JPS62196096A - Control of induction motor - Google Patents

Abstract

PURPOSE:To prevent noise of an induction motor at a standstill state, by a method wherein an excitation component correction circuit is provided for variably setting the excitation component of primary current corresponding to the operation state. CONSTITUTION:An excitation component correction circuit 10 outputs correction value of the excitation component command corresponding to actual position P and speed command value omegar0, and multiplies the correction value to excitation component set value Im1 so as to produce the command Im0. When the induction motor is at low speed or stopped or when a required torque is small, a target value of the excitation component Im is made small. In this constitution, primary current value I0 at standstill state is made small and generation of noise due to harmonics contained there is prevented. Also when the required torque is small, the excitation component Im is made small thereby the primary current I0 is made small and the efficiency can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control method for an induction starter, and particularly to a control method suitable for an induction motor using vector sterilization and pulse width modulation control. It is.

[Conventional technology]

Easy-to-control current machines were used for positioning control devices used in recirculation systems of nuclear power plants, but IiI
Brush machines were indispensable for sinking machines, which were subject to considerable wear and tear. For this reason, induction motors, which have a simpler structure and are easier to maintain, have come into use in recent years.

In order to obtain control characteristics similar to that of a current machine using an induction JL motive, the 1tllH method, commonly referred to as vector control, is used.

Generally, in an induction t4JJ machine, when the entire primary current I fl is supplied to the primary stator, a magnetic flux φ is generated between it and the secondary rotor due to the excitation component. -Next 'FIL a I o is the excitation component 1. and a torque component II orthogonal thereto are vectorially synthesized, and the torque τ generated in the rotor is proportional to the product of this torque component Is and the magnetic flux.

τ, oc1. ×１１・・・・・・－・・・
(1)φoc1. Therefore, (1) is τ? "I t + I−Σ ・−−−−−−−
-(3). Vector control method means 1 in 1 operation! The torque and excitation components It, I- in the primary lightning are detected from the voltage, current, etc. of the motor, and this 1. is a constant value and +It is a value that generates the required torque. This method prevents frequent starting, stopping, sudden acceleration and deceleration, etc. in the 1% control of induction motors, which was previously considered difficult. It has become possible to control movements such as violently pulsating the machine with the same precision as with an electric current machine.

FIG. 4 shows an induction motor control system for performing such control. In the figure, a three-phase AC 1! The alternating current from the source is converted into a current, converted into a three-phase alternating current having a predetermined effective value in the motor drive circuit 1, and applied as a primary alternating current to the induction motor IM. The motor control calculation circuit 3 (CTL) inputs the magnetic current on the primary side of the induction motor IM, the output of the voltage detector 6, the output of the position detector 18, the position target value pa, etc., and calculates the vector il+lI# as described above. A control signal for controlling the -next flow is output to the pulse width (PWM) control circuit 2. The pulse width control circuit 2 turns on and off each switching element in the motor drive circuit 1 in response to this control signal, thereby causing a target current to flow through the induction motor IMK.

Here, the primary flow is controlled by pulse width modulation.
This type of control is widely used today because it is small and easy to control accurately.

[Problem that the invention seeks to solve]

In conventional vector control methods, especially for small capacity motors, the excitation component is difficult to control. is controlled to be a constant calculated from the motor constant. On the other hand, when the motor is stationary, the torque may be zero, so the torque component is controlled to be zero. Therefore, at this time, the primary current 0 which is the vector combination of 1 and It is Io = 1.4- from equation (3).
0, and does not become 0 even when stopped. On the other hand, as explained in Figure 44, the -order current is an alternating current generated by pulse width modulation, but as is well known, even though it has a sinusoidal waveform on average, it has a sine waveform as shown in Figure 5. Harmonics (ripples) are superimposed on every phase. The frequency of this harmonic wave is usually several kHz, but since it flows to the motor when it is stopped, there is a problem in that the motor generates extremely harsh noise.

As can be easily seen from equations (2) and (3), the excitation and torque component I- that generates a certain required torque τ is
, I* can have an infinite number of values, but when It=I-, Io becomes the minimum, and VL! The operating efficiency of the tlI machine is the best. However, as mentioned above, 1. = There was a problem that this efficiency was not good with constant M control.

An object of the present invention is to provide a method for controlling an induction motor using a vector control system that can prevent noise when the induction motor is at rest and enable efficient operation.

[Failure to solve the problem]

The present invention achieves its object by providing an excitation component correction circuit that variably sets the excitation component of the primary current according to the operating state of the motor.

[Effect]

When the speed of the induction motor is low or stopped, or when the required torque is small, the excitation component correction circuit has an excitation component of 1. It has a function to reduce the target value of 1.1 when the required torque is small, thereby reducing the total primary current at standstill and preventing the generation of noise due to the harmonics contained therein. By reducing the first-order lI to
E school. can be made smaller to improve efficiency.

〔Example〕

Hereinafter, the details of the present invention will be explained with reference to examples.

The IT diagram shows motor control calculation circuit 3 using the slip frequency method.
This is an example of the method of the present invention.

This embodiment is an example of application to positioning control, and the position controller 11 outputs a speed command ωrQ according to the deviation between the 1-position command value po and the actual position p detected by the position detector 18. The speed controller 12 converts 1 obtained by differentiating the actual position p using a differentiator 19 into a torque component command 1. from the difference between the speed ω of the motive force and the above-mentioned command value ω1o. Outputs ◎.

In the case of position control as in this embodiment, the excitation component correction circuit lO, which is a feature of the present invention, has an actual position p and a speed command value ω1.
A correction value of the excitation component command is output in accordance with G, and this is multiplied by the excitation component correction circuit 1 to generate the same command Iao. On the other hand, the detected values of the three-phase primary current and voltage detected by the current-voltage converter 6 are converted into two-phase equivalent amounts by the vector converter 17, and the slip correction circuit 1
5 calculates a correction value Δω of the slip frequency. A frequency command ω1o, which is obtained by adding this, the slip frequency command ω,0 obtained by multiplying the excitation component command Is4 by a constant fik, and the actual speed ω, is input to the oscillator 14, where it is combined with a sine wave sinωIOt of frequency ω1o. Cosine wave WSω1 perpendicular to this
0 t is output. This output is applied to the vector converter 17 and also to the inverse vector converter 16.

The inverse vector converter 16 converts the three-phase primary IE flow command i from the oscillator 14 output torque and the excitation command Ito@Im.
1e, and from this and the output of the converter 6, the pulse width control circuit 2 controls the primary current of the induction motor IM.

FIG. 2 is a functional explanatory diagram of the excitation component correction circuit 10 suitable for position control, which is a feature of the present invention, and includes function generators F1 and F! have. These outputs are multiplied and output as a correction coefficient, and this is multiplied by a set value of 1.1 to perform correction.

The function generator F1 is for supplying an appropriate output torque according to the speed command ωre. That is.

First, when the speed command ωrQ is small or a stationary speed command, the value of F+ is smaller than 11, thereby preventing unnecessary energy loss and reducing the A sound. On the other hand, when 1 position deviation 1)o9 is large, the speed command ω2o becomes a dog, but in this case, the output of F+ is made larger than 1 to increase the output torque. This makes it possible to improve the responsiveness of the positioning device. However, if the excitation component is too large, the magnetic flux φ will be saturated, so
Make settings to the extent that this does not happen. Additionally, there may be nonlinearity in the motor load. This is Δp; po I)
When the speed command ω-o>0 at 0 and Δp-p, +-p<
0, the speed command ω,, (This is a case where the load size changes when 0, but in order to improve the responsiveness of position determination even in this case, the speed command ω, S to output the excitation command ■1° of the required size when the
Let the value of r1 be f, and f.

Set to .

Does the function generator F2 generate the required load torque corresponding to the load position p? For example, when the smaller the position p requires a larger torque, the characteristics shown in FIG. 2 are preferable. This makes it possible to prevent unnecessary energy loss and improve control performance.

In the above embodiment, it is assumed that the position It control is performed.

In the case of speed control, the excitation component correction circuit 10 is suitably constructed from the function generators Fs and Fa shown in FIG. Among these, the function generator F3 outputs the speed command ω, 0 and the actual speed ω.
This is to supply an appropriate torque according to the deviation Δω,=ω2G−ω. That is, when the deviation Δω is small, by setting Fs to 1, the excitation component command 1
Reduce 11G.

To prevent unnecessary energy loss, improve operational efficiency, and also improve speed control stability. −
When the force deviation Δω2 is large, the output torque is increased by setting Fs>1 to improve the responsiveness of speed control.

Furthermore, even if the speed deviation Δω1 is large, if there is a difference in the characteristics of the motor load depending on whether Δω2 is positive or negative, the value of Fs (greater than 1) can be changed as shown in Figure 3 f, f. Control performance such as responsiveness and stability can be improved by changing the value.

The function generator F4 in Fig. 3 is used to obtain the required load torque corresponding to the speed ω of the load.For example, when a larger torque is required as the speed ω is smaller, the function generator F4 shown in Fig. 3 is used. Characteristics are preferred.

This can prevent unnecessary energy loss and improve control performance.

〔Effect of the invention〕

As is clear from the above embodiments, the present invention has the effect of preventing noise that tends to occur when the motor is stopped due to pulse width modulation control.

In addition, by variably setting the excitation flow depending on the amount of torque required, operational efficiency is improved, control stability is improved,
This has the effect of improving responsiveness.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an embodiment of the present invention, Figures 2 and 3 are functional explanatory diagrams of an excitation component correction circuit suitable for position control and speed control, and Figure 4 is an induction diagram. FIG. 5, a control system diagram of the tlI machine, is a diagram showing an example of voltage/current waveforms generated for pulse width modulation control. 2...Pulse width control circuit, 3...Motor control calculation circuit. 6...d-current voltage converter, 10...excitation component correction circuit. 18...Position detector, IM...Induction motor, F+~
F4...Function generator.

Claims (1)

[Claims] 1. Calculating a speed command from a positional deviation between a detected value of the actual position of an object moved by an induction motor and its target position,
A torque component command is calculated from the speed deviation between the speed command and the detected value of the actual speed of the object, and a primary current equivalent to a vectorial combination of the torque component command and a preset excitation component command is calculated. In a method for controlling an induction motor in which current is controlled by pulse width modulation means so that the current flows through the induction motor, the excitation is performed when the absolute value of the calculated speed command is less than or equal to a predetermined first value. A method for controlling an induction motor, comprising: a correction means for correcting a component command so as to make it smaller than a set value. 2. The correction means has a function of making the excitation component command larger than its set value when the absolute value of the speed command is equal to or higher than the first value or a second value larger than the first value. A method for controlling an induction motor according to claim 1. 3. A function that causes the excitation component command to take different values when the absolute value of the speed command exceeds the first or second value and the speed command is positive and negative. 3. A method for controlling an induction motor according to claim 2, characterized in that the correction means includes the correction means. 4. The correction means according to claim 1, 2, or 3, wherein the correction means has a function of changing the excitation component command according to the detected actual position of the object. How to control an induction motor. 5. Calculate the torque component command from the speed deviation between the target speed and the actual speed detection value of the induction motor, and calculate the primary current equivalent to the vectorial combination of the torque component command and the preset excitation component command. In an induction motor control method for controlling the current to flow through the induction motor, when the absolute value of the speed deviation is less than or equal to a predetermined third value, the excitation component command is corrected to be smaller than the set value. A method for controlling an induction motor, characterized in that a correction means is provided. 6. The correction means has a function of making the excitation component command larger than its set value when the absolute value of the speed deviation is equal to or higher than the third value or a fourth value larger than the third value. A method for controlling an induction motor according to claim 5. 7. A function for causing the excitation component command to take different values when the absolute value of the speed deviation exceeds the third or fourth value and the speed deviation is positive and negative. 7. The method of controlling an induction motor according to claim 6, wherein the correction means includes the correction means. 8. Claims 5, 6, or 7, characterized in that the correction means has a function of changing the excitation component command according to the actual measured power detection value of the induction motor. A method of controlling an induction motor.