Voltage weak DC microgrid

Abstract

This paper describes the behavior of voltage weak dc microgrids. These are dc microgrids with a relatively small system capacitance. The large amounts of stored energy in the passive component of a network has a considerable effect on the size of the fault currents, control and reliability. The use of a complex control approach to stabilize voltage weak microgrids is a possibility that requires further attention. In this paper, however, a simple way to stabilize such a system is proposed by limiting the rate of change of the power electronic interfaces. The small signal analysis of a three node system is analyzed to see the effect of system capacitance, inductance, resistance and PI and Droop values on the control of the system. The small signal analysis is implemented to estimate the rate of change of loads and the effect of step load changes on the system. In the modeling, a combination two types of loads, Constant power loads, and resistive loads, is used to see the effect of on the system stability. The source and converters are modeled as droop controlled current sources in parallel with capacitors.

Stability of DC Distribution Systems: An Algebraic Derivation

“…With respect to inductance, the results of this paper are congruent with previous works [26,37], where a decrease in inductance leads to increased stability. Furthermore, from the equations in the previous section, it can be observed that the impedance (slope) of the droop controlled source has an upper and lower bound.…”

“…P l is the load's power, U l is the voltage at which the load is linearized, and Z l is the (negative) impedance of the load [26].…”

“…However, this approach assumes unidirectional power flow and measurements are essential for accurate impedance estimations [18,[20][21][22]. Secondly, a root locus analysis of the system can be performed and the locations of the poles can be analyzed [23][24][25][26][27]. This approach does not provide rules for stability and often provides little (mathematical) insight into the origin of the (in)stability.…”

Toward the Universal DC Distribution System

“…The low inertia of DC distribution grids results in strict requirements on the control system [30]. It should be noted that low inertia grids are also a problem for future AC grids.…”

Towards a DC distribution system - opportunities and challenges

“…With low system capacitance the short circuit currents can be significantly reduced, however control of these voltage weak systems is more challenging [22]. Protection selectivity in meshed grids is an important topic especially for fast protection strategies.…”