A power conversion apparatus, a photovoltaic module, and a communication device and a photovoltaic system including the same are discussed. The power conversion apparatus includes an inverter unit to perform alternating current (AC) voltage conversion based on direct current (DC) voltage from a solar cell module, a controller to control the inverter unit, and a communication unit to add a carrier frequency signal containing predetermined information to the converted AC voltage and output the AC voltage containing the predetermined information to a grid and, when a level of the converted AC voltage is equal to or less than a predetermined level, to add the carrier frequency signal containing the predetermined information to DC voltage and output the DC voltage containing the predetermined information to the grid. Consequently, it is possible to stably transmit information.