JP3060814B2 - Control circuit of magnetic flux control type inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a magnetic flux control type inverter for driving an AC motor at a variable speed.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration diagram of a conventional flux control type inverter. In FIG. 2, a commercial power supply 1 is connected to a rectifier 2
, And the DC voltage smoothed by the smoothing capacitor 3 is converted into an AC voltage by the inverter 4 and supplied to the AC motor 5. The control circuit 20 inputs a set value of the frequency setter 11 that sets the frequency of the inverter 4 that drives the AC motor 5, and generates a frequency command value f ^* that changes the set value at a constant rate of change. An acceleration / deceleration calculator 21, a magnetic flux pattern generator 22, which generates a magnetic flux command value Φ ^{* based} on a frequency command value f ^* , a rated voltage and a rated frequency of the AC motor 5, and a set value of a torque boost setting device 12 described later. When,
A DC / AC converter 23 for generating an AC magnetic flux command value φ ^{* based} on the magnetic flux command value Φ ^* and the frequency command value f ^* , a voltage detector 13 for detecting a terminal voltage of the AC motor 5, A magnetic flux calculator 24 for calculating the magnetic flux detection value φ _ACT by integrating the output, an adder / subtractor 25 for calculating a deviation between the AC magnetic flux command value φ ^* and the magnetic flux detection value φ _ACT, and an output of the adder / subtractor 25 It comprises a magnetic flux adjuster 26 that generates a pulse width modulation set value by performing a PI operation, and a pulse width modulation circuit 27 that generates a PWM control signal for the inverter 4 based on the pulse width modulation set value.

[0003] The magnetic flux pattern generator 22 calculates a magnetic flux command value Φ ^* by equation (1).

[0004]

Φ ^*は (Rated motor voltage) 定 格 (Rated motor frequency) (1) The calculated Φ ^* is a constant value irrespective of the frequency at which the AC motor 5 is driven. When the operation is performed, the set value of the torque boost setting device 12 is adjusted, and the value of the magnetic flux command value Φ ^* is calculated from the calculated value of Expression (1).
The lower the frequency, the larger the value (referred to as torque boost method), and the AC motor 5 becomes insufficient in torque due to the voltage drop due to the wiring cable between the inverter 4 and the AC motor 5 and the voltage drop due to the primary resistance of the AC motor 5. I try to prevent it.

[0005]

In the magnetic flux control type inverter, the primary magnetic flux Φ of the AC motor is calculated by equation (2).

[0006]

Φ = ∫vdt = ∫ (iR + e) dt = ∫iRdt + ∫edt (2) where, v: motor terminal voltage, i: motor current, R: motor primary resistance, and e: motor back electromotive voltage. . In the equation (2), the value to be corrected by the torque boost on the right side is a constant value by the torque boost setting device irrespective of the motor current. However, there is a problem that the motor is insufficient in torque, which is smaller than the required amount, and is too large when the motor current is small.

An object of the present invention is to provide a control circuit for a magnetic flux control type inverter which solves the above-mentioned problem.

[0008]

According to a first aspect of the present invention, there is provided a control circuit for a magnetic flux control type inverter for driving an AC motor at a variable speed, comprising: an acceleration / deceleration calculator for generating a frequency command value based on a set value of a frequency setter; A magnetic flux converter that generates a magnetic flux command value based on the frequency command value and the rated voltage and rated frequency of the AC motor, a current detector that detects an input current of the AC motor, and a magnetic flux correction value based on an output of the current detector. A magnetic flux correction value calculation circuit that calculates the magnetic flux correction value and the magnetic flux command value, and a DC / AC converter that generates an AC magnetic flux command value from the output of the adder and the frequency command value. A voltage detector for detecting a terminal voltage of the AC motor, a magnetic flux calculator for calculating a magnetic flux detection value based on an output of the voltage detector, and a deviation between the AC magnetic flux command value and the magnetic flux detection value. Comprising a subtractor, and the flux regulator generates a pulse width modulated set value by the output of the subtracter, and a pulse width modulation circuit for generating an inverter control signal by said pulse width modulation value.

According to a second aspect of the present invention, the voltage detector of the first aspect detects the output voltage of the inverter.

[0010]

According to the present invention, an input current of an AC motor is detected, a magnetic flux correction value is calculated from the detected current, and the magnetic flux correction value is added to a magnetic flux command value, so that an appropriate current corresponding to the input current can be obtained. Torque boost can be performed.

[0011]

FIG. 1 is a block diagram of a control circuit of a magnetic flux control type inverter according to an embodiment of the present invention. In FIG.
Components having the same functions as those in FIG. 2 are denoted by the same reference numerals, description thereof will be omitted, and different functions will be mainly described. That is, FIG.
In the control circuit 30, the acceleration / deceleration calculator 21 that generates the frequency command value f ^{* based} on the set value of the frequency setter 11
Magnetic flux converter 3 for generating magnetic flux command value Φ ^{* based} on frequency command value f ^* , rated voltage and rated frequency of AC motor 5
1 and a current detector 1 for detecting an input current of the AC motor 5
4, a magnetic flux correction value calculation circuit 32 for calculating a magnetic flux correction value based on the output of the current detector 14, an adder 33 for adding the magnetic flux correction value and the magnetic flux command value Φ ^* ,
3 and the frequency command value f ^* , the AC magnetic flux command value φ
^* , A DC / AC converter 23 for generating ^* , a voltage detector 13 for detecting a terminal voltage of the AC motor 5,
The third output flux calculator 24 for calculating a magnetic flux detection value phi _ACT, a subtracter 25 for calculating a deviation between the AC magnetic flux command value phi ^* and the magnetic flux detection value phi _ACT, the pulse width by the output of the subtracter 25 Magnetic flux adjuster 26 for generating a modulation set value
And a pulse width modulation circuit 27 that generates an inverter control signal based on the pulse width modulation set value.

Since the magnetic flux converter 31 performs the calculation of the equation (1) described in the conventional example, it may normally have the function of a proportional amplifier, and the magnetic flux correction value calculation circuit 3 for calculating the magnetic flux correction value.
2 can be calculated by multiplying the integral value of the current of the AC motor 5 by a proportional constant corresponding to the primary resistance of the motor. Further, by making the magnetic flux converter 31 have an inversely proportional characteristic in a high frequency region, the magnetic flux weakening control of the AC motor 5 in the high-speed rotation region can be realized.

In the above embodiment, the control is performed by detecting the terminal voltage of the AC motor 5, but when the wiring cable between the inverter 4 and the AC motor 5 is short and the voltage drop of the wiring cable can be ignored, The voltage detector 13 may perform control by detecting the output voltage of the inverter 4. The present invention is also applicable when a plurality of AC motors are operated in a group.

[0014]

According to the present invention, an input current of an AC motor is detected, a magnetic flux correction value is calculated from the detected current, and the magnetic flux correction value is added to a magnetic flux command value, thereby corresponding to the input current. Appropriate torque boost can be performed. In addition, when a plurality of AC motors are group-operated, the present invention is also effective when the AC motors to be additionally operated are directly driven.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a magnetic flux control type inverter showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a magnetic flux control type inverter showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectifier 3 Smoothing capacitor 4 Inverter 5 AC motor 11 Frequency setting device 12 Torque boost setting device 13 Voltage detector 14 Current detector 20 Control circuit 21 Acceleration / deceleration calculator 22 Magnetic flux pattern generator 23 DC / AC converter 24 Magnetic flux Arithmetic unit 25 Addition / subtraction unit 26 Magnetic flux adjuster 27 Pulse width modulation circuit 30 Control circuit 31 Magnetic flux converter 32 Magnetic flux correction value arithmetic circuit 33 Adder

────────────────────────────────────────────────── (5) References JP-A-63-283487 (JP, A) Patent 287397 (JP, B2) Patent 2893885 (JP, B2) Patent 2734606 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02P 5/408-5/412 H02P 7/628-7/632 H02P 21/00

Claims (2)

(57) [Claims] 1. A control circuit for a magnetic flux control type inverter for driving an AC motor at a variable speed, comprising: an acceleration / deceleration calculator for generating a frequency command value based on a set value of a frequency setting device; A magnetic flux converter that generates a magnetic flux command value according to a rated frequency, a current detector that detects an input current of an AC motor,
A magnetic flux correction value calculating circuit for calculating a magnetic flux correction value based on the output of the current detector; an adder for adding the magnetic flux correction value and the magnetic flux command value; and an AC magnetic flux based on the output of the adder and the frequency command value. A DC / AC converter for generating a command value,
A voltage detector that detects a terminal voltage of the AC motor, a magnetic flux calculator that calculates a magnetic flux detection value based on an output of the voltage detector, and an adder / subtractor that calculates a deviation between the AC magnetic flux command value and the magnetic flux detection value, A magnetic flux controller for generating a pulse width modulation set value based on the output of the adder / subtractor; and a pulse width modulation circuit for generating a control signal for the inverter based on the pulse width modulation set value. Control circuit. 2. A control circuit for a magnetic flux control type inverter according to claim 1, wherein said voltage detector detects an output voltage of said inverter.