JPS5989533A - Parallel operation system for inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a system for driving a group of AC motors by operating a plurality of inverter devices in parallel, and particularly relates to a system for driving a group of AC motors by operating a plurality of inverter devices in parallel. This invention relates to a parallel operation system for inverter devices that aims to improve the operation system of '1''.

[Technical issues and problems with the invention]

In the Taisai h1 power supply system using an inverter device, a method is sometimes used in which a plurality of inverter devices are operated in parallel for the purpose of preventing accidents of system failure and improving the reliability of the system.

Further, in a parallel operation system of inverter devices, it is common to provide a margin in the system capacity so that the system can continue to operate steadily even if at least one inverter device fails. At the same time (2) In the event of a failure, the failed inverter device is often disconnected from the load, and the recovered inverter device can be put back into the system. Figure 1 shows the conventional method. It is a block diagram showing an example of a parallel power supply system of inverter devices 1, 2.3.Each inverter device includes a rectifier 10, a DC filter circuit 20,
It is composed of an inverter 3o that converts direct current to alternating current, and an AC breaker 4o that opens and closes the output of the inverter, and power is supplied to the load motor 5 through the output common bus. Also,
FIG. 2 shows an embodiment in which the output of a rectifier that converts alternating current into direct current is used as a common bus bar for the purpose of making the power supply system more compact, economical, and highly efficient. In this case, a rectifier 10, a semiconductor DC breaker 15 using this output as a common bus line, a DC filter circuit 20, and an inverse converter 30 are used.
and an AC breaker 40.

As the load AC motor 50, for example, the characteristics of a hysteresis motor are shown in FIGS. 3 and 4. Figure 3 shows the input power (P, ,
), input current (1,) and its power factor (CO8ψ). The broken line in FIG. 3 shows the case where the input voltage of the hysteresis motor is reduced to a certain value.

The O mark in the figure indicates the rated operating point. The solid line in Figure 4 shows the power factor (cosψ) of the input current and the effective component (1,
, ), and the characteristics of the invalid portion (■yo, ). The broken lines in FIG. 4 are the respective characteristics when slipping occurs. From Figure 3, during synchronous operation (8-(J
) If the load is relatively light or there is sufficient motor output, it is possible to maintain synchronization even during reduced voltage operation. From Figure 4, when operating at reduced voltage; ■ light power factor (cns
ψ) is clearly improved, and it has been experimentally confirmed that the efficiency is further improved.

For example, in the parallel operation system of inverter devices shown in Fig. 1 or 2 C, if one inverter device fails, that faulty device is immediately disconnected from the system and the load is replaced by another normal inverter device. A commonly used method is to continue supplying power to the If one machine is disconnected during parallel operation, the load that was being borne by the momentary failed machine will be borne by the other normal machine, so a sudden step-like change in load will occur on the normal machine. In the case of Fig. 1 or Fig. 2, the load is increased by 1.5 times, and operation must be continued at a load of 10 [3%]. This results in severe use for each inverter, and is also unfavorable from a reliability standpoint.

[Purpose of the invention]

Therefore, in view of the above points, the present invention is directed to
The purpose of this is to reduce the load on the normal inverter in a power supply system that operates multiple inverters in parallel even if one inverter fails, thereby ensuring system reliability. An object of the present invention is to provide a parallel operation method for inverter devices i/l that can continue stable operation.

[Summary of the invention]

In order to achieve this object, the present invention provides that, when one inverter device operating in parallel fails, the output voltage of the inverter device that is normal at that time is lowered within a range that allows the load motor to operate steadily. It is designed to operate at reduced voltage.

[Embodiments of the invention]

Examples of the present invention will be described below. Figure 5 shows the three parts of an inverter device as shown in Figure 1 or Figure 2.
In the parallel operation system, a protection block diagram is shown in the case where one inverter device fails, for example, due to commutation failure while operating the load motor group 50. In this configuration, the same reference numerals as in FIG. 1 indicate the same circuits. FIG. 5 shows a commutation failure detection circuit 61 that detects the level of discharged AC of the capacitor 70 of the DC filter circuit using the secondary current A of the current transformer 80 when the inverter circuit 30 causes a DC short circuit due to a commutation failure. , a control circuit 62 which uses the output signal B of the detection circuit 61 to cause the inverter to fail, a voltage control circuit 63, an inverter control circuit 65, and an AC breaker control circuit 66.

FIG. 6 is a time chart showing the operation control method of the present invention. In this figure, time t. 1 running in parallel to
When commutation fails in one inverter device, for example 1 in FIG. 1, the commutation failure detection circuit 61 detects the level of A in FIG. . The output signal B of this detection circuit 61 quickly stops the faulty inverter and sends a fault signal () to other normal inverters. The normal inverters that have received the failure signal 11 from the failed inverter are, for example, the inverters 2 and 3 in FIG.

The respective output voltages V, , v3 are reduced from their rated values as shown in FIG. By doing so, the normal inverter 2.3 can continue to operate with the load currents I, . At time to, the output voltages V, , V, of each of the normal inverter devices 2 and 3 are constant as shown by the hl'4 line (If the value remains 8, the output currents of the three devices will be The increase is 15 times that of steady operation.As is clear from FIGS. 3 and 4N, by operating at reduced voltage, the hysteresis motor group can be operated very economically.

FIG. 7 shows an embodiment of the voltage control circuit 63, which can be easily constructed from operational amplifiers OAI and OA2, resistors, and capacitors. When a failure signal H from another machine is received, an analog switch (SW) is turned on, a voltage of polarity (g) is applied, and voltage reduction control is performed.

〔Effect of the invention〕

As described above, according to the present invention, in a system in which a power supply system is configured by operating a plurality of inverter devices in parallel and drives a large number of AC motors, particularly hysteresis motors, when at least one inverter device fails, the failure occurs. By sending the failure signal of the inverter device to other normal inverter devices that were operating in parallel, reducing the output voltage of each normal inverter device, and operating the load motor at reduced voltage, the output current of the normal inverter device is almost increased. Therefore, it is possible to provide a highly reliable parallel operation system for inverter devices that allows continuous operation without any interruption.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams showing an example of a conventional inverter parallel operation system, and FIG.
FIG. 5 is a diagram showing the characteristics of the electric motor serving as the load of the present invention.
FIG. 6 is a block diagram showing an embodiment of the present invention, and a time chart 10 showing the operation of the present invention...
20... Self-current filter 30... Inverter circuit
40... High-speed breaker 50... AC motor group 6
1... Commutation failure detector 62... Failure stop control circuit 6
3...Error intensifier 64...Phase control circuit 65
... Inverter control circuit 66 ... Breaker control circuit 70 ... Capacitor 80 ... Current transformer (7317
) Agent: Patent Attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 @

Claims (1)

[Claims] In a system in which a group of AC motors is driven by a power source in which a plurality of inverter devices are operated in parallel, if one inverter device breaks down while the group of motors is in steady operation,
Parallel operation of inverter devices characterized in that other normally operating inverter devices continue to operate by reducing their respective output voltages to below their rated values within a range in which the electric motor can continue steady operation. method.