Circulating current produced in a system of two inverters connected in parallel due to a difference between the zero-vector parameters

This paper analyzes the imbalances that produce circulating current in a system of two three-phase VSI with SVPWM modulation that, sharing the same DC link, is connected to a grid without galvanic isolation. This analysis has identified a principal imbalance: the difference between the zero-vector parameters of the two inverters. This imbalance is specific to the SVPWM modulation. The study proposes the correction of the imbalance by measurement algorithms and Proportional Integral Control (using the Ziegler Nichols method to tune the controller), in order to reduce or eliminate the circulation current and increase system performance. It provides a method that does not use an equivalent circuit or a model, determining the value of the imbalance directly and through a system output signal. It has been used PSIM simulation program (version "9.0.3.400"), and the simulations have been taken into account an "ideal" environment. For all simulated cases, this paper analyzes the principal magnitudes and, to obtain the conclusions, shows power data (input power, output power and system performance), in uncontrolled and controlled operation. The simulations allow verifying the goodness of the proposed methods to detect, quantify, control and correct the imbalance, and to improve the system performance.

Circulating current produced in a system of two inverters connected in parallel due to a difference between the zero-vector parameters Articles