Sensorless PMSM Rotor Position Detection Using Saliency Pulses
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Solution Overview
Problem
Determining the starting position of a permanent magnet synchronous machine (PMSM) rotor without a position sensor is challenging, especially at low speeds or when stationary, as back-EMF is low or nonexistent, leading to unpredictable rotor motion.
Innovation Solution
The method employs high-speed rotational pulses to detect magnetic saliency variations, allowing for the determination of the rotor's magnetic axis without causing movement, followed by applying positive and negative pulses along the magnetic axis to deduce the magnetic direction, enabling accurate rotor position identification with minimal rotor motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back-EMF is used to determine rotor position, then rotor position can be determined during motor operation, but at low speeds or stationary conditions the back-EMF is low or nonexistent making it difficult to determine rotor position
Solution Approach 1:
The patent changes the measurement parameter from back-EMF to magnetic saliency (inductance variations). By measuring the differential inductance along different axes (d-axis and q-axis) using injected current pulses, the system can determine rotor position independently of rotor speed, resolving the contradiction between position measurement accuracy and low-speed operation.
2Measurement precision
If rotor position is determined using magnetic saliency by applying pulses to stator windings, then rotor position can be identified at stationary conditions, but special hardware may be required
Solution Approach 1:
The patent makes the existing current sensors serve dual purposes: they monitor both the motor control currents and the saliency measurement currents. The microcontroller unit (MCU) also performs both motor control functions and position detection functions, eliminating the need for separate dedicated hardware for saliency measurement.
Solution Approach 2:
The system uses its own existing resources (current sensors, MCU, power electronics) to perform the position detection function. The current sensors that are already part of the motor control system are utilized to measure the inductance variations, making the system self-sufficient without additional external hardware.
3Measurement precision
If high strength magnetic field is applied to detect rotor position, then rotor position can be accurately determined, but rotor movement may be caused
Solution Approach 1:
The patent uses periodic current pulses of very short duration injected into the stator windings to measure inductance. These pulsed measurements are performed rapidly without maintaining continuous high current, thus detecting rotor position while minimizing the time during which significant torque could be generated. The measurements are taken during brief intervals when the rotor position is effectively frozen.
Solution Approach 2:
The system performs saliency measurements during brief intervals when no motor torque is being applied, before motor operation begins or during idle periods. This preliminary measurement of rotor position is taken when the rotor is stationary and stable, eliminating the problem of rotor movement during measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for unambiguous and rapid assessment of rotor position and direction, facilitating smooth startup and sensor-less operation of the PMSM with minimal motion, independent of the number of stator poles.
Implementation Method 1
the stator holds conductive coils that may be energized to create a rotating magnetic field
Implementation Method 2
The rotating magnetic field is coordinated with the rotor position to draw the rotor along synchronously
Data Source
AI summary
A method and apparatus for determining rotor position in a stationary rotor of a sensor-less permanent magnet synchronous machine that employs a rotating magnetic field to identify a magnetic axis of the stator without a magnetic direction and then determines magnetic direction by applying pulses along the magnet axis in two polarities.