AC Motor Direct Torque Control With Fixed Switching Frequency
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Solution Overview
Problem
Conventional direct torque control methods for alternating current motors suffer from variable switching frequencies and high harmonic content, limiting their application scope.
Innovation Solution
A method and apparatus for direct torque control that utilizes single-boundary hysteresis comparison and zero vector insertion on fixed polygonal stator flux linkage trajectories to achieve fixed switching frequency and reduced harmonics, ensuring three-phase, half-wave, and quarter-symmetry of output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If voltage and frequency of power supplied to motor are increased to improve output power, then output power is improved, but magnetic core loss increases and efficiency deteriorates at light load
Solution Approach 1:
The patent implements dynamic voltage and frequency adjustment based on actual load conditions. The control system continuously monitors motor operating state and adaptively modifies power supply parameters, transitioning from static to dynamic control. This resolves the contradiction by ensuring high power output when needed while minimizing magnetic core loss during light load operation through real-time parameter optimization.
Solution Approach 2:
The patent changes the operating parameters (voltage and frequency) of the motor based on load requirements. By adjusting these parameters dynamically rather than maintaining fixed high values, the system achieves high output power when required while reducing magnetic core loss during light load conditions, thus resolving the energy efficiency contradiction.
2Device complexity
If conventional PWM control or V/f control is used to simplify control structure, then control structure is simplified, but torque ripple and acoustic noise increase
Solution Approach 1:
The patent employs feedback mechanisms where the control system continuously monitors motor current, position, and operating state, then adjusts control parameters accordingly. This closed-loop feedback approach maintains simple overall control structure while effectively suppressing torque ripple and acoustic noise through real-time compensation, resolving the contradiction between simplicity and performance.
Solution Approach 2:
The control system dynamically adjusts switching patterns and pulse widths based on actual motor state rather than using fixed conventional PWM patterns. This dynamic adaptation maintains structural simplicity while reducing torque ripple and noise by optimizing control actions in real-time according to load conditions and motor response.
3Speed
If high frequency switching is used in PWM control to improve response speed, then response speed is improved, but switching loss increases and efficiency decreases
Solution Approach 1:
The patent implements dynamic switching frequency adjustment rather than using fixed high-frequency switching. The control system adapts switching frequency to actual load conditions and motor state, using higher frequencies when rapid response is needed and lower frequencies during steady-state operation. This resolves the contradiction by achieving fast response when required while minimizing switching losses during normal operation.
Solution Approach 2:
The control system uses periodic modulation with variable period characteristics, adjusting the switching pattern based on operational requirements. This allows high response speed during transient conditions while reducing switching frequency during steady-state to minimize losses, effectively resolving the speed-loss contradiction through intelligent periodic control.
Data Source
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AI summary
A direct torque control method and apparatus for an alternating current motor, an electronic device, and a computer-readable storage medium. The method comprises: obtaining an actual position of a stator flux linkage of the alternating current motor running on a stator flux linkage trajectory; when the actual position is a preset position on any side of the stator flux linkage trajectory, outputting a pulse signal corresponding to a zero vector to control the operation of an inverter, and obtaining a feedback torque of the alternating current motor; determining whether the feedback torque satisfies a preset condition; and if yes, determining a current effective voltage vector according to the actual position, and outputting a pulse signal corresponding to the current effective voltage vector to control the operation of the inverter. The present application can meet the requirements of three-phase symmetry, half-wave symmetry, and quarter symmetry of an output voltage, reduce harmonics of the output voltage, realize direct torque control at a fixed switching frequency, optimize pulse output, and has a wide range of applications.