Design of a high efficiency wireless charging system

Nowadays, the increasing energy demand has made it necessary to use energy efficiently. For this reason, the design of high-efficiency battery charging systems has been an important research topic in recent years. Wireless power transfer (WPT) systems have become popular recently due to their features such as being unaffected by environmental conditions, offering flexibility to the user, and being reliable. In these systems, constant current (CC) and constant voltage (CV) charge control is often preferred because it provides high efficiency and is suitable for battery charging characteristics. A wide variation of the battery load during the entire charging process makes it difficult to charge the battery at CC and CV charging modes. In this case, the selection and control of the suitable compensation topology become important. A variety of WPT compensation topologies are used in electric vehicle battery charging systems. In this thesis, it is aimed to design a wireless EV battery charging system based on an LC-S compensation topology, which can transfer power with high efficiency in both CC and CV charging modes. The design of a high-efficiency WPT system was carried out during the entire charging period, by preventing the performance degradation of the topology with CC output characteristics, especially in the CV charging mode. Within the scope of the thesis, wireless power transfer and CC-CV battery charging were carried out under a single stage converter structure by using the LC-S topology with a semi-bridgeless active rectifier (S-BAR). In CV charging mode, the pulse density modulation (PDM) method has been applied to the LC-S compensation topology over the S-BAR circuit structure. In this way, the proposed WPT system has become controllable at the resonant frequency in both CC and CV charging modes. In addition, soft switching is provided over a wide load range in both charging modes. In this thesis, the proposed WPT system has been designed with a power of 1.05 kW, a switching frequency of 85 kHz, an input voltage of 200 V, and an output voltage of 150 V-210 V for CC and CV battery charging modes. Simulation studies were carried out with the designed system, then experimental studies were carried out on the prototype at a wireless power transmission distance of 15 cm. In experimental studies, the performance of PDM control and phase shift (PS) control was compared, and 6.4% efficiency increase was achieved with PDM at 25% load condition.