Effective Dithering Technique for EMI Reduction in Three Phase DC/AC Inverters

Three phase DC/AC inverters in power electronic applications produce electromagnetic interference (EMI) due to switching of the power semiconductor devices at high frequencies. Dithering the switching frequency is one of the effective and low cost tools to reduce EMI. To maximize the usefulness of the dithering process, the effect of each of its parameters on the EMI reduction needs to be understood. In this paper, the parameters of triangular periodic dithering are investigated to find their values in minimizing EMI for three phase DC/AC inverters. The paper presents that, by increasing the amplitude of the dithering signal and selecting its frequency to be equal to the inverter voltage frequency, the EMI can be reduced. Moreover, by selecting a phase shift of pi/12 between the dithering signal and any of the inverter currents, the EMI is minimized compared to other phase shift amounts. The proposed technique is validated through simulation studies

Multi-Channel-Based Microgrid for Reliable Operation and Load Sharing

This paper presents a novel approach to distribute available power among critical and non-critical loads in microgrids. The approach is based on supplying power over a number of channels with distinguishable frequencies where loads could be served by these channels according to their level of importance. The multi-channel scheme not only offers flexibility to supply loads but also to share power among adjacent microgrids. The control system, which can deal with multi-channel scheme, is presented and different applications that can be offered whereby are discussed. The number of channels that can be supplied by any inverter is determined based on the parameters of the used filter. Moreover, the power exchange efficiencies over the active channels at various power levels are determined and approximated formulas for quick evaluation are presented. To verify the proposed solution performance, simulation and experimental studies were performed. The obtained results demonstrate the effectiveness of using multi-channel scheme for power exchange in microgrid and also confirm the accuracy of the provided formula related to power exchange efficiencies

Optimized Droop Control Parameters for Effective Load Sharing and Voltage Regulation in DC Microgrids

Droop control method is a widely used technique for achieving load sharing in DC microgrid applications. Virtual output impedance (or droop gain) and voltage reference are the main control parameters typically selected based on the power ratings of the sources for proper load sharing. The performance of droop controller is affected significantly by the voltage drops across the transmission line impedances, resulting in a load sharing error and voltage degradation across the microgrid. In this article, a new optimization procedure is proposed to find the optimal droop parameters such that the effect of the line impedances is minimized. An optimization problem along with the required constrains is formulated as the combination of current sharing errors as well as the voltage degradation for various loading conditions. Particle swarm-based technique is then used to provide a solution for this optimization problem. The performance of the droop controller with the optimal droop parameters is verified through a simulation case study implemented on the MATLAB/Simulink environment

Efficient Single Phase Power Factor Improvement Strategy for Microgrid Operation

A strategy to improve the power factor (PF) at the point of common coupling (PCC) for microgrid applications is presented in this paper. The position of the compensating unit is selected to correct the power factor and reduce the harmonic levels of the grid current and PCC voltage in microgrid connected distributed renewable energy sources. The proposed compensation system for power factor improvement (PFI) can be operated dynamically for both linear and nonlinear loads. Fast and efficient algorithm for phase detection in the presence of harmonics has been incorporated to the proposed system. Finally simulation and experimental results are presented to verify the effectiveness of proposed compensation unit

Importance of energy storage system in the smart grid

Recent advances in energy storage and power electronics technologies are offering promising solutions to improve the grid resilience and allow higher renewable energy penetration. Energy storage systems (ESSs) act as energy buffers to aid the operations and lifetime of the grid assets and bridge the gap between supply and demand for renewable energy generation. Currently, there are more than 650 active ESS projects around the globe with a total capacity of 3.83 GW, representing a significant market potential for companies. To that end, this chapter aims to provide a comprehensive overview and classification of ESSs, underlying technologies and working principles, current and future applications, and economic analysis

A Novel Load-Flow Analysis for Stable and Optimized Microgrid Operation

This paper proposes a novel load-flow analysis (LFA) algorithm for droop-based islanded microgrids (DBIM). The standard LFA is not applicable for DBIM due to the absence of a node with fixed reference voltage. As the voltage in the islanded microgrid depends on the droop relations, these relations are included as part of the load-flow equations. The proposed LFA is used with particle swarm optimization to select the droop parameters that optimize the reactive power sharing. Voltage compensation terms are also suggested to improve voltage regulation. By using the proposed LFA, a modeling procedure is suggested to check the stability and stabilize the microgrid. The effectiveness of the proposed methods is verified through different simulation studies

Reliability and Cost Analysis of Solar Photovoltaic and Fuel Cell Based Microgrids

Maintaining a reliable operation in microgrids has significant importance. One factor required for the reliable microgrid operation is to keep certain energy reserve without sacrificing the cost for satisfying any load variation. Reliability and cost optimization of photovoltaic and fuel cell based microgrid system is investigated in this paper. A typical residential load is considered in order to introduce an optimal power sharing approach for cost effective and reliable system operation. A nonlinear frequency droop scheme is then applied to achieve the optimization objectives at the intended operating scenarios. The simulation and experimental results are presented to verify the effectiveness of the proposed technique