energies Review Dynamic Voltage Restorer (DVR): A Comprehensive Review of Topologies, Power Converters, Control Methods, and Modified Configurations Ali Moghassemi 1 and Sanjeevikumar Padmanaban 2, * 1 Department of Electrical Engineering, South Tehran Branch, Islamic Azad University, Tehran 1584743311, Iran; moghassemiali@gmail.com 2 Department of Energy Technology, Aalborg University, 6700 Esbjerg, Denmark * Correspondence: san@et.aau.dk; Tel.: +45-71-682-084 Received: 21 June 2020; Accepted: 21 July 2020; Published: 11 August 2020   Abstract: Power quality is a pressing concern and of the utmost importance for advanced and high-tech equipment in particular, whose performance relies heavily on the supply’s quality. Power quality issues like voltage sags/swells, harmonics, interruptions, etc. are defined as any deviations in current, voltage, or frequency that result in end-use equipment damage or failure. Sensitive loads like medical equipment in hospitals and health clinics, schools, prisons, etc. malfunction for the outages and interruptions, thereby causing substantial economic losses. For enhancing power quality, custom power devices (CPDs) are recommended, among which the Dynamic Voltage Restorer (DVR) is considered as the best and cost-effective solution. DVR is a power electronic-based solution to mitigate and compensate voltage sags. This paper provides a thorough discussion and comprehensive review of DVR topologies based on operations, power converters, control methods, and applications. The review compares the state-of-the-art in works of literature, and comparative study on power quality issues, the DVR principle along with its operation modes, the DVR components, the DVR topologies based on energy storage, the DVR topologies based on single-/three-phase power converters, and the DVR topologies based on control units that have different control processing stages. Furthermore, modified and improved configurations of the DVR, as well as its integration with distributed generations, are described. This work serves as a comprehensive and useful reference for those who have an interest in researching DVRs. Keywords: power quality; dynamic voltage restorer (DVR); power converter; control methods; modified DVR configurations; distributed generation 1. Introduction Over the past few years, the number of sensitive loads such as medical equipment in hospitals and health clinics, schools, prisons, etc. has quadrupled which makes the power quality of the sensitive loads a pressing concern [1]. If the power quality is not high, there could be dire consequences like substantial economic losses, production losses, sensitive and critical loads outage, and missing data [2]. This is why having high power quality is key to the customers, utilities, and also electrical devices producers. Voltage sags, voltage swells, transients, harmonics, fluctuations, flickers, and interruptions are the essential power quality issues [3–6]. They will be all explained further in the following section. These power quality issues and voltage disturbances must be averted when it comes to sensitive and critical loads. To that end, a wide variety of solutions have been presented among which, power electronics-based devices known as Custom Power Devices (CPDs) are considered as the best and the most cost-effective solution for compensating and mitigating voltage disturbances [7,8]. Energies 2020, 13, 4152; doi:10.3390/en13164152 www.mdpi.com/journal/energies