US Patent 9362048 Contactless power feed equipment

At the start of power supply from a power supply device to an induction line, the oscillation frequency of an inverter of the power supply device is set at a predetermined frequency shifted from the resonance frequency of a resonant circuit. After a predetermined time, the frequency is changed from the predetermined frequency to the resonance frequency. Thus, at the start of power supply, only small power is obtained by the resonant circuits in all transport carriages from the induction line in a full-load condition. Thus, total power is suppressed within power that can be supplied by the power supply device, avoiding an overloaded condition of the power supply device.