Modelling and control of a grid-tied power conditioning unit for a megawatt fuel cell system

Abstract

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.

A Grid-Tied Fuel Cell Multilevel Inverter with Low Harmonic Distortions

“…Several articles regarding fuel cell PCUs and their controls are reported in the literature; however, less focus on the grid integration of PEMFCs. Ben Hamad and Kahn [26] presented the three standard PCU configurations for grid-tied fuel cells (Figure 1). These configurations are based on single-stage and double-stage PCU topologies and consist of the string configuration (Figure 1a), the multi-string configuration (Figure 1b), and the centralised configuration (Figure 1c).…”

“…An n-level inverter requires (n − 1) voltage sources, 2(n − 1) switching devices and (n − 1) (n − 2) diodes. By enlarging the voltage levels, the voltage quality is improved, and the waveform is nearly sinusoidal [26]. The voltage across each capacitor at the DC-link side is VDC/2, and each device voltage stress is limited to one capacitor voltage level VDC/2 through clamping diodes.…”

“…Of diode clamped multilevel topologies, the three-level diode clamped inverter is one of the most available topologies in the market. It is widely used in industrial applications for voltage ranging from 2.3 to 6.6 kilovolts (kV) [26].…”