Noise-Shaped Random PWM for Power Converters
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Solution Overview
Problem
Variable speed generators produce tonal noise and electromagnetic interference due to concentrated harmonic peaks in power output signals, which violate noise regulations and degrade converter performance, and conventional random PWM introduces negative effects like undesired current and torque signals.
Innovation Solution
Implementing noise-shaped random pulse width modulation (PWM) by filtering a substantially random distribution of timing values to produce modified PWM timing signals, which are delivered to power converters, effectively mitigating low-frequency distortion and electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional random PWM is used to distribute spectral energy, then tonal noise is reduced, but low-frequency distortion and electromagnetic interference are introduced
Solution Approach 1:
The patent modifies the parameters of random PWM by applying filtering operations to the timing values. A low-pass filter is applied to attenuate high-frequency spectral components, while a high-pass filter removes low-frequency distortion. This parameter modification transforms conventional random PWM into noise-shaped random PWM, resolving the contradiction by eliminating both tonal noise and electromagnetic interference through controlled spectral shaping.
Solution Approach 2:
The patent introduces filtering operations as intermediary elements between the random PWM generation and the power converter. These filters act as mediators that selectively attenuate harmful frequency components (both high-frequency EMI and low-frequency distortion) while preserving the beneficial noise-shaping effect, thus resolving the contradiction without eliminating the random PWM mechanism itself.
2Device complexity
If constant switching frequency is used in power converters, then control is simplified, but harmonic peaks and tonal noise are produced
Solution Approach 1:
The patent transitions from constant switching frequency to dynamic variable switching frequency by implementing random PWM with filtered timing values. The switching frequency becomes a random variable within a specified range, distributed according to a filtered probability density function. This dynamic approach eliminates fixed harmonic peaks while maintaining manageable control complexity through systematic filter design.
3Object-affected harmful factors
If random PWM is applied to power converters, then spectral energy is distributed, but low-frequency distortion occurs
Solution Approach 1:
The patent modifies the spectral distribution parameters of random PWM by applying high-pass filtering to the timing values. This filtering operation removes or attenuates low-frequency components from the spectral distribution, thereby eliminating low-frequency distortion while preserving the beneficial effect of distributing spectral energy across a broader frequency range.
Data Source
AI summary
A power generation system, wind turbine, and method of pulse width modulation (PWM) for power converters are disclosed. The method generally includes generating a substantially random distribution of timing values, applying a filter to the random distribution to produce a modified random distribution, and delivering PWM timing signals based on the modified random distribution to the power converters.