CONTROL AND PERFORMANCE ANALYSIS OF RES BASED MICROGRID

Abstract

Energy is one of the most important, indicative parameters for the economic and industrial development of a country. It is expected that in coming years world energy consumption will be significantly higher than at present. Most of the power produced across the world is from conventional sources. The adverse effect of power generation from these conventional sources has led to alternative renewable energy sources (RES) of power generation. Therefore, the role of RES has increased considerably in current years due to increasing energy demand with minimum ecological impact. Renewable energy sources (RES) such as solar, wind, geothermal, tidal, and hydrogen energy etc. are progressively emerging as a sustainable and cost-effective way to satisfy power demand. Furthermore, due to technological improvements, abundant availability, and satisfactory performance, solar energy is emerging as one of the most popular renewable energy source. For the SPV system to operate reliably and effectively, other energy sources such as wind, fuel cells, batteries, etc., can be integrated with it. The power generated by the SPV system can either be integrated into the utility grid or used by the local loads in the microgrid. Microgrid is a collection of distributed generation (DG), renewable energy sources, and local loads connected to the utility grid. Since the SPV power generation is near to the load, the microgrid offers various advantages, viz. efficiency, lower transmission losses, as well as increased stability. A grid-integrated microgrid offers a way to manage local loads and generation. It could increase the system's overall effectiveness, power quality, and availability of energy for vital loads. Therefore, for developing efficient and cost-effective SPV systems, the study, analysis and control of SPV-based microgrids need to be performed. In the present work, “Control and performance analysis of RES based microgrid”, a system approach is considered for efficient design, development and control of microgrid to provide reliable and good quality. A 10.25 kW, two-stage, three-phase grid integrated SPV based microgrid is designed and developed. In the developed, grid-connected SPV-based microgrid, the output power of the SPV array is governed by a maximum power point tracking (MPPT) vii algorithm by controlling the switching of DC-DC boost converter. The output of the boost converter is coupled to DC link voltage of the voltage source converter (VSC), which is interfaced to the grid at the point of common coupling (PCC). The voltage source converters (VSC), supplies the power produced from the SPV system to the appropriate voltage and frequency, as well as maintain the power balance between the SPV system, load, and grid. Grid integration/synchronization of SPV system is accomplished using the VSC control algorithm, which regulates the operation of VSC to ensure efficient performance. Furthermore, VSC, operating under unity power factor (UPF) mode of operation, control the output of the VSC thus improve the power quality at the PCC by compensating the reactive power, harmonics, and load unbalancing along with the overall efficiency. In this work, various VSC control algorithms viz. conventional synchronous reference frame (SRF) theory, instantaneous reactive power theory (IRPT), unit template and adaptive least mean logarithmic (LMS) based control algorithm have been implemented. Furthermore, it has been observed that overshoots/undershooting, settling time, and oscillations under the dynamic condition in their responses are inevitable with these conventional control algorithms while regulating the DC-link voltage and estimating the fundamental active component of the load current. Additionally power quality issues that affect the distribution grid and consumers viz. unbalance load, low power factor, and excessive reactive power demand are power quality related issues that are observed due to power electronics-based technology. A rise in power electronics-based loads leads to poor power quality at the power distribution. These nonlinear loads produce a harmonic current that circulates to other coupled loads at the point of interconnection (PCC). To address the aforementioned issues, an intelligence based novel modified SRF control algorithm, and adaptive-filter based variable step size least mean logarithmic (VSSLMS), and robust least mean logarithmic square (RLMLS) control algorithms for VSC are designed and developed. The simulation studies for the considered system have been carried out using proposed algorithms, under different operating conditions to validate the feasibility of the proposed control algorithm. viii All the above-aforementioned control algorithms have been designed and developed in MATLAB /Simulink environment. The performance of the proposed control algorithms has been thoroughly investigated using simulation studies and experimentally on the prototype hardware developed in the laboratory. Due to laboratory resource limitations, adaptive control algorithms of VSC are tested in real time on the prototype hardware set-up of DSTATCOM developed in the laboratory using a Micro-Lab box(dSPACE 1202). The various performance parameters are measured and analysed using FLUKE PQ Analyzer. Furthermore, the design and selection of various components viz. interfacing inductors, DC link capacitor, voltage sensing circuits, current sensing circuits, linear, reactive and nonlinear loads to be compensated, are also required for the prototype hardware set-up in the laboratory. Despite the benefits of solar PV power generation, they also pose some risks, such as unintended islanding, safety concerns, reverse power flow, etc. As a result, the grid integration of DG necessitates protection and safety concerns in the distribution network. The detection of the island operations of distributed generators has become very important, in order to ensure the safety of service personnel and electrical components. Microgrid islanding arises as a consequence of faults, breakers accidentally tripping, resulting in a significant threat to the safety of staff, damage to the equipment of utilities, consumers, loss of control over voltage and frequency, etc. Islanding refers to a situation where energized DGs are disconnected from the bulk power grid, providing power only to the local loads for the time being. A comprehensive review, analysis and study of the various islanding detection techniques that have been described and are divided into the following categories: remote, passive, active, signal processing is presented. An active islanding identification based on disturbance injection through the quadrature axis controller has been studied and analysed. Analysis of different islanding detection scheme along with the advantages, disadvantages and limitations are evaluated and summarized. The thesis research work is designed to give good exposure to the design, and development of a solar PV-based microgrid.