Pricing and Electric Vehicle Charging Equilibria Trivikram Dokka Jorge BrunoSonali SenGupta Chowdhury Mohammad Sakib Anwar

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Pricing and Electric Vehicle Charging Equilibria
Trivikram Dokka Jorge BrunoSonali SenGupta
Chowdhury Mohammad Sakib Anwar§
December 13, 2022
Abstract
We study equilibria in an Electric Vehicle (EV) charging game, a cost minimization
game inherent to decentralized charging control strategy for EV power demand man-
agement. In our model, each user optimizes its total cost which is sum of direct power
cost and the indirect dissatisfaction cost. We show that taking player specific price in-
dependent dissatisfaction cost in to account, contrary to popular belief, herding only
happens at lower EV uptake. Moreover, this is true for both linear and logistic dissatis-
faction functions. We study the question of existence of price profiles to induce a de-
sired equilibrium. We define two types of equilibria, distributed and non-distributed
equilibria, and show that under logistic dissatisfaction, only non-distributed equilibria
are possible by feasibly setting prices. In linear case, both type of equilibria are possi-
ble but price discrimination is necessary to induce distributed equilibria. Finally, we
show that in the case of symmetric EV users, mediation cannot improve upon Nash
equilibria.
Keywords : Electric Vehicles, Pricing, Nash equilibrium, Coarse correlated
equilibrium, Mediation, Herding, Dissatisfaction cost
JEL Codes: C61, C72, D4, D11, D82
Advanced Analytics Group, Air Products Plc, United Kingdom. Email: trivikram.dokka@yahoo.co.uk
Department of Digital Technologies, Faculty of Business and Digital Technologies, University of Winch-
ester. Email:Jorge.Bruno@winchester.ac.uk
Economics Section, Queens Management School, Queens University Belfast, United Kingdom. Email:
s.sengupta@qub.ac.uk
§Author for correspondences. Department of Economics, University of Winchester, United Kingdom.
Email: Sakib.Anwar@winchester.ac.uk.
1
arXiv:2210.15035v2 [econ.TH] 12 Dec 2022
1 MOTIVATION AND RESEARCH QUESTIONS
Electric Vehicles (EVs) are widely seen as part of a solution to economically and environ-
mentally sustainable transportation future. With more countries looking to de-carbonize
their economies at an increased pace, more incentives to EV uptake are being proposed
and implemented. However, mass scale EV uptake comes with its own challenges, pri-
mary of them being impact on existing electricity infrastructure. Several researchers in-
vestigate economic and environmental implications of residential charging of electric ve-
hicles (Clement-Nyns et al., 2009; Muratori, 2018). It is widely believed that an efficient de-
mand response is essential to avoid costly infrastructure upgrades and/or blackouts. This
involves alignment of EV charging demand with supply. Such an alignment not only avoids
costly and unnecessary capacity addition but also results in shift to renewable sources. Ini-
tial ideas to achieve this alignment, naturally, were based on incentivizing people via prices
(to charge at non-peak times)(Palensky & Dietrich, 2011; Western-Power-Distribution et
al., 2015). It is argued that the same price signals received by all EV users will result in
herding behavior where, all users shift their charging to low cost periods to avoid peak
periods, resulting in new peaks (Dudek et al., 2019; Valogianni et al., 2020; Western-Power-
Distribution et al., 2015). Herding behavior formation argued in these studies relies di-
rectly on the assumption that EV users are cost minimizers. Ironically, the observations
of herding are made without any reference to the level of EV uptake. In a typical herding
scenario (with high uptake), a EV user receives less power (kWh) than is expected when
charged at full speed, due to congestion or as part of a strategy to move users to different
time of day, hence causing dissatisfaction due to less battery charge received. Without tak-
ing this dissatisfaction in to account the conclusion that charging behaviors result in herd-
ing may not be consistent with expected behavior over time. The motivation for capturing
dissatisfaction explicitly is justified because price as an instrument to control charging be-
havior is only possible when users are (or are not) willing to pay to avoid dissatisfaction. In
fact, more recently user dissatisfaction is explicitly modeled within an algorithmic charg-
ing decision-making set-up (Lin et al., 2021). Similarly, Wu et al. (2022) uses the term in-
convenience cost in the same sense and illustrate optimal mechanisms for EV charging at
public stations. Consistent with this, our first research question is:
Question 1 When users experience indirect costs associated with dissatisfaction will herd-
ing still happen?
Grid managers and DNOs would want to use the flexibility of EV charging (believed
to be flexible load compared to other loads such as household power demand) to achieve
a desired consumption profile which better aligns with grid management objectives (see
2
Valogianni et al. (2020) and references therein). Recent research suggests designing a dy-
namic and adaptive pricing schemes to achieve a desired charging profile (Jacobsen &
Stewart, 2022). Our goal differs from these works in that we seek to find if price profiles
exist which will lead to a desired behavior profile in equilibrium, and if so under what con-
ditions, taking into account congestion aka dissatisfaction. To the best of our knowledge
we are not aware of any work that takes into account dissatisfaction cost or analyzes equi-
librium outcomes. With this motivation, we address our second research question:
Question 2 Does there exist price profiles that will induce a desired charging profile un-
der the given player-specific price independent dissatisfaction costs?
To answer our questions we take a game-theoretic approach to model EV user’s selfish
behavior and use a stylized model that captures the key aspects of EV charging behavior
as an EV charging game. Centralized versus decentralized control of charging has received
much attention in EV related literature. Decentralized setting can be seen through the
game theoretic lens, an approach only taken by relatively few researchers compared to
much more abundant empirical studies. While earlier studies, such as Tushar et al. (2012),
considered a stackelberg approach, closer to our setting, simultaneous form games were
studied in Chakraborty et al. (2017) and Chakraborty and Khargonekar (2014). However,
no studies considered dissatisfaction cost within game-theoretic setting. Our work also
complements the alternative stream of literature that takes a mechanism design approach
to pricing problem, such as Nejad et al. (2017) and Wu et al. (2022).
Price-based or otherwise, the idea of (decentralized) controlled charging relies on the
assumption that EV users will find themselves better off when an agency such as EV aggre-
gator acts as recommender system; under the belief that such an entity has greater (tech-
nological and informational) ability to make better charging recommendations compared
to EV users deciding on their own.1The role of mediating agency is certainly not unique to
this situation, and many economic situations, whether it be resource sharing or contribut-
ing towards a public good, also have this characteristic. Theoretically, such an entity will
recommend (or implement), with users consent, a charging regime which may or may not
satisfy user’s complete demand but may result in lower cost. But, what if users do not find
following agency recommendations better than their own decisions? Therefore, a confir-
mation of existence of such an entity is necessary via game theoretic analysis. This leads
to our final question.
1A number of researchers proposed optimization algorithms under decentralized scenario, see Shen et al.
(2019).
3
Question 3 Will co-ordination (or co-ordinated mediation) help? In other words, if an
agency (aggregator/charging manager) acts as a recommender system of how to charge, will
EV users commit to such an agency, and if they do, does it lead to a different equilibrium
than if they do not?
It is well known that in non-cooperative settings mediated communication is an effi-
cient way to achieve incentive-compatible outcomes via correlation devices aka correlated
equilibrium (Aumann, 1987) and Coarse Correlated Equilibrium (CCE)(Moulin & Vial, 1978).
We adopt CCE to answer if mediated communication leads to different outcomes as against
when EV users behave on their own. CCE, in recent years has received considerable atten-
tion owing to the finding that no-regret play leads to coarse-correlated equilibria (Rough-
garden, 2015). Correlated equilibria have also been associated with evolutionary learning
(Arifovic et al., 2019).
From the structure of games point of view, the games that we study in our work could be
seen to be connected to congestion and budget games, hence a comment on connection
to this literature is in order. The extant literature on congestion games spanning areas of
economics, computer science and operations research fields, mainly focus on existence
and efficiency of equilibria, that too, predominantly (pure) Nash equilibria. For example,
these results commonly establish bounds on price of anarchy and stability. On the other
hand, our questions are not related to efficiency of equilibria, instead, our questions are
motivated by practical observations from EV field trials. In the context of our games, a
desirable outcome may not even be the efficient one as is usually defined. It is conceivable
that games in our work could be modeled via congestion games frameworks, furthermore,
efficiency questions may also be relevant (as discussed in Chakraborty and Khargonekar
(2014)). However, this is not the main focus of our work and we leave it for future study.
The rest of the paper is organized as follows. In Section 2we present a discrete EV
charging game along with the main assumptions. In Section 3, we outline our three main
results that answer the questions stated in Section 1. In Sections 4,5, and 6we present the
details including statements and proofs of the results underlying research questions 1, 2
and 3 respectively.
2 EV CHARGING GAME:MODEL AND ASSUMPTIONS
Consider the following game we call EV charging game (EVCG). There are nplayers. A
typical Player ihas a demand ridiwhich can be fulfilled by choosing to charge in any of
diTtime periods. That is, strategy of a player is a T-dimensional binary vector.
Given a strategy profile (si,si), the dis-utility/cost of Player iis
4
c(si,si) = X
t
btgt(si,si) + X
t
ft(si,si), (1)
where
gt(si,si) =
Ptst
i
Pn
k=1rkst
k
, if Pn
k=1rkst
k>Pt
rist
i, otherwise
ft(si,si) =
hst
iPt
Pn
k=1rkst
k, if Pn
k=1rkst
k>Pt
0, otherwise
with rand Pbeing parameters of the game which are explained as follows: riis the power
rating (in kW ) of Player iwhich informs power transfer rate; Ptis the total available power
(in kW h) in time period t;st
iindicates whether Player icharges at time period tor not;
Pn
k=1st
kis the total number of users who decided to charge in time period t; and hrepre-
sents a dissatisfaction function. Furthermore, each time period is classified according to k
price slabs. In the most general case, k=T. For this reason, typically, charging choices are
modeled as discrete to allow for modeling a complete price discrimination between users,
where users may pay time of day tariffs. However, consumers rarely choose schemes which
employ real-time pricing or several price slabs during the day, this is usually explained as
fear about price volatility. Most common practice is to differentiate between peak and
non-peak times (see Jacobsen and Stewart (2022) and Western-Power-Distribution et al.
(2015)). In our model, btis the price per unit in time t, we will assume a two part price
plan as formalized in the assumption below.
Assumption 1. Two price slabs: peak and non-peak; we superscript peak and non-peak
times with D and N respectively, eg., b N
iis the non-peak price for user i .
Remark 1. Note that the scenario when gt(si,si)<rican be interpreted as congestion or
a deliberate delayed charging strategy as in Wu et al. (2022) to induce a desirable charging
behavior equilibrium.
Assumption 2. h(·)is a continuous and monotone function.
In our analysis we consider two functions: a linear and a logistic one. Linear dissat-
isfaction is also considered in the recent literature, the reason being linear dissatisfaction
rates are more appealing because of simplicity and associated tractability of resulting anal-
ysis. In practice, however, it is likely the dissatisfaction is different across the support. For
example, increase in dissatisfaction is probably higher when a user gets 10 kWh instead of
5
摘要:

PricingandElectricVehicleChargingEquilibriaTrivikramDokkaJorgeBruno†SonaliSenGupta‡ChowdhuryMohammadSakibAnwar§December13,2022AbstractWestudyequilibriainanElectricVehicle(EV)charginggame,acostminimizationgameinherenttodecentralizedchargingcontrolstrategyforEVpowerdemandman-agement.Inourmodel,eachuse...

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