25 inverter design for 2001 future energy challenge (thiết kế bộ nghịch lưu)

PROJECT REPORT INVERTER DESIGN FOR 2001 FUTURE ENERGY CHALLENGE College of Engineering and Computer Science University of Central Florida Orlando, FL 32816 Tel (407) 823-0185 Fax (407) 823-6334 batarseh@mail.ucf.edu Student Team Members : Joy Mazumdar Manasi Soundalgekar Duy Bui Nancy Saldhana Bassem Khoury Steven Pugh Advisor: Dr Issa Batarseh 15th June, 2001 Return to Main Document Signature Page The following students comprised the Future2001 EnergyChallenge team from the University of Central Florida under the guidance of Dr Issa Batarseh Advisor : ( Dr Issa Batarseh ) Date Students : ( Joy Mazumdar ) ( Manasi Soundalgekar ) ( Duy Bui ) ( Nancy Saldhana ) ( Bassem Khoury ) ( Steven Pugh ) Power Electronics group at the University of Central Florida wishes to thank IEEE PELS, DOE and the other organizers of Future 2001 Energy Challenge Competition for providing its students the opportunity to participate in this project TABLE OF CONTENTS List of figures 1.0 Introduction 2.0 Theory of Design Rationale 2.1 Design specifications for the 1.5kW prototype 2.2 DC-DC Converter Stage Design 2.3 2.2.1 Basic circuit operation of DC-DC stage 2.2.2 Design of transformer stage for DC-DC conversion 2.2.3 Output inductor design for DC-DC stage 2.2.4 Design of DC bus capacitor bank PWM DC-AC Inverter Stage Design 2.3.1 Basic half-bridge inverter circuit with resistive load 2.3.2 Half-bridge inverter circuit with resistive inductive load 2.3.3 PWM Concept 2.3.4 Output voltage 2.3.5 Dead time 2.4 Output LC filter design 2.5 Input circuits, EMI filtering, fusing and transient protection 2.6 Output Overload Protection 2.7 DSP Control Design 2.8 Design of the heat sinks 2.9 RC snubber circuit design 2.10 3.0 4.0 Component values for 10kW inverter system Manufacturing Issues 3.1 Electrical mounting and termination 3.2 PCB trace selection 3.3 Heat sink issues 3.4 Wiring considerations Educational Impact 4.1 About UCF 4.2 Power Electronics progress at UCF 4.3 Student participation in the project 4.4 Project development stages 4.5 Educational benefits 5.0 Inverter Operating Instructions 6.0 Simulation results and experimental setup 7.0 Cost Evaluation Spreadsheet 8.0 References 9.0 Appendix A DSP Sampling cycle B ORCAD schematic for PCB layout C Pspice schematic circuit for 1.5kW and 10kW inverter system D Devices and IC datasheets List of figures: Fig1 (a) Block diagram of the proposed inverter system, (b) Circuit diagram of the proposed inverter Fig2 Flat-topped pulse current Fig3 (a) Half-bridge Inverter under resistive load, (b) Switching and output voltage waveform Fig4 (a) Half-bridge with inductive- resistive load, (b) Equivalent circuit, (c) Steady state waveforms Fig5 SPWM and Inverter Output Voltage Fig6 Single SPWM pair of pulses Fig7 Inverter control scheme Fig8 (a)Waveforms for correction of dead time, (b) Inverter leg Fig9 Input protection circuit Fig10 RC Snubber Circuit Fig11 Thermal resistance Fig12 Power panel schematic Fig13 Differential Voltage and current waveform under normal resistive load Fig14 Phase and Phase voltage waveform Fig15 DC positive and negative bus voltage Fig16 Maximum voltage stress across switches MOSFET1, MOSFET2, IGBT1, IGBT2, IGBT3 and IGBT4 Fig17 Load current waveform under unbalanced load conditions Fig18 Output Filter Capacitor voltage waveform under unbalanced load conditions Fig19 Output Filter Inductor current waveform under unbalanced load conditions Fig20 Voltage feedback waveform for DSP Fig 21 Current feedback waveform for DSP Fig 22 Voltage and current waveforms for 10kW system 1.0 Introduction In this report, a design for a high power density 10kW inverter circuit is presented for conversion of energy from DC fuel cells to AC power to be used mainly for domestic utility applications The configuration is achieved using a high frequency dc-dc push-pull converter at the input side followed by a full-bridge PWM inverter and a low-pass filter at the output side Due to the simplified power stage and the application of DSP-based sinusoidal pulse width modulation technique, output voltage Total Harmonic Distortion (THD) is reduced and a relatively smaller overall inverter size is achieved The proposed practical circuit operates from a 48V DC fuel cell input and outputs a regulated 120V AC, 60Hz sinusoidal voltage having 3-wire configuration[4] A complete circuit analysis, design and cost evaluation is presented and supported by PSPICE simulation results As per competition guidelines, a low power inverter has been redesigned, tested and prototyped, to deliver a 1.5kW load Operating waveforms, printed circuit board layout and measured efficiency of the actual circuit are also presented 2.0 Theory of Design Rationale This project will explore the possibility of making alternate sources of energy utility interactive by means of low cost power electronic interface (DC-AC inverter) The constraint towards the above scheme is the input DC voltage from alternate forms of energy is very rarely stable hence the design of the proposed interface has to produce an AC output, which is independent of the input fluctuations[3] The PWM inverter will be digitally controlled using a commercial DSP chip for AC voltage and frequency regulation The implementation of the DSP will have a current controller, voltage controller and a feed forward controller The input voltage from the renewable forms of energy will be 48VDC with fluctuation limit of 42-72V DC The output voltage will be 110/220VAC @60Hz clean sine wave suitable for home applications Since the inverter is for residential use, low cost, high reliability and safety are essential design issues 2.1 Design Specifications for the 1.5kW prototype [1] Input Voltage Range : 42-72 VDC Output Voltage : Single-phase 120/240VAC RMS, 3-wire output 2.2 Output Frequency : 60Hz ± 0.1Hz Output Power Range : x 750Watts continuous Efficiency : > 90% Line and Load regulation : 5% Total Harmonic Distortion : < 5% Input Current limit : 55 Amps Switching Frequency : 50kHz for push pull and 15kHz for inverter bridge Operating temperature : 10° C - 40° C DSP Controls : TMS320F240 Evaluation module Communication Interface : RS232 DC-DC Converter Stage Design [14] A block and circuit diagram for the proposed inverter implementation is shown in Fig (a) and the circuit schematic is shown in Fig 1(b) I dc + Vdc − Push-Pull stage DC-DC Inverter Stage AC-DC Low-Pass Filter iac v ac Fig 1(a): Block diagram representation of the proposed inverter system R1 D1 L1 T1 Q3 n1 n2 D2 n1 n2 D3 R3 C1 iTr Cin Vdc Fuel Cell Q1 50kHz Q2 50kHz R4 D4 R2 C2 15 KHz Q4 15 KHz Q5 15 KHz Q6 15 KHz L2 L4 L3 C3 Load C4 Load Load Vac Fig 1(b): Circuit diagram of the proposed inverter system Iac To reduce the size of the system transformer, the first stage will consist of a high frequency push-pull dcdc converter The second stage consists of two half-bridge inverters arranged in a full bridge configuration The control technique used in the second stage is sinusoidal PWM The third stage represents the low pass filter with passive components, due to the relatively high attenuation of the low harmonic components for the output voltage waveform The input stage consists of power devices Q1 and Q2, transformer T1, inductor L1, L2 and dc bus capacitors C1 and C2 The dc push-pull converter boosts the bus voltage to 240VDC for the inverter to produce 110VAC The output inverter stage consists of power devices Q3 - Q6, output inductors L3, L4 and capacitors C3 and C4 Using the well-known sinusoidal PWM technique, this circuit generates a sine wave output voltage 2.2.1 Basic Circuit Operation of DC-DC stage The push pull converter belongs to the feed-forward converter family With reference to Fig 1(b), when Q1 switches on and Q2 is off, current flows through the 'upper' half of T1's primary and the magnetic field in T1 expands The expanding magnetic field in T1 induces a voltage across T1 secondary, the polarity is such that D2, D4 is forward biased and D1, D3 is reverse biased D2 conducts and charges the output capacitor C2 via L2 and D4 conducts and charges the output capacitor C1 via L1 The components L1, L2 and C1, C2 form a LC filter network When Q1 turns off, the magnetic field in T1 collapses, and after a period of dead time (dependent on the duty cycle of the PWM drive signal), Q2 conducts, causing the current to flow through the 'lower' half of T1's primary and the magnetic field in T1 expands Now the direction of the magnetic flux is opposite to that produced when Q1 conducted The expanding magnetic field induces a voltage across T secondary, the polarity is such that D1, D3 are forward biased and D2, D4 are reverse biased D1 conducts and charges the output capacitor C1 via L1 and D3 conducts and charges the output capacitor C2 via L2 After a period, Q1 conducts and the cycle repeats There are two important considerations to be made when it comes to the design of the push - pull converter: Both transistors must not conduct simultaneously, as this would effectively short-circuit the supply Hence, the conduction time of each transistor must not exceed half of the total period for one complete cycle; otherwise, the conduction will overlap The transformer magnetic flux must be bi-directional; otherwise the transformer may saturate, and cause destruction of Q1 and Q2 This requires that the individual conduction times of Q1 and Q2 are exactly equal and the two halves of the center-tapped transformer primary be magnetically identical These design considerations must be handled by the control, drive circuit and the transformer The average output voltage, Vout , equals the average of the waveform applied to the LC filter: Vout = Vin n2 f S ( Ton,sw1 + Ton,sw ) n1 (1) where, Vout = Average output voltage - Volts Vin = Average supply voltage - Volts n2 = number of secondary turns of the center -tap transformer T n1 = number of primary turns of the center -tap transformer T f S = Switching frequency of MOSFETs Q1 and Q2 - Hertz Ton,sw1 = on time period of Q1 Seconds Ton,sw = on time period of Q2 Seconds The control circuit monitors and controls the duty cycle of the drive waveforms to Q1 and Q2 If Vin increases, the control circuit will reduce the duty cycle accordingly, so as to maintain a constant output Likewise, if the load is reduced and Vout rises the control circuit will act in the same way Conversely, a decrease in Vin or increase in load will cause the duty cycle to be increased Following given is the derivation of all the inverter parameters Relations between primary current, output power, and input voltage: Since the maximum average input power Pin is 1.8kW and if we assume the efficiency of the push-pull converter to be 90%, then the average output power Pout of the DC-DC stage is 1.65kW Pout = 0.9 Pin (2) It can be seen that, the average input power may be given as, Pin = VDCmin ( I pft ) (3) where VDCmin is the minimum DC input voltage, 0.5 is the duty cycle and I pft is the flat-topped pulse current as shown in Fig (2) The flat-topped pulse current is defined as ramp on a step The flat-topped pulse current appears at the transformer center tap i Tr I pft t Fig 2: Flat-topped pulse current The relationship in Equation (3) is valuable since, it gives the equivalent peak flat-topped primary current pulse amplitude in terms of what is known at the outset, the minimum DC input voltage and total input or output power This value is needed to help us select the MOSFET Finally, for the MOSFET selection the maximum voltage stress that the MOSFET has to handle should be known Maximum voltage stress of the MOSFETs: It can be shown that the maximum voltage stress across the MOSFET is given by the following formula, Vms = 3( 2VDCmax ) (4) where VDCmax is the maximum input DC voltage The maximum stress voltage is 30% above twice the maximum DC input voltage Maximum stress comes from the so-called leakage inductance spikes, these come about because there is an effective small Another very important thing from the educational point of view was not a single item has been out sourced for manufacturing Every item has been built in the laboratory including the main transformer, inductors and the PC board 4.4 Project Design Steps After the components were designed and results verified mathematically, the following systematic approach was followed: Identification of vendors: Each student was given the task of identifying vendors for each of the components, analyze their products, compare specs with other vendors, contact them for samples and finally to try and match with the components already existing in our lab This did provide the students the opportunity to have conversations with technical experts from industry Procurement of components: All the components for this project are procured from Digikey An online account was established with Digikey for purchasing components and the students managed the same At end of each week, the list of expenditures was submitted to the administrative department for accounting purposes Therefore, cost over run was always kept in check Designing of magnetic components: A complete systematic design procedure was used for the magnetics design Companies like Magnetics and Micrometals did help the university by sourcing sample cores and bobbins The students using appropriate wire gauge wound the transformer and inductors After the winding, the proper air gap was adjusted and the cores were packed An Impedance Analyzer was used to test the values of the magnetic components and the measured values did match the expected values For example, the output filter inductor was designed for 2mH The result from the impedance analyzer showed Inductance = 1.9mH and the measured resistance was 0.2 ohms PCB Layout: The PCB layout was done using Layout Plus software from ORCAD After finishing the layout the PC board was etched in the lab by using the T-Tech PCB maker, model Quick circuit 5000 Special attention was paid to the PCB trace thickness, separation of analog and digital and power signals for minimizing EMC problems 37 DSP software development: For this project the TMS320F240 evaluation module was used This evaluation module was already available in our lab and hence the same was used The development of software for this DSP requires lot of software development skills and is totally developed by the students The total software is still not complete, some parts needs to be modified further to meet all the specifications and most importantly, the protection mechanism has to be fool proof 4.5 Educational Benefits Overall, the project provided a good learning experience for the five students in terms of providing: • Technical multi-disciplinary design opportunity • Opportunity for project planning and management • Knowledge in manufacturing techniques • Use of professional software packages like ORCAD, PowerSIM, PCB maker, …etc • How to manage expenses and reduce cost • Learning means of effective resource utilization • Team work and the importance of project cooperation • Good technical and commercial Communication skills • Realizing the acute power crisis we may face in the future and think of alternatives • Model for senior design projects 38 5.0 Inverter Operating Instructions Figure 11 below shows the complete panel schematics BATTERY 48V _ BATTERY 12V + + FUELCELL 48V _ + - R2 NC R1 NO MCB1 AUX MCB1 Relay R1 MCB2 Load Fuse DC Cap Idc Push-Pull Transformer dc-dc + _ Inverter Stage dc-ac Low-Pass Filter Vdc Iin Protection Vin IL PWM PWM DSP Analog Output Relay R2 OR GATE Inverter Fault Fuel-cell Ready Fig 11: Power panel schematic Checklist before Powering Up Observe all of the ESD measures when handling components Tighten–up all bolts and screws Correctly, insert all connectors and lock/screw into place Check the interconnection between the power and the control sections Observe the power–on sequence as described below 39 Vc Iac v ac If the unit is frequently powered–down and up, the DC link capacitors retains high voltage even when the main supply to the inverter is OFF Only discharge the unit at the DC link buses through a minimum of 10W All switches should be in OFF position Ground all components and connect all of the shields Board Designations A1 : Power Board : Houses the power devices and the power circuitry A2 : Interface Board : Houses the feedback and the driver circuitry A3 : DSP Evaluation Board Power Up and Operation Guidelines • Make the power connections • Turn ON the power supply to the DSP evaluation board • Turn the power supply for the interface board ( from the Battery bank ) • Put the Main Power supply MCB ON ( the battery supplies the Inverter ) • The auxiliary contact of the MCB turns the battery contactor ON • The main contactor coil is connected through the NC contact of a control relay, which is controlled by the analog output of the DSP • Inverter starts up and the DSP generates a signal “ Inverter ON “ This signal is given to the Fuel Cell Controller • Inverter keeps running on battery till the fuel cell controller generates the signal “ Fuel Cell Ready “ • Once the Inverter controller receives the ready signal from the Fuel Cell controller, the power from the battery is cut off through a contactor, after a finite delay This delay is programmable This feature ensures that the inverter actually runs from the fuel cell supply and not supported by the battery Battery is used only for back up supply 40 • During operation, the “available power level” signal from the fuel cell controller is compared with the “required power level “ signal of the inverter Whenever “required power level” is greater than “available power level”, the battery contactor turns ON • The control relay operates only when the Fuel Cell Ready signal (H = 5V) is received by the inverter controller • Under any fault condition, the driving signal from the Inverter controller is inhibited and “Inverter Trip “ signal is generated This signal also drops out the battery contactor • Inverter Status is available through the 9-pin RS232 port and the same port can be used for troubleshooting the inverter Necessary software will be supplied 41 6.0 Simulation and experimental results The 1.5kw and 10kw circuit has been simulated using Pspice schematics The simulation circuits are shown in Appendix C 480V pk-pk Differential current for a resistive load of 35Ω Fig 12: Differential Voltage and current waveform under normal resistive load Fig 13: Phase and Phase voltage waveform 42 Fig 14: DC positive and negative bus voltage Fig 15 : Maximum voltage stress across switches : MOSFET1,MOSFET2,IGBT1,IGBT2,IGBT3,IGBT4 43 Fig 16: Load current waveform under unbalanced load conditions Fig 17: Output Filter Capacitor voltage waveform under unbalanced load conditions Fig18: Output Filter Inductor current waveform under unbalanced load conditions 44 Fig 19: Voltage feedback waveform for DSP Fig 20: Current feedback waveform for DSP Fig 21: Voltage and current waveforms for 10kW system 45 Experimental Result of 1.5Kw prototype output waveform 46 7.0 Cost Evaluation Spreadsheet The modified cost evaluation spreadsheet prepared by the Organizing Committee is attached for both the 1.5kw prototype and 10kw system A major factor in selection of the components is the rate of obsolescence Care has been taken to ensure that all the selected components especially the power devices and the driver IC’s will be supplied by the respective companies for the next 10 years Hence the servicing of the product will not be affected even if the components are no longer produced In the cost evaluation spreadsheet, exact cost headers considered under the items Losses, Control and Packaging is not very clearly explained Hence we have considered $ 50 for the 1.5kw and $100 for the 10kw system under the item “Other” This includes costs towards • Protection Fuses, PCB Board • Cables ( Control and Power ) • Battery Charger • Surge suppressors • EMI filter • Sensors • Terminal connectors ( ELMAX ) • Electricity, Telecommunication and stationary The design of feedback circuitry and the DSP control scheme including software does not change with the increase of power rating and hence the increase in cost towards these items is not proportional to power rating The costing principle followed should be “Activity based costing” as that is most logical for mass production in a factory The complete process of from the design table to the completed product is broken up into activities and each activity is assigned a cost The prototype is developed totally inside the school lab and hence the spreadsheet calculation may not reflect the exact costing especially the magnetic components 47 2001 FUTURE ENERGY CHALLENGE : 1.5kW COSTING UNIVERSITY: University of Central Florida NAME OF MAIN CONTACT: Dr Issa Batarseh PROJECT NAME: EnergyChallenge 2001 DATE: 15th June, 2001 DEVICE DIODE IGBT MOSFET CAP (ALUM) CAP (ALUM) CAP (FILM) POWER RESISTOR CHOKE TRANSFORMER CONTACTORS CONTACTORS LOSSES CONTROL PACKAGING OTHER (EXPLAIN) TOTAL QTY 4 4 DESIG UNITMEASURE D1-D4 Q3-Q6 Q1-Q2(2 Parallel) C1,C2 560 uF CIN 0.22 uF C3,C4 10 uF R1-R4 50 W L1,L2.L3 2000 UH T1 M1,M2 Relay 200 W VOLT (Vpk) 500 600 200 450 100 400 VOLT (Vrms) 48 48 CUR (Avg) 10 20 45 CUR (Arms) 55 55 UNITEXTENDED COST COST 2.51 10.05 4.86 19.44 8.65 34.58 15.80 31.61 0.10 0.31 7.98 15.96 2.64 10.56 47.76 143.29 9.17 9.17 4.74 9.48 2.83 2.83 16.67 16.67 60.79 45.59 50.00 460.33 2001 FUTURE ENERGY CHALLENGE : 10kW COSTING UNIVERSITY: University of Central Florida NAME OF MAIN CONTACT: Dr Issa Batarseh PROJECT NAME: EnergyChallenge 2001 DATE: 15th June, 2001 DEVICE DIODE IGBT MOSFET CAP (ALUM) CAP (ALUM) CAP (FILM) POWER RESISTOR CHOKE TRANSFORMER CONTACTORS CONTACTORS LOSSES CONTROL PACKAGING OTHER (EXPLAIN) TOTAL QTY 4 DESIG UNITMEASURE D1-D4 Q3-Q6 Q1-Q2(2 Parallel) C1,C2 2200 uF CIN 0.22 uF C3,C4 120 uF R1-R4 100 W L1,L2.L3 180 UH T1 M1,M2 Relay 1000 W VOLT (Vpk) 500 600 200 400 100 250 VOLT (Vrms) 48 48 CUR (Avg) 45 50 100 CUR (Arms) 45 225 225 UNITEXTENDED COST COST 4.10 16.39 11.98 47.91 14.57 87.42 48.84 97.68 0.10 0.31 35.07 70.15 4.24 16.96 61.19 183.56 18.16 18.16 10.65 21.29 2.83 2.83 83.33 83.33 129.20 96.90 100.00 972.09 References Cited [1] Energy Challenge website http://www.energychallenge.org [2] Ying-Yu Tzou; Shih-Liang Jung, “Full control of a PWM DC-AC converter for AC voltage regulation”, Aerospace and Electronic Systems, IEEE Transactions on, Volume: 34 Issue: 4, Oct 1998 Page(s): 1218 –1226 [3] Shireen, W.; Arefeen, M.S., “An utility interactive power electronics interface for alternate/renewable energy systems”, Energy Conversion, IEEE Transactions on, Volume: 11 Issue: 3, Sept 1996 Page(s): 643 –649 [4] Chiang, S.J.; Liaw, C.M., “Single-phase three-wire transformerless inverter”, Electric Power Applications, IEEE Proceedings-, Volume: 141 Issue: 4, July 1994 Page(s): 197-205 [5] Venkataramanan, G.; Divan, D.M., “Pulse width modulation with resonant DC link converters”, Industry Applications, IEEE Transactions on, Volume: 29 Issue: Part: 1, Jan.-Feb 1993 Page(s): 113 -120 [6] Gui-Jia Su; Ohno, T., “A new topology for single phase UPS systems”, Power Conversion Conference – Nagaoka 1997, Proceedings of the, Volume: 2, 1997 Page(s): 913 -918 vol.2 [7] Mohan, N., Undeland, T., Robbin, W., (1995) Power Electronics: Converters, Applications, and Design New York John Wiley & Sons, Inc [8] Rashid M H., Power Electronics: Circuit Devices, and Applications New Jersey.Prentice Hall 1993 [9] Enrique A Tenicela, “A Study of Pulse Width Modulation Techniques in Power Static Inverters ”, a thesis submitted in partial fulfillment of the requirements for the Honors Program at UCF, Orlando, Florida [10] Texas Instrument website http://www.ti.com [11] Pekik Dahono, A Purwadi and Qamaruzzaman, “ A LC Filter design for single phase PWM inverters” [12] US Department of energy website http://www.energy.gov [13] Powerdesigners Inc website http://www.powerdesigners.com [14] Dr Issa Batarseh, “Introduction to Power Electronics”, chapter 4,5 and [ 15] Colonel Wm T Mclyman , "Magnetic Core Selection for Transformers and Inductors" You have reached the end of this final report Use the button below to return to the Main Document Return to Main Document ... feedback waveform for DSP Fig 21 Current feedback waveform for DSP Fig 22 Voltage and current waveforms for 10kW system 1.0 Introduction In this report, a design for a high power density 10kW inverter. .. inductor design for DC-DC stage 2.2.4 Design of DC bus capacitor bank PWM DC-AC Inverter Stage Design 2.3.1 Basic half-bridge inverter circuit with resistive load 2.3.2 Half-bridge inverter circuit... Voltage feedback waveform for DSP Fig 20: Current feedback waveform for DSP Fig 21: Voltage and current waveforms for 10kW system 45 Experimental Result of 1.5Kw prototype output waveform 46