Motor Voltage Harmonic Correction via FFT Distortion Isolation
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Solution Overview
Problem
Existing motor control systems face challenges in effectively isolating and correcting harmonic distortions at low motor speeds due to the reduced difference between fundamental and distortion frequencies, leading to difficulties in filtering and maintaining performance.
Innovation Solution
A control system that includes a current sensing means, correction means, and current control means to generate a correction signal for voltage adjustments, using a synchronous filter to isolate distortion frequencies and operate in both high speed and low speed modes by transforming distortion signals into a DC component and adjusting voltage demands accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency filtering is used to isolate distortion components from fundamental current components, then measurement precision improves at high speeds, but filtering effectiveness deteriorates at low speeds due to reduced frequency separation
Solution Approach 1:
The patent transforms the distortion signal from the time domain to the frequency domain using Fast Fourier Transform (FFT), converting time-varying signals into frequency components. This parameter transformation allows precise identification and measurement of distortion components regardless of motor speed, as frequency domain analysis separates components by their spectral characteristics rather than temporal frequency separation.
Solution Approach 2:
The patent replaces the mechanical/analog frequency filtering approach with a digital signal processing approach using FFT and spectral analysis. Instead of relying on analog filters that require sufficient frequency separation, the system uses computational methods to identify, isolate, and measure distortion components based on their frequency signatures in the spectral domain.
2Stability of the object's composition
If voltage correction signals are applied to compensate for harmonic distortions, then torque output stability improves, but system complexity increases due to additional correction mechanisms
Solution Approach 1:
The patent implements a feedback mechanism where the measured distortion components are used to generate correction signals that are applied to the voltage commands. The system continuously monitors the current, identifies distortion through FFT analysis, calculates appropriate correction signals, and applies them in real-time to compensate for harmonic effects, creating a closed-loop control system that maintains torque stability.
Solution Approach 2:
The patent extracts only the necessary correction information from the full current signal by using FFT to identify specific distortion frequency components. Rather than processing the entire signal or applying complex multi-variable control, the system isolates and processes only the relevant harmonic distortion components for correction, simplifying the control approach while maintaining effectiveness.
Data Source
AI summary
A control system for an electric motor (10) comprises a current sensing means (14) arranged to produce a current sensing output indicative of electric current in the motor, current control means (20) arranged to receive a current demand and to control voltages applied to the motor, and correction means (26) arranged to receive the current sensing output and the current demand, and use them to generate a correction signal. The current control means (20) is arranged to receive the correction signal and to use the correction signal to correct the voltages applied to the motor.