Reactive Current Control in Power Converters After AC Fault Clearance
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Solution Overview
Problem
Existing power conversion devices fail to maintain a constant system voltage immediately after a fault is cleared in AC systems, often resulting in overvoltage transients due to continued reactive power output after fault clearance.
Innovation Solution
A power conversion device with a control system that generates reactive-current command values to limit reactive power output during faults and adjusts these commands post-fault to prevent overvoltage, including embodiments with timer-based and reactive-current regulator configurations to manage reactive power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter continues to output leading reactive power after fault clearance to maintain system voltage, then the system voltage is maintained, but overvoltage transient occurs
Solution Approach 1:
The control device detects AC voltage decrease as a preliminary indicator of fault, activates the timer in advance before fault clearance, and prepares the reactive power limitation strategy beforehand. This preliminary action ensures that when the fault is cleared and voltage is restored, the reactive power is already limited, preventing overvoltage transient while maintaining system voltage stability.
2Object-affected harmful factors
If the reactive power is uniformly limited for a certain amount of time after fault detection, then overvoltage development is inhibited, but constant voltage cannot be maintained immediately after fault clearance
Solution Approach 1:
The control device dynamically adjusts the reactive power limitation strategy based on real-time system conditions. The timer-based control provides dynamic timing for when limitation starts and ends, while the AC voltage feedback continuously monitors system state and adjusts the reactive-current command value accordingly. This dynamic control ensures constant voltage maintenance after fault clearance while preventing overvoltage during the transient period.
Data Source
AI summary
A power conversion device includes: a power converter that converts power between an alternating-current (AC) system and a direct-current (DC) circuit; and a control device that controls the power converter. The control device includes: a command generation unit for generating a reactive-current command value for the power converter based on the AC voltage of the AC system and an AC-voltage command value; and a fault determination unit for determining presence or absence of a fault in the AC system based on the AC voltage. When the fault occurs in the AC system and cleared, the command generation unit generates a reactive-current command value to limit the reactive current output from the power converter.