Neutral Point Voltage Detection for Sensorless PMSM Control
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Solution Overview
Problem
Existing permanent magnet motor control systems face challenges in accurately determining the rotor position and rotation direction, especially at low speeds, due to the limitations of sensor-based solutions and high-frequency waveform injection methods, which are costly and unreliable in high-moisture environments.
Innovation Solution
A method that involves detecting the neutral voltage at a Y-topology stator with three coils, using calibration currents to determine the initial rotor position through Clark transformation and analyzing neutral voltage waveforms to estimate the rotor's position and rotation direction, allowing for vector control without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor-based solutions (Hall-effect sensors) are used to measure rotor angular position, then the rotor position can be accurately detected, but the system reliability decreases due to high failure ratio in high moisture environments and additional costs increase
Solution Approach 1:
The patent extracts the position detection function from external sensors (Hall-effect sensors) and relocates it to the neutral point voltage detection within the existing motor control circuit. By detecting the neutral point voltage waveform and analyzing its zero-crossing points, the system obtains rotor position information without requiring additional sensors, thereby eliminating sensor failure risks in high moisture environments while maintaining detection accuracy
Solution Approach 2:
The neutral point voltage detection circuit serves multiple functions simultaneously: it provides rotor position detection, rotor speed estimation, and rotation direction detection. This multi-functional approach eliminates the need for dedicated position sensors while enhancing system reliability and reducing costs
2Device complexity
If conventional sensorless solutions (back-EMF measurement) are used to estimate rotor position, then costs are reduced, but the measurement precision deteriorates at low speeds because back-EMF is zero at standstill and proportional to rotor speed
Solution Approach 1:
The patent applies preliminary action by injecting a high-frequency calibration current before normal motor operation to excite the motor windings and generate detectable neutral point voltage waveforms. This preliminary excitation enables the detection circuit to capture rotor position information even at standstill or very low speeds where normal back-EMF would be zero, thereby extending the operational range of sensorless control
Solution Approach 2:
The system employs periodic high-frequency calibration current injection at specific intervals to refresh the neutral point voltage waveform data. This periodic excitation ensures continuous availability of accurate rotor position information during low-speed operation, maintaining measurement precision without requiring continuous high-frequency injection that would increase energy consumption
3Measurement precision
If high frequency waveform injection (HFI) solutions are used to detect inductance variation with rotor position, then low speed position detection is improved, but the ability to detect changes in rotary direction is lost at low rotor speeds
Solution Approach 1:
The patent implements feedback by continuously monitoring the neutral point voltage waveform characteristics, including zero-crossing timing and waveform shape, to determine both rotor position and rotation direction. The detection circuit analyzes the sequence and pattern of voltage transitions to identify whether the rotor is rotating clockwise or counter-clockwise, providing real-time feedback on rotation direction even at low speeds where HFI methods fail
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 enables accurate determination of rotor position and rotation direction, even at low speeds, without the need for additional sensors, improving reliability and reducing costs, while maintaining high electro-mechanical conversion efficiency.
Implementation Method 1
the voltage at the neutral point may be detected in substantially real time... The detected voltage at the neutral point ('neutral voltage') may then be analyzed at a controller to determine a position of the rotor
Implementation Method 2
a short instance of calibration current is provided to the windings... The calibration current may have a frequency of 100 Hz and may last for 0.5 to 1 second, going through all six vectors in multiple cycles
Data Source
AI summary
The present disclosure is directed to a permanent magnet motor control method and system. A new structure configuration of a permanent magnet motor has a rotor with two or more permanent magnets attached thereon, a stator wound in a “Y” topology with three coils (windings) arranged at 120 degree among one another, and a neutral point of the wound stator wired in a manner that the voltage at the neutral point may be detected in substantially real time. The detected neutral point voltages are analyzed together with the associated vectors of the excitation current provided to the windings of the stator to determine a speed of the rotor. The determined speed of the rotor is used for vector control.