Maximum efficiency point tracking control scheme for loosely coupled MIMO wireless power charging system

Abstract

This dissertation presents a maximum efficiency point tracking (MEPT) control scheme for a closed-loop wireless power charging (WPC) system for wireless charging of devices. Generally, wireless charging systems need precise output voltage and current with the highest possible efficiency. However, the efficiency and output voltage are very sensitive to mutual inductance and load conditions. Unfortunately, these parameters relate with charging environments. For example, if the position of receiver is changed during charging, the mutual inductance is also changed, and the load conditions varied by amount of charging the battery. Therefore, the WPC system is needed to satisfy the constant output voltage and possible highest efficiency according to sensitive variation of charging environments. To guarantee the constant output voltage, we applied the post-regulation, which is one of the closed loop regulation. To maintain the possible highest efficiency, the maximum efficiency point tracking control scheme and method of mutual inductance real-time tracking are proposed. The proposed MEPT control scheme is adjusting the amplitude and phase of transmitting currents. The WPC system has optimum load impedance. However, load impedance moves away from optimum point by variation of charging environments. The proposed MEPT control scheme can change the load impedance deviated from optimum point, that is, there is optimum currents (solutions). One of the advantages in magnetic resonance wireless power transfer is able to charge the multiple devices simultaneously. However, the most researches are focused on SISO system. The studies of the other cases (SIMO, MISO, and MIMO) system are insufficient. Therefore, we also extended the MEPT control scheme for the other cases in this dissertation. Each case has key points to get the optimum solution. In SIMO system, there are multiple optimum load because there are multiple receivers. However, the system gets only one optimum load because there is one transmitter. Therefore, it is important to choose the optimal point of the SIMO system, among the several optimal load impedance. Next MISO system, there is one more parameter of efficiency then single transmitter system. It is the ratio of transmitting currents. Because there are several transmitters, there is a sign in the mutual coupling value. Therefore, it is essential to control of the phase of the current according to the sign of mutual inductance. The procedure for determining the sign is added to the proposed method of mutual inductance tracking. Finally, in MIMO system, it consider the all things as mentioned in SISO, SIMO, MISO systems. The efficiency equation is very complex, so the particle swarm optimization (PSO) algorithm is used. To reduce the algorithm running time, the subsets are defined. Each subset is independent so we can consider more simple divided WPC system. To experimentally verify the proposed control scheme, SISO, SIMO, MISO, and MIMO wireless power charging system applied the method of real-time tracking of mutual inductance operating at 1 MHz frequency are implemented. As a result, in all the system cases, the proposed MEPT control scheme can track the maximum efficiency regardless of receiver position, load conditions, and number of receivers and transmitters.