Linear optimal operation model and algorithm for active distribution network in rural areas

Abstract: The active energy exchange in distribution networks of rural areas is becoming more significant with the development and access of DGs and Microgrids. Therefore, the optimization scheduling technology for active distribution networks, in which the DGs as a controllable scheduling unit involved in the distribution network OPF operation scheduling to achieve global optimization of energy management, will be the focus of research in the future rural smart distribution grid.The standing point of active energy optimization scheduling for rural distribution network with DGs, based on the research of real-time optimization scheduling for active distribution network which is achieving three objectives of the network loss as small as possible, the node voltage offset as small as possible and the cost of purchasing power as small as possible, focused on the problem of network loss and node voltage offset with DG's output showing a non-linear relationship which makes the scheduling problem becomes a nonlinear multi-objective optimization problem, based on the simulation analysis that distributed generations affect voltage distribution and line losses of distribution network, a linear model and solution methods for active distribution network real-time optimization scheduling is proposed in this paper. The simulation of generations output to voltage distribution and network loss shows that the optimal schedule scheme can be searched in two directions of reducing the voltage deviation and improving the grid voltage level. This obeys a physical principle, that is, the voltage distribution in the network is smooth, the voltage drop will be small, and the current through the line will be very small for constant line impedance. In addition, higher voltage levels lead to lower currents and net losses when transferring the same power. Thus, in this paper, the two optimization directions are achieved by shortening the range of node voltage limits and calculating the highest voltage level of the network at the same voltage deviation.Based on the above research, a optimization model was established in which maximum node voltage to the whole network was the objective, the simplified loop voltage equation was power flow balance constraint, voltage offset limits satisfying iteration reduction and DGs' output limits are the inequality constraints. Subsequently, it makes use of the features that each node voltage phase angle having little difference in distribution networks to transform the loop voltage equation directly into linear function of the DGs' output, thus the optimization-scheduling model for active distribution network was transformed into a linear programming model. Finally, according to a shrinking node voltage deviation limit value and calculating the highest voltage level of the network at the same voltage deviation, the optimal control scheme was obtained, which can also meet the two objectives of minimum voltage deviation and minimum loss.The model and algorithm are validated in an IEEE33 example, and it was proved when the DGs' output was optimized via the proposed method, the voltage distribution became even smoother, the voltage level was near normal, and the network loss became even smaller. Compared to the conventional non-linear optimization model for the distribution operation, the linear model presented in this paper can not only improve the calculation speed but also is guaranteed to obtain an optimal solution in mathematical theory.