In this paper, an analytical expression for the DC bus harmonics on the input capacitor, caused by a three phase pulse width modulation (PWM) inverter of a high speed motor drive system, is derived. As the result, we found that the parasitic line inductance between the battery and the input capacitor, and the input capacitor are indirectly proportional. We can achieve the calculation method of the voltage ripple of the input capacitor including the parasitic components. Furthermore, the voltage ripple of the battery can be calculated by the switching function using the Bessel function.