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Battery charging topology, infrastructure, and standards for electric vehicle applications: A comprehensive review

2021; Institution of Engineering and Technology; Volume: 3; Issue: 4 Linguagem: Inglês

10.1049/esi2.12038

2516-8401

Siddhant Kumar, Adil Usman, Bharat Singh Rajpurohit,

Advancements in Battery Materials

IET Energy Systems IntegrationVolume 3, Issue 4 p. 381-396 REVIEWOpen Access Battery charging topology, infrastructure, and standards for electric vehicle applications: A comprehensive review Siddhant Kumar, Siddhant Kumar orcid.org/0000-0003-3552-0877 School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi, IndiaSearch for more papers by this authorAdil Usman, Corresponding Author Adil Usman adilusman@ieee.org orcid.org/0000-0002-8329-060X School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi, India Correspondence Adil Usman, School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi 175075, India. Email: adilusman@ieee.orgSearch for more papers by this authorBharat Singh Rajpurohit, Bharat Singh Rajpurohit orcid.org/0000-0001-9843-6002 School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi, IndiaSearch for more papers by this author Siddhant Kumar, Siddhant Kumar orcid.org/0000-0003-3552-0877 School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi, IndiaSearch for more papers by this authorAdil Usman, Corresponding Author Adil Usman adilusman@ieee.org orcid.org/0000-0002-8329-060X School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi, India Correspondence Adil Usman, School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi 175075, India. Email: adilusman@ieee.orgSearch for more papers by this authorBharat Singh Rajpurohit, Bharat Singh Rajpurohit orcid.org/0000-0001-9843-6002 School of Computing and Electrical Engineering, Indian Institute of Technology Mandi, Mandi, IndiaSearch for more papers by this author First published: 11 August 2021 https://doi.org/10.1049/esi2.12038AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract The proposed study reports the essential parameters required for the battery charging schemes deployed for Electric Vehicle (EV) applications. Due to efficient power delivery, cost-effectiveness, and environmental acclimation, EVs have emerged as a suitable alternative to the Internal Combustion (IC)-based engines. However, prominent challenges for leveraging the EVs are the suitable availability of battery charging infrastructure for high energy/power density battery packs and efficient charging topologies. Despite the challenges, EVs are gradually being implemented across the globe to avoid oil dependency, which currently has a 5%–7% decline rate of post-peak production. The vast deployment of EVs as private and commercial vehicles has created a major challenge for the grids in maintaining the power quality and peak load demand. This study, therefore, reviews the various battery charging schemes (battery charger) and their impact when used in EV and Hybrid EV applications. The available constituents of the battery chargers such as ac-dc/dc-dc converter topologies, modulations, and control techniques are illustrated in detail. The comprehensive study classifies the charging topologies depending upon the power and charging level. Some appropriate battery charging converter topologies that are suitable for domestic, industrial, and commercial applications like EVs are suggested in the study. In addition, a decision-making inference is developed through a flow chart that decides on the suitable selection of the converter topology based on the required applications. Furthermore, the charging infrastructures along with the converters' design standards are also discussed concisely, which adds a significant contribution to the review article. 1 INTRODUCTION Among various other factors, steady degradation of the ecological system is due to the high emission of toxic gasses from gasoline engines, which are commercially deployed in automobiles as one of their applications. The applications of energy sources like gasoline are rising drastically, which could plummet to half of its current volume in the next 10–14 years [1]. Apart from industrial and domestic applications, automotive vehicles are the most prominent entities of carbon emission [1, 2]. Due to the proliferation in battery technologies and the development of efficient battery chargers, EVs have asserted themselves as the alternate transport medium. If EVs are widely deployed, then they can completely halt carbon (CO2) emission at the operating site [2]. Now, automobile industries have gradually adapted the EV technology for transportation. The battery-operated vehicles, based on their application, have been categorised as Electric Vehicles (EVs), Hybrid EVs (HEVs), and Plug-in Hybrid Vehicles (PHEVs). HEVs are the bridge between gasoline and fully EVs and have a provision of more than one energy sources as a fuel. The PHEVs are the HEV that have the facility to recharge the battery pack by plugging in the charging cable. PHEV is advantageous since a heavy battery pack is not required for recharging. Most of the EVs, now, have the facility of charging cable, and thus, fall into the category of PHEV [3]. With the burgeoning renewable energy applications and charging infrastructures, the demand for EVs is escalating. However, in the present existing infrastructure, the application of EVs is limited since they can be charged only at off-working hours. Therefore, the development of new and advanced fast charging infrastructure has led to the opportunity of charging schemes, paving the way for multi-enhanced applications of EVs [4, 5]. Power electronic converters are the operational and control unit of EVs. Applications of such devices are immense due to their high efficiency, more power capacity, low cost, lightweight etc. The most prominent challenges for wide application are the battery charging method and available infrastructure [6]. Various charging schemes are proposed in [4, 7-9] for various battery-driven vehicles. Currently, the automobile industries are manufacturing the charger with specifications depending upon the charging infrastructure standards available locally. Limited adoption and a gradual expansion are the contrary trade-off for the proper deployment of the technology. PHEVs are, therefore, preferred because of their fuel flexibility and are popular for industrial and commercial applications. Battery charging infrastructure, methodology, and the energy/power density of the battery pack are the most prominent challenges for the application of EVs [4, 5, 10]. Once the infrastructure of battery charging is developed fully, EVs can take over the market. The growing demand and parallel deployment of EVs are, currently, posing a major challenge to the grid power quality. The vast deployment of EVs will invite tremendous harmonics distortion to the utility. Power factor correction (PFC) circuits along with active rectification, therefore, are used to minimise the harmonic distortion, thus improving the efficiency [9-11]. The proposed study intends to summarise existing battery charging topologies, infrastructure, and standards suitable for EVs. The proposed work classifies battery-charging topologies based on the power and charging stages. A decision-making flowchart further aids in selecting suitable battery chargers for desired applications. The flow of the proposed study is as follows: Section 2 deals with the EV power components, Section 3 illustrates battery charging schemes. Section 4 illustrates modulation and control strategies while section 5 emphasises the choice of battery charging topology with the help of a flow chart. Section 6 discusses the available charging infrastructures and battery charging standards, respectively. 2 ELECTRIC VEHICLE COMPONENTS A typical block diagram of the EV is shown in Figure 1. Each block is designed for specification and topology suitable for its required applications. The existing battery charging topologies are listed subsequently in Table 1. FIGURE 1Open in figure viewerPowerPoint Block diagram of a typical electric vehicle TABLE 1. Various AC-DC and DC-DC converter topologies Topology/no. of switches Stage Phase Switching frequency Modulation Isolation Drawbacks Remarks Six switches [12-15], two-level full-bridge [16] Single-stage DAB [14], Two HB-LC resonant [12], two-stage FB BB [13, 16], single-stage BDHB with active shunt filter [15] Single-phase [12-15] Low ( 50 kHz) [12, 15] New modulations technique [14]. PWM [16], Phase shift control for ZVS [12, 15], bipolar [13] Galvanic isolation [12-15] non-isolated [16] Comparatively large transformer is required at lower operating frequency [12, 15], DQ-frame controller has slow response [16] Snubber circuit is not required, lightweight, soft-switching range extends due to new modulation technique, linear power relationship [14]. Two additional LC resonant circuits are used to provide optimal performance [12]. Provide reactive power to utility, five operation modes [13]; omit output ripple capacitor [15], on-board charging, for high power application, DQ-frame controller provides zero steady-state error [16] Eight switches [17-19] Single-stage DAB [19], Two stage [17], half-bridge [18] Three [19], single [17, 18] Medium [19], low [17] high (>50 kHz) [18] SVM [19], PWM [17], soft switching for all devices [18] Galvanic isolation [17-19] Large transformer requirement at lower frequency [19] Reduction in size, weight, and high-power density due to a high-frequency transformer, low harmonic distortion [18, 19], PFC with fewer switches, low switching losses [17] Twelve switches [20] DAB [11, 21-24]; DAB with dual function circuit [25], matrix converter [26] Single stage [11, 20, 24, 26], Two stage [21-23, 25] Single [11, 20-22, 24, 25], three phase [23] Low [25], Medium [20, 23, 27], High (>50 kHz) [11, 24], very high [22] (500 kHz) [21] Carrier based [20], PSM [11, 21, 23, 25], SVM [26], PWM [22], SHBM [24] Medium frequency transformer [20], high frequency transformer [11, 21-25], non-isolation [26] Snubber circuit [20], additional drive circuit for four-quadrant switch operation [11]. Efficiency at higher frequency decreases [23] Better switching condition at carrier-based modulation [20]. Minimal power conversion stage, high switching frequency operation and low switching losses, reduced size [11], wide bandgap switches are used [21], elimination of transformer and DC link capacitor [26]; SiC switches are used [22]; ZCZVS, open-loop PFC [24]; reduction of DC link capacitor, dual LV charging circuit removes power ripple at DC link [25] Sixteen switches [11, 28] Single stage [28], Two-stage [11] Three [28] single phase [11] Medium [28], High [11] Carrier based [28], PWM [11] Transformer isolation [11, 28] Snubber circuit, low load operation [28], limited ZVS range [11] Beneficial switching conditions can achieve using carrier-based modulation. [28], unity PF, fast charger [11] Nine switches with propulsion motor [29] Two-stage [29] Three-phase [29] Low (<25 kHz) [29] PSM [29] Transformer isolation is not required Limited for domestic applications Motor (windings) is used as the inductor for DC converter [29] Three-level PFC, buck boost, 10 SW [17] Quasi two-stage [17] Single-phase [17] Low ( 100 kHz) [34] low (10 kHz) [35] PSM [34], FBM [35] Isolation is not required [34], 3 transformer isolation [35] Primary switching loss increases as output power increases [34], bulky, expensive [35] Less conduction losses, high power application, less output inductor size, easy to increase power handling capacity [34], high power application, current frequency 60 kHz [35] Abbreviations: BDHB, bi-directional half bridge; DAB, dual active bridge; FB, full bridge; FBM, full bridge modulation; HB, half-bridge; PFC, power factor correction; PSM, phase-shift modulation; PWM, pulse width modulation; SHBM, single half-bridge modulation; SOC, state-of-charge; SVM, space vector modulation; ZCS, zero current switching; ZVS, zero voltage switching. The block ‘Grid’ represents an external power source (single phase or three phase) used to power up/charge the battery. The ac-dc converter is single phase or three phase based on the application (on-board or off-board). In addition, the converters can be bidirectional if the application is meant for vehicle-to-grid (V2G). Grid interconnected bidirectional ac-dc converters suffer from issues such as frequency synchronisation (with grid), PFC, and high-quality isolation, thus compromising with the cost and weight [8, 11, 36, 37]. The battery pack consists of batteries and ultracapacitors (UCs). A battery pack may comprise lead-acid, nickel metal hydride (NiMH), or lithium-ion (Li-ion) batteries. In modern battery-powered vehicles (BPVs), li-ion batteries are used for their high energy density, superior specific energy, less discharge rate, compact size, and low maintenance requirements [38]. The dc-ac converter drives the traction motors connected at the load side of the battery pack. Initially, the motor used to be unidirectional, but in modern BPVs, bidirectional dc-ac converters are used for regenerative braking technology. The dc-dc converters are used to drive the dc loads. The PHEVs have the flexibility of fuels that has been shown with the ‘Gasoline Engine’ block in Figure 1 as an alternative fuel source [39, 40]. In modern EVs, ac-dc converters are used for battery charging applications but, as discussed, in many cases dc-dc converters also play a significant role in EVs [27] either for dc loads or in the second stage of the ac-dc converters. Thus, the selection of the optimum design is equally crucial [31, 41, 42]. Apart from efficient converter charging schemes, the literature reports that the battery chemistry (responsible for charging and discharging rates) is an important aspect. In [2, 38, 43] available batteries associated with chemistry, classification, material, effects of charging speed etc. are thoroughly discussed. Further, it elaborates the suitable battery choice based on application. A battery pack consists of a suitable battery and UC. Without the UC, an intense decrease in battery state-of-charge is observed, which decreases the life cycle of the battery. A battery (large energy capacity, low power density) has more time constant, slow response than UC (low energy capacity, high power density); therefore, batteries cannot provide instant energy to the load as compared to UC during acceleration. For achieving fast response, a parallel configuration of batteries is used, but this arrangement increases the size and weight. Therefore, UCs are used in the battery pack for the initial torque provided by the traction motor. They are also used during regenerative braking and reduce the size as well [33]. When compared to the battery, a capacitor has large charging and discharging cycles. During the run time of EVs with regenerative braking, several charging and discharging cycles occurs. The repetition of the acceleration and deceleration phenomenon decreases the life cycle of the batteries. Therefore, series and parallel combinations of batteries parallel with UCs are used to achieve the desired energy and power densities, respectively, to enhance the performance and life of a battery pack [33, 40]. High power density/energy motors are preferably used in EVs; however, the traction mechanism generates the difference between the EVs and the IC engine vehicles, respectively. Advancement in power electronics control has provided an opportunity for different electric motors to find their application in EVs and HEVs. The desired characteristics from a motor for automotive application are high power, high starting torque, high efficiency, wide speed range, fast dynamic response, compact size, low noise, easy to control, high performance, low cost etc. [44, 45]. There are various types of motors available for automotive application such as dc motor, ac inductor motor, brushless dc motor (BLDC), permanent magnet synchronous motor (PMSM), and switched reluctance motor. The PMSM and BLDC motors are widely being deployed over induction motors in commercial and domestic EV applications [46, 47]. Distinct motors have their advantages and limitations, some of them are mentioned below. DC motors were widely used in an early stage of EV application. Their high starting torque and dynamic response with easy control (speed) techniques make them suitable for automotive applications. They have certain disadvantages such as high maintenance and high noise because of the brushes and commutators [48]. Induction motors are ac-operated motors and for fixed voltage and frequency provide a limitation on starting torque. Thus, the variable voltage and frequency control technique is used for their optimum performance. Although induction motors are widely used and require low maintenance, their control (consists of an inverter) schemes are complex compared to dc motors [45]. The BLDC motors are a special type of PMSMs without commutator and brushes. The commutation is done using inverters. Because of electronics commutation, these motors are compact, noiseless (less vibration) and require less maintenance. BLDC motors are preferred for low-power automotive applications [45, 48]. The PMSMs are very high performance motors and available for high power applications. These motors are best suited for high-power and high-performance vehicle applications. Similar to BLDC, they also consist of permanent magnets in the rotor of the machine. A sinusoidal back electromotive force (EMF) is a distinct characteristic of PMSM compared to BLDC where back EMF has a trapezoidal characteristic. PMSMs are the most preferable motor for automotive applications like EVs [49]. The proposed study focusses on the comparison of distinct converter topologies employed for effective battery charging applications. A critical comparative analysis has been carried out in successive sections. Some of the converters have been compared and tabulated in Table 1. The table shows the prominent battery charging topologies that can be adapted to achieve an optimal system based on desired applications. 3 BATTERY CHARGING SCHEMES IN EVs Battery-driven vehicles' powertrain mainly consists of power sources, power converters, and loads. Power converters are the intermediate controllable unit between energy sources and loads and are, therefore, enormously vital in BPVs for efficient charging and discharging. Nowadays, power converters are expected to perform way more than power conversion from a battery to loads only [50]. In advanced drive topology, they also feed the power back to the grid efficiently. To achieve these functions, switching devices such as metal oxide semiconductor field effect transistor (MOSFETs) and insulated gate bipolar transistor (IGBTs) are used with the help of a suitable control mechanism. MOSFETs are operated at a very high frequency (up to a few MHz), whereas IGBTs are feasible for a few kHz but can withstand at very high current (power). High-frequency operation and control assist the converters to possess smaller inductive and capacitive components. Therefore, the size of the converters decreases with increasing operating frequency. With this dynamic change, the power electronic converters became of interest in the field of battery-driven vehicles [51, 52]. As discussed, EVs can consist of different power converters; therefore, suitable design topologies are available based on the application. Power converters are categorised as high and low power application converters (for EVs). High power converters are used to drive traction motors and battery charging [53], whereas low power converters are used for loads such as cooling fans, lights, electronic gadgets etc. The dc-dc converters are used for both applications; thus, MOSFETs or IGBTs are used based on power rating. Similarly, high power ac-dc converters are used as battery chargers [33, 50]. Diode bridge rectifiers (single or three-phase) are widely used for ac-dc power conversion. These uncontrolled rectifiers inject large harmonics into the grid. A high peaky current (to fulfil the average dc) is observed at the rectifier side while extracting a high current from the grid. Some disadvantages such as non-sinusoidal input current (harmonic distortion), output voltage harmonics, and poor input power factor (because of the non-sinusoidal input current drawn from the grid) have been reported [7]. To overcome grid harmonic distortion issues, an electrical network such as an active rectifier, a current filter, a PFC circuit, a resonant converter topology, and a capacitive filter is used. The current filter or ac filters comprise the inductor (L), capacitor (C), LC or LCL. The objective of these filters is to limit the supply current response in its grid-supplied shape while injecting the high-density dc into the battery or next stage [36]. At low power and high operating frequencies, the capacitor input filter can also serve this purpose. The capacitor provides its charge at the switching instant [17, 54, 55]. The rectified power (ac-dc) is fed to another converter, which regulates the voltage level. The conversion of power through two converters is stated as two-stage power conversion and the converters are called two-stage converters. In this way, the conventional rectifier can be termed as a single-stage power converter. It has been reported that two-stage power converters are more feasible for high-power applications. Also, they provide low output ripple [29, 39]. Thus, they are used for high-density battery charging applications. At the final stage, depending on the type of traction motor, dc-ac or dc-dc converters are used to power up the motor. Harmonic distortion imposed on the grid by the battery charger is one of the significant challenges of the application. Heat dissipation from the bridge rectifiers decreases its efficiency, whereas heatsinks increase the converter size and cost. In modern battery chargers, PFC circuits are integrated with the converter for distortion minimisation. The active rectification with zero voltage switching (ZVS)/ZVS technique is used to limit the power dissipation, thereby reducing the converter size [6, 30]. A high operating frequency also decreases the converter size (inductor and capacity), whereas at a higher frequency the converter suffers from electromagnetic (EM) emission. A high rate of change of voltage and current introduces the EM field through the converter layout. The interference of the EM field to the gate drive results in the distortion in switching. The distorted switching scheme introduces additional harmonics into the supply. Electromagnetic interference (EMI) issues are introduced more by high-frequency fast charging as compared to low or moderate charging respectively. The high switching level converter requires a faster transition to avoid high switching losses, consequently, introduces large EM disturbances. For reduction of harmonics, a large EM filter is required [56]. A suitable EMI filter further increases the size of the converter. A large EMI filter is a bottleneck for high power switching converters. The EMI suppression standards are listed in Table 2. TABLE 2. Standards for converter design [57, 58] Operations Standards IEC SAE Charging plugs, socket, and connectors, conductive charging/levels/modes IEC 62196 SAE J1772 Communication for PHEVs IEC61851 J2931/1 Wireless power transfer communication IEC 61980 SAE J2954 DC charging communication IEC61851-24 SAE J2847/2 Charger efficiency and power quality IEC61851 SAE J2894 Communication security IEC 15118 J2931/7 Electromagnetic interference suppression IEC 60940 SAE J2954 Harmonic injection IEC1000-3 SAE-J2894 Interconnection of utility grid with distributed power sources (EVs) IEEE 1547 [59], UL 62109 [10] (IEC does not have) SAE J2954 (unidirectional power flow G2V), J2931/5 (communication) Abbreviations: IEC, International Electrotechnical Council; PHEVs, Plug-in Hybrid Electric Vehicle; SAE, Society of Automotive Engineers; UL, Underwriters' Laboratories. 3.1 DC-DC converter The following subsection explains the application of dc-dc converters in EVs. Usually, dc-dc converters are used to drive dc loads as illustrated in Figure 1. They are also used in the second stage of ac-dc power conversion. In conventional BPVs, they are used to drive traction motors. Gradually, bidirectional dc-dc converters took place to feed the power to the battery (regenerative braking mode). The literature reports that in modern EVs, ac-dc and dc-ac converters are used for the battery charging and traction motor. Thus, the application of dc-dc converters is limited to dc loads and for the second stage of ac-dc converters only. In some cases, dc-dc converters are also used for charging the battery directly from the dc grids [18, 43, 60, 61]. The two widely used isolated dc-dc converters, apart from the conventional non-isolated dc-dc converter, for battery charging applications are illustrated in Figure 2. The galvanic isolation increases the safety margins in high-power operations as shown in Figure 2. Figure 2a shows a full-bridge isolated converter and Figure 2b shows a two-level isolated dc-dc converter. As the number of levels increases, the output current injection capability increases since multiple legs contribute to the total current. The multilevel converter with a certain phase shift in the individual response contributes to the output ripple minimisation. Thus, it can provide better ripple rejection at a lower operating frequency. Therefore, a small ripple rejection filter is required in the integrated system. The converter's leg operated at a lower switching frequency can minimise EMI issues [56] since current sharing reduces the magnetic flux. Although multilevel converters can handle high power, with a small ripple filter, they are recommended for low power applications only. At high power, they start injecting the harmonics into the grid. A three-phase multilevel converter is recommended for high-power fast battery charging applications [50]. As the level increases, the converter's complexity and cost increase. Therefore, it is preferred for off-board charging applications. FIGURE 2Open in figure viewerPowerPoint DC-DC converter topologies, applicable for battery charging in PHEVs. (a) Bidirectional full-bridge (FB) DC-DC boost converter. (b) High power FB interleaved boost converter In [33], the author proposes a highly dense (interleaved) dc-dc boost converter for ultra-fast charging. In [62], different topologies of buck, boost, and buck-boost converters are presented. In this work, single-pole-triple through switches have been used instead of single-pole-double through switches. They are advantageous in reducing the number of inductive components. In this topology, one inductor is used; therefore, the size and weight of the converter reduce. Cao and Ye [63] propose that the switched capacitor (SC)-based MOSFET is more efficient since it replaces IGBTs with SC MOSFET (high-frequency application). The hardware prototype has also been explained for agreement of the statements. It is found that SC MOSFETs-based converters are more efficient for low voltage loads, whereas the boost converter is used for high voltage loads. A few of the other dc-dc converters are listed in the comparison Table 1. 3.2 AC-DC converter This subsection discusses the ac-dc converter topologies in detail. Figure 1 shows that the battery pack is connected to the grid through the ac-dc converter. Parameters such as charging time, quality, harmonic distortion at the input etc. depend on the ac-dc converters [4, 12, 64]. In [9, 41, 43], the importance of the above parameters is extended along with power density, reliability, efficiency, low cost, weight, and volume of converters for EVs application. Similarly, [5, 65] discuss the economics of rapid charging of the battery in EVs and elaborate the market modelling for ac-dc converter topologies in detail. They highlight that a suitable converter topology with an effective design is critical in achieving its application in PHEVs. Single-stage converters are lightweight and low cost and are, therefore, preferred as onboard charging. The different single and two-stage ac-dc converters topologies are ex