Input Reactive Power Control of Bidirectional WPT to Improve System Efficiency
Ravi Kumar Yakala, Debi P. Nayak, Sumit Pramanick
Abstract
Misalignment can significantly affect the mutual inductance of a wireless power transfer (WPT) system, thereby impacting the system's power transfer capabilities and efficiency. Traditionally, to achieve optimal efficiency with constant output power under misalignment, individual closed-loop feedback control needs to be used on both the transmitter and receiver sides. The receiver side phase shift ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> ) is controlled to maintain the constant output power, and the transmitter side phase shift ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> ) is controlled to achieve zero power factor angle (ZPA) for optimal efficiency. The ZPA condition is achieved by making the input reactive power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q_{in}$</tex-math></inline-formula> ) equal to zero. However, this necessitates additional high- bandwidth sensing circuitry, thereby increasing system complexity. Moreover, it also introduces the cross-coupling issue due to formation of multi input multi output (MIMO) system. This paper proposes a simple, decoupled, and fast response control approach for mitigating the impact of misalignment and load variation by employing a single receiver-side PI controller. A closed form analytical relationship between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> has been established in this paper to maintain optimal efficiency while regulating output power under misalignment conditions. The proposed method obtains <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> from the receiver side controller and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> from the derived relation. The proposed control method is validated using an experimental setup of a 1 kW bidirectional wireless power transfer (BWPT) system. The simulation and experimental results of the BWPT system under various loading and misalignment conditions are presented.