Improvement of active power sharing ratio of P/V droop controllers in low-voltage islanded microgrids

Abstract

Abstract-Microgrids provide a coordinated integration of distributed generation units in the electrical power system. By operating in islanded mode, they can increase the reliability of the system or electrify remote areas. For the power sharing and voltage control in low-voltage microgrids, active power/grid voltage droop control is highly suitable. In order to optimize the integration of renewable energy sources in the microgrid, a variant of this droop control, the voltage-based droop (VBD) control, has been presented. A well-known concern about droop controllers is the inherent trade-off between voltage control and power sharing. Therefore, in this paper, an additional control loop is included in the VBD control to improve the active power sharing ratio. In this way, accurate power sharing is achieved, i.e., the DG units respond to load changes exactly according to their droops. Although this modification relies on communication, it does not jeopardize the reliability of the microgrid as if the communication is lost, the basic VBD control still ensures a stable microgrid operation, while operating without the need for communication.

A New Droop Coefficient Design Method for Accurate Power-Sharing in VSC-MTDC Systems

“…In practice, due to the line resistance and dc voltage deviation, the VSCs do not behave rigidly according to the preset characteristics [26], which means the output powers of the VSCs are not inversely proportional to the droop coefficients. Various traditional methods such as [24], [25], attempt to compensate the voltage drop by regulating the dc voltage and thereby reduce the power-sharing error caused by the line resistance. However, the relationship between the powersharing, the droop coefficient and the line resistance is rarely discussed.…”

“…By converting the droop coefficient k into the form of (13), the limit on the virtual resistance can be obtained as r v ≤ 10.52. The length of the dc line in this example is 200 km and a typical value of resistivity of a dc line is 0.02 /km [25] and so the total line resistance is set at R = 4 . Obviously, a line resistance of 4 cannot be ignored in comparison to the maximum virtual resistance r v of 10.52 , which is implied by the minimum droop coefficient.…”

A Virtual Inertia-Based Power Feedforward Control Strategy for an Energy Router in a Direct Current Microgrid Application

“…where SET P is the DC microgrid active power reference, L _n U is the rated LVDC bus voltage, M D is the DC microgrid virtual damping coefficient, and the expression of P/V droop control is[24] …”