Electric distribution systems around the world are seeing an increasing number of utility-owned and non-utility-owned (customer-owned) intelligent devices and systems being deployed. New deployments of utility-owned assets include self-healing systems, microgrids, and distribution automation. Non-utilityowned assets include solar photovoltaic generation, behind-the-meter energy storage systems, and electric vehicles. While these deployments provide potential data and control points, the existing centralized control architectures do not have the flexibility or the scalability to integrate the increasing number or variety of devices. The communication bandwidth, latency, and the scalability of a centralized control architecture limit the ability of these new devices and systems from being engaged as active resources. This paper presents a standards-based architecture for the distributed power system controls, which increases operational flexibility by coordinating centralized and distributed control systems. The system actively engages utility and non-utility assets using a distributed architecture to increase reliability during normal operations and resiliency during extreme events. Results from laboratory testing and preliminary field implementations, as well as the details of an ongoing full-scale implementation at Duke Energy, are presented. INDEX TERMS Distributed control, microgrids, power distribution, power system protection, smart grids.
This paper presents a new multi-level DC-AC-AC converter topology for medium voltage grid integration of Megawatt (MW) scale utility photovoltaic (PV) plants. It is envisioned that a large PV field is divided into many zones, each comprising of two PV arrays. The number of zones depends on the voltage of the grid with which it is interfaced. In the proposed approach, zonal power balancing is achieved by employing a current-sharing technique. The power conversion architecture consists of an IGBT based full-bridge inverter feeding a medium frequency (MF) transformer with three secondary windings. The voltages at the transformer secondaries are then converted to three phase line frequency AC by three, full-bridge AC-AC converters. This also eliminates the 2 nd harmonic power from the DC bus, thereby reducing the capacitor size. By stacking several such modules in series, a high quality multilevel medium voltage output is generated. Further, the bulky line frequency utility interface transformer is eliminated. A new control method is proposed for the series connected modules during partial shading while minimizing the switch ratings. This paper presents the analysis, design example and simulation of a 10 MW PV system with preliminary experimental results on a laboratory prototype.
A series resonant matrix converter (MC) based topology for high power electric vehicle (EV) battery charging is presented. The system performs DC fast charging and is capable of bidirectional power flow, for V2G (vehicle-to-grid) applications. The proposed topology can be divided into three sections: (i) a front-end 3x1 matrix converter, (ii) L r C r series resonant tank and high frequency (HF) transformer, and (iii) a single phase PWM rectifier. The matrix converter takes a three phase line frequency voltage and produces a high frequency (14.94 kHz) AC output. The resonant tank frequency is set to 13.7 kHz and helps to achieve zero voltage switching (ZVS) turn ON and low turn OFF switching losses. The secondary of the transformer is then interfaced to the EV battery bank through a PWM rectifier. The advantages of such a system include high efficiency due to soft switching operation, low VA transformer ratings due to resonant operation, and high power density due to the absence of electrolytic capacitors. A design example rated 30 kW, which charges a 500 V battery system, is presented. Analysis and simulation results demonstrate the performance of the proposed bidirectional topology. Preliminary experimental results are provided for a scaled down prototype operating at 500 W using a 15 kHz ferrite transformer.
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