DEVELOPMENT OF CONTROL FRAMEWORK FOR HYBRID RENEWABLE ENERGY SYSTEM IN MICROGRID

Edin Golubovic
Mechatronics program, PhD Dissertation, 2014

Thesis Jury

Prof. Dr. Asif Sabanovic (Thesis Advisor), Prof. Dr. Mustafa Ünel, Prof. Dr. Metin Gökaşan, Assoc. Prof. Ali Koşar, Asst. Prof. Ahmet Teoman Naskali

Date & Time: May 23, 2014 – 11.30 AM

Place: FENS2008

Keywords : Hybrid energy source, Renewable energy source, Microgrid, Control of switching converters, Control of power electronic interface for hybrid energy source, PV module, Wind turbine, Fuel cell, Battery storage, Switching converters, Sliding mode control, Space vector PWM, Power management for hybrid energy source.

Abstract

Sustainable economic growth and political stability of countries around the world is secured through abundant energy supply. Looking beyond the economic and political reasoning, energy has become the most important player in technological advancement of a modern society as well. Currently, majority of the consumed energy is generated by non-renewable and non-environmentally friendly sources such as petroleum, coal and natural gas. Strong dependence on fossil fuels may lead to energy crisis in future and increased fuel prices. As an alternative to the fossil fuels, renewable energy sources (RESs) are being explored since these sources can guaranty energy security in the long run. World is currently is the transition phase where more and more RESs are being introduced as generators of energy mostly for electricity and heating/cooling needs. RESs are mostly used together with power electronic based devices for power conversion and energy storage systems (ESS). In addition, number of RESs and ESSs at the low voltage side of utility grid may be interconnected together in a pattern that is different from conventional power generation, grouped with the loads in a cluster that can generate and utilize electricity independently from grid or parallel to the grid. This kind of structure is known as the microgrid. Microgrid can be composed of many different energy sources; however, they are usually associated with RESs. Renewable energy sources have different dynamic characteristics when compared to the traditional generation sources. These dynamic characteristics present hurdles in control and integration. Power generated by RESs depends on the environmental conditions and their power output is highly stochastic and often RESs cannot offer necessary support to the operation of microgrid where stable active and reactive power is needed. Nevertheless, combination of different types of RESs, together with the energy storage can offer a viable solution and mitigate power reliability issues. In other words, when different types of RESs are combined into hybrid power generation system, these sources can complement each other in power delivery and a hybrid source based renewable energy system (with proper control) has great potential to provide high quality and reliable power in microgrids. Hybrid energy source brings many advantages to the design and implementation of microgrid systems. Namely, microgrid with hybrid energy sources becomes a structure where all of the sources have similar or same dynamic response. Even though hybrid source may be composed of non-dispatchable sources, as a whole, together with energy storage elements, proper power electronic interfaces and control system this source could be turned into dispatchable source. In the same time, implementation of hybrid energy source increases reliability of the microgrid system, allows for easier realization of plug and play feature and upgradability of the whole system is increased. Additionally overall system complexity is decrease since many control tasks are handled by the hybrid energy source controller.

Main objective of this thesis is to develop a framework for analysis and control of power electronics interfaces in microgrid connected hybrid energy source. Development of the framework is done for the generalized hybrid source comprised of energy source(s), storage element(s), power electronic interfaces and control system. Basically, most important advantages that standardized control scheme brings to the design of the hybrid source are; decreased cost of design; decreased design time; decreased design complexity; increased design flexibility; and scalability of the design.