Phase Loss Detection via DC Bus Voltage Sensing
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Solution Overview
Problem
Existing electric motor systems fail to effectively detect and respond to a loss of phase in three-phase systems, leading to overheating and overloading, particularly when Power Factor Correction (PFC) circuits operate in current-limited mode for extended periods, which can stress system components and reduce reliability.
Innovation Solution
A single sensing circuit is used between the power rectifier and PFC circuit, connected to a microprocessor that compares the output voltage level to a threshold, sending a signal to limit power if the level drops below the threshold, avoiding the need for isolation or differential sensing and allowing the motor to operate safely without phase loss detection issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple isolated or differential circuits are used to detect phase loss before the power rectifier, then phase loss detection capability is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple sensing functions into a single sensing circuit located after the power rectifier. This single circuit monitors the DC bus voltage to detect phase loss conditions, eliminating the need for multiple separate sensing circuits that would be required if sensing were performed before the rectifier. The merging of functions reduces device complexity while maintaining detection capability.
2Reliability
If a timer is used to measure voltage peak frequency after the power rectifier, then phase loss detection is improved, but device complexity increases
Solution Approach 1:
The patent extracts the timing function from the sensing circuit by using the microprocessor's existing timing capabilities to measure the frequency of voltage peaks. Instead of adding dedicated timing hardware to the sensing circuit, the solution uses software-based timing within the microprocessor, which reduces device complexity while maintaining accurate phase loss detection.
3Duration of action of moving object
If PFC circuit operates in current-limited mode for extended periods to manage phase loss, then motor operation is maintained, but component stress and system reliability deteriorate
Solution Approach 1:
The patent implements preliminary detection of phase loss conditions by monitoring DC bus voltage before the PFC circuit needs to switch to current-limited mode. By detecting voltage drops that indicate phase loss early, the system can take preventive action or alert the operator before extended operation in current-limited mode begins, thereby reducing component stress and improving overall system reliability.
Data Source
AI summary
A system for detecting a decrease in or loss of an input phase to a motor. A power rectifier rectifies and combines three input voltages to produce an output voltage to power the motor. A PFC circuit manages the power flowing to the motor. A sensing circuit located between the power rectifier and the PFC senses a voltage level of the power rectifier's output voltage. Alternatively, a sensing rectifier is connected before the power rectifier, and the sensing circuit senses the voltage level of the sensing rectifier's output voltage. A microprocessor compares the sensed voltage level to a threshold voltage level which is indicative of the decrease in or loss of one of the three input voltages, and if the former drops below the latter, then the microprocessor sends a signal to either shut off the motor or cause the PFC circuit to reduce the power flowing to the motor.