Author: Liu, Junwei
Title: Topologies and control of single-stage AC-DC wireless-power-transfer resonant converters with power-factor-correction
Degree: Ph.D.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Wireless power transmission
Power (Mechanics)
Pages: xxviii, 186 pages : color illustrations
Language: English
Abstract: High power wireless power transfer (WPT) technologies have drawn much attention in industrial and academic areas in recent years due to their obvious advantages: convenience and safety (avoidance of electric shock). For applications of high power WPT, such as wireless electric vehicle (EV) charging, power is usually drawn from the power grid and a separate power factor correction (PFC) stage is typically needed to ensure the power quality of the grid. Therefore, a two-stage topology with an AC-DC converter with PFC stage and a DC-DC WPT converter stage is often adopted. Generally, such two-stage topology cannot achieve the highest efficiency because of more power losses in the two-stage conversion while it is also not the most economical as more components are required. Also its control is more complicated because two separate controllers for two stages are required. Recently there has been a lot of research on single-stage AC-DC converters with PFC aimed to reduce power losses, power switch counts, and control complexity. Much of existing research focuses mainly on applying single-stage topologies in transformer-based-isolated converter. There are very few studies on applying single-stage topologies in WPT systems, and it is therefore the aim of this thesis to explore and develop the topologies and control methods of AC-DC WPT resonant converters with single-stage PFC topologies. A new single-phase single-stage AC-DC WPT converter with PFC is proposed, which utilizes the lowest count of power semiconductor devices (6 diodes and 4 switches), compared with conventional two-stage AC-DC WPT converters (9 diodes and 5 switches) and other existing AC-DC WPT converters. Due to the reduced count of power semiconductor devices, the power loss is significantly reduced and a remarkably high efficiency of 90.1% was measured in experiments with power factor and input current THD achieved 0.99 and 15.4%, respectively. A new control method for the topology is also proposed to further improve the power quality, reduce bus voltage, and extend load range of operation. Though it is slightly more complicated due to the introduction of two control parameters, the proposed control method can largely improve the power quality with the measured input current THD below 1% and power factor over 0.99. Furthermore, the bus voltage is largely reduced and controlled to 500V as compared to the original of 723.5V so as to significantly alleviate the voltage stresses of all the power switches and bus capacitor.
A new three-phase single-stage AC-DC WPT converter with PFC is proposed, which also has the lowest count of power semiconductor devices (10 diodes and 4 switches) and reduced power loss compared with other existing three-phase AC-DC WPT converters with PFC. It achieved the maximum efficiency of 91.7% in experiments. Compared to the proposed single-phase topology, this three-phase topology possesses additional advantages of better power quality with power factor and input current THD reached 1.0 and 3.5%, respectively, due to the elimination of the zero-sequence components in input current; and higher power capacity due to the inherent superiority of three-phase power source. As the backend of single-stage AC-DC WPT converters, DC-DC WPT converters are also studied, and a new parameter estimation algorithm requiring only primary-side information under unknown varying misalignment and load conditions, is newly proposed. The proposed algorithm mainly utilizes both the existing fundamental and higher-order harmonics (third-order) in the WPT resonant converter. In experiments, the measured errors of estimations are below 3% and better than other existing methods (maximum errors larger than 8.3%). Such algorithm could be applied in primary-side feedback and control system of DC-DC or AC-DC WPT resonant converters without any additional wireless communication device or secondary-side measurement units and controller, so as to greatly simplify the hardware and reduce the total cost.
Access: open access

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