An Enhanced Low-Voltage Ride-Through for PMVG-Based WTS With Unified Super-Capacitor and Rotor Speed Control

This article presents a super-capacitor energy storage system (SC-ESS)-based low-voltage ride-through (LVRT) scheme for the grid-interfaced permanent magnet vernier generator (PMVG)-based wind turbine system (WTS). The WTSs should be grid code compliant to ride through transient voltage faults by injecting required reactive power to maintain grid stability and reliability. To do this, the proposed unified super-capacitor and rotor speed control (USSC) scheme estimates the real-time wind speed and analyses the WTS power characteristic during grid faults. Then, the presented USSC identifies the optimal operating point that minimizes active power diverted to the SC-ESS. This is achieved by elevated rotor speed operation through WTS aerodynamic characteristics-specific conditional selection of $q$ -axis reference current to the generator. Simultaneously, E.ON grid code-compliant reactive current injection to the grid is performed by ensuring converter rating constraints. Therefore, an enhanced LVRT is achieved through the unified operation of grid side converter, machine side converter, and dc/dc converter, which leads to reduced SC-ESS capacity rating. Simulation comparison and laboratory experiments verify the applicability of the presented scheme for LVRT in a 5-kW-rated PMVG-based WTS.