AC Motor Inverter Control for Torque Pulsation Reduction
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Solution Overview
Problem
Existing AC motor control techniques fail to effectively reduce torque pulsation caused by harmonic currents, as they either fix the harmonic voltage phase or lose half-wave symmetry, leading to generation of even-ordered harmonic voltages and currents that contribute to torque pulsation.
Innovation Solution
A control device for an AC motor that includes an inverter with switching control means to achieve half-wave symmetry in the voltage waveform centered on a fundamental voltage phase of 180 degrees ±180 degrees, allowing the harmonic voltage phase to vary based on the fundamental voltage-rotor phase difference and having harmonic voltage amplitudes inversely proportional to their order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the voltage waveform of the inverter has symmetry with both fundamental voltage phase and harmonic voltage phase fixed to zero, then harmonic current is minimized, but the harmonic current phase cannot be offset-adjusted to avoid torque pulsation
Solution Approach 1:
The patent applies asymmetry by intentionally breaking the half-wave symmetry of the voltage waveform around the fundamental voltage phase of 180 degrees. By making the switching patterns asymmetric in this specific interval while maintaining symmetry elsewhere, the invention enables harmonic voltage phase to become variable and offset-adjustable, allowing the harmonic current phase to be shifted away from the torque axis to reduce torque pulsation.
2Adaptability or versatility
If half-wave symmetry is lost to enable harmonic current phase offset adjustment, then even-ordered harmonic voltages and currents are generated causing torque pulsation
Solution Approach 1:
The patent applies local quality by selectively maintaining half-wave symmetry in specific intervals (centered on fundamental voltage phase of 180 degrees ±180 degrees) while breaking it in other intervals. This localized approach allows the system to generate variable harmonic voltage phases for torque pulsation reduction without generating even-ordered harmonics, as the symmetry is preserved where it prevents even-ordered harmonic generation.
Data Source
AI summary
Provided is a control device of an AC motor, including: an inverter including a switching element; switching control means for controlling the switching element; and phase detection means for detecting a rotor phase of an AC motor, wherein the switching control means controls the switching element so that a voltage waveform of the inverter has half-wave symmetry in an interval of a width centering on a fundamental voltage phase of 180 deg±180 deg, the switching control means controls the switching element so that a harmonic voltage phase of the inverter becomes variable on the basis of a fundamental voltage-rotor phase difference which is a difference between a fundamental voltage phase and the rotor phase of the AC motor, and the switching control means controls the switching element so that a harmonic voltage amplitude of each order of the inverter is inversely proportional to the order.