Switched Reluctance Motor Switch Thermal Stress Reduction
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Solution Overview
Problem
Existing control schemes for switched reluctance motors, particularly during low-speed motoring modes, subject switches to significant thermal stress, leading to premature failures and reduced efficiency in electric drive systems.
Innovation Solution
A method and system that engage a distributed soft chopping routine by alternating PWM signals for both switches of each phase, ensuring at least one switch is always closed and preventing simultaneous opening, thereby distributing thermal stress and prolonging switch and system life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a soft chopping routine is used on one switch of each phase during low-speed motoring mode, then torque output is improved, but thermal stress on the switch increases leading to premature failure
Solution Approach 1:
The patent divides the switching task between two switches (first and second switches) in each phase leg. Instead of relying on a single switch for soft chopping, the control routine alternates between both switches, distributing the thermal stress and operational burden across multiple components. This segmentation prevents any single switch from bearing excessive stress while maintaining the required torque output at low speeds.
Solution Approach 2:
The patent implements periodic alternation between the first and second switches during soft chopping operations. The control routine systematically switches between using the first switch and the second switch in alternating cycles, ensuring that thermal stress is distributed periodically rather than concentrated on one component. This periodic distribution extends switch life while maintaining continuous torque production.
2Power
If hard chopping current is used during nominal speed operation, then power output is improved, but thermal stress on both switches increases simultaneously
Solution Approach 1:
During hard chopping operations at nominal speeds, the patent segments the current chopping function between the first and second switches. By alternating which switch performs the hard chopping action in each cycle, the thermal load is divided between both switches rather than both experiencing maximum stress simultaneously. This maintains power output while reducing peak thermal stress on individual components.
3Speed
If single pulse mode is used during high-speed operation, then speed response is improved, but control complexity increases
Solution Approach 1:
The patent implements a dynamic control strategy that adapts the switching routine based on operating conditions. At high speeds, the system dynamically selects single pulse mode for improved speed response, while at low speeds it transitions to distributed soft chopping for reduced thermal stress. This dynamic adaptation allows the system to optimize for speed response when needed while managing thermal concerns during high-torque operations.
Data Source
AI summary
A method of controlling a motor is provided. The method may determine a speed of the motor, and engage a soft chopping routine on a first switch and a second switch of each phase if the motor speed is relatively low. The first switch may be driven by a first pulse width modulated PWM signal and the second switch being driven by a second PWM signal. The first and second PWM signals may be alternatingly configured such that at least one of the first switch and the second switch is closed at any point during the distributed soft chopping routine and both the first switch and the second switch are never simultaneously open.