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This paper presents a comparative study on the most popular control strategies used to control high power, Direct Drive Wind Turbines. The studied wind turbine is equipped with a supervision scheme in order to fulfil Grid connection requirements (GCR). For the generator-side converter, performances of the Field Oriented Control (FOC) and Direct Torque Control (DTC) are compared. Concerning the grid-side converter, Voltage Oriented Control (VOC) and Direct Power Control (DPC) are examined. The comparison is based on various criteria mainly, steady-state and transient performances. In addition, performances are evaluated in terms of low voltage ride through capabilities (LVRT), power limitation and reactive power control. It has been shown that best power quality features are given by vector control techniques. On the other hand, direct control offers the better dynamic response and power cross-coupling is substantially lower. Furthermore, during fault, the wind turbine does not trip for both techniques. However, vector control is better since it gives low power oscillations

This paper proposes and develops a new direct voltage control (DVC) approach. This method is designed to be applied in various applications for AC drives fed with a three-phase voltage source inverter (VSI) working with a constant switching time interval as in the standard direct torque control (DTC) scheme. Based on a very strong min(max) criterion dedicated to selecting the inverter voltage vector, the developed DVC scheme allows the generation of accurate voltage forms of waves. The DVC algorithm is implemented on a dSPACE DS1104 controller board and then compared with the space vector pulse width modulation technique (SVPWM) in an open loop AC drive circuit. To demonstrate the efficiency of the developed algorithm in real time and in closed loop AC drive applications, a scalar control scheme for induction motors is successfully implemented and experimentally studied. Practical results prove the excellent performance of the proposed control approach.

The photovoltaic (PV) system is one of the renewable energies that attract the attention of researchers in the recent years. The output powers of photovoltaic PV system are crucially depending of the two variable factors, which are the cell temperatures and solar irradiances. Since the maximum power point (MPP) varies, based these variables, appropriate algorithms must be utilized to track the MPP and maintain the operation of the system in it. These algorithms, known as Maximum Power Point Tracking (MPPT), are essential in a PV system. This paper presents evaluations among the most usual MPPT control strategies, doing meaningful studies on merits, demerits and classification of each method. The algorithms, were digitally implemented on the dSPACE DS1104 platform, are Constant voltage (CV), short circuit current (SCC), perturb and observe (P&O) and incremental conductance (IC). The PV system operate at MPPT is used to supply three phase induction motor driving a centrifugal pump. DC/DC boost converter and three phase inverter are connected into between PV generator and motor for power conditioning. The experimental results verify that the proposed MPPT algorithms are able to find real global MPP correctly and quickly. Advantages, disadvantages, and characteristics of different MPPT techniques are studied, evaluated, and compared through extensive computational experiments.

Large scale integration of wind power has become one of the most important challenges of wind industry. To increase wind power penetration on power systems, modern wind farms are required to operate like conventional generating unit. They should participate to frequency and voltage control and stay connected to the grid during severe disturbances. In this context, an aggregate model of a grid connected wind farm is developed in this paper. The wind farm includes 25 direct drive wind turbines of 2 MW rating each. The cluster or multi-machine equivalent representation was used to achieve the necessary accuracy under different incoming winds. This model will be used to investigate the behavior of power systems including wind farms and to improve the planning and the exploitation of electricity systems. A hierarchical control approach is developed to manage wind farm active and reactive generation during voltage dips and to investigate its Low Voltage Ride-Through (LVRT) capacity.

This paper analyses, from a steady state point of view, the potential benefit of a wind farm control strategy whose main objective is to maximize its total energy yield over its lifetime. Unlike the conventional approach in which each wind turbine operation is optimized individually to maximize its own energy capture, the proposed control strategy aims to optimize the whole system by operating some wind turbines at suboptimum points, so that the wake effect within the wind farm is reduced and therefore the total power generation is maximized. The methodology used to assess the performance of both control approaches is presented and applied to a particular study case consisting of three wind turbines. The paper contains a comprehensive wake model considering single, partial and multiple wake effects. The study also takes into account the Blade element theory and actuator disc theory to accurately compute both power and thrust coefficient of each wind turbine. The results suggest a good potential of the proposed concept, since an increase in the annual energy captured by the wind farm from 0.3% up to 3.7% may be achieved (depending on the wind rose at the wind farm location).

To increase the output efficiency of a photovoltaic (PV) system, it is important to apply an efficient maximum power point tracking (MPPT) technique. This paper describes the analysis, the design and the experimental implementation of the tracking methods for a standalone PV system, using two approaches. The first one is the constant voltage (CV) MPPT method based on the optimum voltage, which was deduced experimentally, and considered as a reference value to extract the optimum power. The second one is the increment conductance (IncCond) MPPT method based on the calculation of the power derivative extracted by the installation. The output controller can adjust the duty ratio to the optimum value. This optimum duty ratio is the input of a DC/DC boost converter which feeds a set of Moto-pump via a DC/AC inverter. This paper presents the details of the two approaches implemented, based on the system performance characteristics. Contributions are made in several aspects of the system, including converter design, system simulation, controller programming, and experimental setup. The MPPT control algorithms implemented extract the maximum power point (MPP), with satisfactory performance and without steady-state oscillation. MATLAB/Simulink and dSpace DS1104 are used to conduct studies and implement algorithms. The two proposed methods have been validated by implementing the performance of the PV pumping systems installed on the roof of the research laboratory in INSAT Tunisia. Experimental results verify the feasibility and the improved functionality of the system.