Power Electronics Lab By: Alex M. Bermel : April 20, 2011
Table of Contents Title page 1 Table of Contents 2 Project Scope 4 Problem Statement 4 Health and Safety 5 Customer Needs 6 Economic Analysis 6 Social Analysis 7 Political Analysis 7 Sustainability and Economic Analysis 8 Needs Metric Matrix 9 Requirement Specifications 10 Product Design Specifications 11 Concept Generation 14 Prototype Testing Plan 15-2 -
Alternative Solutions 16 Project Timeline 17 Prototype Estimated Cost and Budget 18 Results and Conclusion 19 References 29 Appendix 30-3 -
Project Proposal Project Scope The objective of this project is to provide a group of adequate experiments that can be sustained in a college level laboratory. Using a Power-pole board, descriptive lab reports will explain to students how to wire and show the results of a Buck Converter, Boost Converter, Buck-Boost Converter, Flyback Converter, and Forward Converter. The scope of this project includes becoming familiar enough with the Power-pole board to help monitor a Power Electronics Lab. Problem Statement Electrical Engineering undergraduate students are not receiving enough practical laboratory experience while attending university. By implementing a Power Electronics Laboratory course, students will benefit greatly from the experience attained and will show competency when dealing with or asked about electronic devices and applications of power electronics. The resources needed to complete this project are miniscule. Any university can implement this lab course by ordering a Power-pole board and setting up a station, with a power supply, in one of their laboratory areas. - 4 -
Health and Safety Attention and adherence to safety considerations is even more important in a power electronics laboratory than is required in any other undergraduate electrical engineering laboratories. Power electronic circuits can involve voltages of several hundred volts and currents of several tens of amperes. By comparison the voltages in many teaching laboratories rarely exceed 20V and the currents hardly ever exceed a few hundred milliamps. In order to minimize the potential hazards, we will use dc power supplies that never exceed voltages above 40-50V and will have maximum current ratings of 5A or less. However in spite of this precaution, power electronics circuits on which the student will work may involve substantially larger voltages (up to hundreds of volts) due to the presence of large inductances in the circuits and the rapid switching on and off of amperes of current in the inductances. For example a boost converter can have an output voltage that can theoretically go to infinite values if it is operating without load. Moreover the currents in portions of some converter circuits may be many times larger than the currents supplied by the dc supplies powering the converter circuits. A simple buck converter is an example of a power electronics circuit in which the output current may be much larger than the input dc supply current. Check for all the connections of the circuit before powering the power-pole board to avoid shorting or any ground looping that may lead to electrical shocks or damage of equipment. - 5 -
Customer Needs For this specific project the customers will be the students and universities that decide to implement a Power Electronics Lab. Besides the safety of the students, the next most important need for customers is accuracy in the results. The current customer needs are as follows: The university needs to have a few Power Pole Boards that the students can work with. Efficiency of the results would mean the measure of efficiency must be accurate enough to produce a common result in the lab. Convenience is quintessential. The customer always comes first, so the board must be easy to implement. Expenses must be in a reasonable range for universities to consider implementing a Power Electronics Lab in their curriculum. Economic Analysis Since resources are scarce in order to fulfill the Power Electronics Lab course it is very economical to implement. The Power-pole board is the main; if only, rarity item that will be the most costly. The Power-pole board that can be used is manufactured by HiRel Systems and costs $1250. This price includes three attachments necessary to achieve the desired experiments needed for the course. Basic engineering tools are needed, such as electrical probes and multimeter to attach to the circuit and analyze different points on the Power-pole - 6 -
board. A Digital Oscilloscope with a RS232 interface is needed to view the current or voltage waveforms across the circuit and can be bought for $400 online. A power supply is needed as well and would cost $50-$100 depending on which company you decide to use. However, a power supply, digital oscilloscope, probes, and multimeter are very common in engineering labs. Social Analysis From an anthropologic standpoint, humans are always trying to excel further to produce the most optimal technologies or ideas. It is our biological characteristics that move us to becoming better people, hence better engineers. By creating this lab the students perspectives on Power Electronics will change and they will receive a more fundamental understanding of the way power works in the field of engineering. Political Analysis The contributions made for this project will be from the university itself. In an ideal world, the university hosting the Power Electronics Lab should be funding the necessary needs for the students. The reason they should supply monetary contribution for the project is because a university s goals are to teach students new ideas so that they can apply them to society and benefit the world by making a more sustainable place. There are really no negative impacts associated with this project since knowledge is a priceless tool that never ceases to prosper in someone. The individuals that play a role in this project are the students; it is their - 7 -
responsibility to make the best out of their college experience. Since most college students are there for themselves, they should be keen to playing their role by obtaining the knowledge necessary to make this project a success. Sustainability and Environmental Analysis The world we live in strives to be more sustainable every day. Power Electronics deals with maximizing the efficiency of input power versus output power. Efficiency should be a businesses biggest concern because it minimizes expenses since there would be very little power loss in an efficient system. Not only does it inevitably save any company money, but it also benefits the environment by reducing carbon emissions and the use of fossil fuels when they are making use of all the inputting power to get the most output power. The modern day s society is becoming more and more fixated with reducing their ecological footprint, which means that companies are more willing to hire engineers that have the knowledge of power applications that can help save the planet. - 8 -
Needs-Metric Matrix METRICS Can test under Lab Time requirements NEEDS Accuracy X X Availability X X Productivity X X X X Convenience X X X Easy Use X Inexpensive X Safety X X Professionalism X X Can be carried around campus Problems can be fixed in a reasonable time Can be afforded by Universities No potentially harmful voltages Are the readings accurate enough Availability of resources - 9 -
Requirement Specifications In order for this project to be executed correctly the five converter experiments must be tested and performed with accurate results and procedures so that they can be repeated by students so that they can learn from it. Many of the tasks that must be performed include: analyzing, documenting, validating and managing project requirements. The laboratory results must be documented for future use. The use of the Digital Oscilloscope will be used to analyze the input and output waveforms and observe the actions of each experiment. Documentation is the most important requirement specification because it will be the sole evidence needed in order to fulfill the needs of the student and make the project Power Electronics lab a success. - 10 -
Product Design Specifications Figure 1: The Power-pole board and its three converter boards. This project is supposed to give real life applications of circuits. Other than obvious power efficiency exercises, I will demonstrate how these converters can be applied to the Power-pole board and positively affect today s society technologies. In order to create this project: The Buck converter will demonstrate reduction in output voltage using a transistor and a diode that have a constant DC current running through both. Energy conservation is a key concept in power electronics. An application of this is in a "maximum power point tracker" commonly used in photovoltaic systems. Maximum power point tracking - 11 -
(MPPT) is a technique that solar battery chargers and similar devices use to get the maximum possible power from the photovoltaic array or array of solar panels. The Boost converter does exactly what its name suggests. It will create an output voltage higher than the source voltage. A normal battery powered system will stack cells in order to increase output voltage. However, this is sometimes impossible in high voltage systems due to lack of space. Boost converters are very efficient because they increase voltage in a system while minimizing occupied space. An application of this is that the NHW20 model Toyota Prius HEV uses a 500 V motor. Without a boost converter, the Prius would need nearly 417 cells to power the motor. However, a Prius actually uses only 168 cells and boosts the battery voltage from 202 V to 500 V using a boost converter. Another smaller scale example would be in portable lighting systems. A white LED typically requires 3.3 V to emit light, and a boost converter can step up the voltage from a single 1.5 V alkaline cell to power the lamp. The Buck-Boost converter will create an output voltage that is greater than or less than the source voltage depending on the state of the switching transistor in the circuit. When the switch is closed, which is known as being in the ON state, the input voltage source is directly connected to the inductor, which results in accumulating energy in the inductor, which directly results to the capacitor supplying energy to the output load. While in the OFF state, the inductor is connected to the output load and capacitor, so energy is transferred from L to C and R. - 12 -
The Flyback Converter can be used in both AC to DC and DC to AC conversion. Basically, a flyback converter is a buck-boost converter with the inductor split to form a transformer. This results in a voltage ratio multiplication and isolation advantages. When the switch is ON state, it creates magnetic flux in the transformer and the diode (indicated as D in Appendix A figure 4) becomes reversed biased and no current flows through it so that the output capacitor now supplies energy to the output load. When the switch is OFF state, the energy in the transformer is transferred to the output of the converter. Applications for this vary from high voltage generation systems like a CRT in a TV/monitor, or in lasers to low power switch mode power supplies like cell phones chargers. The Forward converter is a DC to DC converter that uses both boost and buck converter to provide galvanic isolation, which is the principle of isolating a section of an electrical system. We see this concept used in transformers. A forward converter performs the same operations as the flyback converter, but the forward converter is much more efficient. - 13 -
Concept Generation The project has one main idea, which was chosen due to its particular advantages. It did, however, have its malfunctions and complications that had to be managed throughout the project. Category A: The Main Idea Power Electronics plays a crucial role in minimizing energy consumption. Energy conservation leads to financial savings and benefits the environment at the same time. A Power Electronics class would be a very vital course in any engineers curriculum. It would teach engineers the importance of reaching maximum power efficiency in a system. This is something that a new rising generation should be aware of and many corporations in the energy field will be interested in students that are knowledgeable in this field. Since employers are always looking for employees with field experience, there s no better place in school to get that then in a course Lab corequisite. Category B: The Options Since other universities have already implemented this idea in their classes, I researched different universities and found that the University of Minnesota has had great success in experimenting with a Power Electronics Lab for their students. They use a Schott Power Systems Power-pole board which was available during the start of their program. Yet, due to advancement in technologies a better board to use is manufactured by HiRel Systems LLC. This is the Power-pole board that will be used in - 14 -
this project. The University of Minnesota s lab manual is viewable to the public. It has little explanations to the theory behind their results. Prototype Testing Plan Testing the Power-pole board is a key plan in any project. Testing occurred in the beginning stages of the project to see what each component on the Power-pole board does and should do. To test the daughter board connector (J60) plug in the ±12 V signal supply at the DIN connector and using a DMM Multimeter touch pins 1 and 20 to get a positive 12V display and 3 and 18 to get a negative 12V display. This should ensure that your signal supply is in fact ±12 V. Each of the six converters have a different purpose so in order to make sure each one is properly connected a frequency analysis can be done. Frequency analysis of any converter can be done by injecting a low voltage sinusoidal signal at jumper (J64) also known as the smallsignal AC analysis selection jumper. The use of the Oscilloscope makes sure the output voltages are correct and each converter is acting as they are supposed to in theory. - 15 -
Alternative Solutions Below is an alternative board called the µmodule LED Driver board. It can perform the buck, boost, and buck-boost experiments as well as other topologies. It accepts an input voltage of 3-30 Volts and supports an output voltage up to 32 Volts. Figure 2: The alternative µmodule LED Driver board. - 16 -
Project Timeline Week 1 (August 23 rd -29 th ) Week 2 (Aug. 30 th Sept. 5th) Week 3 (Spetmber6th -12 th ) Week 4 (September 13 th -19 th ) Week 5 (September 20 th -26 th ) Week 6 (Sept. 27 th - Oct. 3 rd ) Week 7 (October 4 th - 10 th ) Week 8 (October 11 th - 17 th ) Week 9 (October 18 th - 24 th ) Week 10 (October 25 th - 31 st ) Week 11 (November 1 st - 7 th ) Week 12 (November 8 th - 14 th ) Week 13 (November 15 th -21 st ) Week 14(November 22 nd -28 th ) Week 15 (Nov. 29 th Dec. 5 th ) Week 16 (December 6 th 12 th ) Project Planning Ordering of Parts Testing of Parts Project Designing Wiring Circuit Testing Circuit Writing Report Presentation - 17 -
Prototype Estimated Cost and Budget As of now the Cost and Budget for this Project is the Power-pole Board. We are using a company called HiRel Systems LLC to order our Power-pole Board that charges $1,250. While testing the Power-pole board a few complications were uncovered. Due to an unknown variable, the two 250 ma fuses went over their specified current rating and blew. To replace and make sure this does not happen again I bought five 250 ma and 250 V radial fuses that met the right requirements for the Power-pole board we are using. This costs about $3.36 plus a $2.22 shipping and handling fee. Regardless of my efforts, the board blew another fuse and became apparent that there was a manufacturing error in one of the micro-controllers. HiRel Systems agreed to take a look at it and fix it, but they said it would cost approximately $300-500 range depending on the problem. - 18 -
Results and Conclusions Buck Converter: Output Voltage Table 1: The theoretical and actual output voltages (Vo) for the Buck Converter (Vin=24 V f= 100 khz L= 106.6 µf RL= 10 Ω) Duty Cycle D [%] Theoretical Output Voltage Vo [V] Vo= Vin*D Actual Output Voltage Vo [V] 0 0 0.333 mv 10 2.4 2.39 20 4.8 4.5 30 7.2 7.11 40 9.6 9.4 50 12 12.1 60 14.4 14.5 70 16.8 16.77 80 19.2 19.2 90 21.6 19.7 100 24 20.1-19 -
Vo [V] Alex Bermel 27 24 21 18 15 12 9 6 3 0 Theoretical vs. Actual 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle [%] Theoretical Actual Figure 3: The theoretical and actual output voltages of the Buck Converter. Observation: The Buck converter accurately follows the equation VO = D*Vin, and so behaves as a DC step down transformer with turns ratio 1:D. The Buck Converter in fact acts like a DC step down transformer. The study of a nonisolated Buck Converter is observed and proven to have a turns ratio of 1:D. The output voltage follows the equation VO = D*Vin very accurately until the duty cycle (D) reaches 90% where it then begins to show some inefficiency. We measure efficiency of the Buck Converter by as η = (VO*IO)/ (Vin*Iin) at two different frequencies. We find the currents through using the current sensors or applying an amp meter across the input and load. - 20 -
Boost Converter: Output Voltage Table 2: The theoretical and actual output voltages (Vo) for the Boost Converter (Vin=10 V f= 100 khz L= 106.6 µf RL= 20 Ω) Duty Cycle D [%] Theoretical Output Voltage Vo [V] Vo=[ 1 1 D Vin] Actual Output Voltage Vo [V] 10 11.1 11.2 20 12.5 12.7 30 14.2 14.5 40 16.667 16.0 50 20 19.6 60 25 21.0-21 -
Output Voltage [V] Alex Bermel Theoretical vs Actual 30 25 20 15 10 5 Theoretical Values Actual Values 0 0 10 20 30 40 50 60 Duty Cycle [%] Figure 4: The theoretical and actual output voltages of the Boost Converter Observation: Because the current rating of the function generator the maximum duty cycle should be 60% or else you risk blowing a fuse in your circuit. As you increase the duty cycle the voltage increases. The actual voltage at 60% is not accurate with the theoretical value because of the current ratings and voltage ratings of the equipment. The Boost converter can be seen to follow the principles of a power converter by having a larger output voltage than input voltage. It can be observed that when the switch is in the ON position the current flows freely through the inductor and energy is stored into it. However, during the OFF state, the stored energy collapses and is released from the inductor and the polarity changes so that it adds more voltage to the input. The results show that the Boost converter does follow the equation Vo = [ 1 1 D Vin]. - 22 -
Buck-Boost Converter: Output Voltage Table 3: The theoretical and actual output voltages (Vo) for the Buck-Boost Converter (Vin=10 V f= 100 khz L= 106.6 µf RL= 20 Ω) Duty Cycle D [%] Theoretical Output Voltage Vo [V] Vo=Vin( D 1 D ) Actual Output Voltage Vo [V] 10 20 30 40 50 60 70 1.11 0.853 2.5 2.07 4.29 3.97 6.68 6.11 10.15 9.34 15.18 13.94 23.31 19.89-23 -
Vo [Volts] Alex Bermel 27 24 21 18 15 12 9 6 3 0 0 10 20 30 40 50 60 70 80 Duty Cyle [%] Chart Title Actual Output Voltage Theoretical Output Voltage Figure 5: The theoretical and actual output voltages of the Buck-Boost Converter Observation: The measured values are lower due to the resistive voltage drops occurring in the inductor, current sensors, switch, and diode which therefore make the measured values lower than the theoretical values. The Buck Boost Converter performs in respect to the output voltage, ripple current. The efficiency is reasonably close to the expected performance. In practice the measured values are lower due to the resistive voltage drops occurring in the inductor, current sensors, switch and diode due to which the measured values are lower than theoretical values. By considering these voltage drops a better match between theory and measurement can be seen. The results follow the expected values by the theoretical formula Vo=Vin( D 1 D ). - 24 -
Flyback Converter: Output Voltage Table 4: The theoretical and actual output voltages (Vo) for the Flyback Converter (Vin=15 V f= 100 khz L= 106.6 µf RL= 10 Ω) Duty Cycle D [%] Theoretical Output Voltage Vo [V] Vo=Vin ( N2 N1 ) ( D 1 D ) Actual Output Voltage Vo [V] 0 10 20 30 40 50 0 0.002 0.833 0.56 1.875 1.33 3.2 2.67 5.0 3.97 7.5 5.66-25 -
OUtput Voltage Vo[Volts] Alex Bermel 8 Outputput Voltage vs Duty Cycle 7 6 5 4 3 2 Theoretical Actual 1 0 0 10 20 30 40 50 Duty Cycle D[%] Figure 6: The theoretical and actual output voltages of the Flyback Converter Observation: The above theoretical formula assumes that the MOSFET and Diode are ideal and have 0 V drop. However, in the actual results, the drop in each switch can be approximately 0.6 V which is significant considering that output voltage is only 5 V. This accounts for error between the calculated and measured values of Vo. The Flyback converter results show that the observed performance of the Flyback converter is moderately close to the expected performance. The input current and output current are correlated to the turns ratio. It has been determined that the ripple in the input current depends on the input voltage, duty cycle, and the frequency applied to the circuit. The exponential increase in the output voltage is expected as the duty cycle increases. The output voltage results follow the expected formula of Vo=Vin ( N2 N1 ) ( D 1 D ). - 26 -
Forward Converter: Output Voltage Table 5: The theoretical and actual output voltages (Vo) for the Forward Converter (Vin=20 V f= 100 khz L= 106.6 µf RL= 10 Ω) Duty Cycle D [%] Theoretical Output Voltage Vo [V] Vo=Vin D Actual Output Voltage Vo [V] 10 20 30 40 2 1.50 4 3.4 6 5.21 8 7.05-27 -
Output Voltage Vo [Volts] Alex Bermel 9 8 7 6 5 4 3 2 1 0 Ouput Voltage vs Duty Cycle 0 10 20 30 40 50 Duty Cycle D [%] Theoretical Actual Figure 7: The theoretical and actual output voltages of the Forward Converter Observation: It is observed that the output voltage predictably follows the theoretical formula. There is a miniscule difference due to the voltage drop across the MOSFET switch, diode, and other components. The Forward Converter s output voltage, as shown above, increases linearly as the duty cycle increases. There is approximately a 0.5 V voltage drop due to the diode and switch in the circuit. The measurement of current at input indicates that during the OFF period the input current is negative due to the reverse current flow from the tertiary winding. The output voltage did follow the equation Vin D respectfully. - 28 -
References Power Electronics by Ned Mohan Power Electronics by Daniel W. Hart Internet University of Minnesota Power Electronics Lab John H. Ventura - 29 -
Appendix A Figure 1: Buck Convertor Figure 1: Buck Convertor Figure 2: Boost Convertor Figure 3: Buck Boost Convertor Figure 4: Flyback Convertor Figure 5: Forward Convertor - 30 -