Rotor Angle Estimation from PWM Current Slopes at Low Speed
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Solution Overview
Problem
Existing sensor-based and sensorless rotor position estimation methods struggle at low speeds and when stationary due to insufficient back electromotive force (BEMF) and reduced current flow, leading to inaccurate detection and increased complexity and cost in motor control systems.
Innovation Solution
A method and device for rotor angle estimation in BLDC and stepper motors that utilize a PWM pattern with a fixed additional duty cycle to measure current slopes in each phase, comparing these slopes to estimate the rotor angle without a position sensor, using a single current sensor and non-overlapping PWM pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor-based methods are used for rotor position detection, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the rotor position detection function from physical sensors and implements it through signal processing of existing current measurements. The rotor angle is estimated by analyzing current slopes and back-EMF signals already present in the motor control system, eliminating the need for separate position sensors while maintaining detection accuracy.
Solution Approach 2:
The patent creates a virtual model of rotor position by estimating rotor angle from electrical signals (current slopes and back-EMF) rather than directly measuring it with physical sensors. This computational copy of position information replaces physical sensing hardware, reducing system complexity while preserving measurement capability.
2Device complexity
If traditional sensorless methods are used, then device complexity is reduced, but measurement precision deteriorates at low speeds
Solution Approach 1:
The patent changes the operational parameters of the motor control system by introducing a fixed additional duty cycle to ensure sufficient current flow during measurement intervals. This parameter modification ensures that current slopes remain measurable even at low speeds, maintaining measurement precision without requiring physical sensors.
Solution Approach 2:
The patent applies preliminary action by adding a fixed duty cycle component before the actual control signal is applied. This ensures that sufficient current is established in advance to enable accurate slope measurements, particularly at low speeds where natural current flow would be insufficient for accurate sensorless detection.
3Measurement precision
If PWM duty cycle is increased to improve current measurement, then measurement precision is improved, but energy consumption increases
Solution Approach 1:
The patent applies partial action by adding only the minimum necessary fixed duty cycle amount required to ensure measurable current slopes. This is excessive compared to the theoretical minimum needed for control, but carefully calibrated to be just sufficient for accurate measurement without substantially increasing overall energy consumption during normal operation.
Data Source
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AI summary
A method for rotor angle estimation for a 3-phase BLDC or stepper motor with a saliency ratio different from 1 includes receiving a requested duty cycle per motor phase from a motor control algorithm or deriving it from an output voltage per motor phase. The method involves providing a PWM pattern to each motor phase during operation, where the PWM pattern per motor phase matches the requested duty cycle or includes an equal fixed additional duty cycle. Current slopes in each motor phase are measured during active PWM pulses, and these measured current slopes or their average are compared to estimate the rotor angle.