PWM Control Pulse Timing Optimization for Electrical Machine EMC
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Solution Overview
Problem
Electrical machines with semiconductor switch-based power converters face challenges in electromagnetic compatibility (EMC) and noise generation due to the frequency spectra of alternating currents, which are not adequately addressed by existing technologies.
Innovation Solution
The method involves determining the frequency spectrum of alternating current components generated during pulse-width-modulated control of semiconductor switches and adjusting pulse durations to minimize the sum spectrum, thereby reducing alternating currents and improving EMC behavior and acoustics. This is achieved by shifting the phase positions of frequency spectra relative to each other, often by 180°, and dynamically optimizing pulse durations based on the clock frequency of the PWM control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse width modulated control is used to convert direct current into multiphase output current, then the electric motor can be driven with controlled current, but alternating current components are generated in the intermediate circuit causing EMC issues
Solution Approach 1:
The invention changes the timing parameters of the PWM control pulses specifically. By adjusting when pulses are generated and terminated across different phases, the alternating current components in the intermediate circuit are minimized. This parameter optimization resolves the contradiction by maintaining controlled current delivery while reducing harmful alternating current generation.
2Reliability
If semiconductor switches are switched over in clocked fashion between conducting and blocking states, then the motor current can be controlled, but alternating currents are generated that must undergo critical EMC assessment
Solution Approach 1:
The invention optimizes the timing parameters of the switching pulses. By carefully selecting when each phase's semiconductor switches are activated and deactivated, the alternating current components generated during switching are minimized. This maintains reliable motor current control while reducing the harmful alternating currents that require EMC assessment.
3Productivity
If conventional PWM control is used, then the electric machine can operate, but noise is generated and the EMC behavior is not optimized
Solution Approach 1:
The invention changes the temporal parameters of the PWM control signals. By optimizing the pulse generation and termination times across different phases, the alternating current components are minimized, which directly reduces noise generation and improves EMC behavior while maintaining normal machine operation.
Data Source
AI summary
A method for operating an electric machine with a power source, an electric motor, and an intermediary power converter, in which an input current of the power source is converted to a multi-phase output current for the electric motor by a pulse width modulated control of a number of semiconductor switches of the converter, wherein the or each pulse is generated at a first point in time and terminated after a pulse duration at a second point in time, in which for each alternating current component, which is generated in the course of the pulse-width-modulated driving of the semiconductor switches in an intermediate circuit of the power source, a frequency spectrum is determined, and in which the pulse durations of the pulses of the pulse width modulated control can be set such that the sum of the frequency spectra of the alternating current components is minimal.