A method of regulating wireless charging of a plurality of power receiving systems in a wireless charging system comprising a wireless power transfer system and a plurality of wireless power receiving systems, each wireless power receiving system comprising a controlled oscillator configured to be coupled to a resonant receiver coil, the method comprising: one or more of the wireless power receiving systems wirelessly providing, to the wireless power transfer system (102, 242), a message indicating a difference between received power and requested power at the wireless power receiving system (104, 114, 124, 202); the wireless power transfer system increasing a transmitted power of the power transfer system (102, 242) in proportion to the differences between received power and requested power at the wireless power receiving systems (104, 114, 124, 202) indicated in the messages; the method further comprising: the wireless power transfer system, if the total requested power of the wireless power receiving systems (104, 114, 124, 202) indicated in the messages exceeds a maximum power output of the wireless power transfer system, sending to at least one of the wireless power receiving systems a message requesting the wireless power receiving system alternating between a power transfer mode and a non-power transfer mode and indicating a duty cycle for the alternating between a power transfer mode and a non-power transfer mode; and the at least one of the wireless power receiving systems in response to receiving the message from the wireless power transfer system (102, 242), alternating the wireless power receiving system (104, 114, 124, 202) between a power transfer mode and a non-power transfer mode based on the indication of a duty cycle provided by the wireless power transfer system (102, 242) to the wireless power receiving system (104, 114, 124, 202); wherein when the wireless power receiving system (104, 114, 124, 202) is in the non-power transfer mode, the wireless power receiving system consumes substantially no power wirelessly transferred from the wireless power transfer system (102, 242), thereby increasing the amount of transmitted power that is available to be received by one or more other ones of the wireless power receiving systems. one or more of the wireless power receiving systems wirelessly providing, to the wireless power transfer system (102, 242), a message indicating a difference between received power and requested power at the wireless power receiving system (104, 114, 124, 202); the wireless power transfer system increasing a transmitted power of the power transfer system (102, 242) in proportion to the differences between received power and requested power at the wireless power receiving systems (104, 114, 124, 202) indicated in the messages; the method further comprising: the wireless power transfer system, if the total requested power of the wireless power receiving systems (104, 114, 124, 202) indicated in the messages exceeds a maximum power output of the wireless power transfer system, sending to at least one of the wireless power receiving systems a message requesting the wireless power receiving system alternating between a power transfer mode and a non-power transfer mode and indicating a duty cycle for the alternating between a power transfer mode and a non-power transfer mode; and the at least one of the wireless power receiving systems in response to receiving the message from the wireless power transfer system (102, 242), alternating the wireless power receiving system (104, 114, 124, 202) between a power transfer mode and a non-power transfer mode based on the indication of a duty cycle provided by the wireless power transfer system (102, 242) to the wireless power receiving system (104, 114, 124, 202); wherein when the wireless power receiving system (104, 114, 124, 202) is in the non-power transfer mode, the wireless power receiving system consumes substantially no power wirelessly transferred from the wireless power transfer system (102, 242), thereby increasing the amount of transmitted power that is available to be received by one or more other ones of the wireless power receiving systems. the wireless power transfer system, if the total requested power of the wireless power receiving systems (104, 114, 124, 202) indicated in the messages exceeds a maximum power output of the wireless power transfer system, sending to at least one of the wireless power receiving systems a message requesting the wireless power receiving system alternating between a power transfer mode and a non-power transfer mode and indicating a duty cycle for the alternating between a power transfer mode and a non-power transfer mode; and the at least one of the wireless power receiving systems in response to receiving the message from the wireless power transfer system (102, 242), alternating the wireless power receiving system (104, 114, 124, 202) between a power transfer mode and a non-power transfer mode based on the indication of a duty cycle provided by the wireless power transfer system (102, 242) to the wireless power receiving system (104, 114, 124, 202); wherein when the wireless power receiving system (104, 114, 124, 202) is in the non-power transfer mode, the wireless power receiving system consumes substantially no power wirelessly transferred from the wireless power transfer system (102, 242), thereby increasing the amount of transmitted power that is available to be received by one or more other ones of the wireless power receiving systems.