Apparatus and method for controlling induction motor

• US 6,166,514 A
• Filed: 09/20/1999
• Issued: 12/26/2000
• Est. Priority Date: 03/19/1997
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Yasuda, Kouji, Suzuki, Masato, Ando, Takeshi, Toyota, Eiichi, Nakata, Kiyoshi, Tanamachi, Tokunosuke
• Primary Examiner(s): Dang, Khanh
• Application Number:
  US09/381,402
• Time in Patent Office: 463 Days
• Field of Search: 318/727, 318/801, 318/810, 318/811
• US Class Current: 318/811
• CPC Class Codes: B60L 15/025 using field orientation; Vector control; Direct Torque Control [DTC]
• CPC Class Codes: B60L 2200/26 Rail vehicles
• CPC Class Codes: B60L 2220/12 Induction machines
• CPC Class Codes: H02P 21/00 Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
• CPC Class Codes: H02P 21/09 Field phase angle calculation based on rotor voltage equation by adding slip frequency and speed proportional frequency
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility

Abstract

In a control apparatus of an induction motor including an inverter for converting a direct current to an alternating current having a variable voltage and variable frequency in accordance with a pulse width modulation control, and a controller for controlling an output voltage of said inverter through a modulation rate which is requested in accordance with an exciting magnetic current component command in a primary current of the induction motor driven by said inverter and a voltage component command corresponding to said respective components which are executed in accordance with a torque current component command, the control apparatus of the induction motor operates to detect a torque current component in accordance with said primary current of the induction motor, to correct said torque current component from a deviation between said detected torque current component value and said command value, to correct an output frequency of said inverter in accordance with said corrected torque current component command, and to limit the size of the modulation rate to less than a predetermined value or less than a predetermined condition. With this construction, in the induction motor, without the change-over from the low speed area to the high speed area (PWM pulse mode is 1 pulse area) where the size of the voltage command exceeds the maximum voltage capable of being output by the inverter, which is determined according to the direct current voltage, a good vector control can be carried out.

Claims

1. In a control apparatus for an induction motor comprising an inverter for converting a direct current to an alternating current having a variable voltage and variable frequency in accordance with a pulse width modulation control, and a controller for controlling an output voltage of said inverter using a modulation rate in the form of an output voltage command which is requested in accordance with an exciting magnetic current component command in a primary current of the induction motor driven by said inverter and a voltage component command corresponding to said respective components which are executed in accordance with a torque current component command, the control apparatus for the induction motor further comprising:

means for detecting a torque current component in accordance with said primary current of the induction motor;

means for correcting said torque current component with respect to a deviation between said detected torque current component value and said command value;

means for correcting an output frequency of said inverter in accordance with said corrected torque current component command; and

means for limiting the magnitude of said modulation rate to less than a predetermined value or less than a predetermined condition.

2. A control apparatus for an induction motor according to claim 1, characterized in that

said modulation rate is normalized in accordance with said magnitude in which said direct current voltage is detected.

3. A control apparatus for an induction motor according to claim 1, characterized in that

during a period where the magnitude of the modulation rate is limited to less than said predetermined value, said exciting magnetic current component command is outputted from a command generating means which generates a predetermined value.

4. A control apparatus for an induction motor according to claim 1, characterized in that

said predetermined value for limiting said magnitude of said modulation rate is established at the maximum voltage capable of being output by said inverter which is determined according to said direct current voltage.

5. A control apparatus for an induction motor according to claim 1, characterized in that

said predetermined condition for limiting the magnitude of the modulation rate is that a pulse number during a phase voltage half-periodic period of said output of said inverter is 1 pulse.

6. In a method of control of an induction motor which in controlling an inverter which converts converting a direct current to an alternating current having a variable voltage and variable frequency and a constant voltage and variable frequency in which an output voltage of said inverter is controlled, and through a modulation rate in the form of an output voltage command which is requested in accordance with an exciting magnetic current component command in a primary current of the induction motor driven by said inverter and a voltage component command corresponding to said respective components which are executed in accordance with a torque current component command, the control method of the induction motor comprising the steps of:

after a transfer from a control of said variable voltage and variable frequency to a control area of said constant voltage and variable frequency, limiting said modulation rate to a predetermined value, and increasing said torque current component command in response to an increase of an output frequency of said inverter.