Improved Indirect Power Control (IDPC) of Wind Energy Conversion Systems (WECS)

In this chapter, a brief general introduction focuses on the well-known topologies of wind energy conversion systems (WECS), on proposed controls and generators by the scientific researchers. One part will be devoted to the latest research that has addressed the performance problems of wind systems and their results (in simulation). There will be also some arguments that reflect the main proposed ideas in this eBook, the proposed selections and their applications in simulation. We present the selecting criteria in particular the type of: generator, controls and theirs application in simulation studies. Also, we discuss in a detailed section on the different contributions of eBook that define the improvement of the proposed algorithms in each chapter. Furthermore, the organization and structure of eBook will be as follow; chapter one is devoted on the state of the art of wind systems and their controls, in particular using the doubly fed induction machine (DFIM). The simulation part is provided in two chapters (3 and 4). The limitations and problems encountered during the realization of this eBook are well described in the following section. After solving problems, very satisfactory simulation results have been found which reflect the quality of the scientific contribution including more papers of conferences; Journal papers were published during this eBook.

The aim of this chapter is to present an overview of the state of technology and discuss some technology tendency in the Power Electronics (PE) used for Wind Power Applications (WPA). Firstly, technological and commercial developments in wind power generation are generally discussed. Next, the wind turbine concept is illustrated and explained using different types of generator. The control structure of wind-turbines (WTs) is explained using DFIG, Asynchronous and Synchronous Generator (ASG and SG). Finally, the last section focuses on a detailed literature review describing DFIG based wind turbine-generator systems in terms of modeling and control strategies.

In this chapter, we present a comparative study of conventional Indirect Power Control (IDPC) algorithm of DFIG-Wind turbine in grid-connection mode, using PI and PID controllers via Maximum power point tracking (MPPT) strategy. Firstly, the conventional IDPC based on PI controllers will be described using simplified model of DFIG through stator flux orientation and wind-turbine model. The MPPT strategy is developed using Matlab/Simulink® with two wind speed profiles in order to ensure the robustness of wind-system by maintaining the Power coefficient (Cp) at maximum value and reactive power at zero level; regardless unexpectedF wind speed variation. Secondly, the rotor side converter (RSC) and Grid side converter (GSC) are illustrated and developed using Space vector modulation (SVM) in order to minimize the stress and the harmonics and to have a fixed switching frequency. In this context, the switching frequency generated by IDPC to control the six IGBTs of the inverter (RSC), and this control algorithm works under both Sub- and Supersynchronous operation modes and depending to the wind speed profiles. The quadrants operation modes of the DFIG are described in details using real DFIG to show the power flow under both modes (motor and generator in the four (04) quadrants. Finally, the conventional IDPC have several drawbacks as: response time, power error and overshoot. In this context, the PID and MRAC (adaptive regulator) controllers are proposed instead of the PI to improve the wind-system performances via MPPT strategy with/without robustness tests. The obtained simulation results under Matlab/Simulink® show high performances (in terms of power error, power tracking and response time) in steady and transient states despite sudden wind speed variation, whereas big power error and remarkable overshoot are noted using robustness tests, so the proposed IDPC can not offer big improvement under parameter variation.

This chapter presents an improved Indirect power control (compared to the conventional one illustrated in chapter: 03) based on robust and suitable controllers (Robust and Intelligent controllers) to control the d-q axes currents (Ird and Irq) respectively. In order to overcome the speed/efficiency trade-off and divergence from peak power under fast variation of wind speed; three intelligent controllers (based on, T1-FLC, T2-FLC and NFC) are proposed to control the rotor direct and quadrature currents (Ird and Irq) instead of PID controllers, for grid-connected doubly fed induction generator (DFIG). The same wind-turbine (DFIG (4kW) and turbine (4.5 kW)) used in last chapter will be developed again in order to make a comparative study between the wind-system performance algorithms. The SVM strategy (to ensure the fixed switching frequency and to minimize the harmonics) is used in RSC for switching signals generation to control the inverter. In this chapter, mathematical model of each proposed controller is described in detail. The MPPT strategy is also developed in the three proposed algorithms in order to extract the maximum wind power by keeping the reactive power equal to zero value. The main aim of the proposed control is to improve the wind system performance despite the sudden wind speed variation and the DFIG’s parameter variation in transient and steady states. The simulation results using the Matlab/Simulink environment (under three proposed modes and using robustness tests) show that the intelligent controller offered high power quality in spite of wind-speed variation have superior dynamic performance and are more robust during parameter variation.