Impact of non-systematic plug-in behavior on EV grid integration studies 

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Technological Environment

EVs will integrate a rapidly changing environment as new technologies break through. The smart grid paradigm is changing the operation of distribution networks, opening up the possibility of synergies between EVs and other technologies. Core factors in the tech-nology environment can be classi ed into EV charging technologies, network technologies and ICTs. OEMs need to know the technical requirements regarding charging equipment and ICTs that have to be developed and deployed in future EVs to make them smart grid compliant.

EV charging technology

Charging technology and its deployment have a direct e ect on the impacts of EVs in power systems and in the exibility services that they can provide.
An AC/DC converter system is required to charge the battery, which can be im-plemented on-board (inside the EV) or o -board (in the charging point, EVSE). To implement advanced smart charging and V2G, a dedicated EVSE is required for control and protection functions (mode 3 for AC or mode 4 for DC charging, according to IEC 61851-1 standard [46]).
Charging technology characteristics and capabilities will a ect EV integration. EVs are large loads: a single-phase home charging station (3.7 to 7.4 kVA) is in the range of a typical household and can have signi cant impacts in LV grids. Increasing charging power (for example from 3.7 to 7.4 kVA) can create greater stress in the distribution grid [47], but it can also increase the exibility potential of EV eets. For example, moving from 3 kVA chargers to 7 or 11 kVA ones can increase the volume of power reserve for frequency response provision by EV eets [25][40]. There are other technical characteristics that can a ect the exibility potential of EVs, such as accuracy to control signals, response times and e ciency of the charging equipment. The e ciency of charging equipment is extremely important, as high energy losses during charging and discharging processes may hinder the economic viability of V2G-based exibility services [48]. Reference [48] characterized the e ciency of a V2G charger, which reached maximum one-way e cien-cies of 90%, but which dropped drastically when charging at levels under 30% of the charger power, shown in Figure 2.3. Capabilities of charging equipment will also determine the exibility services that EVs will be able to provide. Proposed smart control strategies take advantage of various capabilities that are not yet universally deployed in EVs and charging infrastructures, such as bidirectional ows and reactive power provision. Bidirectional chargers are needed to exploit V2X and use EVs as distributed storage units, but currently there are few bidirectional chargers and compatible EVs available in the market. Technical challenges (in particular improving round-trip e ciency) and high costs still need to be overcome [18]. Controllable reactive power provision has been proposed for voltage regulation at LV and MV grids [49][50], but today’s chargers do not provide this capability. This may change with ongoing R&D by OEMs, since this feature could be required by grid codes for bidirectional chargers. Renault, for example, tested a grid-code compliant on-board V2G charger [51]. Finally, battery degradation may represent a major impediment to V2G-based ser-vices, as V2G-induced additional battery cycling can reduce the battery’s lifespan. Battery aging may signi cantly impact the viability of business models for exibility services, and is a major factor in end-user acceptance of V2G [52]. Battery degradation is a com-plex process, ruled principally by two behaviors: calendar aging, dependent on temper-ature and SoC at storage, and cycling aging, dependent on power throughput, depth of discharge and other factors [53]. Recent studies, both experimental and simulation-based, have shown that V2G might signi cantly reduce battery life if not used properly [53], but have only minor e ects if its usage is limited (20 times a year for energy-intensive services like peak-shaving, or for low-impact frequency response) [54]. If peak shaving services are used daily, they can have signi cant impact on battery degradation [55].

Flexibility procurement frameworks

EV exibility today can be exploited where it can be monetized. This can be through the participation of EV aggregators in existing system-wide markets (wholesale or bal-ancing markets), or through energy management systems to optimize electricity bills of end-users. However, there is still no widely accepted framework for the use of exibility at distribution level. Di erent frameworks have been proposed in the literature and in demonstrator projects. According to CEER, models for exibility procurement by DSOs can be divided in the following categories [70]:

Rules-based approach

This refers to grid codes that de ne the technical requirements for grid connection. They are used mainly to maintain the security and stability of the electricity grid, such as disconnection under fault conditions or harmonic distortion limits.
Imposing smart charging or V2G through grid codes might not be viable, as it may impose a barrier to the development of market-based exibility services. However, reac-tive power compensation for voltage regulation (Volt-VAr regulation) has been proposed as a requirement for EV charging connections. While reactive power compensation as grid code has been proposed for of unidirectional EV charging infrastructure [71][50], it may unfairly burden grid access for EVs, as other loads do not have to comply with this requirement. Other solutions besides grid codes could be envisaged to develop reactive power compensation for unidirectional chargers. On the other hand, reactive power com-pensation can more easily be required for V2G-capable EVs, as it is already a requirement for power injecting DER (such as PV panels) in some countries [57][71] and is supported by the IEEE 1547 Standard [72].
Grid codes are de ned at a regional or national level. While many aspects are shared across countries, there are still di erences among requirements and varied treatment for emerging technologies, such as storage and EVs [73]. Compliance with diverse national grid codes may present a barrier for the massive deployment of V2G-capable EVs by OEMs with international presence, as well as creating issues with EVs that can move across national or regional borders (see Section 4.2). This calls for an uniformization of grid codes (speci cally at the distribution level) at a large scale area, such as Europe.

Connection agreements

In this arrangement DSOs work with customers to form an agreement for the provision of exibility. Connection agreements have been successfully implemented for congestion management using smart connections for renewable generation in Europe [74]. Generators with a smart connection are interruptible, which means they can be (partially) curtailed if there is local congestion, but bene t from lower connection costs and shorter delays.
Arrangements for EV charging infrastructure can take two approaches: interruptible contracts or variable capacity contracts (VCC).
Interruptible contracts, similar to those for renewable generation, can (partially) cur-tail EV charging infrastructure according to system conditions. This type of contract leaves direct control of the EV charging process to DSOs, and presents the risk of pre-cluding EV mobility needs, thus potentially meeting with lower user acceptance. My Electric Avenue project tested an interruptible solution where a system temporarily cur-tailed EV charging to respect the limits on the local grid infrastructure [75].
VCCs provide the customer with a variable maximum power they can withdraw from the grid according to a schedule (either xed or dynamic) set by the DSO, while bene-ting them with lower network tari s. For example, users can have a reduced maximum capacity during peak load hours but an increased maximum capacity during o -peak hours [76], as shown in Figure 2.5. This capacity can as well be periodically computed by the DSO (e.g., day-ahead based on load and generation forecasts) as proposed in [77]. This type of contract has recently been proposed for residential users in Spain, where customers can choose a higher subscribed capacity for o -peak hours (from midnight to 8 AM) [78].

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EV status in the grid

V2G-able EVs face great di culties regarding their connection requirements and legal status as exibility providers. Connection requirements can be burdensome, as V2G-capable EVs need to comply with requirements both as producers and consumers, as well as administrative procedures to declare and allow distributed sources to participate as exibility providers. Legal status of V2G installations should also be clari ed and aligned with that of storage, with tari s and charges that prevent double taxation.
Regulators, system operators, and EV and EVSE manufacturers need to work to standardize interconnection requirements to ensure system and end-user safety, while easing administrative procedures. For example, the French regulator issued a series of recommendations regarding the interconnection requirements, mainly for the de nition of the decoupling protection5, as well as simpli cation of administrative procedures [131]. In 2019, Delaware state passed legislation that de ned the perimeter of V2G, de ned clear interconnection procedures (adopting SAE J3072 safety for on-board bidirectional chargers [132]) and allowed net-metering to provide a level-playing eld with utility-scale storage [133]. These measures have been suggested to other states as well [134].

Interactions with grid operators

An important aspect is how the di erent stakeholders interact along the exibility value chain. There are interactions between exibility providers and exibility customers, in this case EV users and DSOs respectively, and interactions between DSOs and TSOs as potential exibility customers, where their level of coordination and cooperation will a ect how local exibility is used.

EV users-DSO interaction

DSOs can procure exibility from end-users directly or indirectly. As mentioned in Section 4.1, DSOs can procure exibility using di erent solutions. By using direct obliga-tions (grid codes) for exibility provision or contract arrangements (such as interruptible contracts), DSOs will directly interact with EV users acquiring permission to directly control the EV charging process.
On the other hand, market-based procurement via exibility platforms usually needs an aggregator that would gather multiple exibility resources. This is currently the case for ancillary services and BRP energy arbitrage as done by existing EV aggregators. It could be expected that a growing number of EVs will become associated to an aggregator’s program, therefore likely to meet communication and control requirements for the smart charging process. This will allow the provision of market-based exibility services to DSOs by EV eets.

DSO-TSO interaction

Currently there is only limited cooperation between DSOs and TSOs. As more DERs are connected into distribution networks and start providing ancillary services, like EVs 5 This de nes the conditions for EV/EVSE disconnection under local fault or islanding conditions. providing frequency response, DSO-TSO cooperation will become increasingly impor-tant to guarantee the safe and reliable operation of the power system. This has been highlighted by the scienti c community [74][135], industry and regulators [70], and was considered as a key aspect in the European Clean Energy Package.
SmartNet is a key demonstrator project that focused on DSO-TSO coordination, considering data exchange, monitoring and the provision of ancillary services from dis-tributed sources [135]. Five possible coordination schemes for exibility procurement by DSOs and TSOs were analyzed and di erent schemes emerged depending on the level of DSO-TSO cooperation, their roles and responsibilities de nition and the level of integra-tion of markets (centralized or decentralized). Higher coordination can present bene ts on operational security and reliability and in asset e ciency, both in centralized and de-centralized schemes, but it also carries higher computational and ICT burden, and poses regulatory issues.
In [74], authors analyzed possible cooperation between DSO and TSO according to the system state for congestion management, considering both operational issues and market issues. They found that cooperation can arise from forward stages (long- and medium- term), by harmonizing practices and data for capacity calculation, at day-ahead (short-term), by joint or coordinated exibility procurement, and in real-time stages, by ensuring grid security in rmness and capacity allocation. Con icts may arise if exible resources (such as EVs) are required by the DSOs and TSOs concurrently. Reference [42] analyzed this issue in a context of distribution congestion management and primary frequency response services. De nition of priorities on exibility procurement, activation and compensation will be needed in these cases.

Table of contents :

Acknowledgements
Lists of Acronyms
Nomenclature
Publications
1 Introduction: towards future smart grids 
1 Towards a low-carbon future
2 Smart grids and the need for exibility
3 Thesis objectives
2 Active integration of EVs into distribution systems 
1 Methodology
2 Technical aspects
3 Economic aspects
4 Regulatory aspects
5 End-user aspects
6 Discussion
7 Partial conclusions
3 Plug-in behavior of EV users: modeling, insights from a large-scale trial and impacts for grid integration studies 
1 Introduction
2 Literature review
3 EV simulation model
4 Insights from a large-scale EV trial and model calibration
5 Impact of non-systematic plug-in behavior on EV grid integration studies
6 Partial conclusions
4 Assessing EV integration in distribution grids: a data-driven approach. 
1 Relevant works on EV integration into distribution grids
2 A data driven methodology to build realistic case studies
3 EV charging impact at the primary substation level
4 EV and PV integration in realistic MV grids
5 Partial conclusions
5 Participation of electric vehicle eets in local exibility tenders: Ana- lyzing barriers to entry and workable solutions 
1 Introduction
2 Looking for decentralized
exibility markets
3 Methodology and case study
4 Results
5 Partial conclusions
6 Final conclusions 
A Detailed models for EV charging 
1 Cost-optimization charging
2 Decentralized valley lling
B Grid reconstruction from GIS data 
1 Datasets
2 Grid reconstruction methodology
C Computational times 
D Complementary results from La Boriette case study 
1 Spatial distribution of EVs and PV installations
2 Maximum line loading
E Resume en francais. 

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