JP2012070492A - Charging and discharging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging and discharging system of a secondary battery for realizing miniaturization and a low loss.SOLUTION: The charging and discharging system comprises: a charging and discharging circuit 51 that charges and discharges multiple secondary batteries; switch circuits 53 and 54 that change a connection state of the multiple second batteries to a serial connection or a parallel connection; and a control circuit 55 that controls the charging and discharging circuit 51 and the switch circuits 53 and 54. By appropriately opening and closing the switch circuits 53 and 54, opposite end voltages of the switch circuits 53 and 54 are lowered than a DC power distribution line voltage when charging, and the opposite end voltages of the switch circuits 53 and 54 are made higher than the DC power distribution line voltage when discharging. Accordingly, the secondary battery cells are charged and discharged by a step-down operation of the charging and discharging circuit 51.

Description

  The present invention relates to a charge / discharge system for a secondary battery that backs up, for example, a solar battery.

  FIG. 13 shows a conventional charge / discharge system for a secondary battery. In a conventional charging / discharging system, a charging circuit and a discharging circuit are used for charging / discharging a secondary battery (see Patent Document 1).

JP 2009-159655 A

  In the conventional charging / discharging system, a charging circuit and a discharging circuit are used for charging and discharging the secondary battery, respectively, and a large-capacity converter is required. Therefore, it is difficult to reduce the size of the entire system. It was. In addition, since the voltage is stepped up and down via the converter, it is difficult to increase the charge / discharge efficiency, and there is a problem that loss occurs.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a small-sized and low-loss charge / discharge system.

  In order to achieve the above object, a charge / discharge system of the present invention is a charge / discharge system in which a plurality of secondary battery cells are connected, and a charge / discharge circuit that charges and discharges the secondary battery cells, and the plurality of 2 It is characterized by comprising connection switching means for changing the connection state of the next battery cell in series or in parallel.

  In this invention, it further comprises a control means for controlling the connection switching means, the control means according to the magnitude relationship between the DC distribution line voltage applied to the charge / discharge circuit and the voltage across the connection switching means. It is preferable to control the connection switching means.

  In the present invention, when the secondary battery cell is charged, the control means connects any of the secondary battery cells in parallel, and makes the voltage across the connection switching means lower than the DC distribution line voltage. It is preferable.

  In the present invention, when the secondary battery cell is discharged, the control means connects any of the secondary battery cells in series, and makes the voltage across the connection switching means higher than the DC distribution line voltage. It is preferable.

  In the present invention, it is preferable that the charge / discharge circuit is constituted by a bidirectional half-bridge converter circuit having a bidirectional switching element on the primary side of the transformer, and performs charge / discharge by a step-down operation.

  In this invention, it is preferable that the charging / discharging circuit has a direct charging / discharging path for charging / discharging directly from the DC distribution line and a charging / discharging path for charging / discharging via the bidirectional half-bridge converter circuit.

  In the present invention, it is preferable that the charge / discharge circuit is constituted by a bidirectional power conversion circuit having a bidirectional switching element, and performs charge / discharge by a step-down operation.

  In this invention, it is preferable that the said charging / discharging circuit has a charging circuit corresponding to each secondary battery cell.

  In this invention, the charging / discharging circuit can be connected in series with any of the secondary battery cells, and is used for discharging, a discharging circuit directly connected to the DC distribution line via a diode in the discharging direction. It is preferable to have a charging circuit that charges a secondary battery cell that is not present.

  In the present invention, the bidirectional switching element is preferably a bidirectional switching element having a lateral transistor structure using GaN / AlGaN.

  According to the charging / discharging system of the present invention, the connection state of a plurality of secondary batteries can be arbitrarily changed in series or in parallel, and the charging / discharging circuit only performs step-down operation in either case of charging or discharging. Thus, the secondary battery can be charged and discharged. Thereby, size reduction and high efficiency of a system can be achieved.

The block diagram which shows the structure of the power distribution system provided with the charging / discharging system by one Embodiment of this invention. The block diagram which shows the structure of the control unit with which the power distribution system was equipped. The block diagram which shows the structure of the charging / discharging system. The block diagram which shows the structure of the charging / discharging circuit of the charging / discharging system. The circuit diagram which shows the modification of the charging / discharging circuit of the charging / discharging system. The block diagram which shows the structure which shows the modification of the same charging / discharging system. The block diagram which shows the structure which shows the modification of the same charging / discharging system. The top view which shows the structure of a bidirectional | two-way switching element (single gate). The enlarged view of the range A in FIG. BB sectional drawing in FIG. The top view which shows the structure of a bidirectional | two-way switch element (dual gate). CC sectional drawing in FIG. The block diagram which shows the conventional charging / discharging system.

  A charge / discharge system for a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example in which the charge / discharge system according to the embodiment is applied to a hybrid point distribution system including a solar battery and a secondary battery and capable of distributing AC power and DC power. As shown in FIG. 1, a home is provided with a power distribution system 1 that supplies power to various devices (such as lighting devices, air conditioners, home appliances, and audiovisual devices) installed in the home. In addition to operating various devices using commercial AC power (AC power) 2 as power, the power distribution system 1 also supplies power from a solar cell (DC power) 3 that generates power using sunlight as power. The solar cell 3 is composed of, for example, a plurality of cells 4. The power distribution system 1 supplies power not only to the DC device 5 that operates by inputting a DC power supply (DC power supply) but also to the AC device 6 that operates by inputting an AC power supply (AC power supply). Note that the solar cell 3 constitutes a DC power source and a self-supporting power generation battery, and the DC device 5 and the AC device 6 constitute a load.

  The power distribution system 1 is provided with a power supply control unit 7 and a DC distribution board (built-in DC breaker) 8 as a distribution board of the system 1. The power supply control unit 7 is configured with, for example, a CPU and is provided with a control unit 7a that performs overall control of the operation of the unit 7. In addition, the power distribution system 1 is provided with a load control unit 9 and a relay unit 10 as devices for controlling the operation of the DC device 5 in the house.

  An AC distribution board 11 for branching an AC power supply is connected to the power supply control unit 7 via an AC power line 12. The power supply control unit 7 is connected to the commercial AC power supply 2 through the AC distribution board 11 and is connected to the solar cell 3 through the DC system power line 13. The power supply control unit 7 takes in AC power from the AC distribution board 11 and DC power from the solar cell 3 and converts these powers into DC power of a predetermined voltage as a device power supply. The power supply control unit 7 outputs the converted DC power to the DC distribution board 8 via the DC power line 14 or to the storage battery unit 16 via the DC power line 15 to output the same power. Or charge. The power supply control unit 7 can not only take AC power from the AC distribution board 11 but also convert the power of the solar cell 3 and the storage battery unit 16 to AC power and supply it to the AC distribution board 11. The power supply control unit 7 exchanges data with the DC distribution board 8 via the signal line 17.

  The DC distribution board 8 is a kind of breaker that supports DC power. The DC distribution board 8 branches the DC power input from the power supply control unit 7, and outputs the branched DC power to the load control unit 9 via the DC power line 18 or via the DC power line 19. Output to the relay unit 10. The DC distribution board 8 exchanges data with the load control unit 9 through the signal line 20 and exchanges data with the relay unit 10 through the signal line 21. The DC distribution board 8, the load control unit 9, and the relay unit 10 have a control unit (not shown).

  A plurality of DC devices 5, 5... Are connected to the load control unit 9. These DC devices 5 are connected to the load control unit 9 via a DC supply line 22 that can carry both DC power and data by a pair of lines. The DC supply line 22 superimposes a communication signal for transmitting data by a high-frequency carrier wave on a DC voltage serving as a power source for the DC device, so-called power line carrier communication. Transport to. The load control unit 9 acquires the DC power supply information of the DC device 5 via the DC power line 18, and which DC device 5 is selected based on the operation command obtained from the DC distribution board 8 via the signal line 20. Know what to control. Then, the load control unit 9 controls the operation of the DC device 5 by outputting a DC voltage and an operation command to the instructed DC device 5 through the DC supply line 22.

  The load control unit 9 is connected via a DC supply line 22 to a switch 23 that is operated when switching the operation of the DC device 5 in the house. The load control unit 9 is connected to a sensor 24 that detects a radio wave transmitted from an infrared remote controller, for example, via a DC supply line 22. Therefore, not only the operation instruction from the DC distribution board 8 but also the operation of the switch 23 and the detection of the sensor 24, a communication signal is sent to the DC supply line 22 to control the DC device 5.

  A plurality of DC devices 5, 5... Are connected to the relay unit 10 via individual DC power lines 25. The relay unit 10 acquires the DC power supply of the DC device 5 through the DC power line 19 and determines which DC device 5 is to be operated based on an operation command obtained from the DC distribution board 8 through the signal line 21. To grasp. The relay unit 10 controls the operation of the DC device 5 by turning on / off the power supply to the DC power line 25 with respect to the instructed DC device 5 using a built-in relay. In addition, a plurality of switches 26 for manually operating the DC device 5 are connected to the relay unit 10, and the DC power line 25 is turned on and off by the relay by operating the switch 26, thereby enabling the DC unit 5 to operate the DC unit 5. The device 5 is controlled.

  The DC distribution board 8 is connected to a DC outlet 27 built in a house in the form of a wall outlet or a floor outlet, for example, via a DC power line 28. If a plug (not shown) of a DC device is inserted into the DC outlet 27, DC power can be directly supplied to the device.

  Further, a power meter 29 capable of remotely metering the amount of use of the commercial AC power supply 2 is connected between the commercial AC power supply 2 and the AC distribution board 11. The power meter 29 is equipped with not only a function of remote meter reading of the amount of commercial power used, but also a function of power line carrier communication and wireless communication, for example. The power meter 29 transmits the meter reading result to an electric power company or the like via power line communication or wireless communication.

  The power distribution system 1 is provided with a network system 30 that enables various devices in the home to be controlled by network communication. The network system 30 is provided with a home server 31 as a control unit of the system 30. The home server 31 is connected to a management server 32 outside the home via a network N such as the Internet, and is connected to a home device 34 via a signal line 33. The in-home server 31 operates using DC power acquired from the DC distribution board 8 via the DC power line 35 as a power source.

  A control box 36 that manages operation control of various devices in the home by network communication is connected to the home server 31 via a signal line 37. The control box 36 is connected to the power supply control unit 7 and the DC distribution board 8 via the signal line 17 and can directly control the DC device 5 via the DC supply line 38. For example, a gas / water meter 39 capable of remotely metering the amount of gas used or the amount of water used is connected to the control box 36 and also connected to the operation panel 40 of the network system 30. The operation panel 40 is connected to a monitoring device 41 including, for example, a door phone slave, a sensor, and a camera.

  When the in-home server 31 inputs an operation command for various devices in the home via the network N, the home server 31 notifies the control box 36 of the instruction, and operates the control box 36 so that the various devices operate in accordance with the operation command. . The in-home server 31 can provide various information acquired from the gas / water meter 39 to the management server 32 through the network N. At the same time, when it is detected from the operation panel 40 that an abnormality has been detected in the monitoring device 41, this is also provided to the management server 32 through the network N.

  FIG. 2 shows the power supply control unit 7 and the charge / discharge system 50 provided in the power distribution system 1. The power supply control unit 7 includes a bidirectional AC / DC converter 42 and a maximum output point control DC / DC converter 45. The bidirectional AC / DC converter 42 performs conversion from DC power to AC power and conversion from AC power to DC power. Therefore, the bidirectional AC / DC converter 42 includes an AC / DC converter 43 that converts and outputs an input AC voltage to a DC voltage, and a DC / AC inverter 44 that converts an input DC voltage to an AC voltage. The AC / DC converter 43 converts the AC voltage input from the commercial AC power supply 2 into a DC voltage and outputs the DC voltage to the DC device 5 and the storage battery unit 16. The DC / AC inverter 44 converts the DC voltage input from the solar cell 3 or the storage battery unit 16 into an AC voltage and reversely flows to the commercial AC power source 2. The charge / discharge system 50 is provided in the power supply control unit 7 or the storage battery unit 16.

  The power supply control unit 7 is provided with a maximum output point control DC / DC converter 45 that outputs the power of the solar cell 3 at a point with the highest power efficiency (maximum power point). The maximum output point control DC / DC converter 45 is connected to the solar cell 3 and is also connected to the bidirectional AC / DC converter 42 and the DC device 5. The maximum output point control DC / DC converter 45 corresponds to the output voltage conversion means.

  The maximum output point control is a kind of voltage output control called so-called MPPT (Maximum Power Point Tracking) control. By the way, the solar cell 3 has a point at which power can be most efficiently output at maximum, that is, a maximum power point. When power is generated under a condition that satisfies this point, power output without waste is possible. However, in the solar cell 3, the IV characteristic changes every moment depending on the amount of solar radiation and temperature, and the maximum power point changes accordingly each time. Therefore, the maximum output point control DC / DC converter 45 automatically changes the input voltage in accordance with the power generation state of the solar cell 3, thereby causing the voltage of the solar cell 3, that is, the maximum power point to follow. 3 is extracted with the most efficient power. The maximum output point control is also called a hill-climbing method, where the output voltage of the solar cell 3 is intentionally changed, and the values before and after the change are compared to check whether the current output is maximum. Repeat.

  The maximum output point control DC / DC converter 45 outputs the electric power obtained by performing tracking control of the solar cell 3 at the maximum output point to a DC distribution line (Vline). When the solar cell 3 generates solar power during the daytime, the combined power J of the solar cell 3 and the storage battery unit 16 is output to the DC device 5.

  When the combined power J is surplus, the commercial AC power supply 2 is reversely flowed through the DC / AC inverter 44 and sold. In addition, when solar power generation cannot be performed due to irregular weather in the daytime, the power of the commercial AC power supply 2 is used as the device power supply of the DC device 5 or the AC device 6.

  At night, when the power stored in the storage battery unit 16 is larger than the amount left as a backup power supply, or when a power failure occurs, the power of the storage battery unit 16 is used as a device power supply. At this time, since the solar cell 3 is not generating power, the output power of the storage battery unit 16 is supplied to the DC device 5, and the DC device 5 and the AC device 6 are operated by this power.

  Since the solar battery 3 cannot generate electricity at night, the storage battery 16 is basically discharged. However, when the storage battery 16 cannot be discharged, the power supply of the commercial AC power supply 2 is used. At this time, the power supply control unit 7 converts the alternating current power of the commercial alternating current power supply 2 into direct current by the AC / DC converter 43 and supplies the direct current power to the DC device 5.

  FIG. 3 shows the configuration of the charge / discharge system 50. The charge / discharge system 50 includes a charge / discharge circuit 51, a secondary battery unit 52, switch circuits (switching matrix: connection switching means) 53 and 54 arranged in a matrix, and a control circuit 55. The storage battery unit 16 is configured by the secondary battery unit 52 and the switch circuits 53 and 54. The charge / discharge circuit 51 charges and discharges the secondary battery 52 according to the operation of the DC device 5 and the voltage across the secondary battery unit 52. The secondary battery unit 52 includes a plurality of secondary battery cells 521, 522, 523, 524, and 525 and functions as a power storage unit of the storage battery unit 16. For example, lithium ion battery cells are used for the secondary battery cells 521, 522, 523, 524, and 525. The switch circuits 53 and 54 are opened and closed in accordance with the control signal input from the control circuit 55, and change the connection state of the secondary battery cells 521, 522, 523, 524, and 525. The control circuit 55 controls the charge / discharge circuit 51 and the switch circuits 53 and 54.

  The switch circuit 53 includes contacts 531a, 531b, 531c, 532a, 532b, 532c, 533a, 533b, 533c, 534a, 534b, 534c, 535a, 535b, and 535c. The switch circuit 54 has contacts 541a, 541b, 541c, 542a, 542b, 542c, 543a, 543b, 543c, 544a, 544b, 544c, 545a, 545b, and 545c. The contacts 531a, 532a, 533a, 534a, 535a of the switch circuit 53 are connected to the positive electrode terminals of the secondary battery cells 521, 522, 523, 524, 525. The contacts 541a, 542a, 543a, 544a, 545a of the switch circuit 54 are connected to the negative terminals of the secondary battery cells 521, 522, 523, 524, 525.

  The contacts 531 b, 532 b, 533 b, 534 b, 535 b of the switch circuit 53 are connected to the charge / discharge circuit 51. The contacts 541b, 542b, 543ba, 544b, and 545b of the switch circuit 54 are connected to the ground. Therefore, for example, when the contact 531a and the contact 531b of the switch circuit 53, the contact 532a and the contact 532b are connected, and the contact 541a and the contact 541b of the switch circuit 54, and the contact 542a and the contact 542b are connected, the secondary battery cell 521 is connected. 522 are connected in parallel. The same applies to other secondary battery cells.

  Also, the contacts 532c, 533c, 534c, 535c, 531c of the switch circuit 53 are connected to the contacts 541c, 542c, 543c, 544c, 545c of the switch circuit 54, respectively. Therefore, for example, when the contacts 541a and 541c of the switch circuit 54 and the contacts 532a and 532c of the switch circuit 53 are connected, the secondary battery cells 521 and 522 are connected in series. The same applies to other secondary battery cells. Thus, the connection state of the secondary battery cells 521, 522, 523, 524, and 525 is changed by appropriately connecting the contacts of the switch circuits 53 and 54, and the voltage across the storage battery unit 16 (both ends of the connection switching means). Voltage) can be changed. For example, it is also possible to connect the secondary battery cells 521 and 522 and the secondary battery cells 523 and 524 in series and connect them in parallel.

  FIG. 4 shows the configuration of the charge / discharge circuit 51. The charge / discharge circuit 51 includes a bidirectional half-bridge type converter circuit having a pair of bidirectional switching elements Q1 and Q2 on the primary side of the transformer 500 and a pair of bidirectional switching elements Q3 and Q4 on the secondary side. Has been. The charge / discharge circuit 51 has a direct charge / discharge path for charging / discharging directly from the DC distribution line and a charge / discharge path for charging / discharging via the bidirectional half-bridge converter circuit. The bidirectional switching elements Q1, Q2, Q3, and Q4 open and close in accordance with a control signal input from the control circuit 55, for example. The control signal for controlling the bidirectional switching elements Q1, Q2, Q3, Q4 is not limited to the control circuit 55, and is configured to be input from, for example, a control circuit provided in the charge / discharge control circuit 51. May be. At the time of charging, the control circuit 55 appropriately controls the connection state of the switch circuits 53 and 54 so that the DC distribution line voltage Vline> the both-ends voltage Vbat of the storage battery unit 16. The transformer 500 oscillates by alternately turning on / off the primary-side bidirectional switching elements Q1, Q2. At this time, the secondary battery constituting the storage battery unit 16 can be charged by always turning on the bidirectional switching element Q3 on the secondary side and always turning off the bidirectional switching element Q4.

  On the other hand, at the time of discharging, the control circuit 55 appropriately controls the connection state of the switch circuits 53 and 54 so that the DC distribution line voltage Vline <the both-ends voltage Vbat of the storage battery unit 16. The secondary battery constituting the storage battery unit 16 can be discharged by always turning off the bidirectional switching element Q3 on the secondary side and always turning on the bidirectional switching element Q4.

  As described above, according to the charging / discharging system 50 including the charging / discharging circuit 51, the connection state of the plurality of secondary batteries can be arbitrarily changed in series or in parallel by the switch circuits 53 and 54. Therefore, the magnitude relationship between the DC line voltage Vline and the voltage Vbat across the storage battery unit 16 can be arbitrarily changed according to the charging or discharging operation. More specifically, the switching circuit is configured so that the voltage Vbat across the storage battery unit 16 is lower than the DC line voltage Vline during charging and the voltage Vbat across the storage battery unit 16 is higher than the DC line voltage Vline during discharging. 53 and 54 are controlled. As a result, the charging / discharging circuit 51 can charge and discharge the battery only by the step-down operation in either case of charging or discharging, so that the size and efficiency of the system can be reduced. Further, since the direct charge / discharge path is provided in addition to the power supply path from the bidirectional half-bridge type converter, the power supply amount of the converter can be reduced. Therefore, the system can be reduced in size and efficiency.

  FIG. 5 shows a configuration of a modification of the charge / discharge circuit 51. The charge / discharge circuit 51 is constituted by a bidirectional power conversion circuit having bidirectional switching elements Q1, Q2. The bidirectional switching elements Q1 and Q2 open and close according to a control signal input from the control circuit 55 or the charge / discharge control circuit 51. Also in the charging / discharging system 50 having this charging / discharging circuit 51, the switching circuits 53, 54 are controlled so that the voltage Vbat across the storage battery unit 16 is lower than the DC line voltage Vline during charging. Then, the bidirectional switching element Q1 is turned on / off (chopper control), and the bidirectional switching element Q2 is always turned on. Further, the switch circuits 53 and 54 are controlled so that the voltage Vbat across the storage battery unit 16 is higher than the DC line voltage Vline during discharging. Then, the bidirectional switching element Q1 is always turned on, and the bidirectional switching element Q2 is turned on / off (chopper control). In the charging / discharging system 50 having the charging / discharging circuit 51, the charging / discharging circuit 51 can charge / discharge the battery only by the step-down operation in either case of charging or discharging. Can be achieved.

  FIG. 6 shows a configuration of a modification of the charge / discharge system 50. In the charging / discharging system 50, the charging / discharging circuit 51 includes a plurality of charging circuits 511, 512, 513, 514, 515, a discharging circuit 510, and the like. Each of the charging circuits 511, 512, 513, 514, 515 corresponds to the secondary battery cells 521, 522, 523, 524, 525 (see FIG. 3) of the secondary battery unit 52. In the charge / discharge system 50, the secondary battery cells 521, 522, 523, 524, 525 are connected in series only at the time of discharge. At the time of charging, the secondary battery cells 521, 522, 523, 524, 525 are connected to the charging circuits 511, 512, 513, 514, 515. For charging secondary battery cells, constant current charging is preferable. In this modification, the charging current can be optimized for each battery by providing a charging circuit for each battery. . Thereby, the lifetime of a secondary battery cell can be achieved.

  FIG. 7 shows a configuration of another modification of the charge / discharge system 50. In the charging / discharging system 50, the charging / discharging circuit 51 includes a discharging circuit 510, a charging circuit 516, a diode 517, and the like. The discharge circuit 510 and the charging circuit 516 are appropriately connected to the secondary battery cells 521, 522, 523, 524, 525 by the switch circuit 53. The diode 517 is interposed between the discharge circuit 510 and the DC distribution line. Instead of the diode 517, an ideal diode constituted by a MOSFET may be used. In the charge / discharge system 50, the switch circuits 53 and 54 are appropriately controlled by the control circuit 55. As a result, several secondary battery cells are connected in series while being sequentially replaced, and discharged through the discharge circuit 510 and the diode 517, while other secondary battery cells not used for discharge are being sequentially replaced. Charging can be performed via the charging circuit 516. For example, when the DC distribution line voltage Vline is 48V, the operation is performed using four 16V secondary batteries. That is, at the time of discharging, three secondary battery cells are connected in series. When charging, one secondary battery cell is charged. Then, the secondary battery cell for discharge and the secondary battery cell for discharge are sequentially replaced by the operation of the switch circuits 53 and 54. Accordingly, the charging current of the secondary battery cell can be optimized while maintaining a state where the secondary battery cell can always be discharged, and the life of the secondary battery can be extended.

  8 to 12 show a bidirectional switching element 100 having a lateral lateral transistor structure that can be applied to the bidirectional switching elements 4, 5, 6, and 7 constituting the DC / DC converter 1 of the present embodiment. Yes. A bidirectional switch element having a lateral transistor structure using GaN / AlGaN has the advantage that there is no loss due to the diode structure, a low loss compared to the FET, and the control circuit can be integrated. Hereinafter, details of the bidirectional switch element 100 having a lateral transistor structure using GaN / AlGaN will be described.

  FIG. 8 is a plan view showing the configuration of the bidirectional switch element 100, FIG. 9 is an enlarged view of a range A, and FIG. 10 is a cross-sectional view along BB. This bidirectional switch element 100 is called a single gate type because only one gate G is provided between the two electrodes D1 and D2.

  As shown in FIG. 10, the substrate 101 of the bidirectional switch element 100 includes a conductor layer 101a and a GaN layer 2b and an AlGaN layer 101c stacked on the conductor layer 101a. In this embodiment, a two-dimensional electron gas layer generated at the AlGaN / GaN hetero interface is used as the channel layer. As shown in FIG. 8, the surface 101d of the substrate 101 has a first electrode D1 and a second electrode D2 connected in series to the DC power source 2 and the load 3, respectively, and the potential of the first electrode D1 and the second An intermediate potential portion S that is an intermediate potential with respect to the potential of the electrode D2 is formed. Further, a control electrode (gate) G is stacked on the intermediate potential portion S. As the control electrode G, for example, a Schottky electrode is used. The first electrode D1 and the second electrode D2 are comb teeth having a plurality of electrode portions 111, 112, 113... And 121, 122, 123. The electrode parts arranged in the are arranged so as to face each other. The intermediate potential portion S and the control electrode G are respectively disposed between the electrode portions 111, 112, 113... And 121, 122, 123. It has a shape (substantially fish spine shape) similar to the planar shape of the space to be formed.

  Next, a lateral transistor structure constituting the bidirectional switch element 100 will be described. As shown in FIG. 9, the electrode part 111 of the first electrode D1 and the electrode part 121 of the second electrode D2 are arranged so that the center lines in the width direction are located on the same line. Further, the intermediate potential portion S and the control electrode G are provided in parallel to the arrangement of the electrode portion 111 of the first electrode D1 and the electrode portion 121 of the second electrode D2, respectively. The distance between the electrode portion 111 of the first electrode D1, the electrode portion 121 of the second electrode D2, the intermediate potential portion S, and the control electrode G in the width direction is set to a distance that can maintain a predetermined withstand voltage. The same applies to the direction perpendicular to the width direction, that is, the longitudinal direction of the electrode portion 111 of the first electrode D1 and the electrode portion 121 of the second electrode D2. Moreover, these relationships are the same also about the other electrode parts 112 and 122, 113, 123 .... That is, the intermediate potential portion S and the control electrode G are arranged at positions where a predetermined withstand voltage can be maintained with respect to the first electrode D1 and the second electrode D2.

  Therefore, when the first electrode D1 is on the high potential side and the second electrode D2 is on the low potential side, when the bidirectional switch element 100 is off, at least between the first electrode D1, the control electrode G, and the intermediate potential portion S. Thus, the current is reliably interrupted (the current is blocked immediately below the control electrode (gate) G). On the other hand, when the bidirectional switch element 100 is on, that is, when a signal having a voltage equal to or higher than a predetermined threshold is applied to the control electrode G, the first electrode D1 (electrode portion 111... -), A current flows through the path of the intermediate potential portion S and the second electrode D2 (electrode portion 121 ...). The same applies to the reverse case. As a result, even if the threshold voltage of the signal applied to the control electrode G is lowered to a necessary minimum level, the bidirectional switch element 100 can be reliably turned on / off, and a low on-resistance can be realized. . In addition, the electrode portions 111, 112, 113... Of the first electrode D1 and the electrode portions 121, 122, 123... Of the second electrode D2 can be arranged in a comb shape, A large current can be taken out without increasing the chip size.

  11 and 12 show the configuration of another bidirectional switch element 300 having a lateral transistor structure using GaN / AlGaN. FIG. 11 is a plan view showing the configuration of the bidirectional switch element 300, and FIG. 12 is a cross-sectional view taken along the line CC. This bidirectional switch element 300 is called a dual gate type because two gates G1 and G2 are provided between two electrodes D1 and D2.

  As shown in FIGS. 11 and 12, the main switch element 300 having a horizontal dual-gate transistor structure is a structure that realizes a bidirectional element with a small loss, with one place maintaining the withstand voltage. That is, the drain electrodes D1 and D2 are each formed to reach the GaN layer, and the gate electrodes G1 and G2 are respectively formed on the AlGaN layer. In a state where no voltage is applied to the gate electrodes G1 and G2, a blank zone of electrons is generated in the two-dimensional electron gas layer generated at the AlGaN / GaN heterointerface immediately below the gate electrodes G1 and G2, and no current flows. On the other hand, when a voltage is applied to the gate electrodes G1 and G2, a current flows through the AlGaN / GaN heterointerface from the drain electrode D1 toward D2 (or vice versa). A withstand voltage is required between the gate electrodes G1 and G2, and it is necessary to provide a certain distance, but a withstand voltage is required between the drain electrode D1 and the gate electrode G1 and between the drain electrode D2 and the gate electrode G2. do not do. Therefore, the drain electrode D1 and the gate electrode G1, and the drain electrode D2 and the gate electrode G2 may overlap via the insulating layer In. The element having this configuration needs to be controlled with reference to the voltages of the drain electrodes D1 and D2, and it is necessary to input drive signals to the two gate electrodes G1 and G2, respectively (for this reason, it is called a dual gate transistor structure). .

  In addition, this invention is not restricted to the structure of the said embodiment, The charging / discharging circuit which charges / discharges a some secondary battery cell, and the switch circuit which changes the connection state of a some secondary battery cell in series or in parallel It suffices if the configuration is provided.

50 Charging / discharging system 51 Charging / discharging circuit 53, 54 Switch circuit (connection switching means)
55 Control circuit 521,522,523,524,525 Secondary battery cell

Claims (10)

  A charge / discharge system to which a plurality of secondary battery cells are connected, wherein a charge / discharge circuit that charges and discharges the secondary battery cells and a connection switching that changes a connection state of the plurality of secondary battery cells in series or in parallel A charging / discharging system comprising means. Further comprising control means for controlling the connection switching means,
2. The control unit according to claim 1, wherein the control unit controls the connection switching unit according to a magnitude relationship between a DC distribution line voltage applied to the charge / discharge circuit and a voltage across the connection switching unit. Charge / discharge system.   When the secondary battery cell is charged, the control means connects any of the secondary battery cells in parallel, and makes the voltage across the connection switching means lower than the DC distribution line voltage. The charge / discharge system according to claim 2.   The control means connects any of the secondary battery cells in series when discharging the secondary battery cell, and makes the voltage across the connection switching means higher than the DC distribution line voltage. The charge / discharge system according to claim 2 or claim 3.   5. The charge / discharge circuit includes a bidirectional half-bridge converter circuit having a bidirectional switching element on a primary side of a transformer, and performs charge / discharge by a step-down operation. The charge / discharge system according to claim 1.   6. The charge / discharge circuit includes a direct charge / discharge path for directly charging / discharging from the DC distribution line and a charge / discharge path for charging / discharging via the bidirectional half-bridge converter circuit. The charge / discharge system according to 1.   5. The charge / discharge circuit according to claim 1, wherein the charge / discharge circuit includes a bidirectional power conversion circuit having a bidirectional switching element, and performs charge / discharge by a step-down operation. system.   The charge / discharge system according to any one of claims 1 to 4, wherein the charge / discharge circuit includes a charge circuit corresponding to each secondary battery cell.   The charging / discharging circuit can be connected in series with any of the secondary battery cells, and is connected directly to the DC distribution line via a diode in the discharging direction, and a secondary battery not used for discharging. The charge / discharge system according to claim 8, further comprising a charging circuit that charges the cell.   The charge / discharge system according to any one of claims 5 to 7, wherein the bidirectional switching element is a bidirectional switching element having a lateral transistor structure using GaN / AlGaN.

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