TYPE-2 FUZZY LOGIC CONTROLLERS FOR RENEWABLE ENERGY SYSTEMS

Abstract

The uncertainty in the availability of wind speed and solar radiation is a bottleneck, to export bulk amount of power from the wind and solar energy systems to the utility grid. For reliable grid operation, the modern grid codes demand fault ride through (FRT) capability from the distributed generation sources. Designing a robust control strategy for e ective power sharing, fault ride through and grid interacted operation is a challenging task to the control engineers due to uncertainty in the operating conditions. In response to this challenge, this thesis, proposes a novel control strategy with interval type-2 fuzzy sets (IT-2 FSs), for handling the uncertainties in network operating conditions. The IT-2 FSs, with its third dimension and foot print of uncertainty (FOU) in the membership functions (MFs) o ers an additional degree of freedom in the controller design to take the uncertainties into account. The type-2 fuzzy logic controllers (FLCs) are designed for the wind energy system with varying levels of complexity of the plant model. The feasibility of the controller for real-time applications is investigated through the simulations on Real time digital simulator (RTDS). The controller is implemented on a digital signal processor (DSP) based DSPACE 1104 module, interfaced through RTDS in the Hardware-in-loop (HIL) environment. The main focus of this thesis is to investigate the applicability of type-2 fuzzy logic for real-time wind energy systems through designing controllers for the power electronic converters of doubly fed induction generator (DFIG), with varying network operating conditions. The core objectives of this research work are formulated as Preliminary study on applicability of type-2 FSs for wind energy systems and optimization of its parameters with MATLAB based simulations Design and performance analysis of Type-2 FLC, for a grid connected DFIG under the uncertainties of grid faults and load changes Performance analysis of Type-2 FLC with an IEEE-34 bus distributed network, connected with DFIG based wind energy system Design and analysis of type-2 FLC for a microgrid, connected with DFIG, PV system and battery storage system. The type-2 FSs have been recognized as a suitable tool for modeling the numerical and linguistic uncertainties. In order to establish its applicability for renewable energy systems, iii type-2 FLC is designed and tested under various possible contingencies. As a preliminary study, type-2 FLC is designed for grid connected DFIG and comparative performance analysis is done with the type-1 FLC. Tuning the control parameters of type-2 FLC is a challenging task, because the plant model is complex and sensitive. To get the optimal controller parameters, a constrained optimization problem is formulated, and solved using an evolutionary optimization method i.e. genetic algorithm. In order to study the e ect of FOU, the performance is evaluated with perturbed parameters. Doubly fed induction generator is very sensitive to voltage variations in the grid, which pose limitations for wind power plants during the grid integrated operation. Handling the uncertainty in wind speed and grid faults is a major challenge to compliant with the modern grid code requirements. This work proposes a new control strategy for rotor side converter using interval type-2 fuzzy sets which can counter the e ects of uctuations in wind speed and low voltage during severe grid fault conditions. A 2 MW DFIG connected to the grid is modeled in simulation software RSCAD and interfaced with real time digital simulator (RTDS) to perform the analysis with real-time simulations . The RTDS platform is considered by many research laboratories as real-time testing module for controller prototyping and also for hardware in the loop (HIL) applications. The controller performance is evaluated in HIL con guration, by performing the real-time simulations under various parameter uncertainties. The proposed controller can improve the low voltage ride through capability of DFIG compared to that of proportional integral (PI) and type-1 fuzzy controller. Distributed generation (DG) systems based on renewable energy sources are seen as a reliable and alternative to the conventional energy sources such as coal and oil. Designing an e ective control strategy for DGs is a challenging task, if the distribution network comprises unbalanced loads and variable network parameters. The presence of third dimension in the type-2 membership function o ers an additional degree of freedom in the design of the proposed controller to contribute to power oscillations damping and voltage recovery following disturbances in the network. The vector control with proposed strategy for DFIG is able to handle uncertainties in the operating conditions in the network like faults, load changes and wind speed. The performance of the controller is evaluated through real time simulations on IEEE 34-bus distribution network with various network uncertainties. The real time simulations carried out on RTDS shows that the proposed strategy outperformed the type-1 FLC and PI counterparts. The results presented in this work are more realistic, since the computational delays and signal conversion delays are taken into account.This work distribution proposes using the and implementation design of a novel DFIG strativ egy intervalcontrol fuzzy type-2reliable sets for grid interaction of, when connected to an network unbalanced . Accurate power sharing in a microgrid with DGs is a challenging task due to various uncertainties in the network operating conditions. This work proposes a new control scheme for power sharing in a microgrid comprising DFIG based wind energy system, photo voltaic (PV) system and battery storage, operating in both grid connected and islanding conditions. A robust intelligent controller is designed for power sharing to counter the e ects of nonlinearities in the model and uncertainties in the operating conditions. The special features of the type-2 fuzzy sets are explored, to ascertain its suitability to handle the uncertainties associated with the rules and MFs. The performance of the proposed scheme is veri ed through a comparative analysis with the conventional PI controller, considering the IEEE 34 bus system as a microgrid, under various network disturbances. Further the feasibility of the controller for real-time applications is demonstrated through hardware-in-loop simulations in the RTDS environment