applied sciences Article Phase Balancing and Reactive Power Support Services for Microgrids Anastasis Charalambous 1 , Lenos Hadjidemetriou 1 , Lazaros Zacharia 1 , Angelina D. Bintoudi 2 , Apostolos C. Tsolakis 2 , Dimitrios Tzovaras 2 and Elias Kyriakides 1, * , † 1 KIOS Research and Innovation Center of Excellence and Department of Electrical and Computer Engineering, University of Cyprus, 1678 Nicosia, Cyprus; charalambous.anastasis@ucy.ac.cy (A.C.); hadjidemetriou.lenos@ucy.ac.cy (L.H.); zacharia.lazaros@ucy.ac.cy (L.Z.) 2 Information Technologies Institute, Center for Research & Technology Hellas, 57001 Thessaloniki, Greece; bintoudi@iti.gr (A.D.B.); tsolakis@iti.gr (A.C.T.); dimitrios.tzovaras@iti.gr (D.T.) * Correspondence: elias@ucy.ac.cy † Passed away 28 October 2019. Received: 31 October 2019; Accepted: 21 November 2019; Published: 24 November 2019   Abstract: Alternating current (AC) microgrids are expected to operate as active components within smart distribution grids in the near future. The high penetration of intermittent renewable energy sources and the rapid electrification of the thermal and transportation sectors pose serious challenges that must be addressed by modern distribution system operators. Hence, new solutions should be developed to overcome these issues. Microgrids can be considered as a great candidate for the provision of ancillary services since they are more flexible to coordinate their distributed generation sources and their loads. This paper proposes a method for compensating microgrid power factor and loads asymmetries by utilizing advanced functionalities enabled by grid tied inverters of photovoltaics and energy storage systems. Further, a central controller has been developed for adaptively regulating the provision of both reactive power and phase balancing services according to the measured loading conditions at the microgrid’s point of common coupling. An experimental validation with a laboratory scale inverter and a real time hardware in the loop investigation demonstrates that the provision of such ancillary services by the microgrid can significantly improve the operation of distribution grids in terms of power quality, energy losses and utilization of available capacity. Keywords: AC microgrid; ancillary services; asymmetrical loading conditions; grid-tied inverter; phase balancing; power factor compensation; reactive power support 1. Introduction Smart grids are proposed to drive forward the traditional electrical grids to a more flexible, secure, reliable and efficient networks. The development of smart grids requires complex frameworks which should be supported by the appropriate infrastructure (e.g., advanced metering, information and communication technology (ICT)). In addition, renewable energy sources (RES) are able to play a key role in the sustainability of future grids. However, their variable and unpredictable nature cannot be easily handled in a global context. Moreover, the electrification of thermal loads and the expected increase of electrical vehicles (EVs) will increase significantly the already rising demand. To satisfy this climbing demand, improvements will be required on the current infrastructure, adding significant costs to the distribution system operator (DSO) and grid owner. Alternating current (AC) microgrids (MGs) are introduced to deal with all these issues since a better coordination among the distributed energy resources (DERs) can be achieved to support the local loads and enable the more efficient utilization of existing infrastructure. Appl. Sci. 2019, 9, 5067; doi:10.3390/app9235067 www.mdpi.com/journal/applsci