A Three-Phase to Single-Phase Midpoint Matrix Converter Using a Free-wheeling Switch for an Inductive Power Transfer System

Abstract

Inductive power transfer (IPT) systems can improve the practicalities of a power delivery circuit. The contactless structure of IPT reduces the risk of sparking and electric shock, as well as provides good mobility for the IPT recipient during power transfer. Furthermore, the absence of moving parts on the transmitter and receiver circuits increases system reliability. The complexity of an IPT system that is connected to a three-phase voltage source can be reduced by utilizing a direct converter, such as a three-phase to single-phase Midpoint Matrix Converter using a Free-wheeling Switch (MMCFS). Additionally, the series-none compensation can also be applied in a high quality and coupling factors configuration. This dissertation explores the application of the MMCFS in a self-oscillating, series-none IPT system. Two types of pulse-density modulation were proposed to run the converter: Non-successive Injection Modulation (NIM) and Successive Injection Modulation (SIM). Theoretical equations were formulated to estimate the characteristics of the MMCFS-based IPT (MMCFS-IPT) system. In addition, simulation models were created in PLECS to predict the IPT behavior in an ideal case. To validate the equations and the simulations, an experimental setup was designed and built for unidirectional power transfer. The setup consisted of programmable three-phase input voltage, the MMCFS, a primary compensation capacitor, a coupled inductor, a rectifier, and a resistive load. The converter used a field-programmable gate array to control a network of insulated-gate bipolar transistors. Experimental data were measured using a RCL meter, multimeters, oscilloscopes, and a thermal camera for further analysis. In the case of unidirectional power transfer, SIM could produce three times the maximum output power compared to NIM using the same input voltage characteristics. Additionally, the current damping ratio, transfer efficiency and voltage gain depend on the series-none IPT coupling factor (k). The simulation results also confirmed that the proposed converter is capable of performing bi-directional power transfer using the series-series IPT configuration. In practice, applying NIM to MMCFS-IPT enables the converter to deliver as much power as 142 W to the resistive load based on a three-phase input amplitude of 70.8 Vrms. Power transfer can also be regulated through an on-off control system. The MMCFS-IPT prototype achieves an overall efficiency of around 80% based on a k of 0.53. The experimental results are in close agreement with both theoretical calculations and simulation results. This research demonstrates that MMCFS can be used as an alternative to the rectifier-inverter topology in an IPT system in order to reduce system complexity, size and cost.