An optimal design method of voltage drop for DC distribution system based on investment cost

Generally, DC power plant applied to the telecommunication area consists of a charger, batteries and a distribution system. To engineer the capacity of DC power plant, the voltage drop in the distribution path must first be determined, which affects battery capacity, cable size and electric loss. Therefore, the optimal design of the voltage drop in the distribution path is important from an economical point of view. In this paper, an optimal design method of the voltage drop in the DC distribution path is proposed as a function of distribution loop length. The proposed method is used to minimize the total annual cost of the battery, cable and electricity caused by electric loss. The battery discharge characteristic curve, which has a nonlinear characteristic, is used to engineer battery capacity. The initial cost of the battery is derived by using a piecewise-linear model of a nonlinear curve as a function of the voltage drop. The initial cost of the cable is derived as a function of the voltage drop and the distribution loop length. The annual electricity cost caused by electric losses is derived as a function of the voltage drop. The initial costs of battery and cable stated above are transformed into annual costs under the assumptions of life cycle, interest, etc. Consequently, the voltage drop required to minimize the total annual cost, the sum of annual costs of battery, cable and electric loss, is derived as a function of distribution loop length