JPH0570388B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit responsible for synchronous switching between a commercial power source and a multiple current source inverter.

For example, when controlling the air volume of a fan or blower, it is operated on commercial power when the output is high, and when the operation is stopped, an inverter (the output frequency is set considerably lower than the commercial frequency) is used in preparation for the next operation. ) to drive at low speed or stop. In such a driving method, it is necessary to switch the power source from an inverter to a commercial power source, or vice versa.

By the way, for example, in order to switch from inverter operation to commercial operation of a drive motor such as a fan blower, it is necessary to match the frequency, voltage, and phase of the two, and without this, inrush current will flow and the load motor will generate abnormal torque. occurs. In particular, inrush current is strongly affected by phase difference, and phase matching is an important requirement for power supply switching.

On the other hand, when driving a motor load with a large capacity current source inverter, since the inverter output is a rectangular wave, there are many harmonic components and large torque pulsations. In order to compensate for this, we adopted a multiplexing method of current source inverters in which the outputs of several current source inverters are shifted symmetrically to the left and right around a single waveform, thereby making the waveform of the load current as close to a sine wave as possible. ing.

Now, in multiplexing current source inverters, each unit inverter must have a certain phase difference depending on the number of multiplexed units. Accordingly, it is necessary to ensure that the phase of each unit inverter does not change even when switching in synchronization with the commercial power supply.

The purpose of this invention is to accurately prevent phase errors by detecting phase matching when switching between the inverter power source and the commercial power source, and sequentially setting the phases of each unit of the inverter at regular intervals for synchronization. The purpose is to enable synchronous switching and maintain equal capacity sharing among each unit of the inverter at the time of switching.

The illustrated embodiment will be specifically described below. FIG. 1 is a circuit diagram of a 3-multiplex 18-phase inverter, where 1 is a commercial power supply. 2, 3, and 4 are current source unit inverters each having a forward conversion section and an inverse conversion section, and the voltage of the commercial power source 1 is applied via a transformer 5 to the input side of each forward conversion section. The inverse converter outputs of the unit inverters 2, 3, and 4 are passed through separate transformers 6, 7, and 8 to obtain a total sum output, which is then supplied to the load motor 9 via the contactor K1. Further, the commercial power source is connected to the load motor 9 through the contactor K2. 10 is a frequency command setter, the output signal of which is guided to a V-F converter 12 via a ramp function generator 11. 13,1
4 and 15 are unit inverters 2 and 3, respectively.
The input pulse selection circuits for and 4 receive pulse signals with phases of +20°, 0°, and -20° from the V-F converter 12, respectively, and receive pulse signals of +20° and 0°, respectively, from the synchronizing pulse generation circuit described later. ,−20°
The system receives pulses having a phase of , and prompts to sequentially switch the pulse to be used based on a phase and frequency matching signal, which will be described later. This input pulse selection circuit 13,
The specific circuits of 14 and 15 are as shown in Figure 2.
Timing circuits 13a, 14a, 15a and switching circuits 13b, 14b, 15b are configured by the connections shown. Reference numerals 16, 17 and 18 are pulse distributors for controlling the inverse converters of the unit inverters 2, 3 and 4, respectively, which perform a pulse distribution function based on the selection pulses of the input pulse selection circuits 13, 14 and 15, respectively. amplifiers 19, 20,
21 to control the inverse conversion elements of each unit inverter 2, 3, 4. This pulse distributor 1
A synchronization signal is supplied in order to match the R, S, and T phases of 6, 17, and 18. 22
is a power factor angle detection circuit which obtains the output current and output voltage of the unit inverter 3 from the transformer 23 and current transformer 24, respectively, and detects the power factor. Reference numeral 25 denotes a frequency coincidence detection circuit, which compares the pulse frequency regulated by the input voltage to the V-F converter 12 with the commercial frequency and obtains an output signal by matching the two frequencies. 26 is a phase coincidence detection circuit which obtains the output of the unit inverter 3 via the transformer 23 and obtains the commercial power supply voltage via the transformer 30;
An output is obtained by well-known means when the phases of both voltages match. 27 is an AND gate which performs an AND operation on each output signal of the frequency coincidence detection circuit 25 and phase coincidence detection circuit 26 and outputs the signal to the input pulse selection circuit 13.
Supplied as a pulse switching command. 28 is a synchronous pulse generation circuit which inputs the output from the transformer 5 via the transformer 29 and simultaneously inputs the output from the power factor detection circuit 2.
2, each input pulse selection circuit 13, 1 receives a pulse synchronized with the commercial power supply voltage based on each input.
As input signals of 4 and 15, the phase difference is +
Supply while maintaining the angles of 20°, 0°, and -20°. The specific configuration of this synchronous pulse generation circuit is shown in FIG.
Zero cross circuits Z1, Z2, Z3 receiving outputs from 1, F2, F3, the zero cross circuit Z1,
Differentiation circuit H that differentiates each output signal of Z2 and Z3
1, H2, H3, the relevant differentiation circuit H1, H2, H3
A waveform shaping circuit W responsible for shaping the waveform of the input from the waveform shaping circuit W receives power factor signals from the waveform shaping circuit W and the power factor detection circuit 22 to obtain pulses having phases of +20°, 0°, and −20°, respectively. Pulse generation circuit P1, P
It consists of 2 and P3.

In the above configuration, during normal inverter operation, upon starting, contactor K1 is first closed, and load motor 9 is connected to each unit inverter 2,
3 and 4, and the pulse period from the V-F converter 12 gradually becomes shorter with the action of the ramp function generator until the frequency corresponds to the output of the frequency setter 10. At this time, each input pulse selection circuit 13, 14, 15 is connected to a V-F converter 12.
By setting to select +20° pulse, 0° pulse, and -20° pulse from
6, 17, 18 and amplifiers 19, 20, and 21, the unit inverter 3 generates a 20° leading waveform (unit inverter 2 waveform) and a 20° delayed waveform (unit inverter 4 waveform). ) overlaps and operates in a manner that brings it closer to a sine wave. In this operation, signals are sequentially transmitted to each pulse distributor 16, 17, and 18 in order to match the phases. In this way, the load motor 9
Inverter power is supplied from each unit inverter 2, 3, 4 via the transformer 6, 7, 8 and contactor K1 in sequence.

Now, such unit inverters 2, 3,
The power supply from 4 to the load motor 9 is less efficient than the power supply from a commercial power source, and in particular, the power supply from about 90
% or less, it is necessary to switch to using commercial power for normal operation from the perspective of energy conservation, but we will explain the transition from inverter operation to operation using commercial power in a step-by-step manner. .

First, with the contactor K1 closed and the load motor 9 connected to the unit inverters 2, 3, and 4 in that order, the output level of the frequency setter 10, that is, the input level to the V-F converter, is converted to the V-F converter. The period of the output pulse of the device is determined so that it corresponds to the commercial power supply frequency. At this time, when the frequencies of unit inverters 2, 3, and 4 match the commercial frequency, a frequency match detection circuit 25 supplies a frequency match signal. Then, when the output voltage phase of the unit inverter 3 and the phase of the commercial power source 1 match, an output (switching command) is issued from the phase coincidence detection circuit 26, and is sent to the timing circuit 13a of each input pulse selection circuit 13 through the AND gate 27. Added.

By the way, before the switching command is issued from the AND gate 27, the synchronous pulse generation circuit 28
, each component and power factor detection circuit 22 in FIG.
+20° phase pulse with respect to the commercial frequency due to the action of
A 0° phase pulse and a −20° phase pulse are created, and each is added as one input to the input pulse selection circuit.

Therefore, when a switching command is input to the input pulse selection circuit 13, the timing circuit selects, for example,
At the falling edge of the +20° phase pulse from the V-F converter 12, the pulse is switched to the +20° synchronizing pulse output from the synchronizing pulse generating circuit 28. Next, a command is sent from the switching circuit 13b to the timing circuit 14a in the input pulse selection circuit 14 to switch to the 0° phase commercial synchronizing pulse at the falling edge of the 0° phase pulse from the V-F converter 12. At the same time, a switching command is issued to the timing circuit 15a. As a result, the switching circuit 15b -
It is applied to the 20° phase commercial synchronous pulse distributor 18 and also provides a synchronous switching permission signal. By closing the contactor K2 in response to this synchronization switching permission signal, the commercial power supply 1 and the inverter power supplies from each unit inverter 2, 3, and 4 are wrapped through the contactors K2 and K1, respectively, and power is supplied to the load motor 9. It comes down to doing it. After performing this lap operation for some time, the contactor K1 is opened (this operation can be performed automatically or manually), and the load motor 9 is supplied with power exclusively from the commercial power source 1.

Although the above explanation shows an example of a 3-multiplex 18-phase inverter, generally n-multiplex (n
can be applied to all natural numbers except 1). Furthermore, the phase difference between each unit inverter is not limited to 20° and can be set arbitrarily.

As described above, the synchronous switching device between a multiplex current source inverter and a commercial power source according to the present invention operates a plurality of unit inverters with a desired phase difference, multiplexes them, and supplies power to a load. In a current source inverter, each unit inverter is equipped with an input pulse selection circuit that selects one of two input pulses based on a control command, and each input pulse selection circuit receives an input from a frequency setting device. A pulse that has a frequency corresponding to the level and a desired phase difference, and a pulse that is synchronized with the commercial power supply and has the same phase difference as above are received as input signals, and are obtained at the output of each of the above unit inverters. When the overall output of the current source inverter (if the number of unit inverters is odd, the output of the unit inverter with the 0° phase center is also acceptable) and the output of the commercial power supply have the same frequency phase, one input pulse selection circuit The selection pulse is switched, and the selection pulses of the remaining input pulse selection circuits are sequentially switched, and after the switching of all input pulse selection circuits is completed, the power supply is switched through a lap operation. Based on this configuration, even in the case of a multiple current source inverter, switching between the pulse from the V-F converter for inverter control and the commercial synchronous pulse is performed for each unit inverter at the time of synchronized switching between the inverter power supply and the commercial power supply. Since this is performed sequentially, synchronization can be achieved without causing phase errors. ○ With this device, the unit inverter can be adjusted to 20°.
Since the pulses used by each unit inverter are switched in a relatively short period of time, there is no room for the capacity allocation of each unit inverter to be disrupted.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of this invention, Fig. 2 is a circuit diagram showing an embodiment of the present invention;
3 are circuit diagrams showing a part of FIG. 1 in detail. 1... Commercial power supply, 2, 3, 4... Unit inverter, 9... Load motor, 10... Frequency setting device, 12... V-F converter, 13, 14, 15
... Input pulse selection circuit, 25 ... Frequency coincidence detection circuit, 26 ... Phase coincidence detection circuit, 28 ... Synchronization pulse generation circuit.

Claims (1)

[Claims] 1. In a multiple current source inverter that operates multiple unit inverters with a desired phase difference and multiplexes the output of each of these unit inverters to supply power to a load, two input pulses are applied to each unit inverter. It has an input pulse selection circuit that selects one of these and controls each unit inverter, and each input pulse selection circuit has a frequency corresponding to the input level from the frequency setting device and a desired phase difference. a circuit means for supplying as input signals a pulse signal generated by the above-mentioned pulse signal and a pulse having the same frequency as the commercial power supply voltage and the same phase difference as the above-mentioned phase difference, and a current-source inverter obtained from the output of each of the above-mentioned unit inverters. When the output and the output of the commercial power supply have the same frequency and the same phase, the selection pulse of one input pulse selection circuit is switched, and the selection pulses of the remaining input pulse selection circuits are sequentially switched, and all input pulses are selected. A synchronous switching device for a multiple current source inverter and a commercial power source, characterized by comprising circuit means for supplying a power source switching permission command when circuit switching is completed.