In this study, we propose a voltage estimation method for the radial distribution network with distributed generators (DGs) using high-precision measurements (HPMs). The proposed method uses the section loads center for voltage estimation because individual loads are not measured in the distribution system. The bus voltage was estimated through correction of the section load center by using an HPM at the end of the main feeder. The correction parameter of the section load center was calculated by comparing the initial voltage estimates and the measurements of the HPMs. After that, the voltage of the main feeder was re-estimated. Finally, the bus voltage in the lateral feeder was estimated based on the voltage estimates in the main feeder and the current measurements in the lateral feeder. The accuracy of the proposed algorithm was verified through case studies by using test systems implemented in MATLAB, Simulink, and Python environments. In order to verify the utilization of the proposed method to the practical system, a test with injection of approximately 5% of normally distributed random noise was performed. Through the results of the case studies, when an HPM is installed at the end of the main feeder, it demonstrated that the voltage estimation accuracy can be greatly improved by the proposed method. Compared with the existing methods, the proposed method was less affected by PV and showed robustness to measurement noise.

With climate anomalies and ecosystem destruction caused by global warming, reducing carbon emissions is becoming increasingly important. Consequently, the power industry is investing in new sectors such as expanding renewable energy and utilizing DC grids to enhance energy efficiency and reduce coal fuel usage. The use of DC systems for carbon emission reduction is expected, and low-voltage direct current (LVDC) systems are continuously being investigated as efficient power systems. Existing studies have primarily focused on power conversion design and operation, but studies on the protection system configuration for the electrical safety of end users are insufficient. Therefore, this study analyzes the characteristics of resistors and capacitors in series (RCS) mid-point grounding in uni-polar LVDC systems for use at the end of LVDC systems and reviews protection systems against electrical shock and ground faults using DC residual current devices (DC-RCDs) and insulation monitoring devices (IMDs). Through fault tests, the appropriateness of using the protection system with these devices in RCS mid-point grounding configurations is verified. The fault test demonstrated that the RCS mid-point grounding LVDC system could detect and protect against faults within 80 ms using a DC-RCD. Additionally, it was confirmed that faults could be detected and cleared within 4 min using an IMD in the event of a high-resistance fault, enabling the use of IMD which was not feasible in grounding systems. Our research results contribute to the use of LVDC systems by establishing a protection system based on relatively inexpensive mechanical circuit breakers instead of high-cost semiconductor-based breakers often mentioned for consumer protection devices.

As the interconnection of renewable-energy-based distributed generations (DGs) to the distribution system increases, the local and temporary voltage and current problems, which are difficult to resolve with the existing operation method, are becoming serious. In this study, we propose a short-term operational method that can effectively resolve voltage and current violations caused by instantaneous output fluctuations of DGs in a system with a high hosting capacity of renewable energy sources. To achieve the objectives, a modified heuristic network reconfiguration method, and a method determining the maximum power output limit of individual DGs are proposed. We propose a cooperative method for controlling the power output fluctuations of renewable-energy-based DGs, which includes voltage control, network reconfiguration, and power curtailment. The proposed algorithm was verified through case studies by using a test system implemented in MATLAB environments. It can effectively resolve violations caused by DGs while minimizing the number of switching operations and power curtailment. The proposed method is an appropriate operation method to be applied to the real system as it can cope with the instantaneous output fluctuation of DGs, which was not dealt with in the existing operation method.