Inductive power transfer (IPT) has become a hot topic and is supposed to have a wide range of application in the future. This thesis focuses on the IPT system with multiple pickups in the lighting application. A multiple pickup system can power more than one pickup at the same time and the power consumption varies with a different number of pickups connecting in the circuit. A problem with the multiple pickup system is that at light load the power supply consumes a large amount of reactive power for a small active power demand. The aim of the design is to build a power supply with a constant current output. The designed circuit is supposed to reduce the reactive power demand and keep zero voltage switching (ZVS) in all range of load.

This thesis selects the half bridge inverter and LCL-T network as the topology. The characteristic of the LCL-T network is first analyzed under first harmonic approximation. The trade off between the constant current output, reactive power demand, and ZVS is interpreted. The system is proposed to work at a higher frequency for a light load. In addition, the effects of higher order harmonics on the switching current and apparent power are also given in the form of calculations. Subsequently, the parameters in the topology of the half bridge inverter and LCL-T network are determined. The control circuit is built to realize automatic frequency switching according to the load condition. The next step is to simulate the designed circuit in LTspice and construct it in the lab. The result of simulation and experiment verifies that the reactive power demand is reduced with a higher frequency at light load. Constant current output and ZVS are ensured at the same time in all range of load. But the efficiency of the system does not show a clear improvement since the loss is dominated by the cable loss, which is determined by the requirement of cable current and the pickup design.