Sensorless Rotor Angle Estimation from PWM Current Slopes
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Solution Overview
Problem
Existing sensor-based and sensorless rotor position estimation methods for BLDC and stepper motors face challenges at low speeds and when stationary, leading to inaccurate alignment and increased energy consumption, while existing sensorless techniques struggle with weak back electromotive force (BEMF) and current flow.
Innovation Solution
A method and device for rotor angle estimation in BLDC and stepper motors that utilize a PWM pattern with a fixed duty cycle addition and current slope measurements, normalizing current slopes across phases to emphasize inter-phase saliency differences, enabling accurate rotor angle estimation without physical sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless methods are used to eliminate position sensors, then device complexity and cost are reduced, but measurement precision deteriorates at low speeds due to insufficient BEMF and current flow
Solution Approach 1:
The patent changes the measurement parameter from BEMF/voltage (which is weak at low speeds) to current slope (di/dt). By measuring the rate of change of current during PWM active periods and normalizing these slopes, the system achieves reliable rotor position detection even when BEMF and current magnitudes are insufficient, thus resolving the measurement precision deterioration at low speeds.
2Measurement precision
If traditional sensor-based methods are used for position detection, then measurement precision is maintained, but device complexity and cost increase
Solution Approach 1:
The patent makes the motor's own current characteristics serve the dual purpose of both driving the motor and providing position information. By utilizing the current slopes that naturally occur during PWM operation and normalizing them to extract position information, the system eliminates the need for separate position sensors while maintaining measurement precision through intelligent signal processing of existing electrical parameters.
3Device complexity
If sensorless techniques are used, then device complexity is reduced, but reliability deteriorates due to signal weakness and noise interference
Solution Approach 1:
The patent implements a feedback mechanism where current slopes are measured during PWM active periods, normalized to remove common-mode variations, and used to continuously update rotor position estimates. This closed-loop approach with multiple measurements and normalization enhances reliability by compensating for noise and signal weaknesses, allowing robust position detection without physical sensors.
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.