A controller (28) implantable within the body of a patient as part of a left ventricular assist device (LVAD) system and a method therefore are provided. According to one aspect, the controller includes processing circuitry (36, 70, 72) configured to determine a voltage difference by determining a difference between a first voltage (64) obtained from an internal coil (18) of the controller and a target voltage (68), and is further configured to encode the voltage difference to produce an encoded voltage difference message. The internal coil is configured to transmit the encoded voltage difference message to a power transmitter (22) to enable closed loop control of power transfer from the power transmitter to the controller to drive the voltage difference toward zero.