JPH0510910B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a power converter that converts alternating current to direct current.

[Technical background and problems of the invention]

In a converter in which two sets of three-phase thyristor bridges that can flow current in both forward and reverse directions are connected in antiparallel, the input power supply voltage is
Va is determined from the relationship of Ed=1.35Va(1+K)COSβ where Ed: DC voltage Va: Effective value of input power supply voltage Ki: Power supply voltage fluctuation rate Bi: Phase control advance angle.

In other words, the phase control advance angle β is normally set in the range of 30° to 45°, and the input power supply voltage Va is determined with the power supply voltage fluctuation rate k being ±0.1. There are values such as 0.1 to -0.3, and if the input power supply voltage Va is determined under this condition of k=-0.3, the input power factor of the converter will be poor. This has the disadvantage that the utilization rate of the converter is poor and the input power supply capacity is increased.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a power converter that can operate stably even when the voltage fluctuation rate of the input power source is large and has a high input power factor.

[Summary of the invention]

In order to achieve the above objects, the present invention converts AC power supplied from an input AC power source into DC power and supplies it to a load, and converts regenerative DC power from the load side into AC power to convert the AC power supplied from the input AC power source into AC power. A power conversion device having a function of regenerating power to the load includes a diode provided between the power conversion device and the load in a direction to block regenerated power, and at least two diodes provided in parallel and series connection to the diode. a resistor, a switch connected in parallel to at least one of the resistors, and a control means for controlling opening and closing of the switch in accordance with a voltage fluctuation rate of the input AC power source during power regeneration from the load to the input AC power source. It is equipped with the following.

[Embodiments of the invention]

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

FIG. 1 is a main circuit configuration diagram of a power converter according to the present invention. 1 is an AC input power supply, 3 is a converter with two sets of 3-phase thyristor bridges connected in antiparallel that can flow current in both forward and reverse directions, 4 is a diode, 5 and 6 are resistors, 7 is a switch, and 9 is a switch. It's a load. The converter 3 converts the DC power into DC power, which is supplied to the load 9 via the diode 4.
On the contrary, the DC power from the load 9 is inversely converted by the converter 3 via the resistor 6 and the switch 7 or the resistor 6 and the resistor 5, and is fed back to the AC input power source 1.

Next, a specific embodiment of a control circuit for a power converter according to the present invention is shown in FIG.

In the figure, the same reference numerals as in FIG. 1 indicate the same or equivalent parts. 101 is a voltage setting device for setting the voltage of the load 9; 102 is the voltage setting device 10;
an adder 103 for matching the voltage reference signal set in step 1 with the voltage feedback signal detected by the voltage detection circuit 108 that detects the voltage of the load 9; a voltage control circuit; 104 is the voltage control circuit 103;
The current reference signal which is the output of the current detector 21, 2
105 is a current control circuit that amplifies the current deviation signal that is the output of the adder 104, and 107 is the current control circuit 10.
This is a phase control circuit which inputs a phase control signal which is an output of 5 and outputs a firing signal for the thyristor of the converter 3. 106 is a forward/reverse converter switching logic circuit that outputs a switching signal for selecting the positive side thyristor or the reverse side thyristor of the converter 3 based on the current feedback signal and the current reference signal, and this output signal is sent to the current control circuit 105 and the phase control circuit. Given. Based on this signal, the phase control circuit 107 outputs a firing signal to the positive thyristor or the reverse thyristor.

Next, 8 is a current detector that detects the current that returns from the load 9 to the AC input power supply 1 through the converter 3, 201 and 202 are comparison circuits, and 203 and 204
A current level setting device receives the current detected by the current detector 8 and the signals set by the current level setting devices 203 and 204. Reference numeral 205 denotes a storage circuit to which the output signals of the comparison circuits 201 and 202 are applied, and the switches are turned on and off based on the output signals.

The above control circuit attempts to control the voltage of the load 9 to the voltage set by the voltage setting device 101, and now returns the DC power from the load 9 to the AC input power supply 1 through the thyristor on the opposite side of the converter 3. Suppose that Here, the voltage Va of AC input power supply 1
is power supply fluctuation rate k = ±0.1, phase control advance angle β = 30°
Suppose that it is determined by If the voltage fluctuation rate of the AC input power supply 1 is within -0.1, the current from the load 9 passes through the resistor 6, switch 7, and then the converter 3.
At this time, when the voltage fluctuation rate is about to go from -0.1 to -0.3, for example, the current from the load 9 flowing through the resistor 6 tends to increase. This current is detected by the current detector 8, and the current level setter 2
When the value is greater than the value set in 03, the comparator circuit 2
01 gives a signal to the memory circuit 205 and switches the switch 7.
turn off. When switch 7 turns off, resistor 5
is inserted, so the current decreases. When the voltage of the AC input power supply 1 returns to its original value, the current decreases further. When this current falls below the current value set by the current level setter 204, the comparator circuit 202 gives a signal to the memory circuit to turn on the switch 7. Turn on to return to the initial state.

In other words, even if the voltage of the AC input power supply 1 drops significantly, the feedback current from the load 9 is suppressed by the resistor, eliminating overloads, overcurrents, and commutation failures of the converter, ensuring stable operation. Furthermore, it is possible to provide a power converter with a high input power factor.

3 and 4 show other embodiments according to the invention. In this figure, the same reference numerals as in FIG. 2 indicate the same or equivalent parts, so the explanation will be omitted. First, in FIG. 3, 301 is a voltage detection circuit that detects the voltage of AC input power source 1, 302 is a comparison circuit, and 30
3 is a voltage level setter. Voltage setting device 301
The voltage of the AC input power supply 1 detected by the comparator circuit 3
02 is compared with the value set by the voltage level setter 302, and if the power supply voltage is lower than the set value, the comparison circuit 302 turns off the switch 7 and suppresses the current from the load 9 by inserting the resistor 5. ,
The same effect as in FIG. 2 can be obtained.

In addition, in FIG. 4, 401 is a voltage detection circuit that detects the output voltage of converter 3, 402 is an adder, and 401 is a voltage detection circuit that detects the output voltage of converter 3;
03 is a voltage level setter, and 404 is a comparison circuit. The output voltage of converter 3 detected by voltage detection circuit 401 and the voltage of load 9 detected by voltage detection circuit 108 are subtracted by adder 402. The output signal of the adder 402 is compared with the voltage value set by the voltage level setter 403 in a comparator circuit 404, and the switch 7 is turned on and off based on the output signal.
Now, while the power from the load 9 is being fed back to the AC input power source 1 through the resistor 6, the switch 7, and the opposite thyristor of the converter 3, the voltage of the AC input power source 1 drops significantly, and the load 9 When the voltage difference with the current voltage exceeds the value set by the voltage level setter 403, the switch 7 is turned off and the current is suppressed.

〔Effect of the invention〕

As described above, according to the present invention, a power conversion system that enables stable operation even when the voltage fluctuations of the AC input power supply are large, and that can also greatly improve the input power factor compared to conventional ones. equipment can be provided.

[Brief explanation of the drawing]

Fig. 1 is a main circuit diagram of a power exchanger to which the present invention can be applied, Fig. 2 is a control circuit diagram of a power converter of the present invention, and Figs. 3 and 4 show other embodiments of the present invention. It is a control circuit block diagram shown. 1... AC input power supply, 21, 22... Current detector, 3... Converter, 4... Diode, 5,
6...Resistor, 7...Switch, 8...Current detector, 9...Load, 101...Voltage setting device, 10
2,104,402... Adder, 103... Voltage control circuit, 105... Current control circuit, 106...
Forward/reverse converter switching logic circuit, 107... Phase control circuit, 108... Voltage detection circuit, 109...
...Current detection circuit, 201,202,404...Comparison circuit, 203,204...Current level setter,
205... Memory circuit, 301, 401... Voltage detection circuit, 302... Comparison circuit, 303, 403...
...Voltage level setting device.

Claims (1)

[Claims] 1. A function of converting AC power supplied from an input AC power source to DC power and applying it to a load, and converting regenerated DC power from the load side to AC power and regenerating it to the input AC power source. A power conversion device having: a diode provided between the power conversion device and the load in a direction to block regenerated power, and at least two resistors provided in parallel and series connection with the diode; At least one of this resistor
A power converter characterized by comprising: a switch connected in parallel to each other; and a control means for controlling opening/closing of the switch according to a voltage fluctuation rate of the input AC power source during power regeneration from the load to the input AC power source. Device. 2. The power conversion device according to claim 1, wherein the control means detects the input AC power supply voltage and issues an on/off command according to the detected level. 3. The power conversion device according to claim 1, wherein the control means issues an on/off command depending on the level of current flowing through the resistor. 4. The power converter according to claim 1, wherein the control means issues an on/off command depending on the difference between the output voltage of the power converter and the voltage of the load.