Electric Motor Control Device Reducing Magnetic Noise via Asynchronous PWM
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Solution Overview
Problem
Existing control methods for electric motors in electric vehicles face issues with harsh magnetic noise and vibration due to harmonic components, particularly during switching between different pulse modes, which affects the continuity of output voltage control and increases harmonic-induced vibration.
Innovation Solution
A control device and method that generates PWM signals by superimposing a third harmonic on the fundamental sine wave frequency, using an asynchronous carrier signal with a frequency independent of the inverter output, to reduce magnetic noise and vibration, and employs wide band gap semiconductors for the switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple control modes (PWM, asynchronous overmodulation, one-pulse) are used with mode switching control, then the output voltage control can be achieved across different operating regions, but harsh magnetic noise occurs during switching between modes
Solution Approach 1:
The patent extracts and eliminates the mode switching control mechanism that causes magnetic noise. By using only asynchronous PWM control without switching to other modes, the harmful switching transitions are removed while maintaining output voltage control capability through the asynchronous PWM strategy across all operating regions.
Solution Approach 2:
The asynchronous PWM control method is designed to handle all operating regions universally without requiring mode switching. The control strategy adapts to different voltage and frequency requirements within the asynchronous PWM framework, making it multi-functional across the entire operating range.
2Device complexity
If one-pulse mode is used in high speed range, then the control can be simplified, but vibration caused by harmonic component increases
Solution Approach 1:
The patent maintains continuous asynchronous PWM control action across all speed ranges including high speed range, avoiding discontinuous one-pulse mode. This continuous control action reduces harmonic components and vibration while keeping the control system relatively simple through the unified asynchronous PWM approach.
3Adaptability or versatility
If mode switching control is implemented, then different control strategies can be applied to different regions, but the output voltage control is not completely continuous
Solution Approach 1:
The patent removes the mode switching control structure that disrupts output voltage continuity. By maintaining a single asynchronous PWM control mode without switching to other strategies, the output voltage control becomes completely continuous while still adapting to different operating regions through the asynchronous PWM parameters.
Data Source
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AI summary
There is provided a control device for an electric motor that controls the operation of the electric motor by outputting PWM signals to switching elements included in an inverter. The control device for the electric motor includes a voltage-command generating unit 21 configured to generate, as voltage commands Vu*, Vv*, and Vw*, a superimposed wave signal obtained by superimposing, on a sine wave having an inverter output frequency FINV as a fundamental frequency, a third harmonic of the sine wave and a PWM-signal generating unit 23 configured to generate PWM signals U, V, W, X, Y, and Z by comparing the amplitudes of the voltage commands output by the voltage-command generating unit 21 and the amplitude of a carrier signal CAR.