PWM Base Frequency Dithering for Electric Powertrain Noise Reduction
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Solution Overview
Problem
Electric powertrains in electrified vehicles generate audible noise due to vibrations caused by fixed PWM frequencies, concentrating noise energy at specific sideband and harmonic frequencies, which existing technologies fail to effectively mitigate.
Innovation Solution
A controller is configured to dither the base frequency of a PWM signal by an amount based on the rotational speed of the electric machine, distributing energy across sidebands and harmonics to reduce audible vibrations, and toggle between DPWM and SVPWM modes to optimize the PWM spectrum and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a fixed PWM frequency is used to operate the inverter, then the control system is simple and stable, but audible noise and vibrations are generated due to concentrated energy at specific sideband and harmonic frequencies
Solution Approach 1:
The patent applies dynamics by varying the PWM switching frequency over time rather than using a fixed frequency. The controller dynamically adjusts the switching frequency within a range centered around a base frequency, causing the spectral energy to spread across multiple frequencies rather than concentrating at specific sidebands and harmonics. This dynamic frequency variation effectively reduces audible noise while maintaining acceptable control complexity through systematic frequency modulation.
2Object-generated harmful factors
If the PWM switching frequency is varied to reduce noise energy concentration, then audible vibrations are reduced, but the control system complexity increases
Solution Approach 1:
The patent implements periodic action by systematically varying the PWM switching frequency in a controlled manner. The frequency is modulated periodically around a base frequency with a defined variation range, creating a structured approach to noise reduction. This periodic frequency variation spreads the spectral energy distribution over time, reducing peak energy concentrations at specific sideband and harmonic frequencies, thereby diminishing audible vibrations while maintaining manageable control complexity through systematic modulation patterns.
3Object-generated harmful factors
If dithering is applied to the base frequency to distribute energy across sidebands, then noise amplitude at specific frequencies is reduced, but the control algorithm becomes more complex
Solution Approach 1:
The patent applies parameter changes by modifying the PWM switching frequency parameter dynamically. The controller varies the switching frequency within a defined range centered on a base frequency, changing this critical parameter to spread the spectral energy distribution. This frequency parameter modification effectively reduces the amplitude of noise energy at specific sideband and harmonic frequencies, while the control algorithm complexity is managed through systematic parameter variation rather than complex control logic.
Data Source
AI summary
A vehicle powertrain includes an inverter coupled with an electric machine and a controller. The controller may be configured to dither a base frequency of a pulse width modulated (PWM) signal, by less than an amount that is based on a rotational speed of the machine and the base frequency, to operate the inverter such that energy at sidebands and harmonics of the base frequency are reduced by distributing the energy to reduce audible vibrations of the powertrain.