###### Abstract  
Modern distribution grids may suffer problems of voltage distortion, especially along radial low-voltage feeders with a high penetration of intermittent, unbalanced and distorted loads and generation sources. It is a challenge to develop an effective voltage-regulation method using a straightforward implementation. This paper proposes a novel method for local voltage control and balancing using a shunt-connected energy storage system. The compensation principles are explained, and a complete controller design is proposed. The algorithm is designed to be implemented in power electronic converters that provide the interface between the storage and the grid. The original contribution is the development of a low-level control method, which includes voltage balancing and a method to minimize the compensator current and is to be implemented in power electronic converters that provide the interface between the storage and the grid. The calculation of active and reactive compensator currents is explained with relation to the estimated grid impedance. The efficacy of the designed controller is verified by laboratory experiments. It is shown that voltage regulation using the proposed method is achieved with less apparent power compared to a system where only reactive power is used. The controller presents a very good dynamic response to rapid voltage variations, such as unbalanced voltage dips. The applicability and constraints of the method are discussed with respect to the present state of the art in low-voltage-grid voltage regulation. voltage control; power quality; energy storage +
Footnote †: journal: Applied  
15 November 2022  
117 November 2022  
Footnote †: journal: Applied  
15 November 2022  
Footnote †: journal: Applied  
Having many factors that influence the voltage profile [6], power quality issues are mostly observed in rural areas, typically characterized by radial topology and utilization of overhead lines with high feeder impedance. Methods for voltage regulation in distribution networks may include [7; 8]:  
* Transformers with on-load tap changers (OLTC)--only at the substation point, but they provide no information or control of the voltage along the feeder;
* Network reinforcement--an increased cross section or meshed network decreases grid impedance and, thus, voltage drop;
* Custom power systems--a variety of costly power-electronics-based solutions dedicated to industry [9];
* DER power curtailment or load drop--though effective, causes a reduction in user comfort and/or revenue;
* Demand side management--requires a costly information and communication technologies (ICT) infrastructure;
* Reactive power control--found to be ineffective and difficult to coordinate in LV networks;
* Optimal integration of DER in the distribution system [10];
* Introduction of energy storage systems (ESS)--a costly solution; however, a decrease in prices is expected, making it a possible, attractive solution [1]. One of the most prospective techniques, which avoids extra investments, is the implementation of voltage-regulation strategies in the power electronic converters that provide the interface between DERs, EV chargers and ESS on one side and the grid on the other. The interaction of a DER with the distribution network is regulated by grid codes, which typically utilize generation units for voltage regulation in a very limited way. Even if technically feasible [11], grid codes do not refer to voltage unbalance, which may become a serious issue with the growing penetration of single-phase loads or single-phase generation. It is easy to violate voltage limits in separate phases, while three-phase values are within the limits. Grid codes for storage systems and interactive grid EV charging stations are being developed [12; 13]. Local voltage regulation by reactive power injected by PV inverters [14] and by active power curtailment [15; 16] are both extensively studied methods. The efficiency of both methods highly depends on grid-impedance parameters.