JP2678991B2 - Inverter parallel operation method - Google Patents

Description

The present invention relates to a parallel operation system of inverters used as an AC power supply device. [Prior Art] In some cases, a plurality of inverters are operated in parallel in order to increase the power supply capacity or to increase reliability by using a redundant machine. In order to connect the outputs of a plurality of inverters to each other and operate them in parallel, it is necessary to match the magnitude and phase of their output voltages. For this reason, the following methods have been conventionally used. FIG. 1 shows an example of a system having a common oscillator and a reactive cross current compensation circuit. 1,2,3 are inverters, 4 is a load, 5,6,7 are current detectors for detecting the output current of each inverter, 3 is a circuit for comparing the output currents to detect a reactive cross current, 9, 10,1
1 is a voltage adjusting circuit attached to each inverter, and 12 is a common oscillator. The frequency and phase of each inverter are regulated by the common oscillator 12. Therefore, the effective cross current between the inverters is suppressed to a small value. Each inverter has an automatic voltage adjustment function by the voltage adjustment circuit,
If there is a difference between the output voltages, an invalid cross current is generated in the output circuit. This invalid cross current is detected by the invalid cross current detection circuit 8 and is fed back to each inverter to operate so as to match the output voltage of each inverter. The current is also suppressed to a small value. FIG. 2 shows an example of a system having an individual oscillator. 1-11
Is the same as in FIG. 1, 13, 14 and 15 are individual oscillators attached to each inverter, and 16 is a synchronizing circuit. The individual oscillators operate synchronously by the action of the synchronizing circuit 16 and regulate the frequency and phase of the respective inverters. Therefore, in this case as well, both the effective cross flow and the invalid cross flow are suppressed to small values. FIG. 3 shows an example of a system having an effective cross current compensation circuit in addition to the invalid cross current compensation circuit. 1 to 12 are the same as in FIG.
17,18,19 are power detectors for detecting the output power of each inverter, 20 is a circuit for comparing the output powers to detect an effective cross current, and 21,22,23 are transfer circuits. The effect of suppressing the reactive cross current is the same as that in FIG. 1, but in this method, even if there is a phase difference in the output of each inverter, if a difference occurs in the effective output power, this difference is detected by the effective cross current detection circuit 20, The effective cross current is suppressed to a smaller value because it is fed back to the oscillation circuit of each inverter and operates to match the phase of each inverter. [Problems to be Solved] In each of the above conventional methods, a common circuit as a system is required in addition to an individual circuit attached to each inverter as a cross current compensation circuit, a common oscillator, and a synchronization circuit.
Therefore, there are the following two drawbacks. One is that adding another inverter to the existing system (or removing it) requires very laborious adjustments on site. The cross current compensation circuit calculates the current or power to be shared by each inverter from the system output, compares this with the current or power actually shared by each inverter, and minimizes any difference between the two. Give feedback to do so.
Therefore, if the number of inverters is changed, it must be readjusted. If an individual oscillator is used, it is necessary to readjust the synchronization circuit. And in any case, the work to connect the control circuit of the existing system and the control circuit of the new inverter is required, and meticulous attention and adjustment for a long time are required, and the system must be stopped during that time. There wasn't. Another drawback is that it is difficult to realize high reliability by redundant parallel operation because there is a system common circuit.
When a redundant machine is used to increase the reliability of the system, the failure rate of the redundant part is proportional to the product of the failure rates of the respective elements, and can be dramatically reduced. However, if there is a common part, its failure rate is added to the system failure rate as a sum, and thus the reliability of the redundant system having the common part is mainly determined by the reliability of the common part. Therefore, according to the conventional method, although the main circuit of the inverter can be made redundant, a considerable part of the control circuit remains as a common circuit, so that the system cannot be made highly reliable. [Means for Solving Problems] The present invention eliminates these drawbacks, enables extremely simple and short-time expansion work, and realizes a highly reliable system. It provides an inverter parallel operation method without any circuit. [Embodiment] The drawing shows an embodiment of the present invention, in which 1,4,5,9 are the same as in FIG. 13 is the same individual oscillator as in FIG. 2, 17 is the same power detector as in FIG. 3, 24 is a circuit that changes the oscillation frequency of 13 according to the output power, 25 is a controller for adjusting the set value of the oscillation frequency, Reference numeral 26 is a voltage regulator for adjusting the set value of the output voltage. 28 and 29 represent other inverter blocks having the same contents as 27. The characteristics shown in FIG. 5 are given between 17, 24 and 13 between the output power and the output frequency of the inverter 1, that is, the characteristic that the frequency slightly decreases as the output power increases. Further, by 5 and 9, the characteristic as shown in FIG. 6, that is, the characteristic that the output voltage slightly decreases as the output current increases is provided between the output power source and the output voltage of the inverter. When two inverters having such characteristics are operated in parallel, the following is done. First, operate one unit and apply the load. Next, operate the second unit and adjust the frequencies of 25 and 26 of the second unit to roughly match the frequency and voltage to the first unit. And
When the output voltages of the two inverters are in phase with each other, they are connected in parallel. Then, the operating points of the two inverters move to the point where the oscillation frequencies coincide with each other according to the characteristics of FIG. 5 to stably share the output power, and a small amount of reactive cross current flows and the two inverters flow.
The operating point moves until the output voltages coincide with each other according to the characteristic of 1), and the output voltage is supplied to the load 4. If the power sharing ratio between the two inverters is appropriate, adjust the sharing ratio with the frequency adjuster of either inverter (increase or decrease the frequency of the person who wants to increase the sharing). Lower the frequency of the one you want). If the reactive cross current is large between the two inverters, it can be adjusted by the voltage regulator of one of the inverters so that the reactive cross current becomes 0. Lower the larger voltage). Even when the number of units in parallel is three or more, the processes can be performed in parallel in the same manner. In FIG. 4, the method of providing the output current-output voltage characteristics of FIG. 6 by the current detector 5 and the voltage adjusting circuit 9 has been described, but it is possible to provide the characteristics as shown in FIG. 6 without 5 and 9. However, such a case is also included in the present invention. It will be appreciated that the parallel operating performance characteristics described above are similar to the operation of a rotary alternator. That is, the AC generator driven by the prime mover has a characteristic that the rotation speed decreases as the load increases, and therefore stable parallel operation is possible. On the other hand, in a general inverter, since the frequency is determined by the oscillator, it is irrelevant to the load power and direct parallel operation is impossible.
The present invention is a system that enables direct parallel operation by providing an inverter with a power-dependent characteristic of a frequency similar to that of an AC generator. [Effect] According to the present invention, it is completely unnecessary to connect control circuits to each other between inverters that perform parallel operation,
Parallel operation can be performed simply by connecting the output circuit, and no complicated adjustment is required. Therefore, the on-site extension work is extremely simple, and it is possible to perform the uninterruptible extension work while keeping the power source alive. The fact that this uninterruptible construction has become possible matches the needs of important loads such as power supplies for computers in recent years, and its industrial significance is great. Further, even when performing redundant parallel operation for high reliability, it is possible to eliminate the common part, which was impossible in the past, so that a power supply system with extremely high reliability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are examples of a block diagram of a conventional inverter parallel operation system, FIG. 4 is an example of a block diagram of the present invention, and FIGS. 5 and 6 are used for the present invention. It is a characteristic diagram, 1,2,3 …… inverter, 4 …… load, 5,6,7 …… current detector, 8 …… reactive cross current detection circuit, 9,10,11 …… voltage adjustment circuit, 12 ... Common oscillator, 13,14,15 ... Individual oscillator, 16 ...
… Synchronization circuit, 17,18,19 …… Power detector, 20 …… Effective cross current detection circuit, 21,22,23 …… Phase shift circuit, 24 …… Oscillation frequency control circuit, 25 …… Oscillation frequency controller, 26 …… Output voltage regulator, 27,28,29 …… Inverter block.

Claims (1)

(57) [Claims] In an inverter parallel operation method in which a plurality of inverters used as AC power supplies are operated in parallel, a circuit that detects the output power of each inverter and an individual oscillator and a circuit that changes and compresses the frequency of the individual oscillator according to the detected output power And a frequency adjusting means for giving the output frequency an output power dependent characteristic, a voltage adjusting means for giving an output current dependent characteristic such that the output voltage changes according to the output current, and a manually set value. An inverter parallel operation method comprising: a frequency adjuster and a voltage adjuster for adjusting the inverter.