Feedforward Current Control for Induction Machine Sensor Faults
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Solution Overview
Problem
Control of induction machines is challenging due to the non-linear relationship between electromagnetic torque and rotor-flux and stator current, especially in the event of current sensor failure where traditional feedback current control systems may fail.
Innovation Solution
A feedforward current control method is employed, which determines a forward path voltage command based on a command current, measured rotor position, and estimated motor parameters, and further accounts for an estimated disturbance signal due to rotor fluxes to generate a reference voltage signal for the inverter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback current control is used, then current control accuracy is improved, but system reliability deteriorates under current sensor failure
Solution Approach 1:
The feedforward current control calculates the required voltage commands in advance based on the motor model and desired current trajectory, enabling current control to continue even when current sensors fail. This preliminary calculation of control actions bypasses the need for real-time current measurement feedback.
Solution Approach 2:
The patent introduces an observer as an intermediary component that estimates the motor state (current, flux, speed) based on available measurements (voltage, position, speed) and the motor model. This observer mediates between the limited sensor inputs and the control algorithm, providing the necessary state information without requiring functional current sensors.
2Reliability
If feedforward current control is used, then fault tolerance is improved, but control precision deteriorates
Solution Approach 1:
The patent combines feedforward control with feedback mechanisms by using an observer that continuously estimates the motor state and compares it with actual measurements. This feedback loop corrects estimation errors and maintains control precision even under fault conditions, bridging the gap between feedforward fault tolerance and feedback precision.
Solution Approach 2:
The patent replaces the physical current sensor measurement mechanism with a mathematical observer-based estimation mechanism. This substitution uses the motor model and available sensor data (voltage, position, speed) to compute the current state, eliminating the dependency on physical current sensors while maintaining control accuracy through model-based estimation.
3Adaptability or versatility
If field oriented control is used, then control capability is improved, but system complexity increases
Solution Approach 1:
The observer serves multiple functions simultaneously: it estimates current, rotor flux, and speed; provides state information for the feedforward controller; and enables fault detection and tolerance. This multi-functionality reduces the need for separate components, managing system complexity while maintaining enhanced control capability.
Data Source
AI summary
A method for controlling an induction machine includes: determining a forward path voltage command based on: a command current, the measured rotor position, and a set of estimated motor parameters regarding the induction machine; determining an estimated disturbance signal corresponding to a voltage generated in the induction machine due to rotor fluxes; determining a reference voltage signal based on both of the forward path voltage command and the estimated disturbance signal; and commanding, based on the reference voltage signal, an inverter to apply an output voltage to the induction machine and thereby causing an output current to be generated in a stator winding of the induction machine.