Motor Control Unit PWM Switching Frequency Reduction
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Solution Overview
Problem
Motor control units for electric motors face challenges in reducing heat generation and switching losses in the drive circuit, which can increase the size of the control unit and affect efficiency.
Innovation Solution
A motor control unit with a switching frequency reducer that adjusts PWM counts for each phase within a current control period to minimize the number of switching events, thereby reducing heat generation and switching losses without altering the total PWM counts across phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the switching elements are controlled with high PWM frequency to improve motor control precision, then the motor control precision is improved, but the heat generation and switching losses increase
Solution Approach 1:
The patent combines multiple PWM periods into one current control period, allowing the controller to manage switching events across multiple PWM cycles. This merging approach reduces the total number of switching operations while maintaining the required control precision over the extended time window
Solution Approach 2:
The patent implements periodic switching reduction by strategically selecting which PWM periods within the current control period will have switching events. Instead of uniform high-frequency switching, the system uses periodic intervals with reduced switching activity, lowering overall switching losses while maintaining control effectiveness
2Temperature
If the number of switching events is reduced to lower heat generation, then the heat generation is reduced, but the motor control responsiveness may deteriorate
Solution Approach 1:
The patent dynamically adjusts the switching strategy based on the specific PWM period within the current control period. The controller selectively applies switching reduction to certain phases and PWM periods while maintaining higher switching activity in critical control moments, creating a dynamic balance between heat reduction and responsiveness
Solution Approach 2:
The patent changes the PWM count parameters strategically across different PWM periods within the current control period. By varying the PWM counts and switching timing parameters dynamically, the system maintains control responsiveness while reducing the total number of switching events and associated heat generation
3Power
If the PWM counts are increased to improve motor performance, then the motor performance is improved, but the heat generation from increased switching events increases
Solution Approach 1:
The patent segments the current control period into multiple PWM periods, allowing different PWM count strategies to be applied to different segments. High PWM counts are used when motor performance is critical, while lower switching activity is used in segments where performance requirements are lower, optimizing the balance between power delivery and heat generation
Data Source
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AI summary
A motor control unit (12) includes a PWM count calculator (46), a PWM count setter, and a PWM count changer. The PWM count calculator calculates first PWM counts of phases. Each first PWM count is calculated for a current control period (Ta). The PWM count setter sets the first PWM count of each phase as a second PWM count of a corresponding phase. The second PWM count is set for each of PWM periods (Tc) included in the current control period. The PWM count changer changes the second PWM count (Tc) of at least one of the phases, without changing the total of the second PWM counts of the at least one phase within the current control period (Ta), such that the number of times switching elements corresponding to the at least one phase are switched within the current control period is reduced.