Sensorless Motor Control via Neutral Point Voltage
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Solution Overview
Problem
Existing sensorless motor control techniques for sinusoidal machines face challenges in accurately determining rotor position, especially in motors with low per-unit mutual inductance, leading to limited resolution and potential acoustic noise issues during low-speed operation.
Innovation Solution
A control system that measures the neutral point voltage in specific inverter states to estimate rotor position, utilizing the position-dependent components of the neutral point voltage and DC link voltage measurements, while minimizing acoustic noise by integrating these measurements within normal PWM periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless techniques using current sensors and algorithms are used to determine rotor position, then the system can operate without dedicated position sensors, but the measurement precision and resolution of rotor position estimation deteriorates
Solution Approach 1:
The patent introduces an intermediary measurement approach by using neutral point voltage as an intermediate signal that correlates with rotor position. Instead of directly measuring rotor position through complex current analysis, the neutral point voltage serves as a mediator that provides position information through its relationship with DC link voltage, thereby improving measurement precision while maintaining sensorless operation.
Solution Approach 2:
The patent changes the measurement parameter from current-based estimation to voltage-based estimation. By measuring neutral point voltage and comparing it with DC link voltage, the system transforms the measurement approach to achieve higher position estimation accuracy. This parameter change enables better resolution without requiring additional sensors or complex algorithms.
2Measurement precision
If neutral point voltage measurement is performed outside normal PWM periods for position estimation, then measurement accuracy may improve, but acoustic noise increases and productivity decreases
Solution Approach 1:
The patent merges the position estimation measurement with the normal PWM control periods. By performing neutral point voltage measurements during active PWM states rather than outside them, the system combines two functions (control and measurement) into a unified process. This eliminates additional switching events that would generate acoustic noise while maintaining sufficient measurement accuracy for position estimation.
Solution Approach 2:
The patent ensures continuous useful action by integrating position estimation measurements into the ongoing PWM control cycle. The neutral point voltage is measured during normal PWM active states, maintaining continuous control operation without interruption or additional switching events. This continuous approach prevents the generation of acoustic noise associated with periodic measurement interruptions.
3Object-generated harmful factors
If neutral point voltage measurement is performed during active PWM states, then acoustic noise is reduced, but the component of voltage varying with inductance becomes smaller and harder to extract
Solution Approach 1:
The patent employs feedback by comparing the measured neutral point voltage with the DC link voltage. This comparison provides a reference that enables extraction of the position-dependent voltage component. The feedback mechanism allows the system to isolate the useful position information from the total neutral point voltage signal, overcoming the difficulty of extracting small inductance-related components during active PWM states.
Solution Approach 2:
The patent makes the voltage measurement system multi-functional by using the same neutral point voltage measurement for both control purposes and position estimation. The measured voltage serves dual purposes: maintaining PWM control and providing position information through comparison with DC link voltage. This universal approach eliminates the need for separate measurement circuits while achieving accurate position detection.
4Measurement precision
If DC link voltage measurement is used to generate position estimation, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent makes the DC link voltage measurement multi-functional, using it for both power supply monitoring and position estimation. The same voltage measurement circuit serves dual purposes: ensuring proper power supply levels and providing reference voltage for rotor position calculation. This universal approach improves measurement precision without adding separate measurement systems or increasing device complexity.
Data Source
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AI summary
A control system is provided for an AC electric motor which comprises a rotor and a stator and a plurality of phase windings connected in a star formation, each winding having one end connected to a common neutral point and another end arranged to have a terminal voltage applied to it. The control system comprises switching means arranged to control the terminal voltages applied to the windings and control means arranged to control the switching means so as to switch it between a plurality of states in each of a sequence of PWM periods. The control means is further arranged to measure the voltage at the neutral point at sample times within the PWM periods and to generate from the measured voltages an estimation of the rotational position of the rotor.