Switched Reluctance Torque Compensation for Sensorless Low-Speed Control
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Solution Overview
Problem
Accurate determination of rotor position in switched reluctance (SR) machines, especially at low speeds or rest, is challenging without direct position sensors, leading to inefficiencies and undesired retarding torque due to parasitic currents.
Innovation Solution
A system and method for torque compensation in SR machines using a controller to determine and actuate a target current based on commanded main and parasitic currents, adjusting for rotor speed, to compensate for retarding torque caused by parasitic currents during low-speed operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensor-less operation with parasitic current injection is used to estimate rotor position, then direct position sensors can be eliminated reducing cost and complexity, but accurate determination of rotor position at low speeds or rest becomes difficult due to weak error signals
Solution Approach 1:
The patent extracts the position sensing function from dedicated hardware sensors and implements it through software-based observer algorithms that process current measurements from power electronics sensors, eliminating mechanical position sensors while maintaining position detection capability
Solution Approach 2:
The patent changes the operating parameters by injecting parasitic current pulses at specific amplitudes and durations into idle phases, and by adjusting observer gain parameters to enhance the error signal strength for accurate position estimation at low speeds where conventional methods fail
2Loss of information
If parasitic current is injected into idle phases to estimate rotor position, then position information can be obtained without direct sensors, but undesired retarding torque is produced when the SR machine operates in motoring quadrant
Solution Approach 1:
The patent applies preliminary anti-action by calculating and injecting compensating current into the controlling phase that opposes the retarding torque effect of parasitic current in idle phases. The controller proactively counteracts the harmful torque before it significantly impacts machine performance, allowing position estimation to continue without net torque loss
Solution Approach 2:
The patent converts the harmful retarding torque effect into a beneficial measurement opportunity by using the parasitic current injection as both a position sensing mechanism and a controlled experimental input, where the known current waveform and timing provide precise rotor position information while the compensating current recovers the torque effect
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
Enhances rotor position accuracy and reduces undesired torque, improving SR machine performance and efficiency by accurately determining rotor position and compensating for parasitic effects.
Implementation Method 1
Some SR machines may have a control system with sensor-less operation which estimate the position and speed of the rotor relative to the stator without the use of a conventional direct position sensor. Such controls systems may estimate rotor position by injecting a current pulse into one or more idle phases of the stator of the SR machine.
Implementation Method 2
A SR machine is typically an electric machine configured to convert electrical energy into rotational torque or rotational torque into electrical energy for any one of a variety of different applications
Data Source
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AI summary
A system (102) and method for torque compensation in a switched reluctance (SR) machine (104) disposed on a machine (100) is disclosed. The system (102) may comprise a SR machine (104), an inverter (122) and a controller (124). The controller (124) is in operable communication with the inverter (122) and is configured to determine a commanded main current associated with energization by a main current (138) of a first portion of the plurality of windings (130) for a controlling phase (132), and determine a commanded parasitic current associated with energization by a parasitic current (140) of a second portion of the windings (130) in a non-controlling phase (134). The controller (124) is further configured to determine an offset current (142) based on the commanded parasitic current, and determine a target current (136) based on a first sum of the commanded main current and the offset current (142), and command the inverter (122) to actuate the target current (136) in the first portion of the windings (130) during the controlling phase (132).