Linear Hall FOC Sensing for PMSM Startup and Low-Speed Torque
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Solution Overview
Problem
Sensored Field Oriented Control (FOC) motor drive systems for Permanent Magnet Synchronous Motors (PMSMs) face challenges in minimizing space and cost while maintaining high startup reliability and low-speed torque production, as they require delicate and expensive angular sensors.
Innovation Solution
The use of two perpendicularly arranged linear Hall devices to sense orthogonal magnetic field components, allowing for the calculation of angular position and velocity, and subsequent generation of phase signals to control the motor currents, thereby eliminating the need for additional sensors and reducing system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical encoders are used for sensorless FOC motor drive systems, then startup reliability and low-speed torque production are improved, but system cost and complexity increase
Solution Approach 1:
The patent replaces expensive optical encoders with inexpensive linear Hall effect sensors. The Hall sensors are lower-cost components that, while having different characteristics, can provide sufficient measurement capability for FOC when used in a specific configuration (perpendicular arrangement for 2D field sensing), thereby reducing system cost while maintaining functional reliability
Solution Approach 2:
The patent combines two linear Hall sensors arranged perpendicularly to create a 2D magnetic field sensing system. By merging the outputs of these two sensors through mathematical processing (calculating magnitude and phase angle), the system achieves functionality comparable to more complex angular sensors while using simpler, cheaper components
2Reliability
If optical encoders are used for sensorless FOC motor drive systems, then low-speed torque control is improved, but system space and cost increase
Solution Approach 1:
The patent substitutes compact linear Hall sensors for bulkier optical encoders. Hall sensors have a smaller physical footprint and can be mounted closer to the rotor, reducing the overall space required for the sensing system while maintaining the capability for accurate low-speed torque control through proper signal processing
3Device complexity
If linear Hall devices are used instead of optical encoders, then system cost and space are reduced, but measurement precision may be affected
Solution Approach 1:
The patent transitions from measuring only the radial magnetic field component (single dimension) to measuring both radial and tangential components (two dimensions) using perpendicularly arranged Hall sensors. This 2D measurement approach provides sufficient information to calculate both magnitude and phase angle of the back-EMF, achieving angular position measurement precision comparable to optical encoders while using simpler sensors
Solution Approach 2:
The patent implements a feedback mechanism where the outputs of the two Hall sensors are continuously processed to calculate the instantaneous magnitude and phase angle of the magnetic field. This feedback processing compensates for the inherent limitations of linear Hall sensors, maintaining measurement precision through mathematical transformation of the sensor signals
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 provides a compact, low-cost motor control system with high startup reliability and improved low-speed torque control, achieving results comparable to systems using optical encoders without the need for additional sensors, while minimizing space and cost.
Implementation Method 1
The so called 'Hall Effect' occurs when a magnetic field is oriented perpendicular to an electric current. The magnetic field generates a voltage difference across a conductor, called the Hall Voltage, in a direction which is perpendicular to both the direction of the magnetic field and the direction of the current flow. By measuring the Hall voltage, the magnitude of the magnetic field is possible to determine.
Data Source
Figure 1A~1B
Figure 2~3
Figure 4~6
AI summary
In described examples, a motor control system (800) for a permanent magnet synchronous motor (PMSM) uses two linear Hall devices (801, 802) to produce a first signal indicative of a strength of a first magnetic field component produced by a set of rotor (820) magnets and to simultaneously produce a second signal indicative of a strength of a second magnetic field component produced by the rotor (820) magnets that is approximately orthogonal to the first magnetic field component. An angular position and angular velocity of the rotor (820) is calculated (807) based on the first signal and the second signal. A plurality of phase signals (809a-809c) is produced based on the calculated angular position and angular velocity. Current in a plurality of field windings of the motor is controlled using the plurality of phase signals (809a-809c).