Electronic pole changing-based induction motor control system and control method thereof
The present invention relates to an electronic pole changing-based induction motor control system and a control method thereof. Such induction motor control system comprises an induction motor, an inverter and a DC power supply. The inverter is connected with the motor and the DC power supply respectively, for converting a direct current supplied by the DC power supply to an alternating current supplied to the motor. The motor comprises N three-phase windings ( 11, 12; 31, 32 ). The inverter comprises N inversion driving units ( 21, 22; 41, 42 ) and at least one control unit. Each inversion driving unit is connected with one three-phase winding. The control unit controls the inversion driving unit to generate a current of the three-phase winding connected thereto, and frequency, amplitude and phase of the current can be controlled by the control unit. The control unit alters current directions or phase angles of at least part of the three-phase windings according to a synchronous rotational speed of the motor, making N three-phase windings form at least two pole-pair numbers. The induction motor control system enhances the low-speed torque and broadens the speed governing operation range, thereby enhancing the control accuracy and operation efficiency, and simplifying a peripheral transmission mechanism.
1. An electronic pole changing-based induction motor control system, comprising a motor, an inverter and a DC power supply; the inverter connected with the motor and the DC power supply respectively, for converting a direct current supplied by the DC power supply to an alternating current supplied to the motor; characterized in that, the motor comprises N three-phase windings, wherein N is an integer bigger than 1; the inverter comprises N inversion driving units and at least one control unit; each inversion driving unit is connected with one three-phase winding; the control unit controls the inversion driving unit to generate a current of the three-phase winding connected thereto; the control unit comprises a synchronous rotational speed operation module, for calculating a synchronous rotational speed of the motor; and the control unit alters current directions or phase angles of at least part of the three-phase windings according to the synchronous rotational speed of the motor, making said N three-phase windings form at least two pole-pair numbers, wherein one or more rotational speed threshold values are set and one rotation speed threshold value corresponds to one pole-pair number.
2. The electronic pole changing-based induction motor control system according to claim 1 , wherein the inversion driving unit comprises three output ends, each three-phase winding comprises three sub-windings, and input ends of said three sub-windings are respectively connected with said three output ends of the inversion driving unit.
3. The electronic pole changing-based induction motor control system according to claim 1 , wherein said N three-phase windings form a NY structure or a N Δ structure or an aYbΔ structure, wherein both a and b are integers bigger than 1, and a+b=N.
4. The electronic pole changing-based induction motor control system according to claim 1 , wherein the inverter comprises one control unit which controls said N inversion driving units respectively; or the inverter comprises a plurality of control units, and each control unit controls one or more inversion driving units.
5. The electronic pole changing-based induction motor control system according to claim 1 , wherein the control unit is one or more of MCU, DSP, FPGA and CPLD.
6. A control method of the electronic pole changing-based induction motor control system according to claim 1 , characterized in that, the control unit controls the inversion driving unit to generate a current of the three-phase winding connected thereto; the control unit alters current directions or phase angles of at least part of the three-phase windings according to the synchronous rotational speed of the motor, making said N three-phase windings form at least two pole-pair numbers; and
the control unit controls said N inversion driving units according to the synchronous rotational speed of the motor, to alter the current directions or phase angles of at least part of the three-phase windings, making the motor switch between the at least two pole-pair numbers.
7. The control method of the electronic pole changing-based induction motor control system according to claim 6 , wherein each said rotational speed threshold value equals a synchronous rotational speed to which a fundamental frequency corresponds when the motor forms the pole-pair number which corresponds to the rotational speed threshold value.
8. The control method of the electronic pole changing-based induction motor control system according to claim 6 , wherein at least one rotational speed threshold value is greater than a synchronous rotational speed to which a fundamental frequency corresponds when the motor forms the pole-pair number which corresponds to the rotational speed threshold value, and other rotational speed threshold values equal the synchronous rotational speeds to which the fundamental frequency corresponds when the motor forms the pole-pair numbers which correspond to these rotational speed threshold values; an increased amplitude of said at least one rotational speed threshold value is set according to flux-weakening property of the motor.
9. The control method of the electronic pole changing-based induction motor control system according to claim 7 , wherein when the synchronous rotational speed of the motor increases to one of the rotational speed threshold values, the control unit alters the current directions or phase angles of at least part of the three-phase windings, making the pole-pair numbers formed by said N three-phase windings decrease; and
when the synchronous rotational speed of the motor decreases to one of the rotational speed threshold values, the control unit alters the current directions or phase angles of at least part of the three-phase windings, making the pole-pair numbers formed by said N three-phase windings increase.
10. The control method of the electronic pole changing-based induction motor control system according to claim 8 , wherein when the synchronous rotational speed of the motor increases to one of the rotational speed threshold values, the control unit alters the current directions or phase angles of at least part of the three-phase windings, making the pole-pair numbers formed by said N three-phase windings decrease; and
when the synchronous rotational speed of the motor decreases to one of the rotational speed threshold values, the control unit alters the current directions or phase angles of at least part of the three-phase windings, making the pole-pair numbers formed by said N three-phase windings increase.
11. The control method of the electronic pole changing-based induction motor control system according to claim 6 , wherein the inversion driving unit comprises three output ends, each three-phase winding comprises three sub-windings, and input ends of said three sub-windings are respectively connected with said three output ends of the inversion driving unit.
12. The control method of the electronic pole changing-based induction motor control system according to claim 6 , wherein said N three-phase windings form a NY structure or a NΔ structure or an aYbΔ structure, wherein both a and b are integers bigger than 1, and a+b=N.
13. The control method of the electronic pole changing-based induction motor control system according to claim 6 , wherein the inverter comprises one control unit which controls said N inversion driving units respectively; or the inverter comprises a plurality of control units, and each control unit controls one or more inversion driving units.
14. The control method of the electronic pole changing-based induction motor control system according to claim 6 , wherein the control unit is one or more of MCU, DSP, FPGA and CPLD.
15. The control method of the electronic pole changing-based induction motor control system according to claim 14 , wherein each said rotational speed threshold value equals a synchronous rotational speed to which a fundamental frequency corresponds when the motor forms the pole-pair number which corresponds to the rotational speed threshold value.
16. The control method of the electronic pole changing-based induction motor control system according to claim 14 , wherein at least one rotational speed threshold value is greater than a synchronous rotational speed to which a fundamental frequency corresponds when the motor forms the pole-pair number which corresponds to the rotational speed threshold value, and other rotational speed threshold values equal the synchronous rotational speeds to which the fundamental frequency corresponds when the motor forms the pole-pair numbers which correspond to these rotational speed threshold values; an increased amplitude of said at least one rotational speed threshold value is set according to flux-weakening property of the motor.
17. The control method of the electronic pole changing-based induction motor control system according to claim 14 , wherein when the synchronous rotational speed of the motor increases to one of the rotational speed threshold values, the control unit alters the current directions or phase angles of at least part of the three-phase windings, making the pole-pair numbers formed by said N three-phase windings decrease; and
when the synchronous rotational speed of the motor decreases to one of the rotational speed threshold values, the control unit alters the current directions or phase angles of at least part of the three-phase windings, making the pole-pair numbers formed by said N three-phase windings increase.