Droop Control In DC Microgrid Research Articles

An Adaptive Discrete Piecewise Droop Control in DC Microgrids

An Adaptive Discrete Piecewise Droop Control in DC Microgrids

Autonomous transient power management strategy based on improved droop control for DC microgrid

Autonomous transient power management strategy based on improved droop control for DC microgrid

Design of Nonlinear Droop Control in DC Microgrid for Desired Voltage Regulation and Current Sharing Accuracy

It is well known that there is a design tradeoff between voltage regulation and load current sharing in conventional linear droop control for several parallel-connected distributed sources in a DC microgrid. To improve both performance areas, this article proposes a design method to identify the nonlinear droop curve coefficient with the desired bus voltage regulation and current sharing accuracy in a specified heavy load range, while a linear droop function with a negative droop resistance is used to tighten the bus voltage regulation in the light load range. The design procedure of load boundary and the effect of negative droop resistances on the system stability are analyzed in detail. Also, a boost-up and curve-fitting method can further improve the voltage regulation and achieve smooth transition between light load and heavy load. In this way, no additional voltage compensation loop is needed. Two parallel-connected DC converters are finally built to verify the theoretical analysis.

Impedance Detection Based on Ripple Analysis and Current Sharing Control in DC Microgrid

In the operation of DC micro grid, the uniform load distribution is beneficial to the stable operation of the system and prolongs the service life of the system. In order to solve the influence of line impedance on traditional droop control in DC micro-grid, an impedance detection method based on ripple analysis and the structural characteristics of the DC micro-grid system is proposed. The high-frequency harmonic component of microgrid output current and voltage is mainly from the transistor switching frequency. By using the Fourier transform to analyze the high-frequency harmonic component of the voltage and current detected by the converter, the impedance information is obtained, and then the droop control is compensated base on it. In this paper, the compensation method is extended to the application of multiple devices in parallel. This method does not directly operate the system, so it has done no harm to the power quality. Finally, the feasibility of the proposed method in normal working conditions and its effectiveness in the case of communication interruption and load change is verified by RT-LAB hardware in loop experiment.

Decentralized Droop Control in DC Microgrids Based on a Frequency Injection Approach

Power sharing control among grid forming dc sources employing a conventional voltage droop approach meets inaccurate load sharing and unacceptable voltage regulation performance. Thereby, communication-based secondary and supervisory controllers have been presented to overcome the aforementioned issues. Furthermore, with the aim of eliminating communication system, frequency-based droop approaches have been introduced for low-voltage dc grids where the frequency of the superimposed ac signal onto the dc voltage is proportional to the output power. However, in reality, dc grid structures can be applied to medium and high voltage applications with different X/R ratios. This paper generalizes the frequency-based droop scheme for dc microgrids with different low, medium, and high X/R ratios. Obtained simulation and experiment results demonstrate the effectiveness of the proposed control method.

Power-Based Droop Control in DC Microgrids Enabling Seamless Disconnection From Upstream Grids

This paper proposes a local power-based droop controller for distributed energy resource converters in dc microgrids that are connected to upstream grids by grid-interface converters. During normal operation, the grid-interface converter imposes the microgrid bus voltage, and the proposed controller allows power flow regulation at distributed energy resource converters’ output. On the other hand, during abnormal operation of the grid-interface converter (e.g., due to faults in the upstream grid), the proposed controller allows bus voltage regulation by droop control. Notably, the controller can autonomously convert from power flow control to droop control, without any need of bus voltage variation detection schemes or communication with other microgrid components, which enables seamless transitions between these two modes of operation. Considering distributed energy resource converters employing the power-based droop control, the operation modes of a single converter and of the whole microgrid are defined and investigated herein. The controller design is also introduced. Furthermore, the power sharing performance of this control approach is analyzed and compared with that of classical droop control. The experimental results from a laboratory-scale dc microgrid prototype are reported to show the final performances of the proposed power-based droop control.