JPH026292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground protection circuit for an inverter that connects an AC power distribution system and an AC output terminal, and performs both interconnected operation and independent operation with the system.

For example, as shown in FIG.
The inverter 3a and the load 4a are connected via the AC switch 2a, and the inverter 3b and the load 4b are connected via the AC switch 2b.
These inverters 3a and 3b are connected to power generation equipment such as solar cells (not shown), and when the AC system is healthy, they perform interconnected operation with the grid and send out power to the grid, or in somewhat special cases, they take in power from the grid. It charges the storage battery installed on the DC side of the inverter, and when there is a power outage in the grid, the inverter disconnects the output end from the grid and operates independently from the grid, supplying power to the load independently. A system that does this is conceivable.

The inverter used in such a system is required to be protected from ground faults such as electrical leakage in the load in either of the two operating modes described above.

Incidentally, such an inverter for a power generation system is currently in the research and development stage, and there is no established grounding protection technology yet.

In addition, there are systems that use an inverter as a constant voltage, constant frequency power source rather than a power generation system, and normally operate the inverter in forward conversion operation and float charge the storage battery, and in the event of a power outage, disconnect from the grid and perform reverse conversion operation to supply power to the load. However, even with this system, there is no established grounding protection technology.

As mentioned above, the purpose of the present invention is to provide grid and grid-connected operation,
An object of the present invention is to provide a ground protection circuit for an inverter that can reliably detect a ground fault in a load regardless of the operating mode of an inverter operated in two modes of independent operation.

According to the present invention, in an inverter that performs interconnected operation with an AC distribution system or disconnects from the grid to supply power to a load, the AC distribution system side and the inverter side from the branch point between the load and the inverter A current interrupting means operated by differential current detection is provided,
Furthermore, this can be achieved by grounding a line on the inverter side of the current interrupting means on the inverter side, and providing a switch that interrupts the grounding wire during operation connected to the inverter system.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the method of the present invention,
In the figure, 11 is an AC power distribution system, and 14 is an inverter whose AC output terminal is connected to the AC power distribution system 11 and the load 15. At times, the load 1 is operated in connection with the AC distribution system 11.
5.

On the side of the AC distribution system 11 from the branch point between the load 15 and the inverter 14, there is a first
An earth leakage breaker (ELB) 12a using a differential CT is provided as a current interrupting means, and a switch contact is also provided on the AC power distribution system 11 side to disconnect the inverter 14 and the system 11, which is operated by the inverter 14 when the system 11 is out of power. 13a and a PT (transformer) 16 for detecting system voltage.

In addition, an earth leakage breaker (ELB) 12b using a differential CT is provided as a second current interrupting means operated by differential current detection on the inverter 14 side from the branch point between the load 15 and the inverter 14, and further on the inverter 14 side. A line is grounded, and a switch contact 13b is provided in the middle of the wiring to the ground, which serves to cut off the connection of the inverter 14 with the system 11 during operation.

Note that contacts 13a and 13b are AC switch 1
3. As shown in the figure, interlocking mechanical contacts such as contactors are used to reduce the leakage current when the circuit is opened.
Although it is advantageous in terms of strength against fault current, etc.
Other equipment may be used as long as the conditions that it is a switch and that 13a and 13b can operate simultaneously are met.

Further, a combination of an earth leakage protection relay and a circuit breaker may be used instead of the earth leakage breakers 12a and 12b. In that case, if both conductors are inserted into the through hole as the primary conductor, the protective relay can be saved. Furthermore, considering the nature of the accident, it is desirable to use various types of circuit breakers for both circuit breakers and to shut them off all at once.

Next, to explain the operation, when the system is normal, the inverter 14 is connected to the AC power distribution system 11, but at this time, since the earth leakage breaker 12a is installed at the receiving end of the consumer, In the event of a ground fault such as electric shock or leakage, the earth leakage circuit breaker 12a trips to cut off the supply of fault current.

In addition, in the event of a power outage in the grid 11, the inverter 14 detects an abnormality in voltage, frequency, etc. from the grid voltage detection PT 16, operates the AC switch 13, opens the contact 13a, disconnects the grid 11, and almost At the same time, contact 13b is closed to ground one of the AC terminals of inverter 14. In this way, when a ground fault occurs in an AC charging part (non-grounded side) such as the load 15, the earth leakage breaker 12b trips and the supply of the fault current is cut off.

Assuming that the ground circuit of the inverter 14 remains connected when the inverter 14 is connected to the grid 11, for example, even if an electric shock occurs in the load 15, the fault current will in the worst case result from a fault in the earth leakage circuit breakers 12a and 12b. This becomes the sum of the detected currents and increases compared to the case without grounding. Therefore, especially the earth leakage breaker 1
It is dangerous when 2b is not present.

Although the above-mentioned embodiment shows an example using a single-phase inverter, a ground fault in a load device or the like can be detected in a three-phase inverter by similarly switching the grounding circuit. In this case, the grounding of the 3-phase 200V distribution line can be 1-phase grounding, neutral point grounding, 2-phase center point grounding, etc., and the voltage applied to the faulty part in each case is slightly different. However, it is still possible to detect ground faults and it is still necessary to switch the ground circuit.

As described above, the inverter grounding protection circuit of the present invention is applicable to power generation systems using solar cells, fuel cells, etc. and so-called uninterruptible power supplies that charge storage batteries by forward conversion operation of the inverter when the system is normal. When an inverter connects the AC output terminal to the AC distribution system and performs interconnected operation with the grid, or disconnects from the grid and supplies power to the load, there is always an unbalanced current between the load and the power supply source. There is a cut-off means that detects and operates, and because the intermediate potential of one line or phase of the power supply source is grounded, it will always detect when a ground fault occurs in the load or the wiring that supplies power to it. and can be blocked.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a solar power generation system, and FIG. 2 is a circuit diagram showing an embodiment of the ground protection circuit of the present invention. 1...Pole transformer, 2a, 2b...AC switch, 3a, 3b...Inverter, 4a, 4b...
Load, 11...AC distribution system, 12a, 12b...
...Earth leakage breaker, 13...AC switch, 13a,
13b...Switch contact, 14...Inverter,
15...Load, 16...PT for grid voltage detection.

Claims (1)

[Claims] 1 In an inverter that is connected to the AC power distribution system or disconnected from the system to supply power to the load, it operates by detecting a difference in current between the AC power distribution system side and the inverter side from the branch point between the load and the inverter. A current interrupting means is provided, and a switch is further provided to ground a line of the current interrupting means on the inverter side and further on the inverter side, and to interrupt the grounding wiring when the inverter is connected to the grid. Inverter ground protection circuit.