An optimal reactive power control method for distribution network with soft normally-open points and controlled air-conditioning loads

The paper proposes an optimal reactive power control method for distribution systems with soft normally-open points (SNOP) and considering the direct load control (DLC) of thermostatically controlled air-conditioning loads. The starting voltage constraints of aggregate air-conditioning loads connected into a distribution network is studied according to the direct control mode and the starting characteristic of air-conditioning load. Using the flexible regulating capacity of power flow of SNOP, an optimal model of reactive power flow for distribution systems with SNOP is established to meet the voltage quality of sensitive loads and the starting requirements of aggregate air-conditioning loads. In the model, the load balancing commands of different DLC aggregators, the on/off status of thermostatically controlled air conditioner, the power regulating command of SNOP, the voltage adjusting and reactive power compensation devices are comprehensively controlled in the constraints of reduction balance and starting voltage of air-conditioning loads, as well as the conventional network and voltage constraints. And a multi-objective functions are developed for the objectives of solving the low-voltage problems, minimizing the comfort impacts on users of air-conditioning and minimizing the active power loss of distribution systems. Finally, the simulation results of a practical 53-bus 10 kV distribution system demonstrate the accuracy and effectiveness of the proposed method.