Sensorless PMSM Startup Under Windmilling Conditions
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Solution Overview
Problem
Existing sensorless permanent magnet synchronous motors (PMSMs) face challenges in determining initial rotor position and speed during startup, especially when windmilling, as conventional methods like encoders and Hall sensors increase costs and complexity, and back-EMF and speed observer methods fail to provide information before startup.
Innovation Solution
A motor controller implements a field-oriented control (FOC) vector control routine with a speed proportional-integral (PI) control loop and a measure-and-synchronize (MAS) stage to estimate rotor position and speed before startup, deactivating the speed PI control loop and field-weaken control during a delay period, using a speed observer to converge on accurate values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If encoders or Hall sensors are used to measure rotor position and speed, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The motor controller uses its own existing voltage sensing circuits and control algorithms to estimate rotor position and speed during the startup phase, without requiring external sensors. The system serves itself by utilizing back-EMF measurements and speed observer algorithms that are already part of the control architecture, eliminating the need for additional encoders or Hall sensors.
Solution Approach 2:
The patent replaces mechanical sensor systems (encoders, Hall sensors) with an electronic estimation system using software algorithms. The speed observer and back-EMF-based estimation methods substitute physical sensing mechanisms with computational approaches, reducing hardware complexity while maintaining measurement capability.
2Device complexity
If back-EMF or speed observer methods are used in sensorless motors, then device complexity is reduced, but reliability deteriorates during windmilling conditions
Solution Approach 1:
The controller implements a preliminary startup phase before normal operation begins. During this delay period, the system actively estimates rotor position and speed using voltage sensing and speed observer algorithms, even when the motor is windmilling. This preliminary estimation ensures reliable initialization of the FOC algorithm before the motor enters its normal operational mode.
Solution Approach 2:
The system continuously monitors phase voltages and currents during the startup delay period, using this feedback information to update the speed observer and refine position estimates. The feedback loop ensures that the estimation algorithms adapt to actual motor conditions, improving reliability under windmilling scenarios.
3Measurement precision
If a delay period is implemented for position and speed estimation, then measurement precision is improved, but loss of time increases
Solution Approach 1:
During the startup delay period, the controller continues to execute useful functions by actively estimating position and speed rather than remaining idle. The voltage sensing circuits remain active, and the speed observer algorithm continuously processes data, transforming what would be wasted time into a productive estimation phase that prepares the system for smooth startup.
Solution Approach 2:
The system applies a moderate delay period that is sufficient to achieve accurate estimation without being excessively long. The delay duration is optimized to provide just enough time for the speed observer to converge on accurate position and speed values, balancing the need for precision with the desire for quick startup.
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
Enables smooth startup of PMSMs without additional sensors, reducing costs and complexity by accurately estimating rotor position and speed, preventing torque shock, and ensuring synchronized motor control.
Implementation Method 1
sensorless motors may implement algorithms that use the back-EMF (back electromotive force) generated in the stator winding to determine rotor position
Data Source
Figure 1
Figure 2A~3
Figure 4A~5B
AI summary
To avoid control failure resulting from startup of a PMSM that is windmilling (15), initial speed and position are determined before startup (5). A controller uses a FOC routine having a speed PI control loop, field-weaken control, a current PI control loop, and a speed observer. When the controller receives an instruction to start the PMSM (20), it delays startup and executes an "estimation" stage (30,35), in which the controller executes the FOC routine but with the speed PI control loop and the field-weaken control disabled. The estimation stage is repeated multiple times (35), with estimates converging to actual speed and position through successive iterations. When estimated speed and position values have stabilized, the motor is started (40) using the estimates as initial speed and position for driving the PMSM. The FOC routine (45), with the speed PI control loop and the field-weaken control enabled, is used to drive the PMSM.