Page 5 - Industrial Technology Extra 7th September 2020
P. 5
current rise is a function of the motor inductance giving rise to current ripple. The ripple is directly
and total resistance. Ideal design intuition is to proportional to the applied frequency and as the
decide the PWM frequency so as to allow sufficient frequency of the PWM is increased further, the
time for the current to reach its steady state for each ripple affect reduces to an acceptable range. This
cycle. But it is not always the right approach. current ripple has a number of detrimental impacts
If the PWM frequency is increased beyond this on motor performance, including non-linear torque
threshold value, there is insufficient time for the behaviour, since output torque is proportional to
current to reach its steady state, and the current current. Hence, the frequency is chosen such that
oscillates between two non-steady state values, the torque ripple doesn't impact the application
September 2020 • INDUSTRIAL TECHNOLOGY EXTRA • p5
