Operation and Control of Microgrid In Islanded and Grid-Connected Modes of Operation

Abstract

A reliable energy source is important in daily life. Emerging concerns about primary energy availability, as well as the aging infrastructure of current electrical transmission and distribution systems, are placing greater emphasis on power supply sustainability, safety, and quality. To construct and upgrade existing infrastructures, large amounts of invest- ments will be necessary, but perhaps the most appropriate technique to meet demands and expectations is to embrace creative concepts, tech- nologies, and modern grid architecture. Future energy systems will have to keep up with technical advancements, societal standards, environmen- tal concerns, and economic conditions. As a result, security mechanisms, operational safety, environmental protection, power quality, supply afford- ability, and energy efficiency must all be assessed in innovative ways to respond to new requirements. In this sense the control is decentralized and power flows bidirectionally, distribution grids are being converted from passive networks to active networks. This sort of network facilitates the integration of distributed generation (DG), renewable energy sources (RES), and energy storage systems (ESS), as well as the ability to inte- grate power generation and consumer demand in real-time. Because of the limitations of traditional power generated by fossil fuels, the role of power generation has always been critical. And this has been a source of concern due to environmental pollution and other issues. With the remarkable ad- vancement of technology in past few years, several countries have directed their attention to how to successfully harness renewable energy to gener- ate power. In this regard, microgrids are receiving an increasing amount of research and innovation due to their particular benefits in the imple- mentation of renewable resources. In the past few years, there has been significant growth in energy de- mand. It is a concern because of the large quantity of energy dissipated while transferring energy over long distances. The microgrid, which con- sists of distributed generation sources (DGs), is an excellent solution for reducing losses because it provides electricity close to the endpoint cus- tomers. Typically, the microgrid should be able to operate independently iii (islanded) as well as in conjunction with the grid. Photovoltaic systems, wind farms, fuel cells, and micro-turbines are examples of DGs that are primarily classified as non-renewable and renewable energy resources. The recurrent nature of these sources causes significant stability difficulties in the power distribution network. Control and protection are required to sustain stable operation in the islanded mode of operation in terms of con- trolling the voltage and frequency enabling proportionate power-sharing. The voltage and frequency restoration must be maintained in an islanded AC microgrid to achieve proper power-sharing. This thesis work summarises the architecture, classification, and char- acteristics of microgrid study in islanded and grid-connected operation modes. With a focus on PE-based DG inverters, control strategies for microgrids in both the operation modes are described and assessed. The output impedance of a PE-based DG has a significant impact on the par- allel system and power distribution. Droop control is widely employed since multiple DGs operate simultaneously. However, power-sharing in- efficiencies occur as a result of inconsistent line impedance, lowering the system’s overall efficiency. To avoid being reliant on the DG inverter out- put line impedances, a control technique for accurate and proportional power-sharing with f/V restoration that pools an improved droop control with a virtual output impedance control with both the resistive and in- ductive output line impedances is designed. Then the entire microgrid system’s state-space small-signal modeling and analysis are established. Meanwhile, the strategy’s performance is enhanced in anticipation of a significant step-change in the operational power loads. In the grid-connected operating mode, the effectiveness of a microgrid in- corporating DGs would be improved in terms of power supply consistency for users. And among the most significant aspects of integrating a DG into the grid is islanding detection. Various islanding detection approaches have been developed over decades to improve the speed and accuracy of islanding detection. Furthermore, with new advancements such as micro smart grids on the horizon, there must be a compelling need for automatic islanding detection and mode switching to be included in the control. It’s also critical that the islanding detection methods work well in unhealthy iv grid environments. This work also proposes an islanding detection method based on Phase-Locked Loop (PLL) and a piezoelectric acoustic sensor. The PLL controller is one of the most often used fundamental concepts for grid synchronization solutions, and microgrid control includes PLL when integrated into the grid for synchronization. In islanded mode, it utilizes the phase angle generated through the droop controller, and in the grid- connected mode, it utilizes the angle by the PLL. This study focused on the three phase PLLs for grid synchronization and developed a PLL-based islanding detection method, as well as the design and dimensions of the piezoelectric acoustic sensor that was utilized for islanding detection. The islanding detection and automatic mode switching are efficiently achieved with the PLL and piezoelectric acoustic sensor. According to virtual and real-time hardware in loop (HIL) simulation models, the proposed control techniques can provide voltage amplitude and frequency restoration, as well as proportional power-sharing in the islanded mode of operation. There is also quick and effective islanding detection and automatic mode switching in the grid-connected mode of operation. The Typhoon-402 hardware test-bed and the Typhoon HIL virtual system have been used to validate the proposed controller’s per- formance.