JPS61293170A - Power converter - Google Patents

Abstract

PURPOSE:To obtain a power converter which produces the desired AC power as an independent power source by controlling the switching operation of a frequency converter in response to the output voltage of an inverter, the output voltage of the power converter and the polarity of the output current. CONSTITUTION:A transformer 3 is connected with the output side of an inverter 2, a frequency converter 4 having switches 41-44 is connected in series between the secondary side output terminals of the transformer 3, and an output eL is obtained from the connecting point and the secondary side neutral point of the transformer 3. A control signal forming circuit 105 inputs the output voltage value of a power converter, and a signal representing the polarity of the output current iL of the converter, and rives the converter 4 by a frequency lower than the output frequency of the inverter 2 in response to the values. Thus, the desired low frequency AC power can be stably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a power conversion device, and particularly to a power conversion device equipped with a frequency conversion circuit that directly converts a high frequency into a low frequency.

[Background of the invention]

2. Description of the Related Art In power converters equipped with inverters that generate alternating current from direct current, attempts have been made to increase the frequency in order to make them smaller and improve their performance. A typical example is a power conversion device equipped with an AC-AC frequency converter [Comparison of high-frequency results of devices that connect a DC power supply to a power distribution network]. A comparison o
f high-freqvevcy linksche
mes for in ter facing a d
c 5 sources to utility grid
, IEEE-JAS-82), pp. 759-76
Discussed on page 6.

This power converter converts direct current into alternating current using a self-commutated high-frequency inverter, passes it through a high-frequency transformer, rectifies it, converts it into direct current that has the same frequency as the interconnected commercial power supply, and then converts it back to a separately-commutated inverter. Connect to commercial grid via. and,
Higher frequencies allow transformers to be smaller and lighter.

However, when used as an independent power source without being connected to the grid, even if a frequency converter consisting of a rectifier and separately excited inverter is connected after going through a high-frequency transformer, commutation is impossible because there is no power source. Therefore, the separately excited inverter cannot be operated and the desired AC power cannot be obtained. Furthermore, even if a separately excited inverter is replaced with a self-excited inverter, there is a problem in that the reactive power of the load cannot be processed and the desired AC power cannot be obtained.

[Purpose of the invention]

An object of the present invention is to provide a power conversion device equipped with a frequency conversion circuit that can be operated as an independent power source.

[Summary of the invention]

The gist of the present invention is to control the switching operation of the frequency conversion circuit by adapting to the polarity and timing of the inverter output voltage and the polarity and level of the circuit current in order to obtain desired AC power with small waveform distortion.

[Embodiments of the invention]

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

In the figure, 1 is a DC power supply, 2 is a transistor 21.2
2, 23, 24 An inverter constructed using switching elements such as diodes, 3 a transformer, 4 a frequency conversion circuit constructed using a gate turn-off thyristor 41°4.2, 43, 44, 5 and 6 7 is a capacitor handle of a filter for improving the output voltage waveform, and 7 is a current detector.

Reference numeral 100 denotes an inverter control circuit 101 and a level detector 103 for detecting the level of current flowing through the filter steering wheel 5. and gate turn-off thyristor 41,
This control circuit includes a control signal forming circuit 105 that forms control signals 42, 43, and 44.

The operation will be explained using FIG. The inverter control circuit 101 alternately turns on and off the transistors 21 and 22 at regular intervals. Note that the periods between t1 and t2 and between t4 and t5 are non-lap periods for preventing the power supply 1 from being short-circuited by 21 and 22.

Furthermore, in order to operate the output voltage of the inverter 2 by pulse width control as shown in e, so that the output voltage of the power converter becomes a sine wave, the transistors 23 and 24 have a width of 21.22.
and then turn on alternately with a predetermined time delay necessary to form the output voltage e.

Performs off operation. 101 outputs a signal S1' indicating the polarity of the output voltage of the power conversion device and a signal S2 indicating the polarity of the output voltage e of the inverter 2, and supplies them to the control signal format circuit 105. Signal S1 is the illustrated signal that discriminates between O~π and π~2π rad, and signal S2 is T, and e at every interval.
is an illustrated signal indicating the polarity of . A current iL of the reactor 5 shown in FIG. 2 detected by the current detector 7 is applied to the level detector 103. 103 forms a signal S3 that discriminates between the positive area of jL and the page area, and is supported by 105.

105 is 41, -81, from the signals S-1, 82, 83.
S2・53orS1・82・8342...Sl・S
2.530rS11S2.5343-81.52-83
orSILS2・8344=-81]2・S'3orS
Outputs the signal shown to control the gate turn-off thyristor 41°4.2, 43.44 under the conditions of 1, S2, and S3.

The frequency conversion circuit 4 is controlled on and off by signals 1 and 05, and forms a voltage eL shown in the figure with a frequency lower than the inverter frequency from the inverter output voltage e, and improves the waveform by filters 5 and 6. A desired sinusoidal AC voltage is obtained.

Next, the operation of the embodiment including the level detector 104 shown by the broken line in FIG. 1 will be explained using FIG. 3. The difference from the previous embodiment is that the level detector 103. ．． 1
As shown in FIG. 3, 04 is provided with a level for discriminating so that a signal is output at +18 or higher and -To or lower.

iL is +■.

Only in the case of -hi, the signal S3 is level and iL is -I.

The signal S4 outputs the level only in the following cases.

105 is the signal 81. S2, 41 from 83.84...
Under the conditions of Sl, S2, S3, 540rS1, S2, gate turn-off thyristor 41°42.43.44
Outputs the indicated signal that controls the

The frequency conversion circuit 4 is controlled on and off by a signal given from 105, and can obtain a desired alternating current voltage as an output. Furthermore, since the frequency conversion circuit can be controlled according to the level of the circuit current, the circuit can operate in a predetermined manner even if the load suddenly changes or the load conditions change, and an AC voltage with a good waveform can be obtained.

Another embodiment is shown in FIG. The difference from the embodiment shown in FIG. 1 is that a control signal forming circuit 105 is controlled by a timing control circuit 1.02.

In the embodiment shown in FIG. 1, the control signal of the frequency conversion circuit changes when the polarity of the signal S2 changes 1, 1t4e t
7... Time and signal S3 or 83. This is the time point t6, t2', tt6', . It is not switched in accordance with the inverter output voltage e.

In the embodiment shown in FIG. 4, the control signal forming circuit 105 is controlled in consideration of the pulse width of e.

The operation of the timing control circuit 102 will be explained using FIG. Let us take as an example the operation when the output signals of 101 that drive circuits 21, 22, 23, and 24 are given in the relationship shown, and the circuit current jL is positive. In the embodiment of FIG. 1, the signals 41 and 42 are uniquely given in a time relationship independent of the pulse width te of the inverter output voltage e, as shown in FIG. 5(a). However, depending on the characteristics of the switch elements 41 to 44, a wrap period may be provided at the time of switching. In the embodiment shown in FIG. 4, the switching time is controlled according to the pulse width te, as shown in FIG. 5(b).

If the inductance in the loop of the switching circuit caused by the converter and wiring is calculated, and the amplitude of the inverter output voltage e is 29, and the current in the circuit is iL, then the switching time 1 of the switching element of the frequency conversion circuit 4 is tw=f ( L+ Bpr IF
L) is given by. The pulse width t of e changes during one cycle,
For example, for a small t-work of t, 1,2 in a period of ~t□3
1. , the voltage is mostly taken at tw, no voltage is generated on the output side, and in the period from t22 to t24 where t is large, it is 1, >> 1.

Therefore, an output of approximately t1 width can be obtained. In order to obtain a good output waveform, a voltage with a width of t0 as much as possible is output, so as shown in FIG. 4, 102 obtains data for obtaining a signal S2 and a width of t8 from 101, and timing data. In addition, level detection is performed by obtaining iL data from 7. S2. First, a signal S6 for controlling switching timing is formed from the t0 width data, timing data, and current level, and the signal S6 is controlled to control 105 to form a signal as shown in FIG. 5(b). Note that the portion forming the signal S6 can be composed of R and OM having data determined by the circuit conditions shown in the above equation. According to this embodiment, since the operation of the frequency conversion circuit can be further controlled according to t, , iL, the switching time can be shortened and the output waveform can be improved.

Note that, as in the embodiment of FIG. 1, 104 is removed and 103
Of course, only the polarity signal can be used.

FIG. 6 shows a specific embodiment of the control circuit ↓00. In the figure, 201 is an oscillation circuit, 202 is a counter, and 203
204 is a ROM, 205 is a counter, 206 is a latch, 207 is a non-lap period forming circuit, 208 is a constant voltage control circuit, 209 and 21.0 are level detection circuits, 211 is a ROM, and 212 is a non-lap period forming circuit. This is a switching control circuit.

The output signal of 201 is counted by 202 to form the signal S2 shown in FIG.

Reference numeral 203 uses a mono multivibrator or the like to form non-lap periods t1-t2 and t4-t5 shown in FIG. 2 to form drive signals 21.degree.22. The address corresponding to one cycle of the converter from 202, the address corresponding to the voltage transformation control from 208, and the data given to 204 to change the pulse width of the inverter output voltage e shown in FIG.
It is output from 04 and given to 205. 205 sets the data given from 204, and sets the time point at which the polarity of the S2 signal changes, for example, t□.

From time t4..., counting is performed using the clock signal from 201, and when the counting is completed, a set signal is output to 206. 2
06 holds the signal S2 at the time when the set signal was applied, and outputs the signal to 207.

207, like 203, removes the non-lap period from the signal given from 206. 23 and 24 drive signals are formed. 209 and 210 input the detected circuit current jL, which is compared with a set value by a comparator, and outputs the signal S3. form S4, 2
11 address.

212 is 2 in order to obtain the switching timing shown in FIG.
Data representing one cycle from 02 and t□.

Data at time t4, data corresponding to voltage control and S2 are obtained from 208, and an address given to 211 is output. 211 is the given 81°83, S4. and outputs data according to S6, and completes 41 to 44.

In the embodiments shown in FIGS. 1 to 4, the switching elements 21 to 24 constituting the inverter 4 are transistors, and the switching elements 41 to 44 constituting the frequency conversion circuit 4 are gate turn-off thyristors. Of course, it can be changed to a functional element. Further, although the explanation has been made using a single-phase circuit, it is of course possible to use a three-phase circuit or other multi-phase circuits.

〔Effect of the invention〕

According to the present invention, a high-frequency inverter output can be frequency-converted and converted into a low-frequency stable alternating current, so it is possible to realize a power conversion device that can be operated as an independent power source.

[Brief explanation of drawings]

1 is a circuit diagram of a power conversion device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, and FIG. 3 is an explanatory diagram of the operation of another embodiment shown in FIG. Figure 4 is a circuit diagram of another embodiment,
FIG. 5 is an explanatory diagram of the operation of the embodiment shown in FIG. 4, and FIG. 6 is a block diagram of the control circuit 100. 2... Inverter, 3... Transformer, 4... Frequency conversion circuit, 5... Reactor, 6... Capacitor,
7... Current detector, 101... Inverter control circuit, 102... Timing control circuit, 103, 104
. . . Level detector, 105 . . . Control signal forming circuit.

Claims (1)

[Claims] 1. An inverter, a transformer connected to the output of the inverter, a switch connected in series between the output terminals of the converter, and a connection point between the neutral point of the converter and the switch. In the power conversion device configured to output from the inverter, the switch is operated according to the output voltage of the inverter, the output voltage of the power conversion device, and the polarity of the output current of the power conversion device, A power conversion device characterized by forming alternating current with a frequency lower than the output frequency. 2. In claim 1, the switch is operated according to the output voltage of the inverter, the output voltage of the power converter, the polarity of the output current of the power converter, and the magnitude of the output current. A power conversion device characterized by: 3. In claim 1, the output voltage of the inverter, the output voltage of the power converter, the polarity of the output current of the power converter, the magnitude of the output current, and the voltage of the output voltage of the inverter. A power conversion device characterized in that the switch operates according to a pulse width. 4. In claim 1, the switch is operated according to the output power of the inverter, the polarity of the output voltage and output current of the power converter, and the pulse width of the output voltage of the inverter. A power conversion device characterized by: