Mohammad Javad Morshed

Integral terminal sliding mode control to provide fault ride-through capability to a grid connected wind turbine driven DFIG

With the increased number of wind turbines being directly connected to the power grid comes new challenges regarding grid integration. Fault ride through capability during voltage sags are among the most challenging issues. Conventional ride through techniques result in a compromised control of the turbine shaft and grid current during deep voltage sags. In this paper, an integral terminal sliding mode controller is designed to control the Rotor Side Converter during deep voltage sags. In addition, to further improve the performance of the DFIG during voltage sags, an inverter and three single phase transformers are placed in series with the generator which is controlled using a Fuzzy logic controller. Computer experiments were carried out to validate the proposed control approach. Results clearly show that the proposed controller is very effective in maintaining the currents and voltages of the DFIG bus within acceptable ranges during deep voltage sags, hence preventing damages to the rotor side converter and ensuring the WT remains connected to the grid during such faults.

A comparison study between two sliding mode based controls for voltage sag mitigation in grid connected wind turbines

This paper deals with power quality restoration in grid-connected wind turbines subject to voltage sags. Since traditional voltage sag approaches cannot compensate for deep voltage sags, we design two sliding mode based voltage mitigation schemes for the rotor side converter of a DFIG-based wind turbine: an Integral Terminal Sliding Mode Control (ITSMC) and a standard SMC (SSMC). A detailed comparison study illustrating the performance of both methods is carried out under varying sag conditions. The methods are compared in terms of their ability to compensate for voltage sags and restore power quality when such faults occur. While the design aims at mitigating voltage sags with varying depths, a special focus is attributed to deep voltage sags since they represent the most frequent and costly power quality problem in DFIG-based wind turbines.

A feedback linearization control scheme for maximum power generation in wind energy systems

As the penetration of wind turbines into the power grid increases, greater emphasis is placed on designing advanced control approaches for optimum power generation. This paper proposes a novel control scheme for a DFIG-driven variable speed wind energy system. The approach aims at reaching optimum performance in terms of power generation at the point of common coupling. The control scheme is derived based on the feedback linearization technique, allowing both decoupling and linearization of the nonlinear multivariable system. The proposed approach is based on the theory of feedback linearization and is aimed at achieving optimum power generation at any wind speed within the operating range. Application of the proposed approach to a DFIG-based variable speed wind turbine has led to optimum operations at various speed ranges. Simplicity and ease of implementation of the overall scheme along with its fast dynamic response in addition to the optimum power production are the main positive features of the proposed approach.

Integral terminal Sliding Mode Control for maximum power production in grid connected PV systems

Photovoltaic (PV) systems have gained an ever increasing popularity as a renewable energy source. However, designing control schemes that ensure maximum power extraction for grid-connected PV arrays while properly mitigating grid faults is still a challenging problem in the control community. This paper proposes an integral terminal sliding mode control (ITSM) scheme for grid-connected PV arrays. The approach aims at maximizing power extraction while mitigating the effects of disturbances caused by irradiance fluctuations and oscillations in the bulk voltage. Effective elimination of the voltage drag and maximum power point tracking are among the positive features of the proposed approach. Efficiency of the proposed approach was assessed using a simulation study involving several operating conditions and various faulty situations.

Second order integral terminal sliding mode control for voltage sag mitigation in DFIG-based wind turbines

A second order integral terminal sliding mode control (SOITSMC) is proposed in this paper for a rotor side converter (RSC) of a DFIG-based wind turbine. The design is based on a novel sliding manifold and aims at improving the turbines performance while minimizing chattering. The controller performance and its robustness were studied under voltage sag conditions and parameter variations. Simulation results, carried out using realistic scenarios, confirmed the system robustness against parameter variations and its effectiveness in mitigating voltage sags. The performance of the proposed approach was further compared to that of a standard SMC approach in terms of voltage sag mitigation abilities and chattering alleviation. While both SMC approaches were able to mitigate the effects of voltage sags and protect the rotor circuit against over-currents, the proposed ITSMC was shown to be more effective than CSMC in mitigating deep voltage sags and reducing the chattering effect.