PWM Current-Slope Rotor Angle Estimation at Low Motor Speeds
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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 sensorless techniques struggle with insufficient back electromotive force and current flow.
Innovation Solution
A method and device for rotor angle estimation in BLDC and stepper motors that utilize PWM patterns with added duty cycles 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
1Measurement precision
If traditional sensor-based methods are used for rotor position estimation, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the position sensor from the motor control system, replacing it with a sensorless estimation method that uses existing current measurements and PWM control signals to determine rotor position, thereby reducing device complexity while maintaining measurement precision
Solution Approach 2:
The system uses its own existing operational parameters (current slopes during PWM active periods) to self-determine rotor position without external sensors, making the system self-sufficient and eliminating additional hardware components
2Device complexity
If sensorless methods are used to eliminate position sensors, then device complexity is reduced, but measurement precision deteriorates at low speeds
Solution Approach 1:
The patent changes the operational parameters by measuring current slopes during the active PWM periods and utilizing the duty cycle information, which provides sufficient signal strength even at low speeds, thereby maintaining measurement precision while keeping the system simple
Solution Approach 2:
The system performs preliminary measurements of current slopes during the PWM active periods before rotor position estimation is needed, ensuring that sufficient data is available even when back EMF is weak at low speeds
3Device complexity
If existing sensorless techniques are used, then device complexity is reduced, but reliability deteriorates due to insufficient BEMF and current flow at low speeds
Solution Approach 1:
The patent changes from relying on BEMF and current flow to measuring current slopes during PWM active periods, which provides reliable measurement signals even when BEMF is insufficient at low speeds and stationary conditions
Solution Approach 2:
The system continuously measures current slopes during each PWM active period, ensuring uninterrupted and reliable rotor position estimation throughout the entire speed range including low speeds and stationary conditions
Data Source
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.