Voltage Stability Enhancement in Active Distribution Networks with AHP-Based PV/BESS Placement and Fuzzy Smart Thermostat Demand Response

The increasing penetration of distributed photovoltaic generation and the growth in electricity demand can intensify voltage stability challenges in distribution networks, particularly at electrically weak buses. This paper proposes a voltage-stability-oriented framework that coordinates photovoltaic systems, battery energy storage systems, and smart thermostat demand response to improve distribution network operating conditions under load growth scenarios. Three voltage stability indices are used: the voltage deviation index, the stability index, and the voltage stability margin. They are combined using the analytic hierarchy process (AHP) to obtain a unified bus-level stability score, which is used to identify weak buses for photovoltaic and battery energy storage system placement. A voltage-stability-based smart thermostat demand response strategy is then developed using a Mamdani fuzzy inference system. Its inputs are the electricity price, photovoltaic power, occupancy level, and AHP-derived weakness score. A first-order thermal model converts the resulting set-point adjustments into changes in electrical load. The framework is evaluated on the IEEE 33-bus distribution system under different load growth scenarios. The results show that the integrated framework increases the minimum bus voltage from 0.903 p.u. to 0.945 p.u. and reduces the total daily energy losses by 50.54%.