Reactive Power Converter Control Under Unbalanced Grid Faults
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Solution Overview
Problem
Reactive power compensation devices face issues with control margin deterioration and potential shutdown due to overvoltage or overcurrent when interconnected to power grids with small short-circuit capacity, especially during unbalanced failures like one-phase ground faults, leading to increased voltage in sound phases.
Innovation Solution
Incorporating a power converter with self-turn-off switching elements and a converter control unit that includes an AC voltage detection unit and an output limit unit to detect grid voltage and limit reactive power output when necessary, ensuring the device operates within its control margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reactive power is outputted during unbalance failure, then reactive power compensation is achieved, but voltage for sound phase further increases causing control margin deterioration
Solution Approach 1:
The control method dynamically adjusts the reactive power output based on real-time detection of grid voltage conditions. During unbalance failure, the controller detects the voltage reduction in affected phases and automatically limits reactive power output to prevent excessive voltage rise in sound phases, while maintaining full reactive power compensation capability when grid conditions are normal.
Solution Approach 2:
The system implements feedback control by continuously detecting grid voltage information and using this information to determine whether to limit reactive power output. The AC voltage detection unit provides real-time voltage data to the control unit, which adjusts reactive power output accordingly to maintain control margin while ensuring compensation capability.
2Reliability
If reactive power compensation is maintained during grid failure, then grid stabilization is achieved, but device may be stopped for protection due to overvoltage or overcurrent
Solution Approach 1:
The control method takes preliminary anti-action by proactively limiting reactive power output before overvoltage or overcurrent conditions occur. By detecting unbalance failure and automatically adjusting reactive power output in advance, the system prevents the development of harmful overvoltage and overcurrent conditions that would trigger protection shutdown, thereby maintaining continuous operation and grid stabilization capability.
3Adaptability or versatility
If grid voltage varies significantly, then adaptive control is required, but control performance deteriorates when control margin is insufficient
Solution Approach 1:
The system changes operating parameters dynamically by adjusting reactive power output levels based on detected grid voltage conditions. When unbalance failure is detected, the control parameter (reactive power output) is changed from full compensation level to a limited level, ensuring sufficient control margin is maintained while preserving adaptive control capability for different grid conditions.
Data Source
AI summary
A reactive power compensation device includes a power converter and a converter control unit, and compensates reactive power of an AC power grid by output reactive power of the power converter. The converter control unit includes an AC voltage detection unit and an output limit unit. The AC voltage detection unit detects voltage information of the AC power grid to which the power converter is connected. The output limit unit determines whether or not the output reactive power of the power converter needs to be limited, on the basis of the voltage information detected by the AC voltage detection unit, and in a case where the output reactive power needs to be limited, limits the output reactive power of the power converter.