JPS63157685A - Controller for ac motor - Google Patents

Abstract

PURPOSE:To reduce torque ripple and loss, by compensating for component corresponding to the unbalanced one of the main circuit impedance of each phase on the output voltage of the converter of each phase. CONSTITUTION:From a speed control circuit 9 and a magnetic flux attenuating control circuit 10, the output of secondary magnetic flux signal according to a deviation between speed setting signal and speed feedback signal, and the speed feedback signal is generated. To a primary current vector detecting circuit 7, the input of each-one-phase primary current of an induction motor 5 detected by current detectors 41-43 is provided, and actual torque component current and excitation component current are detected. From current control circuits 12, 13, a deviation between the detected values and command values of the torque component current and excitation component current is applied to a two-phase/three-phase converter circuit 14. Besides, from an output voltage compensation circuit 16, according to the signal of the torque component current and excitation component current which are two-phase/three-phase-converted, the output of compensation control signal corresponding to the unbalanced impedance of a main circuit is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an AC motor, and particularly to a control device suitable for a variable speed induction motor.

[Conventional technology]

As a control device for this scale, for example, Japanese Patent Application Laid-Open No. 59-6149
As disclosed in Publication No. 3, the primary current flowing through each phase winding of an AC motor is detected, and these detected currents are input to a primary current vector detection circuit to generate excitation parallel to the secondary magnetic flux axis. It is divided into two components: the current component (d) and the torque current component (I) perpendicular to the secondary magnetic flux axis, and the deviation is determined by comparing these with their respective command values. A method is known in which control signals for each phase are created, and these control signals are used to control converters for each phase to control the AC voltage supplied to each phase winding of an AC motor.

[Problem that the invention seeks to solve]

However, this conventional control method assumes that the primary current flowing through each phase winding of the AC motor to be controlled is balanced, and controls the AC motor by considering it as a two-axis model in which three phases are converted to two phases. However, no consideration was given to the unbalance of the phase currents due to differences in the interferers of the phases of the main circuit through which the primary current flows.

On the other hand, as the capacity of AC motors increases, the capacity of the crane required to assemble and disassemble them also increases. It has become necessary to divide the child into two.

When dividing the stator into two parts like this 5, make sure that the end part of the coil located at the dividing point does not cross over the dividing point.
It was found that when the connections were changed, the impedance of each phase winding became unbalanced, and the primary current flowing therein also became unbalanced. Furthermore, since the main circuit wiring through which the primary current flows is relatively long and the current is large, it is common that the wiring for each phase is not installed all at once, but is installed separately.

Therefore, the length of the wiring for each phase is different, or the surrounding environment in which it is installed is different for each phase wiring, and in this case too, the impedance of the main circuit of each phase becomes unbalanced.
This causes imbalance in the secondary current.

If an unbalance occurs in the primary currents flowing through the windings of each phase as described above, a problem arises in that torque ripple occurs in the AC motor and loss increases.

Therefore, an object of the present invention is to provide a control device for an AC motor that can balance the primary current flowing through each phase winding and reduce torque ripple and loss of pulse even if the main circuit impedance of each phase is unbalanced. There is a K when it comes to making a gift.

[Means for solving problems]

In order to achieve the above object, the present invention converts the unbalanced portion of the main circuit impedance of each phase into a voltage, and controls the converter of each phase so that its output voltage is corrected by the unbalanced voltage. It is characterized by

[For production]

Since the output voltage of the converter of each phase is corrected by the voltage corresponding to the unbalance of the main circuit impedance of each phase, the primary current flowing to each phase winding even if the main circuit impedance of each phase is unbalanced. becomes balanced.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to FIG. 1. In the figure, 1 is a three-phase AC power supply, 2 is a power transformer, 21.22.2
3 is the secondary winding of the power transformer 20, which is connected to converters 31, 32, and 33, which are made by connecting two sets of three-phase grid-connected converters in antiparallel and are capable of flowing current in both forward and reverse directions; 42 and 43 are current detectors, 5 is an induction motor, 6 is a speed detector for the induction motor, and each winding of the U phase, ■ phase, and W phase of the induction motor 5 is connected to the converter 31.
．． 32.33, and the commercial AC supplied from the secondary windings 21, 22.23 of the power transformer 20 is directly converted into AC of a predetermined frequency by the converters 31, 32.33, and then supplied to the induction motor. 8 is a speed setting device for setting the speed of the induction motor 4, and 9 is a deviation between the speed reference signal set by the speed setting device 8 and the speed feedback signal detected by the speed detector 6. 10 is a magnetic flux weakening control circuit that inputs the speed feedback signal and outputs a secondary magnetic flux signal. 11 inputs the torque component current (command value), excitation component current (command value), and speed feedback signal. This is a control circuit that outputs the first frequency of the induction motor 50. 7 is a current detector 41, 42, 43
12.13 This is a primary current vector detection circuit for inputting the primary current of each phase of the induction motor detected from the motor to detect the actual torque component current and excitation component current.
are current control circuits that amplify the deviations between the detected values and command values of the torque component current and excitation component current, respectively. 14
converts the output signals of the current control circuits 12 and 13 from the 2-phase to the 3-phase
Even a 2-phase/3-phase conversion circuit for converting the phase. The above configuration is similar to the conventional example.

In this embodiment, the torque component current (command value) is further
and a 2-phase/3-phase conversion circuit 15 for converting the excitation component current (command value) from 2-phase to 3-phase, and the output of this 2-phase/3-phase conversion circuit 15 is input to convert the converters 31, 32 . 3
3 is controlled so that the output α pressure is corrected by the tortoise pressure corresponding to the unbalance of the main circuit impedance.
An output voltage correction circuit 16 is provided which outputs the I1H1-4M signal.

By the way, the voltage force sum equation of an induction motor is given by the following equation.

Here, ml"tj"ll: Phase voltage of induction motor "1m+
”I□R1,: Primary resistance R1 of induction motor:
Secondary resistance of induction motor! 1m+ 'I eH11w: Primary current of each phase of induction motor 'tm+ '*wt "1w" Secondary current of induction motor 's@+ Leve Lsw * Self-inductance M of primary winding of induction motor: 1 of induction motor Mutual inductance el of the next winding, θ5. θ,: Phase angle of the primary current of the induction motor,: Self-inductance of the secondary winding of the induction motor, M: Mutual inductance of the secondary winding of the induction motor.

If there is unbalance in the primary resistance and primary inductance of the induction motor, *R1*~R+v ”e Rl
e HL@@SL@9~L1. becomes. Therefore, the primary side resistance and primary side inductance can be expressed by the following formula.

Here, n: Primary side equilibrium resistance R□R,, R,
: Primary side unbalanced resistance, : Primary side balanced inductance L++eLv+Lw : Indicates primary side unbalanced inductance.

Furthermore, considering the resistances R, , R, , R, and inductances L, , L, , of the main circuit wiring, etc., the impedance drop is as follows.

Therefore, each phase voltage v@9 v91 to be given to the induction motor
Since the unbalanced component and the balanced component of the main circuit impedance drop can be separated, this unbalanced component, that is, the voltage shown in equation (6) below, is calculated by the output voltage correction circuit 16, and the corresponding correction control signal is By adding to the control background that is the output of the phase/three-phase conversion circuit 14, the converters 31, 32 . ．． Since the output voltage of each of 33 can be changed, it is possible to flow a balanced three-phase current in each phase of the induction motor.

In addition to calculating the voltage corresponding to the unbalanced component using equation (6), as shown in FIG.
'91□IW□ and the output current of the 2-phase/3-phase conversion circuit 16 in FIG. 2! I? ! It can also be obtained by using the control circuits 51, 52, and 53 to obtain an output that makes the deviation from vl 1v zero.

〔Effect of the invention〕

As explained above, according to the present invention, the unbalanced portion of the main circuit impedance of each phase is corrected by the output voltage of the converter of each phase, so even if the main circuit impedance of each phase is unbalanced, the AC A balanced current can be passed through each phase winding of the motor, and its torque ripple and loss can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control device for a variable speed induction motor according to an embodiment of the present invention, and FIG. 2 is a block diagram showing another example of a circuit for determining the voltage corresponding to the unbalanced component of the main circuit impedance. It is. 31.32,33...Converter, 41,42
゜43...Current detector, 5...Induction motor, 6...Speed detector, 7...Primary current vector detection circuit, 14.15・・・・・・2 phase/
3-phase conversion circuit, 16... Output voltage correction circuit. Figure 1 7 = 1 vine, dragon N/7! -Leader figure 2

Claims (1)

[Claims] 1, comprising an AC motor and a converter that converts AC into AC of a predetermined frequency and voltage and supplies it to each phase winding of the AC motor,
In a device that divides the secondary current into an excitation current component and a torque current component and controls each component separately, the main circuit impedance drop of each phase of the AC motor is divided into a balanced component and an unbalanced component, and a control signal corresponding to the balanced component is generated. An AC motor comprising: a control circuit for outputting an output; and a correction control circuit for outputting a correction control signal corresponding to the unbalanced amount; and the converter is controlled by the control signal and the correction control signal. control device.