A robust sensorless start-up method using four step sequence for LCI system

This paper proposes a new senseless start-up method using a closed loop current control and a flux estimator without position sensor, and it is composed of four step sequence. Step 1 is applied for detection of the initial rotor position, and an initial rotor position is estimated around 1% of accuracy within 150ms. Step 2 is applied for a stable start-up state from the standstill through a closed loop current control, and is up to 3% of the rated speed of synchronous machine. Step 3 and 4 are used in the range generating a sufficient back-emf, and employ a flux estimator. The flux estimator consists of field flux model and flux voltage model, and rotor position/speed are estimated by using a phase locked loop. Field flux model is applied up to 5% of the rated speed. Performance of the proposed start-up method is evaluated by Simpower/Matlab simulation at overall speed range. To verify a feasibility of the proposed method, a 5kVA prototype of load commutated inverter (LCI) system is implemented. Experimental results show the proposed sensorless start-up method works well in the overall sequence region.