Electric Vehicles (EVs) and the
Smart Grid
Amandeep Chugh Nabeel Nasir
IIT Bombay
Why are they called EVs?
• Uses an electric motor to provide all or part of the mechanical drive power [1]
• Batteries for storage
• Electricity stored
– Charged from Grid – Generated
New Bottle – Old Wine?
• Electric Vehicles have been around since
1900s
New Bottle – Old Wine?
• Electric Vehicles have been around since 1900s
Thomas Alva Edison and an electric car in 1913
New Bottle – Old Wine?
• Electric Vehicles have been around since 1900s
• So what’s with this new buzz for EVs?
• What has changed?
What’s new in EVs
Affordability
Low cost for electricity
Vast battery life improvements
Capacity => Better Range
Power draw => Better Acceleration
Charging - no additional infrastructure
Advent of IT in EVs
eg: App Support for the Ford Focus EV
Communication with outside environment
Support to Power Grid
Feature Pure EV Hybrid EV (HEV)
Plug-in Hybrid EV
(PHEV)
Electric Motor
Plug-in & Charge ×
Alternate Source
of Power
×
Internal Combustion
Engine
Internal Combustion
Engine
Storage
For generated electricity
Types of EVs
Regenerative Braking
Load Lowering
ICE -> Run generator -> Generate electricity -> Store
Charging Options for EVs
Input Voltage (V)
Input Current (Amps)
Charge Power (kW)
Time to Charge Level 1 120 V
AC 12–16 A ~ 1.4 kW 8 to 14 hrs Level 2 208 – 240 V
AC 12 A - 70 A 3.3 – 15.4 kW 4-8 hrs Level 3 300-600 V
DC 125+ 50 – 70 kW 20 – 50 min
Added Dimensions to Smart Grids
• Storage
– Large distributed storage
– EV = House-hold battery used for driving sometimes
– Store during off-peak hours – Use at peak hours
– Tapping Renewable energy
• Vehicle to Grid (V2G)
Vehicle to Grid (V2G)
• Based on the following claim:
– “Average car in the US is parked 90% of the time”
• Discharge battery, Supply to grid
• Provide Grid support services for an incentive
• Discharge power of EV is more important than Energy Capacity
• Expectation - Fleet of vehicles
V2G in Grid Support Services
• Peak Load Shaving
– Charge at lower cost times & use at higher cost times
OR
– Discharge to grid during forecasted peak grid hours
– Impact in Grid Stability is less – Incentive is less
V2G in Grid Support Services
• Ancillary Services
– “those services necessary to support the transmission of electric power to maintain reliable operations of the interconnected transmission system.”
– Accounts for 5–10% of total electricity cost
• Positives of V2G: [Kempton]
– quick response time – low standby costs
– low capital cost per kW
V2G in Ancillary Services
1. Spinning Reserves
– Typically provided by generators synchronized to the network
– Used when a generator trips offline or a transmission/distribution facility fails
– Frequency of event - Rare – Response time - ~10 mins
– Duration of the power dispatch - short
V2G in Ancillary Services
V2G as Spinning Reserves - Discussion
– Fleet of V2G as spinning reserves?
– Incentives – High
– Can be communicated to subscribers in ~10mins – Short Duration of use
– How many EVs can provide an equivalent kW of a generator?
– How much power has to be drawn from a vehicle?
– Communication Infrastructure with utility?
V2G in Ancillary Services
2. Frequency-Response Regulation
– Frequency stabilization due to imbalance in load and supply
– Area Control Error (ACE) - instantaneous mismatch between supply and demand – Regulated up or down by generators on
automatic generation control (AGC)
– Frequency of event – Very Frequent (signals sent every 2-6 seconds)
– Response time - Almost real-time
– Duration of the power dispatch – Varying
V2G in Regulation - Discussion
– Pool of already plugged-in V2Gs
– Automatic control to Grids after plug-in
– Setting up EVs difficult – real-time constraints – Frequent charge-discharge cycles
– Effect on Battery lifetime
V2G in Ancillary Services
Other Issues in V2G
• DC – AC conversion
• Aggregation Size requirements
• Sizing up distribution-side transformers
• Optimal discharge power from batteries to Grid
– Utility wants faster response (High power)
– Customers want more battery life (Low power)
EV CHARGING
Outsourcing Battery Charge
● Charging time - ~5-6hrs for full charge at 120V for 40miles (PHEV)
● Battery Swapping
● Analogous to a 'full tank refill'.
● Long Distance, indispensible.
● Transition from PHEVs to pure EVs
● Optimization Problems:
– Number of batteries to stock
– Placement of Station
Impact on Load
Impact on Load
●
Time-Based Pricing
– Expected supply-demand balance
– Peaks at low-price hours
●
Central Utility Control
– Centralized allocation of Charging Slots.
● Static
● Dynamic
Dynamic Slots
● On Demand Slots
● Inputs
– Initial Battery Charge
– Time of Journey
– Destination
● Forecasted Traffic Conditions – User Driving Style
– Regenration Capacity of Vehicle
– Battery Swapping Stations
● Cost of refill (station Dependent)
● Distance from Source
●
Output
– Availability of Charging slot
– Dynamic cost of charging
– Route Selection
● Battery swappers (Long Distance/High cost of Charging)
● Traffic
Charging Service Provider
● CSP
– Parallel to conventional electricity provider.
● Optimize Scheduling
– Regulate Peak power
CSP
Static Charging Slots
● User Charging Profiles
– Diversity in usage (Ex. Night Duty)
– High Penalty or Denial for defaulting (Strict slot following)
– Slot subject to availability.
– Different from time slot pricing.
● Initial battery charge
● Battery level threshold (for V2G)
● Number of cycles – charged/discharged (for V2G)
References
• Letendre. Steven, Paul Denholm, and Peter Lilienthal, 2006, "Electric and Hybrid Vehicles: New Load or New Resource?”, Public Utilities Fortnightly, December 2006
• Kempton, W. and J. Tomić. 2005. "Vehicle to Grid Fundamentals:
Calculating Capacity and Net Revenue", Journal of Power Sources, Volume 144, Issue 1, 1 June 2005
• Sundstrom, O.; Binding, C., “Flexible Charging Optimization for Electric Vehicles Considering Distribution Grid Constraints,” IEEE Transactions on Smart Grid, 3(1), 2012.
• Dickerman L, Harrison J. “A new car, a new grid.” IEEE Power and Energy Magazine 2010;8(2):55–61.
• Taylor J, Maitra A, Alexander M, Brooks D, Duvall M. “Evaluation of the impact of plug-in electric vehicle loading on distribution system
operations.” In: Power & Energy Society General Meeting 2009; 2009.p.
1–6.
