Power conversion system and power supply device

Abstract

To provide a power conversion system and a power supply device capable of stabilizing system operation and effectively utilizing an output of a solar cell even when the output of the solar cell is low.SOLUTION: In a power conversion system 2, a PV converter 21 receives an output of a solar cell 3 and supplies DC power to an intermediate electric path 25. A BT converter 22 performs bidirectional power conversion between a storage battery 4 and the intermediate electric path 25. An inverter 23 converts an intermediate voltage Vi into an alternating voltage and performs an interconnection operation of outputting the alternating current to a system electric path 5. If the magnitude of the output of the solar cell 3 is a threshold value or less, a control unit 24 stops the interconnection operation of the inverter 23 and performs forced charge control for charging the storage battery 4 to the BT converter 22 by using DC power supplied via the intermediate electric path 25.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion system and a power supply device. [Background technology]

[0002] The power conversion system of Patent Document 1 includes a power conversion device, a solar power generation device, a grid-connection relay, and a storage battery. The power conversion device includes a first DC / DC converter, a second DC / DC converter, an inverter, and a control unit.

[0003] The first DC / DC converter is configured to be able to step up a first DC voltage supplied from the solar power generation device to a DC link voltage. The second DC / DC converter is configured to step down the DC link voltage to a second DC voltage and supply it to the storage battery. The inverter converts the DC link voltage to an AC voltage and outputs the AC voltage to the grid.

[0004] The control unit controls and manages the entire power conversion device, and switches between connecting the power conversion device to the grid and disconnecting it from the grid by turning on and off the grid connection relay. For example, in the charging mode, the control unit disconnects the power conversion device from the grid and charges all of the power generated by the solar power generation device into the storage battery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-133870 A Summary of the Invention [Problem to be solved by the invention]

[0006] The output of a solar power generation device (solar cell) varies depending on the weather, the time of day, etc. However, if the output of the solar power generation device is too low, the operation of a power conversion device (power conversion system) becomes unstable, and the power conversion device cannot effectively utilize the output of the solar power generation device.

[0007] Therefore, an object of the present disclosure is to provide a power conversion system and a power supply device that can stabilize the operation of the system and effectively utilize the output of the solar cell even when the output of the solar cell is low. [Means for solving the problem]

[0008] A power conversion system according to an embodiment of the present disclosure includes a PV converter, a BT converter, an inverter, and a control unit. The PV converter receives an output from a solar cell and supplies DC power to an intermediate circuit. The BT converter performs bidirectional power conversion between a storage battery and the intermediate circuit. The inverter performs a grid-connected operation of converting an intermediate voltage, which is the voltage of the intermediate circuit, into an AC voltage and outputting the AC current to a grid circuit. The control unit controls the BT converter and the inverter. If the magnitude of the output from the solar cell is equal to or less than a threshold, the control unit stops the grid-connected operation of the inverter and performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied via the intermediate circuit. The PV converter converts the output of the solar cell into the DC power by maximum output power tracking control, and the BT converter adjusts the power supplied to the storage battery so that the intermediate voltage becomes a predetermined value during the forced charging control. A power conversion system according to an embodiment of the present disclosure includes a PV converter, a BT converter, an inverter, and a control unit. The PV converter receives an output from a solar cell and supplies DC power to an intermediate circuit. The BT converter performs bidirectional power conversion between a storage battery and the intermediate circuit. The inverter performs a grid-connected operation of converting an intermediate voltage, which is a voltage of the intermediate circuit, into an AC voltage and outputting the AC current to a grid circuit. The control unit controls the BT converter and the inverter. If the magnitude of the output from the solar cell is equal to or less than a threshold, the control unit stops the grid-connected operation of the inverter and performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied via the intermediate circuit. The PV converter includes at least one PV switching element, and performs a PV short-circuit operation of applying a voltage generated by the solar cell to the intermediate circuit by maintaining the at least one PV switching element in an on state or an off state. The BT converter includes at least one BT switching element, and performs a BT short-circuit operation in which the intermediate voltage is applied to the storage battery by maintaining the at least one BT switching element in an on state or an off state.

[0009] A power supply device according to an embodiment of the present disclosure is electrically connected to a PV converter that receives an output from a solar cell and supplies DC power to an intermediate circuit via the intermediate circuit. The power supply device includes a BT converter that performs bidirectional power conversion between a storage battery and the intermediate circuit, and a BT control unit that controls the BT converter. If the magnitude of the output from the solar cell is equal to or less than a threshold, the BT control unit performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied via the intermediate circuit. The PV converter converts the output of the solar cell into the DC power by maximum output power tracking control, and the BT converter adjusts the power supplied to the storage battery so that the intermediate voltage, which is the voltage of the intermediate circuit, becomes a predetermined value during the forced charging control. A power supply device according to an embodiment of the present disclosure is electrically connected to a PV converter that receives an output of a solar cell and supplies DC power to an intermediate electric circuit via the intermediate electric circuit. The power supply device includes a BT converter that performs bidirectional power conversion between a storage battery and the intermediate electric circuit, and a BT control unit that controls the BT converter. If the magnitude of the output of the solar cell is equal to or less than a threshold, the BT control unit performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied via the intermediate electric circuit. The PV converter includes at least one PV switching element, and performs a PV short-circuit operation in which the voltage generated by the solar cell is applied to the intermediate electric circuit by maintaining the at least one PV switching element in an on-state or an off-state. The BT converter includes at least one BT switching element, and performs a BT short-circuit operation in which an intermediate voltage, which is the voltage of the intermediate electric circuit, is applied to the storage battery by maintaining the at least one BT switching element in an on-state or an off-state. Effect of the Invention

[0010] As described above, the present disclosure has the advantage that, even when the output of the solar cell is low, the operation of the system can be stabilized and the output of the solar cell can be effectively utilized. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing a power supply system including a power conversion system according to an embodiment. [Diagram 2] FIG. 2 is a circuit diagram showing a PV converter provided in the power conversion system. [Diagram 3] FIG. 3 is a circuit diagram showing a BT converter included in the power conversion system. [Figure 4] FIG. 4 is a circuit diagram showing an inverter included in the power conversion system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The following embodiments generally relate to a power conversion system and a power supply device. More specifically, the present disclosure relates to a power conversion system electrically connected to a solar cell and a storage battery, and a power supply device. Note that the following embodiments are merely examples of the embodiments of the present disclosure. The present disclosure is not limited to the following embodiments, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0013] The power conversion system and the power supply device of the embodiment are mainly used in apartment buildings, detached houses, office buildings, commercial buildings, hotels, factories, stores, etc. However, the power conversion system and the power supply device of the embodiment may be used in facilities other than those mentioned above.

[0014] (Embodiment) (1) Overview of the power supply system FIG. 1 shows the configuration of a power supply system 1 including a power conversion system 2 of this embodiment.

[0015] The power supply system 1 includes a power conversion system 2, a solar cell 3, and a storage battery 4. The power conversion system 2 is electrically connected to the solar cell 3 and the storage battery 4. Furthermore, the power conversion system 2 is also electrically connected to a grid circuit 5 via a filter 27 and a switch 28.

[0016] The power conversion system 2 controls the power exchanged between the solar cell 3, the storage battery 4, and the grid circuit 5. For example, the power conversion system 2 charges the output (generated power) of the solar cell 3 to the storage battery 4, and causes a reverse flow to the grid circuit 5. In addition, the power conversion system 2 causes the discharged power of the storage battery 4 to flow reversely to the grid circuit 5.

[0017] The solar cell 3 has a solar panel that generates DC power from received sunlight. That is, the output of the solar cell 3 is DC power.

[0018] The storage battery 4 is a secondary battery capable of being charged and discharged, and includes, for example, a lithium ion battery, a nickel-metal hydride battery, or a lead storage battery.

[0019] The system electric circuit 5 is an electric circuit of a commercial power system having, for example, a nominal voltage of 200 V or 100 V and a frequency of 50 Hz or 60 Hz. Various electric loads are connected to the system electric circuit 5, and the electric loads are operated by AC power supplied from the system electric circuit 5.

[0020] The power conversion system 2 includes a PV (Photovoltaics) converter 21, a BT (Battery) converter 22, an inverter 23, a control unit 24, and an intermediate circuit 25. The PV converter 21, the BT converter 22, and the inverter 23 are electrically connected to a common intermediate circuit 25. The PV converter 21 converts the output of the solar cell 3 into DC power and supplies the DC power to the intermediate circuit 25. The BT converter 22 is electrically connected to the storage battery 4 and the intermediate circuit 25, and performs bidirectional power conversion between the storage battery 4 and the intermediate circuit 25. The inverter 23 performs a grid-connected operation of converting an intermediate voltage Vi, which is the voltage of the intermediate circuit 25, into an AC voltage and outputting the AC current to the grid circuit 5. The control unit 24 controls the BT converter 22 and the inverter 23. If the magnitude of the output of the solar cell 3 is equal to or less than a threshold, the control unit 24 stops the grid-connected operation of the inverter 23 and performs forced charging control to cause the BT converter 22 to charge the storage battery 4 using the DC power supplied via the intermediate circuit 25.

[0021] The power supply device PS2 is a power supply device electrically connected to the PV converter 21 via the intermediate electric circuit 25. The PV converter 21 converts the output of the solar cell 3 into DC power and supplies the DC power to the intermediate electric circuit 25. The power supply device PS2 includes a BT converter 22 and a BT control unit 242. The BT converter 22 is electrically connected to the storage battery 4 and the intermediate electric circuit 25, and performs bidirectional power conversion between the storage battery 4 and the intermediate electric circuit 25. The BT control unit 242 controls the BT converter 22. If the magnitude of the output of the solar cell 3 is equal to or less than a threshold, the BT control unit 242 performs forced charging control to cause the BT converter 22 to charge the storage battery 4 using the DC power supplied via the intermediate electric circuit 25.

[0022] The above-described power conversion system 2 and power supply device PS2 can stabilize the operation of the system and effectively utilize the output of the solar cell 3 even when the output of the solar cell 3 is low.

[0023] (2) Power conversion system configuration The configuration of the power conversion system 2 will be described below.

[0024] The power conversion system 2 includes power supply devices PS1-PS3.

[0025] The power supply device PS1 includes a PV converter 21 and a PV control unit 241. The power supply device PS2 includes a BT converter 22 and a BT control unit 242. The power supply device PS3 includes an inverter 23 and an INV (Inverter) control unit 243. The PV control unit 241, the BT control unit 242, and the INV control unit 243 constitute the control unit 24. The PV control unit 241, the BT control unit 242, and the INV control unit 243 are configured to be able to transmit and receive signals to each other via a wireless path or a wired path, and the operations of the PV converter 21, the BT converter 22, and the inverter 23 can be linked. In addition, the power conversion system 2 preferably further includes an intermediate electric circuit 25, a capacitor 26, a filter 27, a switch 28, and an output measuring unit 29.

[0026] (2.1) Intermediate circuit The intermediate electric circuit 25 has a pair of conductors, and is electrically connected to the PV converter 21, the BT converter 22, and the inverter 23. That is, the PV converter 21, the BT converter 22, and the inverter 23 are electrically connected to the common intermediate electric circuit 25.

[0027] A capacitor 26 is connected between the pair of conductors of the intermediate electric circuit 25. The capacitor 26 smoothes the DC voltage applied to the intermediate electric circuit 25. In this case, the intermediate voltage Vi, which is the voltage of the intermediate electric circuit 25, becomes the voltage across the capacitor 26 (the voltage between the pair of conductors of the intermediate electric circuit 25).

[0028] (2.2) PV converter An input end of the PV converter 21 is electrically connected to the solar cell 3, and an output end of the PV converter 21 is electrically connected to the intermediate circuit 25. The PV converter 21 converts the output of the solar cell 3 into DC power and supplies the DC power to the intermediate circuit 25.

[0029] Specifically, the PV converter 21 of this embodiment includes a boost chopper circuit. The PV converter 21 boosts the DC power generation voltage Vg output by the solar cell 3, and applies the DC boosted voltage to the intermediate circuit 25. If the nominal voltage of the grid circuit 5 is 200V, the intermediate voltage Vi generated in the intermediate circuit 25 by the boosted voltage of the PV converter 21 becomes 283V or more. When the PV converter 21 stops the boost operation, the input terminal and the output terminal of the PV converter 21 are electrically short-circuited, and the PV converter 21 performs a PV short-circuit operation in which the power generation voltage Vg is applied to the intermediate circuit 25.

[0030] 2 shows a circuit configuration of the PV converter 21 of this embodiment. The PV converter 21 includes PV switching elements 21a and 21b, diodes 21c and 21d, an inductor 21e, and a filter 21f.

[0031] The filter 21f is provided at the input stage of the PV converter 21 and attenuates noise components contained in the output of the solar cell 3. For example, the filter 21f includes capacitors 21g and 21h, and a common mode choke coil 21i. The common mode choke coil 21i is connected in series to the output terminals of the solar cell 3 and attenuates common mode noise. The capacitor 21g is connected between the output terminals of the solar cell 3 and functions as an X capacitor to attenuate normal mode noise. The capacitor 21h is connected in parallel to the capacitor 21g via the common mode choke coil 21i and functions as an X capacitor to attenuate normal mode noise.

[0032] The inductor 21e is connected in series to the positive electrode of the solar cell 3 via the filter 21f. The inductor 21e may be connected in series to the negative electrode of the solar cell 3 via the filter 21f. The inductor 21e may be composed of one inductor or two or more inductors. The PV converter 21 may include two or more inductors connected in series to the positive electrode and the negative electrode of the solar cell 3 via the filter 21f. The connection form of the inductor 21e to the solar cell 3 is not limited to a specific connection form.

[0033] Each of the PV switching elements 21a, 21b is, for example, an IGBT (Insulated Gate Bipolar Transistor). The collector of the PV switching element 21a is electrically connected to the positive electrode of the solar cell 3 via an inductor 21e and a filter 21f. The emitter of the PV switching element 21a is electrically connected to the collector of the PV switching element 21b. The emitter of the PV switching element 21b is electrically connected to the negative electrode of the solar cell 3 via a filter 21f. In other words, the PV converter 21 is a half-bridge converter having a series circuit of the PV switching elements 21a, 21b, with the PV switching element 21a serving as a high-side switching element and the PV switching element 21b serving as a low-side switching element.

[0034] The gates of the PV switching elements 21a, 21b are electrically connected to a PV control unit 241. The PV control unit 241 outputs gate signals to be applied to the gates of the PV switching elements 21a, 21b, and performs switching control to drive each of the PV switching elements 21a, 21b on and off.

[0035] Diode 21c is connected in anti-parallel to PV switching element 21a, i.e., the anode of diode 21c is electrically connected to the emitter of PV switching element 21a, and the cathode of diode 21c is electrically connected to the collector of PV switching element 21a.

[0036] Diode 21d is connected in anti-parallel to PV switching element 21b, i.e., the anode of diode 21d is electrically connected to the emitter of PV switching element 21b, and the cathode of diode 21d is electrically connected to the collector of PV switching element 21b.

[0037] Then, the PV control unit 241 causes the PV converter 21 to perform a boost operation by alternately turning on (off) each of the PV switching elements 21a, 21b. In the PV converter 21 performing the boost operation, the PV switching elements 21a, 21b perform a switching operation in which they are alternately turned on (off), thereby boosting the generated voltage Vg of the solar cell 3 and applying the DC boosted voltage to the intermediate circuit 25.

[0038] The PV control unit 241 performs maximum power point tracking (MPPT) when converting the power generation voltage Vg of the solar cell 3 into a DC boost voltage. That is, the PV control unit 241 controls the boost operation of the PV converter 21 so that the operating point becomes the maximum power point.

[0039] In addition, the PV control unit 241 stops the boost operation of the PV converter 21 by maintaining each of the PV switching elements 21a, 21b in the off state. In the PV converter 21 that has stopped the boost operation, the diode 21c is rendered conductive by the power generation voltage Vg of the solar cell 3. As a result, the input terminal and the output terminal of the PV converter 21 are electrically short-circuited, and the PV converter 21 performs a PV short-circuit operation in which the power generation voltage Vg is applied to the intermediate circuit 25.

[0040] (2.3) BT Converter A first input / output terminal of the BT converter 22 is electrically connected to the storage battery 4, and a second input / output terminal of the BT converter 22 is electrically connected to the intermediate electric circuit 25. The BT converter 22 generates DC power to be supplied to the intermediate electric circuit 25 from the discharge power of the storage battery 4. The BT converter 22 is also supplied with DC power from the intermediate electric circuit 25 and generates charging power to charge the storage battery 4. That is, the BT converter 22 performs bidirectional power conversion between the storage battery 4 and the intermediate electric circuit 25.

[0041] Specifically, the BT converter 22 of this embodiment includes a chopper circuit. The BT converter 22 boosts the DC battery voltage Vb of the storage battery 4 and applies the boosted DC voltage to the intermediate circuit 25. The BT converter 22 also drops the intermediate voltage Vi and applies the DC stepped-down voltage to the storage battery 4, thereby supplying a charging current to the storage battery 4. The BT converter 22 is also capable of performing a BT short-circuit operation in which the intermediate voltage Vi is applied to the storage battery 4.

[0042] 3 shows a circuit configuration of the BT converter 22 of this embodiment. The BT converter 22 includes BT switching elements 22a and 22b, diodes 22c and 22d, an inductor 22e, and a filter 22f.

[0043] The filter 22f attenuates noise components contained in the charging current and discharging current of the storage battery 4. For example, the filter 22f includes capacitors 22g and 22h, and a common mode choke coil 22i. The common mode choke coil 22i is connected in series to the storage battery 4 to attenuate common mode noise. The capacitor 22g is electrically connected between the positive and negative electrodes of the storage battery 4 to function as an X capacitor and to attenuate normal mode noise. The capacitor 22h is connected in parallel to the capacitor 22g via the common mode choke coil 22i to function as an X capacitor and to attenuate normal mode noise.

[0044] The inductor 22e is connected in series to the positive electrode of the storage battery 4 via the filter 22f. The inductor 22e may be connected in series to the negative electrode of the storage battery 4 via the filter 22f. The inductor 22e may be composed of one inductor or two or more inductors. The BT converter 22 may include two or more inductors connected in series to the positive electrode and the negative electrode of the storage battery 4 via the filter 22f. The connection form of the inductor 22e to the storage battery 4 is not limited to a specific connection form.

[0045] Each of the BT switching elements 22a and 22b is, for example, an IGBT. The collector of the BT switching element 22a is electrically connected to the positive electrode of the storage battery 4 via an inductor 22e and a filter 22f. The emitter of the BT switching element 22a is electrically connected to the collector of the BT switching element 22b. The emitter of the BT switching element 22b is electrically connected to the negative electrode of the storage battery 4 via a filter 22f. That is, the BT converter 22 is a half-bridge converter having a series circuit of the BT switching elements 22a and 22b, in which the BT switching element 22a serves as a high-side switching element and the BT switching element 22b serves as a low-side switching element.

[0046] The gates of the BT switching elements 22a and 22b are electrically connected to the BT control unit 242. The BT control unit 242 outputs gate signals to be applied to the gates of the BT switching elements 22a and 22b, and performs switching control to turn on and off each of the BT switching elements 22a and 22b.

[0047] The diode 22c is connected in anti-parallel to the BT switching element 22a, i.e., the anode of the diode 22c is electrically connected to the emitter of the BT switching element 22a, and the cathode of the diode 22c is electrically connected to the collector of the BT switching element 22a.

[0048] The diode 22d is connected in anti-parallel to the BT switching element 22b. That is, the anode of the diode 22d is electrically connected to the emitter of the BT switching element 22b, and the cathode of the diode 22d is electrically connected to the collector of the BT switching element 22b.

[0049] The BT control unit 242 alternately turns on (off) the BT switching elements 22a and 22b, thereby causing the BT converter 22 to perform a step-up operation or a step-down operation.

[0050] In the BT converter 22 that performs the boost operation, the BT switching elements 22a, 22b are alternately turned on (off) to boost the battery voltage Vb of the storage battery 4 and apply the DC boosted voltage to the intermediate circuit 25. If the nominal voltage of the system circuit 5 is 200V, the intermediate voltage Vi generated in the intermediate circuit 25 by the boost operation of the BT converter 22 becomes 283V or more.

[0051] In the BT converter 22 that performs a step-down operation, the BT switching elements 22a, 22b perform a switching operation in which they are alternately turned on (off), thereby stepping down the intermediate voltage Vi and applying a DC charging voltage to the storage battery 4.

[0052] In addition, the BT control unit 242 maintains the BT switching element 22a in the ON state and maintains the BT switching element 22b in the OFF state, thereby performing a BT short-circuit operation to apply the intermediate voltage Vi to the storage battery 4. In the BT converter 22 performing the BT short-circuit operation, the intermediate voltage Vi is applied to the storage battery 4 via the BT switching element 22a.

[0053] (2.4) Inverter The inverter 23 performs a grid-connection operation of converting the intermediate voltage Vi into an AC voltage and causing AC power to flow backward to the grid circuit 5 via the filter 27 and the switch 28. By performing the grid-connection operation, the inverter 23 coordinates the AC power output by the inverter 23 with the grid power supplied to the grid circuit 5 from the commercial power source.

[0054] 4 shows a circuit configuration of the inverter 23 of this embodiment. The inverter 23 includes switching elements 23a-23d, diodes 23e-23h, inductors 23i and 23j, and a capacitor 23k.

[0055] The four switching elements 23a-23d are connected in a full bridge configuration. Specifically, a series circuit of the switching elements 23a and 23b and a series circuit of the switching elements 23c and 23d are connected in parallel. The series circuit of the switching elements 23a and 23b and the series circuit of the switching elements 23c and 23d are each connected in parallel to a capacitor 26 of an intermediate electric circuit 25. Of the switching elements 23a and 23b, the switching element 23a is a high-side switching element, and the switching element 23b is a low-side switching element. Of the switching elements 23c and 23d, the switching element 23c is a high-side switching element, and the switching element 23d is a low-side switching element.

[0056] The four diodes 23e-23h are connected in anti-parallel to the switching elements 23a-23d, respectively.

[0057] One end of the inductor 23i is electrically connected to the connection point between the switching elements 23a and 23b. One end of the inductor 23j is electrically connected to the connection point between the switching elements 23c and 23d. Both ends of the capacitor 23k are electrically connected to the other ends of the inductors 23i and 23j. That is, the inductors 23i, 23j and the capacitor 23k function as a filter that attenuates noise components included in the output of the inverter 23.

[0058] Each gate of the switching elements 23a-23d is electrically connected to the INV control unit 243. The INV control unit 243 outputs a gate signal to be applied to each gate of the switching elements 23a-23d to perform switching control for driving each of the switching elements 23a-23d on and off. The INV control unit 243 alternately turns on (off) the pair of the switching elements 23a and 23d and the pair of the switching elements 23b and 23c, thereby causing the inverter 23 to perform DC / AC conversion for converting the intermediate voltage Vi into an AC voltage. The AC power output by the inverter 23 is supplied to the grid circuit 5 via the filter 27 and the switch 28.

[0059] The filter 27 attenuates noise components included in the output of the inverter 23. For example, the filter 27 includes capacitors 27a, 27b, and a common mode choke coil 27c. The common mode choke coil 27c is connected in series to the output terminal of the inverter 23 and attenuates common mode noise. The capacitor 27a is connected between the output terminals of the inverter 23 and functions as an X capacitor to attenuate normal mode noise. The capacitor 27b is connected in parallel to the capacitor 27a via the common mode choke coil 27c and functions as an X capacitor to attenuate normal mode noise.

[0060] Switch 28 is provided in the electric path between filter 27 and electric grid 5. When switch 28 is turned on, the electric path between filter 27 and electric grid 5 is connected. When switch 28 is turned off, the electric path between filter 27 and electric grid 5 is interrupted. Note that, although switch 28 has a double-pole configuration in FIG. 4, switch 28 may have a single-pole configuration.

[0061] (2.5) Control Unit The control unit 24 has a function of controlling the PV converter 21, the BT converter 22, and the inverter 23. The control unit 24 in this embodiment includes a PV control unit 241, a BT control unit 242, and an INV control unit 243. The PV control unit 241 controls the PV converter 21, the BT control unit 242 controls the BT converter 22, and the INV control unit 243 controls the inverter 23.

[0062] Each of the power supply devices PS1-PS3 includes a computer. Each computer executes a program to realize a part or all of the functions of the PV control unit 241, the BT control unit 242, and the INV control unit 243. The computer includes a processor that operates according to a program as a main hardware configuration. The type of the processor is not important as long as it can realize the function by executing the program. The processor is composed of one or more electronic circuits including a semiconductor integrated circuit (Integrated Circuit) or an LSI (Large Scale Integration). Here, it is called an IC or an LSI, but the name changes depending on the degree of integration, and it may be called a system LSI, a VLSI (Very Large Scale Integration), or an ULSI (Ultra Large Scale Integration). A field-programmable gate array (FPGA), which is programmed after the manufacture of the LSI, or a reconfigurable logic device that can reconfigure the connection relationship inside the LSI or set up the circuit partition inside the LSI, can also be used for the same purpose. The electronic circuits may be integrated into one chip or provided on multiple chips. The multiple chips may be integrated in one device, or may be provided in multiple devices. The program is recorded on a non-transitory recording medium such as a computer-readable ROM, an optical disk, or a hard disk drive. The program may be stored in the recording medium in advance, or may be supplied to the recording medium via a wide area communication network including the Internet.

[0063] (2.6) Output measurement section The output measuring unit 29 has a function of measuring the magnitude of the output (output value) of the solar cell 3. The output measuring unit 29 transmits data of the measured output value of the solar cell 3 to the PV control unit 241, the BT control unit 242, and the INV control unit 243.

[0064] Specifically, the output measuring unit 29 measures the generated power value as the output value of the solar cell 3 by monitoring the result or process of the MPPT performed by the PV control unit 241. Then, the output measuring unit 29 transmits data on the generated power value to the PV control unit 241, the BT control unit 242, and the INV control unit 243. In this case, it is preferable that a part or all of the functions of the output measuring unit 29 are realized by a computer included in the power supply device PS1 executing a program.

[0065] Alternatively, the output measuring unit 29 may measure the generated power value by detecting the generated voltage Vg and generated current of the solar cell 3.

[0066] (3) Operation of the power conversion system The operation of the power conversion system 2 will now be described.

[0067] The output measuring unit 29 measures the power generation value of the solar cell 3. Then, the output measuring unit 29 transmits data on the power generation value to the PV control unit 241, the BT control unit 242, and the INV control unit 243. Therefore, the PV control unit 241, the BT control unit 242, and the INV control unit 243 can monitor the power generation value of the solar cell 3 by acquiring the data on the power generation value.

[0068] Then, the PV control unit 241, the BT control unit 242, and the INV control unit 243 compare the power generation value of the solar cell 3 with a predetermined threshold value. If the power generation value is equal to or greater than the threshold value or is 0 (zero), the PV control unit 241, the BT control unit 242, and the INV control unit 243 set the operation mode of each to the normal mode. If the power generation value is greater than 0 and less than the threshold value, the PV control unit 241, the BT control unit 242, and the INV control unit 243 set the operation mode of each to the forced charging mode. That is, the control unit 24 switches the operation mode of the control unit 24 between the normal mode and the forced charging mode according to the comparison result between the power generation value and the threshold value. For example, the operation mode is set to the normal mode during the daytime and at night when the amount of solar radiation is greater than that at dawn and dusk. Also, the operation mode is set to the forced charging mode during the daytime and at dawn and dusk when the amount of solar radiation is less than that at daytime, and during rainy and cloudy days.

[0069] The threshold value is preferably a value that does not cause the grid-connected operation of the inverter 23 to become unstable if the magnitude of the output of the solar cell 3 is greater than the threshold value. If the inverter 23 performs DC / AC conversion when the input is too small, the DC / AC conversion operation is likely to become unstable. Therefore, by setting the threshold value as described above, the inverter 23 can stably perform DC / AC conversion if the power generation value of the solar cell 3 is greater than the threshold value.

[0070] Specifically, the threshold value is preferably greater than 0 and equal to or less than 25% of the upper limit of the output of the solar cell 3. Furthermore, the threshold value is preferably greater than or equal to 5% of the upper limit of the output of the solar cell 3 and equal to or less than 25% of the upper limit.

[0071] (3.1) Normal mode The PV control unit 241 operating in the normal mode controls the boost operation of the PV converter 21 according to the amount of power generated by the solar cell 3, the charge level of the storage battery 4, and the balance between the supply and demand of power in the grid circuit 5. For example, the PV control unit 241 controls the boost operation of the PV converter 21 by MPPT as necessary, or controls the boost operation of the PV converter 21 at an operating point where the output is lower than the maximum power point.

[0072] The BT control unit 242 operating in normal mode controls charging and discharging of the storage battery 4 by the BT converter 22 according to the amount of power generated by the solar cell 3, the charge level of the storage battery 4, and the balance between the demand and supply of power in the grid circuit 5.

[0073] The INV control unit 243 operating in the normal mode performs reverse power flow control by the inverter 23 according to the power generation amount of the solar cell 3, the charge level of the storage battery 4, and the balance between the demand and supply of power in the grid circuit 5, and the like.

[0074] (3.2) Forced charging mode The PV control unit 241, the BT control unit 242, and the INV control unit 243 operating in the forced charging mode perform the following forced charging control.

[0075] First, during forced charging control, the INV control unit 243 or a switch control unit (not shown) turns off the switch 28, thereby disconnecting the inverter 23 (the power conversion system 2) from the grid electric circuit 5.

[0076] The PV control unit 241 operating in the forced charging mode performs forced charging control that controls the boost operation of the PV converter 21 by MPPT.

[0077] The INV control unit 243 operating in the forced charging mode performs forced charging control to stop the inverter 23. Specifically, the INV control unit 243 maintains each of the switching elements 23a-23d of the inverter 23 in the off state to stop DC / AC conversion.

[0078] The BT control unit 242 operating in the forced charging mode performs forced charging control to cause the BT converter 22 to charge the storage battery 4 using DC power supplied via the intermediate circuit 25. Since the inverter 23 is stopped in the forced charging mode, the BT converter 22 charges the storage battery 4 using all of the power generated by the solar cell 3.

[0079] Specifically, the BT control unit 242 that performs the forced charging control adjusts the power supplied by the BT converter 22 to the storage battery 4 so that the intermediate voltage Vi becomes a predetermined value. That is, the BT converter 22 performs constant voltage control of the input intermediate voltage Vi, while lowering the intermediate voltage Vi to generate a DC step-down voltage, and applies the DC step-down voltage to the storage battery 4 to supply a charging current to the storage battery 4. For example, if the nominal voltage of the grid circuit 5 is 200V, the charging current of the storage battery 4 is adjusted so that the intermediate voltage Vi becomes a constant value of 283V or more. In this way, when the storage battery 4 is charged during charging control in the forced charging mode, the intermediate voltage Vi is maintained at a constant value. As a result, even when the forced charging mode is returned to the normal mode and the inverter 23 starts the grid-connected operation, the AC power output by the inverter 23 can be quickly coordinated with the grid power of the grid circuit 5.

[0080] When the inverter 23 performs DC / AC conversion when the input is too small, the operation of the inverter 23 tends to become unstable. Therefore, the INV control unit 243 stops the inverter 23 in the forced charging mode where the generated power value is greater than 0 and less than the threshold value. Therefore, even when the generated power is small, it is possible to prevent the operation of the inverter 23 from becoming unstable. Furthermore, the BT converter 22 charges the storage battery 4 using all the generated power of the solar cell 3. Therefore, even when the generated power is small, the generated power can be effectively used.

[0081] That is, even when the output of the solar cell 3 is low, the power conversion system 2 can stabilize the operation of the system and effectively utilize the output of the solar cell 3.

[0082] (4) First Modification The comparison process between the power generation value and the threshold value by the control unit 24 (PV control unit 241, BT control unit 242, and INV control unit 243) preferably has a hysteresis characteristic. In this case, the threshold value is composed of a stop threshold and a start threshold. The start threshold is a value larger than the stop threshold. Then, when the control unit 24 is operating in the normal mode, if the power generation value becomes equal to or smaller than the stop threshold, the control unit 24 shifts from the normal mode to the forced charging mode and performs the forced charging control. When the power generation value becomes larger than the stop threshold while operating in the forced charging mode, the control unit 24 shifts from the forced charging mode to the normal mode and performs the normal control. That is, when the magnitude of the output of the solar cell 3 becomes equal to or smaller than the stop threshold, the control unit 24 starts the forced charging control, and when the magnitude of the output of the solar cell 3 becomes larger than the start threshold, the control unit 24 stops the forced charging control. The hysteresis width, which is the difference between the start threshold and the stop threshold, is preferably about 2-3% of the upper limit value of the output of the solar cell 3.

[0083] In this modification, the power conversion system 2 can suppress the occurrence of chattering when starting and stopping the forced charging control.

[0084] (5) Second Modification The control unit 24 (the PV control unit 241, the BT control unit 242, and the INV control unit 243) operating in the forced charging mode may perform the following forced charging control.

[0085] The INV control unit 243 operating in the forced charging mode performs forced charging control to stop the inverter 23.

[0086] The PV control unit 241 and the BT control unit 242 operating in the forced charging mode switch the content of the forced charging control depending on the magnitude relationship between the power generation voltage Vg and the battery voltage Vb.

[0087] Specifically, if the generated voltage Vg is less than the battery voltage Vb, the PV converter 21 receives the generated voltage Vg as an input, boosts the generated voltage Vg of the solar cell 3 by MPPT that switches the PV switching elements 21a, 21b, and outputs the boosted voltage to the intermediate circuit 25. Then, the BT converter 22 performs a BT short-circuit operation to apply the intermediate voltage Vi to the storage battery 4, thereby supplying a charging current to the storage battery 4.

[0088] Furthermore, if the generated voltage Vg is equal to or higher than the battery voltage Vb, the PV converter 21 performs a PV short-circuit operation of applying the generated voltage Vg to the intermediate circuit 25. The BT converter 22 receives the intermediate voltage Vi as input, and applies a stepped-down voltage obtained by stepping down the intermediate voltage Vi to the storage battery 4 by MPPT that switches the BT switching elements 22a, 22b, thereby supplying a charging current to the storage battery 4.

[0089] As described above, the control unit 24 of this modification switches the content of the forced charging control depending on the magnitude relationship between the generated voltage Vg and the battery voltage Vb. As a result, the power conversion system 2 can improve the power conversion efficiency of the forced charging control.

[0090] (6) Third Modification The PV switching elements 21a, 21b of the PV converter 21, the BT switching elements 22a, 22b of the BT converter 22, and the INV switching elements 21a-21d of the inverter 23 are preferably switching elements made of a semiconductor material including gallium nitride (GaN) or silicon carbide (SiC).

[0091] A switching element made of a semiconductor material containing GaN or SiC is a so-called wide band gap device, and the use of a wide band gap device makes it possible to increase the switching frequency and reduce power loss due to switching.

[0092] The switching element made of a semiconductor material containing SiC is configured as a FET having a parasitic diode. In this case, the parasitic diode of the FET can be used as the diodes 21c, 21d, 22c, 22d, and 23e to 23h.

[0093] A switching element made of a semiconductor material including GaN does not have a parasitic diode. Therefore, instead of providing an anti-parallel diode separately from the switching element, the switching element may be operated in reverse conduction mode. In this case, the diodes 21c, 21d, 22c, 22d, and 23e to 23h can be omitted.

[0094] (7) Fourth Modification In the PV converter 21 in FIG. 2, the switching element 21a is not an essential component and can be omitted.

[0095] In addition, the specific circuit configuration of the PV converter 21 is not limited to a half-bridge circuit as long as it is configured to include at least one PV switching element. In addition, the PV converter 21 may be configured to perform a PV short-circuit operation in which the generated voltage Vg of the solar cell 3 is applied to the intermediate circuit 25 by maintaining at least one PV switching element in an on state or an off state.

[0096] The specific circuit configuration of the BT converter 22 is not limited to a half-bridge converter as long as it is configured to include at least one BT switching element. In addition, the BT converter 22 may be configured to perform a BT short-circuit operation in which the intermediate voltage Vi is applied to the storage battery 4 by maintaining at least one BT switching element in an on state or an off state.

[0097] Furthermore, the PV switching elements 21a and 21b, the BT switching elements 22a and 22b, and the switching elements 23a-23d may be FETs (Field Effect Transistors). In this case, parasitic diodes of the FETs may be used as the diodes 21c, 21d, 22c, 22d, and 23e-23h.

[0098] Furthermore, the control unit 24 may be provided separately from the power supply devices PS1-PS3 and configured to centrally control the PV converter 21, the BT converter 22, and the inverter 23. In this case, the functions of the PV control unit 241, the BT control unit 242, and the INV control unit 243 may be realized by one computer executing a program.

[0099] The power conversion system 2 may also be configured to charge the storage battery 4 with power supplied from the grid 5. In this case, it is preferable that the inverter 23 performs bidirectional power conversion.

[0100] (8) Summary A power conversion system (2) according to a first aspect of the embodiment includes a PV converter (21), a BT converter (22), an inverter (23), and a control unit (24). The PV converter (21) receives an output from a solar cell (3) and supplies DC power to an intermediate circuit (25). The BT converter (22) performs bidirectional power conversion between the storage battery (4) and the intermediate circuit (25). The inverter (23) performs a grid-connected operation of converting an intermediate voltage (Vi) that is a voltage of the intermediate circuit (25) into an AC voltage and outputting the AC current to a grid circuit (5). The control unit (24) controls the BT converter (22) and the inverter (23). If the magnitude of the output from the solar cell (3) is equal to or less than a threshold, the control unit (24) stops the grid-connected operation of the inverter (23) and performs forced charging control to cause the BT converter (22) to charge the storage battery (4) using DC power supplied via the intermediate circuit (25).

[0101] The above-described power conversion system (2) can stabilize the operation of the system and effectively utilize the output of the solar cell (3) even when the output of the solar cell (3) is low.

[0102] In the power conversion system (2) of the second aspect according to the embodiment, in the first aspect, the threshold value is preferably a value that does not cause the grid-connected operation to become unstable if the magnitude of the output of the solar cell (3) is greater than the threshold value.

[0103] The above-described power conversion system (2) can stabilize the operation of the system.

[0104] In the power conversion system (2) of the third aspect according to the embodiment, in the first or second aspect, the threshold value is preferably greater than 0 and equal to or less than 25% of the upper limit of the output of the solar cell (3).

[0105] The above-described power conversion system (2) can more reliably stabilize the operation of the system.

[0106] In the power conversion system (2) of the fourth aspect of the embodiment, in any one of the first to third aspects, the threshold value is preferably a value that is 5% or more and 25% or less of the upper limit value of the output of the solar cell (3).

[0107] The above-described power conversion system (2) can more reliably stabilize the operation of the system.

[0108] In the power conversion system (2) of the fifth aspect according to the embodiment, in any one of the first to fourth aspects, the threshold value is preferably a stop threshold value and a start threshold value that is greater than the stop threshold value. The control unit (24) starts the forced charging control when the magnitude of the output of the solar cell (3) becomes equal to or less than the stop threshold value, and stops the forced charging control when the magnitude of the output of the solar cell (3) becomes greater than the start threshold value.

[0109] The above-described power conversion system (2) can impart a hysteresis characteristic to the process of comparing the magnitude of the output of the solar cell (3) with a threshold value.

[0110] In the power conversion system (2) of the sixth aspect according to the embodiment, in any one of the first to fifth aspects, it is preferable that the PV converter (21) converts the output of the solar cell (3) into DC power by maximum output power tracking control. It is preferable that the BT converter (22) adjusts the power supplied to the storage battery (4) so ​​that the intermediate voltage (Vi) becomes a predetermined value during forced charging control.

[0111] The above-described power conversion system (2) can quickly start the grid-connected operation when the forced charging control is stopped.

[0112] In the power conversion system (2) of the seventh aspect according to the embodiment, in any one of the first to fifth aspects, it is preferable that the PV converter (21) includes at least one PV switching element (21a, 21b) and maintains the at least one PV switching element (21a, 21b) in an on state or an off state to perform a PV short-circuit operation of applying a power generation voltage (Vg) of the solar cell (3) to the intermediate current path (25). It is preferable that the BT converter (22) includes at least one BT switching element (22a, 22b) and maintains the at least one BT switching element (22a, 22b) in an on state or an off state to perform a BT short-circuit operation of applying an intermediate voltage (Vi) to the storage battery (4).

[0113] The above-described power conversion system (2) can improve the power conversion efficiency of the forced charging control.

[0114] In the power conversion system (2) of the eighth aspect according to the embodiment, in the seventh aspect, each of the PV converter (21) and the BT converter (22) is preferably a half-bridge converter.

[0115] The above-described power conversion system (2) can easily realize the PV short-circuit operation and the BT short-circuit operation.

[0116] In the power conversion system (2) of the ninth aspect according to the embodiment, in the seventh or eighth aspect, during forced charging control, if the power generation voltage (Vg) is lower than the battery voltage (Vb) of the storage battery (4), it is preferable that the PV converter (21) converts the output of the solar cell (3) into DC power by maximum output power tracking control that switches at least one PV switching element (21a, 21b), and the BT converter (22) performs a BT short-circuit operation. If the power generation voltage (Vg) is higher than the battery voltage (Vb), it is preferable that the PV converter (21) performs a PV short-circuit operation, and the BT converter (22) charges the storage battery (4) by maximum output power tracking control that switches at least one BT switching element (22a, 22b).

[0117] The above-described power conversion system (2) can improve the power conversion efficiency of the forced charging control.

[0118] In the power conversion system (2) of the tenth aspect of the embodiment, in any one of the first to ninth aspects, it is preferable that the power conversion system (2) further includes an output measuring unit (29) that measures the magnitude of the output of the solar cell (3).

[0119] The above-described power conversion system (2) makes it easy to monitor the magnitude of the output of the solar cell (3).

[0120] In the power conversion system (2) of the eleventh aspect of the embodiment, in any one of the first to tenth aspects, it is preferable that at least one of the PV converter (21), the BT converter (22), and the inverter (23) includes at least one switching element (21a, 21b, 22a, 22b, 23a-23d) made of a semiconductor material including gallium nitride or silicon carbide.

[0121] The above-described power conversion system (2) can achieve a higher switching frequency and a reduced power loss due to switching.

[0122] A power supply device (PS2) according to a twelfth aspect of the embodiment is electrically connected to a PV converter (21) that receives an output from a solar cell (3) and supplies DC power to the intermediate circuit (25) via the intermediate circuit (25). The power supply device (PS2) includes a BT converter (22) and a BT control unit (242). The BT converter (22) performs bidirectional power conversion between the storage battery (4) and the intermediate circuit (25). The BT control unit (242) controls the BT converter (22). If the magnitude of the output from the solar cell (3) is equal to or less than a threshold, the BT control unit (242) performs forced charging control to cause the BT converter (22) to charge the storage battery (4) using DC power supplied via the intermediate circuit (25).

[0123] The power supply device (PS2) described above can stabilize the operation of the system and effectively utilize the output of the solar cell (3) even when the output of the solar cell (3) is low. [Explanation of symbols]

[0124] 2. Power Conversion System 21 PV Converter 22 BT Converter 23 Inverter 24 Control Unit 241 PV control section (control section) 242 BT control unit (control unit) 243 INV control unit (control unit) 25 Intermediate circuit 29 Output measurement section 21a, 21b PV switching element (switching element) 22a, 22b BT switching element (switching element) 23a-23d Switching elements 3. Solar Cells 4. Storage battery 5 Grid line PS2 power supply Vi Intermediate voltage Vg Generated voltage Vb Battery voltage

Claims

1. a PV converter that receives an output from the solar cell and supplies DC power to the intermediate circuit; a BT converter that performs bidirectional power conversion between a storage battery and the intermediate circuit; an inverter that performs a grid-connection operation to convert an intermediate voltage, which is a voltage of the intermediate electric circuit, into an AC voltage and output the AC current to a grid electric circuit; A control unit that controls the BT converter and the inverter, When the magnitude of the output of the solar cell is equal to or less than a threshold, the control unit stops the grid-connected operation of the inverter and performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied through the intermediate current path. The PV converter converts the output of the solar cell into the DC power by maximum output power tracking control, The BT converter adjusts the power supplied to the storage battery during the forced charging control so that the intermediate voltage becomes a predetermined value. Power conversion systems.

2. A PV converter that receives the output of a solar cell and supplies DC power to an intermediate circuit; a BT converter that performs bidirectional power conversion between a storage battery and the intermediate circuit; an inverter that performs a grid-connection operation to convert an intermediate voltage, which is a voltage of the intermediate electric circuit, into an AC voltage and output the AC current to a grid electric circuit; A control unit that controls the BT converter and the inverter, When the magnitude of the output of the solar cell is equal to or less than a threshold, the control unit stops the grid-connected operation of the inverter and performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied through the intermediate current path. The PV converter includes at least one PV switching element, and performs a PV short-circuit operation in which a voltage generated by the solar cell is applied to the intermediate circuit by maintaining the at least one PV switching element in an on state or an off state; The BT converter includes at least one BT switching element, and performs a BT short-circuit operation of applying the intermediate voltage to the storage battery by maintaining the at least one BT switching element in an on state or an off state. Power conversion systems.

3. Each of the PV converter and the BT converter is a half-bridge converter. The power conversion system of claim 2 .

4. During the forced charging control, If the generated voltage is lower than the battery voltage of the storage battery, the PV converter converts the output of the solar cell into the DC power by maximum output power tracking control that switches the at least one PV switching element, and the BT converter performs the BT short-circuit operation. If the generated voltage is higher than the battery voltage, the PV converter performs the PV short-circuit operation, and the BT converter charges the storage battery by maximum output power tracking control that switches the at least one BT switching element.

4. The power conversion system according to claim 2 or 3.

5. The threshold value is a value at which the interconnection operation does not become unstable if the magnitude of the output of the solar cell is greater than the threshold value.

5. The power conversion system according to claim 1.

6. The threshold value is greater than 0 and is equal to or less than 25% of the upper limit of the output of the solar cell.

6. The power conversion system according to claim 1 .

7. The threshold value is a value that is 5% or more and 25% or less of an upper limit value of the output of the solar cell.

7. The power conversion system according to claim 1.

8. The threshold value comprises a stop threshold value and a start threshold value that is greater than the stop threshold value, The control unit is When the magnitude of the output of the solar cell becomes equal to or less than the stop threshold, the forced charging control is started. When the output of the solar cell becomes greater than the start-up threshold, the forced charging control is stopped.

8. A power conversion system according to any one of claims 1 to 7.

9. Further comprising an output measuring unit for measuring the magnitude of the output of the solar cell.

9. The power conversion system of claim 1.

10. At least one of the PV converter, the BT converter, and the inverter has at least one switching element made of a semiconductor material including gallium nitride or silicon carbide.

10. The power conversion system of claim 1.

11. A power supply device electrically connected to a PV converter that receives an output from a solar cell and supplies DC power to an intermediate circuit via the intermediate circuit, a BT converter that performs bidirectional power conversion between a storage battery and the intermediate circuit; A BT control unit that controls the BT converter, the BT control unit performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied through the intermediate current path when the magnitude of the output of the solar cell is equal to or less than a threshold value; The PV converter converts the output of the solar cell into the DC power by maximum output power tracking control, The BT converter adjusts the power supplied to the storage battery during the forced charging control so that an intermediate voltage, which is a voltage of the intermediate current path, becomes a predetermined value. power supply.

12. A power supply device electrically connected to a PV converter that receives an output from a solar cell and supplies DC power to an intermediate circuit via the intermediate circuit, a BT converter that performs bidirectional power conversion between a storage battery and the intermediate circuit; A BT control unit that controls the BT converter, the BT control unit performs forced charging control to cause the BT converter to charge the storage battery using the DC power supplied through the intermediate current path when the magnitude of the output of the solar cell is equal to or less than a threshold value; The PV converter includes at least one PV switching element, and performs a PV short-circuit operation in which a voltage generated by the solar cell is applied to the intermediate circuit by maintaining the at least one PV switching element in an on state or an off state; The BT converter includes at least one BT switching element, and performs a BT short-circuit operation in which an intermediate voltage, which is a voltage of the intermediate current path, is applied to the storage battery by maintaining the at least one BT switching element in an on state or an off state. power supply.

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