A wireless power receiver for receiving wireless power from a wireless power transmitter and for transmitting a control packet to the wireless power transmitter in a wireless power transfer system, includes a power pick-up unit configured to receive wireless power from the wireless power transmitter via magnetic coupling with the wireless power transmitter, and to convert an AC signal generated by the wireless power to a DC signal, a communication/control unit configured to receive the DC signal from the power pick-up unit, and to perform control of the wireless power and a load configured to receive the DC signal from the power pick-up unit, wherein the communication/control unit is configured to transmit a control error packet including a control error value for the wireless power to the wireless power transmitter in a first time interval or a second time interval.