Power Converter Over-Modulation Control for Narrow Pulse Suppression
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Solution Overview
Problem
Conventional power converters experience narrow pulse occurrences and induction failures due to high carrier wave frequencies, even when the modulation factor is lower than π/4, leading to voltage vibration and potential failures.
Innovation Solution
A power converter design that includes a switching element and a control unit capable of generating a modulated wave synchronized with an output voltage command and a carrier wave with a higher frequency, where the power conversion unit operates in an over-modulation mode by stopping switching for a period longer than one cycle of the carrier wave when the modulation factor is between π/4 and the mode switching modulation factor, specifically in the first period including the positive peak value of the output voltage command.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the carrier wave frequency is increased to improve power converter performance, then the output voltage increases, but narrow pulses occur and induction failures are likely to happen
Solution Approach 1:
The invention changes the modulation factor parameter to trigger over-modulation mode when the modulation factor is equal to or higher than π/4. This parameter change suppresses narrow pulse occurrence by adjusting the relationship between modulated wave amplitude and carrier wave, thereby preventing induction failures while maintaining high output voltage capability
Solution Approach 2:
The invention dynamically switches between asynchronous PWM mode and synchronous PWM mode based on output frequency and modulation factor. By transitioning to synchronous mode with over-modulation control when conditions are met, the system adaptively prevents narrow pulses while maintaining high carrier frequency benefits
2Power
If the modulation factor is increased to maximize output voltage, then the output voltage command is optimized, but narrow pulses occur around peak values
Solution Approach 1:
The invention uses the modulation factor as a trigger parameter, switching to over-modulation mode when modulation factor ≥ π/4. This parameter-based control prevents narrow pulses around peak values by ensuring the modulated wave amplitude relationship with carrier wave is properly maintained, while still achieving maximum output voltage command effectiveness
3Device complexity
If asynchronous PWM mode is used to simplify control, then the carrier wave frequency can be increased, but narrow pulses occur even when modulation factor is lower than π/4
Solution Approach 1:
The invention dynamically transitions from asynchronous PWM mode to synchronous PWM mode with over-modulation control when the modulation factor reaches π/4. This dynamic mode switching maintains control simplicity at low frequencies while preventing narrow pulses at high frequencies, resolving the contradiction between control simplicity and narrow pulse suppression
Data Source
AI summary
A power converter includes a control unit that generates a modulated wave synchronized with an output voltage command and a carrier wave having a frequency higher than a frequency of the modulated wave, the control unit controlling the power converter by comparing the modulated wave and the carrier wave to output a switching signal for driving a switching element. When a modulation factor in converting DC power into AC power is equal to or higher than a mode switching modulation factor and is lower than π/4, the power converter converts the DC power into the AC power in an over-modulation mode, in which switching of the switching element is stopped for a period longer than one cycle of the carrier wave, in a first period in which an output voltage command is positive and timing of a positive peak value of the output voltage command is included.