Phase Loss Detection in PMSM Variable Speed Drives
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Solution Overview
Problem
Existing methods for detecting a loss of one or more phases in a synchronous electric motor with permanent magnets are limited, as they either require the motor to be stationary, do not detect all phases simultaneously, or cause additional oscillations or torque loss when detecting phase loss during operation.
Innovation Solution
A method implemented in a variable speed drive that injects a reference flux current based on a reference torque current and speed or position measurement, allowing for detection of phase loss without affecting torque control, by applying currents along control ramps and comparing rms current or voltage moduli with predetermined values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference flux current is injected into the motor windings during operation, then phase loss detection capability is improved, but additional oscillations and torque loss occur
Solution Approach 1:
The patent applies a reference flux current that is intentionally kept below the level required for full torque production. By using a reduced current amplitude (excessive action in detection capability but partial in torque generation), the system achieves sufficient phase loss detection while minimizing harmful oscillations and torque disturbances during motor operation
Solution Approach 2:
The reference flux current serves as an intermediary signal that enables indirect detection of phase loss conditions. Instead of directly monitoring phase connections, the system injects this intermediary current and observes its interaction with the motor windings, allowing phase loss detection without directly interfering with the primary torque-producing current paths
2Reliability
If phase loss detection is implemented during motor operation, then real-time protection is improved, but detection complexity increases
Solution Approach 1:
The control device is designed to perform multiple functions: it generates the reference flux current for detection purposes, measures the resulting motor currents, processes the current signals to detect phase losses, and maintains normal motor control. This multi-functional approach consolidates detection and control operations into a single integrated system, reducing overall complexity despite the added detection capabilities
Solution Approach 2:
The system continuously measures the currents in the motor windings and feeds this information back to the control device. By comparing the measured currents against expected values during reference flux current injection, the system automatically detects phase loss conditions in real-time without requiring additional complex external monitoring equipment
3Measurement precision
If detection methods are applied when motor is stationary, then detection accuracy is improved, but operational continuity deteriorates
Solution Approach 1:
The patent implements periodic injection of reference flux current during motor operation at predetermined intervals. This periodic detection approach allows the system to maintain continuous operation while periodically verifying phase integrity, thus achieving both operational continuity and adequate detection accuracy without requiring the motor to be stationary for extended periods
Data Source
Figure 1
Figure 2~3
AI summary
The present invention relates to a method implemented in a variable speed drive (1) for detecting the loss of one, two, or three phases in a three-phase permanent magnet synchronous motor (PMSM) while running or stopped, said drive operating a closed-loop control. The method consists of applying a reference flux current (Idref) to the control of the variable speed drive (1) and determining the loss of one or more phases according to various criteria.