PWM-Based Motor Position Estimation for Smooth FOC Control
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Solution Overview
Problem
Existing motor control systems face challenges in achieving smooth operation from zero speed to maximum speed with high efficiency and low vibration and acoustic noise, particularly in applications like cordless power tools and robotics, due to variations in rotor position estimation accuracy.
Innovation Solution
A motor controller system that utilizes a pulse width modulation (PWM) signal generation, position determination based on motor transitions, and updated position estimation using PWM count intervals to enhance rotor position resolution, combined with Field-Oriented Control (FOC) techniques for precise motor control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional position determination methods are used, then the system is simple, but the rotor position estimation accuracy deteriorates
Solution Approach 1:
The control system segments the position determination process into multiple intervals based on PWM cycle counts. By dividing the rotor rotation into discrete PWM cycles and counting them, the system achieves higher position resolution without requiring complex hardware. Each PWM cycle represents a discrete angular increment, allowing precise position tracking through simple counting operations.
Solution Approach 2:
The patent introduces a temporal dimension to position measurement by using PWM cycle counting over time intervals. Instead of measuring position directly through complex spatial sensors, the system measures the number of PWM cycles required to rotate through specific angular intervals, transforming a spatial measurement problem into a temporal counting problem that is easier to implement with high precision.
2Measurement precision
If high position resolution is achieved through traditional methods, then measurement accuracy improves, but system complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical or optical position sensing systems with an electronic PWM-based counting system. Instead of using high-resolution encoders or other complex position sensors, the system uses a microcontroller to generate PWM signals and count the number of cycles required to traverse known angular intervals, achieving high resolution through software-based measurement rather than complex hardware.
Solution Approach 2:
The system changes the measurement parameter from direct angular position to PWM cycle count. By measuring the number of PWM cycles rather than directly measuring angle, the system achieves higher effective resolution because the PWM frequency can be made very high, allowing many cycles to occur within a single mechanical rotation, thereby increasing the counting resolution.
3Use of energy by moving object
If Field-Oriented Control is implemented for high efficiency, then motor efficiency improves, but control complexity increases
Solution Approach 1:
The patent implements Field-Oriented Control using feedback from the PWM cycle counting system. The measured position and speed information, derived from counting PWM cycles between position transitions, feeds back to the control algorithm to dynamically adjust the stator current vectors. This closed-loop feedback enables efficient FOC operation while using a relatively simple measurement mechanism.
Solution Approach 2:
The system uses the PWM generation infrastructure to serve dual purposes: both driving the motor and providing the measurement signal for position determination. The same PWM signal that controls the motor inverter also serves as the timing reference for position measurement, eliminating the need for separate measurement hardware and simplifying the overall control system while maintaining FOC efficiency.
Data Source
AI summary
According to some embodiments, a motor controller for controlling a motor includes a position interface configured to receive a motor position signal indicative of a position of the motor, and a pulse width modulation (PWM) unit configured to generate a PWM signal for driving the motor. An angle and speed unit is configured to determine a speed and a position of the motor based on transitions in the motor position signal, wherein transition intervals are defined between the transitions, determine a PWM count of cycles in the PWM signal during a first transition interval of the transition intervals, and update the position of the motor during a second transition interval of the transition intervals based on the PWM count to generate an updated position. A controller is configured to send a control signal for controlling the motor to the PWM unit based on the speed and the updated position.