Sensor-less Electric Motor Control via Dynamic Gain Scaling
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Solution Overview
Problem
Control systems for electric motors face challenges in maintaining stable operation when position sensors fail, leading to potential motor shutdowns, especially at low speeds, and require smooth transitions between sensor-based and sensor-less control methods.
Innovation Solution
The system employs a switching module to alternate between sensor-based and sensor-less position detection, using back-EMF or high-frequency injection, with a position determining module that includes PID controllers and sample and hold operations to manage gains and filter outputs, ensuring stable control and torque management as a function of rotor flux frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensor-less control is used when position sensor fails, then motor operation can be maintained, but control stability deteriorates especially at low speeds
Solution Approach 1:
The patent adjusts control parameters dynamically based on operating conditions. Specifically, it modifies the bandwidth of the position determining module and the gains of PID controllers as a function of rotor flux frequency to maintain stable control across different speed ranges during sensor-less operation
Solution Approach 2:
The system implements dynamic switching between sensor-based and sensor-less control modes, and within sensor-less mode, dynamically adjusts control parameters (bandwidth, PID gains) based on rotor flux frequency to adapt to changing operating conditions and maintain stability
2Reliability
If switching between sensor-based and sensor-less control is implemented, then reliability is improved, but transient disturbances are generated during switching
Solution Approach 1:
The sample and hold module captures the output state before switching occurs, and the position determining module prepares adjusted parameters in advance based on predicted operating conditions, enabling smoother transitions with reduced transients
Solution Approach 2:
The patent introduces intermediate processing elements (sample and hold module, filtered output combination) that mediate between the two control modes during switching, blending outputs and reducing abrupt transitions that cause harmful transients
3Speed
If bandwidth of position determining module is increased to improve response, then control responsiveness is improved, but stability deteriorates during sensor-less operation
Solution Approach 1:
The bandwidth of the position determining module is made dynamic rather than fixed. It is adjusted as a function of rotor flux frequency, allowing higher bandwidth (faster response) at higher speeds and lower bandwidth (better stability) at lower speeds where sensor-less operation is more challenging
Solution Approach 2:
The system changes the bandwidth parameter of the position determining module based on operating conditions ( rotor flux frequency), optimizing the trade-off between response speed and stability for each operating regime
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 approach enables continuous motor operation above a low speed threshold, smooth transitions between control modes, and enhanced stability during sensor-less operation, preventing shutdowns and maintaining control even at low rotor flux frequencies.
Implementation Method 1
The sensor-less position detection module is configured to detect the rotor position error of the motor by using back electromotive force from the motor
Implementation Method 2
The sensor-less position detection module is configured to detect the rotor position error of the motor by using back electromotive force from the motor or by using high frequency injection
Data Source
AI summary
A switching module switches between receiving a first output from a sensor and a second output from a sensor-less position detection module each indicating a rotor position error of a motor. A position determining module determines a rotor position of the motor based on an output of the switching module and generates a control signal to control a parameter of the motor. A sample and hold module operates on a sum of the output of the switching module and an output of the sample and hold module from a prior instance of switching between the first and second outputs. The position determining module scales the output of the sample and hold module using first and second gains to generate first and second scaled outputs, and generates the control signal based on the output of the switching module and the first and second scaled outputs.