POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 16 | NUMBER: 1 | 2018 | MARCH Advanced Control of the Dynamic Voltage Restorer for Mitigating Voltage Sags in Power Systems Dung VO TIEN 1 , Radomir GONO 1 , Zbigniew LEONOWICZ 2 , Trinh TRAN DUY 3 , Luigi MARTIRANO 4 1 Department of Electrical Power Engineering, Faculty of Electrical Engineering and Computer Science, VSB–Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic 2 Faculty of Electrical Engineering, Wroclaw University of Science and Technology, Wybrzeze Stanislawa Wyspianskiego 27, 50-370 Wroclaw, Poland 3 Faculty of Electric Power Systems, Vinh University of Technology Education, Hung Dung street, Vinh, Vietnam 4 Department of Electrical Engineering, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy dung.vo.tien.st@vsb.cz, radomir.gono@vsb.cz, zbigniew.leonowicz@pwr.edu.pl, duytrinhktv@gmail.com, luigi.martirano@uniroma1.it DOI: 10.15598/aeee.v16i1.2350 Abstract. The paper presents a vector control with two cascaded loops to improve the properties of Dy- namic Voltage Restorer (DVR) to minimize Voltage Sags on the grid. Thereby, a vector controlled struc- ture was built on the rotating dq-coordinate system with the combination of voltage control and the current control. The proposed DVR control method is mod- elled using MATLAB-Simulink. It is tested using bal- anced/unbalanced voltage sags as well as fluctuant and distorted voltages. As a result, by using this controlling method, the dynamic characteristics of the system have been improved significantly. The system performed with higher accuracy, faster response and lower distortion in the voltage sags compensation. The paper presents real time experimental results to verify the performance of the proposed method in real environments. Keywords Current controller, dynamic voltage restorer, power quality, voltage controller, voltage sags, Voltage Source Converter (VSC). 1. Introduction Voltage sags are one of the most common events that affect power quality in the distribution system. The major causes of voltage sags are faults of a grid, such as a single line to the ground, phase to phase, two- phase to the ground, three-phase faults due to ac- cidents, lightning, wind, animals, and other causes. Other causes include transformer energizing, switching capacitor banks, and the starting of large induction motors [6] and [12]. Voltage sags can be symmetric or asymmetric depending on the causes of sags. Although voltage sags occur in a short time (from 0.5 cycle to 1 minute) [11], it may affect the operation of equipment (stalling of motors, tripping of sensitive loads, and inaccuracy of control devices). These effects can give a rise in serious production problems, causing huge economical losses for consumers. According to an investigation of Schneider Electric in [13], voltage sags were the largest power quality problems in US distribution system, as shown in Fig. 1. It is also a serious problem in Vietnam electric power system. There are many methods for mitigating voltage sags, such as UPS (Uninterruptible Power Sup- ply), SVC (Static VAR Compensator), DSTATCOM (Distribution-Static Compensator), DVR (Dynamic Voltage Restorer). The structure of SVC is simpler than DVR but it has the incapability to control active power flow. The energy capacity of the DVR is higher than that of the UPS which has the same power rat- ing. Additionally, the size of a DVR is smaller than that of the DSTATCOM. Furthermore, it is the cheap- est in comparison with the UPS and the DSTATCOM c  2018 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 36