The discussion has been simplified to allow rapid estimates of bulk capacitance. Several other factors affect the system performance and can be taken into account when selecting bulk capacitors for a motor drive design. These include:

Frequency response – Capacitor frequency response varies between types of capacitors and between capacitors with different values. Often, the recommendation is to provide more than one value of capacitor on the motor power supply. The larger value capacitors typically provide the best low-frequency response, while smaller value capacitors provide better high-frequency response.

Capacitor type – There is a wide variation of capacitor types; in general for the large values we discuss here, electrolytic capacitors are normally preferred. But even within electrolytic capacitors there are some chemistry enhancements which improve the durability and other characteristics of the component, including variation in ESR. For smaller values, ceramic capacitors can be preferred. Capacitor vendors have information on selection criteria for the vendors products.

PWM duty cycle – If the motor operates continuously without pulse-width modulation, many of the concerns with supply variation are less relevant. Conversely, if the duty cycle is about 50%, this is assumed to be the worst case conditions. Other cases, either very low duty cycle (for example, 10% on time) or very high duty cycle (for example, 90% on time) do not require the same level of bulk capacitance we have discussed.