Droop-controlled inverters are thought to be an excellent interface for distributed generation of future power grids. Ease of installation, fully decentralized power sharing and simple procedures for expansion/reconfiguration make this type of control attractive for practical applications, in particular for microgrids. However, such microgrids appear to exhibit instabilities severely limiting the allowed ranges of control settings. Moreover, modelling approaches based on time-scale separation, that were successfully used for decades for stability assessment of conventional power systems, appeared to be inappropriate for microgrids, calling for new methods, specific to microgrids, to be developed. In this paper, we present a method for tuning inverter control parameters (namely droop coefficients and virtual impedance) that guarantees stable operation under arbitrary interconnection of inverters to the grid. The proposed method lays the foundation for plug-and-play architectures for inverter-based microgrids.

In this paper, a hybrid measurement and model-based method is proposed which can estimate the dynamic state Jacobian matrix in near real-time. The proposed method is computationally efficient and robust to the variation of network topology. A numerical example is given to show that the proposed method is able to provide good estimation for the dynamic state Jacobian matrix and is superior to the model-based method under undetectable network topology change. The proposed method may also help identify big discrepancy in the assumed network model.

High-penetration levels of distributed photovoltaic (PV) generation on an electrical distribution circuit present several challenges and opportunities for distribution utilities. Rapidly varying irradiance conditions may cause voltage sags and swells that cannot be compensated by slowly responding utility equipment resulting in a degradation of power quality. Although not permitted under current standards for interconnection of distributed generation, fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions. As side benefit, the control of reactive power injection at each PV inverter provides an opportunity and a new tool for distribution utilities to optimize the performance of distribution circuits, e.g., by minimizing thermal losses. We discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters. An important design decision that weighs on the speed and quality of communication required is whether the control should be centralized or distributed (i.e., local). In general, we find that local control schemes are able to maintain voltage within acceptable bounds. We consider the benefits of choosing different local variables on which to control and how the control system can be continuously tuned between robust voltage control, suitable for daytime operation when circuit conditions can change rapidly, and loss minimization better suited for nighttime operation.

We present information-theory analysis of the tradeoff between bit-error rate improvement and the data-rate loss using skewed channel coding to suppress pattern-dependent errors in digital communications. Without loss of generality, we apply developed general theory to the particular example of a high-speed fiber communication system with a strong patterning effect