Inverter Ground Fault Detection Using Zero Vector Sampling
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Solution Overview
Problem
Existing methods for detecting ground faults in inverters using leg-shunt resistors are ineffective, as they cannot accurately determine the occurrence of a ground fault due to limitations in current detection regions and voltage utilization levels, which can lead to motor damage and safety risks.
Innovation Solution
A method that involves detecting output currents for three phases, determining voltage and current levels, applying a zero vector through pulse-width modulation, and sampling currents within a zero vector zone to determine if the sum of output currents exceeds a preset ground fault level, triggering a protection operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If current detection is performed using leg-shunt resistors, then fabrication cost is reduced, but ground fault detection capability is lost
Solution Approach 1:
The method applies preliminary action by intentionally creating a zero-vector state before performing current detection. During this zero-vector period, all switching elements are turned off, creating a known state where any detected current must be leakage current rather than load current, enabling ground fault detection capability with leg-shunt resistors
Solution Approach 2:
The method changes the operational parameter by utilizing the zero-vector state (where all switching elements are off) as a detection window. By sampling currents during this specific time period when normal power conversion is suspended, the system can detect ground faults using the same leg-shunt resistors without requiring additional hardware
2Device complexity
If conventional current detection method is used with leg-shunt resistors, then device complexity is reduced, but measurement precision for ground fault detection deteriorates
Solution Approach 1:
The method creates a preliminary detection opportunity by introducing a zero-vector period where all switching elements are turned off. During this predetermined time window, the system samples currents to detect ground faults, transforming the limitation of leg-shunt resistors into an advantage by using this specific operational state for measurement
Solution Approach 2:
The method maintains continuous ground fault detection capability by integrating the detection process into the normal PWM switching cycle. The zero-vector state is incorporated as part of the continuous switching operation, allowing detection to occur repeatedly throughout operation without interrupting the overall power conversion function
Data Source
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AI summary
The present invention relates to a method for detecting a ground fault in an inverter. The method for detecting the ground fault in the inverter in a current detection using leg-shunt resistors includes detecting output currents of three phases of the inverter, determining whether or not a voltage utilization of the inverter is not less than a preset allowable voltage level, and determining an occurrence or non-occurrence of the ground fault on the inverter.