System connection system

Abstract

To reduce the power loss of an interconnection system, the cost of manufacture and the weight.SOLUTION: An interconnection system includes an inverter circuit 31 capable of operating in a discharge mode for converting DC power to AC power to output it and a charge mode for converting input AC power to DC power to output it. The interconnection system comprises: a first capacitor 32a connected between a first DC voltage line DCL1 and a neutral line NL1 for autonomous operation; a second capacitor 32b connected between a second DC voltage line DCL2 and the neutral line NL1 for autonomous operation; a first DC voltage between the first DC voltage line DCL1 and the neutral line NL1 for autonomous operation; a DC voltage detection section 33 for detecting a second DC voltage between the second DC voltage line DCL2 and the neutral line NL1 for autonomous operation; a neutral line voltage adjustment circuit 34 for adjusting the power storage amount of first and second capacitors 32a, 32b; and a second control section 26 for controlling the neutral line voltage adjustment circuit 34 so as to reduce difference between the first DC voltage and the second DC voltage.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a system interconnection system capable of supplying power to a load during a power outage in a power system.

Background Art

[0002] Patent Document 1 discloses a system including a power conditioner that converts DC power output from a power generation unit into AC power and outputs it to a single-phase three-wire output terminal, and an inverter that operates in a charging mode of converting AC power input from a single-phase two-wire input / output terminal into DC power to charge a storage battery and a discharging mode of converting DC power from the storage battery into AC power and outputting it from the single-phase two-wire input / output terminal. In this system, a transformer for switching the power distribution method between single-phase two-wire and single-phase three-wire, and from single-phase three-wire to single-phase two-wire is connected between the single-phase two-wire input / output terminal of the inverter and a single-phase three-wire wiring path connected to the load and the output terminal of the power conditioner.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, since a transformer for switching the power distribution method is provided between the single-phase two-wire input / output terminal of the inverter and the single-phase three-wire wiring path, or a new inverter for outputting power to the single-phase three-wire wiring is provided, the power loss, manufacturing cost, and weight of the system interconnection system increase.

[0005] The present invention has been made in view of such points, and an object thereof is to reduce the power loss, manufacturing cost, and weight of the system interconnection system.

Means for Solving the Problem

[0006] To achieve the above object, an aspect of the present invention is characterized in that a neutral line constituting a single-phase three-wire wiring is provided with the first and second DC voltage lines, and the voltage of the neutral line is controlled by turning on and off a switching element.

[0007] Specifically, an aspect of the present invention is that a system connection system includes a power conditioner that converts DC power output from a power generation unit into AC power and outputs it, and based on the energy stored in a power storage unit, the DC power input to the first and second DC voltage lines is converted into AC power and output to the first and second AC voltage lines in a discharge mode, and an inverter circuit operable in a charging mode of converting the AC power input to the first and second AC voltage lines into DC power and outputting it to the first and second DC voltage lines, a first capacitor connected between the first DC voltage line and the neutral line, a second capacitor connected between the second DC voltage line and the neutral line, a DC voltage detection unit that detects a first DC voltage between the first DC voltage line and the neutral line and a second DC voltage between the second DC voltage line and the neutral line, a neutral line voltage adjustment circuit having a switching element and adjusting the stored charge amounts of the first and second capacitors according to the duty ratio of the switching element, a first switching unit that switches which of a power grid, the first and second AC voltage lines, and the neutral line is connected to a power input terminal of a load, a second switching unit that turns on and off the connection between a connection terminal of the power conditioner and the power input terminal of the load, a neutral line voltage control that controls the duty ratio of the switching element of the neutral line voltage adjustment circuit so as to reduce the difference between the first and second DC voltages, and a control unit that performs switching control for controlling the first and second switching units.

[0008] As a result, the first and second AC voltage lines and the neutral line can be used as a single-phase three-wire wiring, eliminating the need for a transformer for switching the power distribution system as in Reference 1. To control the voltage of the neutral line, it is sufficient to provide the first and second capacitors, a DC voltage detection unit, a neutral line voltage adjustment circuit, and a control unit. Since the neutral line voltage adjustment circuit can mainly be composed of switching elements, the power loss, manufacturing cost, and weight of the system connection system can be reduced compared to the case of providing a transformer as in Reference 1.

[0009] Also, in the above aspect, the switching control is such that, in the self-operating state where the first switching unit is controlled to connect the first and second AC voltage lines and the neutral line to the power input terminal of the load, based on the difference between the AC power output from the connection terminal of the power conditioner and the power consumption of the load, the charging amount and discharging amount of the power storage unit and the second switching unit are controlled.

[0010] As a result, in the self-operating state, based on the difference between the AC power output from the connection terminal of the power conditioner and the power consumption of the load, the connection between the first and second AC voltage lines, the neutral line, and the load, and the connection terminal of the power conditioner can be controlled. Therefore, when it is determined that the state is not suitable for charging the power storage unit with the power output from the power conditioner based on the difference between the AC power output from the connection terminal of the power conditioner and the power consumption of the load, it becomes possible to prevent the charging of the power storage unit with the power output from the power conditioner.

[0011] Also, in the above aspect, the switching control is such that, in the self-operating state where the first switching unit is controlled to connect the first and second AC voltage lines and the neutral line to the power input terminal of the load, based on the DC bus voltage which is the voltage between the first and second DC voltage lines, the second switching unit is controlled.

[0012] Accordingly, in the self-driving state, based on the DC bus voltage, the connection between the first and second AC voltage lines, the neutral line, and the load and the connection terminals of the power conditioner can be controlled. Therefore, when it is determined that the state is not suitable for charging the power storage unit with the power output from the power conditioner based on the DC bus voltage, it becomes possible to prevent the charging of the power storage unit with the power output from the power conditioner.

[0013] Further, in the above aspect, the power conditioner further includes a voltage and current detection unit that detects the voltage and current output from the connection terminals of the power conditioner. In a state where the power grid is not powered off, the control unit further performs power conversion control to control the inverter circuit so that reverse power flow in which power from the power storage unit flows into the power grid does not occur based on the voltage and current detected by the voltage and current detection unit.

[0014] Accordingly, based on the voltage and current detected by the voltage and current detection unit, the discharge amount and charge amount of the power storage unit can be controlled.

Advantages of the Invention

[0015] According to the present invention, the power loss, manufacturing cost, and weight of the grid connection system can be reduced.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0018] (Embodiment 1) FIG. 1 shows a grid connection system 1 according to Embodiment 1 of the present invention. This grid connection system 1 includes a first power conditioner 10, a second power conditioner 20, and a current sensor CT.

[0019] The first power conditioner 10 includes a first DC / DC converter 11, a first DC / AC inverter 12, a first control unit 13, and a single-phase three-wire connection terminal 14. The first power conditioner 10 converts the DC power output from the solar panel 70 as a power generation unit into AC power corresponding to the voltage of the single-phase three-wire connection terminal 14 and outputs it from the single-phase three-wire connection terminal 14. When the single-phase three-wire power grid 50 is connected to the single-phase three-wire connection terminal 14, the first power conditioner 10 is connected to the power grid 50 and outputs the AC power from the single-phase three-wire connection terminal 14 to the load 60.

[0020] The first DC / DC converter 11 converts the output voltage of the solar panel 70 into a predetermined voltage and outputs it.

[0021] The first DC / AC inverter 12 converts the output voltage of the first DC / DC converter 11 into an AC voltage and outputs it. The switching elements in the first DC / AC inverter 12 are controlled by the PWM signals output by the first control unit 13.

[0022] Also, while causing the AC power output from the first DC / AC inverter 12 to be output from the single-phase three-wire connection terminal 14, the first control unit 13 controls the first DC / AC inverter 12 based on the voltage of the single-phase three-wire connection terminal 14. As a general control method, the first control unit 13 receives the measured value of the voltage of the single-phase three-wire connection terminal 14, and based on the sine value of the phase angle of the voltage of the single-phase three-wire connection terminal 14, generates an active component current command value, and based on the cosine value of the phase angle of the voltage of the single-phase three-wire connection terminal 14, generates a reactive component current command value. The sine value and cosine value of the phase angle of the voltage of the single-phase three-wire connection terminal 14 are obtained by a PLL that receives the voltage of the single-phase three-wire connection terminal 14 as an input signal. Next, the first control unit 13 obtains an output current command value by adding these active component current command values and reactive component current command values. The output current command value has the same phase as the voltage of the single-phase three-wire connection terminal 14. Then, the first control unit 13 performs feedback control of the PWM signal so that the value of the output current of the first DC / AC inverter 12 follows the output current command value. Thereby, when connecting to the power system 50 at the single-phase three-wire connection terminal 14, the first power conditioner 10 can be connected to the power system 50.

[0023] The second power conditioner 20 includes a second DC / DC converter 21, a second DC / AC inverter 30, first to third switching units 22 to 24, a voltage and current detection unit 25, and a second control unit 26.

[0024] The second DC / DC converter 21 converts the output voltage of the power storage unit 80 into a predetermined voltage and outputs DC power to the first and second DC voltage lines DCL1 and DCL2 shown in FIG. 2.

[0025] As shown in FIG. 2, the second DC / AC inverter 30 includes a smoothing capacitor C, an inverter circuit 31, first and second capacitors 32a and 32b, a DC voltage detection unit 33, a neutral line voltage adjustment circuit 34, a filter circuit 35, first and second connection terminals 36a and 36b, and a neutral line connection terminal 36c, and first and second self-standing terminals 37a and 37b, and a neutral line self-standing terminal 37c.

[0026] The smoothing capacitor C is connected to the first and second DC voltage lines DCL1 and DCL2 and smoothes the output of the second DC / DC converter 21.

[0027] The inverter circuit 31 can operate in a discharge mode in which DC power input to the first and second DC voltage lines DCL1 and DCL2 based on the energy stored in the power storage unit 80 is converted into AC power and output to the first and second AC voltage lines ACL1 and ACL2, and a charge mode in which AC power input to the first and second AC voltage lines ACL1 and ACL2 is converted into DC power and output to the first and second DC voltage lines DCL1 and DCL2.

[0028] Specifically, the inverter circuit 31 includes switching elements S1 and S2 connected in series between the first and second DC voltage lines DCL1 and DCL2, and switching elements S3 and S4 connected in series between the first and second DC voltage lines DCL1 and DCL2. Between the intermediate node of the switching elements S1 and S2 and the intermediate node of the switching elements S3 and S4, switching elements S5 and S6 whose collectors are connected to each other are connected in series. The anode of a diode D1 is connected to the central node of these switching elements S5 and S6, and the cathode of the diode D1 is connected to the first DC voltage line DCL1.

[0029] The first capacitor 32a is connected between the first DC voltage line DCL1 and the neutral line NL1 for self-sustained operation.

[0030] The second capacitor 32b is connected between the second DC voltage line DCL2 and the neutral line NL1 for self-sustained operation. The capacitance values of the first and second capacitors 32a and 32b are set equal to each other.

[0031] The DC voltage detection unit 33 includes a first voltage sensor 33a that detects a first DC voltage between the first DC voltage line DCL1 and the neutral line NL1 for independent operation, and a second voltage sensor 33b that detects a second DC voltage between the second DC voltage line DCL2 and the neutral line NL1 for independent operation.

[0032] The neutral line voltage adjustment circuit 34 adjusts the stored charges of the first and second capacitors 32a and 32b. Specifically, the neutral line voltage adjustment circuit 34 includes first and second adjustment switching elements S7 and S8 connected in series in order from the first DC voltage line DCL1 side between the first and second DC voltage lines DCL1 and DCL2, and a first reactor R1 connected between the midpoints of the first and second capacitors 32a and 32b and the midpoints of the first and second adjustment switching elements S7 and S8. The neutral line voltage adjustment circuit 34 adjusts the stored charges of the first and second capacitors 32a and 32b according to the duty ratios of the first and second adjustment switching elements S7 and S8.

[0033] The filter circuit 35 includes second and third reactors R2 and R3 provided on the first and second AC voltage lines ACL1 and ACL2 respectively, and third and fourth capacitors 35a and 35b connected in series with each other between the first and second AC voltage lines ACL1 and ACL2. The midpoint of the third and fourth capacitors 35a and 35b is connected to the neutral line NL2 for interconnection operation.

[0034] The first and second interconnection terminals 36a and 36b are connected to the first and second AC voltage lines ACL1 and ACL2 respectively. The neutral line interconnection terminal 36c is connected to the neutral line NL2 for interconnection operation.

[0035] The first and second independent operation terminals 37a and 37b are connected to the first and second AC voltage lines ACL1 and ACL2 respectively. The neutral line independent operation terminal 37c is connected to the neutral line NL1 for independent operation.

[0036] The first switching unit 22 switches which of the power system 50, the first and second AC voltage lines ACL1 and ACL2 (the first and second independent terminals 37a and 37b), and the neutral line NL1 for independent operation (neutral line independent terminal 37c) is to be connected to the power input terminal of the load 60.

[0037] The second switching unit 23 turns on and off the connection between the single-phase three-wire connection terminal 14 of the first power conditioner 10 and the power input terminal of the load 60.

[0038] The third switching unit 24 turns on and off the connection between the first and second connection terminals 36a and 36b and the neutral line connection terminal 36c of the second DC / AC inverter 30 and the power system 50.

[0039] The voltage and current detection unit 25 detects the voltage and current output from the single-phase three-wire connection terminal 14 of the first power conditioner 10.

[0040] The second control unit 26 is constituted by, for example, a CPU.

[0041] The second control unit 26 performs switching control for controlling the first to third switching units 22 to 24 by executing a program.

[0042] The switching control controls the first switching unit 22 to connect the power grid 50 to the power input terminal of the load 60 when the power grid 50 is not powered off, and to connect the first and second AC voltage lines ACL1, ACL2 and the neutral line NL1 for self - operation, that is, the first and second self - supporting terminals 37a, 37b and the neutral line self - supporting terminal 37c, to the power input terminal of the load 60 when the power grid 50 is powered off. Also, basically, the switching control controls the second switching unit 23 to turn on the connection between the single - phase three - wire connection terminal 14 of the first power conditioner 10 and the power input terminal of the load 60 when the power grid 50 is not powered off. Also, basically, the switching control turns on the connection between the first and second connection terminals 36a, 36b and the neutral line connection terminal 36c of the second DC / AC inverter 30 and the power grid 50 when the power grid 50 is not powered off, and disconnects the connection between the first and second connection terminals 36a, 36b and the neutral line connection terminal 36c of the second DC / AC inverter 30 and the power grid 50 and controls the third switching unit 24 to connect the first and second self - supporting terminals 37a, 37b and the neutral line self - supporting terminal 37c of the second DC / AC inverter 30 to the load 60 when the power grid 50 is powered off.

[0043] Also, in the self - operation state where the switching control controls the first switching unit 22 to connect the first and second AC voltage lines ACL1, ACL2 and the neutral line NL1 for self - operation to the power input terminal of the load 60, based on the DC bus voltage between the first and second DC voltage lines DCL1, DCL2, the AC power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10, and the power consumption of the load 60, the switching control controls the second switching unit 23, the second DC / AC inverter 30, and the second DC / DC converter 21. Hereinafter, the AC power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10 is denoted as P1, the power output from the second DC / AC inverter 30 to the first and second AC voltage lines (the first and second self - supporting terminals 37a, 37b) ACL1, ACL2 and the neutral line for self - operation (the neutral line self - supporting terminal 37c) NL1 based on the energy stored in the power storage unit 80 is denoted as P2, and the power consumption of the load 60 is denoted as PL.

[0044] Specifically, the switching control by the second control unit 26 repeats the operations shown in the flowchart of FIG. 3 in the self-driving state. Hereinafter, the operations shown in the flowchart of FIG. 3 will be described.

[0045] First, in S101, the second control unit 26 turns on the second switching unit 23.

[0046] Next, in S102, the second control unit 26 determines whether the DC bus voltage between the first and second DC voltage lines DCL1 and DCL2 is equal to or higher than a preset threshold value. If the DC bus voltage is not equal to or higher than the preset threshold value, the process proceeds to the process of S103. On the other hand, if the DC bus voltage is equal to or higher than the preset threshold value, the process proceeds to the process of S104.

[0047] In S103, the second control unit 26 determines whether the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 is equal to or less than the power consumption of the load 60. If the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 is equal to or less than the power consumption of the load 60, the process proceeds to the process of S105. On the other hand, if the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 is not equal to or less than the power consumption of the load 60, the process proceeds to the process of S106.

[0048] In S104, the second control unit 26 turns off the second switching unit 23 and proceeds to S108.

[0049] In S105, the second control unit 26 causes the second DC / DC converter 21 to output DC power based on the energy stored in the power storage unit 80 to the second DC / AC inverter 30. Further, the second control unit 26 operates the inverter circuit 31 of the second DC / AC inverter 30 in the discharge mode. That is, the second control unit 26 causes the second DC / AC inverter 30 to convert the output power of the second DC / DC converter 21, that is, the DC power based on the energy stored in the power storage unit 80, into AC power and output it to the first and second AC voltage lines (the first and second self - supporting terminals 37a, 37b) ACL1, ACL2. At this time, since the second switching unit 23 is on, the following Equation 1 holds.

[0050] P2 = PL - P1 ≧ 0 ··· (Equation 1) In S106, the second control unit 26 determines whether the surplus power obtained by subtracting the power consumption of the load 60 from the AC power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10 exceeds the chargeable power of the power storage unit 80. If the surplus power does not exceed the chargeable power of the power storage unit 80, the process proceeds to S107. On the other hand, if the surplus power exceeds the chargeable power of the power storage unit 80, the process proceeds to S104.

[0051] In S107, the second control unit 26 operates the inverter circuit 31 of the second DC / AC inverter 30 in the charge mode. That is, the second control unit 26 causes the second DC / AC inverter 30 to convert the surplus power obtained by subtracting the power consumption of the load 60 from the AC power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10 into DC power and output it to the second DC / DC converter 21. Further, the second control unit 26 performs voltage conversion on the DC power output by the second DC / AC inverter 30 and outputs it to the power storage unit 80. Thereby, the power storage unit 80 is charged. At this time, the following Equation 2 holds.

[0052] P2 = PL - P1 < 0 ··· (Equation 2) In S108, the second control unit 26 causes the second DC / DC converter 21 to output DC power based on the energy stored in the power storage unit 80 to the second DC / AC inverter 30. Further, the second control unit 26 operates the inverter circuit 31 of the second DC / AC inverter 30 in the discharge mode. That is, the second control unit 26 causes the second DC / AC inverter 30 to convert the output power of the second DC / DC converter 21, that is, DC power based on the energy stored in the power storage unit 80, into AC power and output it to the first and second AC voltage lines (the first and second independent terminals 37a, 37b) ACL1, ACL2. At this time, since the second switching unit 23 is off, the following equation 3 holds.

[0053] P2 = PL ··· (Equation 3) In S109, the second control unit 26 determines whether or not the power storage unit 80 can be charged with surplus power based on information from the power storage unit 80. If the power storage unit 80 can be charged with surplus power, the operation of this flowchart is started from the beginning. If the power storage unit 80 cannot be charged with surplus power, the process returns to the process of S108.

[0054] Further, the second control unit 26 performs neutral point voltage control by executing a program.

[0055] Neutral line voltage control is a control for causing the neutral line voltage adjustment circuit 34 to adjust the stored charges of the first and second capacitors 32a and 32b so as to reduce the difference between the first and second DC voltages based on the first and second DC voltages detected by the DC voltage detector 33 in the self-operating state. Specifically, in the self-operating state, when the first DC voltage is greater than the second DC voltage, the second control unit 26 increases the duty ratio of the on-period of the first adjustment switching element S7 and decreases the duty ratio of the on-period of the second adjustment switching element S8. On the other hand, when the second DC voltage is greater than the first DC voltage, the second control unit 26 increases the duty ratio of the on-period of the second adjustment switching element S8 and decreases the duty ratio of the on-period of the first adjustment switching element S7. Also, when the first DC voltage and the second DC voltage are equal to each other, the duty ratio of the on-period of the first adjustment switching element S7 and the duty ratio of the on-period of the second adjustment switching element S8 are set to 50%. Further, the neutral line voltage control also includes an operation of controlling the first and second adjustment switching elements S7 and S8 so that the sum of the first and second DC voltages becomes constant during self-operation.

[0056] Furthermore, in a state where the power grid 50 is not out of power, that is, in the interconnected operation state, the second control unit 26 further performs power conversion control for calculating power based on the current and voltage detected by the voltage-current detector 25 and controlling the inverter circuit 31 so that reverse power flow in which power from the power storage unit 80 flows into the power grid 50 does not occur. That is, the inverter circuit 31 is controlled so that the sum of the output power of the first power conditioner 10 calculated by the voltage-current detector 25 and the output power of the second DC / AC inverter 30 does not exceed the power consumption of the load 60, that is, so that the relationship PL = P1 + P2 holds.

[0057] Further, when the second control unit 26 detects a reverse power flow from the second power conditioner 20 to the power system 50 by a current sensor CT (to be described in detail later), it performs control to prevent the discharge from the power storage unit 80. Here, the grid-connected operation state is a state in which the power system 50 is connected to the power input terminal of the load 60 and the connections between the first and second grid-connected terminals 36a and 36b and the neutral grid-connected terminal 36c of the second DC / AC inverter 30 and the power system 50 are turned on. By the above power conversion control, the number of times of detecting a reverse power flow by the current sensor CT can be reduced.

[0058] Further, the current sensor CT detects a reverse power flow in which current flows from the first and second grid-connected terminals 36a and 36b and the neutral grid-connected terminal 36c of the second power conditioner 20 to the power system 50. Although schematically illustrated, the current sensor CT is realized by, for example, a CT (Current Transformer) type current sensor.

[0059] Next, a general operation of the grid-connected system 1 configured as described above will be described with reference to FIGS. 1, 4, and 5.

[0060] First, when the power system 50 is not in a power outage state, as shown in FIG. 4, the second control unit 26 controls the first switching unit 22 to connect the power system 50 to the power input terminal of the load 60. Further, the second control unit 26 controls the second switching unit 23 to turn on the connection between the single-phase three-wire connection terminal 14 of the first power conditioner 10 and the power input terminal of the load 60. Furthermore, the second control unit 26 controls the third switching unit 24 to turn on the connection between the first and second connection terminals 36a, 36b and the neutral line connection terminal 36c of the second DC / AC inverter 30 and the power system 50. Therefore, the single-phase three-wire connection terminal 14 of the first power conditioner 10 and the load 60, and the first and second connection terminals 36a, 36b and the neutral line connection terminal 36c of the second DC / AC inverter 30 are connected to the power system 50. At this time, since the single-phase three-wire connection terminal 14 of the first power conditioner 10 is connected to the power system 50, the first control unit 13 of the first power conditioner 10 receives the measured value of the voltage of the single-phase three-wire connection terminal 14, that is, the system voltage, and based on the sine value of the phase angle of the system voltage, generates a current command value for the active component, and based on the cosine value of the phase angle of the system voltage, generates a current command value for the reactive component. The sine value and cosine value of the phase angle of the system voltage are obtained by a PLL that receives the voltage of the single-phase three-wire connection terminal 14 as an input signal. Next, the first control unit 13 obtains an output current command value by adding these current command values for the active component and the current command value for the reactive component. Therefore, the output current command value has the same phase as the system voltage. Then, the first control unit 13 performs feedback control of the PWM signal so that the value of the output current of the first DC / AC inverter 12 follows the output current command value. Thereby, the first power conditioner 10 can be interconnected with the power system 50.

[0061] When the power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 exceeds the power consumption of the load 60, the power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 is sent to the load 60, and the surplus power from the first power conditioner 10 is sent to the power grid 50. In FIG. 4, the direction of the power sent from the first power conditioner 10 to the load 60 is indicated by reference symbol X1, the direction of the power between the power grid 50 and the load 60 is indicated by reference symbol X2, and the direction of the power toward the load 60 is indicated by reference symbol X3. At this time, the second control unit 26 of the second power conditioner 20 executes power conversion control so that the relationship PL = P1 + P2 holds. Also, when a reverse power flow to the power grid 50 is detected by the current sensor CT, the inverter circuit 31 of the second DC / AC inverter 30 is not made to operate in the discharge mode. Therefore, discharge from the power storage unit 80 is not performed.

[0062] On the other hand, when the power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 is less than the power consumption of the load 60, as shown by the arrow X2 surrounded by parentheses in FIG. 4, power is sent from the power grid 50 to the load 60. Then, the power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10, the power output from the first and second connection terminals 36a, 36b and the neutral wire connection terminal 36c of the second DC / AC inverter 30, and the power sent from the power grid 50 are supplied to the load 60. At this time, the second DC / AC inverter 30 outputs power so as to follow the power consumption of the load 60.

[0063] When the power system 50 transitions from a non-power outage state to a power outage state, as shown in FIGS. 1 and 5, the second control unit 26 controls the first switching unit 22 to connect the first and second self-sustaining terminals 37a, 37b and the neutral line self-sustaining terminal 37c (neutral line NL1 for self-sustaining operation) to the power input terminals of the load 60. Further, the second control unit 26 controls the third switching unit 24 to disconnect the connection between the first and second connection terminals 36a, 36b and the neutral line connection terminal 36c of the second DC / AC inverter 30 and the power system 50. Thereby, the first and second self-sustaining terminals 37a, 37b and the neutral line self-sustaining terminal 37c (neutral line NL1 for self-sustaining operation) of the second DC / AC inverter 30 are connected to the load 60. And in this self-sustaining operation state, the second control unit 26 controls the second switching unit 23 based on the DC bus voltage which is the voltage between the first and second DC voltage lines DCL1, DCL2, the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10, and the power consumption of the load 60. Specifically, the second control unit 26 turns the second switching unit 23 on and off by repeating the operation of the flowchart of FIG. 3 described above.

[0064] When the second switching unit 23 is turned on in the self-sustaining operation state, as shown in FIG. 1, the single-phase three-wire connection terminal 14 of the first power conditioner 10 is connected to the first and second self-sustaining terminals 37a, 37b and the neutral line self-sustaining terminal 37c of the second DC / AC inverter. And when the power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 exceeds the power consumption of the load 60, the DC bus voltage is not equal to or higher than a preset voltage threshold value, and the storage unit 80 can be charged by the surplus power, the second DC / AC inverter 30 converts the surplus power obtained by subtracting the power consumption of the load 60 from the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 into DC power and outputs it to the second DC / DC converter 21. Further, the second DC / DC converter 21 performs voltage conversion on the DC power output by the second DC / AC inverter 30 and outputs it to the storage unit 80. Thereby, the storage unit 80 is charged.

[0065] At this time, the following Equation 4 holds.

[0066] P2 = PL - P1 < 0 ··· (Equation 4) On the other hand, in the self - operating state, even when the power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10 exceeds the power consumption of the load 60, if the DC bus voltage is equal to or higher than a preset voltage threshold value, or if the charging of the power storage unit 80 by the surplus power is not possible, as shown in FIG. 5, the second control unit 26 turns off the second switching unit 23.

[0067] Therefore, the following Equation 5 holds at this time.

[0068] P2 = PL ··· (Equation 5) Also, in the self - operating state, when the power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10 is lower than the power consumption of the load 60, as shown by the arrow X2 surrounded by parentheses in FIG. 1, the power output from the first and second self - operating terminals 37a, 37b and the neutral - line self - operating terminal 37c of the second DC / AC inverter 30 and the AC power output from the single - phase three - wire connection terminal 14 of the first power conditioner 10 are supplied to the load 60 together.

[0069] Therefore, the following Equation 6 holds at this time.

[0070] P2 = PL - P1 ≧ 0 ··· (Equation 1) In this embodiment, since the first and second AC voltage lines ACL1, ACL2 and the neutral line for self - operation NL1 are used as single - phase three - wire wiring, an external converter such as a transformer for switching the power distribution system as in Reference 1 becomes unnecessary. To control the voltage of the neutral line for self - operation NL1, it is only necessary to provide the first and second capacitors 32a, 32b, the DC voltage detection unit 33, the neutral - line voltage adjustment circuit 34, and the second control unit 26. Since the neutral - line voltage adjustment circuit 34 is mainly composed of the first and second adjustment switching elements S7, S8, compared with the case of providing an external converter such as a transformer as in Reference 1, the power loss, manufacturing cost, and weight of the system connection system 1 can be reduced.

[0071] Also, in the power system 50 in a power failure state, since the single-phase three-wire connection terminal 14 of the first power conditioner 10 is connected to the first and second independent terminals 37a, 37b, and the neutral line independent terminal 37c of the second DC / AC inverter 30, the first power conditioner 10 regards the voltages of the first and second independent terminals 37a, 37b, and the neutral line independent terminal 37c of the second DC / AC inverter 30 as the system voltage, and outputs an AC voltage having the same phase as the voltages of the first and second independent terminals 37a, 37b, and the neutral line independent terminal 37c from the single-phase three-wire connection terminal 14.

[0072] Also, when the second control unit 26 turns off the second switching unit 23 in the self-sustaining operation state when the surplus power obtained by subtracting the power consumption of the load 60 from the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10 exceeds the chargeable power of the power storage unit 80, it is possible to prevent the overvoltage protection function from operating due to an increase in the DC bus voltage or an increase in the input voltage to the power storage unit 80 and the second DC / DC converter 21 and the second DC / AC inverter 30 from stopping. In this way, in the self-sustaining operation state, by controlling the second switching unit 23 based on the difference between the AC power output from the single-phase three-wire connection terminal 14 of the first power conditioner 10, the power consumption of the load 60, and the chargeable power of the power storage unit 80, it is possible to stably supply power to the load 60 and charge the output power of the first power conditioner 10 to the power storage unit 80.

[0073] Also, in the self-sustaining operation state, the single-phase three-wire connection terminal 14 of the first power conditioner 10 is pseudo-connected to the second DC / AC inverter 30 to supply power to the load 60. Therefore, when it is determined that the surplus power amount based on the difference between the AC power output from the first and second independent terminals 37a, 37b and the neutral line independent terminal 37c of the second DC / AC inverter 30 and the power consumption of the load 60 exceeds the chargeable amount of the power storage unit 80, the second switching unit 23 can disconnect the second DC / AC inverter 30 from the load 60 to enable stable power supply.

[0074] Also, since the second control unit 26 turns off the second switching unit 23 when the DC bus voltage is equal to or higher than the threshold value in the self-driving state, it is possible to prevent the overvoltage protection function from operating due to an increase in the DC bus voltage or an increase in the input voltage to the power storage unit 80 and stopping the second DC / DC converter 21 and the second DC / AC inverter 30.

[0075] Also, by providing the voltage and current detection unit 25, the second control unit 26 can obtain the output power amount of the first power conditioner 10, and thereby can know the power consumption amount of the load 60. Therefore, the second control unit 26 can know the total output power amount of the first power conditioner 10 and the second power conditioner 20, the power consumption amount of the load 60, and the charge and discharge amount of the power storage unit 80.

[0076] (Embodiment 2) FIG. 6 shows the system connection system 1 according to Embodiment 2 of the present invention. In the present Embodiment 2, the voltage and current detection unit 25 is not provided in the second power conditioner 20. Further, the first control unit 13 of the first power conditioner 10 transmits the power generation amount of the solar panel 70 to the second control unit 26 of the second power conditioner 20 by wired communication or wireless communication.

[0077] The second control unit 26 of the second power conditioner 20 executes control of the inverter circuit 31 based on the power generation amount of the solar panel 70 transmitted by the first control unit 13 as the power conversion control. Further, the first power conditioner 10 can reduce the frequency of the switching operation of the second switching unit 23 by adjusting the output power amount according to a command from the second control unit 26 of the second power conditioner 20.

[0078] Since other configurations are the same as those in Embodiment 1, the same reference numerals are given to the same configurations and the detailed description thereof is omitted.

[0079] In the above embodiment, the solar cell panel 70 is used as the power generation unit. However, a generator that utilizes renewable energy other than sunlight, such as wind power, or a cogeneration system may also be used as the power generation unit.

Industrial Applicability

[0080] The present invention is useful as a system connection system capable of supplying power to a load during a power outage in a power grid.

Explanation of Signs

[0081] 10 First power conditioner 14 Single-phase three-wire connection terminal 22 First switching unit 23 Second switching unit 25 Voltage and current detection unit 26 Second control unit 32a First capacitor 32b Second capacitor 31 Inverter circuit 33 DC voltage detection unit 34 Neutral line voltage adjustment circuit 60 Load 70 Solar cell panel (power generation unit) 80 Energy storage unit S7 First adjustment switching element S8 Second adjustment switching element DCL1 First DC voltage line DCL2 Second DC voltage line ACL1 First AC voltage line ACL2 Second AC voltage line NL1 Neutral line for self-operation

Claims

A power conditioner that converts DC power output from a power generation unit into AC power and outputs it, An inverter circuit operable in a discharge mode that converts DC power input to first and second DC voltage lines based on energy stored in a power storage unit into AC power and outputs it to the first and second AC voltage lines, and a charge mode that converts AC power input to the first and second AC voltage lines into DC power and outputs it to the first and second DC voltage lines, A first capacitor connected between the first DC voltage line and the neutral line, A second capacitor connected between the second DC voltage line and the neutral line, A DC voltage detection unit that detects a first DC voltage between the first DC voltage line and the neutral line and a second DC voltage between the second DC voltage line and the neutral line, A neutral line voltage adjustment circuit having a switching element that adjusts the stored charge amounts of the first and second capacitors according to the duty ratio of the switching element, A first switching unit that switches which of a power grid, the first and second AC voltage lines, and the neutral line is connected to a power input terminal of a load, A second switching unit that turns on and off the connection between a connection terminal of the power conditioner and the power input terminal of the load, A control unit that performs neutral line voltage control for controlling the duty ratio of the switching element of the neutral line voltage adjustment circuit so as to reduce the difference between the first and second DC voltages, and switching control for controlling the first and second switching units, The switching control controls the charge amount and discharge amount of the power storage unit and the second switching unit based on the difference between the AC power output from the connection terminal of the power conditioner and the power consumption of the load in an independent operation state in which the first switching unit is controlled to connect the first and second AC voltage lines and the neutral line to the power input terminal of the load. A system connection system characterized by that.

2. In the system connection system according to claim 1, The switching control controls the second switching unit based on a DC bus voltage that is the voltage between the first and second DC voltage lines in an independent operation state in which the first switching unit is controlled to connect the first and second AC voltage lines and the neutral line to the power input terminal of the load. A system connection system characterized by that.

3. In the system connection system according to claim 1 or 2, It further includes a voltage and current detection unit that detects the voltage and current output from the connection terminal of the power conditioner. The control unit controls the second switching unit based on the voltage and current detected by the voltage and current detection unit. A system connection system characterized by this.

4. A power conditioner that converts DC power output from a power generation unit into AC power and outputs it, A discharge mode in which the DC power input to the first and second DC voltage lines based on the energy stored in the power storage unit is converted into AC power and output to the first and second AC voltage lines, and the first and second AC voltage lines An inverter circuit operable in a charge mode in which the AC power input to the first and second DC voltage lines is converted into DC power and output to the first and second DC voltage lines, A first capacitor connected between the first DC voltage line and the neutral line, A second capacitor connected between the second DC voltage line and the neutral line, A DC voltage detection unit that detects a first DC voltage between the first DC voltage line and the neutral line and a second DC voltage between the second DC voltage line and the neutral line, A neutral line voltage adjustment circuit having a switching element and adjusting the power storage amount of the first and second capacitors according to the duty ratio of the switching element, A first switching unit that switches which of the power grid, the first and second AC voltage lines, and the neutral line is connected to the power input terminal of the load, A second switching unit that turns on and off the connection between the connection terminal of the power conditioner and the power input terminal of the load, A voltage and current detection unit that detects the voltage and current output from the connection terminal of the power conditioner, It includes a neutral line voltage control that controls the duty ratio of the switching element of the neutral line voltage adjustment circuit so as to reduce the difference between the first and second DC voltages, and a switching control that controls the first and second switching units. A control unit, In a state where the power grid is not powered off, the control unit further performs power conversion control for controlling the inverter circuit so that reverse power flow of power from the power storage unit to the power grid does not occur based on the voltage and current detected by the voltage and current detection unit. A system connection system characterized by this.

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