JPS6056395B2 - Control method of synchronous motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a synchronous motor with improved drive characteristics of a synchronous motor with compensation windings.

Synchronous motors driven by self-limiting frequency converters can be roughly divided into those with compensation windings and those without.

Conventionally, in a synchronous motor having a compensation winding, a compensation current is passed in accordance with the magnitude of the armature current, but in many cases the ratio is kept constant. In recent years, as the performance of thyristor motors has improved, they have entered the field of rapid load fluctuations, rapid acceleration/deceleration, field weakening control, etc. as a means to compete with DC motor drive systems. Driving with a cycloconverter is an effective method. However, in order to improve the characteristics, the size of the rotating machine may be reduced, or due to cost considerations, the size of the rotating machine may be reduced.
If the converter is designed to its limits, saturation of the magnetic flux or overvoltage may occur during severe loads or in the field weakening control region, and the required performance may not be met. Particularly when the load is severe, such as a steel mill motor, and the load is 225% or 275%, and there are sudden fluctuations, the saturation and overvoltage of the motor cannot be ignored. To make it easier to understand the operation of a synchronous machine with a compensation winding, we will explain it using a vector diagram.There is a compensation winding perpendicular to the field winding, and each
Let it be the q-axis. Assuming that the armature current always flows in the q-axis direction, the vector diagram shown in FIG. 1 can be obtained by increasing or decreasing the compensation current with respect to a certain constant armature current I. However, since the resistance component is small compared to the reactance component of the electric motor, this was ignored. Figure 1a shows the case where a compensation current is applied so that the internal induced voltage Ei matches the no-load induced voltage Eo, and Figure 1 shows the case where the compensation current is applied so that the terminal voltage Et matches the no-load induced voltage Eo. be. At point a, the terminal voltage increases or decreases according to the magnitude of leakage reactance and current.
On the other hand, the internal induced voltage increases or decreases.
In order to examine the degree of increase and decrease in these voltages, consider, as an example, the case where the leakage reactance is 0 and the leakage current is 2.75 using the unit method. Assuming that the compensation current shown in FIG. 1a is applied, and the motor is operated in the field weakening region, and the speed is twice the base speed, the terminal voltage is expressed by the following equation. In other words, the terminal voltage, which was 1 when no load was applied, nearly doubles.

On the other hand, the internal induced voltage Ei at the base speed when the compensation current shown in FIG.

In this example, the system is assumed to be linear, but in an actual machine, the influence of saturation of magnetic flux is significant, and the influence of saturation is particularly significant when the internal induced voltage exceeds the rated value. As a result, the torque coefficient with respect to current decreases and machine loss increases. If the ratio of the compensation current to the armature current is set to a certain value in this way, good drive characteristics over the entire speed range cannot be expected, especially when a heavy load is applied. By changing the ratio of compensation current to armature current according to the speed, the present invention prevents the negative effects of saturation of the internal magnetic flux of the rotating machine and overvoltage to the frequency converter, and also provides a synchronous motor that can achieve the required performance. The purpose is to provide a control method.

In the present invention, the compensation shown in FIG. 1a is performed in a region where the speed is relatively small and no excessive voltage is generated, and the compensation shown in FIG. 1 is performed in a region where the motor voltage is limited such as in a field weakening region. The basic configuration as a specific example is shown in the second section.
As shown in the figure. In A, 1 is a frequency converter, 2 is a synchronous motor having a field winding 3 and a compensation winding 4, 5 is a polyphase position detector composed of a Hall generator or a Selsyn generator, and 6 is a speed detector. There is a speed generator to detect. The motor compares the output of the speed command device 19 with the actual speed using a comparator 18, and the speed control circuit 17 determines the amount of armature current. This value is multiplied by the signal from the position detector in a multiplier 16 to give an instantaneous current value command for each phase, which is compared with the actual armature current in a comparator 15 and sent to the frequency converter 1 by a current control circuit 12. An arc pulse is sent. On the other hand, field winding 3,
A current command amount is given to the compensation winding 4 by a current command circuit 36 and a compensation winding current command circuit 46 which is a main part of the present invention, and compared with the actual current by comparators 35 and 45, and the current command amount is given to the current control circuit 32, 42 sends an ignition pulse to the converter 31,41. Current transformers 13, 33, 43 and current detection circuit 1 are installed in the armature winding, magnet winding, and compensation winding to detect current.
4, 34, and 44 detect the respective currents. Further, power is supplied to each converter by three-phase power supplies 7, 8, and 9, respectively. FIG. 3 is a block diagram of a specific embodiment of the compensation winding current command circuit which forms the main part of the present invention.

In the figure, a speed signal 462 is generated by forming a dead zone generation circuit with resistors R1 to R5, diodes Dl and D2, and an operational amplifier 0A1, and applying bias amounts 463 and 464 to generate a first ratio region and a third ratio region, which will be described later. Determine the area of the ratio of . Resistors R6 to Rll, diodes D3, D male Zener diodes Z1, and operational amplifiers 0A2 and 0A3 form an absolute value amplification circuit, and a bias amount 465 provides a compensation current ratio in the first region. Z1 gives the compensation current ratio in the second region. Compensation current ratio 466 is multiplied by armature current command value 461 using multiplier M1 to obtain compensation winding current command value 467. FIG. 4 shows the compensation winding current ratio 466(N) for the speed signal 462(N) in FIG.
There is a table showing the value of K). In the first region 1, K is given by the product of the bias amount 465 and -Rll/RlO, and N1 is the bias amount 463, 464 of the negative zone generation circuit and R3/R
1 and R4/R2, and the tilt of the area 3 is given by R5/R1 and R5/R2, respectively. Further, K in the region 2 is given by the Zener voltage of the Zener diode Z1. N2 is determined by the Zener voltage and the direction of K. The characteristics when the electric motor is driven with the above configuration will be explained with reference to FIG. 5 for the case where the rotation direction is unidirectional.

Speed N. Assume that the field is in a weaker field region, and the field current is 1f.
is N. -1f0/N. Also K
is the speed N. Let us consider the case where N1 and N2 are determined so that they fall into the third region. The terminal voltage Et and the internal magnetic flux φ1 are considered as the motor characteristics in this case, and the values at no load are shown by broken lines and the characteristics at load are shown by solid lines. In this example, N is reduced by taking the load. Although there is a slight increase in Et in the vicinity, φi does not exceed the rated value, and especially in the field weakening region, it is larger than when no load is applied, but as the overall magnetic flux is decreasing, it becomes a value with less saturation. There is. On the other hand, although Et is larger in the low speed range than when there is no load, since Et itself is smaller than the rated value, no overvoltage occurs to the converter. FIG. 6 shows another embodiment of the present invention, and only the compensation winding part is shown, but it has a configuration in which a switch 48 and an impedance 47 consisting of a resistor and an inductance are provided in parallel with the compensation winding. .

It is assumed that the entire input current of this circuit always flows at a compensation current ratio according to the second region, and when the speed changes, the compensation current ratio follows the first region.
When the ratio is in the first ratio region, the switch is closed and the compensation current is shunted through the additional impedance 47, so that the compensation current ratio follows the first ratio region.

[Brief explanation of the drawing]

Figures 1A and b are vector diagrams of a synchronous motor, Figure 2 is a configuration diagram showing an embodiment of the present invention, Figure 3 is a partially detailed diagram of Figure 2, and Figure 4 is the operation of Figure 3. FIG. 5 is a diagram for explaining the operation of the present invention, and FIG. 6 is a compensation winding circuit diagram of a synchronous motor for explaining another embodiment of the present invention. 1... Frequency converter, 2... Synchronous motor, 3... Field winding, 4... Compensation winding, 5... Position detector, 6... Speed detector, 7, 8, 9... Power supply, 12, 32, 42.
...Current control circuit, 15, 35, 45...
・Current comparator, 16... Multiplier, 17... Speed control circuit, 18... Speed comparator, 19...
・Speed command device, 36, 46... Current command circuit,
13, 33, 43... Current transformer, 14, 34, 4
4... Current detection circuit.

Claims (1)

[Claims] 1. In a synchronous motor equipped with an armature winding, a field winding, and a compensation winding, and whose drive is controlled by a frequency converter,
A predetermined speed (N) before entering the field weakening control range from zero speed
In the first speed range up to 1), the ratio of the compensation current to the armature current is set to the first ratio, and in the second speed range exceeding a predetermined speed (N2) within the field weakening control range, the compensation for the armature current is set to the first ratio. The ratio of the current to the armature current is a second ratio, and in a third speed range between the first speed range and the second speed range, the ratio of the compensation current to the armature current is from the first ratio to the second ratio. A method for controlling a synchronous motor, characterized in that the magnitude of a compensation current is controlled with respect to the magnitude of an armature current so that the magnitude of the armature current changes.