Optimization of the Fuel Cell Renewable Hybrid Power Systems

This chapter presents the main research directions identified in the literature to be of great interest in the hybrid power systems (HPSs). The tracking control of the maximum power point (MPP) and maximum efficiency point (MEP) must be implemented to harvest the available energy from renewable energy sources (RES) and efficiently operate the proton exchange membrane fuel cell (PEMFC) system, respectively. Because the PEMFC system based on the power-following control will power with delay the smooth part of the needed power on the DC bus, the energy storage systems (ESS) based on the batteries must be hybridized with power storage devices to sustain the power variability on the DC bus due to a variable RES power and dynamic load demand. Besides the power-following control to ensure the charge-sustained mode for the battery, the optimization strategies must be implemented for the PEMFC system to improve the fuel economy, especially for the FC vehicles. In fact, these directions will be detailed in the chapters of this book based on the research results presented recently in the literature.

The hybrid power systems can efficiently produce energy using an optimal combination of renewable energy generation systems, but in order to continuously sustain the required load demand, a backup energy source is necessary. The proton exchange membrane fuel cell system can be used as a non-polluting solution for the backup energy source, instead of a diesel generator. The variability of the renewable energy and load demand in the power flow balance on the common bus will be mitigated by the proton exchange membrane fuel cell system and energy storage system. The architecture of the hybrid power system may be based on a common DC or AC bus or an AD/DC hybrid bus, each of which has advantages and disadvantages. The energy storage system may use a semi-active or active topology, depending on control objectives imposed to be implemented by its side. This chapter will analyze a hybrid power system based on a common DC bus using a semi-active topology for the energy storage system. Energy Storage System. The most used technologies for energy and power storage devices used in energy storage system have been presented in this chapter. The models used for the proton exchange membrane fuel cell system, battery, ultracapacitors, wind turbine, photovoltaic panel, power converters, and load demand were also briefly presented. Performance indicators for the efficient use of a proton exchange membrane fuel cell system and renewable energy sources have been mentioned in the last sections of this chapter, along with the main objectives and research directions for the hybrid power systems and the chapter conclusions.

A brief comparison of the energy management strategies and the optimization algorithms used is performed in this chapter. The load-following (LFW) strategy for a proton exchange membrane fuel cell (PEMFC) is proposed to sustain the power flow balance on the DC bus of a hybrid power system (HPS) with the battery operating in charge-sustaining mode. This battery operating mode has many advantages (like small size), especially for FC vehicles where space is vital. In addition, the state of charge (SoC) for battery is almost constant, so there is no need for SoC monitoring as in rule-based strategies. The power-following (PFW) strategy for stand-alone FC/renewable HPSs is the variant of the LFW control using as input the difference between the load and available renewable energy instead of the load. The excess of energy during light load stage can supply an electrolyzer or can be sold if FC HPS is connected to the network. Optimization of the FC HPS operation may be performed using well-known optimization algorithms such as the global maximum power point tracking (GMPPT) algorithms, global maximum efficiency point tracking (GMEPT) algorithms, or fuel economy algorithms. An advanced fuel economy strategy using fueling regulators switching is presented and analyzed in this chapter as fuel economy under constant and variable load. A pulse mitigation strategy using an anti-pulse control for the hybrid storage system (HSS) based on battery and ultracapacitors is also proposed and analyzed in this chapter. The design and performance evaluation are presented for both strategies.

The main goal of this chapter is to analyze the asymptotic Perturbed-based Extremum Seeking Control (aPESC) schemes. Comparative analysis of the aPESC schemes and their variant for global search is made based on performance indicators such as searching speed, searching accuracy, tracking efficiency, and searching resolution for renewable hybrid energy systems based on renewable energy sources (such as photovoltaic and wind energy). The performance indicators such as fuel economy and electrical energy efficiency have been used for the fuel cell system. Designing and stability analysis of the global aPESC schemes is performed in case of a nonlinear system with a fast or slow dynamic part such as hybrid power systems based on renewable energy and fuel cell sources, respectively. Modeling for local search based on same case studies is also presented.

In this chapter, a systematic analysis of improvements in net power of the proton exchange membrane fuel cell (PEMFC) systems will be presented. The PEMFC systems together with the energy storage systems (ESS) are the main energy sources of the hybrid power system (HPS) powering a variable load. The battery charging–discharging should not be performed frequently because this reduces its lifetime, so the charge-sustaining mode based on the load-following control of the FC power generated is proposed. The FC power may be controlled via the fuel and air regulators, and the controller of the FC boost converter. So, three control inputs are available to operate the PEMFC system for best improvement in FC net power. One control input will be used to implement the load-following mode for the FC system, and the other two or only one will be used to optimize the FC net power. Thus, seven FC net power maximization strategies have been analyzed in this chapter compared to a reference commercial strategy. Finally, the FC net power maximization strategies have been analyzed using performance indicators such as the electrical energy efficiency, the fuel consumption efficiency, and the fuel economy.

In this chapter, a systematic analysis of fuel-saving strategies for proton exchange membrane fuel cell (PEMFC) systems is made. The PEMFC system together with the energy storage systems (ESS) must ensure the variable load request. To avoid frequent battery charging and discharging cycles (which reduces its lifetime), the charge-sustained operation mode is proposed based on load-following control of the generated FC power. The FC power may be controlled via the fuel and air regulators, and the controller of the FC boost converter. So, three control inputs are available to operate the PEMFC system for best fuel economy. One control input will be used to implement the load-following mode for the FC system, and the other two or only one will be used to optimize the fuel economy. Thus, seven fuel economy maximization strategies have been analyzed in this chapter and compared to a reference commercial strategy. Finally, solutions to obtain the best fuel economy, such as switching strategies based on load level, are presented.

The energy harvested from a photovoltaic (PV) system that is partially shaded depends on maximum power point tracking (MPPT) algorithm used. The MPPT algorithms are compared using different criteria proposed in the literature, but a ranking of them may be made only using an evaluation index based on these criteria. The analysis of the criteria used by two evaluation indexes based on four and eight criteria reveals some issues related to objective evaluation of the MPPT algorithms. So, an evaluation index based on seven criteria that can be used for objective evaluation of the MPPT algorithms is proposed in this chapter. The evaluation of the global asymptotic perturbed extremum seeking control (GaPESC)-based MPPT algorithm using the aforementioned evaluation is performed using the evaluation index based on seven criteria to validate that the percentage score is comparable with that obtained by the best MPPT algorithms using the evaluation index based on four and eight criteria, respectively. Also, the behavior and performance of GMMP searching and tracking using the GaPESC-based MPPT algorithm have been analyzed for dynamic sequences of the PV patterns without and with noise.

The performance of the power-following control to mitigate the energy variability on the DC bus will be analyzed in this chapter under constant and variable load, without and with variable power from the renewable energy sources. The power-following control has been designed to compensate the power flows balance with less energy support from the battery, which will be operated in charge-sustained mode. Thus, the low frequency variation of the power flows on the DC bus will be sustained by the proton exchange membrane fuel cell system based on the power-following control of the air or fuel regulator. The performance of the most efficient energy strategies and best fuel economy strategies proposed in Chap. 5 and 6 for a renewable fuel cell hybrid power systems is analyzed in this chapter. The advantages of using an electrolyzer instead of a dump load to ensure the charge-sustained mode for the battery are also highlighted.