Power factor corrected level‐1 DC public green‐charging infrastructure to promote e‐mobility in India
2019; Institution of Engineering and Technology; Volume: 13; Issue: 2 Linguagem: Inglês
10.1049/iet-pel.2019.0009
ISSN1755-4543
AutoresVisal Raveendran, Manjula G. Nair,
Tópico(s)Advanced battery technologies research
ResumoIET Power ElectronicsVolume 13, Issue 2 p. 221-232 Research ArticleFree Access Power factor corrected level-1 DC public green-charging infrastructure to promote e-mobility in India Visal Raveendran, Corresponding Author visalraveendran@gmail.com orcid.org/0000-0003-4670-1681 Department of Electrical and Electronics Engineering, Amrita Vishwa Vidyapeetham Amritapuri, IndiaSearch for more papers by this authorManjula G. Nair, orcid.org/0000-0003-4636-0821 Department of Electrical and Electronics Engineering, Amrita Vishwa Vidyapeetham Amritapuri, IndiaSearch for more papers by this author Visal Raveendran, Corresponding Author visalraveendran@gmail.com orcid.org/0000-0003-4670-1681 Department of Electrical and Electronics Engineering, Amrita Vishwa Vidyapeetham Amritapuri, IndiaSearch for more papers by this authorManjula G. Nair, orcid.org/0000-0003-4636-0821 Department of Electrical and Electronics Engineering, Amrita Vishwa Vidyapeetham Amritapuri, IndiaSearch for more papers by this author First published: 03 January 2020 https://doi.org/10.1049/iet-pel.2019.0009Citations: 1AboutSectionsPDF 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 onEmailFacebookTwitterLinked InRedditWechat Abstract With the growing popularity of electrified transportation across the world, there have been extensive reports of research involving plug-in electric vehicles (PEVs), electric vehicle charging facilities (EVCFs) and their integration to the main electric grid, besides sustainable energy resources for powering these vehicles. This study proffers a power factor corrected level-1 DC public green-charging infrastructure accompanied by an integrated control, for electric light motor vehicles, compliant with recently formulated Indian charging standards. Power factor correction of plug-in electric vehicle charging current, solar photo-voltaic grid integration and charging of energy storage system is achieved using control of bidirectional AC/DC converters. A firmware and user interface for multimode off-board DC charging, with green, fast and semi-fast charging modes are investigated. Intelligent control for fast charging is also presented to reduce its pernicious impact on the grid. The simulation and hardware results verify the prime performance objectives of improving the local power quality and renewable energy utilisation with multimode charging, in the Indian context. The effectiveness of the proposed infrastructure is further demonstrated by a simulated use case, where 30 PEVs are randomly charged, in various modes, at this EVCF during busy commute hours. 1 Introduction Newly industrialised countries have a hard time trying to adopt e-mobility in their transport sector. All modes of mechanised transport depend heavily on non-renewable fossil fuels for powering the internal combustion-engine vehicles (ICVs) or pollutant coal for steam engines, which are major contributors to air pollution and greenhouse gas emissions. At the current rate of exploitation of fossil fuels and untenable environmental pollution, the future of humanity is at risk. However, a shift to electric mobility, however, does not ensure full independence from fossil fuels as the latter assumes a major role in the generation of electricity. The former merely offsets the points of emission on a geographical location. Two main issues with electrified transportation impact the mains electrical power distribution system, spurred by concurrent charging of hundreds of unpredictable plug-in electric vehicles (PEVs), and the quality of power associated with the electronic-chargers, to power-up the PEVs. Dubey and Santoso [1] investigated PEV charging impacts on the residential distribution network and discussed the associated power quality issues. The study by Zaidi et al. [2] has shown that higher power levels for PEV charging in the distribution network demand FACTS devices for power quality improvement. Reactive power support using renewable energy (RE) integration grid tie inverter is also proposed by Zaidi et al. [2]. Several topologies for power factor correction (PFC) and RE integration are proposed in the literature [1, 3-5], which are discussed in detail in Section 2. For electric vehicle charging facilities (EVCFs) to be designated a green facility, and e-mobility to be classified as a low-emission transport medium, RE sources associated with a reliable backup energy storage system (ESS) need to be integrated with the EVCF [6, 7]. Following that note, incorporation of power factor corrective measures [8, 9] and maximum utilisation of RE for the generation of electricity to mobilise urban transport [10] are unavoidable. In addition, a well-planned, cost-effective and standardised charging infrastructure will galvanise the commercial sector to switch over to PEVs, for their prime needs of passenger and goods transport. 1.1 Paper organisation The primary objective of this study is to develop an integrated controller for bidirectional power flow, PFC and multimode operation of a solar powered EVCF. For this, a detailed literature review is presented in Section 2. Based on the findings, an integrated controller for EVCF compliant with Indian standards is proposed in Section 3. The bidirectional power flow and harmonic elimination are realised using a shunt active filter (SAF) controller algorithm (Section 3.2). Its controller is tested in simulation and hardware (Section 4.1). The multimode charging, with three modes, green, fast, and semi-fast, is proposed in Section 3.3 and realised in hardware in Section 4.2. Within the multimode charging, an intelligent fast charging control is also proposed to minimise grid overloading issues in Section 3.4 and tested in simulations in Section 4.2.3. Finally, a simulation case study with 30 PEVs charging in the proposed EVCF is conducted in Section 4.3 to study a possible load profile of the EVCF. 2 State-of-the-art This section presents the issues, latest research, and standards, both global and in the Indian context in the area of PEV charging infrastructure and its grid integration. 2.1 Power quality issues due to charging equipment In linear circuits, as voltage and currents are sinusoidal, the power quality issue arises from the displacement power factor. In non-linear circuits, with non-sinusoidal currents, power quality issues arise from both displacement and distortion power factor [11]. Loads that draw non-sinusoidal current from the sinusoidal voltage source cause harmonics. Battery chargers, typically, are equipped with rectifiers at the input stage that cause current harmonics in the distribution system [12, 13]. Generally, lower priced models of chargers do not handle this requirement effectively. Saber et al. [14] propose a PFC scheme based on unidirectional, current-source active rectifier for charging PEVs. An on-board PFC scheme was also discussed in [15], in which the converters in the PEV are controlled to refine the power quality. However, this increases the complexity and weight of the on-board charger. 2.2 Need for public green charging infrastructure in India Electric vehicle supply equipment (EVSE), owned for private use, is categorised as 'private' and open to the public at large, is termed 'public' or 'commercial'. Currently, in India, nearly 80% of charging PEVs occurs at home. Repercussions of charging PEVs at home include the following: Individuals may not necessarily own commercial PEVs and commercial PEVs may constitute fleet of vehicles parked at warehouses. EVSE needs to be installed in a garage, concomitant with costly wiring upgrades and modifications. Without the recommended wiring modifications, draining 2–3 kW of electrical power, over durations of up to 10 h, may be fire hazardous or cause significant damage to the original wiring. The cost of installation and maintenance of the EVSE has to be borne by the home owner. Charging from solar photo-voltaic (PV) cells is not a viable option during workdays, as the PEV may not be parked at home during normal business hours. Storing energy in ESS at home is not economically viable. High-end home charging appliances are built-in with smart charging features [16] whereby charging can be accomplished in an interactive mode. An intelligent module within the charging equipment communicates with the main power grid, to charge the PEV during off-peak hours. This practice is referred to as valley filling. Other than the high initial cost, the inherent downside with the valley filling approach is that with a high penetration of PEVs, numerous vehicles may initiate charging in a residential area, at the start of the off-peak hour. This would entail sudden spikes in power demand, ensuing in overloading of distribution transformers, affecting the quality of power. This underscores the inevitability of integrating charge-management strategies with the charging equipment. The authors of [17, 18] addressed the impact of PEV charging loads on the power-distribution grid, from the aspects of technical operation and utility market environment. Abousleiman and Scholer [19] implement a smart charging feature in Chrysler's PEV RAM vehicle. Scheduling and planning of charging strategies are heavily influenced by local demographics. In regions with wind power dominant grid mix (per cent share of a particular resource in the grid [20]), the energy will be excess during night hours. In these areas, home charging will be beneficial. In regions with PV power dominant grid mix, charging during morning hours needs to be promoted. The grid mix may vary within the country [21]. A PV dominant grid mix was assumed for the analysis conducted in this research. The carbon dioxide (CO2) emissions of PEVs, for a particular grid mix in the Northern states of India, were compared with cars run on petrol (gasoline), which emit CO2 about 2.33 kg per litre. In Table 1, the term km/l (eq) is the equivalent mileage of PEV compared to the (11–12) km/l for petrol cars in urban areas. Based on [22, 23], Table 1 compares the greenhouse gas emissions of PEVs with petrol engines. Data shows that PEVs charged from electricity generated from coal, instead of reducing air pollution, may worsen it. PEVs charged from renewable sources significantly reduce CO2 emissions. Northern parts of India have a carbon intensive grid-mix, with a share of about 43% coal in electricity generation. Thus, in India, electrified transportation together with renewable intensive grid-mix is the right solution to develop sustainable futuristic cities. Table 1. PEV emissions in India-Northern region, according to the type of electricity source Electricity source km/l (eq) CO2 emission, kg Grid mix (India – northern region) (%) thermal (coal) 13 1.941 43 hydro 2466 0.01 14 solar 213 0.116 17 wind 1658 0.014 25 2.3 Standardising the PEV charging infrastructure PEVs can be charged either by means of conductive charging or through inductive means [24]. Globally accepted, standards for PEV charging are published by the International Electrotechnical Commission (IEC) [25, 26] and Society of Automotive Engineers (SAE) [27]. EVCF can be integrated into the mains grid in a number of ways. Topologies for the integration of DC fast charging stations to microgrids have been discussed in [28]. 2.3.1 Global standards The standards pertinent to PEV charging are further subdivided into standards for communication interface, connectors, charging process, vehicles, supply stations, and communication between all the entities involved in the charging process. Charging infrastructure standards: IEC differentiates charging as 'types' and 'modes' whereas SAE refers to them as 'levels'. This study considers conductive charging which is currently popular, in which charging levels are classified as mode 1, mode 2, mode 3 etc. according to IEC 62196 and AC level 1, AC level 2 and DC fast charging according to SAE J1772 [28, 29]. IEC 61851 and SAE J2293 define the energy transfer system requirements for charging PEVs. In [30], a comparison among the charger topologies, power levels and infrastructure for PEV charging were discussed. In the global scenario, PEV industry has not agreed to follow a common standard for charging and connectors. Charging process standards: The charging process is coordinated by a well-defined communication standard that defines the interaction between various entities involved in the charging process. These standards establish norms for communication between EVCFs, between EVCF and grid operator, between EVCF controller and EVSEs within a facility, between EVSE and PEV and between PEV and grid operator [26, 27]. The standards for digital communication are stipulated in ISO 15118 and DIN SPEC 70121 [31]. A typical communication and energy transfer interface between a PEV and an EVSE is shown in Fig. 1. It has a digital and analogue communication interface for communication between the charging control units in EVSE and PEV, and a power interface for charging the PEV battery. The EVCF station controller communicates with such several EVSEs within the EVCF and supervises the charging process. A typical EVSE is furnished with user interface (UI) options such as selecting the PEV model, charging mode, PEV authentication via radio-frequency identification or smart cards, payment options such as debit cards or contract billing etc. To control the PEV charging process and billing services, a communication and data exchange protocol between the entities involved is unavoidable. In retail markets, stakeholders, with different roles, intervene in the billing process. The European Commission's Grid 4 Vehicles (G4V) project [32] studied the agent-based communication model for PEV charging in detail, in which, the stakeholders involved in PEV charging are clearing house, distribution system operator, metering service provider, retailer, information and communications technology gateway operator and the customer [33]. This model can be implemented in India, at a later stage, on complete deregulation of the Indian electricity market and activation of the smart grid paradigm. Power quality standards: IEC 61000 standard recommends modern charging equipment to include a PFC stage in their design, to minimise the harmonic issues [34]. The electromagnetic compatibility (EMC) requirements for PEV chargers include limits of distortion power factor, i.e. harmonic current injected into the AC system by electrical and electronic equipment, defined by IEC 61000-3-2, IEC 61000-3-3, and IEC 61000-3-12 depending on the power levels of the equipment [34]. The IEEE standard 519–2014 also defines limits for harmonic currents and voltages in power system [35]. The total harmonic distortion (THD) and total demand distortion (TDD) in current waveform per the standard [35] is given by (1)where n is the harmonic order and is the current component of order n. Of these, TDD is more accurate in determining the current harmonics and generally accepted for measurement of the EMC levels. Fig. 1Open in figure viewerPowerPoint EV–EVSE communication interface 2.3.2 Indian standards The standardisation of PEV charging by governments of Europe and the USA plays a beneficial, constructive role in the faster adoption of PEVs in India. However, non-compliant (standard) PEVs and EVCFs will set back the adoption of e-mobility in India. The PEV industry in India is still in a nascent stage, with very few electric vehicle (EV) brands, and limited paucity of charging infrastructure. Some of the key players serving the urban transportation market for people and merchandise are light motor vehicles (LMVs) [36]. Pure electric variants of LMVs or electric-LMVs (e-LMVs), in urban areas, will greatly improve the local air quality. During the early stages of electrified transportation, India's prevailing power grid is incapable to comply with the charging power-level requirements of globally leading PEVs. Besides, the Indian electric utility is not fully deregulated, and per the current trends, the retail purchase option for charging PEVs is not popular. A well-defined tariff scheme exclusively for PEV charging is still under development, and the billing is constrained by the conventional structure. A tariff for slow charging PEVs, from BSES Rajadhani Power Ltd. Utility in Delhi for slow charging can be referred from [37]. As a step towards promoting environmentally clean transport, the Indian Government has propounded the Bharat EV Charger specifications for standardisation of protocols, charging infrastructure, and regulation of EVCFs in charging networks [38]. This draft standard, prepared by Automotive Research Association of India, includes the specifications for AC and DC charging, charger classifications, charging power levels, communication requirements between PEV and EVSE via Controller Area Network (CAN) protocol, between PEV-Central Server via Open Charge Point Protocol (OCPP) [39] and between PEV-Central Management System via Internet, billing methods, connector specifications, cable specifications, and safety requirements related to PEV charging. The charging power levels are exhibited in Table 2. Level-1 DC is suitable for two-wheelers, three-wheelers and small to medium four-wheelers. Medium to high-end four-wheelers can be charged at level-2 DC, which has higher voltage and power levels. Level-2 DC may require special EVCFs and is beyond the scope of this study. Indian Government has promoted several plans for acceptance of PEVs through India Smart grid forum [40]. A number of new policies have been drafted and approved by individual states as well as the central Indian Government to promote electrified transportation in India [41, 42]. Some recommendations in [40] include the time of use (TOU) electricity tariff for PEVs, at home and public charging, all payment options for PEV charging, multiple ownership options such as power supplier model, franchisee model, and LEASE model, incentives for PEV owners. The power quality standards followed in India are the same as the International Standards discussed in Section 2.3.1. Table 2. DC public charging levels as per Bharat standard [38] Level Vehicle Power, kW Voltage, V Typical location level 1 DC 2 W, 3 W, small 4 W 10 48 railway, metro, malls, markets, workplaces, institutions level 1 DC small–medium 4 W 15 72 railway, metro, malls, workplaces, hospitals, institutions level 2 DC medium–high end 4 W 30 up to 750 highways, bus terminals, markets, industrial areas level 2 DC high end 4 W 150 up to 1000 highways, bus terminals, markets, industrial areas 2.4 Related work The power quality improvement techniques employed for PEV charging can be divided into two categories: (a) using different converter topologies for the off-board EVSE or on-board PEV charger, (b) separate filtering equipment to filter out the harmonics entering the distribution system. To address (a), a PFC based on interleaved boost converters for PEV on-board charger is discussed in [1]. The advantage of interleaving is that they significantly enhance current quality and can also handle higher power levels using parallel configuration. However, the disadvantages include complex control, coordination and synchronous operation of multiple parallel units, non-compatibility with variable frequency control techniques etc. Housing the bulky converters for high power charging is also a concern. To address (b), several passive, active, and hybrid filter configurations are proposed in the literature. Among this, SAF is the most widely accepted one as they do not have a limitation of passive filters such as resonance, current limiting inability, bulkiness or tuning issues. Since SAF is employed in high-voltage (HV) power systems, it can easily handle an EVCF. The quality of SAF action depends primarily on the reference current generation technique employed. Kumar and Bansal [3] reported a detailed review on time domain, frequency domain, and soft computing methods for reference current generation of SAF. All of them have their advantages and disadvantages. This work particularly focuses on time domain methods as frequency domain methods require constant signal window and soft computing methods require large training data. A SAF using a low voltage (LV) battery charger aux power module to filter the harmonics in HV single phase on-board PEV charger is proposed in [5]. The idea is interesting and results are promising, however, higher power ratings demand three-phase off-board chargers. Moreover, LV circuits in the PEV are not capable of handling high harmonic ripple energy. Tarisciotti et al. [4] proposed a model predictive control of SAF, but only unidirectional 'Q' transfer is achieved. Dey and Mekhilef [43] proposed a modification to one of the most popular D–Q-axis/synchronous reference frame theory for SAF reference current generation. However, the presence of several proportional–integral (PI) controllers in the control loop makes it difficult to handle the dynamic variation in harmonic currents in the system. The performance of hybrid SAF controller is evaluated in [44] by implementing separate control loops to filter different harmonic components. The controller is effective in eliminating the harmonics but the response is slow, about 168 ms, due to the multiple PI controllers. In addition, bidirectional operation is not discussed. Another contribution in this area is by Biricik and Komurcugil [45] using the three-phase three level 4-switch topology and hysteresis current control technique. This has better response, lesser losses, and reduced system components. The drawback of this topology is the capacitor voltage fluctuation as it provides a path for unbalanced harmonic current flow for one of the phases. Moreover, the bidirectional operation is not possible. Zaidi et al. [2] discussed reactive power support using the RE integration grid tie inverter, but harmonic elimination is not achieved. Similarly, the controllers discussed above do not offer PV integration to grid along with the harmonic elimination and ESS charging capability in a single unit. 2.5 Main contributions To address these issues an integrated controller for bidirectional power flow, PFC and multimode operation of a solar powered EVCF are proposed in this study. The SAF control algorithm is capable of both harmonic elimination and bidirectional power flow control [8, 9]. The control algorithm has a good dynamic response and shows excellent performance in unbalanced loads and transient conditions. The controller supports PV grid integration, ESS charging and harmonic elimination through coordinated control. The model is suitable for off-board dc charging in three-phase systems. The control algorithm is simple to realise in hardware and can be implemented in both analogues, digital signal processor/field programmable gate array devices. The model is tailor-made for level-1 DC public green-charging infrastructure, suitable for e-LMVs from the L4 through L7 categories [36]. These include three-wheelers and four-wheelers with maximum continuous power drain <15 kW. City cars and light passenger cars with 'A' and 'B' classifications can also be charged at the proffered power levels. The proposed model can be scaled up, and used for fast charging at higher power levels as well. Simulation and software development of a power factor corrected charging system, with a comparison study among different modes of charging, are discussed in detail on a scaled down hardware prototype model. The specifications of the proposed EVCF infrastructure are compliant with the Bharat standard (draft) [38] for PEVs in India. To the extent of our knowledge, this is the first study to propose a power factor corrected and green EVCF with multimode charging, compliant with Indian standards. 3 Proposed level-1 DC charging infrastructure for public spaces 3.1 Proposed EVCF architecture A schematic diagram of the proposed commercial EVCF is shown in Fig. 2. The AC/DC bidirectional inverter and EVSEs are connected to a common point inside the EVCF [point of common coupling (PCC)]. The energy sources of EVCF include grid, solar PV, and ESS. PV and ESS are connected to the DC link of the AC/DC bidirectional converter through DC–DC converters. The AC/DC converter is connected to the grid through a filter inductor. The firing pulses for bidirectional converter are generated by PFC controller based on the net load current of PEVs, power availability from PV and ESS. The EVSEs are of level-1 DC type with input AC and output DC power (section 3.3). Three modes of DC off-board charging, green, fast, and semi-fast, are explored. These charging modes are explained in Section 3.3. EVCF system design ratings are mentioned in Section 4.2.1. Owing to the nascent stage of the Indian PEV market and unavailability of a smart grid environment, smart charging and scheduling controller features have not been adopted due to the economic and grid compatibility issues. The proposed solution in this work reduces dependence on the electrical grid, improves power quality and maximises utilisation of RE. An architecture depicting the interaction between various units within the EVCF, developed for this study, is shown in Fig. 3. The key sub-systems are PV-ESS AC/DC bidirectional converter, an EVSE, a station controller, and a PC-monitor. Fig. 2Open in figure viewerPowerPoint Block diagram of the proposed power factor corrected EVCF Fig. 3Open in figure viewerPowerPoint Interaction between various units within the EVCF 3.2 Controller design for bidirectional power flow control and PFC PEV charging can distort both current and voltage at the PCC, since harmonic current causes a harmonic voltage. One principal objective of this study is to eliminate harmonic currents drawn from the main grid. A bidirectional power-flow-control with distortion power-factor-correction (PFC action) is proposed here. The insulated-gate bipolar transistor (IGBT)-based three-phase converter, at the output of PV–ESS combination is dynamically controlled to operate in inverter mode or rectifier mode, along with the elimination of the current harmonics caused during the EV charging process. In inverter mode, the power from the PV–ESS combination is used for charging PEVs, and excess, to the grid. In rectifier mode, grid power is used to charge the ESS. The phasor diagram with rectifier and inverter modes of operation is shown in Fig. 4, where the V-trace and I-trace are in phase in the rectifier mode, and in the opposite phase for the inverter mode [46]. The twin objective of bidirectional power flow control and PFC was accomplished by an algorithm used for power quality conditioning devices, proposed by the authors of [8, 9]. The prime advantage of the selected algorithm is that a single controller is able to perform both the functions concurrently. According to this algorithm, for balanced conditions, the instantaneous grid voltage for the three phases can be represented as (2)The instantaneous load current for phase 'a' can be represented as (3)Similarly, and can be written, where are instantaneous grid voltages of three phases; are instantaneous load currents of three phases; are phase angles of fundamental currents in a, b, and c phases; are phase angles of the nth harmonic currents in a, b, and c phases; is grid voltage amplitude; are three-phase fundamental current amplitudes; are three-phase nth harmonic current amplitudes (4) (5)The unit amplitude voltage vector for phase 'a' (6)To ensure unity power factor on the grid side, the reference current for phase 'a' is given by (7)The switching current reference for the PV inverter will be (8)where is a factor derived by the supervisory controller, based on the maximum power pointing tracking the power of PV, state of charge (SoC) of ESS and current EV load. controls the bidirectional power exchange through the AC–DC converter [8]. The hysteresis control technique was used for the current control of the inverter. The control block diagram for the dynamic power control and PFC action is shown in Fig. 5. The sensed grid voltages, load currents, and AC/DC converter currents for three phases were sensed and fed to the converter controller. The PFC algorithm was realised in MATLAB simulations with the help of second-order low pass filter, sample and hold circuit, multipliers and a hysteresis current controller [8]. In Section 4.1, various operating modes of the AC–DC converter are compared, under test conditions T1–T5 by varying factors. Fig. 4Open in figure viewerPowerPoint Inverter and rectifier modes of operation with bidirectional converter Fig. 5Open in figure viewerPowerPoint Control block diagram for bidirectional AC–DC converter control with PFC action 3.3 EVSE design and multimode charging As per the current draft standards in India, level-1 DC peak power for charging of small four-wheelers has been specified at 15 kW. The specifications used in this study were derived based on this reference value. In the green charging mode, maximum priority is assigned for power from solar PV, whereas in the fast mode all charging powe
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