Improved control strategy of dual star permanent magnet synchronous generator based tidal turbine system using sensorless field oriented control and direct power control techniques

Abstract

ABSTRACT This paper presents a grid-connected tidal stream system with a focus on the reduction of the number of sensors needed by the control scheme. The electromechanical converter is a dual star permanent magnet synchronous generator (DS-PMSG) driven by a horizontal axis marine current turbine (HA-MCT). The generator is controlled via the field-oriented control (FOC) strategy, the speed and the position of the rotor are estimated using an extended Kalman filter (EKF), and the speed is regulated using a fuzzy logic controller. The grid side converter (GSC) consist of a two level voltage source inverter controlled by a virtual flux-based direct power control strategy (VF-DPC), and the current is filtered using an LCL filter. The system is simulated using Matlab/Simulink environment, the simulation results show the efficacy of the proposed control scheme, fuzzy speed regulator, and the EKF estimator, where relative mean error (MRE) of speed tracking is only 0.004, and MRE of estimated speed is as low as 7.3e-6, but a low rotor position estimation error of 1.76 degrees can be observed, however, the high number of pole pairs of the generator amplifies the effect of position error, causing divergences between the controlled dq currents seen by the control scheme and the real dq current that flows in the machine, and a decrease of system effeciency; however, the stability is not affected.