Motor PWM Switching Frequency Randomization for EMI and Noise
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Solution Overview
Problem
Existing motor control systems using constant frequency pulse-width modulation (PWM) generate significant amplitudes at particular frequencies, leading to undesirable electromagnetic disturbances and audible noises.
Innovation Solution
Implement a controller circuit that uses a random number generator to vary the switching frequency, eliminating the need for predetermined look-up tables and generating a set of bits to determine the switching frequency, thereby reducing these disturbances and noises.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If constant frequency PWM is used for motor control, then the motor operation is simple and stable, but significant amplitudes at particular frequencies cause electromagnetic disturbances and audible noises
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant switching frequency to a dynamic variable switching frequency. The controller circuit randomly varies the switching frequency around a nominal value, which eliminates the fixed spectral components that cause electromagnetic disturbances and audible noises while maintaining effective motor control
Solution Approach 2:
The patent implements parameter changes by modifying the switching frequency parameter from a fixed constant to a randomly varying value. This change in the frequency parameter distribution spreads the spectral energy across a broader range, reducing peak amplitudes and mitigating harmful electromagnetic emissions and audible noise
2Object-affected harmful factors
If a random number generator is used to vary switching frequency, then electromagnetic interference and audible noise are reduced, but the device complexity increases
Solution Approach 1:
The patent replaces what would traditionally require complex hardware modifications with a software-based random number generator implementation. This substitution achieves frequency variation and electromagnetic interference reduction through algorithmic control rather than mechanical or complex electrical circuit changes
Solution Approach 2:
The controller circuit generates its own random frequency variation signals using an integrated random number generator, eliminating the need for external frequency modulation hardware. The system serves itself by producing the necessary frequency diversity internally through software or firmware implementation
Data Source
AI summary
A controller circuit is configured to generate, using a random number generator, a set of bits and determine a switching frequency using the set of bits. The controller circuit is further configured to control a switching circuit to switch at the switching frequency to drive a motor.