JPH06138963A - Reactive power controller - Google Patents

Abstract

PURPOSE:To produce the invalid power of cycloconverter as much as possible during a motor is stopped and to suppress the voltage rise by passing a circulating current to each phase of a transformer secondary winding rating. CONSTITUTION:Primary current Iu, Iu, and IW of a transformer 1 corresponding to the U-W phases of the motor are detected by current detecting devices 11, 12 and 13. A voltage detecting device 14 detects a system voltage V1, calculating the reactive power amount of each phase based on the values. A reactive power arithmetic circuit 15 compares the generation reactive power amount with a generation reactive power reference P0, outputting gate phase control signals 7, 8, 9 from a forward three-phase bridge connection thyrister rectifier 2 and a backward three-phase bridge connection thyrister rectifier 3 so that the circulating current within the current value subtracting the exciting current of the motor from the current capacity of the secondary winding of the transformer 1 can flow. Thus, the reactive power of the cycloconverter can be produced as much as possible during the motor is stopped and the voltage rise can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive power controller for a circulating current type cycloconverter for a squirrel cage induction motor.

[0002]

2. Description of the Related Art FIG. 3 shows a main circuit configuration of a conventional circulating current type cycloconverter for a squirrel cage induction motor (hereinafter referred to as a cyclo). In the figure, the main circuit of the cyclone is
It is composed of a transformer 1, a forward direction three-phase bridge connection thyristor rectifier 2, a reverse direction three-phase bridge connection thyristor rectifier 3, a circulating current suppressing reactor 4, and a squirrel cage induction motor 5. A motor current and a circulating current flow in the secondary winding of the transformer 1.

On the other hand, in order to compensate the reactive power of the delay generated by the cyclo, a phase advance capacitor 6 is connected to the same system as the cyclo, as shown in FIG. The capacity of the phase advancing capacitor 6 is generally determined by adding the allowable voltage fluctuation to the maximum reactive power generated by the cyclo. Here, since the reactive power generated by the cyclo increases as the motor current increases, the maximum reactive power is often the reactive power generated during rated load operation (or in some cases overload operation). The circulating current in this case is 10% of the motor rated current.

Since the phase advancing capacitor capacity thus determined is a fixed value, the advance reactive power of the phase advancing capacitor is larger than the delay reactive power which occurs when a load is lighter than the rated load. The voltage rise exceeds the allowable voltage fluctuation of the system. In order to prevent this, the control is performed so that the circulating current is increased by the amount by which the load becomes lighter and the delayed reactive power decreases to make the reactive power generated by the cyclone constant.

As shown in FIG. 4, the reactive power operation circuit 10 for controlling the reactive power at a constant level as described above has a system voltage V.
₁ and U-phase, V-phase, and inputs the total current I ₁ of the W-phase, calculates the reactive power of the system, comparing the amount of reactive power and the reactive power reference P ₀ to be the Cyclo occurs Then, the gate phase control signals 7, 8 and 9 of the forward direction three-phase bridge connection thyristor rectifier 2 and the reverse direction three-phase bridge connection thyristor rectifier 3 for controlling the circulating current are output so that the deviation becomes zero. Has been done.

[0006]

By the way, in the conventional reactive power constant control, as described above, the reactive power amount is controlled to be constant in the U-phase, V-phase, and W-phase collectively, so that the motor is stopped. There were the following problems. That is, the cyclone motor current is a combination of the torque current and the motor exciting current, and the motor current while the motor is stopped is only the exciting current. The exciting current has a three-phase AC waveform as shown in FIG. 5 while the motor is rotating, but when the motor is stopped, each of the U phase, V phase, and W phase becomes DC. This DC current value varies depending on the position where the motor rotor stops. For example, if it stops at point A in FIG.
The maximum value of the exciting current flows continuously in the phase, V phase and W
A half of the maximum exciting current continuously flows through the phase. Since the sum of the exciting current and the circulating current is the current flowing through the secondary winding of the transformer, if the exciting current is large, the circulating current cannot flow so much and the reactive power generated is small. In this case, of the U-phase, V-phase, and W-phase, when the exciting current of the U-phase, which is the maximum exciting current, is passed, the circulating current that can be passed through the secondary winding of the transformer is passed as the maximum value, and the others. V phase of
The W phase also carries the same amount of circulating current as the U phase. Therefore, in this case, since the circulating current does not flow up to the rated current value of the transformer for the V phase and the W phase, there is a problem that the amount of generated reactive power becomes insufficient and the voltage of the system may rise more than the allowable voltage fluctuation. It was

The present invention has been made to solve the above problems, and an object of the present invention is to provide a reactive power control device that suppresses a voltage rise within the allowable voltage fluctuation of the system even when the squirrel cage induction motor is stopped.

[0008]

In order to achieve the above object, a reactive power control apparatus of the present invention comprises a transformer, a forward direction three-phase bridge connection thyristor rectifier, a reverse direction three-phase bridge connection thyristor rectifier, and a circulation circuit. In a circulating current type cycloconverter for a squirrel-cage induction motor, which is composed of a current control reactor and a squirrel-cage induction motor, a primary side of the transformer corresponding to each phase of U-phase, V-phase and W-phase of the motor. A current detector that detects the current, a voltage detector that detects the voltage of the system, and U-phase, V-phase,
The amount of reactive power generated in each phase of the W phase is calculated, the generated reactive power amount is compared with the generated reactive power reference, and the deviation between the two is 0.
The forward direction three-phase bridge connection thyristor rectifier and the reverse direction three-phase bridge connection so that a circulating current within a current value obtained by subtracting the exciting current of the motor from the current capacity of the secondary winding of the transformer And a reactive power calculation circuit that outputs a gate phase control signal of the thyristor rectifier.

[0009]

According to the present invention, the U phase, V of the squirrel cage induction motor is used.
The main circuit current on the transformer primary side corresponding to each phase of W phase and W phase is detected, and U phase, V phase, W up to the transformer secondary winding rating.
By circulating the circulating current in each phase, the maximum reactive power of the cyclone can be generated even when the squirrel-cage induction motor is stopped, so that the voltage rise can be suppressed within the allowable voltage fluctuation of the system.

[0010]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention. The difference from the circuit diagram of FIG. 3 already described is that the U-phase, V
Current I on the primary side of the transformer 1 corresponding to each of the W and W phases
_U, the current detector 11, 12, 13 for detecting the I _V, I _W
The other circuit configurations are the same, and therefore the same parts will be described with the same reference numerals.

As shown in FIG. 1, the main circuit configuration of a cyclo to which the present invention is applied is the same as that of the conventional one, a transformer 1, a forward direction 3-phase bridge connection thyristor rectifier 2, a reverse direction 3-phase bridge connection thyristor rectifier 3, It is composed of a circulating current suppressing reactor 4 and a squirrel cage induction motor 5.

In order to control the reactive power of such a cyclo, the reactive power control device of the present embodiment, as shown in FIG. 2, is a transformer 1 corresponding to each phase of the U phase, V phase and W phase of the motor. Current detectors 11, 12, 13 for detecting the primary currents I _U , I _V , I _W , a voltage detector 14 for detecting the system voltage V ₁ , and the currents I _U , I _V , I _W and voltage V ₁
From the U phase, the V phase, and the W phase are calculated, the generated reactive power amount and the generated reactive power reference P ₀ are compared, and the transformer 1 is set so that the deviation between them becomes zero. Gate of forward three-phase bridge-connected thyristor rectifier 3 and reverse three-phase bridge-connected thyristor rectifier 3 so that circulating current within a current value obtained by subtracting the exciting current of the squirrel-cage induction motor from the current capacity of the secondary winding Phase control signals 7, 8, 9
And a reactive power calculation circuit 15 that outputs

Next, the operation of this embodiment will be described.
Assuming that the vehicle stops at point A in FIG.
The maximum value of the exciting current flows in the phase, and the current of 1/2 the maximum value of the exciting current flows in the V phase and the W phase. Therefore,
According to this embodiment, a circulating current of (transformer secondary winding rated current-exciting current maximum value) can be passed through the U phase,
Since a circulating current of (transformer secondary winding rated current−excitation current / current maximum value × 1/2) can be passed through the V phase and the W phase, the amount of reactive power generated by this cyclone is the V phase and the W phase. The phase also causes the circulating current to flow up to the rated current value of the transformer, which is a larger value than the conventional device.

[0014]

As described above, according to the present invention,
Since a large reactive power can be generated even when the electric motor is stopped, there is an excellent effect that a voltage increase in the system can be suppressed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an input / output circuit diagram of a reactive power arithmetic circuit of the present invention.

FIG. 3 is a main circuit diagram of a conventional circulating current type cycloconverter for a squirrel cage induction motor.

4 is an input / output circuit diagram of the reactive power arithmetic circuit of FIG.

FIG. 5 is an excitation current waveform diagram during rotation of the squirrel cage induction motor.

FIG. 6 is an excitation current waveform diagram when the squirrel cage induction motor is stopped.

[Explanation of symbols]

1 ... Transformer, 2 ... Forward three-phase bridge connection thyristor rectifier, 3 ... Reverse three-phase bridge connection thyristor rectifier, 4 ... Circulating current suppressing reactor, 5 ... Squirrel cage induction motor, 6 ... Leading capacitor, 7 ... U phase Gate phase control signal, 8 ... V phase gate phase control signal, 9 ... W phase gate phase control signal, 10 ... Reactive power arithmetic circuit, 11 ... U phase current detector, 12 ... V phase current detector, 13 ... W phase Current detector,
14 ... Voltage detector, 15 ... Reactive power calculation circuit.

Claims (1)

[Claims] 1. A circulating current for a squirrel cage induction motor comprising a transformer, a forward three-phase bridge connection thyristor rectifier, a reverse three-phase bridge connection thyristor rectifier, a circulating current control reactor, and a squirrel cage induction motor. Type cycloconverter, U phase, V phase, W of the electric motor
A current detector that detects the current on the primary side of the transformer corresponding to each phase, a voltage detector that detects the voltage of the system, and U-phase, V-phase, and W-phase based on this current and voltage Is calculated, the generated reactive power is compared with the generated reactive power reference, and the exciting current of the electric motor is calculated from the current capacity of the secondary winding of the transformer so that the deviation between the two becomes zero. A forward power 3-phase bridge connection thyristor rectifier and a reverse power 3-phase bridge connection thyristor rectifier configured to output a gate phase control signal so as to pass a circulating current within a subtracted current value. Characteristic reactive power control device.