Sensorless FOC Motor Controller Using Q-Axis Stall Detection
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Solution Overview
Problem
Existing sensorless Field Oriented Control (FOC) motor systems face challenges in accurately detecting motor stall conditions, particularly under transient and start-up conditions, and are susceptible to false detections due to motor parameter variations and sensorless control frequency lock.
Innovation Solution
A motor control system that utilizes a stall detector to compare the applied q-axis voltage with dynamically generated high and low thresholds based on an estimated q-axis voltage, incorporating a debounce filter and timer to prevent false detections, and employs a low computational intensity approach.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless FOC control is used to reduce system complexity, then device complexity is reduced, but stall detection accuracy deteriorates under transient and start-up conditions
Solution Approach 1:
The patent changes the detection parameter from direct current measurement to estimated q-axis voltage comparison. By using the relationship between q-axis voltage and motor speed in FOC systems, the patent transforms the stall detection problem into a voltage threshold comparison problem, which is more reliable under transient conditions and reduces false detections.
Solution Approach 2:
The patent introduces an intermediary estimation mechanism using the FOC controller's existing voltage estimation circuitry. Instead of directly measuring stall conditions, the system uses the estimated q-axis voltage as an intermediary parameter that indirectly indicates motor rotation status, leveraging existing control infrastructure.
2Ease of manufacture
If traditional stall detection methods are used, then implementation is simple, but false detections increase during motor wobbling and transient conditions
Solution Approach 1:
The patent implements dynamic threshold adjustment based on motor operating conditions. The high and low thresholds for q-axis voltage comparison are adapted according to motor speed and load conditions, allowing the detection system to distinguish between normal transient wobbling and actual stall conditions, thereby reducing false detections.
Solution Approach 2:
The patent incorporates feedback from the FOC control loops to continuously monitor q-axis voltage and compare it against dynamically adjusted thresholds. The system uses the existing feedback infrastructure of the FOC controller to provide continuous stall detection without adding complex external monitoring systems.
3Reliability
If comprehensive stall detection is implemented to improve reliability, then detection accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent makes the existing FOC controller's voltage estimation circuitry serve multiple functions: both motor control and stall detection. By using the same voltage estimation infrastructure for both purposes, the patent avoids duplicating computational resources and achieves reliable stall detection without increasing overall system complexity.
Solution Approach 2:
The patent enables the FOC controller to perform stall detection using its own existing computational resources and voltage estimation capabilities. The controller serves itself by leveraging its internal state variables and control algorithms to detect stalls, eliminating the need for separate dedicated detection hardware or complex external monitoring systems.
Data Source
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AI summary
A motor control system for controlling operation of a motor having a plurality of windings includes a gate driver to provide a control signal to one or more switching elements controlling a voltage applied to the plurality of windings and a Field Oriented Control (FOC) controller configured to generate a PWM signal for coupling to the gate driver, wherein the FOC controller comprises a d-axis control loop configured to generate an applied d-axis voltage and a q-axis control loop configured to generate an applied q-axis voltage. A stall detector is configured to calculate an estimate of the q-axis voltage and compare the applied q-axis voltage to a threshold based on the estimate in order to detect a stall condition of the motor.