Multivariable Coordinated Control Strategy for Efficiency Optimization Without Real-Time Wireless Feedback Communication in Wireless Power Transfer

Abstract

This paper presents a constant-frequency multi-variable coordinated control strategy based on a series-series compensated dual-active-bridge wireless-power-transfer converter to eliminate real-time wireless feedback communication (RTWFC) and optimize efficiency. The use of switch-controlled capacitors as the primary and secondary resonant capacitors allows the continuous change of the compensation capacitance for the inverter soft-switching and reactance matching, respectively. The output voltage is regulated by tuning the phase-shift angle in the active rectifier bridge. The optimal load resistance for efficiency improvement is matched by adjusting the phase difference between the rectifier voltage and current based on the load and mutual inductance estimation. Moreover, the phase shift of the inverter, which is load-independent, and the coupling coefficient between the coils are positively correlated. Nevertheless, the drawbacks of the proposed control strategy are that optimal load matching is only valid for heavy load and constant current cannot be realized while keeping the constraint of the decoupled control. The proposed control strategy is experimentally validated on a prototype. The efficiency improvement is 5% compared to the conventional voltage tuning with a diode rectifier at the rated output power and in the normal position, and the peak efficiency reaches 93.6% at a 24 V output under the coupling coefficient of 0.3. In addition, a faster transient response was demonstrated in the proposed control strategy without RTWFC for output regulation.

Keywords

• Wireless power transfer
• soft switching
• control strategy
• efficiency optimization
• switch-controlled capacitor