Performance of Electrical Vehicles P M V Subbarao Professor Mechanical Engineering Department Eligibility of A Reliable Horse …

Vehicle Performance Basic vehicle performance variables are: Maximum Cruising Speed Gradeability Pick-up (Acceleration) The maximum speed of a vehicle can be easily found by the intersection point of the tractive effort curve with the resistance curve (rolling resistance plus aerodynamic drag) in the tractive effort vs. vehicle speed diagram.

Tractive Effort Required Vs Vehicle Speed Instantaneous Tractive Effort demanded by a vehicle:

Tractive Effort Available Vs Vehicle Speed InstantaneousTractive Effort made available by Power unit:

Tractive effort vs. vehicle speed with a traction motor of x =2 and No Gear box.

Proposed configurations for an Electric Vehicle

Tractive effort vs. vehicle speed with a traction motor of x =2 and three-gear transmission

Tractive effort vs. vehicle speed with a traction motor of x =4

The Type of Prime Mover for Light Vehicle Sales in Two Decades

Functional block diagram of a typical electric propulsion system

Motors in 2017 EVS Tesla Models S & X : Three phase, four pole AC induction motor with copper rotor Drive inverter with variable frequency drive and regenerative braking system.

Energy Consumption The energy consumption per unit distance in kWh/km is generally used to evaluate the vehicle energy consumption. Energy consumption is an integration of the power output at the battery terminals. For propelling, the battery power output is equal to resistance power and any power losses in the transmission and the motor drive, including power losses in electronics. The power losses in transmission and motor drive are represented by their efficiencies ηt and ηm respectively. Thus, the battery power output can be expressed as

City Cycle : Total traction energy and energies consumed by drags and brakin

Regeneration The major advantage of EV is the possibility of regeneration during breaking. When regenerative braking is effective on an EV, a part of that braking energy is recovered by operating the motor drive as a generator and restoring it into the batteries. The regenerative braking power at the battery terminals can also be expressed as where road grade or deceleration (dV/dt) or both of them are negative. α (0 < α <1) is the fraction of the total braking energy that can be applied by the electric motor, called the regenerative braking factor

Net Energy Consumption The regenerative braking factor α is a function of the applied braking strength and the design of the power train. The net energy consumption from the batteries is

Travel Range The travelling distance between two charges is called effective travel range. This is determined by the total energy carried by the batteries, the resistance power, and the effectiveness of the regenerative braking (α). The efficiency of a traction motor varies with its operating points on the speed–torque, where the most efficient operating area exists. In power train design, this area should overlap with or at least be as close as possible to the area of the greatest operation.

The Model X's all-wheel drive system uses two motors (one for the front and the other for the rear wheels). The Tesla Model X 100D features an official EPA rated range of up to 295 mi, and a European NEDC testing cycle estimated range of 565 km.

Battery Technologies The viable EV batteries consist of the lead-acid battery, nickel based batteries such as nickel/iron, nickel/cadmium, and nickel–metal hydride batteries, and lithium-based batteries such as lithium polymer and lithium-ion batteries. The energy or power losses during battery discharging and charging appear in the form of voltage loss. Thus, the efficiency of the battery during discharging and charging can be defined at any operating point as the ratio of the cell operating voltage to the thermodynamic voltage.

Energy Efficiency of A battery The efficiency of the battery during discharging: The efficiency of the battery during charging:

Selection of Storage Technology Energy density Lead-acid batteries 100 kJ/kg (30 W-h/kg) Lithium-ion batteries 600 kJ/kg Compressed air, 10 MPa 80 kJ/kg (not including tank) Conventional capacitors 0.2 kJ/kg Ultracapacitors 20 kJ/kg Flywheels 100 kJ/kg Gasoline 43000 kJ/kg

Energy and Power Needs Rate is a problem. Example: refill a gas tank with 15 gal in 5 min. The energy rate is roughly that of 20 major campus buildings! It is costly and problematic to fill batteries quickly.