Sensorless BLDC Motor Control for Low-Speed Reversal Stability
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Solution Overview
Problem
Brushless direct current (BLDC) motors face challenges in accurately controlling angular velocity and position at low speeds and during reversals, leading to potential synchronization loss and stalling, due to inaccuracies in angular position and velocity estimators.
Innovation Solution
A motor controller that switches between closed-loop and open-loop modes based on threshold angular velocity, using estimated and forced target currents and positions to maintain synchronization, decoupling estimators at low speeds and reversals to prevent inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sensor-less BLDC motors rely on back electromotive force (BEMF) detection to determine angular position, then the system avoids costly sensors, but measurement precision deteriorates at low speeds and during reversals
Solution Approach 1:
The system dynamically switches between two control modes based on operating conditions: at high speeds, it uses sensor-less BEMF detection for cost efficiency, while at low speeds and during reversals, it transitions to a mode using estimated angular position and forced target current to maintain control accuracy. This dynamic adaptation resolves the contradiction by optimizing the measurement approach according to speed conditions.
Solution Approach 2:
The controller changes the control parameters based on speed thresholds. Above a threshold angular velocity, it uses calculated target current based on velocity error; below the threshold, it switches to forced target current and forced angular position. This parameter change strategy maintains measurement effectiveness across different operating ranges while avoiding sensor costs.
2Measurement precision
If the motor operates at low speeds or during reversals using estimated angular position and velocity, then synchronization may be lost, but adding sensors to improve precision increases device complexity and cost
Solution Approach 1:
The control system segments the operating range into high-speed and low-speed regions, applying different control strategies to each segment. This segmentation allows the system to maintain precision in the problematic low-speed segment without adding sensors, while keeping the overall system complexity manageable by using simple threshold-based mode switching.
Solution Approach 2:
The controller acts as an intermediary that processes the estimated angular position and velocity information and transforms it into appropriate control signals. By using forced target current and forced angular position as intermediate control variables, the system maintains synchronization at low speeds without requiring complex sensor hardware.
3Speed
If the motor controller uses calculated target current based on velocity error, then the motor can maintain target angular velocity, but at low speeds the control becomes unstable leading to stalling
Solution Approach 1:
The controller dynamically adjusts the control strategy based on speed conditions. At high speeds where velocity error calculation is effective, it uses calculated target current for accurate speed control. At low speeds where this method becomes unstable, it dynamically switches to forced target current and forced angular position, preventing stalling and maintaining reliable operation throughout the entire speed range.
Solution Approach 2:
The system changes the control parameters based on a threshold angular velocity. Above the threshold, it uses calculated target current derived from velocity error to maintain speed accuracy. Below the threshold, it switches to forced target current and forced angular position parameters, ensuring stable and reliable motor operation at low speeds and during reversals.
Data Source
AI summary
A motor controller is operable to control a motor. The motor has a first terminal and the motor controller includes an angular velocity transmission path having an input and an output. A current generator includes a velocity-torque input, an angular position input, and a motor drive output. The velocity-torque input is coupled to the output of the angular velocity transmission path. An angular velocity feedback path is coupled between a first terminal and a first location on the angular velocity transmission path. The first location is between the input and the output of the angular velocity transmission path. A current feedback path is coupled between the first terminal and a second location on the angular velocity transmission path. The second location is disposed between the first location on the angular velocity transmission path and the velocity-torque input of the current generator.