Grid Converter Synchronization Fault Prevention
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Solution Overview
Problem
Power converters in electrical grids are prone to tripping due to severe short duration voltage dips, leading to synchronization errors and prolonged recovery times, which disrupt industrial operations.
Innovation Solution
A hybrid phase locked loop (PLL)-based control scheme that utilizes a delayed signal cancellation (DSC) PLL during normal operation and switches to a single input fuzzy logic controller (SFLC) PLL during voltage dips to rapidly re-synchronize the converter with the grid, ensuring smooth transition back to DSC-PLL upon recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PLL control mode is used during voltage dips, then the converter maintains stable operation under normal conditions, but the converter trips and loses synchronization during severe voltage dips
Solution Approach 1:
The control system dynamically switches between two PLL control modes based on grid conditions. During normal operation, the conventional PLL mode is used for stable synchronization. When voltage dips are detected, the system transitions to an enhanced PLL control mode that is specifically designed to maintain synchronization under severe grid disturbances, thereby preventing converter tripping and maintaining operational continuity.
Solution Approach 2:
The enhanced PLL control mode modifies critical control parameters such as phase-locked loop bandwidth, gain factors, and synchronization thresholds to accommodate severe voltage dip conditions. These parameter adjustments allow the converter to maintain accurate synchronization even when grid voltage magnitude and frequency deviate significantly from nominal values, preventing synchronization loss during voltage dips.
2Reliability
If the converter undergoes capacitor pre-charging process after voltage dip recovery, then the converter ensures safe resumption of operation, but the recovery time is prolonged
Solution Approach 1:
The enhanced PLL control mode maintains capacitor charge levels within acceptable operating ranges even during voltage dip events by adjusting power flow control and energy management. This preliminary action ensures that when the voltage dip ends, the capacitors are already sufficiently charged to immediately resume normal converter operation without requiring a lengthy pre-charging delay, thus reducing recovery time while ensuring safe resumption.
Solution Approach 2:
The control system maintains continuous synchronization tracking and power conversion functionality throughout the voltage dip event using the enhanced PLL mode, rather than completely shutting down. This continuity of useful action allows the converter to seamlessly transition back to normal operation immediately upon voltage dip recovery, eliminating idle recovery time while ensuring safe and stable resumption of full power operation.
3Reliability
If the converter trips during voltage dips, then the converter protects itself from synchronization errors, but industrial manufacturing facilities and grid customers experience adverse effects
Solution Approach 1:
The dynamic switching between conventional and enhanced PLL control modes enables the converter to adapt its protection strategy to actual grid conditions. During severe voltage dips, the enhanced mode maintains synchronization and prevents unnecessary tripping, ensuring continuous operation and avoiding disruption to industrial facilities and grid customers, while still providing protection against genuine synchronization failures.
Solution Approach 2:
The enhanced PLL control mode converts the potentially harmful voltage dip disturbance into an manageable condition by actively compensating for its effects through adaptive control. This allows the converter to not only survive the voltage dip but to maintain stable operation and synchronization, transforming what would normally be a fault condition requiring protective tripping into a routine disturbance that the system can ride through, thereby ensuring continuous productivity.
Data Source
AI summary
A method and system of controlling a power converter coupled between one of a motor drive inverter and a grid-tie inverter within an electric grid. The method comprises operating the power converter in a first PLL control mode that establishes a state of synchronization with the electric grid, detecting a grid disturbance voltage dip event; keeping the power converter synchronized and preserving charge of a set of dc-link capacitors, switching from the first PLL control mode to a second PLL control mode of operation of the power converter to obtain fast re-synchronization after dip period ends, and reverting to operation in the first PLL control mode upon re-establishing of the state of synchronization.