JP2013229960A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power converter in which safety is enhanced during self-sustained operation.SOLUTION: A power conversion means capable of self-sustained operation for supplying power to a load in a state disconnected from a power system comprises: power conversion means (converter 110, inverter 130, capacitors 120A, 120B, 150A and 150B, reactors 140A and 140B); a switch 190 for switching between a state connected with a power system and a state disconnected from a power system; a terminal block 180 for self-sustained operation which connects and disconnects a load to be supplied with power during self-sustained operation; a ground fault detector 100 for detecting ground fault in the previous stage of the power conversion means; and a ground fault detector 160 for detecting ground fault in the subsequent stage of the power conversion means and in the previous stage of the switch 190 and terminal block 180 for self-sustained operation.

Description

  The present invention relates to a power conversion device interconnected with a grid.

  In general, power converters connected to the grid have a function of detecting ground faults on the input side and output side. If this happens, immediately detect a ground fault to ensure safety. The function of detecting a ground fault determines a place to install after assuming a place where there is a possibility of ground fault.

  For example, Patent Literature 1 discloses a power conditioner for photovoltaic power generation, which is one of power conversion devices interconnected with a grid. In this power conditioner, as shown in FIG. 1 of Patent Document 1, a relay for connecting and disconnecting a ZCT (zero phase current transformer), which is a function of detecting a ground fault, with the system It is installed in the rear stage. In this case, when a ground fault occurs on the negative electrode side of the solar cell, there is a path through which the ground fault current flows through the ground to the positive side of the solar cell via the ground on the system side. Since it penetrates, it can be detected that a ground fault has occurred by detecting the zero-phase current.

  A function that allows the power conversion device to supply power to the user's load (electrical device) only when the power conversion device connected to the system (system connection power conversion device) is disconnected due to a system abnormality or the like (Hereinafter referred to as a self-sustaining operation function).

Japanese Patent No. 4206998

  In conventional grid-connected power converters that have a self-sustaining operation function, a ground fault at the time of grid connection is assumed, but it is not assumed to detect a ground fault at the time of autonomous operation. There is a problem in that it is impossible to detect a ground fault when a person or a contractor makes an electric shock and cannot secure safety.

  The present invention has been made in view of the above, and immediately detects a ground fault when a ground fault occurs in any of a grid-connected state and a self-sustaining operation state. It is an object of the present invention to obtain a power converter with improved safety that can safely stop the power converter.

  In order to solve the above-described problems and achieve the object, the present invention is a power conversion device capable of independent operation that supplies power to a load in a state of being disconnected from a power system, and converts DC power to AC power. Power conversion means for conversion, switching means for switching between a state connected to the power system and a state disconnected from the power system, a connection means for connecting and disconnecting a load to be supplied with power during self-sustaining operation, and the power A first ground fault detection means for detecting a ground fault before the conversion means; and a second ground fault detection that is a subsequent stage of the power conversion means and performs ground fault detection before the switching means and the connection means. And means.

  According to the present invention, even if a ground fault occurs on the output side (load side) during self-sustained operation, it can be reliably detected, and a power converter with improved safety can be obtained. There is an effect.

FIG. 1 is a diagram illustrating a configuration example of a power converter according to the present invention. FIG. 2 is a diagram illustrating a configuration example of the power conversion device. FIG. 3 is a diagram illustrating a configuration when the power conversion apparatus of FIG. 1 is grid-connected. FIG. 4 is a diagram showing a path of a ground fault current when a ground fault occurs in the configuration shown in FIG. FIG. 5 is a diagram illustrating a configuration when the power conversion device of FIG. 1 is operating independently. 6 is a diagram illustrating a path of a ground fault current when a ground fault occurs in the configuration illustrated in FIG. FIG. 7 is a diagram showing a configuration and a ground fault current path when the power conversion device of FIG. 2 is operating independently.

  Hereinafter, embodiments of a power conversion device according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a diagram illustrating a configuration example of a power converter according to the present invention. The power conversion device of the present embodiment includes an input device 90, a ground fault detector 100, a converter 110, capacitors 120A and 120B, an inverter 130, reactors 140A and 140B, capacitors 150A and 150B, and a ground fault. A detector 160, a controller 170, a terminal block 180 for independent operation, a switch 190, and a system voltage 200 are provided. This power conversion device is a power conversion device that is connected to the grid, and has a self-sustaining operation function of supplying power to a user's load in a state of being disconnected from the grid.

  The input device 90 is a device that outputs DC power, and is, for example, a DC power source or a solar battery. The ground fault detectors 100 and 160 are circuits for detecting a ground fault, and for example, detect a ground fault by monitoring a ground fault current. For example, a device capable of detecting a zero-phase current such as ZCT is used. In addition, if it has the same function and a ground fault detection is possible, it will not be limited to this.

  Converter 110 is configured by a semiconductor switch or the like, receives DC power output from input device 90 as input, and charges capacitors 120A and 120B with a desired DC voltage. A connection point (an intermediate potential point of the converter 110 output) between the capacitors 120A and 120B connected in series is grounded. Inverter 130 is configured by a semiconductor switch or the like, and outputs a desired AC voltage with DC voltage charged in capacitors 120A and 120B as an input.

  Reactors 140A and 140B and capacitors 150A and 150B filter the respective outputs of inverter 130. Note that the configuration of FIG. 1 is not limited as long as the same function can be realized.

  The controller 170 generates and outputs a control signal for on / off control of the semiconductor switches of the converter 110 and the inverter 130. In addition, all control of the power converter is performed, such as stopping the operation of the power converter upon receiving the output of the ground fault detector 100 or the ground fault detector 160.

  The terminal block 180 for independent operation is a place where electric power is output from the power converter during the independent operation, and the user can connect the load device 210. The switch 190 opens and closes an electrical connection between the inverter 130 side and the system side. Examples of the switch 190 include an MC (magnet contactor) and a relay. However, the switch 190 is not limited to this as long as it has the same function.

  The configuration shown in FIG. 2 is also conceivable, but the configuration shown in FIG. 1 is desirable for improving safety. The reason will be shown separately.

  FIG. 3 is a diagram illustrating a configuration when the power conversion apparatus of FIG. 1 is grid-connected. In this configuration, a ground fault current flows as shown by a thick broken line in FIG. 4 in both cases where a ground fault occurs on the system side and when a ground fault occurs on the input side. Therefore, the ground fault detectors 100 and 160 can detect each ground fault.

  Moreover, FIG. 5 is a figure which shows a structure when the power converter device of FIG. 1 is operating independently. In this configuration, a ground fault current flows as shown by a thick broken line in FIG. 6 in both cases where a ground fault occurs on the load side and when a ground fault occurs on the input side. Therefore, the ground fault detectors 100 and 160 can detect each ground fault.

  FIG. 7 is a diagram showing a configuration and a ground fault current path when the power conversion device of FIG. 2 is operating independently. In this configuration, when a ground fault occurs on the input side, a ground fault current flows as indicated by a thick broken line, so that the ground fault detector 100 can detect the ground fault. However, when a ground fault occurs on the load side, the ground fault cannot be detected because a ground fault current flows as shown by a thick broken line without passing through the ground fault detector 160. At this time, safety cannot be ensured when the user and the contractor are in danger of receiving an electric shock.

  As described above, the power conversion device according to the present embodiment includes a ground fault detector 110 that performs ground fault detection in the previous stage of converter 110 and a stage subsequent to inverter 130 and is connected to the power system and the power system. And a ground fault detector 160 that performs ground fault detection in the previous stage of a connection terminal (a terminal block for self-sustaining operation 180) that connects a load during self-sustaining operation. As a result, it is possible to reliably detect a ground fault that has occurred on the output side (power system side, load side) of the power converter, both in the state connected to the power system and during independent operation. And safety can be improved.

  As described above, the power conversion device according to the present invention is useful as a power conversion device capable of independent operation for supplying power to a load while being disconnected from the system.

90 Input device 100, 160 Ground fault detector 110 Converter 120A, 120B, 150A, 150B Capacitor 130 Inverter 140A, 140B Reactor 170 Controller 180 Stand-alone terminal block 190 Switch 200 System voltage

Claims (2)

A power conversion device capable of independent operation that supplies power to a load in a state disconnected from the power system,
Power conversion means for converting DC power to AC power;
Switching means for switching between a state connected to the power system and a state disconnected from the power system;
A connection means for connecting and disconnecting a load to be supplied with power during self-sustaining operation;
First ground fault detection means for performing ground fault detection before the power conversion means;
A second ground fault detection means that is a subsequent stage of the power conversion means and that detects ground faults in the previous stage of the switching means and the connection means;
A power conversion device comprising:   The power converter according to claim 1, wherein the second ground fault detection unit performs ground fault detection by monitoring a zero-phase current.

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