Experimental results of a DC bus voltage level control for a load-controlled marine current energy converter

Abstract

This paper investigates three load control methods for a marine current energy converter using a vertical axis current turbine (VACT) mounted on a permanent magnet synchronous generator (PMSG). The three cases are; a fixed AC load, a fixed pulse width modulated (PWM) DC load and DC bus voltage control of a DC load. Experimental results show that the DC bus voltage control reduces the variations of rotational speed by a factor of 3.5 at the cost of slightly increased losses in the generator and transmission lines. For all three cases, the tip speed ratio λ can be kept close to the expected λopt. The power coefficient is estimated to be 0.36 at λopt; however, for all three cases, the average extracted power was about ~ 19%. A maximum power point tracking (MPPT) system, with or without water velocity measurement, could increase the average extracted power.