PMSM Rotor Phase Inference via DC Link Voltage Comparison
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Solution Overview
Problem
Existing methods for inferring the rotor phase and rotation speed of free-running permanent magnet synchronous motors without position sensors are costly and complex, often requiring comparators or multiple A/D ports, which increase costs and mounting area.
Innovation Solution
A control unit that uses a DC power supply, inverter, and microcomputer to infer rotor phase and rotation speed by comparing inter-line voltages with a threshold voltage, allowing for rotor phase differentiation and rotation speed inference, enabling the motor to be restarted without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position sensor is used to directly detect the rotor phase and rotation speed, then the detection accuracy is improved, but the cost and device complexity increase
Solution Approach 1:
The patent replaces the mechanical position sensor system with an electrical measurement system. Instead of using a physical sensor to detect rotor position and speed, the invention measures the voltage across the DC link capacitor and uses this electrical signal to infer rotor phase and rotation speed through calculation, thereby eliminating the need for mechanical sensors and reducing device complexity
Solution Approach 2:
The patent utilizes the motor's own operating characteristics during free run to generate the measurement signal. The voltage generated across the DC link capacitor during free run contains information about rotor position and speed, allowing the system to self-diagnose and determine rotor parameters without external sensing components
2Adaptability or versatility
If comparators are used to compare inter-line voltages for inferring rotor phase and rotation speed, then the inference capability is improved, but the cost and mounting area increase
Solution Approach 1:
The patent replaces the comparator-based electrical circuit system with a computational approach using a microcomputer. Instead of using hardware comparators to determine rotor parameters, the invention uses software algorithms that process the DC link voltage measurement data to calculate rotor phase and rotation speed, thereby eliminating comparator circuits and reducing mounting area
Solution Approach 2:
The patent changes the approach from direct voltage comparison to mathematical parameter extraction. By measuring the DC link capacitor voltage and analyzing its characteristics through computational algorithms, the system extracts rotor position and speed information without requiring direct inter-line voltage comparison circuits
3Measurement precision
If multiple A/D ports are used to measure three-phase output terminal voltage, then the measurement capability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the DC link capacitor voltage measurement serve multiple functions. This single measurement simultaneously provides information for determining rotor phase, rotation speed, and for controlling the inverter, replacing what would otherwise require multiple separate measurement channels and A/D ports
Solution Approach 2:
The patent merges multiple measurement functions into a single measurement system. By combining the measurement of DC link capacitor voltage and using computational processing, the system achieves what would otherwise require separate measurements of three-phase output terminal voltages through multiple A/D ports
Data Source
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AI summary
If magnitude relations between the output terminal voltage based on a DC negative terminal of the inverter and a threshold voltage that is a fixed value are compared, polarity thereof is changed at a predetermined rotor phase. The magnitude relation, for example, can be detected by an inexpensive and simple apparatus such as a level shift circuit and a NOT circuit. The rotor phase of the permanent magnet synchronous motor is inferred on the basis of changes in the magnitude relation and if it is differentiated, a rotation speed can be inferred. If the inferred values of the rotor phase and rotation speed are fed back to synchronous operation or vector control, the free-running permanent magnet synchronous motor can be restarted.