Power supply system

Abstract

To provide a power supply system capable of outputting the same rating power during system interconnection operation and during autonomous operation while suppressing the increase of components.SOLUTION: Any one of system interconnection operation and autonomous operation is selected by operating a first relay Ry1 and a second relay Ry2. In the case of system interconnection operation, the first relay Ry1 connects two first reactors in series, thereby forming between a DC / AC power converter 2 and a load 4 an LCL filter consisting of two first reactors L1 connected in series, a first capacitor C1, and a second reactor L2. In the case of autonomous operation, the first relay Ry1 connects the two first reactors L1 in parallel, thereby forming between the DC / AC converter 2 and the load 4 an LC filter consisting of the two first reactors L1 connected in parallel, and a second capacitor C2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power supply system that includes a DC / AC power converter capable of operating in connection with a power grid and that can switch between grid-connected operation and stand-alone operation. [Background technology]

[0002] FIG. 8 is a diagram showing the configuration of a conventional power supply system 30 disclosed in Non-Patent Document 1. As shown in FIG. 8, the power supply system 30 includes a DC / AC power converter 2 capable of operating in a grid-connected manner with a power grid 1. A DC power source 3, such as a solar power generation system or a storage battery, is connected to the DC / AC power converter 2. The DC / AC power converter 2 is an inverter that converts a direct current (DC) voltage supplied from the DC power source 3 into an alternating current (AC) voltage. The power supply system 30 includes a first relay Ry1 that can switch between a grid-connected operation in which power is supplied from the power grid 1 and the DC / AC power converter 2 to a general load 4a, and an independent operation in which power is supplied from the DC / AC power converter 2 to a critical load 4b. The power supply system 30 includes two first reactors L1, one first capacitor C1, one second reactor L2, and one second relay Ry2.

[0003] During grid-connected operation, the first relay Ry1 comes into contact with the upper contact shown in Fig. 8, thereby forming an LCL filter between the DC / AC power converter 2 and the general load 4a, which is made up of two first reactors L1, a first capacitor C1, and a second reactor L2 connected in series. Then, the controller 21 of the DC / AC power converter 2 adjusts the power between the DC power source 3 and the power grid 1 based on the detected value of the current of the first reactor L1.

[0004] During stand-alone operation, the first relay Ry1 contacts the lower contact shown in Fig. 8 and the second relay Ry2 closes the contact, forming an LC filter consisting of two first reactors L1 and a first capacitor C1 connected in series between the DC / AC power converter 2 and the important load 4b. Then, the controller 21 controls the power supplied to the important load 4b. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Yaskawa Electric "Block diagram of solar power generation power conditioner Enewell-SOL P3A"<URL:https: / / www.e-mechatronics.com / product / environment / esol-p3 / block / index.html> Summary of the Invention [Problem to be solved by the invention]

[0006] The conventional power supply system 30 shown in FIG. 8 supplies power to a general load 4a during grid-connected operation, but only to a critical load 4b during islanded operation. Therefore, a power supply system that can supply power to all loads is required. Furthermore, the first reactor L1 and first capacitor C1 that form the LC filter during islanded operation are not specifically designed for islanded operation and therefore do not support three-phase loads. Therefore, the rated power of the power supply system 30 during islanded operation may be lower than that during grid-connected operation. For example, while the rated power during three-phase grid-connected operation is a maximum of 9.9 kW, the rated power during islanded operation may be a single-phase maximum of 4 kW or a maximum of 4 kW x 2.

[0007] In order to solve these problems, a power supply system 40 of Comparative Example 1 shown in FIG. 9 can be considered. FIG. 9 is a diagram showing the configuration of the power supply system 40 of Comparative Example 1. As shown in FIG. 9, the power supply system 40 includes a DC / AC power converter 2 that can operate in a grid-connected manner with a power grid 1. A DC power source 3 is connected to the DC / AC power converter 2. The power supply system 40 includes a first relay Ry1 and a second relay Ry2 that can switch between a grid-connected operation in which power is supplied from the power grid 1 and the DC / AC power converter 2 to a load 4, and an independent operation in which power is supplied from the DC / AC power converter 2 to the load 4. The power supply system 40 includes four first reactors L1, and one each of a second reactor L2, a first capacitor C1, a second capacitor C2, and a third relay Ry3.

[0008] During grid-connected operation, the first relay Ry1 contacts the upper contact shown in Fig. 9 and the second relay Ry2 contacts the right contact shown in Fig. 10, thereby forming an LCL filter consisting of two first reactors L1, a first capacitor C1, and a second reactor L2 connected in series between the DC / AC power converter 2 and the load 4. Then, based on the detected current value, the controller 21 of the DC / AC power converter 2 adjusts the power between the DC power source 3 and the power grid 1.

[0009] During islanded operation, the first relay Ry1 contacts the lower contact shown in Fig. 9, the second relay Ry2 contacts the left contact shown in Fig. 10, and the third relay Ry3 closes its contact, thereby forming an LC filter consisting of two first reactors L1 and a first capacitor C1 connected in parallel between the DC / AC power converter 2 and the load 4. Then, the controller 21 controls the power supplied to the load 4. Thus, the power supply system 40 of Comparative Example 1 supplies power to all of the loads 4 even during islanded operation, unlike the power supply system 30 of the prior art which supplies power only to the important load 4b during islanded operation.

[0010] Furthermore, unlike the power supply system 30 of the prior art, the power supply system 40 of Comparative Example 1 has a first reactor L1 and a second capacitor C2 that form an LC filter during stand-alone operation, which are specially designed for stand-alone operation. Therefore, the power supply system 40 of Comparative Example 1 can output the same rated power during stand-alone operation as during grid-connected operation.

[0011] However, in grid-connected operation, emphasis is placed on current THD (Total Harmonic Distortion) and the current distortion rate must be kept low, so the inductance of the first reactor L1 of the LCL filter used in grid-connected operation must be set high. In isolated operation, emphasis is placed on the target value of voltage THD, and the voltage distortion rate must be kept low even when dealing with a nonlinear load. Therefore, the capacitance of the second capacitor C2 of the LC filter used in grid-connected operation must be set high. Therefore, in the power supply system 40 of Comparative Example 1, the components constituting the LC filter used in grid-connected operation and the components constituting the LCL filter used in grid-connected operation are not common. As a result, the power supply system 40 of Comparative Example 1 has a larger number of filter components and a larger filter size than the power supply system 30 of the prior art.

[0012] In order to prevent such an increase in the number of filter components, a power supply system 50 of Comparative Example 2 shown in Fig. 10 can be considered. Fig. 10 is a diagram showing the configuration of the power supply system 50 of Comparative Example 2. As shown in Fig. 10, the power supply system 50 includes a DC / AC power converter 2 that can operate in a grid-connected manner with a power grid 1. A DC power source 3 is connected to the DC / AC power converter 2. The power supply system 50 includes a first relay Ry1 that can switch between a grid-connected operation in which power is supplied from the power grid 1 and the DC / AC power converter 2 to a load 4, and an independent operation in which power is supplied from the DC / AC power converter 2 to the load 4. The power supply system 50 includes two first reactors L1, and one each of a first capacitor C1, a second reactor L2, a second relay Ry2, a third relay Ry3, and a fourth relay Ry4.

[0013] During grid-connected operation, the first relay Ry1 contacts the contact on the right side shown in Fig. 10 and the second relay Ry2 and fourth relay Ry4 both close their contacts, thereby forming an LCL filter consisting of two first reactors L1, a first capacitor C1, and a second reactor L2 connected in series between the DC / AC power converter 2 and the load 4. Then, the controller 21 of the DC / AC power converter 2 adjusts the power between the DC power source 3 and the power grid 1.

[0014] During stand-alone operation, the first relay Ry1 contacts the contact on the left side shown in Fig. 10, the third relay Ry3 and the fourth relay Ry4 both close their contacts, and the second relay Ry2 opens its contact, thereby forming an LCL filter consisting of two first reactors L1, a first capacitor C1, and a second reactor L2 connected in series between the DC / AC power converter 2 and the load 4. Then, the controller 21 controls the power supplied to the load 4.

[0015] As described above, the power supply system 50 of Comparative Example 2 can use the same components for the LCL filter regardless of whether the system is grid-connected or stand-alone. Therefore, the number of components constituting the filter is the same as that of the power supply system 30 of the prior art. However, as shown in FIG. 10 , the power supply system 50 of Comparative Example 2 requires connecting the neutral point of the power grid 1 and the midpoint of the first capacitor C1 of the LCL filter to the DC input of the DC / AC power converter 2. The current at the midpoint of the first capacitor C1 is then detected to control the neutral point current when the voltage distortion factor deteriorates due to a nonlinear load. Therefore, compared to the power supply system 30 of the prior art, the power supply system 50 of Comparative Example 2 requires additional wiring for connecting to the neutral point and control system components for detecting and controlling the current at the midpoint of the first capacitor C1 of each phase. Furthermore, the power supply system 50 of Comparative Example 2 may experience heat generation in the wiring and components when the current flowing through the neutral point increases. Furthermore, the power supply system 50 of Comparative Example 2 requires an improvement in the calculation capability of the controller 21 due to the increased complexity of the control, and an improvement in the accuracy of current detection.

[0016] Therefore, an object of the present invention is to provide a power supply system that can output the same rated power during grid-connected operation and during stand-alone operation while suppressing an increase in the number of parts. [Means for solving the problem]

[0017] A power supply system according to the present invention includes a DC / AC power converter capable of operating in a grid-connected manner with a power grid, and is capable of switching between a grid-connected operation in which power is supplied to a load from the power grid and the DC / AC power converter, and an independent operation in which power is supplied to the load from the DC / AC power converter, and the power supply system includes a first relay, a second relay, a third relay, a first reactor, a second reactor, a first capacitor, and a second capacitor, and either the grid-connected operation or the independent operation is selected by operation of the first relay and the second relay, and during the grid-connected operation, The first relay connects the two first reactors in series, thereby forming an LCL filter between the DC / AC power converter and the load, which is made up of the two first reactors connected in series, the first capacitor, and the second reactor; and during the stand-alone operation, the first relay connects the two first reactors in parallel, and the third relay closes its contact, thereby forming an LC filter between the DC / AC power converter and the load, which is made up of the two first reactors connected in parallel and the second capacitor.

[0018] The present invention provides a power supply system that can output the same rated power during grid-connected operation and grid-independent operation while suppressing an increase in parts, by forming an LCL filter including two first reactors connected in series during grid-connected operation and forming an LC filter including two first reactors connected in parallel during grid-independent operation.

[0019] In one aspect of the power supply system according to the present invention, the capacitances of the first capacitor and the second capacitor may be set so that the resonant frequency of the LCL filter formed during the grid-connected operation and the resonant frequency of the LC filter formed during the stand-alone operation are the same frequency.

[0020] The power supply system according to the present invention may be applicable to any of single-phase two-wire, single-phase three-wire, and three-phase four-wire power distribution systems. [Effects of the Invention]

[0021] The present invention can provide a power supply system that can output the same rated power during grid-connected operation and during stand-alone operation while suppressing an increase in the number of parts. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram showing a connection configuration during grid-connected operation of a power supply system according to a first embodiment. FIG. [Figure 2] 1 is a diagram showing a connection configuration during independent operation of the power supply system of the first embodiment. FIG. [Figure 3] 1 is a table showing a comparison of the number of parts in the power supply system of the first embodiment, the power supply system of the prior art, and the power supply systems of comparative examples 1 and 2. [Figure 4] 1 is a comparison table of the power supply system of the first embodiment, a power supply system of the prior art, and power supply systems of comparative examples 1 and 2. [Figure 5] FIG. 1 is a diagram illustrating the relationship between the capacitance of a capacitor and the resonant frequency in an LC filter. [Figure 6] FIG. 10 is a diagram showing a connection configuration during grid-connected operation of a power supply system according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing a connection configuration during independent operation of a power supply system according to a second embodiment. [Figure 8] FIG. 1 is a diagram showing the configuration of a conventional power supply system. [Figure 9]FIG. 1 is a diagram showing a configuration of a power supply system according to a first comparative example. [Figure 10] FIG. 10 is a diagram showing the configuration of a power supply system according to a second comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0023] First Embodiment A power supply system 10 according to a first embodiment will be described below with reference to FIGS. 1 to 5. FIG. 1 is a diagram showing a connection configuration of the power supply system 10 during grid-connected operation. FIG. 2 is a diagram showing a connection configuration of the power supply system 10 during stand-alone operation. As shown in FIGS. 1 and 2, the power supply system 10 includes a DC / AC power converter 2 capable of operating in grid-connected operation with a single-phase two-wire power system 1. A DC power source 3, such as a solar power generation system or a storage battery, is connected to the DC / AC power converter 2. The DC / AC power converter 2 is an inverter that converts a DC voltage supplied from the DC power source 3 into an AC voltage. The power supply system 10 includes a first relay Ry1 and a second relay Ry2 that can switch between grid-connected operation in which power is supplied from the power system 1 and the DC / AC power converter 2 to a load 4, and stand-alone operation in which power is supplied from the DC / AC power converter 2 to the load 4. The power supply system 10 includes two first reactors L1, one second reactor L2, one first capacitor C1, one second capacitor C2, and one third relay Ry3.

[0024] The power supply system 10 selects either grid-connected operation or stand-alone operation depending on the operation of the first relay Ry1 and the second relay Ry2. As shown in FIG. 1, the first relay Ry1 contacts the upper contact and the second relay Ry2 contacts the right contact, causing the power supply system 10 to enter a state of grid-connected operation. During grid-connected operation, the third relay Ry3 opens its contact, so no voltage is applied to the second capacitor C2. Then, as shown in FIG. 2, the first relay Ry1 contacts the lower contact, the second relay Ry2 contacts the left contact, and the third relay Ry3 closes its contact, causing the power supply system 10 to enter a state of stand-alone operation.

[0025] Furthermore, the first relay Ry1 has the function of switching between a state in which two first reactors L1 are connected in series and a state in which two first reactors L1 are connected in parallel. As shown in Figure 1, when the first relay Ry1 contacts the upper contact, the two first reactors L1 are connected in series. When the first relay Ry1 contacts the lower contact, the two first reactors L1 are connected in parallel. Each of the two first relays Ry1 has an inductance of 150 μH. Therefore, when the two first reactors L1 are connected in series, the inductance is 300 μH, and when the two first reactors L1 are connected in parallel, the inductance is 75 μH.

[0026] During grid-connected operation, as shown in Fig. 1, the first relay Ry1 contacts the upper contact, the second relay Ry2 contacts the right contact, and the third relay Ry3 opens its contact, so that an LCL filter consisting of two first reactors L1 connected in series, a first capacitor C1, and a second reactor L2 is formed between the DC / AC power converter 2 and the load 4. Then, the controller 21 of the DC / AC power converter 2 controls the current in the first reactor L1 while monitoring it, thereby adjusting the power between the DC power source 3 and the power grid 1.

[0027] During stand-alone operation, as shown in Fig. 2, the first relay Ry1 contacts the lower contact, the second relay Ry2 contacts the left contact, and the third relay Ry3 closes its contact, so that an LC filter consisting of two first reactors L1 and a first capacitor C1 connected in parallel is formed between the DC / AC power converter 2 and the load 4. Then, the controller 21 controls the voltage of the second capacitor C2 while monitoring it, thereby controlling the power supplied to the load 4.

[0028] In grid-connected operation, it is necessary to prioritize current THD and reduce the current distortion rate, so the inductance of the reactor in the LCL filter used in grid-connected operation must be set high. Therefore, in power supply system 10, during stand-alone operation, two first reactors L1 are connected in parallel to form a reactor with an inductance of 75 μH in the LC filter, while during grid-connected operation, the two first reactors L1 are connected in series to form a reactor with an inductance of 300 μH in the LCL filter.

[0029] In islanded operation, the target value of voltage THD is important, and voltage distortion must be kept low even when dealing with a nonlinear load, so the capacitance of the second capacitor C2 of the LC filter used in islanded operation must be set high. Therefore, in power supply system 10, the capacitance of the first capacitor C1 of the LCL filter used in grid-connected operation is set to 38 μF, while the capacitance of the second capacitor C2 of the LC filter used in islanded operation is set to 150 μF.

[0030] In this way, the power supply system 10 forms an LCL filter suitable for grid-connected operation during grid-connected operation, and an LC filter suitable for grid-connected operation during grid-independent operation, so that the power supply system 10 can output the same rated power during grid-connected operation and grid-independent operation. Furthermore, because these LCL filters and LC filters can share components for the two first reactors L1, the power supply system 10 can suppress an increase in the number of components constituting the filters. Therefore, the power supply system 10 can output the same rated power during grid-connected operation and grid-independent operation while suppressing an increase in the number of components.

[0031] 3 is a table showing a comparison of the number of parts among the power supply system 10 of the first embodiment, the power supply system 30 of the prior art, the power supply system 40 of Comparative Example 1, and the power supply system 50 of Comparative Example 2. As shown in FIG. 3, the power supply system 10 of the first embodiment has more parts than the power supply system 30 of the prior art, which cannot output the same rated power during grid-connected operation and during stand-alone operation, but has fewer parts than the power supply system 40 of Comparative Example 1 and the power supply system 50 of Comparative Example 2.

[0032] Furthermore, unlike the power supply system 50 of Comparative Example 2, the power supply system 10 does not require connecting a neutral point to the DC / AC power converter 2, nor does it require control of the neutral point current. Figure 4 is a comparison table of the power supply system 10 of the first embodiment, the power supply system 30 of the conventional technology, the power supply system 40 of Comparative Example 1, and the power supply system 50 of Comparative Example 2. As shown in Figure 4, the power supply system 10 of the first embodiment is able to output the same rated power during grid-connected operation and during stand-alone operation, while requiring a small number of components. In addition, compared to the power supply system 50 of Comparative Example 2, it also has the advantage of requiring fewer objects to be controlled, since it does not require connecting a neutral point or controlling the neutral point current.

[0033] 5 is a diagram showing the relationship between the capacitance and resonant frequency of a capacitor in an LC filter. If the resonant frequency of the LC filter is F, the inductance of the reactor is L, and the capacitance of the capacitor is C, the relationship between the resonant frequency F, the inductance L, and the capacitance C satisfies the following equation (1).

[0034]

number

[0035] FIG. 5 is a graph showing the relationship between the capacitance of the capacitor in the LC filter and the resonant frequency calculated using Equation 1 when the reactor inductance is 300 μH and 75 μH. In the case of grid-connected operation, the two first reactors L1 are connected in series, resulting in an inductance of 300 μH, and the capacitance of the first capacitor C1 is 38 μF. As shown in FIG. 5, the resonant frequency is 1500 Hz. In the case of islanded operation, the two first reactors L1 are connected in parallel, resulting in an inductance of 75 μH, and the capacitance of the first capacitor C1 is 150 μF. As shown in FIG. 5, the resonant frequency is 1500 Hz. In this way, in the power supply system 10, the capacitances of the first capacitor C1 and the second capacitor C2 are set so that the resonant frequency of the LC filter formed during grid-connected operation and the resonant frequency of the LC filter formed during islanded operation are the same frequency. Therefore, the power supply system 10 can achieve the same resonant frequency characteristics in both grid-connected operation and stand-alone operation.

[0036] Generally, the inductance of a reactor tends to decrease as the current flowing therethrough increases. By connecting two first reactors L1 in series during grid-connected operation, the power supply system 10 can achieve both high current and high inductance. Furthermore, a high-current, low-inductance reactor generally tends to have large current ripples as the inductance decreases. By connecting two first reactors L1 in parallel during stand-alone operation, the power supply system 10 can suppress heat generation per first reactor L1 even under conditions where the inductance is reduced.

[0037] <Second embodiment> Next, a power supply system 20 according to a second embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing a connection configuration of the power supply system 20 during grid-connected operation. FIG. 7 is a diagram showing a connection configuration of the power supply system 20 during stand-alone operation. As shown in FIGS. 6 and 7, the power supply system 20 includes a DC / AC power converter 2 capable of operating in grid-connected operation with a three-phase, four-wire power system 1. A DC power source 3, such as a solar power generation system or a storage battery, is connected to the DC / AC power converter 2. The DC / AC power converter 2 is an inverter that converts a DC voltage supplied from the DC power source 3 into an AC voltage. The power supply system 20 includes a first relay Ry1, a second relay Ry2, and a third relay Ry3, one for each of the R phase, the S phase, and the T phase. The power supply system 20 includes first reactors L1, two for each of the R phase, the S phase, and the T phase. A second reactor L2, a first capacitor C1, and a second capacitor C2 are provided for each of the R phase, S phase, and T phase.

[0038] The power supply system 20 selects either grid-connected operation or stand-alone operation depending on the operation of the first relay Ry1 and the second relay Ry2. As shown in Fig. 6, the first relay Ry1 contacts the upper contact and the second relay Ry2 contacts the right contact for three phases, i.e., the R, S, and T phases, thereby placing the power supply system 20 in a state of grid-connected operation. During grid-connected operation, the third relay Ry3 opens its contact, so no voltage is applied to the second capacitor C2. Then, as shown in Fig. 7, the first relay Ry1 contacts the lower contact, the second relay Ry2 contacts the left contact, and the third relay Ry3 closes its contact for three phases, i.e., the R, S, and T phases, thereby placing the power supply system 20 in a state of stand-alone operation.

[0039] Furthermore, the first relay Ry1 provided for each of the R, S, and T phases has the function of switching between a state in which two first reactors L1 are connected in series and a state in which two first reactors L1 are connected in parallel. As shown in FIG. 6, when the first relay Ry1 contacts the upper contact, the two first reactors L1 are connected in series. When the first relay Ry1 contacts the lower contact, the two first reactors L1 are connected in parallel. As shown in FIG. 7, each of the first relays Ry1 has an inductance of 150 μH. Therefore, when the two first reactors L1 are connected in series, the inductance is 300 μH, and when the two first reactors L1 are connected in parallel, the inductance is 75 μH.

[0040] During grid-connected operation, as shown in Fig. 6, the first relay Ry1 contacts the upper contact, the second relay Ry2 contacts the right contact, and the third relay Ry3 opens its contact, so that an LCL filter consisting of two first reactors L1 connected in series, a first capacitor C1, and a second reactor L2 is formed between the DC / AC power converter 2 and the load 4 in each of the R, S, and T phases. Then, the controller 21 of the DC / AC power converter 2 controls the current in the first reactor L1 while monitoring it in the three phases of the R, S, and T phases, thereby adjusting the power between the DC power source 3 and the power grid 1.

[0041] During stand-alone operation, as shown in Fig. 7, the first relay Ry1 contacts the lower contact, the second relay Ry2 contacts the left contact, and the third relay Ry3 closes its contact, so that an LC filter consisting of two first reactors L1 and a first capacitor C1 connected in parallel is formed between the DC / AC power converter 2 and the load 4 in each of the R, S, and T phases. Then, the controller 21 controls the voltage of the second capacitor C2 while monitoring the voltage of the second capacitor C2 in the three phases of the R, S, and T phases, thereby controlling the power supplied to the load 4.

[0042] Like the power supply system 10 of the first embodiment, the power supply system 20 forms an LCL filter suitable for grid-connected operation during grid-connected operation, and forms an LC filter suitable for grid-connected operation during grid-independent operation, so that the power supply system 20 can output the same rated power during grid-connected operation and grid-independent operation. Furthermore, because these LCL filters and LC filters can share components for the two first reactors L1, the power supply system 20 can suppress an increase in the number of components constituting the filters. Therefore, the power supply system 20 can output the same rated power during grid-connected operation and grid-independent operation while suppressing an increase in the number of components.

[0043] Furthermore, in the power supply system 20, the capacitance of the first capacitor C1 is set to 38 μF and the capacitance of the second capacitor C2 is set to 150 μF in each of the R phase, S phase, and T phase, so that, similar to the power supply system 10 of the first embodiment, the resonant frequency is 1500 Hz in both grid-connected operation and stand-alone operation.

[0044] <Supplementary information on the embodiment> The power supply system of the present invention is not limited to the above-described embodiment and can be embodied in various forms within the scope of the present invention. For example, the inductance of the first reactor L1 does not have to be 150 μH. Furthermore, the power supply system of the present invention can be applied to any of single-phase two-wire, single-phase three-wire, and three-phase four-wire power distribution systems. [Explanation of symbols]

[0045] 1 Power system, 2 DC / AC power converter, 3 DC power supply, 4 Load, 4a General load, 4b Important load, 10, 20, 30, 40, 50 Power supply system, 21 Controller, C1 First capacitor, C2 Second capacitor, L1 First reactor, L2 Second reactor, Ry1 First relay, Ry2 Second relay, Ry3 Third relay.

Claims

1. Equipped with a DC / AC power converter that can be operated in conjunction with the power grid, A power supply system capable of switching between a grid-connected operation in which power is supplied to a load from the power grid and the DC / AC power converter, and an independent operation in which power is supplied to the load from the DC / AC power converter, The power supply includes a first relay, a second relay, a third relay, a first reactor, a second reactor, a first capacitor, and a second capacitor; Either the grid-connected operation or the stand-alone operation is selected by the operation of the first relay and the second relay, During the grid-connected operation, the first relay connects the two first reactors in series, thereby forming an LCL filter between the DC / AC power converter and the load, the LCL filter being configured by the two first reactors connected in series, the first capacitor, and the second reactor; and during the stand-alone operation, the first relay connects the two first reactors in parallel, and the third relay closes its contact, thereby forming an LC filter between the DC / AC power converter and the load, the LC filter being made up of the two first reactors connected in parallel and the second capacitor.

2. 2. The power supply system according to claim 1, a power supply system characterized in that the capacitances of the first capacitor and the second capacitor are set so that the resonant frequency of the LC filter formed during the grid-connected operation and the resonant frequency of the LC filter formed during the stand-alone operation are the same frequency.

3. 3. The power supply system according to claim 1 or 2, A power supply system that can be applied to any of single-phase two-wire, single-phase three-wire, and three-phase four-wire power distribution systems.

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