Voltage Control Using Moving Average PWM for Torque Ripple
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Solution Overview
Problem
The PWM waveform used in rotating electric machines leads to inefficiencies, increased striking current, and torque ripple due to its harmonic effects on magnetic flux and torque production.
Innovation Solution
A voltage control device and method that utilize a moving average of output voltages to smooth the magnetic flux in alternating-current rotating electric machines, achieved by comparing the moving average value with the instantaneous value of a sinusoidal modulation wave to generate control pulses for switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If PWM waveform is used for voltage control, then voltage generation is achieved, but magnetic flux oscillation causes torque ripple and striking current
Solution Approach 1:
The patent introduces a moving average filter as an intermediary between the PWM voltage command and the actual voltage output. This filter processes the voltage command to eliminate high-frequency oscillations before they reach the inverter, thereby reducing torque ripple and striking current while maintaining effective voltage control
Solution Approach 2:
The patent changes the parameter of voltage command by applying a moving average operation that transforms the raw PWM voltage signal into a smoothed voltage command. This parameter transformation eliminates harmful high-frequency components while preserving the essential control functionality
2Power
If triangular wave comparison PWM is used, then voltage waveform is generated, but waveform distortion occurs in inverter output
Solution Approach 1:
The moving average filter serves as an intermediary processing stage that refines the voltage command waveform before it is applied to the inverter. This intermediary step removes distortion-causing high-frequency components while maintaining the fundamental voltage waveform needed for motor control
3Speed
If instantaneous voltage control is applied, then response speed is fast, but magnetic flux oscillation increases
Solution Approach 1:
The patent implements a dynamic balance between fast response and stability by using a moving average filter with an appropriately selected time constant. This dynamic parameter allows the system to respond quickly to changes in load and speed requirements while simultaneously filtering out high-frequency oscillations that cause magnetic flux instability
Solution Approach 2:
The moving average time constant is optimized to achieve the right balance between response speed and magnetic flux stability. By carefully selecting this parameter, the system maintains fast dynamic response while effectively suppressing magnetic flux oscillations
Data Source
AI summary
A voltage control device that controls an output voltage by turning on/off a switching element by a control pulse, the voltage control device including a modulation wave generation unit that generates a sinusoidal wave based on a driving voltage and a driving frequency as a modulation wave, an arithmetic unit that calculates, at any discrete time point [t], a moving average value of a voltage [v] output every time duration [δ] smaller than a time cycle of the modulation wave in a time period [t−Nδ to t−δ] tracing back N (a positive integer) steps from the discrete time point [t] in accordance with Expression (1) below, and a control pulse generation unit that generates the control pulse in accordance with a result of a comparison between the moving average value and an instantaneous value of the modulation wave at the discrete time point [t].[Expression 1]∑ i=1Nv(t-iδ)N(1)