It is expected that large capacity distributed generation systems including photovoltaic (PV) power systems will be installed in future systems. Though the introduction of PV systems offers advantages to the system, there are certain problems to be raised by large penetration of PV systems. One of the main problems is voltage increment due to reverse power flow created during off-peak period as supply power and PV generation is larger than demand. In this paper, appropriately controlling input power of customer controllable load, heat pump water heater (HPWH), is proposed to mitigate voltage violation.