This paper presents the simulation results of a grid-connected wind driven doubly fed induction machine (DFIM) together with some real machine performance results. The modeling of the machine considers operating conditions below and above synchronous speed, which are actually achieved by means of a double-sided PWM converter joining the machine rotor to the grid. In order to decouple the active and reactive powers generated by the machine, stator-flux-oriented vector control is applied. The wind generator mathematical model developed in this paper is used to show how such a control strategy offers the possibility of controlling the power factor of the energy to be generated.

A PI-based control algorithm to govern the net reactive power flowing between wind farms composed of doubly fed induction generators (DFIG) and the grid is proposed in this paper. The motivation underlying consists in demonstrating that secondary voltage control strategies may take advantage of such wind farms as if they were continuous reactive power sources. For that purpose, the local control structure of DFIGs is first described in some detail. The open-loop behavior of a 33 660-kW DFIG wind farm regarding the net power factor is then analyzed via simulation. Based on this study, a net reactive power control algorithm is devised for wind farms made up exclusively of DFIGs. Experimental results obtained by testing it both local and remotely, over a real wind farm located in Navarre-northern Spain-are also provided. In particular, net reactive power set-points supplied remotely to the wind farm are derived by an Optimal Power Flow (OPF) algorithm running at the operation central office of the utility company.

Based on the stator-flux-oriented electromechanical model of a doubly fed induction machine (DFIM), this paper presents two different approaches to wind farm modeling. Particularly, the overall control system of the DFIM is modeled in detail, so that tuning equations that allow adjusting the parameters of its proportional-integral (PI) compensators straightforwardly are provided. In addition to validating the wind generator model proposed, experimental tests carried out on a 660-kW doubly fed induction generator (DFIG) prove that such a control system makes it possible to govern separately its stator-side or net active and reactive powers. The two wind farm models proposed, which are assumed to be made up of DFIM type generators exclusively, are mainly devised to assist the design and test of closed-loop control algorithms for the wind farm total power factor. They generally imply significantly different computational loads, so that the second may be regarded as a simplified version of the first one. The net active and reactive power performances of both wind farm models are finally compared via simulation, which allows identifying the stronger and weaker points associated to each model

This paper presents a hydrogen powered hybrid solid oxide fuel cell-steam turbine (SOFC-ST) system and studies its optimal operating conditions. This type of installation can be very appropriate to complement the intermittent generation of renewable energies, such as wind generation. A dynamic model of an alternative hybrid SOFC-ST configuration that is especially suited to work with hydrogen is developed. The proposed system recuperates the waste heat of the high temperature fuel cell, to feed a bottoming cycle (BC) based on a steam turbine (ST). In order to optimize the behavior and performance of the system, a two-level control structure is proposed. Two controllers have been implemented for the stack temperature and fuel utilization factor. An upper supervisor generates optimal set-points in order to reach a maximal hydrogen efficiency. The simulation results obtained show that the proposed system allows one to reach high efficiencies at rated power levels.