Evaluation index of energy consumption economy of pure electric vehicle

There are qualitative differences between pure electric vehicles and fuel vehicles in terms of drive systems and power sources, which leads to great differences in energy consumption and economic evaluation indicators and evaluation methods between the two vehicles. Power batteries are the only power source for pure electric vehicles, and the energy storage density cannot reach the level of fuel, which shortens the driving range of the vehicle. Therefore, reducing energy consumption rate and improving energy consumption economy are more important for pure electric vehicles.

The commonly used indicators for the economic evaluation of energy consumption of pure electric vehicles are based on a certain speed or cycle driving conditions, and are measured by the energy consumption of a certain mileage of the vehicle, mainly including continuous driving range and energy consumption per unit mileage.

The driving range is the continuous driving range of a pure electric vehicle battery pack after it is fully charged, which can be divided into constant speed driving range and cyclic working condition continuous driving range. This indicator is of positive significance for the comprehensive evaluation of battery packs, motors and transmission efficiency of pure electric vehicles, and the practicability of electric vehicles. However, this indicator is related to the battery capacity and battery level of the battery assembly of pure electric vehicles, and is not comparable between different models and the same models equipped with different capacity battery packs. Even if the same vehicle is equipped with the same capacity and the same battery, the driving range will fluctuate due to the influence of the battery pack status, weather, environmental factors and other operating conditions.

The energy consumption per unit mileage can be further divided into the AC energy consumption rate of the grid per unit mileage and the DC energy consumption rate of the battery pack. Among them, the AC energy consumption rate is affected by the efficiency of different types of charging equipment; the DC energy consumption rate is only based on the energy state of the on-board battery pack, which is free from the influence of the charger, and can more directly reflect the actual performance of pure electric vehicles.

Alternating current energy consumption refers to the value obtained by dividing the electric energy obtained from the power grid by the continuous driving range after a pure electric vehicle has recharged the power battery to the capacity before the test after a prescribed test cycle, namely
Ei=Ed/S

In the formula, Ei (W.h/km) is the AC energy consumption rate of pure electric vehicles; Ed (W.h) is the energy from the grid during the charging of the battery.

The cyclic driving range refers to the maximum driving range that can be achieved after being fully charged and based on the requirements of certain sports conditions. The sports conditions are mainly New European driving cycle (NEDC) cycle conditions.

NEDC cycle conditions of pure electric vehicles consist of 4 urban cycles and 1 suburban cycle. Theoretically, the test distance is 11.022km, and the test time is 19min40s, as shown in Figure 1. In the figure, ① represents the urban cycle, ② represents the suburban cycle, and ③ represents the basic urban cycle.
The basic circulating conditions in the urban area are shown in Figure 2.

Evaluation index of energy consumption economy of pure electric vehicle
Figure 1 NEDC cycle conditions of pure electric vehicles
Evaluation index of energy consumption economy of pure electric vehicle
Figure 2 Basic cycle conditions in the urban area

A basic urban cycle time is 195s, of which parking is 60s, accounting for 30.77% of the cycle time; acceleration is 42s, accounting for 21.54% of the cycle time; constant speed is 59s, accounting for 30.26%; deceleration is 34s, accounting for 17.44%. The theoretical driving distance of a basic city cycle is 1017m, and the average speed is 18.77km/h.
Figure 3 shows the basic circulation conditions in the suburbs.

Evaluation index of energy consumption economy of pure electric vehicle
Figure 3 Basic cycle conditions in suburbs

A suburban cycle time is 400s, of which parking is 40s, accounting for 10%; acceleration is 109s, accounting for 27.25%; constant speed is 209s, accounting for 52.25%; deceleration is 42s, accounting for 10.50%, the theoretical driving distance of a suburban cycle is 6956m, and the average speed is 62.60km/h.