Sensorless Switched Reluctance Motor Control via Freewheeling
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Solution Overview
Problem
Switched reluctance motors face limitations due to the need for position sensors, which reduce reliability, increase costs, and limit applicability, especially in environments where sensor mounting is not feasible, and existing sensorless control methods suffer from error accumulation and limited universality due to model dependency and complex data acquisition.
Innovation Solution
A position sensorless step-wise freewheeling control method that detects the rotor position at the start of minimum phase inductance by switching the main switch's upper and lower tubes in the power converter, entering DC negative voltage forced freewheeling and zero voltage natural freewheeling states based on winding current thresholds, allowing direct determination of the switch-on position without external sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position sensors are used in switched reluctance motors, then rotor position detection accuracy is improved, but motor reliability is reduced and system complexity increases
Solution Approach 1:
The patent extracts and eliminates the position sensor component from the switched reluctance motor system. By using the existing power converter switches and diodes to create forced freewheeling states, the system can detect rotor position through current characteristics without requiring additional sensors, thereby improving reliability while maintaining position detection accuracy
Solution Approach 2:
The patent makes the power converter circuit serve dual functions: both power switching and position sensing. The existing switches and diodes in the power converter are utilized to create freewheeling paths that enable position detection, allowing the circuit to serve itself rather than requiring separate dedicated sensing hardware
2Measurement precision
If position sensors are installed in switched reluctance motors, then rotor position can be detected, but motor cost and system complexity increase
Solution Approach 1:
The patent makes the power converter components perform multiple functions. The switches and diodes that are already present in the power converter are used both for their primary power conversion function and for creating freewheeling paths that enable position detection, eliminating the need for separate sensing circuitry and reducing overall system complexity
Solution Approach 2:
The patent removes the position sensor component entirely from the system. By extracting this unnecessary component and using only the existing power converter elements for position detection, the system complexity and cost are reduced while maintaining the capability to detect rotor position
3Reliability
If model-based sensorless control methods are used, then position detection can be achieved without sensors, but error accumulation occurs and position detection accuracy degrades
Solution Approach 1:
The patent replaces complex computational modeling with a simpler electrical characteristic-based detection method. Instead of using neural networks or lookup tables that require extensive computation and are prone to error accumulation, the system uses the natural current characteristics during forced freewheeling states to directly determine rotor position, reducing computational complexity and improving accuracy
Solution Approach 2:
The patent implements a feedback mechanism where the phase current characteristics during forced freewheeling are continuously monitored. By detecting the current rise and fall patterns that occur during the freewheeling intervals, the system obtains real-time rotor position information without relying on pre-built models, thereby avoiding error accumulation from model aging or inaccuracies
4Measurement precision
If phase current gradient method is used to detect rotor position, then minimum inductance position can be obtained, but the method is not suitable for phase current chopping control and speed adjustment range is reduced
Solution Approach 1:
The patent uses a dynamic control approach where the switching states are actively manipulated to create forced freewheeling conditions. By dynamically controlling the switches and diodes to force current through specific paths during freewheeling intervals, the system can adapt to different operating conditions including chopping control and various speed ranges, unlike static gradient-based methods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances real-time performance, dynamic response, and stability, eliminating the need for additional hardware and flux linkage data storage, enabling broader application and improved reliability of switched reluctance motor systems.
Implementation Method 1
a power converter composed of main switch and diodes
Data Source
AI summary
A position sensorless step-wise freewheeling control method for a switched reluctance motor having dual switched-mode power converters for each phase doesn't require any additional external hardware, any rotor-position sensor, or storage of flux linkage data of the motor. After the upper and lower tubes of the main switch are switched off, and the phase of the switched reluctance motor enters into a negative voltage forced freewheeling state, the phase current is detected. When the phase current falls to a preset threshold, one of the upper or lower tubes is switched on and the phase enters into a zero voltage natural freewheeling state. When the phase current reaches a peak value, the rotor position becomes the start position of the minimum phase inductance and the rotor position is used as the switch-on position of the main switch. The upper and lower tubes are then switched on.