Sensorless Rotor Position Detection Using PWM Voltage Sampling
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Solution Overview
Problem
Existing methods for controlling multiphase synchronous motors, particularly at low speeds, face challenges in accurately determining rotor position without sensors, leading to instability and noise issues due to reliance on high-frequency current injection and zero-crossing detection, which are ineffective at low speeds and high loads.
Innovation Solution
A controller method that sets a phase to a floating state, applies alternating voltages across other phases during PWM cycles, and determines rotor position based on voltage samples, using phase tracking observers to estimate position and speed with increased resolution, thereby avoiding high-frequency current injection and stabilizing control at low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-frequency current injection is used to determine rotor position, then position detection capability is improved, but noise increases and stability deteriorates at low speeds
Solution Approach 1:
The patent replaces high-frequency current injection (electrical method) with voltage sampling during PWM cycles (control method), eliminating the need for mechanical or electrical disturbance signals while maintaining position detection capability through phase tracking observers
Solution Approach 2:
The patent introduces phase tracking observers as an intermediary computational mechanism that processes voltage samples to estimate rotor position and speed, avoiding direct high-frequency signal injection while achieving accurate low-speed position detection
2Measurement precision
If zero-crossing detection is used to determine rotor position, then position information is obtained, but the method becomes ineffective at low speeds and high loads
Solution Approach 1:
The patent changes the detection parameter from zero-crossing voltage (which fails at low speeds) to phase voltage samples taken during PWM cycles, with processing through phase tracking observers that adapt to varying speed and load conditions, maintaining effectiveness across the full operating range
3Device complexity
If sensorless control is implemented, then device complexity is reduced, but measurement precision of rotor position deteriorates
Solution Approach 1:
The patent replaces physical position sensors with a sensorless control system using phase tracking observers that process voltage samples during normal PWM operation, achieving accurate position estimation without additional hardware complexity
Solution Approach 2:
The patent enables the motor control system to use its own operational voltage samples during PWM cycles to determine rotor position, eliminating the need for separate sensing systems while maintaining measurement precision through computational observers
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 stable and precise speed and position control at very low speeds without sensors, improving torque application and reducing noise, by utilizing voltage sampling and phase tracking observers to determine rotor position effectively.
Implementation Method 1
a 12-Step Sensorless Drive for Brushless DC Motors Based on Back-EMF Differences
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
The disclosure relates to a controller and associated method for controlling a multiphase synchronous motor with a rotor and a plurality of windings for receiving a plurality of motor vectors, the method comprising, for a motor flux vector: setting a first winding of the motor to a floating state in which the first winding is electrically floating; setting a voltage across a second winding of the motor for a first period; receiving first voltage samples associated with the first winding in the first period; setting the voltage across the second winding of the motor to a second period, in which the first period and the second period are periods of one or more pulse width modulation cycles, in which a polarity of the voltage across the second winding in the second period is opposite to a polarity of the voltage across the second winding in the first period; receiving second voltage samples associated with the first winding in the second period; and determining a position of the rotor based on the first and second voltage samples.