Electrical Design of V2G – System Architecture

Hello my name is Sam Abbott and I’m  a technical specialist here at Cenex.   In this video we will be building on  the learnings of the previous step   by exploring different system  architectures for vehicle-to-grid systems.

In the previous step we learned how  in a conventional EV charging system   supplied with mains electricity from the grid via  the distribution network there is a rectification   process to convert from AC to DC in order  to charge the vehicle’s battery we also saw   that for V2G systems in order to discharge  the EV battery we need an inversion process   to do the opposite and convert back from DC to AC.   There are two system architectures possible  distinguished by where the power electronics are   located and consequently whether the electricity  that is transferred between the electric vehicle   supply equipment or EVSE and the vehicle in  both charging and discharging modes is AC or DC.

We will now look at these two  system designs in more detail.

Firstly let’s take a look at DC V2G systems. In  the DC V2G system we have direct rectification   for charging and inversion for discharging  performed in the EVSE the energy transfer   between the EVSE and the vehicle is therefore  in DC as with conventional DC charging the   on-board charger including the vehicle design for  conventional AC charging is bypassed and not used.

DC V2G is already possible  via the CHAdeMO protocol   however CHAdeMO is only used by a limited number  of vehicles typically from Japanese manufacturers   such as the Nissan Leaf the Nissan e-NV200  and the Mitsubishi Outlander plug-in hybrid.

Indeed these are the vehicles which feature most  often in the V2G trials that have been completed   in Europe to date. The majority of vehicles,  in Europe at least, implement DC charging   using a combined charging system or CCS which  is, as of now, does not yet support V2G.   We will see how progress is being made  to change this later on in week one.

In comparison AC V2G shifts the power electronics   onto the vehicle the energy transfer between  the EVSE and the vehicles is therefore AC and   the rectification and inversion for charging  and discharging happens on board the EV.

As we shall see later on in this course  most of the existing V2G demonstrations   are DC V2G systems. That said in 2019 an  AC V2G trial was done using Renault Zoe’s   in Utrecht, the Netherlands. The Renault  Zoe is somewhat unique amongst EVs   although the model that allow 43 kilowatt charging  is no longer available you can still purchase a   Zoe capable of 22 kilowatt AC charging which is  unusual for a vehicle in the super mini segment.

Renault avoids the additional size and weight  of an onboard charger capable of 22 kilowatts   by using the powertrain electronics essentially  the drive motor in regenerative braking mode   to charge the battery. It is  believed that in this trial   the power train electronics are also being  used for discharging the battery for AC V2G.

There is also fairly frequent news of vehicle  manufacturers including AC V2G functionality   in their vehicles in 2020 the industry was  excited by the speculation that Tesla model 3s   already on our roads were V2G capable following  a teardown of the vehicle’s on-board charger   however this rumour was swiftly debunked   nonetheless Volkswagen have come out and said that  they want all their EVs to support V2G most likely   AC V2G by 2022 and the now available Hyundai  Ioniq 5 already has some limited AC V2G capability   with a feature called vehicle to load which  we will discuss in a step later on this week.   Note that the links to the news articles  shown on this slide will be included   in the text beneath this video should  you wish to which to find out more

We have performed a SWOT analysis to assess  the relative strengths and weaknesses   the DC and AC V2G system architectures. Firstly  for DC V2G the key strengths are that V2G has   already been implemented by the CHAdeMO protocol  in a system that is less reliant on the vehicle   manufacturer including costly vehicle power  electronics which some may be reluctant to do.   On the other hand this means that a  DC V2G chargepoint will be higher cost   than an AC or DC conventional chargepoint or  even an AC V2G chargepoint of equivalent power.  

There is the opportunity for more widespread use   of DC V2G once it is implemented  via CCS which is planned for 2025

Additionally placing the power electronics in  the EVs where the increased size and weight are   less of a problem could allow higher power V2G to  take place which may be useful in some situations   and finally the greatest threat to  V2G would be more key EV manufacturers   backing AC V2G in their strategy as per the  announcement made by Volkswagen in 2021.

For AC V2G the strengths weaknesses opportunities  and threats are often the inverse of those for   DC V2G systems a key point to note is that lower  cost of AC V2G charging at charging infrastructure   could lead to a more widespread deployment  at longer dual-time locations that are more   suitable for V2G as we shall see later on in this  course the issues with AC V2G are firstly that   it’s not currently implemented by any standard  and therefore is at a lower level of maturity   and secondly that in comparison to DC  V2G systems it is more reliant on the   large traditionally somewhat risk-averse  vehicle OEMs to develop the technology.

So hopefully that has given you enough  information to understand the two different   V2G electrical system architectures using  the SWOT analysis to help. Have a go   answering this question in the discussion  section it’s a tricky question to answer  

and there are definitely no wrong answers: Do you  think one of the two architectures will dominate   or perhaps there will be a mixture of the two?

Thank you for listening and  enjoy the rest of the course.