JPS648531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for connecting a commercial power source and an inverter in a power supply system that allows power to be supplied to a load from a commercial power source and also from an inverter. This relates to a switching operation method.

In order to switch between the commercial power supply and the inverter without any interruption, as shown in Fig. 1, a pair of thyristors 3 and 4 and forced commutation are installed between the load 1 and the LC filter 13 in the output stage of the inverter 2. A first selection switch 6 consisting of a circuit 5 is provided, and a second selection switch 11 consisting of a pair of thyristors 8 and 9 and a forced commutation circuit 10 is provided between the load 1 and the commercial power source 7. 7 to the inverter 2 or from the inverter 2 to the commercial power source 7 to selectively supply power to the load 1 is already known. According to this method, for example, it is possible to start supplying power by the inverter 2 driven by the DC power supply 12 at the same time as the commercial power supply 7 stops supplying power. However, the forced commutation circuit 10 is required, which inevitably increases the number of parts, increases the size of the device, and further increases cost.

On the other hand, there is a system shown in FIG. 2 as a switching system that does not have a forced commutation circuit. According to this method, the device can be made smaller and lower in cost by eliminating the need for a commutation circuit, but the first and second selection switches 6 and 11 are turned on simultaneously and the inverter 2 is operated. AC 1/2 to prevent becoming disabled
It was necessary to provide a period during which the power supply was stopped for a period equivalent to a cycle or longer. Such a drawback also occurred when the selection switches 6, 11 were constructed of electromagnetic switches as shown in FIG. In the circuits shown in Figures 1 to 3, if the output voltage of the inverter 2 and the voltage of the commercial power supply 7 are the same value and phase, parallel operation is possible, but if If a difference occurs in the output voltage and phase between the two, commutation failure of the thyristor inverter 2 will occur. That is, since the voltage detection points for voltage control of inverter 2 are at both ends of load 1, control becomes unstable, voltage and phase differences occur, a large inverter current flows, and commutation may fail. . For this reason, in the systems shown in FIGS. 2 and 3, the power supply suspension period is set for a period equivalent to 1/2 to several AC cycles, and the commercial power source 7 is switched to the inverter 2 or vice versa.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a switching operation method between a commercial power source and an inverter, which allows a parallel operation period to be set and the AC power source to be switched.

To achieve the above object, the present invention provides a method for switching from a state in which power is supplied to a load by a commercial power source to a state in which power is supplied to the load by a voltage-controlled inverter; A method for switching from a state in which power is supplied to the load by an inverter to a state in which power is supplied to the load by the commercial power supply, the method comprising: switching the voltage-controlled inverter or the commercial power supply to the load; driving the inverter so that the output voltage and phase of the voltage-controlled inverter are approximately equal to the output voltage and phase of the commercial power source before connecting the voltage-controlled inverter to the voltage-controlled inverter; operating the voltage-controlled inverter and the commercial power source in parallel by fixing the voltage-controlled inverter and the commercial power source to a value before starting the parallel operation of the voltage-controlled inverter and the commercial power source;
Next, the present invention relates to a switching operation method between a commercial power source and an inverter, which includes disconnecting the commercial power source or the voltage-controlled inverter from the load.

According to the present invention, the output voltage of the inverter is fixed to the value immediately before the parallel operation during the parallel operation period, so even if there is a potential difference between the voltage of the commercial power supply and the output voltage of the inverter, the potential difference is The current is kept almost constant, preventing the current from increasing due to the potential difference, and allowing the inverter to continue operating normally. Furthermore, if there are no significant fluctuations in the inverter output voltage during parallel operation using the conventional method, parallel motion can be continued without much problem.
If the voltage fluctuates significantly for some reason when parallel operation starts, excessive current may flow to the inverter. In the present invention, since the output voltage of the inverter is fixed during parallel operation, large voltage fluctuations do not occur and excessive current does not flow through the inverter.
In this way, if it becomes possible to set up a parallel operation period, it becomes possible to switch the power supply without momentary interruption, and it also becomes possible to switch the power supply without momentary interruption using a relatively low-cost selection switch with a slow response time. .

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

In FIG. 4 showing the power supply device according to the embodiment of the present invention, reference numerals 1, 2, 6, 7, 11 to 13 are shown.
Components indicated by are substantially the same as those indicated by the same reference numerals in FIGS. 1 to 3. In this example,
Rectifier 1 with DC power supply 12 connected to commercial power supply 7
4 and a storage battery 15. Further, the first and second selection switches 6 and 11 are constituted by magnetic switches that turn on and off the contacts by means of first and second electromagnetic drive sections 16 and 17.

In order to operate the inverter 2 synchronously and in parallel with a fixed output voltage and a fixed phase, first, one input terminal connected to the inverter output line 18 and the other input terminal connected to the commercial power line 19 are connected. A phase comparator 20 is provided. A DC output corresponding to the phase difference between the output voltage of the inverter 2 and the commercial power supply voltage is obtained from the phase comparator 20, and this is output through the contact a of the switch 21.
It becomes the input of the VCO, that is, the voltage controlled oscillator 22. Further, the phase comparison output is held in a holding circuit 23, and when the switch 21 is turned on to contact b, the held output becomes an input to the oscillator 22. The gate signal forming circuit 24 supplies the inverter 2 with a gate signal having a frequency and phase corresponding to the frequency and phase of the output signal of the oscillator 22.

In order to control the output voltage of the inverter 2 by the output voltage and output current, the gate signal forming circuit 24 and the inverter output line 18 are connected by the voltage detection line 25 and the contact a of the switch 26. , when the switch 26 is turned on to the contact b, the voltage holding circuit 27 is connected to the gate signal forming circuit 2.
Connected to 4. Since the voltage holding circuit 27 is connected to the inverter output line 18, it holds the current inverter output voltage. Further, a current detector 33 is provided for overcurrent detection, and is connected to the gate signal forming circuit 24.

FIG. 5 shows the inverter 2 of FIG. 4, which includes four bridge-connected thyristors S ₁ ,
S ₂ , S ₃ , S ₄ , four diodes D ₁ , D ₂ , D ₃ , D ₄ connected in antiparallel to each thyristor, and commutation thyristors S ₅ , S ₆ , S ₇ , S ₈ and commutation reactor
It consists of L ₁ , L ₂ , commutation capacitors C ₁ , C ₂ , and an output transformer T.

FIG. 6 shows the gate signal forming circuit 24 of FIG.
An amplifier 28 for obtaining the rectangular wave output shown in Figure A, an inverting amplifier 29 for obtaining the output shown in Figure 7B, and phase control for controlling the phase of the output of the oscillator 22 using the inverter output voltage V or the inverter output current I. It consists of a circuit 30, an amplifier 31 for outputting the phase controlled rectangular wave shown in FIG. 7C, and an inverting amplifier 32 for obtaining the opposite phase controlled rectangular wave shown in FIG. 7D. Each thyristor S ₁ to _{S 4} of the inverter 2 has a seventh
_The output voltage _of the inverter 2 is controlled by _the gate signals shown in Figures A to D, _and the output voltage of the inverter ₂ is as shown in Figure 7E _. Determined by the width of the output pulse, etc.

When power is supplied from the commercial power supply 7 to the load 1 in the apparatus shown in FIG. 4, the second selection switch 11 is turned on and the first selection switch 6 is turned off. On the other hand, when power is supplied by the inverter 2, the inverter 2 is operated in synchronization with the commercial power source 7 during the entire period in which the inverter 2 is being supplied with power by the commercial power source 7 or immediately before the inverter 2 starts supplying power. That is, the switches 21 and 26 are connected to contact a, and the output voltage of the inverter 2 and the output voltage of the commercial power supply 7 are controlled to be equal in phase, and the output voltage of the inverter 2 is set to a preset reference voltage. Inverter 2 is controlled so that the value is equal to the value. As a result, the inverter 2 and the commercial power supply 7 are substantially in a synchronous operation state.

Next, while keeping the second selection switch 11 that selects the commercial power source 7 on, turn on the first selection switch 6 that selects the inverter 6, and at the same time turn on the changeover switches 21 and 26 to their respective contacts b. throw into. As a result, the commercial power supply 7 and the inverter 2
Parallel operation will begin. At this time, a holding circuit 27 that holds the output voltage immediately before turning on the first selection switch 6 is connected to the gate signal forming circuit 24 of the inverter 2, and the inverter output line 1
Since the connection with the inverter 8 is cut off, the output voltage of the inverter 2 is fixed to the holding voltage of the holding circuit 27. At the same time, the input of the oscillator 22 is also connected to the phase comparison output holding circuit 23 via the contact b of the switch 21, so that the phase and frequency of the output voltage of the inverter 2 remain in the state immediately before the first selection switch 6 is turned on. Fixed. If the output voltage, phase, and frequency of inverter 2 are fixed in this parallel operation,
Even if there is a potential difference and a phase difference between the output voltage of the inverter 2 and the voltage of the commercial power supply 7, if the commercial power supply 7 is constant, the inverter 2 will not operate so that the difference between them will increase. The current based on the potential difference does not increase to a level that causes commutation failure of the thyristors _S1 to _S4 , and no problem occurs even if a parallel operation period of several to several tens of AC cycles occurs.

After the parallel operation for a short time as described above, the second selection switch 11 is turned off, and at the same time, the changeover switches 21 and 26 are turned on to contact a, and power supply to only the inverter 2 is started. As a result, the fixation of the output voltage is released, and the inverter 2 performs a voltage control operation such that the output voltage becomes equal to the reference voltage. After the inverter 2 starts supplying power, if the commercial power source 7 continues to be able to supply power, the inverter 2 is operated in synchronization with the commercial power source 7, and if the commercial power source 7 is unable to supply power, In this case, the control loop by the phase comparator 20 is opened, and the gate signal of the inverter 2 is formed by a fixed oscillator.

Similarly, when switching from power supply from the inverter 2 to power supply from the commercial power supply 7, turn on the second selection switch 11 and turn on the changeover switches 21 and 26 to contact b.
The inverter 2 is operated in parallel with the output voltage magnitude and phase fixed, and then the first selection switch 6 is turned off.

As is clear from the above, according to this method,
It becomes possible to provide a parallel operation period, and it becomes possible to switch power sources without providing a power supply stop period. Therefore, even if the first and second selection switches 6 and 11 have slow response speeds, continuous power supply can be performed, and the cost of the device can be reduced.

Next, FIG. 8 showing a power supply system according to another embodiment of the present invention will be described. However, parts common to the circuit of FIG. 4 are given the same reference numerals and their explanations will be omitted. In this embodiment, one input terminal of the phase comparator 20 is connected between the inverter 2 and the filter 13, so that phase detection can be performed without being influenced by the commercial power supply voltage during parallel operation. Therefore, the phase comparator 20 and the oscillator 22
Without providing a holding circuit between the inverter 2 and the inverter 2, synchronous operation is performed even during parallel operation, and only the output voltage of the inverter 2 is fixed. The method shown in FIG. 8 is the same as the method shown in FIG. 4, except that the phase of the inverter is not fixed during parallel operation and is synchronized with the commercial power supply.

However, a protection method is added when an overcurrent flows through the inverter 2. That is, the second selection switch 11 has a thyristor switch 34 of a natural commutation type consisting of a pair of thyristors 35 and 36 in addition to the contact 11a of the magnetic switch, and a current detector 33 detects the inverter output line. When it is detected that 18 is overcurrent, the gate signals of thyristors S ₂ and S ₄ or S ₁ and S ₃ of inverter 2 are cut off, and the power supply by inverter 2 is cut off, and at the same time, the thyristor switch is cut off. 34 is turned on, and the power supply is switched to the commercial power supply 7. This protection method protects against inrush current when starting parallel operation of inverter 2 and commercial power supply 7, overcurrent during parallel operation, and overcurrent when inverter 2 is operated independently. Applicable.
This enables overcurrent protection without providing a switch circuit with a fast response speed.

In the method shown in Fig. 8, phase detection is performed using filter 1.
3, it is possible to perform phase and frequency control favorably during parallel operation. In addition, if the phase and frequency of the method shown in FIG. 8 fluctuate significantly during parallel operation for some reason, problems similar to those of the conventional method may occur. Therefore, the eighth
The scheme shown is used when large variations in phase and frequency do not occur.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be further modified. For example, during parallel operation, the inverter output voltage is fixed, but the phase and frequency are not fixed, and they are not synchronized with the commercial power supply, so there is no problem even if there is no control. In this way, even if the inverter 2 is left to take its own course without any control, the phase and frequency hardly change within a short period of time, and the inverter 2 can continue to operate.

Further, the circuit for fixing the voltage, the circuit for fixing the phase, etc. may be modified in various ways. For example, voltage detection may be performed between the inverter 2 and the filter 13. Furthermore, in the system shown in FIG. 4, the phase of the inverter output may be detected between the inverter 2 and the filter 13, and input to the phase comparator 20 via a phase shifter for phase correction. Further, in FIG. 8, a phase shifter for correction may be provided between the inverter 2 and the phase comparator 20. Furthermore, the first and second selection switches 6 and 11 shown in FIG. 4 may be replaced by natural commutation type thyristor switches shown in FIG.

[Brief explanation of drawings]

1, 2, and 3 are block diagrams showing conventional power supply switching systems, FIG. 4 is a block diagram showing a power supply system according to an embodiment of the present invention, and FIG. 5 is a block diagram showing the power supply system according to an embodiment of the present invention. A circuit diagram showing an example of an inverter,
6 is a block diagram showing the gate signal forming circuit of FIG. 4, FIG. 7 is a waveform diagram showing the waveforms of each part of FIG. 6 and the output voltage of the inverter, and FIG. 8 is a diagram showing another embodiment of the present invention. FIG. 3 is a block diagram showing a related power supply system. In the symbols used in the drawings, 1 is the load, 2 is the inverter, 6 is the first selection switch,
7 is a commercial power supply, 11 is a second selection switch, 23
2 is a phase comparison output holding circuit, and 27 is a voltage holding circuit.

Claims (1)

[Claims] 1. Switching from a state in which power is supplied to a load by a commercial power source to a state in which power is supplied to the load by a voltage-controlled inverter, or by the voltage-controlled inverter. A method for switching from a state in which power is being supplied to the load to a state in which power is supplied to the load by the commercial power source, the method comprising: before connecting the voltage controlled inverter or the commercial power source to the load; driving the inverter so that the output voltage and phase of the voltage controlled inverter are approximately equal to the output voltage and phase of the commercial power supply; operating the voltage-controlled inverter and the commercial power source in parallel by fixing the voltage-controlled inverter and the commercial power source to a value before starting the parallel operation of the voltage-controlled inverter and the commercial power source; A switching operation method between a commercial power source and an inverter, comprising: disconnecting the load from the load. 2 The parallel operation fixes the output voltage of the voltage-controlled inverter, but synchronizes the phase of the output voltage of the voltage-controlled inverter with the phase of the voltage of the commercial power source while connecting the inverter and the commercial power source. The first claim is to operate in parallel.
How to switch between a commercial power source and an inverter as described in section.