Local control of heat pump water heaters for voltage control with high penetration of residential PV systems

In Japan, large amount of photovoltaic (PV) systems will be installed in the future power system due to rising environmental concern. Large installation of these PV systems causes voltage rise at the end of the distribution line due to reverse power flow. In order to alleviate this problem, load control at the customer end is considered as a major study of this research. In this paper, heat pump water heater (HPWH) has been proposed as customer controllable equipment because of large energy consumption and flexibility in operating time. Local control of HPWHs is proposed for voltage control in such a way, when voltage at a node becomes closer to maximum allowable voltage, local controller placed at that node operates HPWHs to prevent voltage rise. The operating pattern of HPWH is determined based on customer hot water demand, hot water tank energy level and nearest node voltage in order to avoid voltage violation and not to affect participating customers with hot water shortage. In the voltage control method, primary control priority for operating HPWH is set to maintain reasonable hot water and then set to avoid the voltage rise. It is found that proposed local control method not only minimize the voltage rise problem but also maintain customer convenience.