Energy storage system and power conversion device

Abstract

To provide a power storage system which can dissolve imbalance of voltage among each wire of a single-phase three-wire system in service interruption and simplify a DC / AC inverter.SOLUTION: A hybrid type power storage system 1 comprises: a bidirectional DC / DC converter 2; a DC / AC inverter 3; a DC / DC converter 4; and a control unit 5, wherein the bidirectional DC / DC converter 2 comprises: a bidirectional step-up / down circuit 2A comprising a first capacitor C1; a bidirectional inversion step-up / down circuit 2B comprising a second capacitor C2, and the control unit 5 executes charge / discharge control of the first capacitor C1 by the bidirectional step-up / down circuit 2A and charge / discharge control of the second capacitor C2 by the bidirectional inversion step-up / down circuit 2B so that first voltage of the first capacitor C1 equals to second voltage of the second capacitor C2 when a power system is in a service interruption state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A conventional power conversion device for photovoltaic power generation is known, for example, from Patent Document 1. As shown in Fig. 4, the power conversion device described in Patent Document 1 includes a boost chopper composed of a capacitor C13, a choke coil L11, a switching element S11, and a diode D11, and a DC / AC inverter (two half-bridge inverters) composed of capacitors C11 and C12 connected in series and having equal capacitances, and switching elements S12 to S15.

[0003] In the power conversion device described in Patent Document 1, the voltage input from the solar cell PV is smoothed by capacitor C13 and then boosted by a boost chopper. The boost chopper outputs the boosted voltage to both ends of capacitors C11 and C12, which then divide the voltage equally. The DC / AC inverter is able to output a single-phase three-wire signal by connecting the connection point of capacitors C11 and C12 to the neutral line of a single-phase three-wire system.

[0004] However, when the power conversion device described in Patent Document 1 is used for independent output during a power outage in the power grid (hereinafter referred to as a power outage), a voltage imbalance (unbalanced load) may occur between RN and NS due to differences in the specifications (for example, variations in power consumption and inrush current) of the load connected between RN and NS on the output side of the DC / AC inverter. In this case, the divided voltages of capacitors C11 and C12 do not become equal, causing a problem in that the output voltage of the DC / AC inverter drops on the side with a heavy load and rises on the side with a light load.

[0005] Known power conversion devices that address the above problems include, for example, the one described in Patent Document 2. As shown in Fig. 5, the power conversion device (DC / AC inverter) described in Patent Document 2 includes: capacitors C21 and C22 connected in series and having the same capacitance; a neutral voltage adjustment circuit configured with switching elements S27 and S28 and a reactor L21; an inverter circuit configured with switching elements S21 to S26 and a diode D21; a filter circuit; and a control unit (CPU).

[0006] The DC / AC inverter described in Patent Document 2 operates in response to an imbalance in the independent output voltages (first DC voltage and second DC voltage) during a power outage and independent output as follows: When the first DC voltage (voltage between the first DC voltage line DCL1 and the neutral line NL) is greater than the second DC voltage (voltage between the neutral line NL and the second DC voltage line DCL2), the control unit increases the on-duty ratio of the switching element S27 and decreases the on-duty ratio of the switching element S28. On the other hand, when the second DC voltage is greater than the first DC voltage, the control unit increases the on-duty ratio of the switching element S28 and decreases the on-duty ratio of the switching element S27.

[0007] By the above control, in the DC / AC inverter described in Patent Document 2, even if a voltage imbalance occurs between the first AC voltage line ACL1 and the neutral line NL and between the second AC voltage line ACL2 and the neutral line NL of a single-phase three-wire system, the divided voltages of capacitors C21 and C22 can be controlled to be equal voltages. Note that even if the switching elements S25 and S26 and the diode D21 are removed from the inverter circuit and a half-bridge configuration is used, operation that can accommodate voltage imbalances is possible.

[0008] However, the DC / AC inverter described in Patent Document 2 has a problem in that the presence of a neutral voltage adjustment circuit and a detection unit and the like required to control the neutral voltage adjustment circuit leads to an increase in size and complexity of the DC / AC inverter.

[0009] A hybrid energy storage system, which is an energy storage system with a solar power generation function, includes a DC / DC converter connected to a solar cell, a bidirectional DC / DC converter connected to a storage battery, and a DC / AC inverter connected to the DC / DC converter and the bidirectional DC / DC converter. A hybrid energy storage system is also required to operate in response to voltage imbalances between the lines of a single-phase three-wire system during a power outage, but adding a neutral line voltage adjustment circuit to the DC / AC inverter causes the same problems as the DC / AC inverter described in Patent Document 2. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 9-65657 [Patent Document 2] Patent Publication No. 2021-93861 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power storage system and a power conversion device that can eliminate the voltage imbalance between the lines of a single-phase three-wire system during a power outage and can simplify the DC / AC inverter. [Means for solving the problem]

[0012] In order to solve the above problems, the power storage system according to the present invention comprises: a DC / DC converter connected to the power generation device; a bidirectional DC / DC converter connected to a storage battery; a DC / AC inverter having a DC end connected to the DC / DC converter and the bidirectional DC / DC converter and an AC end connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system; A control unit; A power storage system comprising: The bidirectional DC / DC converter a bidirectional step-up / step-down circuit including a first capacitor and performing step-up and step-down operations; a bidirectional inverting step-up / step-down circuit including a second capacitor connected in series with the first capacitor and performing an inverting step-up operation and an inverting step-down operation; a first voltage of the first capacitor and a second voltage of the second capacitor are applied to the DC / AC inverter, and a connection point of the first capacitor and the second capacitor is connected to the neutral line; The control unit controls charging and discharging of the first capacitor by the bidirectional step-up / step-down circuit and charging and discharging of the second capacitor by the bidirectional inverting step-up / step-down circuit so that the first voltage and the second voltage are equal when the power grid is in a power outage state.

[0013] In this configuration, the bidirectional DC / DC converter includes a bidirectional buck-boost circuit and a bidirectional inverting buck-boost circuit, and the control unit controls the charging and discharging of the first capacitor using the bidirectional buck-boost circuit and the charging and discharging of the second capacitor using the bidirectional inverting buck-boost circuit so that the first voltage and the second voltage are equal during a power outage, eliminating the need for the neutral voltage adjustment circuit provided in conventional DC / AC inverters.This configuration therefore makes it possible to eliminate voltage imbalances between the lines of a single-phase three-wire system during a power outage and simplify the DC / AC inverter.

[0014] In the power storage system, The control unit When the first voltage is greater than the second voltage, a first charge / discharge control is executed in which the bidirectional step-up / step-down circuit performs a step-down operation to discharge the first capacitor, and the bidirectional inverting step-up / step-down circuit performs an inverting step-up operation to charge the second capacitor; When the first voltage is smaller than the second voltage, a second charge / discharge control is executed in which the bidirectional step-up / step-down circuit is caused to perform a step-up operation to charge the first capacitor, and the bidirectional inverting step-up / step-down circuit is caused to perform an inverting step-down operation to discharge the second capacitor.

[0015] The power storage system includes: the bidirectional DC / DC converter includes a third capacitor connected between the connection ends on the storage battery side and shared by the bidirectional buck-boost circuit and the bidirectional inverting buck-boost circuit; When the remaining capacity of the storage battery is zero or the storage battery is in a fully charged state, and the generated power of the power generation device is applied to the DC terminal of the DC / AC inverter via the DC / DC converter, In the first charge / discharge control, the first capacitor is discharged to charge the third capacitor, and the third capacitor is discharged to charge the second capacitor; The second charge / discharge control may be configured to discharge the second capacitor to charge the third capacitor, and discharge the third capacitor to charge the first capacitor.

[0016] In order to solve the above problem, a power conversion device according to the present invention includes: A bidirectional DC / DC converter and a DC / AC inverter having a DC end connected to the bidirectional DC / DC converter and an AC end connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system; A control unit; A power conversion device comprising: The bidirectional DC / DC converter a bidirectional step-up / step-down circuit including a first capacitor and performing step-up and step-down operations; a bidirectional inverting step-up / step-down circuit including a second capacitor connected in series with the first capacitor and performing an inverting step-up operation and an inverting step-down operation; a first voltage of the first capacitor and a second voltage of the second capacitor are applied to the DC / AC inverter, and a connection point of the first capacitor and the second capacitor is connected to the neutral line; The control unit controls charging and discharging of the first capacitor by the bidirectional step-up / step-down circuit and charging and discharging of the second capacitor by the bidirectional inverting step-up / step-down circuit so that the first voltage and the second voltage are equal when the power grid is in a power outage state. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a power storage system and a power conversion device that can eliminate voltage imbalances between the lines of a single-phase three-wire system during a power outage and that can simplify the DC / AC inverter. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing a power storage system according to the present invention; [Figure 2] 10 is a diagram showing a current flow when the bidirectional chopper performs a step-down operation and the bidirectional inverting chopper performs an inverting step-up operation in the power storage system according to the present invention. FIG. [Figure 3] 10 is a diagram showing a current flow when the bidirectional chopper performs a step-up operation and the bidirectional inverting chopper performs an inverting step-down operation in the power storage system according to the present invention. FIG. [Figure 4] FIG. 1 is a diagram showing a conventional power conversion device for solar power generation. [Figure 5] FIG. 1 illustrates a conventional DC / AC inverter with a neutral voltage regulation circuit. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a power storage system and a power conversion device according to the present invention will be described with reference to the accompanying drawings.

[0020] 1 shows a hybrid power storage system 1 according to one embodiment of the present invention. The hybrid power storage system 1 is a power conversion device (power storage system) having a solar power generation function, and includes a bidirectional DC / DC converter 2, a DC / AC inverter 3, a DC / DC converter 4, a control unit 5, DC terminals T1 to T4, and independent output terminals U, O, and W.

[0021] DC terminals T1 and T2 are terminals that connect the bidirectional DC / DC converter 2 and the storage battery BT. DC terminals T3 and T4 are terminals that connect the DC / DC converter 4 and the solar cell PV (corresponding to the "power generation device" of the present invention). Independent output terminals U, O, and W are terminals that connect the DC / AC inverter 3 and the first voltage line, neutral line, and second voltage line of a single-phase three-wire system.

[0022] The independent output terminal U is connected to the first voltage line, the independent output terminal O is connected to the neutral line, and the independent output terminal W is connected to the second voltage line. A load (e.g., a home appliance) is connected between the independent output terminals UO (between the first voltage line and the neutral line) and between the independent output terminals OW (between the neutral line and the second voltage line).

[0023] The hybrid energy storage system 1 includes a grid connection terminal (not shown) connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system via a path separate from the independent output terminals U, O, W, and a relay circuit (not shown) provided between the DC / AC inverter 3 and the independent output terminals U, O, W and the grid connection terminal. The relay circuit, for example, disconnects the electrical connection between the DC / AC inverter 3 and the grid connection terminal when the power grid is in a power outage state (during a power outage), and disconnects the electrical connection between the DC / AC inverter 3 and the independent output terminals U, O, W when the power grid is in a power-on state (during power supply).

[0024] The bidirectional DC / DC converter 2 includes a bidirectional chopper 2A corresponding to the "bidirectional buck-boost circuit" of the present invention, and a bidirectional inverting chopper 2B corresponding to the "bidirectional inverting buck-boost circuit" of the present invention. The bidirectional chopper 2A performs a step-up operation and a step-down operation under the control of the control unit 5. The bidirectional inverting chopper 2B performs an inverting step-up operation and an inverting step-down operation under the control of the control unit 5. The inverting step-up operation is a step-up operation in which the output polarity is inverted relative to the input polarity, and the inverting step-down operation is a step-down operation in which the output polarity is inverted relative to the input polarity.

[0025] The bidirectional chopper 2A is composed of a first capacitor C1, a switching element Q1, a diode D1, a switching element Q2, a diode D2, a choke coil L1, and a third capacitor C3.

[0026] One end of the first capacitor C1 is connected to a DC end Ta of the DC / AC inverter 3, and is also connected to a DC end T1 on the storage battery BT side via a switching element Q1 and a choke coil L1. The other end of the first capacitor C1 (a connection point X1 with a second capacitor C2, described later) is connected to an independent output end O via the DC / AC inverter 3, and is also connected to a DC end T2 on the storage battery BT side. The third capacitor C3 is connected between the DC ends T1 and T2. The switching element Q2 is connected in parallel to the first capacitor C1 via the switching element Q1, and is also connected in parallel to the third capacitor C3 via the choke coil L1. Diodes D1 and D2 are connected in parallel in the reverse direction to the current paths of the switching elements Q1 and Q2.

[0027] The bidirectional inverting chopper 2B is composed of a second capacitor C2, a switching element Q3, a diode D3, a switching element Q4, a diode D4, a choke coil L2, and a third capacitor C3.

[0028] One end of the second capacitor C2 is connected to the other end of the first capacitor C1. The other end of the second capacitor C2 is connected to the DC end Tb of the DC / AC inverter 3 and to the DC end T1 on the storage battery BT side via switching elements Q3 and Q4. The choke coil L2 is connected in parallel to the second capacitor C2 via the switching element Q4 and to the third capacitor C3 via the switching element Q3. Diodes D3 and D4 are connected in parallel in the reverse direction in the current path of the switching elements Q3 and Q4.

[0029] As described above, the first capacitor C1 and the second capacitor C2 are connected in series to form a voltage divider circuit. It is preferable that the first capacitor C1 and the second capacitor C2 have the same capacitance.

[0030] The switching elements Q1 to Q4 may be semiconductor switches such as MOSFETs (metal oxide semiconductor field effect transistors), SiC (silicon carbide) MOSFETs, GaN (gallium nitride) MOSFETs, etc. The diodes D1 to D4 may be external diodes independent of the switching elements Q1 to Q4, or parasitic diodes of the switching elements Q1 to Q4, or both.

[0031] The DC / AC inverter 3 includes an inverter circuit including a fourth capacitor C4, switching elements Q5 to Q8 and diodes D5 to D8, a filter circuit including choke coils L3 and L4, a fifth capacitor C5 and a sixth capacitor C6, DC terminals Ta and Tb, and AC terminals Tu, To and Tw.

[0032] The fourth capacitor C4 is connected between the DC terminals Ta and Tb. The connection point X2 of the switching elements Q5 and Q6 is connected to the AC terminal Tw via a choke coil L4, and the connection point X3 of the switching elements Q7 and Q8 is connected to the AC terminal Tu via a choke coil L3. The connection point X4 of the fifth capacitor C5 and the sixth capacitor C6 is connected to the AC terminal To. The AC terminals Tu, To, and Tw are connected to the independent output terminals U, O, and W and the grid connection terminal (not shown) via a relay circuit (not shown).

[0033] The DC / DC converter 4 includes a seventh capacitor C7, an eighth capacitor C8, a choke coil L5, a switching element Q9, and diodes D9 and D10.

[0034] The seventh capacitor C7 is connected between the DC terminals T3 and T4, and the eighth capacitor C8 is connected between the DC terminals Ta and Tb. The choke coil L5, switching element Q9, and diodes D9 and D10 form a boost chopper between the seventh capacitor C7 and the eighth capacitor C8. The diode D9 is connected in parallel in the reverse direction to the current path of the switching element Q9.

[0035] The control unit 5 includes drive circuits for the switching elements Q1-Q9 for turning the switching elements Q1-Q9 on and off, and a control circuit for sending control signals to the drive circuits. The control unit 5 may be configured with an analog circuit, a digital circuit such as a microcontroller or DSP, or a circuit that combines analog and digital circuits. The control unit 5 also includes a sensor unit that detects the voltage across the terminals of the first capacitor C1 (corresponding to the "first voltage" of the present invention) and the voltage across the terminals of the second capacitor C2 (corresponding to the "second voltage" of the present invention).

[0036] The control unit 5 controls the charge and discharge of the first capacitor C1 by the bidirectional chopper 2A and the charge and discharge of the second capacitor C2 by the bidirectional inverting chopper 2B so that the voltages of the first capacitor C1 and the second capacitor C2 are equal during a power outage. When current is applied, the control unit 5 does not control the voltages of the first capacitor C1 and the second capacitor C2 to be equal.

[0037] During a power outage and when power is supplied from the storage battery BT to the independent output terminals U, O, and W (during independent output), if the voltage of the first capacitor C1 is equal to the voltage of the second capacitor C2, the control unit 5 causes the bidirectional chopper 2A to perform a step-up operation or a step-down operation, and causes the bidirectional inverting chopper 2B to perform an inverting step-up operation or an inverting step-down operation. This stabilizes the voltage of the first capacitor C1 and the voltage of the second capacitor C2 (maintaining a state in which the voltage of the first capacitor C1 and the voltage of the second capacitor C2 are equal).

[0038] During isolated output, if a voltage imbalance (unbalanced load) occurs between the first voltage line and neutral line and between the second voltage line and neutral line of a single-phase three-wire system, unless the voltages of the first capacitor C1 and the second capacitor C2 are controlled to be equal, the isolated output voltage between the isolated output terminals UO and OW will also become unbalanced. Therefore, the control unit 5 executes the following control to equalize the voltages of the first capacitor C1 and the second capacitor C2.

[0039] For example, if an unbalanced load occurs, causing the voltage of the first capacitor C1 to rise above the target voltage and the voltage of the second capacitor C2 to fall below the target voltage, the control unit 5 causes the bidirectional chopper 2A to perform a step-down operation and the bidirectional inverting chopper 2B to perform an inverting step-up operation (corresponding to the "first charge / discharge control" of the present invention). Figure 2 shows the current flow at that time.

[0040] In Figure 2 and Figure 3 described below, it is assumed that the storage battery BT is in a state where it can be charged and discharged (the storage battery BT is not fully charged and the remaining capacity is not zero), and that the power generated by the solar cell PV is boosted by the DC / DC converter 4 and applied to both ends of the fourth capacitor C4.

[0041] In the bidirectional chopper 2A in the state shown in Figure 2(A), switching element Q1 is on and switching element Q2 is off, so current flows through the path of first capacitor C1 → switching element Q1 → choke coil L1 → DC terminal T1 (→ storage battery BT), and energy is stored in choke coil L1. In the bidirectional chopper 2A in the state shown in Figure 2(B), switching elements Q1 and Q2 are off, so the energy stored in choke coil L1 is released, and current flows through the path of choke coil L1 → DC terminal T1 (→ storage battery BT) → DC terminal T2 → diode D2. Due to this voltage step-down operation of the bidirectional chopper 2A, the first capacitor C1 is discharged and the storage battery BT is charged, so the voltage of the first capacitor C1 drops.

[0042] In the bidirectional inverting chopper 2B in the state shown in Figure 2(A), switching element Q3 is on and switching element Q4 is off, so current flows from DC terminal T1 to switching element Q3 to choke coil L2 to DC terminal T2, and energy is stored in choke coil L2. In the bidirectional inverting chopper 2B in the state shown in Figure 2(B), switching elements Q3 and Q4 are off, so the energy stored in choke coil L2 is released, and current flows from choke coil L2 to second capacitor C2 to diode D4 to choke coil L2. In the bidirectional inverting chopper 2B, the period shown in Figure 2(A) is longer than the period shown in Figure 2(B). Due to this inverting boost operation of the bidirectional inverting chopper 2B, the storage battery BT is discharged and the second capacitor C2 is charged, so the voltage of the second capacitor C2 rises.

[0043] By controlling the bidirectional chopper 2A to perform a step-down operation and the bidirectional inverting chopper 2B to perform an inverting step-up operation (first charge / discharge control), the voltage of the first capacitor C1 becomes equal to the voltage of the second capacitor C2. As a result, the imbalance between the independent output voltage between the independent output terminals UO and OW is eliminated. Although not shown in FIG. 2, the first charge / discharge control includes two states: one in which switching element Q1 is on and switching elements Q2 to Q4 are off, and another in which switching element Q3 is on and switching elements Q1, Q2, and Q4 are off.

[0044] On the other hand, if an unbalanced load occurs, causing the voltage of the first capacitor C1 to drop below the target voltage and the voltage of the second capacitor C2 to rise above the target voltage, the control unit 5 controls the bidirectional chopper 2A to perform a voltage step-up operation and the bidirectional inverting chopper 2B to perform an inverting voltage step-down operation (this corresponds to the "second charge / discharge control" of the present invention). Figure 3 shows the current flow at this time.

[0045] In the bidirectional chopper 2A in the state shown in Figure 3(A), switching element Q2 is on and switching element Q1 is off, so the storage battery BT is discharged, current flows from DC terminal T1 to choke coil L1 to switching element Q2 to DC terminal T2, and energy is stored in choke coil L1. In the bidirectional chopper 2A in the state shown in Figure 3(B), switching elements Q1 and Q2 are off, so the storage battery BT is discharged and the energy stored in the choke coil L1 is released, and current flows from DC terminal T1 to choke coil L1 to diode D1 to first capacitor C1 to DC terminal T2. Due to this boost operation of the bidirectional chopper 2A, the storage battery BT is discharged and the first capacitor C1 is charged, so the voltage of the first capacitor C1 rises.

[0046] In the bidirectional inverting chopper 2B in the state shown in Figure 3(A), switching element Q4 is on and switching element Q3 is off, so current flows from second capacitor C2 to switching element Q4 to choke coil L2 to second capacitor C2, and energy is stored in choke coil L2. In the bidirectional inverting chopper 2B in the state shown in Figure 3(B), switching elements Q3 and Q4 are off, so the energy stored in choke coil L2 is released, and current flows from choke coil L2 to diode D3 to DC terminal T1 (to storage battery BT). In the bidirectional inverting chopper 2B, the period shown in Figure 3(A) is shorter than the period shown in Figure 3(B). Due to this inverting step-down operation of the bidirectional inverting chopper 2B, second capacitor C2 is discharged and storage battery BT is charged, so the voltage of second capacitor C2 drops.

[0047] By controlling the bidirectional chopper 2A to perform a step-up operation and the bidirectional inverting chopper 2B to perform an inverting step-down operation (second charge / discharge control), the voltage across the first capacitor C1 and the voltage across the second capacitor C2 become equal. As a result, the imbalance between the independent output voltage across the independent output terminal UO and the independent output voltage across the independent output terminal OW is eliminated. Although not shown in FIG. 3, the second charge / discharge control includes two states: one in which switching element Q2 is on and switching elements Q1, Q3, and Q4 are off, and another in which switching element Q4 is on and switching elements Q1 to Q3 are off.

[0048] 2, when the remaining capacity of the storage battery BT is zero, the control unit 5 causes the bidirectional chopper 2A to perform a step-down operation, discharging the first capacitor C1 and charging the third capacitor C3, and causes the bidirectional inverting chopper 2B to perform an inverting step-up operation, discharging the third capacitor C3 and charging the second capacitor C2. In this way, by charging and discharging the third capacitor C3 without charging or discharging the storage battery BT, the voltage of the first capacitor C1 and the voltage of the second capacitor C2 become equal.

[0049] 3, when the remaining capacity of the storage battery BT is zero, the control unit 5 causes the bidirectional inverting chopper 2B to perform an inverting step-down operation, discharging the second capacitor C2 and charging the third capacitor C3, and causes the bidirectional chopper 2A to perform a step-up operation, discharging the third capacitor C3 and charging the first capacitor C1. In this way, by charging and discharging the third capacitor C3 without charging or discharging the storage battery BT, the voltage of the first capacitor C1 and the voltage of the second capacitor C2 become equal.

[0050] In addition, when the remaining capacity of the storage battery BT is zero in the state of Figure 2 or Figure 3, and there is surplus power in the power generated by the solar cell PV that cannot be used up even when supplied to the independent output terminals U, O, and W, the control unit 5 supplies the surplus power to the storage battery BT when charging the third capacitor C3, thereby charging the storage battery BT.

[0051] When the storage battery BT is in a fully charged state in the state shown in Figure 2 or Figure 3, during the first charge / discharge control and the second charge / discharge control, as described above, the voltage of the first capacitor C1 and the voltage of the second capacitor C2 can be made equal by charging / discharging the third capacitor C3 instead of charging / discharging the storage battery BT.

[0052] As described above, in the hybrid energy storage system 1, the bidirectional DC / DC converter 2 includes the bidirectional chopper 2A and the bidirectional inverting chopper 2B, and the control unit 5 controls the charge and discharge of the first capacitor C1 by the bidirectional chopper 2A and the charge and discharge of the second capacitor C2 by the bidirectional inverting chopper 2B so that the voltage of the first capacitor C1 and the voltage of the second capacitor C2 are equal during a power outage, thereby eliminating the need for a neutral line voltage adjustment circuit that is included in conventional DC / AC inverters. Therefore, the hybrid energy storage system 1 makes it possible to eliminate voltage imbalances between the lines of a single-phase three-wire system during a power outage and to simplify the DC / AC inverter 3.

[0053] Furthermore, in the hybrid power storage system 1, during power outages and energization, the step-up / step-down ratio of the step-up / step-down operation performed by the bidirectional DC / DC converter 2 is shared between the bidirectional chopper 2A and the bidirectional inverting chopper 2B, thereby improving the power conversion efficiency of the bidirectional DC / DC converter 2. The improvement effect is particularly significant when a low-voltage storage battery BT is connected.

[0054] For example, if the voltage of the storage battery BT is 100 [V] and the voltage across the terminals of the fourth capacitor C4 is 400 [V], the bidirectional DC / DC converter 2 must be operated with a voltage difference of 300 [V]. If the bidirectional DC / DC converter 2 were composed only of the bidirectional chopper 2A, the bidirectional chopper 2A would perform step-up / step-down operation with a voltage difference of 300 [V], which would result in a deterioration in power conversion efficiency.

[0055] In contrast, in this embodiment where the bidirectional DC / DC converter 2 is composed of a bidirectional chopper 2A and a bidirectional inverting chopper 2B, the bidirectional chopper 2A is operated at a voltage difference of 100 [V] (the voltage of the first capacitor C1 is 200 [V]), and the bidirectional inverting chopper 2B is also operated at a voltage difference of 100 [V] (the voltage of the second capacitor C2 is 200 [V]). In this way, in this embodiment, the voltage difference can be reduced from 300 [V] to 100 [V], improving the power conversion efficiency of the bidirectional DC / DC converter 2.

[0056] Although the embodiments of the power storage system and the power conversion device according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0057] The power storage system according to the present invention is a power storage system comprising: a DC / DC converter connected to a power generation device; a bidirectional DC / DC converter connected to a storage battery; a DC / AC inverter having a DC end connected to the DC / DC converter and the bidirectional DC / DC converter and an AC end connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system; and a control unit, wherein the bidirectional DC / DC converter comprises a bidirectional buck-boost circuit including a first capacitor and performing a step-up operation and a step-down operation, and a bidirectional inverting buck-boost circuit including a second capacitor connected in series to the first capacitor and performing an inverting step-up operation and an inverting step-down operation, wherein a first voltage of the first capacitor and a second voltage of the second capacitor are applied to the DC / AC inverter, and the junction of the first capacitor and the second capacitor is connected to the neutral line, and the configuration of the control unit can be modified as appropriate as long as it controls the charge and discharge of the first capacitor by the bidirectional buck-boost circuit and the charge and discharge of the second capacitor by the bidirectional inverting buck-boost circuit so that the first voltage and the second voltage are equal when the power grid is in a power outage.

[0058] For example, the bidirectional step-up / step-down circuit of the present invention is not limited to the bidirectional chopper 2A, and the bidirectional inverting step-up / step-down circuit of the present invention is not limited to the bidirectional inverting chopper 2B.

[0059] In the above embodiment, the output voltage (generated voltage) of the solar cell PV is input to the DC / DC converter 4, but a direct current output voltage output from a power generation device other than the solar cell PV may also be input to the DC / DC converter 4. Also, a charge / discharge stand equipped with a DC / DC converter that controls the charge / discharge of a battery mounted on the electric vehicle may be added.

[0060] A power conversion device according to the present invention is a power conversion device comprising: a bidirectional DC / DC converter; a DC / AC inverter having a DC end connected to the bidirectional DC / DC converter and an AC end connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system; and a control unit, wherein the bidirectional DC / DC converter comprises a bidirectional buck-boost circuit including a first capacitor and performing a step-up operation and a step-down operation; and a bidirectional inverting buck-boost circuit including a second capacitor connected in series to the first capacitor and performing an inverting step-up operation and an inverting step-down operation, wherein a first voltage of the first capacitor and a second voltage of the second capacitor are applied to the DC / AC inverter, and the junction of the first capacitor and the second capacitor is connected to the neutral line, and the configuration of the control unit can be modified as appropriate as long as it controls the charge and discharge of the first capacitor by the bidirectional buck-boost circuit and the charge and discharge of the second capacitor by the bidirectional inverting buck-boost circuit so that the first voltage and the second voltage are equal when the power grid is in a power outage state.

[0061] For example, a power storage system obtained by removing the configuration for performing the solar power generation function (such as the DC / DC converter 4 and the part of the control unit 5 that controls the DC / DC converter 4) from the hybrid power storage system 1 of the above embodiment corresponds to the power conversion device according to the present invention. [Explanation of symbols]

[0062] 1 Hybrid energy storage system 2 Bidirectional DC / DC Converter 2A bidirectional chopper 2B Bidirectional inverting chopper 3 DC / AC inverter 4 DC / DC converters 5. Control section

Claims

1. a DC / DC converter connected to the power generation device; a bidirectional DC / DC converter connected to the storage battery; a DC / AC inverter having a DC end connected to the DC / DC converter and the bidirectional DC / DC converter and an AC end connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system; A control unit; A power storage system comprising: The bidirectional DC / DC converter comprises: a bidirectional step-up / step-down circuit including a first capacitor and performing a step-up operation and a step-down operation; a bidirectional inverting step-up / step-down circuit including a second capacitor connected in series with the first capacitor and performing an inverting step-up operation and an inverting step-down operation; a first voltage of the first capacitor and a second voltage of the second capacitor are applied to the DC / AC inverter, and a connection point of the first capacitor and the second capacitor is connected to the neutral line; The control unit controls charging and discharging of the first capacitor by the bidirectional step-up / step-down circuit and charging and discharging of the second capacitor by the bidirectional inverting step-up / step-down circuit so that the first voltage and the second voltage are equal when the power grid is in a power outage state. A power storage system characterized by:

2. The control unit When the first voltage is greater than the second voltage, a first charge / discharge control is executed in which the bidirectional step-up / step-down circuit performs a step-down operation to discharge the first capacitor and the bidirectional inverting step-up / step-down circuit performs an inverting step-up operation to charge the second capacitor; and When the first voltage is lower than the second voltage, a second charge / discharge control is executed in which the bidirectional step-up / step-down circuit is caused to perform a step-up operation to charge the first capacitor, and the bidirectional inverting step-down circuit is caused to perform an inverting step-down operation to discharge the second capacitor. The power storage system according to claim 1 .

3. the bidirectional DC / DC converter includes a third capacitor connected between the connection ends on the storage battery side and shared by the bidirectional buck-boost circuit and the bidirectional inverting buck-boost circuit; When the remaining capacity of the storage battery is zero or the storage battery is in a fully charged state, and the generated power of the power generation device is applied to the DC terminal of the DC / AC inverter via the DC / DC converter, In the first charge / discharge control, the first capacitor is discharged to charge the third capacitor, and the third capacitor is discharged to charge the second capacitor; In the second charge / discharge control, the second capacitor is discharged to charge the third capacitor, and the third capacitor is discharged to charge the first capacitor. The power storage system according to claim 2 .

4. a bidirectional DC / DC converter; a DC / AC inverter having a DC end connected to the bidirectional DC / DC converter and an AC end connected to a first voltage line, a neutral line, and a second voltage line of a single-phase three-wire system; A control unit; A power conversion device comprising: The bidirectional DC / DC converter comprises: a bidirectional step-up / step-down circuit including a first capacitor and performing a step-up operation and a step-down operation; a bidirectional inverting step-up / step-down circuit including a second capacitor connected in series with the first capacitor and performing an inverting step-up operation and an inverting step-down operation; a first voltage of the first capacitor and a second voltage of the second capacitor are applied to the DC / AC inverter, and a connection point of the first capacitor and the second capacitor is connected to the neutral line; The control unit controls charging and discharging of the first capacitor by the bidirectional step-up / step-down circuit and charging and discharging of the second capacitor by the bidirectional inverting step-up / step-down circuit so that the first voltage and the second voltage are equal when the power grid is in a power outage state. A power conversion device characterized by:

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