# Phase Balancing and Reactive Power Support Services for Microgrids
## 1 Introduction
Advanced operational capabilities of power electronic based DERs can also be employed to compensate power quality phenomena such as harmonics, interharmonics and current/voltage unbalances [14; 15; 16; 17; 18]. Hence, smart and multi-functional inverters are capable of providing multiple ancillary services to the DSO. In the literature, active and reactive power control are thoroughly investigated for grid connected MGs [19; 20; 21]. Various controllers are proposed for MGs to regulate the active and reactive power of RES to minimize network losses and voltage limits. A centralized active power management controller is developed in a university campus MG to reduce the exchanged active power at the MG's PCC including peak shaving and constant active power modes [20]. In addition, a reactive power management controller is also proposed to improve the power factor at the MG's PCC and increase the available capacity of the lines [21]. In References [19; 20; 21], the focus of power management strategies is to regulate the positive sequence active and reactive power in order to improve the efficiency of the distribution grid. However, the phase unbalanced conditions of the loads have not been considered in any of the aforementioned works. Few works can be found in the literature considering asymmetric loading compensation of MGs. Initially, shunt active power filters are proposed to compensate the unbalance loading conditions and the harmonic distortions in MGs [22]. In addition, dedicated hardware devices are proposed to switch single phase PVs to different phases according to the loading conditions [23]. However, the development of these solutions come with a significant capital cost for the system operator or for the consumer. Another solution to compensate loading asymmetries and harmonic distortions at the building level is proposed in References [24; 25; 26]. The grid tied inverter of a PV or ESS is enhanced with advanced capabilities to compensate prosumer asymmetries. This solution requires additional sensors to measure the loading asymmetries at each building. In addition, the buildings that are not equipped with PVs or ESS with enhanced capabilities cannot compensate the asymmetries imposed by their loads. In Reference [27], the authors proposed the measurement of the loading asymmetries at every building within the MG and developed an unbalance current sharing control algorithm to compensate the current unbalances on the loads. The development of such approach requires intense communication traffic since measurements from every building need to be collected. A centralized phase balancing controller is proposed in Reference [28] for low voltage distribution grids. The total asymmetric current of the grid is allocated according to the availability of each inverter using adaptive weights. However, the authors did not consider reactive power compensation. In the literature, there are also sensor-less control approaches for compensating asymmetries [29; 30; 31]. The authors in Reference [29] propose a novel estimation of the prosumer negative sequence current and then utilize this knowledge to compensate asymmetries at building level using an advanced PV grid tied inverter controller. Further, a sensor-less voltage unbalance compensation scheme is proposed in References [30; 31]. The voltage asymmetries are measured locally at every PV or ESS to balance the asymmetries of the MG. However, voltage unbalance compensation is applicable only in islanded operation where the grid impedances are quite higher than in grid connected mode and hence will have greater impact on voltage unbalance. The contribution of this paper is the development of a novel microgrid central controller (MGCC) (secondary level controller) for fair compensation between reactive power (Q) and phase balancing (PB) at the MG's PCC. In addition, another contribution of this paper is the development of a new PV/ESS inverter controller to enable the provision of Q and PB ancillary services.