Switching Frequency Modulation for Switched Reluctance Machine Ripple
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Solution Overview
Problem
Conventional SR machine control techniques result in inconsistent current ripple due to constant switching frequency, leading to undesirable machine behavior and increased power losses when attempting to mitigate these issues with higher frequencies.
Innovation Solution
A control system and method that modulates the switching frequency of SR machines based on rotor position and machine inductance, decreasing frequency with increasing inductance and increasing it with decreasing inductance, to reduce current ripple without significantly increasing overall switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching frequency is permanently increased to mitigate current ripple, then current ripple is reduced, but power loss of the electric drive increases significantly
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed switching frequency to a variable switching frequency that changes based on rotor position. The controller dynamically adjusts the switching frequency throughout the rotor's rotation cycle, using higher frequencies when current ripple is problematic and lower frequencies when it is acceptable, thereby resolving the contradiction between current ripple reduction and power loss minimization
Solution Approach 2:
The patent changes the parameter of switching frequency from a constant value to a variable value that depends on rotor position. By modulating the switching frequency according to the rotor's angular position, the system optimizes current ripple characteristics at different operational phases while minimizing overall power consumption, effectively resolving the technical contradiction
2Device complexity
If conventional constant switching frequency control is used, then device complexity is low, but current ripple becomes inconsistent leading to undesirable machine behavior
Solution Approach 1:
The patent implements feedback by using rotor position information (from sensors or sensorless estimation) to continuously adjust the switching frequency. The controller receives feedback about the rotor's angular position and uses this information to modulate the switching frequency accordingly, ensuring consistent current delivery while maintaining relatively simple system architecture
Solution Approach 2:
The patent makes the control system multi-functional by having the same controller perform both standard motor control functions and the additional function of adaptive switching frequency modulation based on rotor position. This universal approach improves current consistency without requiring separate dedicated hardware for each function, thereby managing complexity effectively
Data Source
AI summary
A control system (128) for controlling a switched reluctance (SR) machine (110) having a rotor (116) and a stator (118) is provided. The control system (128) may include a converter circuit (122) operatively coupled to the stator (118) and including a plurality of switches (132) in selective communication with each phase of the stator (118) and a controller (130) in communication with each of the stator (118) and the converter circuit (122). The controller (130) may be configured to determine a position of the rotor (116) relative to the stator (118), and generate a modulated switching frequency (152) based on the rotor position.