Comparison between alternative droop control strategy, modified droop method and control algorithm technique for parallel-connected converters

Abstract

Most of the active current sharing methods are based on a communication network. The communication link is also used with the improved droop control methods to achieve a precise load current sharing and regulate the voltage at the common DC bus. Conversely, the conventional droop method that is considered a decentralized method becomes more attractive for controlling parallel-connected converters in DC microgrids. The conventional droop methods' main drawbacks are associated with the unequal load current sharing and voltage deviation at the common DC bus. In this paper, the modified droop method as a conventional droop method is augmented with a virtual droop and adaptive voltage control gains to improve the load current sharing and the voltage regulation, respectively. In contrast with other improved droop approaches, the control approach proposed in the paper does not require a communication link to exchange information between parallel modules. Instead, it uses the converters' theoretical load regulation characteristics to estimate the voltage set point for each converter locally. The proposed virtual resistive gain manipulates the modified droop method to regulate each module's droop gain, which ensures equal current sharing. The proposed method also eliminates the tradeoff between current sharing difference and voltage regulation by implementing the adaptive voltage control, which compares the estimated voltage at the point of common coupling with the rated bus value and adjusts the droop gains based on the compared values to ensure a constant voltage at various load conditions. The load current sharing and voltage restoration improvements of the proposed method versus the modified droop method and the control algorithm technique are observed in this paper. The proposed method's effectiveness is demonstrated by MATLAB/Simulink simulation and validated by an experimental prototype.