and the switching elements S2, S3 are alternately turned on and off.

  Therefore, in this embodiment, in the power converter provided with the bidirectional inverter, when the battery E is charged, the heat generation of each of the switching elements S1 to S4 is suppressed. Cooling is possible with a small cooling means, and the apparatus can be miniaturized.

The embodiment is not limited to the above, and may be embodied as follows, for example.
O Each switching element S1-S4 and 5th switching element S5 which comprise the conversion part 13 may use not only IGBT but MOSEFT and a power bipolar transistor, for example. Since the MOSFET has a parasitic diode, unlike the case where an IGBT having no parasitic diode is used as a switching element, the trouble of connecting the diode becomes unnecessary and the configuration is simplified.

  The AC power supply 12 is not limited to the system power supply, and may be configured to supply AC generated by a generator. For example, in a hybrid vehicle, a motor generator is used as a traveling motor, and the battery E is charged with electric power generated when the motor generator functions as a generator. Therefore, in the case of a hybrid vehicle, the motor generator may be configured to be electrically connectable to the input terminals 15a and 15b of the conversion unit 13 via a switch.

  ○ When the converter 13 does not function as a bidirectional inverter and performs only the operation of converting alternating current to direct current, the converter 13 is not limited to the configuration connected to the charger 17 and is directly connected to an electric device that operates with direct current. It is good also as a structure connected via a connector.

The following technical idea (invention) can be understood from the embodiment.
(1) In the invention described in claim 1 or claim 2, a MOSFET is used as each switching element, and the diode connected in antiparallel to each switching element is constituted by a parasitic diode of the MOSFET.

(2) In the invention according to claim 1 or 2, an insulated gate bipolar transistor is used as each of the switching elements.
(3) A series circuit of the first switching element and the second switching element and a series circuit of the third switching element and the fourth switching element are connected in parallel, and a diode is connected in antiparallel to each switching element. A switching element control method in a bidirectional inverter provided with a bridge circuit,
When the alternating current input from the alternating current power source is converted into direct current, a period in which the first switching element and the fourth switching element are simultaneously switched in a state in which the reverse flow of the direct current output is suppressed by the diode; The switching element control method of controlling each said switching element so that the period which switches a 2nd switching element and a 3rd switching element simultaneously may alternate.

The circuit diagram of the power converter device in a 1st embodiment. (A) is a schematic diagram showing the relationship between the on / off states of switching elements S2 and S3 and switching elements S1 and S4 and current waveforms, and (b) is the on / off state and current waveforms of switching elements S2 and S4. The schematic diagram which shows the relationship. (A), (b) is a circuit diagram explaining operation | movement when switching element S2, S3 is switched simultaneously, (c), (d) is a circuit explaining operation | movement when only switching element S2 is switched. Figure. (A), (b) is a circuit diagram explaining operation | movement when switching element S1, S4 is switched simultaneously. (A), (b) is a circuit diagram explaining operation | movement when only switching element S4 is switched. The circuit diagram which shows the power converter device of 2nd Embodiment. The circuit diagram explaining operation | movement of the bidirectional inverter of a prior art.

Explanation of symbols

  D1, D2, D3, D4, D5 ... diode, S1 ... first switching element, S2 ... second switching element, S3 ... third switching element, S4 ... fourth switching element, S5 ... fifth switching element, T1, T2 ... Period, 11 ... Power converter, 12 ... AC power supply, 13 ... Conversion unit, 14a, 14b ... Coil, 15a, 15b ... Input terminal, 16a ... First output terminal, 16b ... Second output terminal, 18 ... A control device as a control means.

Claims (2)

A power conversion device including a conversion unit that is connected to an AC power source and converts AC input from the AC power source into DC,
A bridge circuit in which a series circuit of a first switching element and a second switching element and a series circuit of a third switching element and a fourth switching element are connected in parallel, and a diode is connected in antiparallel to each switching element. When,
An input terminal connected via a coil to a connection point between the first switching element and the second switching element and a connection point between the third switching element and the fourth switching element of the bridge circuit;
A first output terminal having an anode connected to a connection point between the first switching element and the third switching element of the bridge circuit via a diode on the connection point side;
A second output terminal connected to a connection point between the second switching element and the fourth switching element;
When the alternating current input from the alternating current power source is converted into direct current, a period for simultaneously switching the first switching element and the fourth switching element and a period for simultaneously switching the second switching element and the third switching element are provided. And a control means for controlling each of the switching elements so as to alternate with each other.   A fifth switching element is connected in antiparallel with the diode connected to the first output terminal, and the control means is configured to switch each of the switching units constituting the conversion unit in a state where the output terminal is connected to a DC power source. The power converter according to claim 1, wherein the element is controlled so as to convert direct current supplied from the direct current power source into alternating current and output the alternating current to the input terminal.

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