Permanent Magnet Synchronous Motor Back-EMF Averaging at Low Speed
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Solution Overview
Problem
Permanent magnet synchronous machines face challenges in determining the angle and angular velocity of the rotor at low speeds due to a low signal-to-noise ratio of the back EMF, leading to unreliable startup and synchronization issues, especially when the rotor is not at standstill.
Innovation Solution
A method and device for determining the rotor's angle and angular velocity using at least two induced voltages by an analog-to-digital converter, averaging module, and estimation module, which improves the signal-to-noise ratio through averaging over a variable number of measured values, allowing reliable estimation even at low speeds without an encoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back EMF measurement is used for sensorless operation, then robustness and high performance are achieved in medium to high speed range, but signal-to-noise ratio becomes very low at low speeds
Solution Approach 1:
The patent applies preliminary action by bringing the rotor to a predefined synchronization position before the actual acceleration phase. This preliminary positioning enables the system to establish reliable initial conditions for sensorless operation, allowing accurate angle and speed detection to begin from a known state rather than from standstill where back EMF signals are too weak.
Solution Approach 2:
The patent implements dynamics by dynamically switching between two operational modes: a synchronization mode for initial positioning and a sensorless back EMF mode for normal operation. The system transitions from a controlled synchronization phase with defined voltage vectors to autonomous sensorless operation once the rotor reaches the synchronization position, optimizing performance across different speed ranges.
2Reliability
If additional synchronization stage is added to improve startup reliability, then rotor positioning is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the synchronization voltage generator to serve multiple functions: it generates voltage vectors for rotor synchronization positioning, provides controlled acceleration during startup, and enables smooth transition to sensorless operation. This multi-functionality eliminates the need for separate dedicated synchronization hardware, reducing overall system complexity while maintaining high startup reliability.
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 reliable startup and synchronization of the permanent magnet synchronous machine at low speeds by accurately determining the rotor's angle and angular velocity, eliminating the need for additional synchronization stages and ensuring stable operation.
Implementation Method 1
measuring the voltage induced by the magnetic flux, also known as the back electromagnetic force (back EMF)
Implementation Method 2
calculates at least two averaged voltages over a variable number N of measured values of the at least two digitized voltages
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A permanent magnet synchronous machine comprises a rotor and a device for determining the rotor's angle and angular velocity by means of a back-acting electromagnetic force, detectable from at least two voltages induced by the rotor, during sensorless operation of the permanent magnet synchronous machine. The device includes an analog-to-digital converter that digitizes the at least two induced voltages, an averaging device that calculates at least two averaged voltages over a variable number N of measured values of the at least two digitized voltages, a setting module that determines the variable number N as a function of the rotor's rotational speed, and an estimation module that estimates the rotor's angle and angular velocity based on the at least two averaged voltages. A corresponding method is also described.