Brushless doubly-fed motor control system

A method of controlling a motor driving a load at infinitely variable speeds between substantially zero speed and an upper speed limit while maintaining substantially synchronous operation at any such speed, the motor occasionally slipping from synchronous operation when the torque requirements of the load excessively exceed the driving torque of the motor, the method comprising the steps of:

• providing a motor having a brushless rotor unit without slip rings and with rotor windings, with the motor also having a stator unit with stator windings comprising first and second polyphase stator systems;
• applying power to the first stator system from an electric power grid at a system frequency of the grid;
• monitoring a parameter of the power received by the motor from the electric power grid and producing a motor power input signal corresponding to the monitored parameter;
• establishing a reference signal according to a desired motor operation strategy;
• generating excitation power at a controlled frequency and amplitude which are controlled in response to the monitored motor power input signal and the established reference signal;
• injecting the excitation power at the controlled frequency and amplitude into the second stator system to maintain substantially synchronous operation of the motor at any motor speed between substantially zero speed and the upper speed limit;
• maintaining motor operation in an induction mode while continuing to drive the load after the motor has slipped from synchronous operation by continuing to apply power to the first stator system from the electric power grid at the system frequency of the grid while ceasing to inject excitation power into the second stator system a frequency and amplitude required to maintain synchronous operation at the increased load torque which caused the motor to slip from synchronous operation;
• and
• pulling the motor into synchronous operation from the induction mode of operation by generating excitation power of the required frequency and amplitude for synchronous operation at the increased load torque.

A method of controlling an AC variable speed drive driving a load, the drive having a converter and a brushless doubly-fed motor with a rotor and a stator, the rotor having rotor windings without slip rings and the stator having stator windings comprising first and second polyphase stator systems, the first stator system of the drive receiving power from an electric power grid at a system frequency of the grid, the method comprising the steps of:

• sensing a parameter of the power received by the drive from the electric power grid and producing a power sensor signal corresponding to the sensed parameter;
• establishing a reference signal according to a desired motor operation strategy;
• controlling the drive by processing the power sensor signal and the established reference signal and generating a controller signal;
• converting power received from a converter power source with the converter in response to the controller signal to produce excitation power at an excitation frequency;
• and
• injecting the converted excitation power at the excitation frequency into the second stator system for operating the motor with a linear torque-speed characteristic at any motor speed between substantially zero speed and an upper speed limit of the motor.

An AC variable speed drive system which receives power from an electric power grid at a system frequency of the grid and drives a mechanical load, the system comprising:

• a brushless doubly-fed motor having a rotor and a stator, the rotor having rotor windings without slip rings and the stator having stator windings comprising first and second polyphase stator systems, with the first stator system receiving the power from the grid, and with the motor having an upper speed limit;
• sensor means for sensing a parameter of the power received by the drive system from the grid and producing a power sensor signal corresponding to the sensed parameter;
• reference means for establishing a reference signal according to a desired motor operation strategy;
• controller means for receiving and processing the power sensor signal and the reference signal and for generating a controller signal to operate the motor with a linear torque-speed characteristic;
• and
• converter means for receiving and converting power from a converter power source into excitation power having an excitation frequency in response to the controller signal, with the converter means coupled to inject the excitation power into the second stator system at the excitation frequency to operate the motor with the linear torque-speed characteristic at any speed between substantially zero speed and the upper speed limit.

A frequency source excitation power generator for generating excitation power at a required frequency and amplitude to excite a motor driving a load, the motor having a brushless rotor unit and a stator unit, the rotor unit having rotor windings without slip rings and the stator unit having stator windings comprising first and second polyphase stator systems, with the first stator system receiving power from an electric power grid at a system frequency of the grid, and the second stator system receiving the excitation power, the frequency source excitation power generator for use with a sensor for sensing a parameter of the power received by the motor from the grid and for producing a power sensor signal corresponding to the sensed parameter, the frequency source excitation power generator comprising:

• a controller comprising reference means for establishing a reference signal in accordance with a desired motor operation strategy, the controller for receiving and processing the power sensor signal with the reference signal and for producing a controlled frequency and amplitude signal to operate the motor with a linear torque-speed characteristic;
• and
• a converter for converting the power received from a converter power source into excitation power of variable frequency and amplitude in response to the controlled frequency and amplitude signal, and for injecting the excitation power into the second stator system to operate the motor with the linear torque-speed characteristic at a speed and torque required to drive the load according to the desired motor operation strategy.

A frequency source excitation power generator for generating excitation power at a required frequency and amplitude to excite a motor driving a load, the motor having a brushless rotor unit and a stator unit, the rotor unit having rotor windings without slip rings and the stator unit having stator windings comprising first and second polyphase stator systems, with the first stator system receiving power from an electric power grid at a system frequency of the grid, and the second stator system receiving the excitation power, the frequency source excitation power generator for use with a sensor for sensing a parameter of the power received by the motor from the grid and for producing a power sensor signal corresponding to the sensed parameter, the motor occasionally slipping from synchronous operation when the torque requirements of the load excessively exceed the driving torque of the motor, the frequency source excitation power generator comprising:

• a controller comprising reference means for establishing a reference signal in accordance with a desired motor operation strategy, the controller for receiving and processing the power sensor signal with the reference signal and for producing a controlled frequency and amplitude signal, the controller also including means for maintaining motor operation in an induction mode after the motor has slipped from synchronous operation by continuing to apply power to the first stator system from the electric power grid at the system frequency of the grid while ceasing to inject excitation power into the second stator system a frequency and amplitude required to maintain synchronous operation at the increased load torque which caused the motor to slip from synchronous operation, and with the controller further including means for pulling the motor into synchronous operation from the induction mode of operation by generating excitation power of the required frequency and amplitude for synchronous operation at the increased load torque;
• and
• a converter for converting the power received from a converter power source into excitation power of variable frequency and amplitude in response to the controlled frequency and amplitude signal, and for injecting the excitation power into the second stator system to maintain substantially synchronous operation of the motor at a speed and torque required to drive the load according to the desired motor operation strategy;
• wherein the controlled frequency and amplitude signal is produced in response to the means for maintaining motor operation in an induction mode and the means for pulling the motor into synchronous operation.

An AC variable speed drive controller for controlling an AC variable speed drive driving a load, the drive receiving power from an electric power grid at a system frequency of the grid, the drive comprising a brushless doubly-fed motor and a power electronic converter, the motor having a rotor and a stator unit, the rotor having rotor windings and the stator unit having stator windings comprising first and second polyphase stator systems, the motor having an upper speed limit, the power electronic converter receiving power from a converter power source and producing therefrom excitation power at an excitation frequency, the first stator system receiving power from the grid and the second stator system receiving the excitation power from the power electronic converter, the controller comprising:

• reference means for establishing a reference signal according to a desired motor operation strategy;
• and
• a processor for processing a power sensor signal and the reference signal, the power sensor signal produced by a power sensor which senses a parameter of the power received by the motor from the grid and produces the power sensor signal in response to the sensed parameter, the processor generating therefrom a controller signal for delivery to the power electronic converter which produces the excitation power at the excitation frequency in response to the controller signal, the processor generating the controller signal to drive the load according to the desired motor operation strategy irrespective of variations in the load by controlling the excitation power received by the second stator system of the motor to operate the motor with a linear torque-speed characteristic at any speed up to the upper speed limit.

An AC variable speed drive system which receives power from an electric power grid at a system frequency of the grid and drives a mechanical load, the system comprising:

• a brushless doubly-fed motor having a brushless rotor unit without slip rings and with rotor windings, and a stator with stator windings comprising first and second polyphase stator systems, the first stator system receiving the power from the grid;
• a sensor of a type which senses a parameter of the power received by the drive system from the grid and produces a power sensor signal corresponding to the sensed parameter;
• a reference device which establishes a reference signal according to a desired motor operation strategy;
• a controller for generating a controller signal in response to the power sensor signal and the reference signal to operate the motor with a linear torque-speed characteristic;
• and
• a converter for converting power from a converter power source in response to the controller signal to produce therefrom excitation power at an excitation frequency, with the converter coupled to the motor for injecting the excitation power into the second stator system at the excitation frequency for linear torque-speed characteristic motor operation.

A frequency source excitation power generator for generating excitation power at a required frequency and amplitude to excite a motor driving a load, the motor having a brushless rotor unit without slip rings and with rotor windings and a stator unit with stator windings comprising first and second polyphase stator systems, the first stator system receiving power from an electric power grid at a system frequency of the grid, and the second stator system receiving the excitation power, the frequency source excitation power generator for use with sensor means for sensing a parameter of the power received by the motor from the grid and for producing a power sensor signal corresponding to the sensed parameter, the frequency source excitation power generator comprising:

• a control device including a reference device of a type which establishes a reference signal in accordance with a desired motor operation strategy, with the control device receiving and processing the power sensor signal with the reference signal and producing therefrom a controlled frequency and amplitude signal to operate the motor with a linear torque-speed characteristic;
• and
• a converter of a type which converts the power received from a converter power source into excitation power of variable frequency and amplitude in response to the controlled frequency and amplitude signal, the converter being capable of being coupled to the motor to inject the excitation power into the second stator system for operating the motor with the linear torque-speed characteristic at a speed and torque required to drive the load according to the desired motor operation strategy.