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Wind Mill Technology Blanca Naudín Aparicio Supervisor HeikoSteenbuchVester Electrical Power Engineering Autumn Semester 2010 SDU University of Southern Denmark 1 1. Synopsis1 “The aim of this project is to build a model which controls the electrical power from a wind mill. When the generator is connected to the grid, the generator shall deliver constant power. The rotor is through a power electronic circuit and a transformer connected to the grid. A power electronic circuit controls the induction generator slip. Power, voltage, current and speed are measured through transducers. A digital signal processor is controlling the system.” “This project is dealing with control, regulation and supervision of electrical power from a wind mill. The electrical power from the wind mill must be constant with use of “slip regulation” The wind mill generator, which is an induction machine with wound-rotor, is electrically connected with at “stiff” electrical power grid. The wind mill generator is mechanical connected with a dynamometer. The dynamometer is the primary mover.” 1This synopsis is a description of the main task of the project, from “Project: Wind Mill Technology, the University of Southern Denmark, Electrical Power Engineering”. 2 2. Preface2 The first known use of the use of wind dates back to 3,000 BC with the first Egyptian sailing ships. In the seventh century in Persia came the first windmill that was used for pumping water or grinding grain. In Europe the windmills also appeared in the seventh century. From these Europeans machines resulted the well known Dutch windmills, which were very sophisticated in a mechanical way. In the United States of America was created the first horizontal shaft mill with multiblade by Daniel Halladay in 1854, this windmill was used to pump water in isolated zones. Because of his slowly movement, this machines weren't created to generate electricity. In 1890, the Danish Goverment launched a program aimed at developing wind power production, and this program was leaded by the teacher La Cour. Poul La Cour's machine launched in 1892, was the first one conceived, designed and built to generate electricity. He was considered the danish's Edison, and his work established the first steps in manufacturing modern windmills. The aerodynamic theory was not enough developed, so his machines were simple clasic rotors with low performance. Since the late nineteenth and early twentieth century Joukowski, Sabinin and Drzewieky in Russia; Betz and Prandt in Germany; Constantin and Eiffel in France developed the aerodynamics theory. The design criteria of these investigators were adjusted to the new generations of wind turbines. At the end of the World War II, and as a result of fossil fuel shortages, European goverments were interested in the use of renewable energy. During that period measurement methodologies were developed in several countries. This period lasted until the mid-sixties, when the world economy recovered. The electrification was extended enough to cover most rural areas, and wind power plants were not competitive with conventional plants. As an example, a Danish company started manufacturing two-and three-bladed wind turbines at that time. It is also known that in the 50's appeared the first alternating current turbines. In 1973, as a result of the oil crisis occurred because of the Arab-Israeli conflict, began another stage in the area of using wind as an energy source, sharing the stage with photovoltaic solar energy. Back in the eighties wind power receives a boost when environmental issues became first order problems. As a result of the above mentioned energy crisis of 1973 appeared the first research programs relating to wind energy, both national and supranational. Since the 1980s they have seen an exponential increase, both in unit power ratings and overall capacity. The theory of modern wind turbines has not been established before the 20th century. Currently wind turbines with three blades and horizontal shaft prevail. The driven electric generators are of the asynchronous or synchronous type, with or without interposed 3 gearbox. Modern systems are designed for variable speed operation which makes power electronic devices play an important part in wind energy conversion. Nowadays, the most common rated of wind turbines is 1-2 MW. But it is also produced wind turbines with a rated power above 2 MW. Manufacturing has reached the state of a high-tech industry. Countries prominent for the amount of installed wind turbine systems feeding into the grid are in Europe Denmark, Germany and Spain. Outside Europe it is the United States of America and India who stand out with large rates of increase. The market and the degree of contribution to the energy consumption in a country has been strongly influenced by National support schemes, such as guaranteed feed-in tariffs or tax credits. Kyoto protocol and UN Climate Change Conference 2009 (which replaces Kyoto protocol) also help renewable energies to have a key role in the supply of electricity. In UN Climate Change Conference 2009, the final goal that was intended to a global reduction in CO2 emissions by at least 50 % compared to 1990. Climate changes, earth’s fossil energy resources limited and the strong political opposition against strengthening nuclear power in many parts of the world contributes more and more to the world’s ever rising need of renewable energy in the future. And the future in windmill is off-shore wind parks. Without the interference of forests and population centers, the huge white sails of the windmills at sea generate more power. Denmark it was clear as early as 1991, when he inaugurated the first prototype offshore wind farm, known as offshore wind in the jargon of the industry. So I can say that more and more countries will join to this clean way to generate electricity that will help the world to avoid climate change. 2 my preface is based in the following books and websites: -Z. Lubosny (2003). “Wind turbine Operation in Electric Power Systems”. Springer. -T. Burton, D. Sharpe, N. Jenkins, E. Bossanyi (2001). “Wind energy handbook”. John Willey & Sons, Ltd. -Manfred Stiebler (2008). “Wind Energy Systems for Electric Power Generation”. Springer-Verlag Berlin Heidelberg. http://es.wikipedia.org/wiki/Conferencia_sobre_el_Cambio_Clim%C3%A1tico_de_la_ONU_2009 http://www.cubasolar.cu/biblioteca/energia/Energia40/HTML/articulo06.htm 4 3. List of contents 1. Synopsis1 ..................................................................................................................... 1 2. Preface2 ........................................................................................................................ 2 3. List of contents ............................................................................................................ 4 4. Introduction ................................................................................................................. 5 5. Main report .................................................................................................................. 6 5.1. Generator ..................................................................................................................... 6 5.2. AC/DC converter ....................................................................................................... 22 5.3. Inverter and Pulse Width Modulating (PWM). ......................................................... 33 5.4. Control. ...................................................................................................................... 37 5.4.1. LabView. ........................................................................................................................ 37 5.4.2. Arduino. ......................................................................................................................... 41 5.5. Power board. .............................................................................................................. 45 6. Conclusion. ................................................................................................................ 52 7. List of lecture. ............................................................................................................ 53 8. Time schedule & working plans. ............................................................................... 54 9. List of symbols. ......................................................................................................... 56 10. Project presentation. .................................................................................................. 57 11. Process description. ................................................................................................... 59 12. Appendices. ............................................................................................................... 60 5 4. Introduction The requirement of this project is to control, regulate and supervise the electrical power from a wind mill. The electrical power from the wind mill must be constant with use of “slip regulation”. This semester, I have had two subjects:  Control Engineering and Signal Processing.  Power Electronics and Electric Machinery. In these two subjects, I have specific information about the different parts in which my project is divided. So I have applied it during my study. The project can be solved with knowledge in electric machines, power electronics, control engineering, signal processing, project management and basic knowledge within mathematics, electrical physics, circuit theory, digital and analogue electronics, electronic data processing. My limitations in this project have been my little knowledge about electronics. The control of the induction machine has been the harder part. When I began the project, it took me a long time to identify all the components and its function into the control system. After the identification of all the devices, I started testing. my limitations in this area have been the bad performance of the induction machine. The experiments has delayed my work, because of I have made them several times the same tests, to be sure of getting the right values. I have found some alternatives while doing this project. But, at the end, time ran out faster than I expected. I delayed the planning so I could begin the control system. I have also found much work in the theoretical part about the PWM and the powerboard. To solve my problem, first, I wrote all the theoretical parts without making a lot of measurements. So in a short period of time, I did measurements for the control system, and perhaps I would need longer time to do it. I have improved the knowledge in electronics systems and learned the new software Labview. So this project has helped me to gain better understanding on working electronic systems mixed with machines. 6 5. Main report 5.1. Generator The machines used to work as generator in windmills are the asynchronous machine or the synchronous machine. It depends of the country, but the most common machine used in Denmark is the asynchronous. Asynchronous machine have a lot of advantages vs. synchronous machines. The asynchronous machine, especially in the form of cage induction machine is a robust and low cost generator. They are very flexible machines, and with an electronic controller, the speed of the generator can be allowed to vary with the speed of the wind. Although, they also have disadvantages. Asynchronous generators require relatively complicated electronic controllers. They are usually not started without an energized connection to an electric power grid, unless they are designed to work with a battery bank energy storage system. But the cost and performance of such a system is generally more attractive than the alternative systems using a synchronous generator. The asynchronous is also known as induction machine. This machine can work in three stages, as a generator, a motor or a brake. In my project I use the induction machine as a generator to transform the mechanical energy from the wind into electrical energy. There are two types of induction machine: the wound-rotor machine and the squirrel-cage machine. In my case, I use the one with slip regulation, because this has been previously set in the project by teachers. In my project the mechanical energy is produced by a dynamo who works as a motor. The induction machine, to work as a generator, needs to get a higher speed than the synchronous one. This is shown in the curve beside. Plot 1. Torque-speed curve of an induction machine. 7 1. Theoretical study. Asynchronous rotating machines consist of a stator with a preferably three-phase winding, and a rotor carrying either a cage winding or a polyphase coil winding. Rotor voltage is produced in rotor coils by stator, that’s the reason why they are called asynchronous machines. Figure 1. Three-phase induction machine. The Ring Asynchronous Machine’s rotor has a three phase winding group. Generally the three phase rotor’s winding is star(Y) connected and rotor conductor’s points are connected with rings of rotor shaft. Then rotor wrapping is short circuit by slipping brushes. So the rotor current can be measured from rotor’s brushes and the motor can be controlled and set up its speed adding external resistor. The machine works in a simple way. The stator is supplied by a three phase current, so a counter clockwise magnetic field (Bs), is induced in the air gap between stator and rotor. This magnetic field rotates with the synchronous speed ns. The machine is working as a generator, the shaft is rotating with a determinate speed (in reality, this movement is provided by the wind), so that, the rotor is also rotating with a higher speed than the synchronous. So the magnetic field and the rotor turning induce a voltage in the rotor coil, which also generates a magnetic field (Br). According to Lenz’s law, the rotor rotates in the direction of the rotating field such that the relative speed between the rotating field and the rotor winding decreases. The difference between the rotor speed n and the synchronous speed ns is called the slip and is defined as Formula 1 The equation of the magnetic field’s speed n (sync) is shown below, where p is the poles and f1 is the stator frequency. Formula 2 Formula 3 The equation above is the induced voltage E, electromagnetic force (emf), caused by a loop of conductor with a side of length l moving in a direction parallel to the magnetic field, B, at a speed v. The rotor has to be connected with the grid, so it can supply a current with a different frequency (f2). This frequency is calculated as 8 Formula 4 I need to get the equivalent circuit to study an asynchronous machine, so, in laboratory I have been making test to know the performance characteristics of the machine. The machine that I have used is the following one: Feedback 64-520/ Three Phase Sync/Async Motor/Generator-Slip Ring Supply 220 V Δ 380V Υ Rated at 415/380 V 300w 3000 r.p.m at 50 Hz Power requirement 380/415 V Three Phase AC After making the tests that are going to be described later, I get the equivalent circuit of the induction machine. This circuit allows me to make a theoretical study about the machine. In this circuit it is shown the line and phase voltage and the resistance values and inductance values, all are in ohms (Ω). Figure 2. The equivalent circuit of an asynchronous generator. 15 2. Practical study. The tests that have been done in laboratory are described below: 2.1 MEASUREMENT OF STATOR RESISTANCE Assuming that the windings of the three motor phases are identical, I just get the value of resistance in one of the three windings. To do this, I use a polymeter. What is really important to get is the resistance per phase, so it is independent of the type of connection. The equation to get the resistance is the following one: Formula 24 We do not use that equation, because I measure directly the stator resistance with the polymeter after the machine have been running for a while. The obtained value is: 2.2 BLOCKED ROTOR TEST – SHORT CIRCUIT TEST Through this test, I determine the values of rotor resistance and reactances. To do this, the rotor must be perfectly fixed, not turning, thus the slip is the unit. Under these conditions, I apply to the machine a balanced three-phase voltage which will increase from zero to the voltage that supplies the nominal stator current. This voltage will be always lower than the nominal one. The equations used to calculate the parameters are shown below. Formula 25 Formula 26 Formula 27 Formula 28 Formula 29 16 Formula 30 Figure 6. Short circuit of the induction machine. To make measurements, I have set 300 W (he rated power of the machine) per three phases. This experiment is made with the rated stator current, but this value was not given in the characteristic plate of the machine. I have measured the power, the line voltage and the current flowing through the stator. With this test I also get the relation between stator and rotor. I measure linear voltage in both sides of the machine, stator and rotor. Previously I have set 380V in the stator. The following equation shows the relation: 17 Formula 31 With the turns ratio “a” value I can calculate and . 2.3 NO LOAD TEST In general, in this test, the engine is fed at the rated voltage and frequency. I measure the power consumption, the current flowing through each phase and the voltage applied to the stator. In this test, the shaft power output is not measured (there is no load, therefore the rotor circuit is opened and current does not flow through the phase), so that, I measure all the losses power (iron, copper in the stator, and friction). Therefore, the no load test lets me to measure these losses, and from them the parameters in the core machine, using the following equations: Formula 32 Formula 33 Formula 34 Formula 35 Formula 36 18 Figure 7. No load circuit. We have set the rated linear voltage (380 V). Then, I have measured the power per phase, the voltage and the current flowing through the stator. 2.4 Load test: Determination of T-s curve To determine the characteristic curve T-s from the machine, I will be testing different values of load, obtaining different values of mechanical torque to each value of speed. At the beginning of this test, I will start measuring with the machine working as a motor and the dynamometer as a load. When I get to 3000 rpm, I change the connections in 19 the dynamometer and it starts working as a motor and the asynchronous machine as a generator. I modify the speed over the rated value (3000 rpm), so that I are producing power. I obtain different points of the characteristic curve. I measure the voltage, the current, the power, the torque and the speed. Plot 4. Torque-speed in the real asynchronous machine from the laboratory. The graph is very similar to the experimental one, as I explained before. I have had a lot of problem doing this test, due to the machine is relatively new. I did the experiment several times. At the beginning, I got very low values of torque, when the speed was close to the maximum speed (our maximum speed is close to 3450 r.p.m.). I expected higher values of torque, to reach -1 Nm, but in the test, it was not possible. Then, with my calculations, I realized that this machine does not approach to -1 Nm. The chart shows the values that I got from the machine working with feedback. 20 Test Generator No. V1(V) V2(V) V3(V) I1(A) I2(A) I3(A) Power factor Real Power (W) Torque Nm Speed rpm 1 371 367 375 0.30 0.32 0.29 -0.192 65 0.064 2984 2 374 368 374 0.30 0.32 0.29 -0.153 51 0.085 3011 3 376 368 375 0.30 0.33 0.30 -0.175 60 0.119 3053 4 376 368 375 0.33 0.36 0.33 -0.260 99 0.172 3106 5 376 369 374 0.40 0.43 0.41 -0.294 134 0.248 3178 6 375 369 375 0.44 0.47 0.46 -0.303 155 0.295 3212 7 376 369 376 0.55 0.58 0.57 -0.311 198 0.401 3272 8 378 370 374 0.61 0.63 0.62 -0.319 222 0.448 3307 9 377 369 376 0.66 0.69 0.68 -0.319 242 0.501 3340 10 376 369 373 0.75 0.77 0.76 -0.326 277 0.589 3390 11 377 371 373 0.79 0.81 0.80 -0.329 295 0.633 3409 12 377 370 374 0.87 0.89 0.88 -0.329 324 0.720 3449 13 376 369 375 0.93 0.94 0.94 -0.329 345 0.785 3479 14 377 370 374 0.96 0.97 0.96 -0.331 357 0.818 3480 15 377 370 374 0.95 0.97 0.96 -0.331 357 0.821 3483 16 377 371 375 0.95 0.97 0.96 -0.333 357 0.826 3481 Chart 1. Values from the feedback program. To sum up the practical study, the asynchronous machine is working in a right way as a generator, but not as I expected. It has given me a lot of problems with measurements, several times, I have been testing it, following the same standard and each time, I have obtained different values. One of the reasons is that the machine is new, and the brushes did not make good contact with the rings correctly. After running the machine several times, problems were less. 3. Conclusion. In Denmark, the asynchronous machine is one of the most popular machines used in windmills, because of its simplicity and effectiveness. In this type of machine, I have access to the coil of the rotor. The electronic devices used in control the machine, are connected to the rotor coil. And this machine is perfect for this purpose. The more important value to control is the rotor current, so this machine fits to the requirements in the control. My theoretical study was based on experiments, so maybe, noticeable mistakes have been done. I used correct formulas taken from recommended books. In the experiments, I 21 follow the standardization in testing asynchronous machines, but measurements depend on the instruments used, and they are unpredictable. And the fact that the machine is a new one, and at the beginning it does not work as I expected, has delayed a lot my work. 22 5.2. AC/DC converter AC/DC converters are used in the wind turbine generator systems to connect and purposes. Structure of converter system includes rectifier (AC/DC converter), filter and inverter (DC/AC). It works between power system and asynchronous machine terminal. In my case I are connecting converter to the machine rotor terminal and second side I should connect to converters transformer. In this chapter I will describe my AC/DC converter. 1. Construction I have some various structure of rectifier. To build it I can use controllable or uncontrollable elements. First one are for example thyristors or MOS-FETs, second one are diodes. During the AC/DC construction I can use different elements. In my project, the rectifier will be a six-pulse bridge for three-phase input and it will consist of diodes. This part of converter is responsible for transform current of a given voltage, frequency and number of phases into DC current3. After rectifier I have two elements: capacitor and coil. Combination of them is intermediate element which is working as low-pass filter. I are using that because after diode-bridge, I still have harmonic in current and I also need filter to get 1% ripple of output voltage. The 1% is because of DC/AC inverter on power board, for correctly work should get signal no bigger than this 1% of ripples. 2. Theoretical calculations 2.1 Focusing on voltage and current in the circuit. For choosing elements of filter I need to know the values that I are getting from the rotor, how big is DC voltage after bridge and what value of current I have to keep in the output of filter. I start with the rotor calculations. I set power to P=300 [W] with asynchronous speed n=3270 rpm. That means that the slip, for the range of speed n =3270 r.p.m. and ns = 3000 r.p.m, is: 0.09 s s nn sn   When I know the slip, I can calculate next values: 3Manfred Stiebler, Wind Energy Systems for Electric Power Generation, 2008, ISBN 978-3-540-68765-7 23 a) Rotor frequency (3270) 50*0.09 4.5[ ]f Hz b) Voltage at a given speed. Formula 37   3270 0.9 106 9.54[ ] rotor VV   c) Peak voltage at a given speed. Formula 38     ,3270 7,789 peak rot VV We can also calculate a DC voltage that I have after the rectifier bridge. Formula 39     _3270 9,54 32 7,43 3 DC V VV     To calculate the current, I use the equivalent circuit of the rotor. The circuit is present on figure 8. Figure 8. Rotor equivalent circuit (symbol 2nd in the figure is an index and E2s= nrotor V, ). The current that I want to introduce in the input of the bridge, can be calculated using the following formula: Formula 40 , 222 22 3 () rotor n V IR jX  ][5488,1 ][)0422,3()88417,1( ][ 3 54,9 22 2A V I   So the value of the rotor current is I=1.5488 [A] 24 2.2 Values of filter elements I have several types of filter and each has three kinds of passive elements – RLC. Circuits containing two store elements, are known as second-order circuits because their responses are described by differential equations that contain second derivatives4. In my project I are working with low pass filter RLC as it is shown in the figure bellow: Figure 9. Schematic of low pass filter RLC. From the ratio of input and output voltage I obtained the following formula: Formula 41   22 2 2  LLRCR R V V in out   And I made second ordinary transfer function to continue my calculation. Formula 42     LjLRCR R jH  2 I started with the inductance of the rotor calculation, and it depends on the rotor frequency. Formula 43 rot rot f X LLfX   2 22 222  ][5958,107 ][5,42 ][0422,3 2mH Hz L     I got a very high value in the inductance. I checked the inductances in the laboratory and the biggest one that I found had the value of L=64 [mH] (with an internal resistance of R=0,5 [Ω]). That is why next calculations and measurements were based on that value. 4Manfred Stiebler, Wind Energy Systems for Electric Power Generation, 2008, ISBN 978-3-540-68765-7 5Theodore Wildi, Electrical Machines, Drives, and Power Systems, 6th ed., ISBN 0-13-177691-6 31 4. Measurements. After building the converter, I tried to support my theoretical considerations by practical tests. I connect my converter to the induction machine and to the oscilloscope to see the voltage. At first moments, I explored diode-bridge. Characteristics which I get I present bellow, the green signal is the one after the bridge: Plot 8. Three phases and voltage after rectifier. We got a clean signal from the three phases voltages and a good results of the rectified signal. Then, I connected elements of filter and I saw bigger noises on all characteristics. I suppose that is because of a big amount of wires. It could be due to, there was not a good connection between soldered components. Actually I had some problems with generator and feedback system. To get characteristics in the plot 9, I should increase the speed of the machine to n=3400[rpm] and then decreasing it to set the following speed n=3270[rpm]. Only using that way I could get the expecting plot. Plot 9. Three phases and voltage after filter. 32 Despite disruptions, I get the main goal. The green signal in plot 9 shows the voltage after the filter. The graph shows a lot of noise, but it is quite similar to the theoretical results. So finally, I think that my measurement is quite correct. Figure 13. Laboratory measurements. 5. Conclusion. In that part of my project, I changed AC voltage to DC. I have done it using a 6-pulse diode-bridge and a low-pass filter. It took me a lot of time and I have done many calculations focusing with the filter and lots of PSpice simulations. In the report, I present one of the ways to get correctly values of filter and the best calculations which have been made for generator parameters. Rectifier and filter, which were connected, are working. Unfortunately I didn`t get 1% of ripples for voltage after filter. That is why I can`t connect converter with power board system. I have made as much as it possible in the time that I had. I could not focus on details, but finally, I think that is quite good. 33 5.3. Inverter and Pulse Width Modulating (PWM). 1. PWM inverter, Inverters are circuits that convert DC voltage to AC voltage in a desired amplitude and frequency. As the output voltage can be set up, this is made with constant frequency or varying the frequency. Several output voltages can be obtained by using DC voltage inputs, with a constant efficiency performance of the inverter. If the input DC voltage is constant and it cannot be set up, some voltage outputs can be gotten by changing the gain of the inverter. And this action is made by pulse with modulation. The gain of the inverter is the ratio between output ac voltage and input dc voltage. On an ideal inverter, the output voltage should be sinusoidal wave form. In a practical inverter, the output voltage is not totally sinusoidal because there are some harmonics. The bridge circuit of an inverter can be constructed by using transistors, MOSFETs and diodes. In this Project transistors are used like it is shown in the below figure. Figure 14. PWM Inverter. Pulse-width modulation uses a rectangular pulse wave whose pulse width is modulated resulting in the variation of the average value of the waveform. 1.1 Operation: PWM received the 6 pulse signal from microcontroller. In my case, I use Arduino to generate the sinusoidal signal because the powerboard works with digital. 34 For 1-phase, when the transistor 1 conducts, I have the signal A and when the transistor 2 conducts I have the signal B. Plot 10: PWM signal for 1 phase Plot 11. Signals seen in the PWM. On a three phase bridge circuit of inverter, the polarizations can be obtained by switching the sequence of the transistors. When one of the legs of the two switches (transistors) is opened, the other switch is never opened at the same time. And each switch provides a pulse, which has amplitude π, and on the other pulse is seen with an angle (α). As this action occurs in each leg, and, therefore in this way, three phase output voltages can be gotten. And the voltages on the each leg (V (A0), V (B0) and V (C0) can be changed between 0 volt and Vdc/2 volt. In my case, I have a different range of voltage, so what is explained is in theory. The best system to control the asynchronous machines is the change of frequency that inverters use. This change is provided using pulse width modulation (PWM) with a constant input dc voltage. Effective voltage can be gotten, and this voltage can be controlled on this type systems. At the same time, by using this modulation, the harmonics can be reduced. 35 The inverter that is fed by the filter after the ac/dc converter, has two switches transistors and on the each legs. By using PWM control, this can be controlled by changing the obtained angle (α) and contrasting between sinusoidal signal with the according desired frequency and the triangular switching signal. And this action is applied by using microcontroller, which is connected to computer program. In this Project, to fit that purpose, Arduino Duemilanove ATMEGA328 is used. IN the following figure, it is shown this triangular signal and the modulation of PWM. Plot 12. Modulationof PWM. In my project, the function of the Arduino program is to compare the two analogic signals, to convert them into digital. So that, in the output of the microcontroller, I get the U10 signal (modulation PWM). The modulation of PWM is a synchronous modulation, using sinusoidal reference voltages and a triangular carrier voltage. So, the main goal, it is to compare both signal, the one from the tyristors and my sinusoidal reference signal. The results are depending on whether uref > utri or uref < utri. This is shown in the Figure above, for u10 and u20, resulting in the output line-to-line voltage u12. The modulation ratio is defined using reference and triangular voltage amplitudes: Formule 56 m = 36 In my case, I must also focus on the problem of dead time. Plot13. Death time. PWM input signals of the transistors provokes that the transistors T1 and T2 are turned on or off. The situation in which both transistors are working simultaneously, could not happen, because in that situation, a short-circuit could be provoke. That's the reason why it is not possible to obtain the 100% duty cycle, due to the rise and fall times of applying the transistors. So dead time is necessary to add, in the case that, the second transistor turns to be off. Formule 57 Formule 58 Where: VADC0 – Voltage on Analog to Digital Converter input TPWM – PWM signal period 37 5.4. Control. 5.4.1. LabView. Objective : Labview is a software that I use to measure and to calculate control systems. We have made a program for the regulation of the circuit. I measure the speed and the power of the rotor, next I calculate the value of the current of the rotor to send it to the powerboard, to change the voltage and the current to get a constant power. 1. Measurement 1.1 Power of the rotor 1.1.1 Connection I use a powermeter to measure the power of the rotor. To connect the powermeter to Labview, I use a GPIB USB cable. 1.1.2 Program Figure 15. Diagram of power program. I use I/O Instrument to configure the analogique input and to measure the power. 1.2 Speed of the rotor. 1.2.1 Connection. We use 2 cables to connect the speed control panel with the NI USB 6008. 38 1.2.2 Program Figure 16. Diagram of speed program. I use DAQ Assistant to configure the voltage. Next, I choose ai0 for analogique input. 1.2.3 Measurement The objective of this measurement is to find a coefficient between the speed and the voltage. I have connected the rotor and the stator of the induction machine in Star. I have connected the NI USB 6008 from computer to control pannel on “external speed”. Figure 17. Measurement with speed program. After measurement I find the coeffient between the speed and the voltage: For 2900 rpm I have 5.60 V So I have 5.6V  2900 rpm 1V  518 rpm 39 2. Calculation Formula 56 s R ITP mecmecmec 2 2 2..   Formula 57 2 2 2..RsT mecmec I   Formula 58 . .. 2 2R Ts Imecmec   Figure 18. Diagram of calculation of current. I add both power and speed program in the current program to find the value of the rotor current. 40 3. Difficulties and solutions.  Problems. Working with a new software was difficult. Understanding why it is useful Labview in the project. How to acquire the data. I have had some problems configuring and connecting, because there were many types of data (speed, current, voltage, power). How to program to obtain the acquisition of data? The speed program worked but I didn’t find good results, because I have not obtained a signal constant and I were expected to obtain it. The power program was not finish because I needed more time to end it. We didn’t know how to send the value of the current rotor in the microcontroller.  Finding solutions. To solve my problem, I have asked many questions at the teachers, the other groups and I have studied using Labview tutorial.  Future perspectives. We can try to have a good result for the speed program. To finish the power program and to find how to send the value of the current in the arduino software. Conclusion: To sum up, the speed program works to measure the speed of the motor because I have obtained the result to hope. However, the power program need some modification to work. Labview can acquire data, to calculate and to generate a value. To finish the program, I would need more time 47 1.4. Conclusion. The conclusion of my power-board is that I have not been able to calculate the signals from output of inverter board because the power board did not work correctly. But the expected results of the power-board are shown in the figure below. Plot 14. Results of power board. The power board is also connected to the lowpass filter, which will be designed and used to eliminate harmonics. If everything would go on well and I would have a well working power board, I could have had an ideal voltage in the oscilloscope. I have many worked the theoritical part. my results concerning the induction machine seem true, moreover, for the other parts, I have make some measures. In the perspectivation to improve the project, I will make the measurement necessary. Plot 15. Expected three phase voltage after the low-pass filter. 8,9,10Wind Mill Technology Project. This information was given by one of the teachers. 48 2. Tests and measurements: PWM Signal and Power Board. 2.1. Operation. The powerboard received a DC signal between 0 and 5V. When the input voltage is 0, the amplitude of the sinusoidale is 0. Otherwise, when the input voltage is 5V, the amplitude is 5V. Figure 23: Principle to create 1 sinusoidal signal. 2.2. Measurements. 2.2.1. Devices used in laboratory. These are photos which show the elements used in the laboratory and how they are connected to each other. The next picture shows the measurement with the oscilloscope, the output signal of the micro, here, the digital output signal of phase 1. Figure 24. Phase 1 output signal. Sinus table 2 Signals to control 2 IGBT 1 PWM signal Control amplitude [0 ;5V] Arduino PWM Powerboard 49 In this picture, it is showed the power-board with all its elements. Figure 25. Power board. Below, the different signals obtained in the laboratory. That logical signal is my theoretical sinusoidal refrence voltage. Figure 26. Logical signal that I have obtained in the laboratory. 50 In this picture, the time of logical 1st signal is appropriate to adjusted duty cycle. I see that the time of pulse is the same, but setting of duty cycles differs for every phase. This graph can be compared with the one that has been showed before. Figure 27. First logical signal. 2.2.2. Straight from microcomputer outputs. Below in the next pictures, I show the different signals. Firstly, I have to adjust microcomputer to generate signals and I have to use time delay between the generating of the new cycle, with time delay I observe in the oscilloscope that duty cycle is changing in one period as the signal is increasing, and after that, the signal is decreasing. Figure 28. The duty cycle is increasing in one period. 51 Figure 29. The duty cycle is decreasing in one period. The dead time was not calculated, but it was explaine in the PWM theory. 3. Conclusion The conclusion of this part is that the graphs after the micro shows outputs optical signals with time delay and in these signals are increasing duty cycle at the beginning and these signals are decreasing duty cycle to end in one period, in this case observe that the results obtained in the practical part match the results I had to get a theoretical part. In my case, as it was explained above, the power board did not work correctly. So, what it is wrong with the power board, is that I could not measure the output of the power board, because the range of my signal is from 0 to 5 V, so this range is not big enough to generate the harmonics. 52 6. Conclusion. The project, that I explained in the whole report was a complex study during the last 3 months. I have had some problems like the comprehension of some objectives, and the performance some components like the Labview, the Arduino program and the powerboard. Moreover, the achieved results in theory didn’t allow me to work in the laboratory, because in the case of the filter, I should have used a higher value of inductance as I calculated. With the power board, I could not also obtain the output signal, because of the bad performance of the power board in low frequencies and low voltage. The induction machine, as it is a new machine, has also given me a lot of problems during testing. Due to all those inconvenients, I could not finish the main aim of the project, the connection to the grid using the transformator. I have had problems with time. To know the right values of the equivalent circuit took me a long time, due to I did not have the exact results to compare to, no references. One of the main problems was the English language. Although, that problem helped me to make a bigger effort, so I improved my English. My perspective in this project would be to connect the different parts all together, and get the right results in laboratory. I knew that I did not have enough time to study the transformer, because the teacher told me this at the beginning of the project. So I don't know if my wind mill model works in the right way. I thank the help that I have recieved from teachers. 53 7. List of lecture. 1. Books.  [Fundamentals of Electric circuits, 2nd edit, Ch.K. Alexander, M.N.O SAdiku.]  [Modern Control systems, 11th edit R.C. Dorf R.H. Bishop]  [Principles of Electric Machines and Power electronics 2nd edition PC Sen]  [Electrical Machines, drives, and power systems, 6th edition, Theodore Wildi]  [Grid integration of Wind Energy conversion systems 2nd edition, John Wiley & Sons,Ltd]  [Wind Energy Systems for Electric Power Generation. Manfred Stiebler (2008). Springer-Verlag Berlin Heidelberg.] 2. Websites.  http://biblioteca.uns.edu.pe/saladocentes/archivoz/curzoz/Form.%20M%E1quinas%20 Asincronas.pdf  http://rabfis15.uco.es/lvct/tutorial/41/tema19/tema19-4.htm  http://www.scribd.com/doc/305836/maquinas-electricas-la-maquina-y-el-motor- induccion-trifasico  http://www.arduino.cc/es/ 54 8. Time schedule & working plans. 1) Introduction Making a planning was new for me. I have had some problems. Nevertheless, I knew a plannification software that has helped me a little bit: Ganttproject. 2) Divided the work Firstly, I have divided the work in four parts:  Induction machine  AC-to-DC converter & DC link  PWM = DC-to-AC  Labview & microcontroller 3) Meetings:  Supervisor meetings: one times per weeks. I sent an mail at the supervisor to decide the hour for the next meeting. And during the meetings:  searching and studying about topics  making some measurement  deciding the task for the next meeting We have devided the project in three parts:  Theoritical : I study the information about induction machine, converters and transformer  Practical: to make measurements to find values and compare with theoritical.  Report 4) PLANNING: Appendixe2: Planning To start the project, I have used some litterature:  Electrical and wind mill books. 55  Website of wind mill companies. And I used my courses like CES, PEM and PRW.  Softwares : labview , feedback, P-spice , Ganttproject 56 9. List of symbols. B: density of magnetic flux C: capacitor D=Duty cycle : induced voltage on the rotor : Synchronous frequency : Rotor frequency : Frequency for dc voltage H(jaw):transfer function J:Inertia L=inductor value m:weight :coefficient of the depth of the modulation :frequency ratio between of triangular switching signal and desired control frequency n:asynchronous speed :rotor speed :synchronous speed p: number of poles :Mechanical Power :power on the shaft : Air gap power :input power : lost power on the cupper stator : lost power on the cupper rotor : :thermal resistance case mounting surface :thermal resistance junction :thermal resistance between the plate during the cooling bridge :rotor winding resistance :Thevenin Resistivity RLC=low pass filter : equivalent resistance : short circuit resistance r : rate :the core resistivity : stator winding resistivity R:resistance s: slip of rotor :max permissible temperature on the diode bridge :surrounding temperature t:time :integral time :deceleration time :derivative time = torque :Mechanical Torque :Mechanical Frequency :stator current : :short circuit impedance :Power factor : vacuum power : stator resistance : vacuum power : iron power :Efficiency :DC input current for stator :Friction and wind age power loses :stator inductance : magnetism reactance :rotor inductance :Thevenin inductance :short circuit inductance : primary voltage :Voltage on Analog to Digital converter input :DC input voltage :max voltage between line to line :Voltage between A points and 0 point on the inverter circuit :Voltage between B points and 0 point on the inverter circuit :Voltage between C points and 0 point on the inverter circuit :Voltage between A points and B point on the inverter circuit :Voltage between B points and C point on the inverter circuit :Voltage between C points and A point on the inverter circuit :input DC Voltage :output AC voltage : equivalent voltage :Thevenin equivalent voltage :secondary voltage :Peak voltage at given speed :DC voltage after the rectifier. :Input voltage at law pass filter. :stator impedance :rotor impedance :Thevenin equivalent impedance 63