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.

Owing to the ubiquitous penetration of Wi-Fi in our daily lives, Wi-Fi indoor localization has attracted intensive attentions in the last decade or so. Despite some significant progresses, the high accuracy of existing systems is still achieved at the cost of dense access point (AP) deployment. The more practical single AP localization is largely left as an open problem because the hardware-induced time delay “contaminates” the measurement of signal propagation time in the air. In this article, we design and implement M3to tackle this challenge with commodity Wi-Fi cards. M3exploits a multipath-assisted approach that turns the harmful multipath from foe to friend to enable single AP localization: a device can be pinpointed through the combination of azimuths and the relative time of flight (ToF) of Line-of-Sight (LoS) signal and reflection signals, eliminating the need for multiple APs along with their absolute ToF measurements. M3further utilizes frequency hopping to combine multiple channels to form a virtually wider-spectrum channel for higher ToF resolution. As a prominent feature of M3, the channels do not need to be adjacent. Comprehensive experiments demonstrate that M3outperforms the state-of-the-art systems and achieves a median localization accuracy of 71 cm in three environments with a single AP.

Lithium-ion batteries (LIBs) are widely adopted in electric vehicles and electronic equipments due to their high energy density, low self-discharge rate, and long cycle life. However, LIBs suffer from capacity fade with cyclic usage. Prediction of remaining useful life (RUL) is therefore essential for ensuring the reliability and safety of LIBs. This paper proposes a bat-based particle filter (PF) algorithm using a semi-empirical model to predict RUL. The semi-empirical model is adopted as the capacity degradation model. Model parameters are then updated by the bat-based PF algorithm. The prediction results of the proposed prediction approach are compareed with PF methods with different resampling algorithms. Simulation results show that the proposed prediction approach can achieve better performance in RUL prediction.

We focus on the management of power electronic loads (PELs) in direct current (DC) distribution networks due to their promising development. We first build a voltage model of PELs based on which we formulate a demand side management optimization problem that coordinates the bus voltage by minimizing the system operation cost. However, the underlying optimization problem is non-convex. In order to solve this non-convex problem, we first reformulate it as a difference of convex programming problem, and then propose a novel algorithm based on branch and bound to implement the optimal solution. It is shown that the system is guaranteed to converge to the global optimum under the proposed method.

Owing to great potential in smart home and human-computer interactive applications, WiFi indoor localization has attracted extensive attentions in the past several years. The state-of-the-art systems have successfully achieved decimeter-level accuracies. However, the high accuracy is acquired at the cost of dense access point (AP) deployment, employing large size of frequency bandwidths or special-purpose radar signals which are not compatible with existing WiFi protocol, limiting their practical deployments. This paper presents the design and implementation of AWL, an accurate indoor localization system that enables a single WiFi AP to achieve decimeter-level accuracy with only one channel hopping. The key enabler of the system is we novelly employ channel hopping to create virtual antennas, without the need of adding more antennas or physically move the antennas' positions for a larger antenna array. We successfully utilize the widely known "bad" spatial aliasing to improve the AoA estimation accuracy. A novel multipath suppression scheme is also proposed to combat the severe multipath issue indoors. We build a prototype of AWL on WARP software-defined radio platform. Comprehensive experiments manifest that AWL achieves a median localization accuracy of 38 cm in a rich multipath indoor environment with only a single AP equipped with 6 antennas. In a small scale area, AWL is able to accurately track a moving device's trajectory, enabling applications such as writing/drawing in the air.

Electrolytic Capacitor (E-cap) is one of the lifetime bottlenecks in power electronic converters. In the last two decades, various active power decoupling circuits have been proposed to improve the reliability of the DC link by eliminating the DC-link E-caps. However, additional active devices could change the stresses of the existing converters, whether the system reliability is improving or not is still an open question. This paper investigates the reliability of the single-phase H-bridge inverter with active power decoupling circuit. The parameter variations in IGBT lifetime model are considered. The Weibull distribution of the key components is obtained from Monte Carlo analysis, and the reliability of the whole system is estimated by the system Reliability Block Diagram (RBD) method. As a case study, 2 kW single-phase H-bridge inverter with passive E-caps and active power decoupling circuits are presented. It is shown that the active power decoupling method is applied to H bridge inverter, and the lifetime of decoupling capacitor can be improved significantly, but it has different effects on system reliability in different applications. In addition, the difference on system reliability of fixed parameter and parameter variations is shown in conclusions.

LLC resonant converter is most frequently effective DC/DC converter to improve the power density and efficiency of DC charging module in electric vehicle power supply. Soft-switching technique can be applied in the topology to reduce the switch losses. However, DC charging module brings about 27% of failures in Electric vehicles (EV) charge device. The aim of this paper is to evaluate the reliability of a 3.8 kW LLC resonant converter as DC charging module in both component level and system level. The power losses of mainly power components are deduced and the thermal model together with the lifetime model are built to evaluate the reliability of the LLC resonant converter in component level. The converter level reliability is obtained by the component level reliability, Weibull distribution and Reliability Block Diagram (RBD).

In single-phase inverters, DC-link capacitors are installed at the DC-link to buffer the ripple power between the AC side and DC side. Active decoupling methods introduce additional circuits at the DC side or AC side to partially or fully supply the ripple power. So that the demanded DC-link capacitor capacitance can be decreased. However, few research is about the effect of DC side and AC side decoupling on the DC-link capacitor reliability considering its electro-thermal stresses. This paper presents a quantitative analysis on the lifetime of capacitors with power decoupling circuits at the DC side and AC side, respectively. The ripple current spectrum of the capacitors is obtained by double Fourier analysis of a H-bridge inverter with natural sampling PWM modulation. A study case is demonstrated by a 2,000 W H-bridge inverter with 400 V DC-link voltage.

Various power decoupling methods have been proposed recently to replace the DC-link Electrolytic Capacitors (E-caps) in single-phase conversion system, in order to extend the lifetime and improve the reliability of the DC-link. However, it is still an open question whether the converter level reliability becomes better or not, since additional components are introduced and the loading of the existing components may be changed. This paper aims to study the converter level reliability of a single-phase full-bridge inverter with two kinds of active power decoupling module and to compare it with the traditional passive DC-link solution. The converter level reliability is obtained by component level electro-thermal stress modeling, lifetime model, Weibull distribution, and Reliability Block Diagram (RBD) method. The results are demonstrated by a 2 kW single-phase inverter application.

DC power systems connecting to single-phase DC/AC inverters with nonlinear loads will have their DC sources being injected with AC ripple currents containing a low-frequency component at twice the output voltage frequency of the inverter and also other current harmonics. Such a current may create instability in the DC power system, lower its efficiency, and shorten the lifetime of the DC source. This paper presents a general waveform control method that can mitigate the injection of the low-frequency ripple current by the single-phase DC/AC inverter into the DC source. It also discusses the inhibiting ability of the waveform control method on other coexisting harmonics, while the DC source delivers AC power to a nonlinear load. With the application of the waveform control, the average DC output power is supplied by the DC source, while the other harmonics pulsation power can be confined to the AC side (between the capacitors and the AC load). Theoretical analyses and experiment results are provided to explain the operation and the inhibiting ability, and to showcase the performance of the approach in tackling the harmonics. Results validate that the proposed solution can achieve significant mitigation of harmonic component at DC side with nonlinear load as well as a high quality output voltage without the need for extra large capacitive energy storage element implementation.