| Author: | Xu, Fei |
| Title: | Efficiency optimization control of inductive power transfer converters |
| Advisors: | Wong, S. C. (EIE) Loo, K. H. (EIE) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Electric current converters Power electronics Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Electronic and Information Engineering |
| Pages: | xxiv, 146 pages : color illustrations |
| Language: | English |
| Abstract: | Power regulation and efficiency optimization against variations of load, mutual-inductance and self-inductance are major technical challenges for inductive-power-transfer (IPT) technology. In this thesis, optimal control strategies of output regulation and efficiency optimization in a single-stage series-series (S-S) compensated IPT converter for both stationary-inductive-power-transfer (SIPT) and dynamic-inductive-power-transfer (DIPT) are studied in depth, generating results that are of theoretical and practical significance for designing safe, stable and high-efficiency IPT converters. The first work of this thesis aims to maximize the system efficiency of a single-stage SIPT charger by minimizing the overall losses using a constant-power (CP) charging scheme. The single-stage CP SIPT charger employs S-S compensation and adopts an active rectifier on the secondary side. The conditions of zero-voltage-switching (ZVS) and minimum circulating reactive power are first derived. Then, the power losses in the magnetic coupler, inverter and active rectifier are analyzed and optimized under a constant power output condition. Combining the conditions of ZVS, minimum circulating reactive power and minimum overall losses, a novel optimal control strategy that maintains constant power output and maximum efficiency throughout the CP charging process is proposed. The misalignment or change of the air gap distance in a magnetic coupler without ferrite cores would lead to variation of mutual-inductance in a DIPT system. The second part of this thesis aims to optimize the system efficiency of a single-stage DIPT converter considering time varying mutual-inductance. An effective and fast maximum efficiency tracking control strategy for single-stage S-S compensated IPT systems is studied in detail. The maximum efficiency tracking control uses a fast mutual-inductance estimation algorithm to achieve fast tracking of the maximum efficiency point especially when the variation of the gap distance and misalignment of the magnetic coupler are significant. For the magnetic coupler with ferrite cores or aluminum shielding plate in a DIPT system, both mutual-inductance and self-inductance may change when there is misalignment or variation of the air gap distance between the transmitting and receiving coils, which would lead to detuning of the IPT system. When a S-S compensated IPT converter is detuned, the constant current (CC) output characteristic and power efficiency would be deteriorated. In view of the absence of a solution for the natural resonant frequency and output deviation problems caused by variations of mutual-inductance and self-inductance, the third part of this thesis attempts to design an efficiency optimization control strategy with CC output for a single-stage S-S compensated IPT system under varying mutual-inductance and self-inductance. First of all, the proposed control method uses a fast hill-climbing search method to obtain the natural resonant frequency. Then, the mutual-inductance can be estimated accurately when the IPT system operates at the newly determined resonant frequency. Next, the optimal solutions of CC output with maximum efficiency can be obtained to modulate the IPT system based on the new steady-state mathematical models. All the proposed optimal control strategies have been analyzed in detail and validated by simulation and experimental results in three different appropriate IPT converter prototypes. |
| Rights: | All rights reserved |
| Access: | open access |
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