Intelligent uninterruptible power supply system with back-up fuel cell/battery hybrid power source

This paper presents the development of an intelligent uninterruptible power supply (UPS) system with a hybrid power source that comprises a proton-exchange membrane fuel cell (PEMFC) and a battery. Attention is focused on the architecture of the UPS hybrid system and the data acquisition and control of the PEMFC. Specifically, the hybrid UPS system consists of a low-cost 60-cell 300 W PEMFC stack, a 3-cell lead–acid battery, an active power factor correction ac–dc rectifier, a half-bridge dc–ac inverter, a dc–dc converter, an ac–dc charger and their control units based on a digital signal processor TMS320F240, other integrated circuit chips, and a simple network management protocol adapter. Experimental tests and theoretical studies are conducted. First, the major parameters of the PEMFC are experimentally obtained and evaluated. Then an intelligent control strategy for the PEMFC stack is proposed and implemented. Finally, the performance of the hybrid UPS system is measured and analyzed.     

Modeling,control and power management of hybrid photovoltaic fuel cells with battery bank supplying electric vehicle

In this paper, modeling, control and power management (PM) of hybrid Photovoltaic Fuel cell/Battery bank system supplying electric vehicle is presented. The HPS is used to produce energy without interruption. It consists of a photovoltaic generator (PV), a proton exchange membrane fuel cell (PEMFC), and a battery bank supplying an electric vehicle of 3 kW. In our work, PV and PEMFC systems work in parallel via DC/DC converter and the battery bank is used to store the excess of energy. The mathematical model topology and it power management of HPS with battery bank system supplying electric vehicle (EV) are the significant contribution of this paper. Obtained results under Matlab/Simulink and some experimental ones are presented and discussed.     

A single phase parallely connected uninterruptible powersupply/demand side management system

This paper presents the application of a single-phase parallel converter as an uninterruptible power supply and demand side management system. The proposed system consists of a bi-directional inverter that is connected in parallel to the utility system. When the grid system fails, the converter will convert the power from the battery to the AC side (utility side) at the mains voltage and frequency. On the other hand, when the utility is normal the converter will act as a demand side management system. It charges the battery during low load and shaves the transient load at the peak period system. This improves the pattern of the demand variation in the utility side. This paper presents the operational principle of the uninterruptible power supply and demand side management system, laboratory, and simulation results     

The development of an exchangeable PEMFC power module for electric vehicles

This paper develops an exchangeable fuel-cell power module that is replaceable on different light electric vehicles (LEVs). The module consists of a proton exchange membrane fuel-cell (PEMFC) and two battery sets, which provide continuous power for LEVs. The study includes three topics: fuel-cell control, power management, and system modularization and vehicle integration. First, we design robust controllers for the PEMFC to provide a steady voltage or current for charging the battery sets. Second, we develop a serial power train that can provide continuous power for driving the vehicle motors. Third, we modularize a power system that can be easily implemented on different LEVs. We build the system on Matlab™ SimPowerSystem for simulation before road tests, and integrate the power module onto a mobility car and an electric motorbike for experimental verification. Based on the results, the proposed systems are deemed effective.     

Impacts of power management on a PEMFC electric vehicle

This paper discusses the impacts of different power management strategies on a fuel-cell vehicle. The study was carried out in three steps: fuel-cell control, power management, and system integration and verification. First, we identified the models of a proton exchange membrane fuel-cell (PEMFC) and designed robust controllers to improve the PEMFC's performance and efficiency. Second, we developed two power management structures—a serial power train and a parallel power train—which consisted of the PEMFC and secondary batteries to provide sustainable power for an electric mobility scooter. Lastly, we used the scooter's driving cycles to compare the performance and efficiency of these two power trains. Then we implemented the power trains on a microprocessor for road test. Based on the results, both power trains are deemed effective in providing continuous power for driving the scooter. In addition, the serial power train, although it uses an extra battery set, is shown to be more efficient than the parallel one.     

The development of a PEMFC hybrid power electric vehicle with automatic sodium borohydride hydrogen generation

This paper describes the development of a hybrid Proton Exchange Membrane Fuel Cell (PEMFC) electric vehicle consisting of a 3 kW PEMFC, PV arrays, secondary battery sets, and a chemical hydrogen generation system. We first integrate a hybrid PEMFC electric vehicle and design power management strategies. The on-board hydrogen generation system can provide sufficient hydrogen for continuous operation of the PEMFC, and the performance tests demonstrate the effectiveness of the integrated system in providing sustainable power for driving. We then use Matlab/SimPowerSystem? to develop a simulation model and adjust the model parameters using experimental data. The results indicated that the model can effectively predict system responses and can be used for performance evaluation. We also use the simulation model to estimate the mileage and costs of the developed electric vehicle, and we discuss the impacts of component sizes on system costs and travelling ranges.     

Design and implementation of a hybrid regenerative power system combining grid-tie and uninterruptible power supply functions

A hybrid regenerative power system including photovoltaic (PV) and wind powers and combining the functions of the grid?tie system and uninterruptible power supply (UPS) for critical load applications is presented. The proposed system employs six-arm converter topology with three arms for the rectifier? inverter, one arm for battery charging/discharging and two arms for power conversion of the PV module and wind turbine generator. The operation modes include the grid?tie mode and the UPS mode depending on the grid status. A power balance control scheme is presented, which can reduce the grid power and utilise the regenerative power in the most effective way for fulfilling the two requirements of a three-stage charging of the battery and no interruption of the load. Also, the PV and wind powers can be utilised with priority in order to provide the flexibility for adapting to local circumstances. A single-phase 1.2 kW/110 V system is designed and implemented, and the effectiveness of the proposed system and control methodology are verified with some experimental results.     

Optimized power management based on adaptive-PMP algorithm for a stationary PEM fuel cell/battery hybrid system

This research develops an efficient and robust polymer electrolyte membrane (PEM) fuel cell/battery hybrid operating system. The entire system possesses its own rapid dynamic response benefited from hybrid connection and power split characteristics due to DC/DC buck-boost converter. An indispensable energy management system (EMS) plays a significant role in achieving optimal fuel economy and in a promising running stability. EMS as an indispensable part plays a significant role in achieving optimal fuel economy and promising operation stability. This study aims to develop an adaptive supervisory EMS that comprises computer-aided engineering tools to monitor, control, and optimize the performance of the hybrid power system. A stationary fuel cell/battery hybrid operating system is optimized using adaptive-Pontryagin's minimum principle (A-PMP). The proposed algorithm depends on the adaptation of the control parameter (i.e., fuel cell output power) from the state of charge (SOC) and load power feedback. The integrated model simulated in a Matlab/Simulink environment includes the fuel cell, battery, DC/DC converter, and power requirements models by analyzing the three different load profiles. Real-time experiments are performed to verify the effectiveness of EMS after analyzing the simulated operating principle and control scheme.     

Optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply

This paper presents the optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply (UPS). The system involves a photovoltaic, battery and bi-directional inverter that is connected in parallel to the grid. A diesel generator is required when the grid is not available for a longer time. The optimum operation strategy of the system is proposed for the diesel-connected mode (when the grid fails for several hours), while the economic analysis is evaluated for the grid-connected mode. The optimum strategy determines the ‘set point’ value for starting and stopping the diesel generator, resulting in a lower system operation cost within its lifetime. The optimum value is obtained by comparing the cost of the diesel fuel consumption and the battery wear. The economic analysis includes the system operation as UPS and demand side management. The system will reduce the power flow from the mains by increasing the power from the inverter to the load when the tariff is high. However, when the grid tariff is low, the power from the mains is used to charge the battery and to meet the load simultaneously.     

Dynamic performance of an in-rack proton exchange membrane fuel cell battery system to power servers

To improve the reliability and the energy efficiency of data centers, as well as to reduce infrastructure costs and environmental impacts, we experimentally evaluated in-rack powering of servers with a hybrid 12 kW Proton Exchange Membrane Fuel Cell (PEMFC) and battery system. The steady state and the transient performance of the PEMFC and battery in response to dynamic AC loads and real server loads have been evaluated and characterized. The PEMFC system responds quickly and reproducibly to load changes directly from the server rack. Peak efficiency of 55.2% in a single server rack can be achieved. The effect of fuel cell coolant temperature on the hybrid system transient behavior is also captured and evaluated. The observed PEMFC transient responses obtained from the experiments were used to design the size of the energy storage component for the hybrid system. Simulations and analysis of various types of energy storage devices for the hybrid system were carried out. To provide power to meet the most significant transient demand, energy storage capacity greater than 0.3 kWh is required for all battery types, while only 0.053 kWh capacity is required for the ultracapacitor. During charging, the ultracapacitor uses the shortest amount of time to recover to the original SOC, while the charging duration for the lead acid battery is twice as long as that of the ultracapacitor.     

Development of new energy management strategy for a household fuel cell/battery hybrid system

This work aims to construct an efficient and robust fuel cell/battery hybrid operating system for a household application. The ability to dispatch the power demands, sustain the state of charge (SOC) of battery, optimize the power consumption, and more importantly, ensure the durability as well as extend the lifetime of a fuel cell system is the basic requirements of the hybrid operating system. New power management strategy based on fuzzy logical combined state machine control is developed, and its effectiveness is compared with various strategies such as dynamic programming (DP), state machine control, and fuzzy logical control with simulation. Experimental results are also presented, except for DP because of difficulties in achieving real‐time implementation and much faster response to load variation. The given current from the energy management system (EMS) as a reference of the fuel cell output current is determined by filtering out various harmful signals. The new power management strategy is applied to a 1‐kW stationary fuel cell/battery hybrid system. Results show that the fuel cell hybrid system can run much smoothly with prolonged lifetime.     

Advanced concept for dispersed power supply system using AC modules

A method of for estimating the reliability of new conceptual stand-alone dispersed power supply systems using AC modules with self-contained logic was proposed and system reliability estimated using a yearly scale simulation. The AC module is able to supply AC power on each module and has the flexibility to enable construction of a grid-connected system. Power storage devices were required when applying AC modules to the stand-alone power supply system. For these power storage devices, we used a battery with a built-in DC/AC micro bi-directional inverter known as AC battery. To maintain the flexibility of the system extension, the AC modules and AC batteries were controlled by self-contained logic. This logic performs parallel operations for the voltage control inverter and keeps supply and demand in balance.     

A hybrid power source for pulse power applications

Portable 12 V power supplies are used extensively for communications and power tool applications. These devices demand fast response times of the power supply. Fuel cells are generally best suited to continuous power applications and require an initial warm-up period, although they offer the prospect of increased operational duration over a battery for a given weight of portable system. This paper investigates the combination of specific energy performance from the fuel cell system with the specific power and response time of the battery. Two separate hybrid systems have been developed and tested; a planar, 20-cell, polymer electrolyte membrane fuel cell (PEMFC) stack together with either a lead–acid or nickel/cadmium battery; and a conventional 20-cell, bipolar, PEMFC stack. Both systems have been tested under pulse-load conditions at temperatures between −20°C and +40°C, and for comparison, the individual components have undergone similar tests. The hybrid systems have successfully operated continuously for several weeks under load profiles that the fuel cell alone could not sustain.     

Modeling and thermal management of proton exchange membrane fuel cell for fuel cell/battery hybrid automotive vehicle

The proton exchange membrane fuel cell (PEMFC) stack is a key component in the fuel cell/battery hybrid vehicle. Thermal management and optimized control of the PEMFC under real driving cycle remains a challenging issue. This paper presents a new hybrid vehicle model, including simulations of diver behavior, vehicle dynamic, vehicle control unit, energy control unit, PEMFC stack, cooling system, battery, DC/DC converter, and motor. The stack model had been validated against experimental results. The aim is to model and analyze the characteristics of the 30 kW PEMFC stack regulated by its cooling system under actual driving conditions. Under actual driving cycles (0–65 kW/h), 33%–50% of the total energy becomes stack heat; the heat dissipation requirements of the PEMFC stack are high and increase at high speed and acceleration. A PID control is proposed; the cooling water flow rate is adjusted; the control succeeded in stabilizing the stack temperature at 350 K at actual driving conditions. Constant and relative lower inlet cooling water temperature (340 K) improves the regulation ability of the PID control. The hybrid vehicle model can provide a theoretical basis for the thermal management of the PEMFC stack in complex vehicle driving conditions.     

Discrete ejector control solution design,characterization, and verification in a 5 kW PEMFC system

An ejector primary gas flow control solution based on three solenoid valves is designed, implemented and tested in a 5 kW proton exchange membrane fuel cell (PEMFC) system with ejector-based anode gas recirculation. The robust and cost effective combination of the tested flow control method and a single ejector is shown to achieve adequate anode gas recirculation rate on a wide PEMFC load range.In addition, the effect of anode gas inert content on ejector performance in the 5 kW PEMFC system is studied at varying load and anode pressure levels. Results show that increasing the inert content increases recirculated anode gas mass flow rate but decreases both the molar flow rate and the anode inlet humidity.Finally, the PEMFC power ramp-rate limitations are studied using two fuel supply strategies: 1) advancing fuel supply and venting out extra fuel and 2) not advancing fuel supply but instead using a large anode volume. Results indicate that the power of the present PEMFC system can be ramped from 1 kW to 4.2 kW within few hundred milliseconds using either of these strategies.     

Sizing Batteries for Generating Stations

Sizing of storage batteries is straight forward using the formulas in IEEE 485; however the key to proper sizing is the determination of the duty cycle. This paper will discuss voltage considerations, loads and the duty cycle, as they relate to battery sizing. Illustrative examples are provided as required. Although the emphasis of this paper will be on batteries for generating station stationary applications, uninterruptible power supply (UPS) system batteries are also discussed. A UPS system is a constant kVA load and battery sizing, using the kW method discussed, is preferable in this case. The guidance provided will enable the user to determine the requirements for a specific application and properly size the battery. Although this paper discusses generating stations, the material presented is applicable to other installations, including substations, industrial control and communications systems.     

Remodeling of a commercial plug-in battery electric vehicle to a hybrid configuration with a PEM fuel cell

In the present research, a commercial battery-powered pure electric vehicle was suitably modified to convert it into a hybrid one integrating a PEMFC stack. The hydrogen supply system to the stack included a passive recirculation system based on a Ventury-type ejector. Besides, in order to achieve an optimum operation of the PEMFC stack, a discrete state machine model was considered in its control system. The inclusion of a rehabilitation operating mode prevented the stack from possible failures, increasing its lifetime. It was verified that for the rated operating point when supplying power to the vehicle (2.5 kW) the hydrogen consumption decreased, and the actual efficiency (47.9%) PEMFC was increased close to 1%. Field tests performed demonstrate that the range of the hybrid electric vehicle was increased by 78% when compared to the one of the original battery electric car. Also, under the tested experimental conditions in hybrid mode, 34% of the total energy demanded by the electric machine of the vehicle was supplied by the PEMFC stack.     

Numerical modeling and analysis of PEMFC integrated with auxiliary power source

A numerical model is developed from a stationary proton exchange membrane fuel cell (PEMFC) system comprising a PEMFC, a DC‐DC buck converter, an auxiliary power supply (a lithium battery and supercapacitor), and a DC‐AC inverter. The transient and steady‐state performance of the PEMFC system is investigated by means of Matlab/Simulink simulations. It is shown that a good agreement exists between the simulated polarization curve of the PEMFC and the experimental results presented in the literature. In addition, it is shown that the DC‐DC buck converter provides an effective means of stabilizing the output voltage of the PEMFC. Finally, the results confirm the effectiveness of the auxiliary power source in enabling the PEMFC to satisfy the peak load demand. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental analysis of the performance of the air supply system in a 120 kW polymer electrolyte membrane fuel cell system

For analyzing the performance of 120 kW polymer electrolyte membrane fuel cell (PEMFC) system and its air supply system, an air system test bench was built, then applied on a 120 kW PEMFC system test bench composed of air supply subsystem, hydrogen supply subsystem, stack, cooling subsystem and electronic control subsystem. The strategy composed of feedforward table and Piecewise proportional integral (PI) feedback control strategy is employed to regulate the flow rate and pressure of air supply system. Firstly, the air compressor map and the mapping relationship between the speed of air compressor, opening of back-pressure valve and stack current are obtained by carrying out experiments on the PEMFC air system bench. Then, the max output performance, steady-state performance, the startup performance, the dynamic response abilities of PEMFC system are tested, respectively. During the experiments, performances under different test conditions were analyzed by comparing parameters such as voltage inconsistency, average voltage, minimum voltage, voltage range, net power of the PEMFC system, and stack power. The test results show that the air supply system can provide qualified flow rate and pressure for the PEMFC stack. The peak power of the stack is 120 kW and net power of the system is 97 kW when the current is 538 A. The response time from rated net power to idle net power is 12 s and from idle net power to rated net power is 23 s. The overshoot of average voltage and minimum voltage in the process of increasing load is both 0.01 V, which are 0.015 V and 0.02 V lower than that when the load is decreased, respectively. The dynamic response speed and stability of the PEMFC system in the process of decreasing the load are better than those in the process of increasing the load.     

Fuel-cell sharing for a distributed hybrid power system

This paper investigates the benefits of sharing a proton exchange membrane fuel cell (PEMFC) in a distributed hybrid power system. The PEMFC is usually used as backup power in stationary hybrid power systems; however, in that scenario, it might be working only 2% of the time while incurring 20% of the system expenses. Therefore, this paper examines the potential of sharing a PEMFC among multiple power systems. We develop a distributed hybrid power system that comprises several immovable power stations and a fuel-cell vehicle (FCV). Each power station is equipped with solar panels and batteries, while the FCV contains a PEMFC module and can move among the stations to provide sustainable power as needed. We propose power management strategies and show that the total system costs can be significantly reduced by 10.83% and 17.89% when sharing one FCV between three and twelve power stations, respectively. We also design experiments to demonstrate the feasibility of the proposed distributed hybrid power system. In the future, the developed model can be extended to provide further cost reductions by optimizing distributed hybrid power systems with multiple FCVs.