采用迭代求解的电动汽车优化充电算法
Smart Charging of EVs Using Iterative Method

电动汽车优化充电对配电网的安全经济运行具有十分重要的意义。利用配电网辐射状运行结构采用迭代修正节点电压的方法能够大幅降低优化变量的维数，提高计算速度。该方法已被应用于以网损最小为目标函数、常规负荷模型为恒功率负荷、不计及节点电压、支路功率约束的三相平衡配电网中。该文提出了将其推广至一般情形的方法，目标函数为配电网供电能量最小、运行费用最小或利润最大，不再局限于网损最小，负荷模型不再局限于恒功率负荷。而且计及了配电网的三相不平衡、节点电压、支路功率约束。文中分析了负荷模型对优化计算结果的影响。研究发现，当负荷模型只包含恒功率、恒阻抗负荷时，每次迭代中优化模型仍为线性约束凸二次规划模型；当负荷模型包含恒电流负荷时，每次迭代中优化模型不再为线性约束凸二次规划模型，但仍为线性约束凸规划模型。3个算例的仿真结果表明，所提方法收敛性好，计算精度高，速度快，能够改善电压，提高配电网的经济效益。
Coordinated charging of EVs is critical to provide safe and cost effective operation of distribution systems. Utilizing the radial operation structure of distribution network, the method that by correcting the nodal voltages iteratively, a linearly constrained convex quadratic programming model is built at each iteration, can be introduced for coordinated charging of EVs to greatly reduce the dimensions of the optimization variables and thus improve calculation speed. This method has been proposed to minimize the power losses in the balanced distribution network in literature. However, the load model is assumed to be constant power load. The constraints on nodal voltages and thermal loadings of lines and transformers are not taken into account. In this paper, the method that extends this iterative technique to the general case is proposed. As a consequence, the objective function is no longer confined to minimization of power losses. It can be minimization of total power supply, energy cost or maximization of profit. Further, the load model is no longer confined to constant power load. It can be a mix of ZIP load. Furthermore, the imbalance of distribution network, constraints on nodal voltages and thermal loadings of lines and transformers are taken into account. Moreover, the impact of the model of conventional load on this method is investigated. It is found that, if the conventional load is composed of constant power and/or constant impedance load, the linearly constrained convex quadratic programming model can be still applicable at each iteration. Nevertheless, if the conventional load contains constant current load, the linearly constrained convex quadratic programming model cannot be applicable any more. Instead, a linearly constrained convex programming model can be applicable. The precision and high calculation efficiency of the proposed method is validated with some test cases.