燃料电池分布式发电系统.ppt

1、MAN AND ENERGYA case for Sustainable Living through Renewable and Green Energy,Ali Keyhani Professor of Electrical and Computer Engineering The Ohio State University Columbus, OH-43210 ,7/26/2020,1,K,7/26/2020,,2,In part I, the use of energy by man, env

2、ironment and sustainable living were presented. Then the use energy in present time was discussed. Based on British Petroleum (www. B), there is only ten more years of petroleum reserve remain in US , if the current rate of utilization continues. British Petroleum data shows that the Middle East oil

3、 would last only another one hundred years at the current worldwide rate of consumption. British Petroleum data shows that the world can continue to use petroleum at current rate for only another forty years. Challenge of future is to replace petroleum with renewable energy sources.,Distributed Gene

4、ration System Technologies,3,7/26/2020,,Fuel Cell Technology,Fuel Cells : Features and Types Electrochemical energy conversion device. Clean energy source with low emissions. Characterized by the type of electrolyte used by them. Fuel Cells : History First demonstration (in 1839 ) by

5、 Sir William Grove (English physicist) Produced DC electric power by performing electrolysis experiment. Demonstration of the first fully operational fuel cell (in 1959), by Francis Thomas Bacon, (British Engineer) In 1960, General Electric (GE) developed PEM fuel cells for NASA which were used on N

6、ASAs first manned space vehicle .,4,7/26/2020,,Important Fuel Cell Candidates for DG applications,Important Fuel Cell Candidates for DG applications,5,7/26/2020,,Problem Formulation,6,Schematic Diagram of PEM Fuel Cell based Stand-alone DG System Analyze the performan

7、ce and the operating characteristics of stand-alone PEM fuel cell based (5 kW) DG system feeding to the residential loads. Develop dynamic models for PEM fuel cell and for its power conditioning unit (dc/dc boost converter, three-phase dc/ac inverter with L-C filter and transformer ). Develop contro

8、l techniques to achieve desired performance of the system. Determine energy capacity of the storage device needs to be connected at DC bus,7/26/2020,,Problem Formulation-Fuel Cells,7,What are the desired performance characteristics of stand-alone PEM fuel cell based DG system ? Provi

9、de output voltage to residential loads at magnitude 208 V(L-L)/120 V (L-N) and at 60 Hz frequency up to its rated value (5kW). Provide power during peak load demand and during load transients. Output voltage of the system must have low load regulation ( 5 %) - system must be able to maintain steady-

10、state output voltage independent of load conditions up to its rated value. Provide output voltages with low total harmonic distortion (THD) (Reduction in 5th and 7th harmonic) Protect itself from overload conditions such as short circuit faults.,7/26/2020,,Problem Formulation,8,1) Op

11、eration of Power Conditioning Unit (dc/dc boost converter, three-phase dc/ac inverter with L-C filter with transformer ) under Dynamic DC Bus Voltage For 500-W PEM fuel cell (rated current 25 A) output voltage varies between 40 V (no-load) to 23 volts (full load). Output voltage of PEM fuel cell is

12、not constant. As more power is drawn from PEM fuel cell, output voltage of 500- W PEM fuel cell decreases from 40 volts (no-load voltage) to 23 volts (full-load voltage at rated current 25 A). Control techniques are needed - To control the output voltage of PEM fuel cell To control the operation of

13、PEM fuel cell - model is required.,7/26/2020,,Problem Formulation-Fuel Cells,9,2) Determination of Energy Capacity of Storage device to be connected at DC bus PEM fuel cell cannot quickly respond to fast load changes during peak load demand and during load transients. Storage device

14、is required to be connected at the dc bus Energy capacity of the storage device must be determined based on peak load demand and requirement of transient current during load switching. 3) Control of DC/DC Boost Converter Typical output voltage of 500-W PEM fuel cell is 48-60 V. PEM is rated for up t

15、o $250Kw. It can be connected in series or parallel to obtain the desired rating. DC/DC converter boost converter is to boost the output voltage of PEM fuel cell to desired dc bus voltage level (480V 540 V, rated 10 kW). Control technique should be designed - To control the output voltage of the boo

16、st converter such that the dc bus voltage is regulated within 5% of its desired value.,7/26/2020,,Problem formulation-Fuel Cells,10,Control of Three-phase (VSI) DC/AC Inverter The control technique should be designed for inverter 480 V dc/ 208 V ac (L-L), rated 10 kW to satisfy follo

17、wing performance characteristics: Low Load Regulation (less than 5%) The ac output voltage of the DG system should be maintained at 208 V (L-L)/120 V (L-N) independent of load conditions. Minimum THD DG system when feeding to the nonlinear loads, such as rectifiers, switch mode power supplies (SMPS)

18、, must generate minimum harmonics currents. Fast Transient Response System must be able to produce output ac voltage with minimum overshoot or undershoot. Short Circuit Protection System must be able to provide protection from excessive overload conditions,7/26/2020,,Experimental and

19、 simulation Testbed,11,1) Dynamic Modeling Develop dynamic model of PEM fuel cell , rated 500-W, rated current 25 A, 40V (no-load voltage)-23 V(full-load voltage at rated current 25 A) Validate 500- W PEM fuel cell model with published results of SR-12 PEM fuel cell manufactured by Avista Labs. Scal

20、e the model to 5 kW PEM fuel cell, rated current 100 A, 48 V (no-load voltage) - 24 V (V(full-load voltage at rated current 100 A) Simulate PEM fuel cell model to study its dynamic response - Transient response and Steady-state response Develop dynamic model for dc/dc boost converter, (48 V 480 V, r

21、ated 10 kW). Develop dynamic model for three-phase dc/ac inverter (VSI), 480 V dc/ 208 V ac (L-L), rated 10 kW.,7/26/2020,,Distributed Generation Stand-alone,Determination of Energy Capacity of storage device Perform Load following analysis of stand-alone DG system,12,7/26/2020,keyha

22、,Single Family DG System,Following load profile of a typical residential home ( 3000-ft2 house occupied by 2-adults and 4-children) will be used. Average Power Demand (base load) - Less than 5kW - satisfied by PV array unit (rated 5 kW). Peak Load demand = Up to 8 kW Period of peak load d

23、emand = 100 seconds (from 10.30 a.m. to 12.10 p.m.),13,7/26/2020,,Storage Device,Response Time of PEM fuel cell = 20 sec 6 minutes. Storage device should be designed to satisfy peak load demand for 100 seconds. Energy capacity of the storage device is given by: = initial voltage of t

24、he storage device = final voltage of the storage device = capacitance of the storage device Energy to be stored can be given as:,14,7/26/2020,,Storage Device Selection,To perform simulation Model of storage will be developed. The storage device will be selected based on computed ener

25、gy capacity. It will be shown that during 100 seconds period of peak load demand: 1) The discharge current of storage device is high. 2) There exists a voltage drop across the storage device. 3) The state-of-charge (SOC) of the storage device varies.,15,7/26/2020,,Control Problem,Dev

26、elopment of Control Techniques Control of DC/DC Boost Converter Objective of control : Regulate dc bus voltage within 5% from its desired value (480 V).,16,7/26/2020,,DC/DC CONVETER,Model of the Boost Converter is needed. (48 V 480 V, rated 10 kW). DC/DC boost converter can be modele

27、d by state space averaging technique proposed by Middlebrook and Cuk . Inductor current and capacitor voltage are selected as state variables. Input is the output of PEM fuel cell.,17,7/26/2020,,DC/DC CONVERTER MODELING,State space model of DC/DC Boost Converter : Main reasons to use

28、 sliding mode control approach: Sliding mode control has low sensitivity to system parameter variations and uncertainties (load current) in the system. Sliding mode control is based on switching control action. All dc/dc converters use switching devices.,18,7/26/2020,,Control Problem

29、,In boost converter - rate of change of current is much faster than rate of change of output voltage . According to theory of singular perturbations, control problem can be solved by using cascaded control structure with two control loops inner current control loop and outer voltage control loop. In

30、ner sliding mode current controller provides fast response with minimum overshoots or undershoots and linear control techniques can be used to design voltage controller.,19,7/26/2020,,Control Problem,Control of PEM Fuel Cell Output Voltage Objective of control: Regulate the output vo

31、ltage of PEM fuel cell Output voltage of PEM fuel cell can be changed by varying partial pressure of hydrogen or partial pressure of oxygen .,20,7/26/2020,,Fuel Cell Control,Control of PEM Fuel Cell Output Voltage,21,7/26/2020,,Fuel Cell Dynamic Model,As partial press

32、ure of hydrogen at the anode of PEM fuel cell increases, it increases output of PEM fuel cell. Dynamic equations of partial pressure of hydrogen in PEM fuel cell can be given as: Amount of hydrogen consumed in the reaction is directly related to the output current of PEM fuel cell. Flow rate of hydr

33、ogen consumed in the electrochemical reaction is given by,22,7/26/2020,,Fuel Cell Dynamic Model,Hydrogen utilization factor is defined as: High utilization factors (65-85 %) are desired in PEM fuel cell operation as it minimizes the required hydrogen flow. The reference value of hydr

34、ogen flow rate can be computed as : Difference between the required flow rate of hydrogen and flow rate of hydrogen consumed in the electrochemical reaction is fed to the fuel flow controller. Hydrogen flow controller controls the valve on hydrogen line to the PEM fuel cell.,23,7/26/2020,keyhani.1os

35、,DC/AC INVERTER,Control of Three-phase Inverter Inverter model is needed Inverter output line-to-line voltage can be represented by the vector Three-phase inverter output current scan be represented by - , ,24,7/26/2020,,INVERTER MODELING,Inverter Line current vector can be defi

36、ned as - = Transformer primary side - Delta - connected Primary side line-to-line voltage vector Primary side line current vector - Transformer secondary side Wye - connected Secondary side phase voltage vector Secondary side phase current vector Load voltage vector - Load current vector -,25,7/26/2

37、020,,INVERTER MODELING,Primary side voltage , inverter current , load voltage , and secondary side current are selected as the state variables of the model. Model of three-phase dc/ac inverter (VSI) with L-C Filter and delta-wye transformer:,26,7/26/2020,,Voltage and

38、Current Control,Voltage control technique for single inverter system based on perfect control of robust servomechanism problem (RSP) See References. Voltage control technique is combined with a fast current controller using discrete time sliding mode controller for limiting the inverter currents und

39、er overload conditions. RSP Voltage controller is used in outer loop and is cascaded with current controller in the inner loop. M.N. Marwali and A. Keyhani, “Control of distributed generation systems, part I: voltages and currents control,” IEEE Transactions on Power Electronics, Vol. 19, No.6, pp 1

40、541-50, Nov. 2004. M.N. Marwali, J.W. Jung, and A. Keyhani, “Control of distributed generation systems, Part II: Load Sharing Control,” IEEE Transactions on Power Electronics, Vol. 19, No.6, pp. 1551-61, Nov. 2004.,27,7/26/2020,,Control of DC/AC Inverters,The control techniques needs

41、 to achieve: Low Load Regulation Minimum THD Fast Transient Response Short Circuit Protection,28,7/26/2020,,PEM FUEL DYNAMIC PERFORMANCE,Dynamic Model of PEM Fuel Cell The model of 500-W PEM fuel cell , rated 500-W, rated current 25 A, 40V (no-load voltage)-23 V(full-load voltage at

42、rated current 25 A) is developed. Two approaches are used to develop the model. State Space Modeling of PEM Fuel Cell i) Open-circuit Output Voltage ii) Irreversible Voltage Losses iii) Humidification iv) Mass Balance v) Thermodynamic Energy Balance vi) Formation of charge Double Layer,29,7/26/2020,

43、,PEM FUEL DYNAMIC PERFORMANCE,The model is trained and used to obtain: i) V-I characteristics. ii) Polarization curves for different values of input iii) Transient response over short-time period (2-5 seconds) and long-time period (5-6 minutes). Robustness of against the measurement

44、noise is investigated .,30,7/26/2020,,WORKING OF PEM FUEL CELL,31,Oxidation reaction at Anode -,Reduction reaction at Cathode -,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Open-Circuit Output Voltage of PEM Fuel Cell The reversible electric potential of one cell:

45、 : Faradays const. The change in Gibbs free energy: : Partial pressure of hydrogen : Partial pressure of oxygen : Partial pressure of water : Stack temperature : Universal gas const Open-circuit output voltage of one cell: where,32,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Ope

46、n-circuit output voltage of PEM fuel cell: : Reversible cell potential : Number of PEM fuel cell stacks : Standard reference potential at standard operating conditions,33,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Irreversible Voltage Losses in PEM Fuel Cell Output voltage of P

47、EM fuel cell at normal operating conditions is determined by voltage losses in PEM fuel cell. Three types of voltage losses exist: a) Activation losses b) Ohmic losses and c) Concentration losses. A) Activation Losses Governance of sluggish electrode kinetics by the rate of electrochemical reaction

48、at an electrode surface gives rise to activation losses Dominant at low current density (i.e. at the beginning of V-I characteristic curve). The activation losses for a single cell stack can be modeled by Tafel equation:,34,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Ohmic losse

49、s Ohmic resistance of PEM fuel cell that includes the resistance of anode and cathode due to imperfections in electrode manufacturing and the resistance of polymer electrolyte membrane to movement of ions. Ohmic voltage loss for a single PEM fuel cell stack can be given as: Concentration losses Form

50、ation of concentration gradients of reactants at the surface of the electrodes give rise to concentration losses The concentration losses for a single cell stack can be given as: Significant at higher currents ( at the end of V-I characteristics of the PEM fuel cell).,35,7/26/2020,,S

51、TATE SPACE MODELING OF PEM FUEL CELL,Hence, actual output voltage of PEM fuel cell at normal operating conditions :,36,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Humidification in PEM Fuel Cell In PEM fuel cell, conduction of hydrogen ions through the polymer membrane depends o

52、n the membrane humidity. The ohmic resistance of the membrane increases as membrane dries out. Hence, it is essential that membrane remains humidified for efficient operation of PEM fuel cell. Therefore, hydrogen gas and air are passed through the humidifier before reaching the electrodes. The total

53、 vapor transfer through the polymer membrane can be given as : The relative humidity at anode and at cathode can be given as:,37,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Mass Balance in PEM Fuel Cell Material conservation of oxygen at cathode can be given as: Net mole flow ra

54、te of oxygen at cathode is: Rate at which oxygen is consumed at cathode in the reaction can be given as: Net mole flow rate of oxygen at cathode can be given as:,38,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Mass Balance in PEM Fuel Cell Material conservation of hydrogen at ano

55、de can be given as: Net mole flow rate of hydrogen at anode is: Rate at which hydrogen is consumed at anode in the reaction can be given as: Net mole flow rate of hydrogen at anode can be given as:,39,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Mass Balance in PEM Fuel Cell Mate

56、rial conservation of water can be given by subtracting rate of flow water going outside the cell from rate of generation of water in the cell:,40,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,PEM Fuel Cell Stack Temperature Temperature of PEM fuel cell assembly increases as electrochemical reaction proceeds in PEM fuel cell The net increase in temperature of PEM fuel cell assembly can be given by as: Let,41,7/26/2020,,STATE SPACE MODELING OF PEM FUEL CELL,Dynamic equations of partial pressures of hydrogen can be given as: Let w