Power Converter Neutral Point Voltage Control for Torque Ripple Reduction
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Solution Overview
Problem
Conventional power converters for electric motors with multiple winding groups experience torque ripple, vibration, and sound issues due to uneven heat generation among switching elements, which is not effectively addressed by existing technologies.
Innovation Solution
A power converter system with two inverters and a controller that calculates and adjusts voltage instruction values for each winding group to alternate between shifting neutral point voltages above and below the center-of-output value, with a variable switch period based on motor rotation speed to reduce heat unevenness and torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the shift direction of the duty instruction signal is switched at preset intervals to distribute heat generation, then heat distribution among winding groups is improved, but torque ripple and vibration increase
Solution Approach 1:
The patent applies periodic action by switching between first and second neutral point voltage shift patterns at calculated intervals. The controller alternates between shifting the first neutral point voltage upward with the second downward, and vice versa, creating a periodic action that distributes heat generation over time while maintaining smooth torque output.
Solution Approach 2:
The patent changes the neutral point voltage shift direction parameter based on accumulated heat generation amounts. When the heat generation difference between winding groups exceeds a threshold, the controller switches the voltage shift pattern, effectively using parameter changes to balance thermal distribution without causing torque ripple.
2Temperature
If neutral point voltages are shifted to distribute heat, then heat generation unevenness is reduced, but switching frequency and potential torque ripple increase
Solution Approach 1:
The patent employs feedback by calculating the accumulated heat generation amount for each winding group and comparing the difference against a predetermined threshold. This feedback mechanism determines when to switch between voltage shift patterns, ensuring heat distribution is optimized while maintaining smooth switching operations.
Solution Approach 2:
The patent makes the switching between voltage shift patterns dynamic by calculating switch timing based on actual heat generation accumulation rather than fixed intervals. The switch period is adaptively determined based on operating conditions, allowing the system to respond dynamically to thermal states while maintaining operational smoothness.
Data Source
AI summary
A power converter a controller that includes an instruction calculator calculating a first voltage instruction value that is applied to a first winding group, for example. An application voltage to the first winding group is controlled, for example, in a first period so that a first neutral point voltage shifts below a center-of-output value of an outputtable range is outputted, and a second neutral point voltage shifts above the center-of-output value of the outputtable range. The instruction calculator calculates the first instruction value for enabling a switching between the periods, after a lapse of a switch period that is variably calculated based on a preset physical quantity. In such manner, a ripple of a torque or an electric current accompanying the switching between the periods is reduced.