Sensorless AC Motor Controller Using Feed Forward Torque Control
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Solution Overview
Problem
Current AC motor speed control methods require rotor position sensors, which are costly, restrict the motor's operating environment, reduce reliability, and are not suitable for high-torque, low-speed, or fast speed-reversal applications, especially for permanent magnet synchronous motors (PMSM).
Innovation Solution
The implementation of Feed Forward Torque Control (FFTC) that derives torque-related components of motor voltages from a torque command signal and motor parameters, using a load model to determine motor speed without the need for rotor position sensors, allowing operation over a wide speed range including zero speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rotor position sensors are used for speed control, then the motor speed can be controlled accurately, but the cost increases, reliability decreases, and the operating environment is restricted
Solution Approach 1:
The patent extracts and eliminates the rotor position sensor from the motor control system. Instead of using physical sensors to detect rotor position, the invention uses sensorless control techniques that estimate rotor position and speed from electrical measurements (currents and voltages) and motor model parameters, thereby removing the reliability issues and cost associated with physical sensors
Solution Approach 2:
The patent replaces the mechanical/electrical sensor system with a computational estimation system. Rather than physically measuring rotor position with sensors, the system uses mathematical models and algorithms to estimate position and speed from electrical signals, substituting physical measurement with computational analysis
2Ease of operation
If rotor position sensors are used, then speed control is achieved, but the hardware complexity and cost increase
Solution Approach 1:
The patent removes the sensor hardware and associated wiring from the system. The solution eliminates the need for physical position sensors and their connection leads, simplifying the hardware architecture while maintaining speed control functionality through sensorless estimation methods
Solution Approach 2:
The patent makes the existing electrical measurements (current and voltage sensors already present in the motor drive) serve multiple functions. These measurements are used both for basic current control and for estimating rotor position and speed, eliminating the need for dedicated position sensing hardware
3Ease of manufacture
If traditional sensorless control methods are used, then cost is reduced, but the control accuracy and reliability at low speeds and zero speed deteriorate
Solution Approach 1:
The patent implements dynamic adaptation of control parameters based on operating conditions. The system adjusts estimation algorithms and control gains according to speed range, providing optimized performance at low speeds, zero speed, and high speeds. This dynamic adaptation allows accurate torque control across the entire speed range without requiring expensive hardware modifications
Solution Approach 2:
The patent employs feedback mechanisms where the estimated rotor position and speed are continuously refined based on actual motor responses. The system uses feedback from current measurements and motor model predictions to correct estimation errors, improving accuracy particularly at low speeds where traditional sensorless methods fail
4Speed
If back EMF measurement method is used for sensorless control, then high speed operation is achieved, but low speed and zero speed operation becomes impossible
Solution Approach 1:
The patent dynamically switches between different estimation methods based on operating speed. At high speeds, the system uses back EMF-based estimation which is accurate and computationally efficient. At low speeds and zero speed, it transitions to alternative methods such as injection-based or model-based estimation, ensuring continuous accurate control across the full speed range including conditions where back EMF is negligible
Data Source
AI summary
A controller for an AC electric motor, includes a Feed Forward Torque Controller and a load model. The Torque controller directly derives a torque related component of applied motor voltages from a signal representing a torque command input T* and at least one motor parameter. The load model derives a motor speed value including a model of motor speed behavior of the AC electric motor to provide an output signal which represents the motor speed of the AC electric motor. This motor speed output signal is used in determining a frequency of rotation of an applied motor voltage vector. Where an input to the load model is the signal representing the torque command input T*, the load model uses the signal representing the torque command T*, at least over a part of an operating speed range of the AC motor which includes zero speed, to determine the motor speed output signal.