An Integrated Approach to Maximize Efficiency and Reliability of Grid Connected Distributed Energy Sources



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The emergence of local-generation as a technically sound solution for the reliability concerns of the existing power grid has lead in recent times to the concept of microgrid. The microgrid is a network of low-voltage (LV) interconnected loads and distributed-energy resources (DERs) with clearly-defined electrical boundaries. The distributed generation majority rely on either photovoltaic (PV) or wind turbines producing imperfectly-predictable variable power, making it harder for the system operators to match generation and load at every instant. This has created a significant interest in optimal grid integration and control of DER units in terms of efficiency maximization and cost minimization by implementing maximum power point tracking (MPPT) control.

A new scanning method of MPPT control for grid-connected PV systems is proposed and studied. This technique displays high tracking efficiency with low tracking time. The control tracks the global maxima under partial shading conditions and provides a non-oscillatory response under steady-state operation. The performance of the proposed control is compared with perturb and observe (P&O) and incremental conductance (INC) control under varying operating conditions. The simulation and experimental results clearly prove the effectiveness of the proposed MPPT control.

For wind energy conversion systems (WECS) a new adaptive sensor-less MPPT control is proposed. The controller overcomes the trade-off between step size and tracking accuracy, providing a fast tracking response along with avoiding the inconsistent generator-converter efficiency problems. The performance of the proposed control is validated through simulation and experimental results in comparison with P&O MPPT control under varying wind conditions.

The DERs are connected to the microgrid with the help of power electronics interface such as AC-DC, DC-DC and DC-AC converters. The DC-DC and DC-AC converters are coupled with the help of large electrolytic capacitors. The reliability of the system is maximized by reducing the required DC link capacitance and replacing the electrolytic capacitors with high cost and reliable film capacitors. A new DC link reduction control to reduce the required DC link capacitance is proposed. The performance of the proposed control is validated through simulation results for grid connected PV and WECS under reduced DC link capacitance.



MPPT, DC-Link Reduction Control


Portions of this document appear in: Kotti, Radhakrishna, and Wajiha Shireen. "Fast converging MPPT control of photovoltaic systems under partial shading conditions." In 2012 IEEE International Conference on Power Electronics, Drives and Energy Systems (PEDES), pp. 1-6. IEEE, 2012. And in: Kotti, Radhakrishna, Shyam Janakiraman, and Wajiha Shireen. "Adaptive sensorless maximum power point tracking control for PMSG wind energy conversion systems." In 2014 IEEE 15th Workshop on Control and Modeling for Power Electronics (COMPEL), pp. 1-8. IEEE, 2014. And in: Kotti, Radhakrishna, and Wajiha Shireen. "Maximum power point tracking of a variable speed PMSG wind power system with DC link reduction technique." In 2014 IEEE PES General Meeting| Conference & Exposition, pp. 1-5. IEEE, 2014. And in: Kotti, Radhakrishna, and Wajiha Shireen. "An efficient robust MPPT control for grid-connected photovoltaic systems with reduced DC link capacitance." In IECON 2014-40th Annual Conference of the IEEE Industrial Electronics Society, pp. 5462-5467. IEEE, 2014.