JPH0810986B2 - Power converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device, and more particularly to a power conversion device including a frequency conversion circuit that directly converts a high frequency into a low frequency.

[Background of the Invention]

In a power conversion device including an inverter that forms an alternating current from a direct current, attempts have been made to increase the frequency in order to reduce the size and improve the performance. As a typical example, a power converter equipped with a frequency converter for alternating current to alternating current is "Comparison of high-frequency coupling of a system in which a direct current power source is connected to a power distribution network. A comparison of high−freqve
vcy link schemes for inter facing a dc source to
a utility grid, IEEE-IAS-82), pp. 759-766 ".

This power conversion device converts direct current to alternating current by a self-exciting high-frequency inverter, rectifies it after passing through a high-frequency transformer, and converts it to direct current having a pulsation of the same cycle as commercial,
It will be connected to the commercial system again via the separately excited inverter. Further, the use of higher frequency makes it possible to reduce the size and weight of the transformer.

However, if it is used as an independent power supply without being connected to the grid, even if a frequency converter consisting of a rectifier and a separately excited inverter is connected after a high-frequency transformer, there is no power supply and commutation is not possible. Therefore, the separately excited inverter cannot be operated and desired AC power cannot be obtained. Further, even if the separately-excited inverter is changed to the self-excited inverter, the reactive power of the load cannot be processed, and a desired AC power cannot be obtained.

[Object 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 that stably supplies a sinusoidal AC voltage with small waveform distortion even for an arbitrary power factor load that changes from lead to lag. To provide.

[Outline of Invention]

The present invention relates to an inverter that converts a DC input voltage into an AC voltage having a constant output frequency and a pulse width modulated by a modulation wave having a frequency lower than the output frequency, and an AC voltage output of the inverter is a primary winding. Frequency conversion circuit formed by a transformer connected to the transformer and a switching element connected to the secondary winding of the transformer and converting the voltage induced in the secondary winding into a voltage having a different frequency and outputting the voltage. And a second detecting means for extracting a signal indicating the polarity of the output voltage of the inverter, a second detecting means for extracting a signal indicating the polarity of the output voltage of the power converter, and the power conversion device. Control means for turning on and off the switching element of the frequency conversion circuit based on the signals from the three detection means. More, and outputs the AC voltage is lower than the inverter output frequency the modulated wave.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. In the figure, 1 is a DC power supply, 2 is transistors 21, 22, 23, 24
Inverter composed of switching elements such as a diode and a diode, 3 is a transformer, 4 is a frequency conversion circuit composed of gate turn-off thyristors 41, 42, 43 and 44, and 5 and 6 are for improving the output voltage waveform. The filter capacitor and reactor, and 7 are current detectors. Reference numeral 100 denotes an inverter control circuit 101, a level detector 103 for detecting the level of current flowing through the reactor 5 of the filter, and a control signal forming circuit 105 for forming control signals for the gate turn-off thyristors 41, 42, 43, 44. It is a control circuit composed of.

The operation will be described with reference to FIG. The inverter control circuit 101 turns on the transistors 21 and 22 alternately at a constant cycle.
Works off. The period from t _{1 to} t _{2 and the} period from t _{4 to} t ₅ are non-lap periods for preventing the short circuit of the power source 1 due to 21 and 22. Furthermore, since the output voltage of the inverter 2 is operated by pulse width modulation control like e so that the output voltage of the power converter becomes sinusoidal, the transistors 23 and 24 output the output voltage e to 21 and 22. The on and off operations are alternately performed with a delay of a predetermined time required for forming. 101 outputs a signal S1 indicating the polarity of the output voltage of the power converter and a signal S2 indicating the polarity of the output voltage e of the inverter 2, and supplies the signal S1 to the control signal format circuit 105. The signal S1 is the signal shown in the figure for discriminating the periods 0 to π and π to 2πrad, and the signal S2 is the signal shown in the figure showing the polarity of e at each T _P interval. The current i _{L of the} reactor 5 shown in FIG. 2 detected by the current detector 7 is the level detector 10
Applied to 3. 103 forms a signal S3 for discriminating between a positive region and a negative region of i _L and supplies it to 105. 105 indicates signals S1, S2,
From S3 41… S1 ・ S2 ・ S3or ▲ ▼ ・ ▲ ▼ ・ S3 42… S1 ・ S2 ・ ▲ ▼ or ▲ ▼ ・ ▲ ▼ ・ ▲ ▼ 43 ... S1 ・ ▲ ▼ ・ S3 or ▲ ▼ ・ S2 ・ S3 44… S1・ Gate, turn-off, thyristor 41,42,43,44 under the conditions of ▲ ▼ ・ ▲ ▼ or ▲ ▼ ・ S2 ・ ▲ ▼
The illustrated signal for controlling the ON state is output. The frequency conversion circuit 4 is ON / OFF controlled by the signal 105, forms the illustrated voltage e _L of a frequency lower than the inverter frequency from the inverter output voltage e, and improves the waveform by the filters 5 and 6, A desired alternating voltage having a wavy shape is obtained.

Next, the operation of the embodiment including the level detector 104 shown by the broken line in FIG. 1 will be described with reference to FIG. The difference from the above-described embodiment is that the level detectors 103 and 104 are the third ones.
As shown in the figure, a level is provided so as to discriminate so as to output a signal above + I _O and below −I _O. Signal S3 is 1 level only when i _L is + I _O or higher, and signal S4 only when i _L is -I _O or lower
Outputs 1 level. 105 is signal S1, S2, S3, S4 41… S1 ・ S2 ・ S3 ・ ▲ ▼ or S1 ・ S2 ・ ▲ ▼ ・ ▲
▼ ・ or ▲ ▼ ・ ▲ ▼ ・ ▲ ▼ ・ ▲ ▼ 42… S1, S2 ・ ▲ ▼ ・ ▲ ▼ or ▲ ▼ ・ ▲ ▼
・ ▲ ▼ ・ ▲ ▼ ・ or ▲ ▼ ・ ▲ ▼ ・ ▲
▼ ・ S4 43… S1 ・ ▲ ▼ ・ S3 ・ ▲ ▼ or S1 ・ ▲ ▼ ・ ▲
▼ ・ ▲ ▼ ・ or ▲ ▼ ・ S2 ・ ▲ ▼ ・ ▲ ▼ 44… S1 ・ ▲ ▼ ・ ▲ ▼ ・ ▲ ▼ or ▲ ▼ ・ S2
・ ▲ ▼ ・ ▲ ▼ ・ or ▲ ▼ ・ S2 ・ ▲ ▼ ・ S4 condition, gate turn-off, thyristor 41,42,43,4
The illustrated signal for controlling 4 is output. Frequency conversion circuit 4
Is ON / OFF controlled by a signal given from 105, and a desired AC voltage can be obtained at the output. Furthermore,
Since the frequency conversion circuit can be controlled according to the level of the circuit current, a predetermined circuit operation can be performed even if the load changes suddenly or the load condition changes, and an AC voltage having a good waveform can be obtained.

Another embodiment is shown in FIG. The difference from the embodiment of FIG. 1 is that the timing control circuit 102 controls the control signal forming circuit 105. In the embodiment of FIG. 1,
The control signal of the frequency conversion circuit changes when the polarity of the signal S2 changes t ₁ , t ₄ , t ₇ ... time and when the signal S3 or S3, S4 changes t ₆ or t ₂ ′, t ₆ ′ ... time. And the pulse width changes drastically during one cycle. The inverter output voltage e is not adapted and switched.

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

The operation of the timing control circuit 102 will be described with reference to FIG. An example is given in which the output signal of 101 for driving 21, 22, 23, 24 is given in the relationship shown in the figure, and the current i _{L of} the circuit is positive. In the embodiment shown in FIG. 1, the signals 41 and 42 are uniquely given in a time relationship irrelevant to 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 lap period at the time of switching may be provided. In the embodiment of FIG. 4, the switching time is controlled according to the pulse width te as shown in FIG. 5 (b).

Assuming that the inductance in the loop of the switching circuit by the converter and wiring is L, the amplitude of the inverter output voltage e is e _P , and the current of the circuit is i _L , the switching time t _W of the switching element of the frequency conversion circuit 4 is t _W = (L, e _P , i _FL ). pulse width t _e of e varies in one period, for example, during a period of t _e of small t ₁₂ ~t ₁₃ a t _e t _w, no voltage occurs in the taken output side most t _W, the t _e Big t
_In the period from _{22 to} t ₂₄ , t _e >> t _w , and the output is almost t _e . In order to improve the output waveform, a voltage having a width t _e is output as much as possible. Therefore, as shown in FIG. 4, the 102 obtains the data S2 and the data t _e from 101 and the timing data. Also, the level detection is performed by obtaining i _L data from 7. A signal S6 for controlling the switching timing is formed from S2, t _e width data, timing data, and data indicating the current level, and 105 is controlled to form a signal as shown in FIG. 5 (b). The formation portion of the signal S6 can be formed by a ROM having data determined by the circuit conditions shown in the above equation. According to the present embodiment, the operation of the frequency conversion circuit can be further controlled according to t _e and i _L , so that the switching time can be shortened and the output waveform can be improved.

Of course, like the embodiment of FIG. 1, it is possible to omit 104 and use only the polarity signal by 103.

FIG. 6 shows a concrete embodiment of the control circuit 100. In the figure, 201 is an oscillation circuit, 202 is a counter, 203 is a non-lap period forming circuit, 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, and 209 and 210 are levels. A detection circuit, 211 is a ROM, and 212 is a switching control circuit. The output signal of 201 is counted at 202 to form the signal S2 shown in FIG. 2 and provided to 203, 206 and 211. 203
Is the t ₁ shown in Fig. 2 using a mono multivibrator, etc.
~ T ₂ and t ₄ ~ t ₅ non-lap period are formed, and drive signals 21,22
To form. An address corresponding to one cycle of the converter from 202 and an address corresponding to the control amount of the output voltage from 208 are given to 204, and data for changing the pulse width of the inverter output voltage e shown in FIG. Output and give to 205. 205 sets the data given from 204, S2
From the time when the polarity of the signal changes, for example, t ₁ , t ₄ ..., the clock signal from 201 is counted, and when the counting is completed, 2
Output a set signal to 06. 206 holds the signal S2 at the time when the set signal is applied, and outputs the signal to 207. Similarly to 203, 207 forms 23 and 24 drive signals obtained by removing the non-lap period from the signal given by 206. 2
09, 210 inputs the detected circuit current i _L , compares it with a set value by a comparator, forms signals S3, S4 as shown in FIG. 3, and supplies it as an address 211. In order to obtain the switching timing shown in FIG. 5, reference numeral 212 designates data representing one cycle from 202, timing data at t ₁ , t _4, ...
Data corresponding to the control amount of the output voltage is obtained from S ₂ and 208, and a plurality of address signals S ₆ given to 211 are output. 211
Outputs data corresponding to the given S1, S3, S4, and S6, and drives 41 to 44.

In the embodiment 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 switching element having a disconnection function. Further, although the description has been made on the single-phase circuit, it is needless to say that the same can be applied to different main circuit configurations such as three-phase and other multi-phases.

〔The invention's effect〕

According to the present invention, the polarity of the voltage to be output is selected by the polarity signal of the output voltage of the inverter and the polarity signal of the output voltage of the power converter, and the polarity of the current to be flowed by the polarity signal of the output current of the power converter is selected. Since both of them operate the frequency conversion circuit, the switches can be operated according to the polarities of the voltage and current of the inverter voltage source and load, and even if the load has an arbitrary power factor that changes from lead to lag, both are linked. Therefore, an appropriate switch operation can be performed without causing a short circuit, and an sine wave AC voltage with small waveform distortion can be stably supplied to the output. Further, in addition to the control of the frequency conversion circuit, the frequency conversion circuit is controlled by a positive / negative polarity signal obtained from a point where the magnitude of the output current exceeds a predetermined positive / negative level, which is a signal indicating the polarity of the output current of the power conversion device. By controlling, the frequency conversion circuit can be controlled according to the level of the circuit current, so that appropriate switch operation can be performed even in the small current region where the current polarity changes due to ripple etc. and sudden load changes or load conditions change.
The output has the effect of obtaining a sinusoidal AC voltage with small waveform distortion. Further, in addition to the control of the above frequency conversion circuit, by controlling the frequency conversion circuit by the pulse width of the output voltage of the inverter, the switching time of the plurality of switching elements forming the frequency conversion circuit can be shortened, so that it is provided at the time of switching. It is possible to obtain the effect that the waveform distortion generated by the applied lap period can be reduced and a favorable AC voltage having a sinusoidal waveform can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power converter according to an embodiment of the present invention, FIG. 2 is an operation explanatory view of FIG. 1, and FIG. 3 is an operation explanatory view of another embodiment shown in FIG. FIG. 4 is a circuit diagram of another embodiment,
FIG. 5 is a diagram for explaining 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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junto Jifuku 3-1-1 Sachimachi, Hitachi City, Ibaraki Hitachi Ltd. Hitachi factory (56) References U) Special table Sho 57-501007 (JP, A)

Claims (4)

[Claims] 1. An inverter for converting a DC input voltage into an AC voltage having a constant output frequency and a pulse width modulated by a modulating wave of a frequency lower than the output frequency, and an output of the AC voltage of the inverter is a primary winding. A frequency converter formed by a transformer connected to a line and a switching element connected to a secondary winding of the transformer and converting a voltage induced in the secondary winding into a voltage having a different frequency and outputting the voltage. In a power converter including a circuit, first detecting means for extracting a signal (S ₂ ) indicating the polarity of the output voltage of the inverter, and a signal (S ₁ ) indicating the polarity of the output voltage of the power converter. A second detection means for extracting the signal and a third detection means for extracting a signal (S ₃ ) indicating the polarity of the output current of the power converter, and the frequency conversion based on the signals from the three detection means. Circuit switch A power conversion device, wherein an AC voltage having a frequency lower than the inverter output frequency is output by a control unit that turns on and off the ching element. 2. The third detecting means for extracting the signal indicating the polarity of the output current of the power converter according to claim 1, from the point where the magnitude of the output current exceeds a predetermined positive or negative level. Positive and negative polarity signals of the output current (S ₃ , S ₄ )
To obtain the positive and negative polarity signals (S ₃ , S
₄ ) and the polarity signal (S ₂ ) of the output voltage of the inverter and the polarity signal (S ₁ ) of the output voltage of the power converter to control the switching element of the frequency conversion circuit to turn on and off the inverter output. A power conversion device, which outputs an AC voltage of a modulation wave lower than the frequency. 3. The control means for turning on / off the switching element of the frequency conversion circuit according to claim 2, wherein the switching element is turned on / off based on the pulse width Te of the output voltage of the inverter. A power conversion device characterized by the above. 4. The control means for turning on / off the switching element of the frequency conversion circuit according to claim 1, wherein the switching element is turned on / off even based on the pulse width Te of the output voltage of the inverter. A power conversion device characterized by the above.