JP2014054116A - Electrical power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrical power system which reduces capacity of balance transformer required at a self-operation, and stably supplies power to a wide range of loads in a house at low cost.SOLUTION: An electrical power system of one embodiment comprises a solar panel, an inverter that converts output from the solar panel to an alternating current by interconnecting with a single-phase three-wire type power distribution system, a power storage device, a power converter that converts the output from the storage device to an alternating current by interconnecting with the power distribution system to discharge the power storage device, and converts the alternating current being generated in the power distribution system to a direct current to charge the power storage device, a first switch arranged between the power converter and the power distribution system, a transformer, a second switch arranged between the power converter and a primary side of the transformer, and a third switch arranged between a secondary side of the transformer and the power distribution system. When performing a self-operation output, the first switch is opened, the second and third switches are closed, and the inverter is interconnected with the power distribution system in which a system voltage is established by the power converter.

Description

  The present invention relates to a power supply system that operates independently in a single-phase three-wire distribution network.

  Due to the widespread use of natural energy such as solar power generation, more and more houses have installed solar power generation equipment in ordinary houses. A single-phase three-wire system is widely used as a distribution system for residential buildings in Japan, and solar panels are interconnected via a power conditioner. On the other hand, when a power failure occurs due to an earthquake or the like, it is possible to switch to a circuit for output of independent operation and supply power from a dedicated autonomous operation plug.

  In addition, a method has been proposed in which power is supplied to the entire single-phase, three-wire distribution network in the house, instead of a dedicated power plug.

Japanese Patent No. 3327774

  The conventional literature discloses that a single-phase three-wire distribution network operates independently when the inverter is disconnected from the power system. However, in order for the inverter connected to the solar panel to operate independently in a single-phase three-wire system, conventionally, a balance transformer is required for system interconnection in a single-phase-single-phase three-wire system. This balance transformer is a single-phase output solar power conditioner that is necessary for maintaining the voltage balance between the RN phase and the TN phase of the single-phase three-wire, and is a component that is directly connected to an increase in cost.

  Therefore, an object of the embodiment is to realize a power supply system that reduces the capacity of a balance transformer that is required during independent operation and stably supplies power to a wide range of loads in a home at low cost.

  A power supply system according to an embodiment includes a solar panel, an inverter that is connected to a single-phase three-wire distribution system and converts the output of the solar panel into alternating current, a power storage device, and the distribution system. A power converter that converts the output of the power storage device into alternating current to discharge the power storage device, and converts alternating current generated in the power distribution system into direct current to charge the power storage device, and the power conversion A first switch provided between the transformer and the power distribution system, a transformer, a second switch provided between the power converter and a primary side of the transformer, a secondary side of the transformer, and the transformer A third switch provided between the power distribution systems, and when the self-sustained operation is output, the first switch is released, the second and third switches are turned on, and the inverter Link to the distribution system where the system voltage is established by the converter .

1 is a diagram illustrating an overall configuration of a home power supply system according to a first embodiment. It is a figure which shows the open / close state of the switches 7-9 at the time of a self-supporting operation. It is a figure which shows the whole structure of the household power supply system which concerns on 2nd Embodiment.

First Embodiment (Basic configuration)
Hereinafter, the first embodiment of the power supply system will be described in detail with reference to FIG.

  FIG. 1 is a diagram illustrating an overall configuration of a home power supply system including a solar power generation device and a power storage device according to the first embodiment. Reference numeral 1 represents a single-phase three-wire power source drawn from the power system of the power company. The single-phase three-wire power source 1 generates AC 200 V between the RT phases with the N phase as a midpoint. 2 is a solar panel module, and 3 is a storage battery. Reference numeral 4 denotes a home load (various home appliances) connected to a single-phase three-wire power source.

  A solar power conditioner (PCS) 5 includes a control unit 5a, a step-up chopper unit 5b, smoothing capacitors C1 and C2, an inverter 5c, and an LC filter 5d. The step-up chopper unit 5b boosts the voltage of the solar panel 2 under the control of the control unit 5a and performs maximum power point tracking control. The solar panel 2 changes its output voltage and output power according to the amount of sunlight. Moreover, when the load current exceeds a predetermined value corresponding to the amount of sunlight, the output voltage of the solar panel 2 rapidly decreases and the output power decreases. The controller 5a controls the output voltage and current of the solar panel 2 using the boost chopper 5b so that the solar panel 2 operates at the maximum power. This control is called maximum power point tracking control.

  The inverter 5c performs PWM modulation on the DC voltage boosted by the boost chopper unit 5b under the control of the control unit 5a. Here, grid connection means that an AC voltage is output in the same phase as the single-phase three-wire AC generated in the distribution system 21. The LC filter 5d converts the PWM waveform voltage output from the inverter 5c into a sine wave voltage.

  A storage battery PCS 6 includes a control unit 6a, a bidirectional (buck-boost) chopper 6b, smoothing capacitors C3 and C4, a power converter 6c, and an LC filter 6d. The bidirectional chopper 6b boosts the output voltage of the storage battery 3 to discharge the storage battery 3 under the control of the control unit 6a, and charges the storage battery 3 by reducing the voltage of the smoothing capacitor C4 under the control of the control unit 6a. To do. The power converter 6c performs PWM modulation on the DC voltage boosted by the bidirectional chopper 6b under the control of the control unit 5a. The LC filter 6d converts the PWM waveform voltage output from the power converter 6c into a sine wave voltage. Further, when charging the storage battery 3, the power converter 6c converts the AC power provided from the LC filter 6d into DC power under the control of the control unit 6a, and provides it to the bidirectional chopper 6b.

  7 is a switch for selecting whether or not the distribution system 21 is connected to the single-phase three-wire power source 1, 8 is a switch for system interconnection of the storage battery PCS 6, and 9 is a switch that is closed during independent operation. 10 is a transformer for outputting the single-phase primary-phase input to the single-phase three-wire output. Reference numeral 20 denotes a main control unit that comprehensively controls the home power supply system. The main control unit 20 controls the switching of the switches 7 to 9 and controls the solar PCS and the storage battery PCS by giving commands to the control units 5a and 5b.

  The open / closed state of the switch in FIG. 1 indicates a state where the system is grid-connected, and the solar power PCS and the storage battery PCS are grid-connected to the single-phase three-wire distribution system. In the case of grid connection, the solar PCS supplies power to the in-house load together with the single-phase three-wire power source 1. In addition, if the sunlight PCS is sufficiently strong, it supplies power to the power system, the home load, and the storage battery. In addition, when there is sufficient sunshine, there is a margin in power supply to the home load, and when the system voltage is high and power cannot be supplied to the system, surplus generated power is stored in the storage battery.

  Next, the operation when the power system connected to the single-phase three-wire power source 1 fails will be described with reference to FIG. FIG. 2 shows the open / close state of the switches 7 to 9 during the independent operation.

  When the R-T phase system voltage is less than or equal to a predetermined value, the main control unit 20 determines that a power failure has occurred, opens the switch 7, stops the solar PCS 5, opens the switch 8, opens the switch 9, The operation of the storage battery PCS6 is started, and then the operation of the solar light PCS5 is started. At this time, the control unit 6a controls the chopper 6b and the power converter 6d so that the R-T phase voltage of the home power distribution network becomes AC 200V. Thereby, the storage battery PCS supplies power to the single-phase three-wire distribution network in the house via the transformer 10.

  200V home appliances are connected between the home wiring RT phases, and any number of various 100V home appliances are connected between the home wiring RN phases and TN phases, and any number of home appliances are turned on. ing. Therefore, if the switch 8 is simply closed and the self-sustained operation is performed without using the balance transformer 10, the power consumption between the home wiring RN phases and the TN phases generally differs, and the voltage between the home wiring RN phases and the T -N-phase voltage is unbalanced. For example, it is assumed that the voltage between the home wiring RN phase is 130V and the voltage between the TN phase is 70V. In such a case, the 100V home appliance does not operate normally and may be damaged. By supplying the power of the storage battery PCS to the home load via the balance transformer as in the present embodiment, no imbalance occurs in the voltage between the home wiring RN phase and the voltage between the TN phases. Photovoltaic PCS is connected to the voltage output from storage battery PCS and supplies AC200V to the residential load.

  If it is the grid connection state of FIG. 1, the inverter 5c of the sunlight PCS5 and the power converter 6c of the storage battery PCS6 output single-phase 200V. That is, the sunlight PCS 5 always outputs AC 200 V in the same phase as the system voltage, and changes the output current according to the amount of sunlight or the house load. However, as shown in FIG. 2, when the storage battery PCS6 supplies power via the transformer 10 by the above-described switch operation, the transformer secondary voltage is a predetermined voltage of a single-phase three-wire system, that is, between RN phases in Japan. The control unit 6a determines the primary side voltage according to the transformation ratio of the transformer so that the single phase is 100V between the TN phases and the VT phase is 200V. For example, if the transformation ratio between the primary side and the secondary side is 1: 2, the primary side voltage is 100V and the secondary side voltage is 200V. Here, when the solar battery PCS5 is not operated and the storage battery PCS is fully output, that is, when it is considered to be operated independently at a predetermined rated power of 200 V, the kVA capacity of the transformer 10 is required for the rated output. This leads directly to increased costs.

  Therefore, in the present embodiment, the installed solar PCS 5 is connected to the power distribution system that is operating independently by the storage battery PCS 6, thereby enabling power supply from the solar PCS side and the balance transformer. Capacity can be reduced. In the case of performing this self-sustained operation output, the solar power PCS 5 is grid-connected with the self-sustained operation output capacity on the storage battery PCS6 side or less. When the solar PCS 5 is grid-connected at a capacity equal to or higher than the self-sustained operation output capacity on the storage battery PCS 6 side, an imbalance occurs between the RN phase voltage and the TN phase voltage. This is because the magnitude of the in-home load connected between the RN phases is generally different from the magnitude of the in-home load connected between the TN phases. For example, when it is necessary to supply power to the in-house load 6 kVA in the self-sustained operation, the storage battery PCS 6 outputs 3 kVA through the balance transformer, and the solar light PCS 5 is interconnected at a maximum of 3 kVA. In this way, the capacity of the power converter 6c that AC-outputs the power of the storage battery 3 can output ½ of the power consumption of the home load that is to be supplied during the autonomous operation. In the case of FIG. 2, it is the storage battery PCS that establishes the voltage of the home distribution system. First, after the storage battery PCS6 establishes the voltage of the home distribution system, the PV-PCS 5 is interconnected.

  In this embodiment, as shown in FIG. 2, the storage battery PCS 6 supplies power to the home load via the balance transformer 10 only during the independent operation. Although the grid-connected operation may be performed via the balance transformer when the system is connected to the single-phase three-wire power source 1, the self-sustained operation mode is applied when the power system of the single-phase three-wire power source 1 fails. Assuming this, it can be said that charging / discharging through the balance transformer is not always good from the viewpoint of deterioration of efficiency. Therefore, in the present embodiment, a method of outputting from the storage battery PCS via the balance transformer only in the self-sustained operation mode is applied.

  In addition, although this embodiment demonstrated the independent operation at the time of a power failure, for example, when power is insufficient, the user may intentionally switch from the grid interconnection operation to the independent operation. In this case, a signal for instructing the independent operation mode is input to the main control unit 20 from the user via an operation unit (not shown). The main controller 20 opens the switch 7 in response to this signal. Since the subsequent operation is the same as the operation at the time of the power failure described above, a description thereof will be omitted.

[Second Embodiment]
Next, a second embodiment of the power supply system will be described with reference to FIG.

  In the second embodiment of FIG. 3, the direct current link portions 5 e and 5 f of the solar light PCS 5 and the direct current link portions 6 e and 6 f of the storage battery PCS 6 are connected via the switch circuit 14.

  In the case of photovoltaic power generation, the power supply becomes unstable, and therefore, the self-sustained operation output cannot be stably output at a high output in the embodiment of FIG. Therefore, in the embodiment of FIG. 3, the DC link portion of the storage battery PCS6 and the solar light PCS5 is connected via the diode 11 as the backflow prevention means, and this problem is solved.

  When the solar PCS 5 is stopped in a no-load state, the DC capacitor C2 may be charged via the diode 13 of the step-up chopper unit by the power generation of the solar panel, resulting in a high voltage of 400V or higher. . Under such circumstances, if the DC link of the storage battery PCS6 is directly connected to the DC link of the solar PCS, an overcurrent may flow from the potential difference. In order to prevent this, a backflow prevention diode 11 is connected. When the DC link voltage of the solar PCS 5 is high and the DC link voltage of the storage battery PCS 6 is low, the solar PCS 5 may be connected to the grid after the storage battery PCS 6 outputs a self-sustained output to the home distribution system and establishes the system voltage. When the output of the solar PCS 5 decreases, a current flows from the storage battery PCS-side DC link to the DC link of the solar PCS 5 so that the two DC link voltages have the same potential, and the current is stably output from the solar PCS.

  Further, when the power generation amount of the solar panel 2 is large and the direct current link voltage of the solar light PCS becomes equal to or higher than the direct current link voltage of the storage battery PCS, the diode 11 is short-circuited by the switching element 12 to be bypassed. In addition, the power generated by the solar panel can be directly used for charging the storage battery.

  With the configuration and implementation as described above, the capacity of the balance transformer required during the independent operation can be reduced, and power can be stably supplied to a wide range of loads in the home at low cost.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Single phase 3 wire type power supply, 2 ... Solar panel module, 3 ... Storage battery, 4 ... Home load, 5 ... Solar power conditioner (PCS), 5a ... Control part, 5b ... Boost chopper, 5c ... Inverter, 5d ... LC filter, 6 ... Storage battery PCS, 6a ... Control unit, 6b ... Bidirectional chopper, 6c ... Power converter, 6d ... LC filter, 7, 8, 9 ... Switch, 10 ... Balance transformer, 20 ... Main control Part, C1, C2 ... smoothing capacitor.

Claims (6)

Solar panels,
An inverter connected to a single-phase three-wire distribution system to convert the output of the solar panel into alternating current;
A power storage device;
Power conversion for connecting the power distribution system to convert the output of the power storage device into alternating current to discharge the power storage device, and converting the alternating current generated in the power distribution system to direct current to charge the power storage device And
A first switch provided between the power converter and the power distribution system;
A transformer,
A second switch provided between the power converter and the primary side of the transformer;
A third switch provided between the secondary side of the transformer and the power distribution system;
In the case of self-sustained operation output, the first switch is released, the second and third switches are turned on, and the inverter is connected to a power distribution system in which a system voltage is established by the power converter. A featured power supply system.   When the power distribution system is supplied with power from a single-phase three-wire power source, the discharge power of the power storage device is supplied from the power converter to the power distribution system without passing through the transformer. The power supply system according to claim 1.   3. The power supply system according to claim 1, wherein the output of the inverter is controlled to be smaller than the output of the power converter during the self-sustained operation.   4. The power supply system according to claim 1, wherein a direct current side of the inverter and a direct current side of the power converter are connected in parallel.   A backflow prevention means is provided in a path connecting the DC side of the inverter and the DC side of the power converter in parallel, and the solar panel side power is not supplied to the power storage device side. The power supply system according to claim 4.   A switch for short-circuiting the backflow prevention means is provided, and the switch is turned on when a voltage difference between the DC side voltage of the inverter and the DC side voltage of the power converter becomes a predetermined value or less. The power supply system according to claim 5.

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