Charging Stations

 BRACT, Vishwakarma Institute of Technology, Pune

TY. B. tech

Mechanical Engineering Department

HAEV - Home Assignment - TYMEA, Batch 2, Group 5

Guided by - Prof. Dattatray Hulwan

Group Members/Authors - 

Nivedita Bhagwat - RN 31

Pranjali Bhople - RN 38

Vedant Bhosale - RN 41

Harsh Bhutada - RN 44

Chhavi Kumari - RN 52

 

Introduction

Charging station, also called as EV chargers  or electric vehicle supply equipment (EVSE), is a type of equipment that supplies electrical power for charging Plug in EV such as HEV, BEV and also other types of Electric vehicle like buses , trucks ,etc. The EV charging station includes an Electric Vehicle charger, Power Grid, Facility Meter, Energy Controller, Software platform, Network operating center, and other relevant components.

Ev charging requirements usually depend upon the specifications of EV batteries such as power that to be supplied to the battery at the right voltage and current levels to permit charging. Typical capacity and voltage of EV batteries vary among the different EV segments, as shown in Table below. Low-voltage batteries power the  E-2Ws & E-3W and also the first generation e-cars.Second generation e-cars are the upcoming model of e-cars which are powered by high voltage batteries. E-LCVs will include both low-voltage and high-voltage vehicles that depend on their load-carrying capacity.

Working of charging station

EVSE AC Charging Station - Level 1 and Level 2 Chargers

The level 1 and 2 charging station has to provide AC power to the on board charger in an EV that will take care of the charging process. The right amount of power from the grid should be given to the EV battery pack through a pilot wire. The below figure shows representation of a AC charging station (referred from Texas Instruments).

 

  

 

 

Level 1 charger provides maximum output current of nearly 16A. This is because of limitation of household power sockets. While level 2 chargers will provide upto 80 A approx when it is operated by three phase supply. Both the AC chargers( L-1 and L-2) use SAEJ1772 standard plug connectors.

As in the above figure, the  AC power lines (L1 & L2) are attached by a J1772 connector through a Relay.When this relay is closed it will begin the charging process and open when the charging process is completed. Here, the Pilot Signal communication is used to detect battery status. And the host processing system decides how much power should be supplied to the on-board charger.

The Power supply unit consists of an AC/DC converter which takes in the AC power form grid and converts it to DC 15V using a switching circuit. This DC 15V is provided to the Regulator which involves a DC/DC converter which uses three different Buck Regulators so that to regulate 12V, 5V and 3.3V and can be used to power the sensors, displays and controllers in the Charger Unit. The Measurement System consists of V/I Sense circuits which are used to measure the AC current and AC voltage. Above block diagram has a Current transformer (CT) used to measure the input current but shunt or else Flux method can also be used. The voltage is measured on either side of the relay to know if the relay is currently open or closed. Since, the measurement subsystem deals with AC voltage and current will be digitally isolated from the Host Processing Subsystem.

Host Processing Subsystem includes the main Micro-controller which will receive the information from pilot communication. Based on the information it triggers the Relay using Relay driver circuits. It also monitors the current and voltage using the values provided by the measurement subsystem and takes corrective actions whenever required. The controller will also have a display unit, EEPROM and RTC so that to provide useful information like charging time, current status etc to the user board.

Pilot Wire Communication in EVSE (AC charger)

Basically in AC chargers the charging rate,i.e the required input current is actually decided by the EV only. Not every EV’s require the same amount of input charging current. Hence, the AC Charger should communicate with the EV to know the required input current and perform an information before the charging could actually begin, this communication is called the Pilot wire communication.

 

The AC chargers  normally use the J1772 cable which has 2 points on the charger other than that of power lines. These two signal lines help the charger to communicate with the EV through +/-12V PWM signals. By default the signal pins on the EVSE output +12V, this when connected to an EV will get reduced to 9V because of a load resistor present in the EV. This signals to EVSE that the connector has been plugged into an EV. After this the EVSE will send a PWM signal of magnitude 12V. A duty cycle value corresponding to the maximum current it could deliver. If EV is ok with the value of current, then it has to perform a handshake by changing the load resistance and dropping the PWM voltage to 6V after charging begins.

 

Above graph provides information about the communication happening between the EV and the EVSE. Initially, when EVSE is not plugged in the EVSE outputs 12V, as soon as it gets plugged in it drops to 9V and the PWM signal gets started. In this case, the duty cycle of the PWM signal is 50% meaning that the available input current is 30A (Maximum capacity 60A). If  EVs on-board charger could work with this current ,then the EV signals a handshake by changing the load resistance and the PWM signal will drop to 6V. The charging begins at this point and will continue as long as the PWM signal oscillates between 6V and -12V. The EV will change its load resistance again when the charging process is complete to signal the charger to shut down. 

EVSE DC Charging Station - Level 3 Chargers

The level three charging stations are more complex than the Level 1 and Level 2 since the DC/DC conversion for the battery pack has to be done by the EVSE itself. Since a DC EVSE bypasses the on-board charger it should know all vital parameters of the battery pack to charge it safely hence a CAN or PLC (Power Line Communication) should be established between an EVSE and  the BMS of the EV. A Level 3 charger normally uses the CHAdeMO charger socket but other connectors like the J1772 Combined charging connector, Tesla connector are also being adapted by different manufacturers, these chargers can deliver up to 200A directly to your battery pack to charge the EV in less than 30 minutes. A typical simplified DC charging station Subsystem block diagram is shown below. 

 

The system here is over simplified by removing the systems that we discussed earlier in the AC charging system. The Level 3 charger always works on a three phase AC supply, so the AC/DC converter has to take in the 3 Phase supply and convert it to 40V or higher DC. This DC voltage will then be stepped up to a higher level (350 -700 V) as required by the battery pack. The Output Voltage and Current will be decided by the BMS of the EV which will then be communicated to the EVSE through CAN/PLC communication. Most of these level 3 chargers will be placed in charging stations for public access and hence a Human Machine Interface (HMI) arrangement gets mandatory. Some EVSE will also have wireless features like NFC, Bluetooth and Online payment gateway features etc to facilitate easy public usage.

The technology challenge lies with the AC/DC converter and DC/DC converter subsystems of the module. Since the charger draws in high current from the grid a proper Power Factor Correction system is required. Also the Converters are dealing with very high current and the power electronic switches inside them like MOSFET and IGBT cannot handle as a single unit. Hence normally the converter units are split into small units which are then combined in parallel to provide high current.

Types of electric car charging stations

The charging process of electric cars is simple. We just need to simply plug in our car into a charger connected to the charging grid. However not all the Electric Vehicle charging stations also known as Electric Vehicle Supply Equipment are created equal.For some of the charging stations it just simply needs to be plugged into a standard outlet while for others it requires a custom installation. The time duration it takes to charge our car will also differ based on the charger we use.

 

EV chargers typically fall under one of three main categories:

1. Level 1 charging stations
2. Level 2 charging stations
3. DC Fast Chargers (Level 3 charging stations)

Level 1 EV charging stations

Level 1 chargers use  120 V AC plug. They do not require the installation of any additional equipment and can be plugged into a standard outlet. The range per hour of charging is about two to five miles of these chargers and are mostly used at home.

 

Level 1 chargers are the cheapest EVSE option, but  it takes the most time  to charge our car’s  battery.People generally use these type of chargers to charge their car’s overnight. AeroVironment, Duosida, Leviton, and Orion are some of the manufacturers of  Level 1 chargers.

Level 2 EV charging stations

Level 2 chargers use a 240 V (for residential) or 208 V (for commercial) plug, but like Level 1 chargers they can’t be plugged in to the standard wall outlet. They are generally installed by  professional electrician. They can also be installed as part of a solar panel system. They are used for residential as well as commercial charging station.

 

The range per hour of charging is about  10 to 60 miles. They can charge the battery in two hours or less than it making it.They are considered to be an ideal option for  homeowners who need fast charging and  also the businesses who want to offer charging stations to customers.

 

Many electric car manufacturers, like Nissan, have their own Level 2 charger products. Other Level 2 EVSE manufacturers include ClipperCreek, Chargepoint, JuiceBox, and Siemens.

DC Fast Chargers ( Level 3 charging stations)

DC Fast Chargers  also known as Level 3 charging stations offers  60 to 100 miles of range for our electric car  with just time requirement of just 20 minutes for charging.But  they are typically only used in industrial and commercial application. They require highly specialized, high-powered equipment to install and maintain.

 

All electric cars cannot be charged with the use of DC Fast Chargers. Most plug-in hybrid EVs don’t have this charging capability, and some all-electric vehicles cannot be charged with a DC Fast Charger.

 

The Nissan Leaf The Mitsubishi “i”  and are examples of electric cars that are DC Fast Charger enabled.

Chargers/Connectors

Similar to phone charging cables, car charging cables tend to have two connectors, one that plugs into the vehicle socket and the other into the charge point itself.

 

The type of connector we  need varies by vehicle and the power rating ("speed") of the charge point.

Electric vehicles either have a Type 1 or Type 2 socket for slow/fast charging.  CHAdeMO or CCS  are used for DC rapid charging.

 

Most slow/fast charge points have a Type 2 socket. Occasionally they  have a cable attached instead. All DC rapid charging stations have a cable attached with mostly a CHAdeMO and a CCS connector.

 

Most of the  EV drivers purchase a portable charging cable that matches their vehicle’s Type 1 or Type 2 socket so that it's convenient  for them to charge on public networks.

Vehicle side EV connector types

These connector types fit into the socket on our vehicle and can be thought of the same as the phone-side charging connectors on our Apple or Android phone charging cable. Depending on which phone/car we have, different  type of connectors will fit into our phone/car socket.

 

 

 

Slow & Fast Charging

Alternating Current (AC)

Mostly used for top-up charging at home, work and destinations.

Rapid Charging 

Direct Current (DC)

Typically used for en route rapid charging.
There are three types of DC car-side connectors.
All DC rapid charging stations will have cables with both a CHAdeMO and CCS connector attached and we  have to simply  choose which fits to our vehicle socket. Rapid chargers do not consistently charge at their typical power rating to protect the battery.

Chargepoint side EV connector types

Generally used for top-up charging at home, work and destinations. There is really only one kind of chargepoint socket, though some might occasionally use a traditional 3-pin plug to charge from a wall socket as an emergency backup.
 
The Type 2 chargepoint socket is universal, and can be thought of in a similar way to the wall socket for charging iPhones or Android phones (i.e. the socket is the same for each, but the cable is specific to the car/phone type).

Slow & Fast Chargers

Alternating Current (AC)

 
Typically used for top-up charging at home, work and destinations, there is really only one kind of chargepoint socket on slow and fast chargers, though some drivers might occasionally plug into their traditional 3-pin wall socket as an emergency backup.

Rapid Chargers

Direct Current (DC)

All DC units have tethered cables with both CHAdeMO and CCS connectors that match the car-side sockets, so there are no chargepoint - side DC sockets. 

 

Power Rating -

 

There are different power ratings or levels for EVSEs which are based on charging requirements and which in turn determine the input power requirements for charging infrastructure. The table given above on EV charging by power level has normal power charging  which goes up to 22kW and high power charging  which goes up to 200kW. EVSEs with power ratings up to 500kW are globally  made available and  they are largely applicable for heavy vehicles like buses and trucks and other types of vehicles too. Normal power AC charging is acceptable for e-2Ws, e-3Ws and e-cars. Normal power DC charging is unique to India as of  due to the prevalence of LEVs. The use of low-voltage batteries in e-cars. Single-phase AC chargers having a maximum power rating of 7kWwhich are acceptable for LEVs and  also cars having single phase on-board chargers. Three-phase AC chargers with a power rating up to 22kW are required for e-cars with larger onboard chargers. Input power supply for normal power charging can be provided through the standard electricity distribution network. High-voltage e-cars having battery capacities lie between 30-80kWh and high-power DC charging of 50kW is to be used. 

 

In the market,the power level of DC chargers ranges between 25kW and 60kW. Hence, higher powered DC chargers will be  made available in the nearer future. Fastest DC charging takes less time for e-cars and also requires higher electricity power supply including additional infrastructure. Normal power charging points are acceptable for most charging requirements that includes slow or overnight charging of e-cars.

Solar powered charging station

Solar energy and electric vehicle (EV) charging these combination is the key for drastically reducing our dependence on fossil fuels. Electricity comes from a varied  sources and it’s pivotal   that electric vehicles will be powered by renewables. Electric cars are becoming extremely popular and in the upcoming years we expect that nearly anyone who possess a solar energy system will install a solar charging station at  their home.

What is the change in thinking that we need?

Most people believe  that we need to be able to charge our plug-in electric vehicle (PEV) or plug-in hybrid electric vehicle (PHEV)  within 2-4 minutes, similar to pulling over at a gas station and filling up our car with gas. Even though Tesla’s super chargers are trying to do exactly that but  electric charging is going to be different from what people are used to. From now onwards  most people will charge their electric cars with their home solar charging station while they sleep or while they’re at work. Solar charging stations will be used for "topping off” an electric car, giving the owner enough battery charge to return home where that can fully recharge the EV.

 

On-Grid solar charging stations

A grid-tied solar energy system is The most straight forward way to charge our electric car with solar energy in  a grid-tied Solar Energy system.  This solar energy system will feed the power to the grid, regardless of whether our home needs the power at that moment or not. So when our solar energy system is feeding to the grid, and we are at office, the electric power generated at home is sold to the utility company. We will get that power back from the utility company in the form of a credit. When we come back from work and park your car at home, we can use the credit to re-charge our car at home.

A conventional electric vehicle charger that is connected to the grid “will almost always be cheaper” than an Off-Grid charger that stores the power in batteries.

Off-Grid Solar charging station

An Off-Grid electrical car charger is  also  as "Electric Vehicle Autonomous Renewable Charger".In this system there’s no connection to local utilities required.  The solar panel array will feed the battery energy storage system and the entire power needs are drawn from this storage system. Off-grid electrical car chargers can be placed virtually anywhere, as there’s no need for a connection to the electrical grid. The independent solar array canopy catches quite some wind, and for that reason a solid foundation is required. Some of the  off-grid solar energy chargers have a heavy steel base plate which functions as ballast. Those are extremely easy and quick to install, as no foundation or digging is required.

Most electric car owners will completely charge their EV batteries at night at their homes. Therefore for most solar charging stations, the objective is not to fully charge an electric car, but to allow several cars to “top off” their batteries. 

Components needed for a solar charging station

1. EV charger
2. Solar panel array, installed on roof, ground or canopy
3. Battery energy storage system (ESS, in case of an Off-Grid Solar energy charging station)
4. Solid foundation, in case of a stand-alone solar charging canopy (Often used: a steel base plate that functions as ballast, so no foundation is required, simplifying the installation).
5. Intelligent software

As we know electricity comes from a variety of sources but now it's the time to push towards the renewables to take its place. Solar charging stations for home as well as  commercial use will play a vital role in powering electric vehicles with renewable energy.

Operational Expenditure of Starting an EV Charging Station:

The operational cost required to keep the EV charging station business running:
EVSE management software – Such software will let your customers know if there is an empty slot available at your charging station. So that they can even book the slot from this software. Software costs around Rs 50000 per ann.

• Manpower – Running 1 charging station,will need at least 2 people as per the government guidelines. One person would be a trained technician  and will take care of the charging work. Second person will take care of the car parking and maintenance. The salary of these 2 workers will cost around Rs 4-5 lakhs annually.
• Payment Gateway – For online payment options like payment from a card using a swipe machine and also by online payment.
• Internet Connection – For the EVSE management software and the payment gateway should be available at the charging station.
• Land Rent – If you’ve taken the land on rent then we have to pay the land rent
• Marketing & Advertising – Marketing and advertisement will increase the sales.
• Electricity cost – Cost of electricity for charging the electric vehicles.

Battery Swapping

 

Another or alternative method of battery recharging is “Battery Swapping”,in which a depleted  EV battery is removed and replaced by a charged battery. This technology has been tried on various EVs.

Types of Battery swapping:

Manual: A battery swapping station is a standalone device, in which batteries are placed and removed manually from the individual slots, usually by hand. This type is modular and can occupy a minimal space. This uses 2W and 3W battery application so that battery pa k size is smaller and the weight can be handled by 1-2 persons.

Autonomous: A robotic arm can be use in swapping station so that the process of battery swapping can be semi or fully automated. This is used for 4W and e-bus applications for larger,heavier and require mechanical assistance battery pack. But, these swapping station will be more expensive and require more land than manual.

Battery swapping will have distinct advantages over plug in charging and can also confront with several challenges in its development as a mainstream charging method.

The Future of EV Charging Station in India

The government sets to set up 69,000 electric vehicle charging stations by 2030 in India

EV charging infrastructure is going towards utilizing renewable sources of energy like solar and wind, many more and vehicle to grid (V2G) and Bidirectional chargers are steps in this direction. To reduce range anxiety among EV owners and make use of EV chargers easier and wireless charging of EV create a buzz in the automotive marketspace.

With the EV infrastructure Falling down in place, the industry is looking towards to delivering e-mobility solutions that are not restricted to automobiles and develop capability to energize our highways, industrial fleets, and businesses, cities, and utilities, etc.While the community of individuals sharing their charging infrastructure is a potential approach to expand the network of EV charging stations, it is still of ultimate importance to develop  public charging station network for everyone to be able to access

Last year, under the second phase of the Faster Adoption and Manufacturing of EV and HEV (FAME) scheme, the Government sent out invitations to public and private entities to set up charging stations for EV across the nation. Planning is to set up one charging station every 25 km so that to promote the adoption of EV in India. Expected by 2030, there will be approximately 69,000 EV charging stations in India. 

 

Under this scheme, the government is proposing establishing both fast chargers for 4-wheelers and chargers for 2/3-wheelers.This attempt  regarding the scheme from the Government received over  more than 100 proposals from companies in both the public and private sector for opening over 7,000 charging stations. However, only around 2,600 charging stations were approved. Recently, in the Indian market there are a few car manufacturers that took the initiative to enter the  EV segment, including Tata, Hyundai, and Mahindra. 

 

Currently, Tesla  has planned to enter the India Market. With the presence of the world’s leading EV maker and production, it is expected that the buying sentiments for EV will quickly build up.

Conclusion

Technology is continuously advancing, which has allowed for electric vehicle usage to become more and more feasible to travel far distances. Many high grade electric vehicles, such as the Tesla Model S, can easily travel long distances with the given network of charging stations located in Canada. Not only can these high grade electric vehicles travel the distance, but they save money on gas and help promote sustainable travel. Clusters of electric vehicles charging simultaneously on a single residential transformer could potentially require upgrades to that transformer, but individual vehicles are not expected to affect the distribution system. “Quick-charge” stations may pose potential challenges for the distribution system. The use of off-grid solar photovoltaic for EV charging is technically feasible, but it may only be practical in unique circumstances due to economic considerations.