AC Motor Controller Overmodulation Harmonic Switching
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Solution Overview
Problem
The overmodulation PWM control for AC motors experiences instability due to non-uniform voltage amplitude compensation and significant changes in switching frequency, leading to discontinuous output voltage and potential control instability, especially when transitioning near change points in voltage command amplitude.
Innovation Solution
A control device for AC motors that includes a harmonic determining unit, which switches between control modes with and without three-order harmonic superimposition based on predetermined change points and transition degrees, stabilizing the control by adjusting the amplitude of the three-order harmonic component and synchronizing the phase voltage command with the carrier wave, thereby maintaining stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If voltage amplitude compensation is performed in overmodulation PWM control to increase the amplitude of phase voltage command beyond carrier amplitude, then the fundamental voltage amplitude can be increased to cope with high power requirements, but the correction rate changes non-uniformly causing switching frequency changes and output voltage discontinuity
Solution Approach 1:
The patent applies preliminary action by detecting the approach to change points in voltage amplitude characteristics before they occur, and proactively switching between different amplitude characteristics (with/without three-order harmonic) to prevent the harmful effects of passing through change points. This advance detection and switching mechanism resolves the contradiction by preparing the control system in advance to maintain stability while achieving high voltage amplitude.
2Power
If the amplitude of phase voltage command is increased linearly, then the required voltage amplitude is achieved, but the fundamental voltage amplitude does not increase linearly due to non-uniform correction rate
Solution Approach 1:
The patent applies dynamics by dynamically switching between different amplitude characteristics based on the detected voltage command amplitude. Instead of using a fixed linear compensation method, the system adaptively selects between characteristics with and without three-order harmonic superimposition, allowing the correction rate to adjust dynamically and maintain linear relationship between required and fundamental voltage amplitudes across different operating ranges.
3Adaptability or versatility
If three-order harmonic is superimposed on phase voltage command, then the voltage amplitude characteristics change, but switching between control modes with and without harmonic causes instability near change points
Solution Approach 1:
The patent applies feedback by continuously detecting the voltage command amplitude and comparing it with predetermined change points, then using this feedback information to determine when to switch between control modes with and without three-order harmonic superimposition. This closed-loop feedback mechanism ensures stable transitions by switching based on actual operating conditions rather than fixed thresholds, resolving the contradiction between adaptability and stability.
Data Source
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AI summary
An overmodulation PWM control unit (200) includes a voltage amplitude calculating unit (245) for calculating a voltage command amplitude VA of an original voltage command (Vd#, Vq#) based on current feedback control, a voltage amplitude correcting unit (270) for performing linear compensation on the voltage command amplitude so that a fundamental amplitude of a pulse width modulation voltage provided from an inverter (14) may match the original voltage command amplitude (VA), and a harmonic determining unit (300) for determining presence or absence of superimposition of a three-order harmonic component on a phase voltage command. The harmonic determining unit (300) performs switching between presence and absence of the three-order harmonic component based on transition of the original voltage command amplitude (VA) to avoid passing through a change point where discontinuity occurs in the voltage amplitude characteristics representing a relationship between a fundamental amplitude obtained in advance for each of the cases of presence and absence of the superimposition of the three-order harmonic component and the voltage command amplitude required for achieving the fundamental amplitude.