JPH0744874B2 - How to operate a three-phase AC rotating electric machine - Google Patents

Abstract

PURPOSE:To conduct stable operation having no torque ripple by mounting voltage control units to each phase and balancing each-phase current even when respective-phase impedance is not balanced. CONSTITUTION:In a three-phase induction motor 4 in which a single-layer winding is used for a stator, each-phase impedance is not balanced due to the difference of the shapes of respective-phase coil end for the single-layer winding. Voltage control units 6 are fitted among an AC power supply 5 and electric wirings of each phase. The voltage control unit 6 has a high-speed arithmetic function in a computer such as a micro-computer, and arithmetically operates voltage, where a voltage drop section must be compensated at all times, and controls supply voltage applied to respective-phase coil, and each-phase currents are balanced even when respective-phase impedance is not balanced, thus resulting in stable operation having no torque ripple.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a three-phase AC rotating electric machine in which a single-layer winding is used as each phase winding of a stator. The present invention relates to a method of operating a three-phase AC rotating electric machine that can be operated by forcibly balancing currents.

[Technical background of the invention and its problems]

In recent years, the development of motor control technology has been remarkable, and it has become possible to control the speed of a three-phase AC motor, which has been conventionally difficult to control, by using an inverter or cycloconverter, which is equivalent to that of a DC motor. .

By the way, in electric motors such as rolling mills used in the steel industry that require precise control of speed and torque during operation, DC motors have been the main force, but recently control technology has been developed. Therefore, there is a movement to adopt an AC electric motor. In particular, the squirrel-cage induction motor is completely brushless, which is advantageous from the standpoint of maintenance.The rotor structure is robust, and the heat capacity is large and the overload capacity is large. It can be said that it is suitable for rolling mills.

However, the main rolling machine has a low speed and large capacity, and the weight of the electric motor body has reached several hundred tons. It is necessary to be able to remove the upper half.

However, in the case of a DC motor, since the stator is composed of the main pole and the auxiliary pole, it is easy to divide the stator into two parts, but a three-phase induction motor generally uses a two-layer winding. Therefore, when the stator is divided into two parts as shown in FIG. 4, the coil end parts 1a, 1b, 1c, 1d,
Splitting is also required for 1e and 1f, so it is practically difficult to make the stator into a bisection structure.

Therefore, in such a case, if a single layer winding is used as each phase coil of the stator, as shown in FIG.
Since there is no coil across the stator, the stator can be relatively easily divided into two parts even for a three-phase AC motor.

However, when a single-layer winding is used for the stator, as is clear from Fig. 5, the coil end shape of each phase is different, so the impedance of each phase becomes unbalanced. An unbalanced current flows, and a torque ripple having a frequency twice the power supply frequency is generated in the motor torque.
Therefore, in a rolling mill using such a three-phase AC electric motor, if a large torque ripple occurs, uneven luster occurs on the surface of the product, which is not preferable. Further, when the torque ripple frequency coincides with the natural frequency of the shaft type, the ripple increases due to the resonance phenomenon, and there is a problem in terms of strength from the shaft system.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object thereof is to balance each phase current in a three-phase AC rotary electric machine using a single-layer winding for a stator even when an imbalance occurs in each phase impedance. It is intended to provide a method of operating a three-phase AC rotating electric machine capable of performing stable operation without torque ripple.

[Outline of Invention]

In order to achieve the above object, the present invention is based on the following points.

First, in the case of a three-phase AC rotating electric machine using a two-layer winding for the stator, the impedance of each phase is normally balanced, and the equivalent circuit for one phase is as shown in FIG.

On the other hand, in the case of a three-phase AC rotary electric machine that uses a single-layer winding for the stator, the coil end shape of each phase is different, as described above, causing an imbalance in the impedance of each phase. This is due to the fact that the interlinkage magnetic flux of each part is different for each phase, and the equivalent circuit for one phase is as shown in FIG.

Therefore, in the case of the single-layer winding, as is apparent from FIG. 3, the difference in the coil end shape of each phase is added as the reactance 3 as compared with the case of the double-layer winding. Since each phase is unbalanced, each phase current is unbalanced, resulting in a torque ripple.

Therefore, in the present invention, in order to compensate the unbalance of the impedance of each phase component of the reactance due to the difference in the coil end shape of each phase of the single-phase winding, the correction voltage of the reactance component is obtained by complex calculation, and this correction voltage is calculated. By controlling each voltage applied from the three-phase AC power supply to each phase winding of the stator, the phase currents are forcibly balanced for operation.

Example of Invention

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

FIG. 1 is a block diagram of a power supply circuit of a three-phase induction motor as a configuration example for explaining a method of operating a three-phase AC rotating electric machine according to the present invention. In FIG. 1, 4 is a three-phase induction motor using a single-layer winding for a stator, and the impedance of each phase of this three-phase induction motor 4 is unbalanced. Reference numeral 5 is an AC power supply to which the three-phase induction motor 4 is connected. As the AC power supply 5, a commercial power supply whose voltage is normally balanced is used. Reference numeral 6 denotes a voltage control unit provided in each of the three-phase electric phases connecting the three-phase induction motor 4 and the AC power supply 5, that is, the U, V, and W-phase electric paths.
Has a high-speed arithmetic function such as a microcomputer, and always controls the power supply voltage applied to each phase coil by calculating the voltage for correcting the voltage drop due to the reactance 3 in FIG. Is.

Next, the operation of the power supply circuit of the three-phase induction motor configured as described above will be described. Now, as an example, the first
In the figure, consider the case where the impedances of the V and W phases are balanced and the impedance of only the U phase becomes large.

In this case, the equivalent circuit of each phase is V phase, W phase is shown in FIG. 2, and U phase is shown in FIG. That is, the reactance 3 is added only to the U phase with respect to the V phase and the W phase.

Therefore, if the V-phase voltage and the W-phase voltage are Vm, the U-phase voltage must correct the voltage due to the reactance 3, and the corrected voltage is Vc, the value of the reactance 3 is L, and the current is I. For example, Vc = jωLI. Here, j is a unit complex number and ω is an operating angular frequency. Therefore, if the U-phase voltage Vu is controlled to Vu = Vm + Vc by the voltage control unit 6 provided in the U-phase electric circuit and the U-phase voltage is controlled, the respective phase currents are balanced and stable without torque ripple. You can perform the required driving. The above explanation is for the case where the impedance of the U phase is larger than that of the V phase and W phase, but when the impedance of the V phase or W phase is larger than that of the W, U phase or U, V phase. Also in the same manner as described above, the voltage control unit 6
It goes without saying that it is only necessary to perform the calculation by and control the voltage.

As described above, in this embodiment, when the voltage to be corrected for the voltage drop due to the reactance 3 is calculated and the power supply voltage applied to each phase coil is controlled, the correction voltage is obtained by complex calculation. It is also possible to control the phase, and even when the operating frequency is changed by an inverter or the like to control the speed, the current can be balanced in the entire operating frequency range, and stable operation can be performed.

〔The invention's effect〕

As described above, according to the present invention, in the three-phase AC rotating electric machine using the single-phase winding as each phase winding of the stator,
In order to compensate for the unbalance in the impedance of each phase of the reactance due to the difference in the coil end shape of each phase of the single-phase winding, the correction voltage for the reactance is calculated by complex calculation, and the three-phase AC power supply is used according to this correction voltage. Since each voltage applied to each phase winding of the stator is controlled, each phase current can be balanced even when an imbalance occurs in each phase impedance, and the phase of the correction potential is also controlled. Therefore, it is possible to provide a method of operating a three-phase AC rotating electric machine that enables stable operation without torque ripples over the entire operating frequency range, even when the operating frequency is changed to control the speed.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment for explaining a method of operating a three-phase AC rotary electric machine according to the present invention, FIG. 2 is an equivalent circuit diagram of a normal induction motor, and FIG. Equivalent circuit diagram when the impedance is unbalanced by using the phase winding, Fig. 4 shows the coil end of the two-phase winding of the four-pole machine, and Fig. 5 shows the single-phase winding of the four-pole machine. It is a figure which shows a coil end part. 4 ... Three-phase induction motor, 5 ... AC power supply, 6,6a ... Voltage control unit, 7 ... Current detector.

Claims (1)

[Claims] 1. A three-phase AC rotating electric machine using a single-phase winding as each phase winding of a stator, wherein each phase of reactance due to a difference in coil end shape of each phase of the single-phase winding. In order to compensate the impedance imbalance, the correction voltage for the reactance is obtained by complex calculation, and by controlling each voltage applied from the three-phase AC power supply to each phase winding of the stator according to this correction voltage, A method for operating a three-phase alternating current rotating electric machine, comprising forcibly balancing phase currents for operation.