Abstract
This paper provides a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I) and its dynamic behaviours on the μgrid, and power system distribution (PSD). In general, a μgrid is defined as a cluster of different types of electrical loads and renewable energy sources (distributed generations) under a unified controller within a certain local area. It is considered a perfect solution to integrate renewable energy sources with loads as well as with a traditional grid. In addition, it can operate with a conventional grid, for example, by energy sourcing or a controllable load, or it can operate alone as an islanding mode to feed required electric energy to a grid. Hence, one of the important issues regarding the μgrid is the constant power load that results from the tightly designed control when it is applied to power electronic converters. The effect of CPL is incremental negative resistance that impacts the power quality of a power system and makes it at negative damping. Also, in this paper, a comprehensive study on major control and compensation techniques for μgrid has been included to face the instability effects of constant power loads. Finally, the merits and limitations of the compensation techniques are discussed.
Highlights
The development of electronic switch devices has led to penetrations of power electronic applications in a power system [1,2], advanced control approaches, and more renewable energy sources [3], and on the other hand an increase in energy demands that has led to increased environmental problems such as greenhouse gases being emitted from non-renewable energy sources [4,5]; all these factors have contributed to the appearance of new applications in power systems and have taken many forms in modern life [6]
The μgrid is defined by the Consortium for Electric Reliability Technology Solutions (CERTS) in the USA as “An aggregation of loads and micro-sources operating as a single system providing both power and heat”
The instability effects of Constant power loads (CPL) (INR) can be summarised on any power electronic system as mentioned in [2,25] as follows: CPL reduces the equivalent resistance of the system, causes a high inrush current as the voltage builds up slowly from its initial value, makes the system poorly dampened and impacts on the stability [37,38,47,53,54], which causes limit cycle oscillation in the DC bus voltage and currents and may lead to voltage collapse [23,53,55]
Summary
The development of electronic switch devices has led to penetrations of power electronic applications in a power system [1,2], advanced control approaches, and more renewable energy sources [3], and on the other hand an increase in energy demands that has led to increased environmental problems such as greenhouse gases being emitted from non-renewable energy sources [4,5]; all these factors have contributed to the appearance of new applications in power systems and have taken many forms in modern life [6] One of these applications is the μgrid, a new concept for a power system. The μgrid is a combination of distributed generations, including renewable energy sources and storage devices, and different types and electrical loads interface with a power electronic converter under the control approach in order to achieve proper system operation. A brief review of major control and compensation techniques to mitigate the instability effects of constant power loads; and Section 5.
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