High-power Charging Research Articles

A novel phase change based cooling system for prismatic lithium ion batteries

The thermal management of lithium ion battery packs in hybrid and plug in electric vehicles is important, especially during high power charging and discharging processes. To maintain the working temperature of lithium ion batteries in hybrid electric vehicles, a novel boiling heat transfer based thermal management system is proposed and its performance is analyzed and measured in terms of the temperature characteristics of the batteries in the pack. The thermal characteristics of the battery pack are presented in terms of the maximum temperature and the temperature uniformity in the pack. The proposed system uses the fuel, which is propane in the proposed model of the hybrid electric vehicle, to cool the batteries and before it is fed to the internal combustion engine of the vehicle. The fuel is the used to generate electrical energy for charging the batteries or driving the vehicle. A one-dimensional electrochemical model and a three-dimensional thermal model are developed to assess the performance of the proposed system under severe discharging and charging cycles. The effects of the propane boiling temperature and the liquid height in the battery pack on the thermal performance of the battery pack are investigated. The present results show that the proposed battery thermal management system is able to maintain the maximum temperature in the battery at under 35 °C and the temperature uniformity to avoid exceeding a temperature difference of 1 °C between the batteries in the pack, for a 600-s cycle of discharging and charging at a rate of 4 C. Increasing the saturation pressure of the propane pool improves the temperature uniformity in each battery, although it overall increases the maximum temperature in the battery.

A Single-Phase Integrated Onboard Battery Charger Using Propulsion System for Plug-in Electric Vehicles

Plug-in electric vehicles (PEVs) are equipped with onboard level-1 or level-2 chargers for home overnight or office daytime charging. In addition, off-board chargers can provide fast charging for traveling long distances. However, off-board high-power chargers are bulky, expensive, and require comprehensive evolution of charging infrastructures. An integrated onboard charger capable of fast charging of PEVs will combine the benefits of both the conventional onboard and off-board chargers, without additional weight, volume, and cost. In this paper, an innovative single-phase integrated charger, using the PEV propulsion machine and its traction converter, is introduced. The charger topology is capable of power factor correction and battery voltage/current regulation without any bulky add-on components. Ac machine windings are utilized as mutually coupled inductors, to construct a two-channel interleaved boost converter. The circuit analyses of the proposed technology, based on a permanent magnet synchronous machine (PMSM), are discussed in details. Experimental results of a 3-kW proof-of-concept prototype are carried out using a ${\textrm{220-V}}_{{\rm{rms}}}$ , 3-phase, 8-pole PMSM. A nearly unity power factor and 3.96% total harmonic distortion of input ac current are acquired with a maximum efficiency of 93.1%.

Lifecycle costs and charging requirements of electric buses with different charging methods

Electric city buses and high power charging systems have been rapidly developed in recent years. Battery electric buses are energy efficient and emission free but due to the expensive technology, lifecycle costs can be much higher in comparison to diesel or hybrid buses. This research presents a lifecycle cost analysis for a fleet operation of electric city buses in different operating routes. The objective is to define charging power and battery requirements as well as energy consumption and lifecycle costs. A specific simulation tool was developed to comprehensively evaluate electric buses in different operating conditions. The tool allows to systematically generate and simulate different operating scenarios with a chosen bus configuration, charging method and operating route. Based on the simulation results and predefined cost parameters, lifecycle costs are calculated for each operating scenario. The considered charging methods include overnight, end station and opportunity charging. Simulation results are presented for four operating routes which were measured from existing bus lines in Finland and California, USA. The results show that high energy capacity of the battery system is crucial for the overnight charging buses to achieve adequate daily operation whereas the battery size has a minor impact on the energy consumption and lifecycle costs of the fast charging buses. The lifecycle costs of electric buses are heavily impacted by capital costs including purchase costs of the buses and charging devices. When considering 12 years of service life, the end station charging electric buses can have slightly lower lifecycle costs than diesel buses but on average they have 7% higher lifecycle costs. The overnight charging buses have on average 26% and opportunity charging buses 35% higher lifecycle costs than diesel buses.

(Battery Division Research Award Address) Developments of New Ionic Conductors and Their Application to All-Solid-State Batteries

All-solid-state is an ideal form of battery. The all-solid-state battery offers an attractive option owing to their potential in improving the safety and achieving both high power and high energy densities. Despite extensive research efforts, the development of all-solid-state batteries still falls short of expectation largely because of the lack of suitable candidate materials for the electrolyte required for practical applications. Among the electrolytes proposed, the sulphide system is a candidate because of its high ionic conductivity1). The Li10GeP2S12 (LGPS) exhibits high bulk conductivity of over 10- 2 S cm-1 at room temperature and is promising for applications requiring batteries with high power and energy densities2). On the other hand, material variations may provide suitable combinations of the electrodes and the electrolyte. Specifically, new LGPS-type superionic conductors exhibit extremely high conductivity (25 mS cm-1, Li-Si-P-S-Cl system) and high stability (~0 V vs Li metal, Li-P-S system), which enable the generation of high power and ultrafast charging of all-solid-state cells with high energy densities3). The present study reviews the materials varieties and the materials design concepts of the solid electrolytes with the LGPS-type structures. The effects of conductivities and electrochemical stabilities of the electrolytes on the battery characteristics will be discussed.References 1) R. Kanno, et al., J. Electrochem. Soc., 148, (7), A742-A746 (2001).2) N. Kamaya, et al., A. Mitsui, Nature Materials, 10, 682 (2011). 3) Y. Kato, et al., Nature Energy, 1, 201630, (2016).

Modelling and Simulation of Electric Vehicle Fast Charging Stations Driven by High Speed Railway Systems

The aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Actually, long highways are often located far from urban areas and electrical infrastructure, therefore the installations of high power charging areas can be difficult. Specifically, the aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Specifically, this work concentrates on fast-charging electric cars in motorway service areas by using high-speed lines for supplying the required power. Economic, security, safety and environmental pressures are motivating and pushing countries around the globe to electrify transportation, which currently accounts for a significant amount, above 70 percent of total oil demand. Electric cars require fast-charging station networks to allowing owners to rapidly charge their batteries when they drive relatively long routes. In other words, this means about the infrastructure towards building charging stations in motorway service areas and addressing the problem of finding solutions for suitable electric power sources. A possible and promising solution is proposed in the study that involves using the high-speed railway line, because it allows not only powering a high load but also it can be located relatively near the motorway itself. This paper presents a detailed investigation on the modelling and simulation of a 2 × 25 kV system to feed the railway. A model has been developed and implemented using the SimPower systems tool in MATLAB/Simulink to simulate the railway itself. Then, the model has been applied to simulate the battery charger and the system as a whole in two successive steps. The results showed that the concept could work in a real situation. Nonetheless if more than twenty 100 kW charging bays are required in each direction or if the line topology is changed for whatever reason, it cannot be guaranteed that the railway system will be able to deliver the additional power that is necessary.

Generalized Potential Function-Based Cooperative Current-Sharing Control for High-Power Parallel Charging Systems

In this paper, a new decentralized gradient-based cooperative control method is proposed to achieve current sharing for parallel chargers in energy storage-type light rail vehicle systems. By employing a generalized artificial potential function to characterize the interaction rule for subchargers, the current-sharing control problem is converted into an optimization problem. Based on the gradient of the potential function, a decentralized gradient cooperative control law is derived. A general saturation function is introduced in the proposed control to guarantee the boundedness of the control output. The stability of the closed-loop system under the proposed decentralized gradient control is proven with the aid of a Lyapunov function. Simulation results are provided to verify the feasibility and validity of the proposed distributed current-sharing control method.

Energy Consumption and Cost Savings of Truck Electrification for Heavy-Duty Vehicle Applications

An evaluation was made of the application of battery electric vehicles (BEVs) and GenSet plug-in hybrid electric vehicles (PHEVs) to Class-7 local delivery trucks and GenSet PHEV for Class-8 utility bucket trucks over widely real-world driving data performed by conventional heavy-duty trucks. GenSet refers to a PHEV range extension mode in which the PHEV engine is used only to generate electricity and charge the battery if the PHEV battery is out of electrical energy. A simulation tool based on vehicle tractive energy methodology and component efficiency for addressing component and system performance was developed to evaluate the energy consumption and performance of the trucks. As part of this analysis, various battery sizes combined with different charging powers on the e-trucks for local delivery, and utility bucket applications were investigated. The results show that the e-truck applications not only reduce energy consumption but also achieve significant energy cost savings. For delivery e-trucks, periodic stops at delivery sites provide sufficient time for battery charging, and for this reason, a high-power charger is not necessary. For utility bucket PHEV trucks, energy consumption per mile of bucket truck operation is typically higher because of longer idling times and extra high idling load associated with heavy utility work. The availability of en route charging is typically lacking at the worksites of bucket trucks; thus, the battery size of these trucks is somewhat larger than that of the delivery trucks studied.

Effective Voltage Balance Control for Bipolar-DC-Bus-Fed EV Charging Station With Three-Level DC–DC Fast Charger

The development of high-power charging stations with fast chargers is a promising solution to shorten the charging time for electric vehicles (EVs). The neutral-point-clamped (NPC) converter-based bipolar-dc-bus-fed charging station brings many merits, but it has inherent voltage balance limits. To solve this issue, a voltage balance control (VBC) method based on a new modulation together with three-level (TL) dc–dc converter-based fast charger is proposed. Additionally, an effective VBC coordination between the TL dc–dc converter and the NPC converter is formulated. Through the proposed VBC coordination, the controllable balancing region is extended so that additional balancing circuits are eliminated. Meanwhile, the quality of the grid-side currents is improved as the NPC converter has more freedom to control currents. The low-frequency voltage fluctuations in dc buses are removed because the TL dc–dc converter performs most of the balancing tasks. Faster VBC perturbation performance is achieved due to higher available balancing current at TL dc–dc converter side. In addition, the voltage balance limits of both the TL dc–dc converter and the NPC converter are explored. The voltage balancing performances are compared when VBC is located at different sides. Simulation and experimental results are provided to verify the proposed VBC and the VBC coordination.

Application of a hybrid energy storage system in the fast charging station of electric vehicles

Fast charging is a practical way for electric vehicles (EVs) to extend the driving range under current circumstance. The impact of high-power charging load on power grid should be considered. This study proposes an application of a hybrid energy storage system (HESS) in the fast charging station (FCS). Superconducting magnetic energy storage (SMES) and battery energy storage (BES) are included in HESS. Based on the quick response of SMES and the high energy density of BES, power magnitude and power change rate of FCS can be limited by compensation of HESS. A controller is designed to generate real-time power demand to HESS. As a part of the control strategy, the energy regulation control of SMES is highlighted. The regulation control is necessary for SMES to deal with energy imbalance in continuous operation; meanwhile it is beneficial for battery life. Finally, feasibility of this control strategy is verified by simulation.

Comprehensive DC Power Balance Management in High-Power Three-Level DC–DC Converter for Electric Vehicle Fast Charging

With the increasing popularity of electric vehicles, there is an urgent demand to shorten the charging time, so the development of high-power charging stations with fast chargers is necessary to alleviate range anxiety for drivers. The charging station based on the neutral-point-clamped (NPC) converter can bring many merits, but it has unbalanced power problems in the bipolar dc bus. To solve this issue, comprehensive dc power balance management (PBM) in conjunction with high-power three-level dc–dc converter based fast charger is proposed in this paper. The active dc power balance management (APBM) is proposed to assist the central NPC converter in balancing power so that the additional balancing circuit is eliminated; while the passive dc power balance management (PPBM) is proposed to eliminate the fluctuating neutral-point currents and to ensure the balanced operation of fast chargers. The principles of APBM and PPBM are researched, the efficient integration between them is studied, and the overall control scheme for the fast charger is proposed. The power balance limits of APBM are explored, while the circulating currents of PPBM are analyzed. Simulation and experimental results are presented to verify the effectiveness of the proposed fast charger with PBM functions.

Elements of Wireless Power Transfer Essential to High Power Charging of Heavy Duty Vehicles

Scaling wireless charging to power levels suitable for heavy duty passenger vehicles and mass transit bus requires in-depth assessment of wireless power transfer (WPT) architectures, component sizing and stress, package size, electrical insulation requirements, parasitic loss elements, and cost minimization. It is demonstrated through an architecture comparison that the voltage rating of the power inverter semiconductors will be higher for inductor-capacitor-capacitor (LCC) than for a more conventional Series–Parallel (S–P) tuning. Higher voltage at the source inverter dc bus facilitates better utilization of the semiconductors, hence lower cost. Electrical and thermal stress factors of the passive components are explored, in particular the compensating capacitors and coupling coils. Experimental results are presented for a prototype, precommercial, 10 kW wireless charger designed for heavy duty (HD) vehicle application. Results are in good agreement with theory and validate a design that minimizes component stress.

A Modular Multiport Power Electronic Transformer With Integrated Split Battery Energy Storage for Versatile Ultrafast EV Charging Stations

This paper proposes a power converter architecture for the implementation of an ultrafast charging station for electric vehicles (EVs). The versatile converter topology is based on the concept of the power electronic transformer. For the direct transformerless coupling to the medium-voltage grid, a cascaded H-bridge (CHB) converter is utilized. On the level of each submodule, integrated split battery energy storage elements play the role of power buffers, reducing thus the influence of the charging station on the distribution grid. The power interface between the stationary split storage stage and the EV batteries is performed through the use of parallel-connected dual-half-bridge dc/dc converters, shifting the isolation requirements to the medium-frequency range. By choosing several different submodule configurations for the parallel connection, a multiport output concept is achieved, implying the ability to charge several EVs simultaneously without the use of additional high-power chargers. All possible charging station operating modes among with the designed necessary control functions are analyzed. The state-of-charge self-balancing mode of the delta-connected CHB converter is also introduced. Finally, the development of a downscaled laboratory prototype is described, and preliminary experimental results are provided.

Online Embedded Impedance Measurement Using High-Power Battery Charger

This paper presents a new functionality for high-power battery chargers by incorporating an impedance measurement algorithm. The measurement of battery impedance can be performed by the battery charger to provide an accurate equivalent model for battery management purposes. In this paper, an extended control capability of the onboard battery charger for electric vehicles is used to measure the online impedance of the battery. The impedance of the battery is measured by the following: 1) injecting ac current ripple on top of the dc charging current; 2) transforming voltage and current signals using a virtual $\alpha{-}\beta$ stationary coordinate system, a $d{-}q$ rotating coordinate system, and two filtering systems; 3) calculating ripple voltage and current values; and 4) calculating the angle and magnitude of the impedance. The contributions of this paper are the use of the $d{-}q$ transformation to attain the battery impedance, theta, and its ripple power, as well as providing a controller design procedure which has impedance measurement capability. The online impedance information can be utilized for diverse applications such as the following: 1) a theta control for sinusoidal current charging; 2) the quantifying of reactive current and voltage; 3) ascertaining the state of charge; 4) determining the state of health; and 5) finding the optimized charging current. Therefore, the benefit of this method is that it can be deployed in already existing high-power chargers regardless of battery chemistry. Validations of the proposed approach were made by comparing measurement values by using a battery charger and a commercial frequency response analyzer.

Design and Implementation of a High Power Dual-module Parallel Charging System

This paper presents a high-power dual-module parallel charging system which consists of a power converter and digital control software. The power converter consists of an active power factor correction (APFC) circuit and a resonant voltage fed full-bridge converter (RVFFBC). The APFC circuit is used for AC/ DC conversion and power factor correction for improved power quality. The RVFFBC is used to provide stable power for charging the battery by converting the high voltage of the power stage to a lower value. The system software was designed by combining the power control loop into a voltage and current loop to achieve current sharing of the dual-module charging system and to overcome the effect of differences in hardware components. Finally, this paper demonstrates the implementation of a high-power dual-module charging system with a widely varying AC input voltage ranging from 85 ~ 265 Vac. Experimental results verified that the maximum power factor of the system and the Total Harmonic Distortion (THD) were 0.99 and 2.8% respectively. The proposed charging system possesses very high expansibility. The parallel dual-module output DC current of the system is 70 A and the total output power is 4 kW.

Optimization of Sizing and Battery Cycle Life in Battery/Ultracapacitor Hybrid Energy Storage Systems for Electric Vehicle Applications

Electric vehicle (EV) batteries tend to have accelerated degradation due to high peak power and harsh charging/ discharging cycles during acceleration and deceleration periods, particularly in Urban driving conditions. Oversized energy storage system (ESS) meets the high power demand; however, in tradeoff with increased ESS size, volume, and cost. In order to reduce overall ESS size and extend battery cycle life, battery/ultracapacitor (UC) hybrid ESS (HESS) has been considered as a solution in which UCs act as a power buffer to charging/discharging peak power. In this paper, a multiobjective optimization problem is formulated to minimize the overall ESS size, while maximizing the battery cycle life according to the assigned penalty functions. An integrated framework for HESS sizing and battery cycle life optimization applied in a midsize EV, using an Autonomie simulation model, is described and illustrated in this paper. This multidimensional optimization is realized by a sample-based global search oriented DIviding RECTangles (DIRECT) algorithm. The optimization results under Urban Dynamometer Driving Schedule (UDDS) are compared with the battery-only ESS results, which demonstrate significant battery cycle life extension of 76% achieved by the optimized HESS with 72 UC cells.

Performance comparison of thermal energy storage oils for solar cookers during charging

Charging experiments to evaluate the thermal performance of three thermal energy storage oils for solar cookers are presented. An experimental setup using an insulated 20 L storage tank is used to perform the experiments. The three thermal oils evaluated are Sunflower Oil, Shell Thermia C and Shell Thermia B. Energy and exergy based thermal performance parameters are evaluated. A new parameter, the exergy factor, is proposed which evaluates the ratio of the exergy content to the energy content. Sunflower Oil performs better than the other thermal oils under high power charging. Thermal performances of the oils are comparable under low power charging.

Research on Efficiency of High Power Resonant Electric Vehicle Contactless Power Transfer Charger

Compared with traditional charging method, CPT (contactless power transfer) is more convenient and safe while having higher power lose. Therefore, the efficiency of CPT needs to be optimized. In this paper, PSSS (primary side series compensation and secondary side series compensation) model is used to study the efficiency optimization of a high-power CPT. The factors such as coil structure, resonant frequency, and load matching on high-power CPT charging equipment are studied by simulation and experiment. The results show that system efficiency is proportional to mutual inductance values; coil structure mainly affects the mutual inductance values; the mutual inductance of the coils is mainly affected by the diameter of the coils, the distance between the coils, the shape of coil, the number of turns, and so forth. As for the CPT charging system based on full-bridge inverter circuit, the efficiency of the system increases as the frequency increases in the range of 0–50 kHz, while decreases as the frequency is higher than 50 kHz. Load matching also affects the efficiency of high-power CPT charging equipment, and the load matching formula based on an equivalent circuit model is given.

Dynamics of Workplace Charging for Plug-in Electric Vehicles: How Much is Needed and at What Speed?

This paper presents workplace charging needs from two perspectives: the potential needs based on modelling and the needs based on survey results. These approaches both examine workplace needs from what people need to increase usage of the cars, and what workplace charging they will they actually use. The analysis reveals that for California driving patterns, chargers at the workplace can increase electric vehicle miles travelled (eVMT) by approximately 2%-10% for PHEVs and about 6%-9% for a 60-100 mile battery electric vehicle (BEV). The actual number of chargers used depends on the price charged. Both methods show that workplace charging will increase if charging is free versus a priced scenario with no extra benefit in terms of eVMT. The survey shows that 2 out of 10 vehicles will use workplace charging if it is priced between home electricity and gasoline on a cents per mile basis, while 8 out of 10 vehicles will use it if free on any given day. This corresponds to a 2-4 times increase in “needed” chargers depending on assumptions of how many cars one charger can serve per day. Also investigated was the speed of charging needed at work. Most charging of PHEVs can be accomplished with low power charging and 80% of BEV charging can be accomplished with low power. In general low power charging should comprise 80% or chargers, and charging price should be segmented by charging speed to encourage efficient use of high power chargers – reserving high power level 2 charging for those who need it such as some BEVs and utilizing low power chargers for PHEVs and low need BEVs.

Flux‐weakening operation of open‐end winding drive integrating a cost‐effective high‐power charger

In this study, a three-phase drive with a six-leg voltage source inverter and an open-end winding interior permanent magnet synchronous machine designed for traction of an electric vehicle is studied in a flux-weakening operation. The topology allows the functionality of a high-power charger to be obtained, without adding any other supplementary power devices. On the other hand, since there are three independent currents, the control structure has to handle not only the two dq-current components but also a zero-sequence current. If neglected, in comparison with a wye-coupled three-phase drive, this zero-sequence component can cause a higher maximum peak value of the phase currents, additional stator Joule losses, torque ripple, inverter voltage saturation and insulated gate bipolar transistor (IGBT) oversizing. The proposed control strategy consists in adapting a conventional method used for wye-connected machines particularly in flux-weakening operation. This strategy allows the closed-loop control of the zero-sequence current to be maintained in the whole speed range and therefore inverter saturation is avoided. Simulations and experimental results are presented and analysed.

Grid-Connected Integrated Battery Chargers in Vehicle Applications: Review and New Solution

For vehicles using grid power to charge the battery, traction circuit components are not engaged during the charging time, so there is a possibility to use them in the charger circuit to have an onboard integrated charger. The battery charger can be galvanically isolated or nonisolated from the grid. Different examples of isolated or nonisolated integrated chargers are reviewed and explained. Moreover, a novel isolated-high-power three-phase battery charger based on a split-phase permanent-magnet motor and its winding configuration is presented in this paper. The proposed charger is a bidirectional high-power charger with a unity power factor operation capability that has high efficiency.