# Multi-Objective Optimization of LCC-S-Compensated IPT System for Improving Misalignment Tolerance
## 1 Introduction  
In recent years, the use of inductive power transfer (IPT) techniques has received much attention and gained popularity. In contrast to the traditional physical contact charging method, the IPT system caters to inherent advantages of safety, convenience, flexibility and strong environmental adaptability. It is widely applied in many applications, such as consumer electronics, implantable medical devices, light rail vehicles, and electric vehicles [1, 2, 3, 4, 5]. Most of them are battery-powered devices and demand a load-independent constant current (CC) or constant voltage (CV) charging mode [6, 7, 8]. IPT systems utilize an alternating magnetic field as a medium to transmit power in the wireless coupler or loosely coupled transformer (LCT). Due to the large leakage inductances, the wireless coupler or LCT absorbs a large value of reactive power, which needs to be compensated for by resonant topologies. Normally, high system efficiency and large power transfer capability can be achieved without any misalignment conditions between the primary and secondary coils. However, misalignment (vertical, horizontal, or angular) between the primary and secondary coupling coils is inevitable [9, 10, 11], usually resulting in high reactive power, deteriorative outputs and low power transfer efficiency of the system. Therefore, power transfer with a low coupling coefficient has become one of the most challenging issues in an inductive wireless charging system [10, 12]. In order to enhance misalignment tolerance, various design and optimization methods have been proposed, including magnetic coupling mechanism designs, control strategies, compensation topology and parameter optimization [13; 14]. Among these methods, compensation networks are essential to compensate for the high reactive power of the magnetic couplers. Moreover, the compensated circuits offer interesting features such as soft switching, high efficiency and flexible output voltage/current. A compensated resonant network typically consists of multiple passive elements, resulting in a variety of circuit characteristics. The tuning of compensation networks plays a vital role in achieving the misalignment tolerance capability, desired stable output features (CC or CV mode) and desired transfer efficiency with a soft-switching operation [15; 16]. However, it can be difficult for a compensation circuit to achieve all of the above excellent performance characteristics. Design optimization of compensation parameters using analytical method/equations is difficult due to the complexity of IPT systems, especially with high-order compensation topologies. In addition, the parasitic parameters of different elements cannot be accurately estimated using classical analytical equations. Besides, the conventional methods based on parameter sweeping are time-consuming and require multiple trial and error calculations. Meanwhile, practical constraints and objectives cannot easily be included in the conventional methods [17]. For example, the anti-misalignment performance of basic series-series (SS) topology was improved by improving the conventional parameter selection [18]. However, the results of improvement were insufficient, and the input current was unbounded when the coupling coefficient was very small [19]. Combined with series topology in the primary side and T-type configurable topology in the secondary side, a series hybrid wireless charging system with eight compensation elements and a switch was proposed to obtain CC and CV outputs accompanied by high misalignment [20]. When the secondary side coil moves out of the operating region, the current of the inverter can be limited without an extra controller. Considering the power stationarity and soft-switching implementation, a general design method for the primary compensation network was proposed in [21], in which the transmission power fluctuation was below 20% in the effective coupling coefficient range (0.125, 0.25).