Dual Current Controller for Inverter Phase Selection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional protection functions in power networks fail to accurately detect faulted phases for inverter-interfaced renewable energy sources due to differences in fault current signatures compared to synchronous generators, leading to maloperation and potential disconnection of healthy phases or failure in distance protection.
Innovation Solution
The controller adjusts both negative and positive-sequence-current angles to mimic synchronous generator fault current angles, allowing the traditional current-angle-based phase selection method to operate correctly while maintaining the ability to control reactive power, using a proportional resonance controller in the stationary frame to reduce relay delay and eliminate the need for synchronous frame calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the inverter is controlled to generate fault currents with different signatures from synchronous generators, then the inverter can operate independently with its own control objectives, but conventional protection functions fail to accurately detect faulted phases
Solution Approach 1:
The controller dynamically adjusts the fault current signature parameters (magnitude, phase angle, harmonic content) to match synchronous generator characteristics during fault conditions, enabling conventional protection functions to operate accurately while maintaining inverter control flexibility during normal operation
Solution Approach 2:
The inverter controller transitions between different operational modes: during normal operation it maintains independent control objectives, but during fault detection it dynamically adapts its current signature to mimic synchronous generators, allowing both operational requirements to be satisfied at different times
2Reliability
If the protection algorithms are modified to accommodate inverter fault current signatures, then accurate fault detection can be achieved, but the complexity of the protection system increases
Solution Approach 1:
Instead of modifying protection algorithms to recognize inverter signatures, the inverter controller creates a copy of the synchronous generator fault current signature characteristics, allowing existing conventional protection algorithms to function without modification
Solution Approach 2:
Rather than changing the protection system to adapt to the inverter, the approach is inverted: the inverter changes its behavior to adapt to the existing protection system, maintaining simplicity in the protection algorithms
3Measurement precision
If the inverter controller adjusts current angles to mimic synchronous generators, then phase selection accuracy is improved, but the ability to control reactive power independently is reduced
Solution Approach 1:
The controller implements periodic switching between different control modes: during fault detection periods it adjusts current angles to mimic synchronous generators for accurate phase selection, while during normal operation periods it restores independent reactive power control capability
Solution Approach 2:
The controller dynamically adjusts the degree of signature mimicry based on system conditions, allowing flexible transition between prioritizing phase selection accuracy and maintaining reactive power control independence
Data Source
AI summary
A method for correct operation of the current-angle-based phase-selection method (PSM) is based on a proper dual current controller (DCC) for inverter interfaced sources during unbalanced fault conditions. The fault type is determined in the inverter using voltage-angle-based PSM. Accordingly, fault-type zones' bisectors of the current-angle-based are determined. Consequently, an initial negative-sequence current angle reference is determined to force the relative angle between the negative- and zero-sequence currents in the center of its correct fault-type zone. The initial positive-sequence current angle is determined according to reactive current requirements by grid codes. These initial angles are updated for accurate operation of the PSM and appropriate reactive current injection. Negative- and positive-sequence current references are determined in the stationary frame to comply with the reference angles and inverter's thermal limits. These references are regulated by a proportional-resonance controller.