JPS6240931B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection method in a system for interconnected operation of a self-excited inverter and an electric power system when it cannot be determined whether the self-excited inverter or the electric power system is at fault.

In the DC power transmission currently in practical use,
A separately excited inverter is used to convert direct current to alternating current. This is because separately excited inverters are economically advantageous and more reliable than self-excited inverters. However, separately excited inverters cannot be operated unless the power grid is in normal condition, they tend to become unstable unless the grid capacity is several times larger than the inverter capacity, and the power grid supplies lagging power. There are drawbacks such as the need to On the other hand, self-excited inverters do not have the above-mentioned restrictions and can operate independently without a power grid. Furthermore, since it is possible to supply both phase-leading and phase-lag power, it is expected to be effective in stabilizing the grid, and as the reliability of inverters has also improved, grid interconnection using self-excited inverters has become a reality. There is now a possibility to do so.

By the way, as can be seen from the difference in basic characteristics between self-excited inverters and separately excited inverters as mentioned above, it is clear that a technology different from conventional technology is required even for grid connection. be. For example, if a system malfunctions, if a separately excited inverter is used, the system will fail together, but if a self-excited inverter is used, the system can be disconnected and the power system to the load can be provided only by the self-excited inverter; conversely, if the self-excited inverter becomes abnormal, In this case, it is of course possible to separate this and have the grid alone supply power to the load. Here, if it is clearly known which part is abnormal, the problem can be solved by separating the abnormal part, but depending on the cause, it may be difficult to find the abnormal part.

Generally, when two AC power supplies are connected in parallel to supply power to a load, if there is a phase difference between the voltages of the two AC power supplies, a cross current of active power flows from the power supply with a phase lead to the power supply with a phase lag. Furthermore, if there is a difference in voltage amplitude, a cross current of delayed phase reactive power flows from the power source with higher voltage to the power source with lower voltage. The self-excited inverter system and the electric power system are always controlled to appropriately share power, but if this grid-connection operation control circuit malfunctions, each system will be interconnected even if it is normal on its own. Driving becomes impossible.

An object of the present invention is to solve the problem in such a case and to provide a protection method in interconnected operation of a self-excited inverter and a power system, which prevents the power supply to the load from being stopped.

Hereinafter, the present invention will be explained with reference to an embodiment shown in the drawings. In the figure, 1 is a DC power supply, 2 is a self-excited inverter, 3 is a reactor for connection to the power system, 4 and 13 are disconnectors, 5 and 14 are voltage abnormality detectors, 11 is the power system, 12 2 represents the system impedance, and 22 represents the load. As the first DC power source, an AC/DC converter is normally used. The self-excited inverter 2 and the power grid are controlled by a grid-connected operation control circuit (not shown),
The self-excited inverter is operated so that the voltage at the interconnection point 21 is within a predetermined voltage range and does not exceed the capacity of the self-excited inverter. A thyristor circuit breaker is used as the circuit breaker 4 because particularly high-speed opening and closing operations are required.

In such a configuration, with both shield disconnectors 4 and 13 closed and the self-excited inverter and the power grid operating in parallel, the protection interlocking in the event that an abnormality occurs in the self-excited inverter or the power grid is as follows. Do it like this. If it is clear that an abnormality has occurred inside the inverter or in the power system, such as when an inverter fails to commutate or when a ground fault is detected in the power system, It is clear that it is only necessary to disconnect the disconnect switch 4 or 13 connected to the side where the problem occurred. However, as in the above-mentioned cases where an abnormality occurs in the interconnection operation control circuit or when a ground fault occurs near the interconnection point 21 and the voltage at the interconnection point 21 becomes abnormal, it is difficult to immediately determine what is abnormal. If this is not possible, the defective location can be isolated using the following procedure.

If the voltage at the interconnection point 21 is now abnormally reduced, the voltage abnormality detectors 5 and 14 are activated, and the two disconnectors 4 and 13 are opened to interrupt the interconnection operation.
As a result, the voltage states of the voltages V ₁ and V ₂ at the input points of the two shield breakers 4 and 13 can be divided into the following four states. (i) Both V ₁ and V ₂ are normal. (ii) V ₁ is abnormal and V ₂ is normal. (iii) V ₁ is normal and V ₂ is abnormal. (iv) Both V ₁ and V ₂ are abnormal.

First, in case (i), it can be assumed that a so-called cross current occurs between the self-excited inverter and the power grid due to an abnormality in the interconnected operation control circuit, resulting in a voltage abnormality. Therefore, there is a high possibility that power can be supplied to the load without grid-connected operation, so only the shield disconnector 4 is left open, the shield disconnector 13 is turned on, and power is supplied from the power system 11 to the load 22. . If the capacity of the power system is smaller than the capacity required by the load, an overload detector (not shown) may operate and open the circuit breaker 13, but this is not done in a general power system. Automatic reclosing occurs as if the

Next, in case (ii), the self-excited inverter is not used, the disconnector 13 is turned on again, and power is supplied to the load using only the power system, since the voltage control circuit of the self-excited inverter is abnormal. In the case of (iii), the mustard disconnector 13, which indicates an abnormality in the power system, is left open and the mustard disconnector 4 is turned on again. In case (iv), when two power supplies fail at the same time, the disconnectors 13 and 4 are sequentially turned on again after waiting for recovery.

In the circuit shown, the voltage abnormality detector installed on the power supply side of the disconnectors 4 and 13 also serves to detect the voltage abnormality at the interconnection point 21, but of course another voltage abnormality detector is installed at the interconnection point 21. It may be provided. In addition, although the figure shows that the output terminals of two disconnectors are directly connected, the present invention can be applied even if a transformer or the like is connected between them.

As described above, the present invention makes it possible to determine failures when it is unclear whether the self-excited inverter or the power system is defective, or when the grid-connected operation control circuit is defective, thereby making it possible to operate the grid-connected operation system. This makes it possible to improve the reliability of the system.

[Brief explanation of the drawing]

The figure is a diagram showing an example of a grid-connected system to which the present invention is applied. 1...DC power supply, 2...Self-excited inverter, 3...
...Reactor for interconnection, 4,13...Shield disconnector,
5, 14... Voltage abnormality detector, 11... Power system, 12... System impedance, 21... Interconnection point, 22... Load.

Claims (1)

[Claims] 1.Equipped with a grid interconnection reactor connected in series to the output side of the self-excited inverter, and another grid disconnector connected in series to the power supply side of the power system, and In an AC interconnection system configured to supply power to a load from interconnection points whose output sides are connected to each other, a voltage abnormality detector is provided in each of the self-excited inverter and the power grid, and when the interconnection If a voltage abnormality is detected at a point, the two shield circuit breakers are opened together, and if one power supply voltage returns to normal, the circuit connected to the power supply side that has returned to normal is opened. The self-exciting inverter is characterized in that when the disconnector is turned on again and the two power supply voltages are restored to normal, the self-excited inverter or the power system, whichever has a larger capacity, is turned on again. Protection method for interconnected operation between excitation inverter and power grid.