Recent improvements in magnetic material characteristics and switching devices have generated a possibility to replace the electrical buses with highfrequency magnetic links in microgrids. Multiwinding transformers (MWTs) as magnetic links can effectively reduce the number of conversion stages of renewable energy system by adjusting turn ratio of windings according to the source voltage level. Other advantages are galvanic isolation, bidirectional power flow capability, and simultaneous power transfer between multiple ports. Despite the benefits, design, and characterization of MWTs are relatively complex due to their structural complexity and cross-coupling effects. This paper presents all stages of numerical design, prototyping, and characterization of an MWT for microgrid application. To design the transformer for certain value of parameters, the reluctance network method is employed. Due to the iterative nature of transformer design, it presented less computation time and reasonable accuracy. A prototype of designed transformer is implemented using amorphous magnetic materials. A set of experimental tests are conducted to measure the magnetic characteristics of the core and series coupling and open-circuit tests are applied to measure the transformer parameters. A comparison between the simulation and experimental test results under different loads within the medium-frequency range validated both design and modeling procedures.

In this paper a grid-tied residential smart microgrid topology is proposed which integrates energies of a PV, a fuel cell and a battery bank to supply the local loads through a combination of electric and magnetic buses. In contrast to multiple-converter based micro-grids with a common electric bus, using a multi-port converter with a common magnetic bus can effectively reduce the number of voltage conversion stages, size and cost of the renewable energy system and isolates the conversion ports. The resultant topology utilizes a centralized system level control which leads to the faster and more flexible energy management. The proposed micro-grid is able to operate in multiple grid-connected and off-grid operation modes. A fuzzy controlled energy management unit (EMU) is designed to select the appropriate operation mode considering both real-time and long-term-predicted data of the energy generation and consumption. A mode transition process is designed to smooth the mode variation by using a state transition diagram and bridging modes. To improve the microgrid operation performance, appropriate control techniques such as synchronized bus-voltage balance are used. A prototype of the proposed micro-grid and the EMU are developed and experimentally tested for three different energy management scenarios. Energy distribution and energy cost analysis are performed for each scenario to validate the proposed control method.

In this paper, a novel energy management system with two operating horizons is proposed for a residential micro-grid application. The micro-grid utilises the energies of a photovoltaic (PV), a fuel cell and a battery bank to supply the local loads through a combination of electric and magnetic buses. The proposed micro-grid operates in a large number of grid-connected and off-grid operation modes. The energy management system includes a long-term data prediction unit based on a 2D dynamic programming and a short-term fuzzy controller. The long-term prediction unit is designed to determine the appropriate variation range of the battery state of charge and fuel cell state of hydrogen. The efficiency performance of the micro-grid components, predicted energy generation and demand, energy cost and the system constraints are taken into account. The resultant data then is sent to the short-term fuzzy controller which determines the operation mode of the micro-grid based on the real-time condition of the micro-grid elements. A prototype of the proposed micro-grid including the energy management system is developed, and experimental tests are conducted for three different energy management scenarios. The proposed management technique is validated through energy distribution and cost analysis.

This paper presents the development of a residential micro-grid topology based on a combination of common magnetic and electrical buses. The magnetic bus interfaces two low voltage dc buses linking a PV and a fuel cell to a high voltage dc bus connected to a grid-tied single-phase bidirectional inverter. A battery is used to store the surplus energy of the system and stabilise the dc voltage of the fuel cell bus. A synchronised bus voltage balance (SBVB) technique is used to reduce the conduction losses and increase the soft switching operation range of the converters. To improve the maximum power point tracking (MPPT) performance and system efficiency, appropriate control techniques and compensation blocks are designed. The proposed micro-grid is able to operate in multiple grid-connected and off-grid operation modes according to a predictive 2D dynamic programming-based energy management. A mode selection and transition strategy is developed to select the appropriate operation mode and smooth the mode transition. A detailed study of the micro-grid including steady-state operation, small signal modelling, controller design, and energy management is presented. A prototype of the system is developed, and experimental tests are conducted for an energy management scenario.

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Improvements in characteristics of magnetic materials and switching devices have provided the feasibility of replacing the electrical buses with high-frequency magnetic links in small-scale micro-grids. This can effectively reduce the number of voltage conversion stages, size and cost of the microgrid, and isolate the sources and loads. To optimally design the magnetic link, an accurate evaluation of copper loss of the windings considering both the current waveforms and parasitic effects are required. This paper studies the copper loss analysis of a three-winding high-frequency magnetic link for residential micro-grid applications. Due to the non-sinusoidal nature of the voltages and currents, the loss analysis is carried out on a harmonic basis taking into account the variations of phase shift, duty ratio and amplitude of the waveforms. The high-frequency parasitic phenomena including the skin and proximity effects are taken into account. The maximum and minimum copper loss operating conditions of the magnetic link and their dependency on the phase shift angle and the duty ratio of the connected waveforms are studied. A prototype of the micro-grid including the magnetic link is developed to validate the theoretical analysis, evaluate the micro-grid efficiency and perform the loss breakdown.

Recent advances in magnetic material characteristics and solid-state semiconductors have provided the feasibility of replacing the electrical buses with the high-frequency multi-winding magnetic links in small-scale renewable energy systems. This effectively reduces the number of conversion stages and improves the system's efficiency, cost and size. Other advantages are galvanic isolation between the ports, bidirectional power flow capability and flexibility in energy management and control. Despite the advantages, design and development of the multi-winding magnetic links is relatively complex and based on computationally expensive numerical methods. Furthermore, nonsinusoidal nature of voltage and currents, high-frequency parasitic effects and nonlinearity of magnetic material characteristics increase the design complexity. In this paper, the reluctance network modeling as a fast analytical method is used to design a three winding magnetic link. The core and copper losses of the designed component are evaluated taking into account duty ratio, amplitude and phase shift of the non-sinusoidal excitation voltage and currents. The thermal analysis is carried out using an accurate thermal-electric model. A prototype of the magnetic link was developed for application in a residential renewable energy system using amorphous magnetic materials. A set of experimental tests are conducted to measure the electrical parameters, magnetic characteristics, core loss, copper loss and temperature rise of the designed component and the results are compared to the specifications to validate the design procedure.

Improvements in characteristics of magnetic materials and switching devices have provided the feasibility of replacing the electrical buses with high frequency magnetic links in micro-grids. This effectively reduces the number of voltage conversion stages, and the size and cost of the renewable energy system. It also isolates the converter ports which increases the system safety and facilitates bidirectional power flow and energy management. To design the magnetic link optimally, an accurate evaluation of copper loss of the windings considering both current waveforms and parasitic effects is required. This paper studies the accurate copper loss analysis of a three-winding high-frequency magnetic link for residential micro-grid applications. Due to the non-sinusoidal nature of the voltage and currents, the loss analysis is carried out on a harmonic basis taking into account variations of phase shift, duty ratio and amplitude of wave-forms. The high frequency skin and proximity effects are taken into account. The maximum and minimum copper loss operating points of the converter and their dependency on the phase shift and duty ratio of the waveforms are studied and simulation results are presented.