Power Conversion Device Carrier Wave Frequency Control
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Solution Overview
Problem
Conventional power conversion devices experience unnecessary switching loss and voltage ripples due to mode-switching control during high-speed restarts, particularly when transitioning from asynchronous bipolar modulation mode to asynchronous overmodulation mode, leading to increased switching frequency and loss.
Innovation Solution
A power conversion device that generates a first carrier wave with a higher frequency and a second carrier wave with a lower frequency, using a switching signal based on the comparison between the two waves, and adjusts the carrier wave output depending on the modulation factor, stopping switching operations during periods where the modulation wave is greater than the carrier wave in overmodulation mode to minimize switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a higher carrier-wave frequency is set in advance to suppress voltage ripples during overmodulation mode, then the voltage ripple is reduced, but the switching frequency increases unnecessarily leading to increased switching loss
Solution Approach 1:
The patent applies dynamics by making the carrier-wave frequency changeable rather than fixed. The carrier-wave frequency is dynamically adjusted based on the modulation factor: a higher frequency is used when the modulation factor is high (overmodulation mode) to suppress voltage ripples, while a lower frequency is used when the modulation factor is low (normal mode) to reduce switching losses. This dynamic adaptation resolves the contradiction between suppressing ripples and minimizing energy loss.
Solution Approach 2:
The patent changes the parameter of carrier-wave frequency based on the modulation factor. By monitoring the modulation factor and adjusting the carrier-wave frequency accordingly, the system optimizes performance across different operating conditions. This parameter change allows the system to suppress voltage ripples only when necessary (high modulation factor) while maintaining lower switching frequencies during normal operation, thus resolving the technical contradiction.
2Power
If mode switching is executed from asynchronous bipolar modulation mode to asynchronous overmodulation mode during high-speed restart, then the output voltage is increased, but voltage ripples occur due to switching stop during overmodulation mode
Solution Approach 1:
The patent uses dynamics by adjusting the carrier-wave frequency in response to changing operating conditions. During high-speed restart when overmodulation mode is activated, the carrier-wave frequency is increased to maintain sufficient voltage pulses even during switching stop periods, thereby suppressing voltage ripples while still achieving the required output voltage increase.
Solution Approach 2:
The patent changes the carrier-wave frequency parameter based on the modulation factor and operating mode. When transitioning to overmodulation mode during high-speed restart, the system increases the carrier-wave frequency to compensate for the reduced number of voltage pulses, thus suppressing voltage ripples while maintaining the necessary output voltage level.
Data Source
AI summary
To include a carrier-wave generation unit to generate a first carrier wave with a frequency higher than a modulation wave, and a second carrier wave with a frequency lower than the first carrier wave, a comparison unit to compare either the first carrier wave or the second carrier wave to the modulation wave in order to generate a switching signal. The carrier-wave generation unit outputs the second carrier wave when a modulation factor is lower than a threshold value, and outputs the first carrier wave when the modulation factor is equal to or higher than the threshold value. When the modulation factor is equal to or higher than the threshold value, a power conversion unit operates in an overmodulation mode, in which the switching operation is stopped during a period longer than one cycle of the second carrier wave.