JPH05199766A - Control method for static power supply device - Google Patents

Abstract

PURPOSE:To protect a static power supply device to which load as voltage source is connected from an overcurrent state and to prevent abnormal voltage drop. CONSTITUTION:Output current of a static power supply device (inverter) 1 to which load as voltage source is connected is detected by current transformers 5A-5C. When a surplus of detection value exceeding a specific level is detected by an overcurrent detection circuit 6, switches 4A-4C k operated by a control circuit 8 to release the output of the inverter for a short period of time and, at the same time, a phase difference against the inverter 1 of load is detected by polarity of output voltage detected through comparators 7A-7C, and after that, the inverter 1 starts to control so that the phase difference is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for protecting a static power supply device from an overcurrent state and suppressing an abnormal voltage drop.

[0002]

2. Description of the Related Art Conventionally, when an overcurrent condition occurs in a static power supply device, it is general to reduce the output voltage to suppress the current.

[0003]

However, as shown in FIG. 8, the power supply system has, for example, a generator (G) as a load.
When a load 20C that can be a voltage source such as the above is included, if the output voltage of the static power supply device 1 is lowered, the current (cross current) flowing between the static power supply device 1 and the voltage source 20C.
However, there is a problem that the semiconductor element of the static power supply device 1 may be destroyed due to this tendency. In general, when two voltage sources (V) are randomly operated in parallel, the voltage V ′ generated by the phase difference θ between the two becomes V ′ = Vcos (θ / 2). When the phase difference is 30 degrees, the voltage drop is 97%, and when the phase difference is 90 degrees, the voltage drop is 71%, and at the same time an excessive current flows. In FIG. 8, 2 is a smoothing reactor, 3 is a smoothing capacitor, 2
0A and 20B are contactors, and 20D is a load. Therefore, an object of the present invention is to provide a control method for protecting a static power supply device from an overcurrent state and suppressing an abnormal voltage drop.

[0004]

In order to solve such a problem, in the first invention, a static power source to which a semiconductor element controlled with a reference frequency is used as a switching element and a load which can be a voltage source is connected The output current of the device is monitored, and when the output current exceeds a predetermined value, the output of the static power supply device is temporarily opened, and the static power supply of the load is detected from the polarity of each phase voltage separately detected during the period. It is characterized in that the phase difference with respect to the device is detected, and then the phase of the reference sine wave is shifted according to the detected phase difference to start the control of the semiconductor element. In the second invention, a semiconductor element controlled with a reference frequency is used as a switching element, and an output current of a static power supply device to which a load that can be a voltage source is connected is monitored. When the output current exceeds a predetermined value, a predetermined value is determined. It is characterized in that the frequency is controlled to be higher than that of the standard only during the period. Further, in the third invention, a semiconductor element controlled at a reference frequency is used as a switching element, and an output voltage of a static power supply device to which a load that can be a voltage source is connected is monitored, and the output voltage falls below a reference value. It is characterized in that the reference phase of the sine wave signal is changed by 180 degrees for control only during the period.

[0005]

The output current of the static power supply device to which a load that can be a voltage source is connected is monitored, and when this is in an overcurrent state, the static power supply device is stopped for a short time and synchronized to resume operation. Alternatively, the frequency of the static power supply is raised for a short time, and the output voltage of the static power supply is monitored, and if it falls below a predetermined value, the phase of the sine wave signal is inverted to place the static power supply in the overcurrent state. To prevent abnormal voltage drop.

[0006]

1 is a block diagram for explaining a first embodiment of the present invention. In the figure, 1 is a single-phase inverter 1.
A three-phase inverter (static power supply device) consisting of A, 1B, and 1C, 2A to 2C are smoothing reactors, 3A to 3C are smoothing capacitors, 4A to 4C are switches, and 5A to 5C are current transformers (CT), 6 is an overcurrent detection circuit, 7A to 7C are comparators, and 8 is a control circuit. This shows the static power supply side of the power supply system shown in FIG. 8, in which the output current of the three-phase inverter 1 to which a load serving as a voltage source such as the generator G is connected is monitored by CT5A to 5C, and Is compared with a predetermined reference value in the overcurrent detection circuit 6 having a built-in comparator to determine whether or not it is an overcurrent. When it is determined that the current is the overcurrent state, the control circuit 8 introduces the voltage of the system into the comparators 7A to 7C and determines the polarity, and based on the result, the phase difference between the load and the static power supply device is determined. Is detected.

That is, since the polarity of any one of the three phases of the load voltage changes every 60 degrees as shown in FIG. 2, the comparator 7
The polarity signals detected by A to 7C are input to the phase detection unit as shown in FIG. 3 to detect the phase difference between the load and the static power supply device. Reference numeral 9 in FIG. 3 is a gate that outputs to the N side when the polarity signals A, B, and C are positive, and to the I side when the polarity signals A, B, and C are negative, and 10 is an AND gate. Therefore, for example, the polarity signals A, B, C
Are (+), (-), (-) respectively, 2 from the top
An output is obtained from the AND gate 10 in the third stage, whereby the phase difference is 60 degrees, and when the polarity signals A, B, and C are (+), (+), and (-), respectively, the third stage from the top. An output is obtained from the AND gate 10 of the eye, which shows that the phase difference is 120 degrees.

FIG. 4 shows a sine wave signal generator which outputs a sine wave signal based on the output from the phase detector shown in FIG. 3, and is composed of sine wave generators 11A, 11 and 11C, an AND gate 12 and an OR gate 13. ing. In addition, N of the sine wave generators 11A, 11 and 11C indicates a terminal for directly outputting a sine wave signal as shown in the figure, and I indicates a terminal for inverting and outputting the sine wave signal as shown in the figure. this is,
For example, when the phase difference is 60 degrees, the sine wave generators 11A, 1
1B and 11C, which are obtained by inverting each sine wave signal as shown in the drawing, and when the phase difference is 120 degrees, the sine wave generator 11
By outputting the respective sine wave signals A, 11B, and 11C shown in the figure through the AND gate 12 and the OR gate 13, the single-phase inverter 1 according to the phase difference is output.
It controls A, 1B and 1C to match the phase with the load (synchronize).

FIG. 5 is a block diagram for explaining the second embodiment of the present invention. As is apparent from the figure, this embodiment is characterized in that two sine wave oscillators 14A and 14B are provided, and the other points are the same as in FIG. Reference numeral 8A is a control circuit, which has a slightly different function from that shown in FIG. Therefore, in this case as well, when the CTs 5A to 5C and the overcurrent detection circuit 6 detect the overcurrent state, this is notified to the control circuit 8A, so that the control circuit 8A causes the single-phase inverters 1A and 1B. , 1C is switched from the reference frequency 14A to the frequency oscillator 14B which generates a signal having a higher frequency than that of the reference frequency, and is controlled. In this case, the frequency of the oscillator 14B is 14A
Any value may be used as long as it is higher than that, and the frequency may be in the vicinity of 14 A or several times. The frequency may be changed by using a V / F (voltage / frequency) converter instead of using separate oscillators. After that, when the load and the static power supply device are in phase with each other, the overcurrent signal also disappears, so that the inverter can be operated at the original frequency.

FIG. 6 is a block diagram for explaining the third embodiment of the present invention, in which 8B is a control circuit and 15 is a voltage (undervoltage) detection circuit of an inverter. That is, in this embodiment, when the output voltage of the inverter 1 becomes less than or equal to the predetermined value by the voltage detection circuit 15, the control circuit 8B is notified of that, and the section in which the output voltage is less than or equal to the predetermined value by the control circuit 8B is a sine wave. 180 degree phase shift (inversion), and the inverted signal is given to the single-phase inverters 1A, 1B, 1C to be controlled so that the phase difference is smaller than 90 degrees, thereby suppressing overcurrent. This is to prevent an abnormal drop in voltage.

FIG. 7 shows the operation waveform. The figure shows an example of the waveform of the voltage detection circuit.
Like the peak value X (1.414) and the valley value Y (1.41
4 cos 30 ° = 1.225). On the other hand, when the load and the static power supply device are operated in parallel with a phase difference close to 180 degrees, the load drops to near zero. By the way, in order to perform stable power supply to the load, the limit is approximately -25%. In this case, X is 1.061 and Y is 0.91.
9, which corresponds to a phase difference of 83 degrees. When the phase difference is 90 degrees, Y becomes 0.866. Therefore, this is selected as the reference Z for the undervoltage judgment, and when the output of the voltage detection circuit becomes less than this Z value, the Change the phase by 180 degrees. This way
It is possible to suppress an abnormal voltage drop such as -2.

[0012]

According to the present invention, the output current of a static power supply device to which a load that can be a voltage source is connected is monitored, and when it is in an overcurrent state, the static power supply device is stopped for a short time for synchronization. After that, the operation is restarted, or the frequency is raised for a short time, and the output voltage of the static power supply is monitored, and when this falls below a predetermined value, the phase of the sine wave signal is inverted. Therefore, the static power supply device can be protected from an overcurrent state, and an advantage that an abnormal voltage drop can be prevented is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the principle of detecting a phase from the polarity of voltage.

FIG. 3 is a schematic diagram showing a specific example of a phase detection unit.

FIG. 4 is a schematic diagram showing a specific example of a sine wave generator.

FIG. 5 is a configuration diagram for explaining a second embodiment of the present invention.

FIG. 6 is a configuration diagram for explaining a third embodiment of the present invention.

FIG. 7 is a waveform diagram for explaining a third embodiment.

FIG. 8 is a schematic diagram showing an example of a power supply system.

[Explanation of symbols]

1 ... 3-phase inverter (static power supply), 2A to 2C ...
Smoothing reactor, 3A to 3C ... Smoothing capacitor, 4
A-4C ... Switch, 5A-5C ... Current transformer (CT), 6
... Overcurrent detection circuit, 7A to 7C ... Comparator, 8, 8A, 8
B ... Control circuit, 9 ... Gate, 10, 12 ... AND gate, 11A-11C ... Sine wave generator, 13 ... OR gate, 14A, 14B ... Sine wave oscillator, 15 ... Voltage detection circuit.

Claims (3)

[Claims] 1. An output current of a static power supply device to which a semiconductor element controlled by a reference frequency is used as a switching element and a load that can be a voltage source is connected, and when the output current exceeds a predetermined value, the static type The output of the power supply is temporarily opened, the phase difference of the load with respect to the static power supply is detected from the polarity of each phase voltage that is separately detected during that period, and then the reference is determined according to the detected phase difference. A method of controlling a static power supply device, comprising: controlling the semiconductor element by shifting the phase of a sine wave. 2. A semiconductor element controlled by a reference frequency is used as a switching element, and an output current of a static power supply device to which a load that can be a voltage source is connected is monitored. When the output current exceeds a predetermined value, a predetermined value is determined. A control method for a static power supply device, which is characterized in that the frequency is controlled to be higher than a reference frequency for a period. 3. A semiconductor element controlled by a reference frequency is used as a switching element, and an output voltage of a static power supply device to which a load that can be a voltage source is connected is monitored, and a sine wave is output only during a period when the output voltage is lower than a reference value. A control method for a static power supply device, characterized in that the reference phase of the wave signal is changed by 180 degrees for control.