Читать книгу Analysis and Control of Electric Drives - Ned Mohan - Страница 47

The drag force is f_L = 0.046 C_w Au ² and the power required at the constant speed, from Eq. (2-6), is P = f_L u where the speed is expressed in m/s. Table 2-1 lists the drag force and the power required at various speeds for the two vehicles. Since the drag force F_L depends on the square of the speed, the power depends on the cube of the speed.

Traveling at 50 km/h, compared to 100 km/h, requires 1/8th of the power, but it takes twice as long to reach the destination. Therefore, the energy required at 50 km/h would be 1/4th that at 100 km/h.

Fig. 2-10 Actual and linearized friction characteristics.

TABLE 2-1 Drag Force and the Power Required

Vehicle	u = 50 km/h	u = 100 km/h
Cw = 0.3	fL = 62.06 N	P = 0.86 kW	fL = 248.2 N	P = 6.9 kW
Cw = 0.5	fL = 103.4 N	P = 1.44 kW	fL = 413.7 N	P = 11.5 kW