Capacitive DC links are widely used in Voltage Source Converters (VSC) for power balance, voltage ripple limitation, and short-term energy storage. Various passive and active capacitive DC-link solutions have been proposed intending to improve the reliability of the DC links qualitatively, making great effort to diverting the instantaneous pulsating power into extra reliable storage components. In this publication, a generic topology derivation method for single-phase power converters with active capacitive DC link integrated has been proposed, which can derive all existing topologies, and identify a few new topologies. According to the synthesis results, the main achievements in research on capacitive DC-link solutions are reviewed and presented chronologically as well as thematically ordered. Furthermore, the reliability-oriented design procedure is applied to size the chip area of active switching devices and the passive components to fulfill a specific lifetime target and system specification, as well as compare the overall capacitive energy storage, energy buffer ratio, and the cost of different solutions. The cost comparisons are performed with a scalable lifetime target and power rating. It reveals that different conclusions can be drawn with different lifetime targets in terms of cost-effectiveness.

In both normal and fast wireless electric vehicle charging systems, constant current/constant voltage (CC/CV) charging profile, regardless of the variation of the battery state of charge, is one of the most essential characteristics to ensure the battery performance and reliability. The input zero phase angle (ZPA) is able to minimize the system volt-ampere rating, enhance the power transfer capability, and make it easy to achieve soft-switching operation over the full range of battery charging profile. Therefore, the load-independent CC and CV output characteristics with ZPA conditions are necessary for wireless charging systems. However, the existing methods that can achieve these functions either add power switches or need a large number of compensation components, which make the system inefficient, uneconomical, and bulky. In this paper, a unified resonant tuning configuration with minimum passive component counts is proposed to achieve CC and CV outputs at two ZPA operating frequencies. According to the proposed configuration, all the possible inductive power transfer (IPT) and capacitive power transfer (CPT) topologies are analogized. With these topologies, both CC and CV outputs with ZPA are achieved using a minimum number of compensation components and no additional power switches. Among all the simplest IPT topologies, a primary Series-secondary Series and Parallel (S-SP) compensation topology is illustrated to demonstrate the analysis.

The successful commercialization of wireless power transfer (WPT) technology in mobile phones, laptops, and electric vehicles requires a safe, reliable, and efficient charging infrastructure. A metal object, such as a coin, a key, or a nail, however, may be inadvertently exposed, by close proximity, to the magnetic fields generated by the WPT coupler, creating a potential safety hazard and affecting the electrical characteristics of the WPT system. In addition, the magnetic fields may produce adverse symptoms, such as dizziness and breathlessness, in living objects near the charging systems. This article provides a current state of the art review of all available designs for detecting metal and living objects in WPT systems. Working principles and qualitative comparisons in terms of sensitivity, accuracy, and cost of major detection methods are presented to reveal their inherent limitations and available applications. Finally, a number of research topics on foreign object detection are suggested to encourage more researchers to make contributions to the development and commercial application of wireless charging systems.

For the applications where a single capacitor is incapable to meet the needs, multiple capacitors are connected in series or in parallel as a bank to fulfill the capacitance and voltage rating requirements. Even though some commercial products have already existed in the market, most of the design use the same capacitors or combine different types of capacitors by experience, so that the volume, cost, reliability and power loss are not optimized. To the best knowledge, no quantitative design considering all these design aspects is available for capacitor banks. This paper proposes a model-based optimal design method for hybrid capacitor banks consisting of both electrolytic capacitors and film capacitors. Performance factors, such as impedance characteristics, lifetime, power loss, cost, and volume, are modeled and considered in the optimization process. The selection of the capacitance ratio between the two types of capacitors and the number of capacitors connected in parallel are analyzed based on specific design constraints. A case study of the DC-link capacitor bank design for a 5.5 kW inverter is presented to demonstrate the modeling and optimal design process.

This paper investigates the impact of phase-locked loop (PLL) dynamic on the stability of DC-link voltage control (DVC) in voltage source converter (VSC) attached to weak grid. To start with, a small signal model of VSC attached to weak grid in DVC timescale is presented for stability analysis. On the basis, the dynamic characteristics of VSC are analyzed from the perspective of damping and restoring components which can determine the stability. With considering PLL dynamic, it is found that PLL performs as a phase-lag regulation for DVC and generates additional negative damping component in weak grid, thus weakening the stability of VSC. Furthermore, impacts of PLL’s phase-lag characteristics on additional damping and restoring coefficients are evaluated with variation of grid strengths, operating points and PLL bandwidths to reveal the impact mechanism of PLL dynamic on stability of DVC in VSC. Finally, time-domain simulation and StarSim hardware-in-the-loop (HIL) experimental results are conducted to validate the aforesaid stability analysis.

The large amount of harmonic distortion produced by nonlinearity drives may transmit and couple between grid and multiple drives, which changes the stresses of devices as well as the DC-link filters. This paper investigates the lifetime of DC-link capacitors in multiple drives system. Firstly, by decoupling the interactions among grid-connected drives, a simplified equivalent circuit model and its analytical model to obtain the DC-link continuous current in multiple standard and slim drives is proposed, which releases the designers from configuraing the large simulation for multiple drives. Then, applying the lifetime prediction method, the lifetime of DC-link capacitors in multiple drives are investigated, in terms of types of drives, numbers of drives and grid conditions. The results show that the lifetime of the standard drives extend in the multi-drive systems and lifetime of the slim drives decrease in the multi-drive systems, which break the previous mind. Finally, based on the proposed analytical model and lifetime estimation method, the capacitor sizing from reliability aspect for multiple slim drives are given. The outcomes of the lifetime investigation could be a guideline for the design of capacitive DC-link in multi-drive system