Per-Phase Grid-Forming Control for Unbalanced Fault Current Limiting
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Solution Overview
Problem
Existing grid-forming control systems for power converters are vulnerable to overcurrent during unbalanced faults and severely unbalanced loads, as they are limited in current limiting capabilities, especially during unbalanced conditions.
Innovation Solution
A grid-forming control system that includes a phasor determination unit, a GFM controller, and a control loop for each phase of a multi-phase power converter, which determines frequency and voltage references based on active and reactive power measurements, and balancing feedback across phases, enabling effective current and voltage control during unbalanced faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grid-forming control imposes terminal voltage to maintain stable frequency and magnitude, then grid stability is improved, but the converter becomes vulnerable to overcurrent during unbalanced faults
Solution Approach 1:
The system dynamically changes voltage magnitude parameters for each phase based on detected fault conditions. During unbalanced faults, the controller adjusts voltage magnitudes independently for each phase while maintaining frequency stability, allowing the system to respond adaptively to different fault scenarios rather than maintaining fixed voltage parameters
Solution Approach 2:
The control system segments the voltage control into independent per-phase control rather than treating all phases uniformly. Each phase can have its own voltage magnitude reference adjusted according to its specific conditions, enabling selective voltage control that prevents overcurrent in healthy phases while addressing faults in affected phases
2Reliability
If existing current limiting methods are applied to grid-forming converters, then fault current is limited during balanced faults, but current limiting fails during unbalanced faults or with severely unbalanced loads
Solution Approach 1:
The system applies asymmetric control strategies for different fault types by detecting the nature of the fault and applying appropriate current limiting only to affected phases. Healthy phases continue to operate normally while faulted phases receive current limiting control, creating an asymmetric response that maintains overall system reliability
Solution Approach 2:
The control system dynamically adapts its current limiting strategy based on real-time detection of fault conditions. The controller transitions between different control modes (voltage control for healthy phases, current limiting for faulted phases) based on system state, making the current limiting capability effective across varying fault scenarios
3Device complexity
If balanced voltage reference is provided to power converter, then simple control is maintained, but effective control during unbalanced conditions is limited
Solution Approach 1:
The system dynamically adjusts voltage reference complexity based on system conditions. During normal operation, simple balanced voltage references are used. During unbalanced faults, the system automatically transitions to dynamic per-phase voltage magnitude control, providing the necessary complexity only when required by the system state
Data Source
AI summary
Systems, methods, and media for grid forming control having balancing feedback across the phases are provided. The grid forming control can include phasor determination configured to, for each of the plurality of phases, receive a frequency reference and determine an active and reactive power for the phase based on an electrical measurement for the phase and the frequency reference, GFM control configured to, for each of the plurality of phases, determine the frequency reference based on the active power for the phase and balancing feedback across the plurality of phases and determine a voltage magnitude reference for the phase based on the reactive power for the phase and balancing feedback across the plurality of phases, and a control loop configured to, for each of the plurality of phases, determine a control signal for a power converter based on the determined voltage magnitude reference for the phase.