Farhad Shahnia

A standalone microgrid in a remote area may frequently experience overloading due to lack of sufficient power generation and/or renewable-based over generation causing unacceptable voltage and frequency deviation, which in turn lead the microgrid to operate with less resiliency and reliability. Conventionally, such problems are alleviated by load shedding or renewable curtailment. Alternatively, such autonomously operating microgrid clusters in a certain geographical area can be provisionally connected to each other to enable power exchange among them to address the problems of overloading or overgeneration more efficiently and cost-effective way. The power exchange link among the microgrids can be of different types such as a three-phase ac, a single-phase ac, or a dc-link. Power electronic converters are required to interconnect such power exchange networks to the three-phase ac microgrids and control the power-sharing amongst them. Such arrangement is also essential to interconnect microgrid clusters to each other with proper isolation while maintaining autonomy if they are operating in different standards. In this chapter, the topologies, and structures of various forms of power exchange links are investigated and an appropriate framework is established under which power exchange will take place. This approach is a decentralized control mechanism to facilitate power-sharing amongst the converters of the neighboring microgrids without any data communication, that can be implemented at the primary level based on the localized measurements. The dynamic performance of the control mechanism for all the topologies is illustrated through simulation studies in PSIM® to verify that such overloading or overgeneration situations can be effectively alleviated through proper frequency regulation. The chapter also presents a comparative analysis of the topologies in terms of stability and sensitivity.

This chapter briefly discusses the various control principles and techniques for the primary and secondary control of microgrids. More specifically, proper active and reactive power-sharing among the distributed energy resources is discussed under the primary control aspect, whereas dynamic power-sharing ratio modification and regulating the voltage and frequency are discussed under the secondary control. A modified control technique is also discussed for the BESs in comparison to DERs. The advantages and limitations of each suggested technique are discussed and demonstrated by some simulation-based examples. The chapter has also discussed the small signal stability of microgrids, focusing on the most important states of the system, which have a dominating factor in making the system unstable.

The rising electricity demand and the inevitability of reliability improvement and cost reduction are motivating the application of distributed energy resources (DERs) within distribution networks instead of expanding them. The term microgrid refers to a small-scale electricity generation and distribution system in which a cluster of loads is supplied locally by a few DERs and/or battery energy storage systems. Such systems can operate in grid-connected and autonomous modes. For the proper operation of the DERs in such systems while regulating the voltage and frequency in the system, various control levels are required. This chapter discusses the various control structures for microgrids. Examples are provided that demonstrate the dynamics of such systems under the discussed control aspects.

This chapter focuses on short-circuit fault on the feeders supplying residential customers with rooftop photovoltaic (PV) systems. The chapter discusses the sensitivity of the short-circuit fault level and the corresponding current drawn from the distribution transformer, in addition to the node voltages along the low-voltage feeder, following a short-circuit fault. The chapter also demonstrates that various factors such as the PVs’ installation point and rating, as well as the location and type of the fault, impact the study parameters. Furthermore, the chapter illustrates that the time and sequence of the PVs’ isolation following the fault will vary depending on the impedance and location of fault, the PV generation–demand ratio, as well as the network’s earthing type.

Microgrids (MGs) are referred to as isolated and self-sufficient electricity supply systems that well suit remote areas. These systems are generally composed of nondispatchable and dispatchable energy resources to reduce the electricity production cost. Emergencies such as overloading, faults and shortfalls can result in difficulty for the smooth operation of MGs. The main aim of this study is to discuss the operation of MGs by presenting a power transaction management scheme. It focuses on the scenario when MGs are provisionally coupled to resolve the emergency situation and termed clustered MGs. For this purpose, power transaction is taken as an instance of purchasing or selling of electricity amongst healthy and problem MGs. The key objective of a suitable power transaction technique should then be regulating the power amongst the provisionally coupled MGs by adjusting the suitable power generation from all available dispatchable sources. An optimization problem is formulated for achieving this purpose, and its main purpose is to minimize the costs and technical impacts while focusing on the above-considered parameters. Genetic algorithm which is a heuristic optimization technique is used to solve the formulated optimization problem, and the performance of the suitable power transaction strategy is evaluated by several numerical analyses.

In Australia, the policy of introducing high feed-in tariff previously to encourage more consumers to install rooftop solar panels worked really well, and a large number of rooftop solar panels were installed during 2009–2012. This implies that consumers can be encouraged even more to install rooftop solar panels by offering relatively high feed-in tariff, who export electricity in particular during the peak periods or at the locations where it is difficult to supply with existing electricity transmission network. An efficient seasonal time of use feed-in tariff, therefore, can encourage more consumers to install rooftop solar panels, can improve electricity load factor, and can significantly reduce the electricity supply cost to regional consumers. An efficient feed-in tariff can also ensure that customer payback period is reduced and savings in the electricity bills are increased. This efficient feed-in tariff can help to reduce the urgent need of electricity infrastructure to meet the seasonal peak demand and reliance on the inefficient generating station which may need to run to cope with the electricity peak demand.

Microgrids are clusters of distributed energy resources, energy storagesystems and loads which are capable of operating in grid-connected as well as in offgridmodes. In the off-grid mode, the energy resources supply the demand whilemaintaining the voltage and frequency within acceptable limits whereas in the gridconnectedmode, the energy resources supply the maximum or nominal power and thenetwork voltage and frequency is maintained by the grid. This chapter first summarizesthe structure and control principles of microgrids. It then briefly introduces thestructures and control perspectives of distribution static compensators (DSTATCOMs).Finally, some applications of DSTATCOMs are discussed in microgrids. Theintroduced applications are power quality improvement due to the presence ofnonlinear and unbalanced loads, voltage regulation and balancing, and interphasepower circulation in the case of the presence of single-phase energy resources withunequal distribution amongst phases. Each application is illustrated by examples,realized in PSCAD/EMTDC.

The power supply system of future communities can be considered in the form of a small microgrid or a nanogrid which is mainly based on renewable energy resources. Such a system can lead to a sustainable development of electrical systems and can help the current and future generations to access the benefits of electricity without adding more emissions and pollutions to the environment. A nanogrid should have adequate generation capacity in its distributed energy resources (DERs) to supply its demand in the off-grid status. It should also be able to exchange power with an existing utility feeder. The operation principle of a nanogrid is discussed in this chapter. A hybrid nanogrid may consist of one ac bus and one dc bus, which are connected via a power electronics-based converter. Some DERs and loads of the community will be connected to the ac bus of the nanogrid, while some DERs and loads will be connected to its dc bus. The converter facilitates power exchanges among the buses and also controls their voltages, during off-grid operation. The dynamic performance of a small community nanogrid is discussed in detail here.

The power supply system of future communities can be considered in the form of a small microgrid or a nanogrid which is mainly based on renewable energy resources. Such a system can lead to a sustainable development of electrical systems and can help the current and future generations to access the benefits of electricity without adding more emissions and pollutions to the environment. A nanogrid should have adequate generation capacity in its distributed energy resources (DERs) to supply its demand in the off-grid status. It should also be able to exchange power with an existing utility feeder. The operation principle of a nanogrid is discussed in this chapter. A hybrid nanogrid may consist of one ac bus and one dc bus, which are connected via a power electronics-based converter. Some DERs and loads of the community will be connected to the ac bus of the nanogrid, while some DERs and loads will be connected to its dc bus. The converter facilitates power exchanges among the buses and also controls their voltages, during off-grid operation. The dynamic performance of a small community nanogrid is discussed in detail here.

In order to minimize the number of load shedding in a Microgrid during autonomous operation, islanded neighbour microgrids can be interconnected if they are on a self-healing network and an extra generation capacity is available in Distributed Energy Resources (DER) in one of the microgrids. In this way, the total load in the system of interconnected microgrids can be shared by all the DERs within these microgrids. However, for this purpose, carefully designed self-healing and supply restoration control algorithm, protection systems and communication infrastructure are required at the network and microgrid levels. In this chapter, first a hierarchical control structure is discussed for interconnecting the neighbour autonomous microgrids where the introduced primary control level is the main focus. Through the developed primary control level, it demonstrates how the parallel DERs in the system of multiple interconnected autonomous microgrids can properly share the load in the system. This controller is designed such that the converter-interfaced DERs operate in a voltage-controlled mode following a decentralized power sharing algorithm based on droop control. The switching in the converters is controlled using a linear quadratic regulator based state feedback which is more stable than conventional proportional integrator controllers and this prevents instability among parallel DERs when two microgrids are interconnected. The efficacy of the primary control level of DERs in the system of multiple interconnected autonomous microgrids is validated through simulations considering detailed dynamic models of DERs and converters.