JPS60170488A - Driving method of induction motor - Google Patents

Abstract

PURPOSE:To obtain the prescribed torque at a low speed time by calculating a voltage command on the basis of a rated circuit constant of an induction motor, a slip frequency command and an inverter frequency command in accordance with a theoretical equation. CONSTITUTION:The first function generator 51 receives a slip frequency command omegas and an inverter frequency command (omega), and calculates and outputs a voltage component Vd parallel to the direction of the exciting branch current Ie of an induction motor 30 and a voltage component Vq parallel to the direction of a torque branch current Ir. The second function generator 52 calculates a voltage command Vm from the components Vd, Vq and outputs a PWM modulator 34. Thus, the primary terminal voltage of the motor 30 varies so that the current Ir becomes proportional to the slip frequency command omegas, and the torque corresponding to the operating condition is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for driving an induction motor, particularly to improving control characteristics during low-speed driving.

(Prior Art) Fig. 1 shows an example of a conventional drive device for an induction motor. In the figure, 10 is a DC bus, 20 is a three-phase PWM inverter, 30 is an induction motor, and 40 is a speed detection device. 31 is a smoothing capacitor,
32 is a three-phase bridge-connected transistor inverter;
3 is a Haas drive circuit for the transistor inverter 32;
4 is a pulse modulator (PWM modulator); 35 is an adder;
36 is a speed controller, and 37 is a speed command device.

Next, the operation of this drive device will be explained.

During normal operation, the speed controller 36 operates so that the speed reference signal Nr output by the speed command device 37 and the output Wm of the speed detector 40 are equal. The slip frequency command ωS, which is the output of the speed controller 36, is added to the speed Wm of the induction motor 30, which is the output of the speed detector 40, in an adder 35. The output ω of the adder 35 is input to the PWM modulator 34 as a voltage command Vs of the inverter 32, and is also supplied to the PWM modulator 34 as a frequency command.

The output of the PWM modulator 34 is pulse-controlled in accordance with the voltage command Vs, has a fundamental frequency proportional to the frequency command ω, and is supplied to the Heas drive circuit 33. FIG. 2 shows an example of the waveform of the output line voltage of the L-Lanry inverter 32. When the control voltage is high, the voltage Vu during the pulse applied to the induction motor 30 is wide, as shown in +8+ in the figure. When the voltage is low, each pulse becomes narrow rjJ, as shown in FIG. 2(b), and the induction motor current 1u also becomes small.

In this drive method, since the voltage command is dependent on the output of the adder 35, during low speed operation, the voltage drop in the stator winding of the induction motor 30 cannot be ignored with respect to the primary terminal voltage. Due to weak excitation, induction motor generation i・
In addition, during low-speed regenerative operation, the induction motor is strongly excited, resulting in excessive torque generated by the induction motor and excessive current flowing.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional problems.
By configuring the system to be calculated theoretically based on the slip frequency command and the inverter frequency command, it is possible to eliminate the influence of primary resistance on the induction motor terminal voltage during low-speed operation, and to improve control characteristics compared to conventional methods. This paper proposes a method for driving an induction motor that enables the following.

[Embodiment of the Invention] FIG. 3 shows a block diagram of an embodiment of the present invention. In the same figure, the first leap number generator 511J derives the slip frequency command ωS, which is the output of the speed controller 36, and the inverter frequency command ω, which is the output of the adder 35, and the excitation component of the induction motor 30 is Voltage component Vd parallel to the direction of current Ie
and a voltage component Vq parallel to the direction of the torque component current lτ are calculated and output according to the following formula.

Vd=r −1e−ω−Ll(1−α)IT・−o1V
q=r -1r''a+-L・Ie...1211 However, rl: Primary resistance of the induction motor Ll: Primary inductance of the induction motor α: Coupling coefficient of the primary and secondary inductance of the induction motor The primary resistance r1, the -order inductance I71, and the coupling coefficient α of the -order and secondary inductances, which are circuit constants of the electric motor, are stored in advance.

52 is a second function generator, which calculates a voltage command (primary terminal voltage of the induction motor 30) Vm from the voltage component Vd and the voltage component Vq based on the following equation (3), and outputs the PWM modulator 3.
Output to 4.

Vm=F; 〒Ao...... (3) In addition, Fig. 4 shows a vector diagram of the voltage Vd and voltage Vq shown by the above equations (1) and (2). shows.

In this embodiment, a voltage component Vd parallel to the direction of the excitation current Is and a voltage component V parallel to the direction of the l·lux component current Iτ are used.
q theoretically to obtain the voltage command Vm, so that the 1-lux current Iτ is proportional to the slip frequency command ωS,
The primary terminal voltage of the induction motor 3o changes, and torque corresponding to the operating conditions is ensured.

Note that the calculations of equations +11 to (3) above can be easily performed in the calculation section of a microprocessor, so the part shown by the dotted line in FIG. By doing so, the second effect can be obtained without making the device more expensive than the conventional device.

〔Effect of the invention〕

As explained below, the present invention has a configuration in which the voltage command is calculated according to a theoretical formula based on the circuit constant of the induction motor, the slip frequency command, and the inverter frequency command. Since it becomes possible to secure the required torque corresponding to the operating conditions, control characteristics are improved and the induction motor can be driven stably and accurately over its entire control range.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional drive device for an induction motor, FIG. 2 is a waveform diagram showing the output voltage waveform of an inverter in a 1m drive device, and FIG. 3 is a block diagram showing an embodiment of the present invention. Figure 4 is a vector diagram of an induction motor. In the figure, 32-transistor inverter, 34,-
-PWM modulator, 35-adder, 36-speed controller, 37-speed command device, 40-speed detector, 51.52-
Function generator, 500-microprocessor. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Agent: Masuo Oiwa (7) Figure 1 Figure 2 Figure 4 Figure - LLILI (-a) Iy Procedural amendment (voluntary) 60510 Showa year, month, day 1 , Indication of the case Japanese Patent Application No. 59-026441 No. 2 Title of the Invention ``Method for driving a peeping machine 3'' Person making the amendment Representative Hitoshi Katayama Department, Attorney 5, Patent claim of the specification to be amended Scope column 6, the description of the claims in the description of the contents of the amendment, is first corrected as shown in the attached sheet. Claims (1) An inverter that controls the power supplied to the induction motor, a speed detector that detects the speed of the induction motor, a speed command device, and a deviation between the output of the speed detector and the output of the speed command device. A speed controller for amplifying the voltage command and a frequency command for the inverter by providing an adder for adding the output of the speed detector and the output of the speed controller. depends on the output of the speed controller and the inverter l′,
'' A method for driving an induction motor, characterized in that the second frequency command is made dependent on the output of the adder. (2) The induction motor according to claim 1, wherein the voltage command is calculated based on a pre-stored circuit constant of the induction motor, an output of a speed controller, and an output of an adder. Driving method.

Claims (1)

[Claims] +l) An inverter that controls the power supplied to the induction motor;
A speed detector that detects the speed of the induction motor, a speed command device, a speed controller that amplifies the deviation between the output of the speed detector and the output of the speed command device, and the output of the speed detector and the speed control In an induction motor drive method in which an adder is provided to add the outputs of the inverter to create voltage commands and frequency commands for the inverter, the voltage command is made to depend on the output of the speed controller, and the frequency command is made to depend on the output of the speed controller. A method for driving an induction motor, characterized in that the method is made to depend on the output of a two-note adder. (2) The induction motor according to claim 1, wherein the voltage command is calculated based on a pre-stored circuit constant of the induction motor, an output of a speed controller, and an output of an adder. Driving method.