A Study of 10MW Load Commutated Inverter for Gas-Turbine Start-up

This paper proposes a stable sensorless start-up method of the actual 10MW LCI system and analyzed the characteristic of the existing system for the simulation modeling. The 10MW LCI system is modeled to verify the performance of the proposed sensorless methods, controllers, operating modes and so on. The simulation model is designed by applying the operating conditions of the 10MW actual system and parameters of the 200MVA synchronous machine. The proposed sensorless methods for initial start-up of the gas-turbine is composed of the initial rotor position detector and methods for the low speed and high speed range. The operation mode of the LCI system is divided into the forced commutation mode and natural commutation mode according to the rotor speed, and the sensorless methods are applied differently by the operation mode. The sensorless methods are referred to as closed loop current control and flux estimator. The initial rotor position detector is applied to detect rotor position at the standstill of the machine using an induced back-emf by the injection of a field current, and the estimated error is less than 1%. After estimation of the initial rotor position, the LCI system is operated by the closed loop current control at the forced commutation mode, and it operates at less than 10% of the rated speed. The LCI system is operated from 10% to 90% of the rated speed through the flux estimator for the natural commutation mode, and the rotor speed/position is estimated by the phase locked loop. The performance of proposed sensorless start-up and the operation modes of LCI system is verified by the proposed simulation modeling.