JPS5926190B2 - Inverter parallel operation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter parallel operation device that supplies stable power to a load.

FIG. 1 shows a block diagram of a conventional inverter parallel operation system.

In FIG. 1, inverters 11 and 21 consisting of a plurality of unit inverters are connected in parallel to a DC power supply 1 via fuses 10 and 20, respectively, and further inverters 11,
21 is connected to AC switches 13 and 23 via inverter transformers 12 and 22 and waveform shaping filters 34 and 35. The inverter outputs sent out via the AC switches 13 and 23 are connected in parallel to the load 2 via overcurrent detection circuits 14 and 24. Also, fuse 1
Fuse blowout detection circuits 15 and 25 connected to 0 and 20
Detects fuse blowing and sends the fuse blow signal 1
? , 2? is input to the AC switches 13 and 23 as an AC switch open signal. On the other hand, overcurrent detection circuits 14 and 2
The overcurrent signals 18 and 28 detected at 4 are also input to the AC switches 13 and 23 as AC switch open signals.
FIG. 2 shows a known example of a unit inverter constituting the inverter.

1 is a DC power supply, 5CR1 to 5CR4 are main thyristors, 5
CR11-5CR14 are auxiliary thyristors, D1-D4 are free-wheeling diodes, C is a commutating capacitor, L is a commutating reactor, TRI is the primary winding of the inverter transformer, TR
2 represents the secondary winding of the inverter transformer, and TR3 represents the iron core of the inverter transformer.

In this circuit, power is supplied to the load from the secondary winding TS2 of the inverter transformer. Further, ia and ib represent abnormal currents, which will be described later. Since the circuit operation is well known, the description thereof will be omitted. Now, in the invar/return device shown in Fig. 1, one unit inverter, for example, invar 11, for some reason, is connected to the DC power supply 1-SCRII-SC shown in Fig. 2.
When current 18 flows through the closed circuit of R12-DC power source 1, I8 has extremely small impedance in the closed circuit, so
An excessive current occurs, which causes the fuse 10 shown in FIG. 1 to fail. This is detected by the fuse blowout detection circuit 15, and a fuse blowout signal 17 is generated, which causes the AC switch 13 to open. Therefore, the failed inverter 11 side is disconnected, and power is supplied to the load 2 from the healthy inverter 22 side. However, for some reason, one of the unit inverters in the inverter 11 was disconnected from the DC power supply 1-SC in Figure 2.
It is assumed that the frost flow 1b passing through the closed circuit of R3-TRl-SCR2-DC power supply 1 becomes an excessive current. Since there is a reactor in this closed-circuit inverter transformer, I, is smaller than IEh, and at the beginning of this abnormality, the fuse will not blow and the overcurrent detection circuit will not operate. And after a certain time I
When b becomes large, the overcurrent detection circuit operates and the AC switch 13 is opened. If the abnormality continues in this way, the healthy inverter 21 side will not only supply power to the load, but also supply current to the inverter transformer 12 through the AC switch 13. As a result, the healthy side inverter 21 becomes overcurrent and b1 overcurrent detection circuit 2
3 is released. As described above, in the conventional inverter parallel operation protection device, if a small overcurrent abnormality continues in the inverter, the healthy in-parts also become open, making it impossible to supply power to the load. The present invention focuses on the fact that the above phenomenon is caused by the long time required to detect a blown fuse on the faulty inverter side or the time required for the output overcurrent detection circuit to operate. A circuit for detecting this is provided on the power supply side of the waveform shaping pool, and this detection signal is used to open the AC switch without time delay.

A block diagram of one embodiment of the present invention is shown in FIG. 3 below.

Compared with FIG. 1, FIG. 3 differs in the following points. First, the output overcurrent detection circuits 14 and 24 connected to the AC switches 13 and 23 are removed, and the outputs of the AC switches 13 and 23 are directly connected to the load 2. Also, invar l
Primary current Q of transformers 12, 22 overcurrent detection circuit 16,
26 is provided between the inverters 11, 21 and the transformers 12, 22, and the AC switches 13, 23 are opened by the overcurrent detection signals 19, 29. For such AC switches, forced commutation type semiconductor switches are used for loads that require quick response, and natural commutation type semiconductor switches or mechanical switches are used for loads that do not require such quick response. can be used. Next, FIG. 4 shows an embodiment in which the primary current Q overcurrent detection circuits 16 and 26 of the above-mentioned in-parts transformers 12 and 22 are shown for one unit inverter.

Figure 4 shows the auxiliary thyristors SCRll to SCR from Figure 2.
l4, freewheeling diodes D1 to D4, commutating capacitor C,
The commutator L is omitted. A current transformer 30 is provided in the primary winding TRl of the inverter transformer 12 (22), and a resistor 31 is connected in parallel to the secondary output terminal of the current transformer 30. A comparator 33 compares the voltage drop across this resistor 31 with a reference voltage 32 to determine whether or not there is an overcurrent, and outputs an overcurrent detection signal 19. Now, in the inverter parallel operation device shown in FIG. 3, for example, one unit inverter 1 of the inverter 11 is connected to the DC power supply 1-SCR3 of FIG. 4 for some reason.
-TRl-SCR2 - Current 1 passing through the closed circuit of DC power supply 1
Suppose that b becomes an excessive current.

At this time, the current flowing through the current transformer 30 increases and the voltage drop b1 of the resistor 31 becomes larger than the reference voltage 32, so the comparator 33 outputs the inverter transformer primary current overcurrent signal 19. The inverter transformer primary current overcurrent signal 19 is sent to the AC switch 1 on the inverter 111 side.
3 is released. Since the AC switch 13 is opened quickly, the frost flow from the healthy component 21 does not flow into the faulty inverter 11. Therefore, the inverter transformer primary current overcurrent detection circuit 26 on the inverter 21 side does not operate, the AC switch 23 remains conductive, and stable power with small voltage fluctuations can be continuously supplied to the load 2. In the above embodiment, the overcurrent detection circuits 16, 26
However, since it is provided on the power supply side from the waveform shaping filters 34, 35 and the impeller transformers 12, 22, there is no delay due to the filter in overcurrent detection, and the Mf of the transformer
There is no influence from frost flow. In the above embodiment, the overcurrent detection circuit was provided in the primary winding of the inverter transformer, but this detection circuit may also be provided between the secondary winding of the inverter transformer and the waveform shaping filter. It may also be provided at the DC input section of the unit inverter.

When provided in the DC input section, a direct current transformer (DCCT) is used in place of the current transformer 30. Further, the unit inverter may be, for example, a series inverter, a parallel inverter, etc.
The commutation method of the in-parts and the number of in-parts are arbitrary. In the above embodiment, consider the case where the load is completely short-circuited.

When the load 2 is completely short-circuited, the current 1b shown in FIG. 4 increases. When the current 1b becomes an excessive current, the in-parts transformer primary lightning current/frost current detection circuits 16, 25 detect that the current 1b has become an excessive current.
The detection signal 19, 29 immediately opens the AC switches 13, 23 to disconnect the short-circuited load, so the current 1b becomes small. At this time, commutation capacitor C,
The commutation reactor L is connected to the overcurrent 1b by SCRl and SC.
If R4 or SCR2 and SCR3 are selected so that they can be commutated even if the current flows, there is an effect that the inverters 11 and 21 can be protected without blowing out the fuses 10 and 20. The present invention can also be implemented with a parallel operation device that does not include an inverter transformer, such as when single-phase inverters are operated in parallel.

In FIG. 5, single-phase inverters 36 and 37 are used instead of inverters 11 and 21, and inverter transformers 12 and 2 are used.
An example in which 2 is omitted will be shown. Even in this case, the overcurrent detection circuits 16 and 26 are inserted closer to the power source than the waveform shaping filters 34 and 35. In the present invention, an overcurrent detection circuit is provided on the power supply side of the waveform shaping filter, and the AC switch is opened from this detection signal tag. Therefore, there is no delay caused by the filter, and the AC switch on the faulty inverter side is immediately detected after a fault occurs. You can open the switch.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional inverter parallel operation device, Fig. 2 is a circuit diagram showing a conventional example of unit-in-parts, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a block diagram showing the present invention. FIG. 5 is a block diagram of an embodiment of the present invention in which an inverter transformer is omitted. 1...DC power supply, 2...Load, 10,
20... Fuse, 11, 21, 36, 37.
...In parts, 12,22...In parts transformer, 13,23...AC switch,
14, 24... Output overcurrent detection circuit, 16, 26
...Inverter transformer {current overvoltage detection circuit, 19, 29...Inverter transformer primary current overcurrent signal, 30...1...current transformer, 31...・
...Resistance, 32...Reference voltage, 33...
... Comparison circuit, TRl .....-Negative winding of inverter l tranne, TR2 ..... Secondary winding of inverter transformer, TR3 ..... Iron core of inverter transformer, 34, 35... Waveform shaping cedar filter, 36
, 37... Overcurrent detection circuit.

Claims (1)

[Claims] 1. An inverter consisting of a plurality of unit inverters, a filter that shapes the waveform of the output of the inverter, and an AC switch that electrically opens and closes the inverter output, and is connected to a load via the AC switch. In inverter parallel operation equipment, an overcurrent detection circuit is provided on the power supply side from the filter, and an overcurrent detection signal from this overcurrent detection circuit opens the AC switch, allowing the faulty inverter in the equipment to be operated in parallel to be connected to other healthy inverters. An inverter parallel operation device characterized in that the inverter can be disconnected without causing any trouble to the inverter and the load. 2. The inverter parallel operation device according to claim 1, which includes an inverter transformer configured with an appropriate turns ratio between the inverter and the filter. 3. The inverter parallel operation device according to claim 2, wherein the overcurrent detection circuit is provided on the primary side of the inverter transformer. 4. The inverter parallel operation device according to claim 2, wherein the overcurrent detection circuit is provided between the secondary side of the inverter transformer and the filter.