
Uninterruptible Power Supplies 18-11
On the other hand, the droop method has been studied extensively in parallel DC converters. In these
cases, resistive output impedance is enforced easily by subtracting a proportional term of the output
current from the voltage reference. e resistive droop method can be applied to parallel UPS inverters.
e advantages of such an approach are the following: (1) the overall system is more damped; (2) it provides
automatic harmonic current sharing; and (3) phase errors barely aect active power sharing.
However, although the output impedance of the inverter can be well established, the line impedance
is un