Sensorless Brushless Motor Rotor Position Detection
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Solution Overview
Problem
Sensorless brushless motor systems experience jitter during startup, especially under varying loads, due to insufficient information for determining which windings to energize and in what sequence, leading to performance issues and potential motor burnout in applications requiring high initial torque.
Innovation Solution
A system and method for synchronizing sequential phase switching in a multi-phase sensorless brushless motor by sampling voltage values on an undriven winding during a specific window of time, processing these values, and changing the driven windings when the processed values exceed a threshold, to improve torque delivery and reduce jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless control is used to eliminate sensors and reduce cost, then device complexity and cost are reduced, but measurement precision of rotor position deteriorates at low speeds causing jitter
Solution Approach 1:
The patent introduces an intermediary signal processing mechanism that processes the undriven phase voltage to extract rotor position information. By using the undriven phase voltage as an intermediary carrier of position information and applying signal processing techniques, the system achieves accurate position detection without direct sensors, resolving the contradiction between sensorless operation and measurement precision.
Solution Approach 2:
The patent changes the parameter being measured from direct back-EMF (which is weak at low speeds) to the undriven phase voltage, which contains richer position information. By monitoring voltage on the undriven phase during PWM switching intervals and processing this signal, the system maintains accurate position detection across the full speed range including startup conditions.
2Device complexity
If sensorless algorithm operates at low speeds without sufficient information, then sensor cost is eliminated, but reliability deteriorates due to jitter under load
Solution Approach 1:
The patent implements feedback by continuously monitoring the undriven phase voltage and using this information to adjust commutation timing. The processed voltage values provide feedback about rotor position that enables the controller to make informed commutation decisions even at zero or very low speeds, preventing the jitter that would otherwise cause unreliable operation under load.
Solution Approach 2:
The patent performs preliminary action by establishing accurate rotor position detection before attempting high-torque commutation. By processing the undriven phase voltage to determine precise commutation points during startup, the system prepares the correct winding sequence in advance, ensuring reliable high-torque operation when needed without experiencing jitter during the transition.
3Productivity
If commutation is performed without accurate position detection, then productivity is maintained, but harmful factors increase due to motor burnout
Solution Approach 1:
The patent replaces mechanical sensor-based position detection with an electrical field-based measurement system. By measuring voltage on the undriven phase and processing this electrical signal to extract position information, the system achieves accurate commutation control without mechanical or contact-based sensors, preventing burnout while maintaining continuous operation.
Solution Approach 2:
The undriven phase voltage serves as an intermediary that carries position information without requiring direct physical contact or additional sensors. This intermediary signal allows the system to determine commutation timing accurately, preventing incorrect commutation that would lead to motor burnout while maintaining continuous productive operation.
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 enhances the motor's ability to achieve smooth and high-torque startup, reducing jitter and preventing premature motor burnout by accurately determining the commutation points even under unpredictable load conditions.
Implementation Method 1
A motor controller drives a pulse width modulated signal on two windings of a set of three windings in a motor
Implementation Method 2
A plurality of voltage values on an undriven winding of the set of three windings are sampled
Data Source
AI summary
The system and method disclose for the controlling of sequential phase switching in driving a set of stator windings of a multi-phase sensorless brushless permanent magnet DC motor. A motor controller controls a power stage that drives two windings of a set of three windings in the motor with pulse width modulated signal. A plurality of voltage values on an undriven winding of the set of three windings are sampled within a window of time, wherein a period beginning when the driven windings are energized and ending when the driven windings are de-energized encompasses the window of time. The sampled voltage values are processed. When the processed voltage values exceed a threshold, the motor controller changes which two windings are driven.