Circulating Current Control Method For Inductive Power Transfer System

Inductive Power Transfer (IPT) technology is a new power transfer technology,which is based on coupling effect of electromagnetic induction, combining of modernpower electronics technology, magnetic coupling technology and high-powerhigh-frequency transform technology. With the development of modern control theoryand strategy, the electrical equipments can get power from power grid by the contactlessway. The disadvantages and limitations of traditional power supply method brought byelectric connection are eliminated. Thus the power can be transferred safely andflexibly.In IPT system, resonant capacitor voltage distortions and current spikes on thesemiconductor switches easily happen when it isn’t switched at zero-crossing point ofresonant voltage. As a result, the Electro-Magnetic Interference level of the system andthe switching loss are raised, whereas the system transmission stability and efficiencydecrease. This paper is relied on National Natural Science Foundation andschool-enterprise cooperation project. It deeply studies the circulating current problemof primary inverter in IPT system.Firstly, it introduces the research status of IPT and circulating current inhibition athome and abroad, describing the research purpose, significance and main componentsof this paper. Also, the principles, significant parts and key technology of the system,and control requirements of the inverter circuit are analyzed.Then,it mainly analyses the factor, mechanism and hazards of circulating currentof IPT system in parallel load resonant inverter, deducing that the resonant frequencychange and the switch-off time delay are the key factors that resulting in circulatingcurrent. In contrary, the limitations go with the traditional circulating current inhibitionapproaches in the practical system.By analyzing the characters of circulating current before and after thezero-crossing points of resonant voltage and relationship between switching frequencyand resonant frequency, this paper proposed a method of real-time detection for thedirection of circulating current, and regulating the switching frequency in accordancewith resonant frequency dynamically to ensure the switching of switch tubes at thezero-crossing points of the resonant capacitor voltage, realizing ZVS control, and thusto inhibit circulating current. Finally, an experimentation system based on CPLD is set up. Moreover, thehardware circuit and software flowchart are also introduced. In addition, theeffectiveness of this control method is verified through the tests in hardware circuit.