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A method of modifying existing grid-connected inverter models for use in droop-controlled microgrids is presented. The modification involves combination with a model of a grid-forming inverter to accurately represent the coupling between complex power, bus voltage, and frequency. The combination is performed after the individual models are linearized, adding little in terms of computational complexity. The method is applicable to any three-phase inverter operating in a grid-supporting capacity and is scalable for any number of parallel inverters at the same point of connection. To examine the modification process and its effect on model performance, a generic grid-tied inverter model is derived and used as a test case. The newly derived model is modified according to the proposed method. The validity of this process is assessed through comparisons of model predictions—both from before and after modification—to results of hardware experiments. A simple design example is given to demonstrate the application of this process in the design of inverters in distributed-generation-based microgrids. [ABSTRACT FROM PUBLISHER]

In this paper, a new multi-agent control system (MACS) is proposed for smart distribution networks. It can: 1) eliminate the feeders' congestion, 2) globally correct voltage violations, and 3) coordinate the operation of reactive power control devices. In performing its functions, the MACS must prevent overstress on the substation voltage regulator tap changer under all operating conditions, and avoid selective active power curtailment from DG units. This can help to improve reliability, economic revenue, and power quality. A fuzzy rule-based system is employed for decision-making support in MACS. The proposed MACS can achieve the self-healing requirement of smart distribution network. It eliminates feeders' congestion by properly reconfiguring the distribution network. Meanwhile, it amends most of voltage violation problems by coordinated operation of voltage control devices in the distribution system. The MACS overcomes the severe voltage violation problems via distribution network reconfiguration. It is applied to the IEEE 33-bus test feeder. A full dynamic model is constructed using a parallel MATLAB-JADE simulation arrangement. Comparative performance evaluations of the MACS and other schemes are presented under various conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for detecting parasitic dc components in ac grids. The method uses a parallel-connected sensing reactor and a low-cost digital signal processor. From the reactor current, the algorithm derives a sum of even harmonics, considering at the same time their phase shift with respect to the fundamental. The method is insensitive to the measurement noise and offset, and it does not require additional passive filters. Precision better than 100 \muV in 0.4-kV grids is maintained over a wide range of ac voltages. This paper details the detection method, provides the guidelines for the reactor design, and includes the key implementation details related to the signal acquisition—sampling and digital processing. High precision of the new sensor is thoroughly verified on an experimental setup connected to a 0.4-kV grid. [ABSTRACT FROM AUTHOR]

This paper demonstrates a novel cosimulation architecture that integrates hardware testing using power hardware-in-the-loop (PHIL) techniques with larger-scale electric grid models using off-the-shelf non-PHIL software tools. This test bed for distributed integration enables utilities to study the impacts of emerging energy technologies on their system and manufacturers to explore the interactions of new devices with existing and emerging devices on the power system, both without the need to convert existing grid models to a new platform or to conduct in-field trials. This paper describes an implementation of this architecture for testing two residential-scale advanced solar inverters at separate points of common coupling (PCCs). The same hardware setup is tested with two different distribution feeders (IEEE 123 and 8500 node test systems) modeled using GridLAB-D. In addition to simplifying testing with multiple feeders, the architecture demonstrates additional flexibility with hardware testing in one location linked via the Internet to software modeling in a remote location. In testing, the inverter current, real and reactive power, and PCC voltage are well captured by the cosimulation platform. Testing of the inverter advanced control features is currently somewhat limited by the software model time step (1 s) and tested communication latency (24 ms). These limitations could be overcome using faster modeling and communication within the same cosimulation architecture. [ABSTRACT FROM PUBLISHER]