As a result of global energy demand increase, concerns over global warming, and rapid exhaustion of fossil fuels, there is a growing interest in energy system dependence on clean and sustainable energy resources. Attractive power technologies include photovoltaic panels, wind turbines, and biomass power. Fuel cells are also clean energy units that substitute power generators based on fossil fuels. They are employed in various applications, including transportation, stationary power, and small portable power. Fuel cell connections to utility grids require that the power conditioning units, interfacing the fuel cells and the grids, operate accordingly (by complying with the grid requirements). This study aims to model a centralised, single-stage grid-tied three-level diode clamped inverter interfacing a multi-stack fuel cell system. The inverter is expected to produce harmonic distortions of less than 0.5% and achieve an efficiency of 85%. Besides the grid, the system consists of a 1.54 MW/1400 V DC proton exchange membrane fuel cell, a 1.3 MW three-level diode clamped inverter with a nominal voltage of 600 V, and an inductance-capacitance-inductance (LCL) filter. Two case studies based on the load conditions are considered to assess the developed system’s performance further. In case 1, the fuel cell system generates enough power to fully meet this load and exports the excess to the grid. In the other case, a load of 2.5 MW was connected at the grid-tied fuel cell inverter’s output terminals. The system imports the grid’s power to meet the 2.5 MW load since the fuel cell can only produce 1.54 MW. It is demonstrated that the system can supply and also receive power from the grid. The results show the developed system’s good performance with a low total harmonic distortion of about 0.12% for the voltage and 0.07% for the current. The results also reveal that the fuel cell inverter voltage and the frequency at the point of common coupling comply with the grid requirements.

It is a reality that future development in the energy sector is founded on the utilization of renewable and sustainable energy sources. These energy sources can empower to meet the double targets of diminishing greenhouse gas emissions and ensuring reliable and cost-effective energy supply. Fuel cells are one of the advanced clean energy technologies and have demonstrated their ability to be a decent substitute to address the above-mentioned concerns. They are viewed as reliable and efficient technologies to operate either tied or non-tied to the grid and power applications ranging from domestic, commercial to industrial. Among different fuel cell technologies, proton exchange membrane is the most attractive. Its connection to the utility grid requires that the power conditioning system serving as the interface between the stack and the grid operates accordingly. This study aims to model and control a power conditioning system for the grid-connection of a megawatt fuel cell stack. Besides the grid, the system consists of a 1.54 MW/1400 V DC proton exchange membrane fuel cell stack, a 1.3 MW/600 V three-level diode clamped inverter and an LCL filter which is designed to reduced harmonics and meet the standards such as IEEE 519 and IEC 61000-3-6. The power conditioning control scheme comprises voltage and current regulators to provide a good power factor and satisfy synchronization requirements with the grid. The frequency and phase are synchronized with those of the grid through a phase-locked-loop. The modelling and simulation are performed using Matlab/Simulink. The results show good performance of the proposed microgrid as well as the inverter design and control approach with a low total harmonic distortion of about 0.35% for the voltage and 0.19% for the current.

Power generating entities’ connection to utility grids requires power converters to achieve high efficiency and low injected current harmonic distortion. The control of the power converter plays a crucial role in the grid-tied power converter’s performance. Various control techniques for grid-tied inverters ranging from classical to intelligent are introduced in several exist. Evaluating the current state and trend in grid-tied power inverters and related control methods, research shows that most works in this area focus on grid integration using the close-loop and other advanced control approaches. This is because these control methods are preferred since they provide adequate performance in case of uncertainties in the system. This investigation can aprove that PQ open-loop control technique can operate sufficiently and cost-effectively in grid-tied renewable and alternative power systems under normal operating conditions. Hence, this paper aims to assess the performance of a centralized single-stage grid-tied three-level diode clamped inverter connected to a PV-Fuel cell unit. An active and reactive power open-loop control scheme is employed to operate the inverter and achieves a current harmonic distortion below 5%. The system comprises a 150 kW/700 V PV, a 150 kW/1400 V fuel cell, a 265 kW multilevel inverter operating at a rated voltage of 415 V, and an LCL filter. Two operating scenarios are adopted to investigate the system’s responses further. In the first scenario, a local load of 509.2 kW is supplied from the PV-fuel cell inverter. The load also receives the grid’s power to meet the demand as the PV-fuel cell inverter provides only 265 kW. Whereas in the other scenario, the PV-fuel cell unit provides power to supply a local load while transporting the surplus to the grid. The results reveal the developed model’s good performance with a current harmonic distortion of 0.33%.

No abstract

No abstract