Motor Drive Filter Capacitor Selection

Filter capacitor selection in the circuit needs to consider several aspects: capacitor voltage, operating temperature, capacity and so on. Theoretically speaking, the larger the power filter capacitor is, the better. Generally, the large capacitor filters low-frequency waves, and the small capacitor filters high-frequency waves. In order to obtain a larger filter frequency band, it is possible to connect two capacitors, one large and one small, in parallel, generally requiring a difference of more than two orders of magnitude. In the power supply design, the filter capacitor selection principle is C≥2.5T/R. In practical applications, C≥5T/R is generally selected.

Taking the filter capacitor in the motor drive application as an example, the input filter capacitor capacity is directly related to the drive voltage and the maximum power of the driver. Some calculations are required. If the capacitor capacity is too small, the drive performance is insufficient; and the capacity is insufficient. Too large increases the manufacturing cost. In engineering applications, there is a rule of thumb: the value of the filter capacitor is equal to the value of the drive power. However, it should be noted that this is only for single-phase 220V AC full-wave rectification drive applications.

First of all, from the RC time constant Ï„ of the capacitor, the resistance: The greater the Ï„, the smoother the voltage across the R, and the less the ripple voltage for the pulsating power supply. In engineering, ripple requirements can be met when the RC time constant satisfies the following conditions. T is the period of the pulsating power supply, and the cycle T after the full-wave rectification of the 50 Hz mains is: 10 mS.

Therefore, the above two formulas can be obtained; R is the equivalent load resistance; C is the filter capacitor capacity. Therefore, as long as the equivalent load resistance of the motor driver is obtained, the required capacitance of the filter capacitor can be calculated.