Hybrid Cascaded HVDC Fault Ride-Through via LCC-MMC Power Control
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Solution Overview
Problem
Hybrid cascaded HVDC transmission systems face challenges in receiving-end AC fault ride-through, particularly with overcurrent and overvoltage issues due to commutation failures and slow control response speeds, leading to potential device damage and power imbalances.
Innovation Solution
A method is introduced where the LCC on the rectifier side quickly increases its firing angle to reduce DC voltage and power, and MMCs on the inverter side adjust outer-loop active power references to suppress overcurrent and overvoltage, enabling faster fault response and stable operation without relying on inter-station communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LCC on inverter side uses conventional control during AC fault, then commutation failure occurs and DC voltage drops to zero, but this causes sharp increase in DC current and overvoltage on submodule capacitors
Solution Approach 1:
The patent applies preliminary anti-action by having the LCC rectifier side detect receiving-end AC faults and preemptively adjust its output power and voltage. The control method detects faults on the receiving end and the LCC on the rectifier side quickly reduces its output power and DC voltage through firing angle control, counteracting the fault effects before they propagate to cause commutation failure and overcurrent conditions.
Solution Approach 2:
The patent implements preliminary action by enabling the LCC rectifier to detect receiving-end AC faults and adjust its operating parameters in advance. The system performs preliminary fault detection and control adjustment on the sending end, modifying DC voltage and power transmission before the fault fully develops, thereby preventing commutation failure and reducing the severity of overcurrent and overvoltage conditions.
2Reliability
If LCC on rectifier side uses slow control response, then receiving end bears huge surplus power, but this forces submodules in MMC to be overcharged causing overvoltage
Solution Approach 1:
The patent applies feedback by implementing a closed-loop control system where the LCC rectifier continuously monitors receiving-end AC conditions and adjusts its output accordingly. The control method uses feedback from receiving-end voltage and power measurements to dynamically adjust the rectifier's firing angle and output power, ensuring real-time power balance and preventing submodule overcharging and overvoltage conditions.
Solution Approach 2:
The patent implements dynamics by enabling the LCC rectifier to dynamically adjust its operating parameters in response to changing fault conditions. The control system continuously modifies the firing angle and output power based on real-time receiving-end AC voltage and power measurements, allowing the system to adapt quickly to fault conditions and maintain power balance, preventing submodule overvoltage.
3Reliability
If receiving-end AC voltage decreases during fault, then power transmission capacity of MMC weakens, but this results in larger power imbalance between sending and receiving ends
Solution Approach 1:
The patent applies preliminary anti-action by having the LCC rectifier detect receiving-end AC faults and preemptively reduce its output power and DC voltage. This preliminary adjustment counteracts the power imbalance that would otherwise occur when receiving-end voltage decreases, preventing excessive power accumulation and maintaining system stability throughout the fault period.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the LCC rectifier's firing angle and output power parameters in response to receiving-end fault conditions. The control method changes key operating parameters (firing angle, DC voltage, output power) based on real-time fault detection, allowing the system to adapt to varying receiving-end voltage conditions and maintain power balance.
Data Source
AI summary
The present disclosure provides a method for controlling the receiving-end alternating-current (ac) fault ride-through of the hybrid cascaded high-voltage direct-current (hvdc) transmission system. According to the method, a line commutated converter (lcc) on the rectifier side determines the occurrence of a receiving-end ac fault based on a change in an electrical quantity of its dc port, and quickly reduces the dc voltage on the rectifier side by increasing the firing angle, so as to quickly suppress an overcurrent. The mmcs on the inverter side, which use the constant active power control, correct the outer-loop active power reference values to transmit as much active power as possible, thereby reducing the surplus power of the receiving-end system and suppressing an overvoltage for submodule capacitors of the mmcs.