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In an islanded microgrid consisting of parallel-connected inverters, the interaction between an inverter's output impedance (dominated by the inverter's filter and voltage controller) and the impedance of the distribution network (dominated by the other paralleled inverters' output impedances and the interconnecting power cables) might lead to instability. This paper studies this phenomenon using...
In some situations, utilities may try to “save” the fuse of a circuit following temporary faults by de-energizing the line with the fast operation of an upstream recloser before the fuse is damaged. This fuse-saving practice is accomplished through proper time coordination between a recloser and a fuse. However, the installation of distributed generation (DG) into distribution networks may affect...
Repetitive control can be effective in improving current quality when used with grid-connected inverters. Mathematically, a repetitive controller is equivalent to a parallel combination of resonant controllers with high gain at the fundamental frequency and its harmonics, and accordingly good disturbance rejection can be achieved at these frequencies. To ensure stability, a low-pass filter needs to...
This paper is concerned with the control of a line interactive Uninterruptable Power Supply (UPS) system in a Microgrid. In grid connected mode, power can be imported from the grid to charge the battery or it can be injected into the grid to boost the power supplied by the Microgrid. In island mode, the UPS supplies local critical load in parallel with other sources. Power flow is controlled using...
This paper is concerned with the design and practical implementation of a robust digital current controller for a three-phase voltage source grid-connected interleaved inverter. Each phase consists of 5 half-bridge channels connected in parallel. Due to the current ripple cancellation of the interleaving topology, only small output filter capacitors are required which provide high impedance to grid...
An effective introduction of distributed generation (DG) into existing distribution networks (DNs) calls for a review of traditional power system protection concepts and strategies. New issues such as activeness of DNs and bidirectional power flow require new protection solutions. This paper discusses protection issues and challenges arising from the integration of DG into the grid. It presents and...
This paper investigates semiconductor and DC-link capacitor losses in two two-level and two three-level voltage source inverters. The components of the four inverters are selected to have appropriate voltage and current ratings. Analytical expressions for semiconductor losses are reviewed and expressions for DC link capacitor losses are derived for all topologies. Three-level inverters are found to...
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