Current Control for Voltage Asymmetry Faults
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Solution Overview
Problem
Existing current control methods for voltage asymmetry faults in power grids face challenges with prolonged reactive current adjustment times, leading to overcurrent issues due to negative-sequence reactive current imbalances.
Innovation Solution
A method and system that calculate and apply specific current limit values based on post-fault and pre-fault voltage and current parameters to directly limit the magnitude of positive-sequence and negative-sequence reactive currents, preventing overcurrents and reducing adjustment time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If repeated iterative adjustment is used to obtain three-phase currents that meet requirements, then current accuracy is improved, but adjustment time increases excessively
Solution Approach 1:
The patent calculates initial current limits based on pre-fault negative-sequence voltage and post-fault negative-sequence voltage before the fault fully develops. This preliminary calculation provides a head start on the control adjustment, reducing the iterative cycles needed during actual fault response.
Solution Approach 2:
The patent introduces proportional relationships between current limits (I3 proportional to I1, I4 proportional to I2) to directly calculate appropriate current magnitudes without iterative adjustment. This parameter transformation approach converts a time-consuming iterative process into direct mathematical relationships.
2Reliability
If negative-sequence reactive current is injected to compensate voltage asymmetry, then voltage asymmetry impact is reduced, but three-phase current imbalance occurs causing overcurrent
Solution Approach 1:
The patent establishes feedback relationships where current limits are dynamically determined based on the ratio of pre-fault to post-fault negative-sequence voltages. This feedback mechanism automatically adjusts the negative-sequence current magnitude to prevent overcurrent while maintaining voltage asymmetry compensation.
Solution Approach 2:
The patent deliberately introduces asymmetric current limiting where different limits are applied to positive-sequence (I3) and negative-sequence (I4) currents. This asymmetric approach allows the negative-sequence current to compensate voltage asymmetry while being constrained to prevent harmful overcurrent effects.
Data Source
AI summary
A current control method and system for a voltage asymmetry fault is disclosed. When a voltage asymmetry fault occurs, a first current limit value is obtained based on a post-fault positive-sequence voltage and a pre-fault positive-sequence reactive current, and a second current limit value is obtained based on a post-fault negative-sequence voltage and a pre-fault negative-sequence voltage. A third current limit value and a fourth current limit value are obtained based on the first current limit value and the second current limit value. A magnitude of a positive-sequence reactive current is limited by using the third current limit value, and a magnitude of a negative-sequence reactive current is limited by using the fourth current limit value.