A wireless power transfer system includes a transmitter configured to transmit power to a receiver, for example, through coupled resonators. The transmitter receives feedback from the receiver, and uses the feedback to control the power transmission, to control a parameter at the receiver, for example, a rectified voltage output by the receiver. The feedback to the transmitter may be provided, for example, by an out-of-band radio system between the transmitter and receiver, by a reflection coefficient at the transmitter, and/or by an encoded modulation of power in the receiver, for example, in an impedance matching module. The transmitter may control the transmitted power, for example, by controlling a transmitter signal generator voltage (VSIG), a transmitter gate driver voltage (VGD), a transmitter amplifier voltage (VPA), and/or an impedance setting in a transmitter impedance matching module.