In order to extract the most energy from renewable energy sources attention must be
focused on the efficiency of the power conversion of this energy. Up until recently,
only solar photovoltaic systems have had significant design efforts in insuring that
the maximum power at any given moment is extracted and converted to electrical
energy. The principal is called maximum power point tracking [MPPT].
I propose to build a small vertical axis wind turbine based on a design by Ed
Lenz and direct couple this to a Axial Flux Permanent Magnet [AFPM] generator.
The output of the 3-phase AFPM generator will feed power/control electronics that
will rectify and filter the AC output, perform DC-DC conversion to insure proper
output voltage (14 volts here), perform MPPT to insure maximum power output, and
shutdown the turbine in case of a high wind/over-speed condition.
4
ACKNOWLEDGEMENTS
First, I would like to acknowledge the VAWT design of Ed Lenz
(windstuffnow.com). My turbine is based on his design. I want to thank Kevin and
Andrea Noonan at FLN-MAR Rubber & Plastics, Inc. for the fabrication of the
plastic wing ribs and stringers. Many thanks go to Al Stucky, Matt Stucky, Kenny
Aro, and many others at Mass Precision, Inc. MASS Precision fabricated the rotor
axle, rotor struts, pole mount adapter, and pre-shaped the aluminum skin for the
wings of the turbine. Both the above named companies donated (free of charge) the
labor involved in fabricating these parts. Thanks also go to Steve Drake for his
valuable help in riveting the wings and the overall assembly and balancing of the
turbine. Finally, I want to thank W Stephen Woodward for his design idea (Solar-
array controller needs no multiplier to maximize power) published in the December
issue of EDN. The MPPT circuit is based on this design idea.
5
TABLE OF CONTENTS
INTRODUCTION.................................................................................................................................6 BACKGROUND ON WIND TURBINES/POWER GENERATION...........................................7
. THE WIND TURBINE..........................................................................................................................8
. THE ALTERNATOR/GENERATOR ....................................................................................................10
. COMBINED CHARACTERISTICS OF THE WIND TURBINE & GENERATOR ......................................11
. MAXIMUM POWER POINT TRACKING ............................................................................................12 DETAILED PROJECT DESCRIPTION........................................................................................13
Introduction At present, small wind turbines used for RV use or remote 12V power typically do not have Maximum Power Point (MPPT) electronics. They may have a 12 volt charge controller to insure that the battery does not get over-charged, but little control beyond that. My goal is to develop a smart DC-DC converter/wind turbine controller that:
1. Rectifies the 3-phase AC output of the generator. 2. Shutdowns the turbine in case of high wind/overspeed conditions. 3. Performs DC-DC conversion to insure proper voltage output regardless of
rectified turbine input voltage. 4. Performs Maximum Power Point Tracking (MPPT) to insure optimum
power output. I propose to do this by building a small, 2 1/2 ft by 3 1/3 ft Vertical Axis Wind Turbine based on Ed Lenz’s design that appeared in the July 2007 issue of Popular Science. This turbine has a published efficiency of 41%. Using an alternator with an efficiency of ~ 80% should yield an output of ~ 40 watts @ 15 mph. I will locate an off-the-shelf Axial Flux Permanent Magnet generator (AFPM) for this turbine. Linear Tech has a part (LTC3780) that can be used in a buck/boost DC-DC converter. They advertise efficiencies of 95-98% with input voltages of 6-30VDC. I will control the output power of this regulator by adjusting the output voltage to the battery using an analog Maximum Power Point Tracking circuit that consumes less than 2 or 3 milliwatts of power. I plan on using low voltage drop Schottky type diodes (SBR diodes from Diodes, Inc.) in the passive rectifier on the output of the alternator. These diodes have ½ the typical voltage drop (and ¼ the power loss) of a typical rectifier. This design will allow the wind turbine to have some usable output when other non-regulated DC wind turbines are not producing any usable voltage. By adding control electronics to the wind turbine, this may allow one to slightly undersize or oversize the alternator in order to optimize either low wind energy production or maximum high wind power. The turbine design specifications are shown in Table 1.
7
Table 1: Wind Turbine Design Specifications
Background on Wind Turbines/Power generation Almost all commercial wind turbines are Horizontal Axis Wind Turbines (HAWTs). Their axis of rotation is parallel to the ground (horizontal) and air flows through the blades only once. Another name used is “axial flow” for this type of wind turbine. The other type of wind turbine is the Vertical Axis Wind Turbine (VAWT). VAWTs are also called “cross-flow” because the wind passes through the blades twice- once on the upwind side and again on the downwind side. One of the advantages of the VAWT is that there is no need for a yaw control- a control needed by HAWTs to insure that the blades are perpendicular to the wind direction. Another advantage is that VAWTs operate at much lower Tip Speed Ratios (TSR) compared to HAWTs. The TSR is the ratio of the tip speed divided by the undisturbed wind velocity. For HAWTs, this value is typically between 6 and 20. The VAWT to be used here (Lenz turbine) has a TSR of 0.8 to 1.2. At 15
8
mph wind velocity the fully loaded rpm of this turbine should be ~ 134. At this rpm, the turbine should generate little audible noise and allow potentially longer life from the support bearings. Both HAWTs and VAWTs are limited in the amount of power they can extract from the wind. This limit is called the Betz limit after Albert Betz showed in 1928 that the maximum fraction of the power in the wind that can theoretically be extracted is 16/27 (59.3%) [1]. The Betz limit can be briefly explained as follows: If a wind turbine captured 100% of the wind energy flowing through its rotor area, the air on the trailing side of the rotor would be still. Therefore, the wind would stop flowing through the wind turbine rotor. If 0% of the energy available in the wind is captured the wind would have the same energy on the trailing side of the rotor as it did on the leading side. This logic shows that you can capture some of the wind’s energy, but not all of it. How much energy is in the wind?
.The Wind Turbine The power in the wind is directly related to its kinetic energy. We all know that:
KE =1
2mV
2
where m is the mass in kg and V is the velocity in m/s [2]. We also know that the mass of air moving (through a rotor) is the air density times the volume of air flowing per second. This is also equal to the air density x the area x the velocity. Therefore: m
air= !
airAV
We plug this into the above KE formula and we get:
P =1
2!AV
3
where P is the power in watts, ρ is the air density in Kg/m3, A is the swept area of the turbine rotor in m2, and V is the velocity of the wind in m/s [3]. With a design swept rotor area of 8.33 ft2 (0.774 m2)and a wind velocity of 15 mph (6.7 m/s) the potential wind power available is 139 watts. With a published wind turbine efficiency (Cp) of .41 , this should yield ~57 watts (mechanical power) available to the generator [4]. For a wind turbine where the pitch of the blades is fixed, such as the Lenz turbine, there is an optimum, constant TSR that will maximize mechanical power output [6][8]. Figure 1 shows a typical turbine efficiency (Cp) versus TSR (λ) curve for a fixed blade turbine with a constant field generator.
9
Figure 1: The variation of turbine efficiency with TSR (λ) [8].
If our goal is to design a control circuit that optimizes the power output of the wind turbine, then we need a circuit that allows the turbine rotor rpm to change with wind speed. Figure 2 is a graph of turbine power versus rotor rpm for three different wind speeds.
Figure 2: The variation of turbine power with rotor rpm and wind speed [8].
10
It is clear from the above two figures that we need to allow the turbine rotor rpm to vary in order to maximize power output with variable wind speeds. But the above two figures represent only one zone of operation of a wind turbine. Let’s step back and take a look at all the zones. The power output of a turbine can be divided into four operational areas or wind zones [9]. Please refer to Figure 3.
Figure 3: Turbine power versus wind velocity [9].
The zones in Figure 3 for this turbine can be defined as: Zone I -Turbine rotor does not turn (not enough wind) Zone II-Turbine works @ optimum TSR for best power/efficiency (45-180rpm or 5-20 mph) Zone III-Turbine power limited by maximum generator power (180-240 rpm or 20-27 mph) Zone IV-Turbine rotor is stopped/slowed down to avoid damage due to high winds (>240 rpm or >27mph) The reader can deduce that Figures 1 and 2 refer to zone II above. This area of operation clearly needs some type of active control in order to maximize power output. However, the turbine/generator combination may further complicate the power output characteristic in this zone. Let’s explore this characteristic in the next sections.
.The Alternator/Generator The alternator I chose is a Axial Flux Permanent Magnet generator (AFPM) made by SEO YOUNG TECH. CO., LTD (see Appendix A). This unit is a three phase,
11
20 pole generator with a wye connected output. The no load rectified output voltage versus rpm is given in Figure 4 below.
Figure 4: AFPM generator rectified DC voltage vs. rpm.
If we terminate the generator with a load resistance equal to the source resistance of the generator, this should give us the maximum electrical power output. Doing this will drop the output voltage to ½ it’s no load value. Let’s look at the combined output characteristic vs. rpm of the turbine/generator next. .Combined Characteristics of the Wind Turbine & Generator One can calculate the power output of the turbine vs. rotor rpm based on what we have covered so far. Recall that turbine power is proportional to the cube of wind speed. For this turbine, this means that turbine power is proportional to the cube of the rotor rpm (@ optimum TSR). For the generator, Voltage output is proportional to rpm (See Figure 4). This means that generator power is proportional to the square of the rpm because:
P =E
2
R
12
Figure 5 illustrated the relationship between turbine mechanical power output and generator mechanical power input. See Appendix B for these design calculations. This also corresponds to zone II in Figure 3.
Figure 5 From this Figure one can see that below ~ 150 rpm, the generator requires more mechanical input power than what is available from the turbine. If one were to terminate the generator with its ideal load, this would be too much load for the turbine. In order to address this issue, we need a method of controlling the turbine that will automatically adjust or limit the generator output to match the available turbine input power. The general description of the technique to do this is called Maximum (or sometimes Peak) Power Point Tracking (MPPT) [6] [7] [8] [9] [10].
.Maximum Power Point Tracking MPPT has wide use in many different applications. Besides optimizing power versus loading of fixed pitch wind turbines its most popular use is for photovoltaics. It can also be used for small pelton wheel (impulse) water turbines [6].
13
The most popular technique for implementing MPPT is the “perturb and observe” algorithm. This algorithm periodically “bumps” or perturbs the load voltage, and observes the change in power of the source-the turbine/generator in this case- and calculates the phase relationship between load power and generator power as feedback to “climb the hill” of the current vs. voltage curve to the optimum power point. A typical torque vs. rpm curve for a fixed pitch wind turbine is shown in Figure 6 [6].
Figure 6: Torque vs. rpm with dither for MPPT [6]. The circuit I chose to implement was found in a “Design Idea” article in EDN by W Stephen Woodward [7]. The only change I made to this circuit was to change the dither rate from 100 Hz to 10 Hz to allow for the slower inertial time constant of the generator.
Detailed Project Description .Mechanical Design/Construction In Ed Lenz’s turbine, the wing ribs were made of ¾ inch plywood while the rotor axle was made of iron. Iron straps that were welded to the axle supported the wings. The AFPM generator was a homemade unit that was integral to the rotor.
14
The turbine was supported by two pillow block bearings. Plans for this turbine can be found at windstuffnow.com. Please see Figure 7 below. For my turbine, I decided to use an off-the-shelf AFPM generator made by SEO YOUNG TECH. CO., LTD (see Appendix A). Because the bearings are integral to the design of the generator I did not have to be concerned with an upper bearing on the turbine rotor. However, this made balancing the turbine more difficult because the 40-inch long axle would amplify any error in the rotor axle face. Please refer to Figure 8 below. I used 5052 alloy aluminum for the rotor axle and wing struts. I chose marine grade plastic for the wing ribs and stringers. The wing covering specified in the original design was .025” aluminum. I used .032” because that is what the fabricator had on hand. Aluminum rivets were used to attach the wing covering to the plastic ribs. I used VectorWorks (CAD) to design the rotor axle, the two wing struts, and the pole mount adapter. Please see Appendix C for the mechanical drawings. Since the generator face had mounting holes for eight M8 bolts, I used these eight bolts for mounting the lower wing strut and the rotor axle to the generator. I also used eight M8 bolts (and nuts) to attach the top wing strut to the top of the rotor axle. The wing struts are used to support the three wings. Each wing is attached to the struts with six M6 bolts and nuts. All nuts and bolts are stainless steel. The expected life of the turbine rotor assembly is at least 20 years. The original Lenz turbine had a rotor diameter of 3 ft and a rotor height of 4 ft. Because the generator a chose was rated @ 140 rpm (see Appendix A), I scaled down the rotor diameter slightly in order to increase the nominal turbine rpm in a 15 mph wind from 122 rpm to ~135 rpm. With a design TSR of 0.8, the optimum rotor diameter is 30 inches. With a rotor height of 40 inches, the mechanical power output of the turbine –based on a Cp of 0.41- should be 57 watts (see Figure 10). The wings were also scaled down per the scaling recommendations by Ed Lenz at windstuffnow.com. The final turbine rotor size is 30 inches in diameter by 40 inches in height.
15
Figure 7:Lenz Turbine
Figure 8: Design Turbine
16
Figure 9: Overall block diagram of turbine
Figure 10: Overall turbine efficiency
17
.Electrical Design/Construction There are four functions implemented in the electronics. These functions are:
1. Rectification 2. Overspeed/Overvoltage shutdown 3. DC to DC Conversion 4. Maximum Power Point Tracking
These functions are shown in Figure 9. Please note that three of the four circuit functions were simulated in LTSpice (The MPPT circuit was not simulated). Before looking at these we need to look at the expected efficiency of the components that make up the turbine. Referring to Figure 10 and recalling our previous analysis of the total power in the wind we know that with this turbine rotor size, there is 139 watts available in a 15 mph wind. Based on Ed Lenz’s published efficiency of the turbine (Cp of 0.41) we have 57 watts of mechanical power from the turbine rotor. If we assume that the generator has an efficiency of 80%, then we have 45 watts going to the rectifier. Using Super Barrier Rectifier (SBR) diodes should provide us with an efficiency of 95%. The Linear Tech LTC3780 DC-DC Converter has a nominal conversion efficiency of 95%. This gives us 41 watts of power to the load. Let’s examine the four functions of the electronics and their implementation. A simplified schematic showing only the rectifier and the DC-DC converter is shown in Figure 11. The brake switch simply shorts out the generator, causing the turbine rotor to slow down or stop. This switch is used when performing maintenance or in high wind conditions to shutdown the turbine.
Figure 11: Simplified electronics schematic
..The Rectifier The purpose of the rectifier is to convert or rectify the three phase AC output of the generator to DC. Please refer to schematic 1 in Appendix D. I implemented a
18
three phase, two way, six-pulse topology using 6 SBR2060CT low forward voltage drop diodes. The typical voltage drop of these diodes at nominal output power (~40 watts @ 15mph) is less than 0.4 VDC. For higher efficiencies, an active rectifier topology could be used, i.e., Hall-Effect or opto-isolator sensors mounted on the generator shaft that switch Power MOSFETs or IGBJTs at the zero crossing of each phase’s output.
..The Overspeed/Overvoltage shutdown circuit The overspeed/overvoltage shutdown circuit can be seen on schematic 1 in Appendix D. The key simulation parameters for this circuit are shown in Appendix E. The main circuit elements are linear regulator U1, dual op-amp U2, 555 timer U3, and power MOSFET switch Q1. Conn2 is used to connect to a 0.5 ohm, 300-watt diversion load resistor (not shown). U1 uses +Vout (which is connected to a 12V 18ah lead acid battery) to supply a regulated 5.9VDC to the circuit. U2a is a comparator that senses the rectifier output voltage. When the rectifier output voltage exceeds 24 VDC, Zener diode D7 begins to conduct. When rectifier output voltage exceeds 32 VDC,U2a will see 6VDC on pin 2 , its output goes low, triggering timer U3. Timer U3 output goes high and switch Q1 conducts. This puts the 0.5-ohm, 300-watt resistor across the rectifier output. This causes high currents in the generator, slowing down the turbine, and lowering rectifier output voltage to a few volts or so. Also, when Timer U3’s output goes high, this causes U2b output to go low (RUN3780), shutting down the LTC3780 DC-DC converter (see schematic 2). The timer output resets after about 1 minute. Please note that comparator U2a has 4V of hysteresis, which should prevent false triggering. In simulation, switch Q1 never sees more than about 14A or so because of the internal resistance of the generator. And that current drops very quickly. Nevertheless, I sized the diversion load resistor to handle up to 2 kW for 2-3 seconds. Please note that the peak current rating for Q1 is 150A and the peak current rating of each of the rectifiers (D1-D6) is 80A. So we have plenty of design margin here. Resistor R1 is a current sense resistor that is used in the MPPT circuit.
..The DC-DC Converter Please refer to schematic 2 in Appendix D. A simplified schematic is shown in Figure 12 below. The DC-DC Converter uses Linear Tech’s LTC3780 chip. This circuit is unique in that it allows the use of a single inductor while allowing Vin to be below, above , or equal to Vout. It also boasts typical conversion efficiencies of 95%. However, you do pay for these benefits with increased circuit complexity. The circuit uses 4 MOSFET output switches and 4 Schottky diode
19
rectifiers. This circuit allows the rectifier output to vary between 5VDC and 30 VDC while supplying a constant 14.2 VDC output to the battery/load. Please refer to Linear Technology’s application notes for more information on circuit operation. Design calculations for this application are found in Appendix B. Please note that the circuit is designed for 200kHz operation and output increased to 14V @ 8 amps.
Figure 12: Simplified DC-DC converter circuit
..The Maximum Power Point Tracking circuit After significant research on peak power tracking circuits implemented with micro-controllers ([8] [10]), I decided to try a technique where no programming was required. Dr. W Stephen Woodward has published two techniques that do not use a micro-controller [6] [7]. I decided to use the second technique using the LTC3780 DC-DC Converter. The converter in [7], an LTM4607 is in a LGA package and is beyond my soldering abilities. That is why I chose the 24-pin LTC3780. The unique idea in this circuit is how it calculates the instantaneous change in power after perturbing the input voltage. It uses the logarithmic behavior of transistor junctions to calculate the change in power. The basic idea of peak power tracking in this circuit is to match the output power of the DC-DC converter to the output of the turbine-generator combination. The peak power tracking circuit does this by reducing the output voltage set point of the converter until power matching occurs. If the tracking circuit allows the
20
output voltage to go to the programmed set point (14.2VDC here) of the converter, then, at that point, peak power tracking is disabled and the maximum allowed output voltage –and maximum power if the loading is appropriate- occurs. This is where the turbine would be operating in zone 3 of Figure 3. For a description on MPPT circuit operation please refer to [7]. Figure 13 shows the MPPT circuit with the one capacitor changed from 0.01uF to 0.1uF. This slows the dither rate from 100 Hz to 10Hz. Although the circuit was designed for a solar-panel input, it should work well with the rectified turbine/generator input.
Figure 13: MPPT circuit [7]
..Circuit Construction The low frequency rectifier and the Overspeed/overvoltage shutdown circuit were placed on one two-layer printed circuit board (PCB) 3 inches wide by 5 inches long. The high frequency DC-DC converter and the MPPT circuits are placed on one four-layer PCB 4 inches wide by 5 inches long. I believe that by physically separating the high frequency DC-DC converter from the rectifier and the overspeed/overvoltage shutdown circuit should improve the noise immunity of
21
the latter circuits. Photographs of the two PCB’s are shown in Figures 14 and 15. The PCB layout for these boards can be found in Appendix E. There are five common connections between the schematic 1 PCB and the schematic 2 PCB. These are : +Vrect Positive terminal output of the rectifier -Vrect Negative terminal output of the rectifier +Vout Positive terminal output of the DC-DC Converter Gnd Common (ground) of both PCBs RUN3780 To Run pin of LTC3780 converter (enables output) I chose Advanced Circuits (http://www.4pcb.com/) located in Aurora, Colorado for building these prototype boards. The software they provide for free –PCB ARTIST- I found to be a useful tool for schematic capture and PCB layout. The Bill of Material (BOM) for both boards is in Appendix F.
.results summary Recorded a maximum output of 56 watts with
sustained wind speeds of >30 mph. Rectifier circuit functions per design Overspeed/overvoltage circuit functions per
design DC-DC converter functions per design Standby circuit current less than 0.25 mA
Unable to obtain the Turbine Power vs. Wind speed curve because of a faulty sensor (Analog module). MPPT circuit did NOT appear to be functioning.
.discussion I hoped to provide an actual Power vs. Wind speed curve of the turbine to compare with the expected performance shown in Figure 5. However, I was
23
unable to correct a problem with one of the sensors used to record the output current to the battery. For my test methodology, I employed a data logger from Onset Computer Corp., model H22-001. I used three smart sensors that measured wind speed, temperature & relative humidity, and barometric pressure. Please see Figure 16. I also purchased a Flexsmart analog module that has 2 input voltage channels. One channel monitored the output (+Vout) of the DC-DC converter, which supplied charging current to an 18ah 12V lead aid battery. The other channel of the analog module was connected to a Hawkeye 970LCA current transducer. My intent was to monitor the DC output current and voltage of the electronics while also monitoring the meteorological data at the site. The turbine was mounted on a 24-foot tower using a kit purchased from Southwest Windpower, Inc. It was sited on a south-facing ridge behind the RV park in Wilsonville, Oregon. With the right wind conditions, I had hoped to add a 75-100 watt load on the battery, which would allow the turbine to output up to 100 watts. My plans also included monitoring the three-phase output power of the generator and the DC output power from the rectifier. Unfortunately, I simply ran out of time. Please refer to the Project Timeline at the end of this paper. The current sensor problem involved an analog input module. The second channel of the module did not appear to be working. Another module was ordered but was not received before the tower and turbine were taken down. The general rule of thumb about how there will be no wind for two weeks following the installation of a wind turbine did seem to hold. The site recorded a maximum wind speed of 10.22 mph in the 12 days following installation at the site. During this time, I did observe the turbine spinning very easily in the low winds. I observed the DC-DC converter turn-on and saw output power go up to 2 or 3 watts. Unfortunately, this would usually slow down/stall the turbine. This happened numerous times. This behavior is consistent with the MPPT circuit NOT limiting the output power-the circuit did not appear to be functioning. It is possible that either of the two CMOS chips used in the circuit was defective. Or I could have made a layout error when designing the circuit. Clearly, further investigation will be required to find and correct this issue. Approximately two weeks after installation of the turbine, on June 4th, a thunderstorm blew through the area. During the storm, the logger recorded sustained winds of over 30mph. I had connected a Fluke DMM to record the peak current into the battery. It recorded 4.00 amps. I also observed that the turbine was spinning very rapidly, then would slow down abruptly and remain turning slowly for about one minute. This happened twice during the storm. This behavior is consistent with the tripping of the overspeed/overvoltage circuit.
24
On June 6th, water managed to enter the electronic enclosure. I had failed to seal the screw holes that were used to mount the 300-watt diversion load resistor. This water damaged the Overspeed/overvoltage shutdown circuit- which caused spurious and random turbine shutdowns to occur very frequently from that point.
Figure 16: Turbine with wind sensor on guyed tower
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Conclusions A small vertical axis wind turbine was built based on Ed Lenz’s design. The turbine itself is very sensitive to low winds. It is so sensitive that it will start rotating BEFORE the anemometer starts turning. The bearings in the generator are very good, low friction bearings. I remain convinced that the turbine will serve as an excellent test platform for characterization and performance of wind turbine control electronics, including peak power tracking. Three of the four circuits did appear to function as designed. In particular, there were significant challenges in building the Overspeed/overvoltage shutdown circuit and the DC-DC converter because they employed surface mount devices (SMD). The MPPT circuit did not work. Given the time and opportunity, I hope to resolve this and obtain power vs. wind curves of the turbine, with and without peak power tracking, in order to better quantify the promised improvement with MPPT. Perhaps I may also explore implementing the MPPT with a micro-controller. The advantage of using a micro-controller is that one can tailor or adjust the MPPT algorithm to the specific application. The disadvantage of this method is the extra time needed to learn how to program the controller. There are several lessons I learned from this project. I became more proficient with several tools including Maple (math software), VectorWorks (CAD), PCB Artist (schematic capture and layout), and LTSpice (circuit simulation). I learned how to solder SMD’s. I learned how difficult it can be to layout a DC-DC converter. Attention must be paid to where the high frequency, high current paths are in the circuit as well as circuit elements that need to have good noise immunity. And I learned how time consuming a project of this magnitude can be while going to school full-time. My advice to others would be to limit the scope of your project as much as possible and to have a partner in your research project. It is my sincere hope that other students and researchers in their pursuit of harvesting the most energy possible from renewable energy sources will use this paper as a reference.
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Project Timeline May 2008 Project scope defined. Decided to build a small wind turbine with a focus on the load/control electronics August 2008 Purchased generator for turbine. Turbine size now set. Also found two companies interested in fabrication of the turbine. The fabricator for the plastic wing ribs and stringers is: FLN-MAR Rubber & Plastics, Inc. 102 Cabot Street, Suite 8 Holyoke, MA 01040 The fabricator of the aluminum rotor axle, wing struts, pole mount adapter, and the aluminum skin for the wings is: MASS Precision, Inc. 2110 Oakland Rd. San Jose, CA 95131 November 2008 Completed mechanical design of turbine. Turbine parts designed with VectorWorks (CAD) software. December 2008 Turbine assembled and balanced. Will turn in the slightest breeze. Started research on MPPT/Control electronics for wind turbines. February 2009
27
Decided on design of rectifier, MPPT, & DC-DC converter. Started design of Overspeed/overvoltage shutdown circuit. Ordered and received components for wind turbine tower. March 2009 Completed design of rectifier & overspeed/overvoltage shutdown circuit. April 2009 Completed design of DC-DC converter & MPPT circuit. Completed PCB layout of both boards. Started enclosure design. May 22, 2009 Completed and tested PCBs (except for MPPT). Completed enclosure design and assembly. Assembled turbine. Erected tower. Turbine up & flying with meteorological sensors attached to data logger. Ordered Voltage and current sensors from Onset Computer. No significant wind until June 4th. Still unable to log output power of turbine- can record manually only. June 4, 2009 Thunderstorm generates sustained winds of > 30 mph. Recorded peak power output to battery of 56 watts. No load on battery at this time. Turbine did shutdown on overspeed condition twice during storm. June 6, 2009 Shutdown circuit is triggered spontaneously and randomly without reason. Noted that water entered the enclosure and got both PCBs wet. Theorize that this water damaged the high impedance CMOS chips that control the overspeed shutdown circuit. Verified that rectifier and DC-DC converter circuits still working. June 8, 2009 Shutdown turbine, disassembled tower and turbine.
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Appendix A: AFPM generator specifications
SEO YOUNG TECH. CO., LTD. Renewable Energy Devices
SEOYOUNG TECH Co., Ltd. #407, Kumi College Venture Business Center, Bugok-dong, Kumi City, Kyungbuk, Korea 730-711 Tel: +82-54-442-4040 Fax: +82-54-442-4060 e-mail: [email protected] or [email protected] www.evsmotor.co.kr
Model-SYG-A208-100-140 AFPMG For VAWT and HAWT
! ! ! ! ! No. Parameter Symbol units !
1 Rectified DC Voltage E V 12
2 Gen. Output Voltage ! ! AC (3Phase)
3 Rotor ! ! Permanent magnet type (outer rotor)
4 Stator ! ! Coreless type
5 Rectifier loss ! ! Included
6 Output Power Po W 96 (14V@112W)
7 Rated speed w rpm 140
8 Speed Constant KE V/krpm 152
9 Resistance (Line-Line) RT ! 1.24
10 Inductance (Line-Line) L mH 18.4
11 Rotor Inertia J Kg-m2 0.038
12 Electrical Time Constant "# ms 14.84
13 Maximum Winding Temperature CMax oC 130
14 Number of Phase - - 3
15 Number of Pole - - 20
16 Winding type - - Wye
17 Magnet Material - - NdFeB
15 Gen. Weight WM Kg 8.5
16 Gen. Diameter MD mm 245
17 Gen. Length ML mm 56
18 Housing Material - - Aluminum
19 Shaft. Diameter MD mm 30
20 Bearing - - Ball
APLICATION – Small Wind Turbine, Hydro Power, etc.
!
SEO YOUNG TECH. CO., LTD. Renewable Energy Devices
SEOYOUNG TECH Co., Ltd. #407, Kumi College Venture Business Center, Bugok-dong, Kumi City, Kyungbuk, Korea 730-711 Tel: +82-54-442-4040 Fax: +82-54-442-4060 e-mail: [email protected] or [email protected] www.evsmotor.co.kr
No-Load
! [rpm]
0 30 60 90 120 150 180 210 240
Recti
fier
DC
Vo
ltag
e [
V ]
0
4
8
12
16
20
24
28
32
36
40
44
48
!
Load@140rpm
DC Current [ A ]
0 1 2 3 4 5 6 7 8 9 10
Recti
fier
DC
Vo
ltag
e [
V ]
0
3
6
9
12
15
18
21
24
!
!
SEO YOUNG TECH. CO., LTD. Renewable Energy Devices
SEOYOUNG TECH Co., Ltd. #407, Kumi College Venture Business Center, Bugok-dong, Kumi City, Kyungbuk, Korea 730-711 Tel: +82-54-442-4040 Fax: +82-54-442-4060 e-mail: [email protected] or [email protected] www.evsmotor.co.kr
!
!
!
!
!
SEO YOUNG TECH. CO., LTD. Renewable Energy Devices
SEOYOUNG TECH Co., Ltd. #407, Kumi College Venture Business Center, Bugok-dong, Kumi City, Kyungbuk, Korea 730-711 Tel: +82-54-442-4040 Fax: +82-54-442-4060 e-mail: [email protected] or [email protected] www.evsmotor.co.kr
!
!
!
!
!
!
!
!
!
SEO YOUNG TECH. CO., LTD. Renewable Energy Devices
SEOYOUNG TECH Co., Ltd. #407, Kumi College Venture Business Center, Bugok-dong, Kumi City, Kyungbuk, Korea 730-711 Tel: +82-54-442-4040 Fax: +82-54-442-4060 e-mail: [email protected] or [email protected] www.evsmotor.co.kr
Outer Face
Blade Fixing
Wires
!
!
!
34
Appendix B: Design Calculations
(6)(6)
O O
O O
O O
(8)(8)
O O
(4)(4)
O O
O O
O O
O O
O O
(1)(1)
(3)(3)
(2)(2)
O O
(7)(7)
(5)(5)
David ParkerOct. 9, 2008Revised Feb 10, 2009Senior Project : Vertical Axis Wind TurbineBasic Electrical characterisitics of Generator:@ 140 rpm, 3 phase, Y connection:(Vrms=Vdc/1.3)
restart;Pgen d Vdc$Idc;
Pgen := Vdc Idc
Vdc d 14 = 14 Idc d 8 = 8 PF d 0.9 = 0.9
Pgen;112
Iline dPgen
Vdc1.3
$PF$ 3;
Iline := 3.851851852 3
evalf 5 (3) 6.6719
Basic Electrical characterisitics of Generator:@ 180 rpm, 3 phase, Y connection:
restart;Pgen d Vdc$Idc;
Pgen := Vdc Idc
Vdc d 18 = 18 Idc d 6.222 = 6.222 PF d 0.9 = 0.9
Pgen;111.996
Iline dPgen
Vdc1.3
$PF$ 3;
Iline := 2.995777777 3
evalf 5 (7) 5.1890
Calculation of voltage drop in 25 ft of wire[12AWG] (from generator to Converter):
O O
(10)(10)
O O
(9)(9)O O
Rperft d 0.00162 = 0.00162 Irms d 5.1890 = 5.1890 L d 25 = 25
Vdrop d L$Irms$Rperft;Vdrop := 0.210154500
lineloss d VdropVdc1.3
;
lineloss := 0.01517782500
(1)(1)
O O
(5)(5)
O O
O O
(4)(4)
O O
O O
(3)(3)
O O
O O
O O
(2)(2)
David ParkerSept. 25, 2008Oct. 23, 2008-updated rotor height from 36" to 40" (~1.00m)Dec. 23, 2008-added Turbine solidity calculation
Senior Project : Vertical Axis Wind TurbineMatching the Turbine output with the required AFPM generator input power
restart;Power from the turbine rotor:
Pturbine d12$!air$Arotor$Vwind
3$Cp;
Pturbine :=12
!air Arotor Vwind3 Cp
Arotor d Diameterrotor$Heightrotor;Arotor := Diameterrotor Heightrotor
PlotPturb d plot Pturbine, RPMturbine = 0 ..180, color = red :
Mechanical Power required into the AFPM generator:
EoutDCd 0.1$RPMturbine;
(7)(7)
(5)(5)
O O
O O
(6)(6)
O O
O O
EoutDC := 0.1 RPMturbine
Pgen K input dEoutDC
2
Rload$
1!gen
;
Pgen K input :=0.01 RPMturbine
2
Rload !gen
Rload d 3.50 = 3.50 !gen d 0.8
= 800.00# 10 - 3
PlotPgen d plot Pgen K input, RPMturbine = 0 ..180, color = green :
plots display PlotPturb, PlotPgen ;
Turbine GeneratorRPMturbine
0 20 40 60 80 100 120 140 160 180
P
0
20
40
60
80
100
120
140Wind Turbine & Generator Power vs RPM
Turbine solidity calculation:Arotor;
0.76200
O O
(5)(5)
O O
(8)(8)
S d
Nwings$KChordDiameterrotor
;
S := 1.216535433
(5)(5)
(1)(1)
O O
O O
(2)(2)
O O
(4)(4)
O O
O O
(3)(3)
David ParkerSenior Project-Vertical Axis Wind Turbine withMax. Power Point ElectronicsDC-DC Converter Calculations:Chosen controller: Linear Technology LTC3780 Buck-Boost regulatorDesign input range: 7-30 VDCDesign output: 14 VDCDesign current output: 8 Amps (buck), 3 Amps (boost)Jan. 31, 2009Frequency set @ 200Khz by leaving pins 10 & 11 open.Burst mode is active in boost operation and the skip cycle mode is active in buck operation by leaving pin 9 open (floating).
restart;
Vinmin d 7 = 7.00
Vinmax d 30 = 30.00
Vout d 14 = 14.00
Ioutbuck d 8 = 8.00
Ioutboost d 3 = 3.00
freq d 200000 =
200.00# 103!IL d .32 =
320.00# 10 - 3
Cout d 374E-6 =
374.00# 10 - 6 =
RDSon d .0068 =
6.80# 10 - 3
Crss d 285E-12
= 285.00# 10 - 12
Lboost dVinmin
2$ VoutKVinmin
freq$Ioutboost$!IL$Vout2 ;
9.11# 10 - 6
Lbuck dVout$ Vinmax KVout
freq$Ioutbuck$!IL$Vinmax
;
1.46# 10 - 5
Inductor value based on worst case (buck)- will choose 15 uH Coilcraft SER2915H-153KL1 $4.55
Rsenseboost d2$0.160$Vinmin
2$Ioutboost$Vout$!IL$Vinmin
;
Rsenseboost := 0.01190476190
Rsensebuck d2$0.130
2$IoutbuckK!IL;
Rsensebuck := 0.01658163265
Rsense value based on worst case (boost)- will choose 12 milliohm (2 ! 25m" 0.5W)
O O
(12)(12)
(5)(5)
(6)(6)
O O
O O
(7)(7)
O O
O O
(9)(9)
O O
(8)(8)
O O
(11)(11)
(10)(10)
IinputRMSd Ioutbuck$Vout
2$Vout $2$VoutVout K 1 ;
IinputRMS := 4
CapRippleboost dIoutboost$ VoutKVinmin
Cout$Vout$freq ;
CapRippleboost := 0.02005347594
CapRipplebuck dIoutbuck$ Vinmax KVout
Cout$Vinmax$freq ;
Cout will be:(1) 330 uF 25V bulk cap(2) 22 uF 25V Ceramic cap
Cin will be:(1) 22 uF 50V Ceramic cap(2) 3.3 uF 50V ceramic cap
CapRipplebuck := 0.05704099820
Power MOSFET calculations (Fairchild FDD8453LZ):
PowerMOSAboost dVout
Vinmin$Ioutboost
2$1.5$RDSon;
PowerMOSAboost := 0.36720
PowerMOSBbuck dVinmax KVout
Vinmax$Ioutbuck
2$1.5$RDSon;
PowerMOSBbuck := 0.3481600000
PowerMOSCboost dVoutKVinmin $Vout
Vinmin2 $Ioutboost
2$1.5$RDSonC 1.7$Vout3
$IoutboostVinmin
$Crss$freq;PowerMOSCboost := 0.2975544000
PowerMOSDboost dVinmin
Vout $Vout
Vinmin$Ioutboost
2$1.5$RDSon;
PowerMOSDboost := 0.1836000000
Schottky diodes should be rated @ 3-4 ampsRecommend Diodes, Inc. model B340LA
Feedback resistors R1 & R2
O O
(12)(12)
(5)(5)
O O
(17)(17)
(15)(15)
O O
(16)(16)
O O
O O
O O
O O
(14)(14)
O O
(13)(13)
O O
Vsetout d 0.8$ 1CR2R1 ;
Vsetout := 0.8C0.8 R2
R1R2 d 100E3; R1 d 6.00E3;
R2 := 1.00 105
R1 := 6000.
Vsetout;14.13333334
Note: R1 will be a 7.2K resistor in parallel with a 36K resistor from the MPPT circuit.
CA & CB bootstrap caps
qGate dCA$VINTVcc
100;
qGate :=1
100 CA VINTVcc
CA d 0.33EK6 : VINTVccd 6 :
qGate;1.980000000 10-8
qGate is the gate charge of the MOSFET.Will use 0.33 uF X5R caps for CA and CB.For soft-start cap (Css) will use .68 uF capStart up time (seconds) will be:
Tirmp d 1.5$.68;Tirmp := 1.020
43
Appendix C: Mechanical Drawings
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine rotor axle +struts
9 David Parker 11/16/2008
Turbine rotor axle+struts
1
1
2
2
3
3
A A
B B
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine rotor axle
2 David Parker 11/09/2008
Turbine rotor axle
1
1
2
2
3
3
A A
B B
0.635cm
101.6cm+0.2cm
0cm
100.33cm
3.8
1cm
3.1
75
cm
MATERIAL: 5052 OR 6061 ALUMINUM
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine rotor axle end flange
3 David Parker 11/09/2008
Turbine rotor axle3
1
1
2
2
3
3
A A
B B
9.8cm--0.017cm0.035cm
0.8cm+0.04cm
0cm
4cm
General Notes1.The mounting
holes match the M8 threaded mounting holes on the top of the generator. (See generator drawings-SYG-A208-100-140).
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine rotor axle (close up)
5 David Parker 11/09/2008
Turbine rotor axle5
1
1
2
2
3
3
A A
B B
0.635cm
3.8
1cm
3.1
75
cm
2.9
95
cm
9.8
cm
General Notes1.Tube is centered on
center of flange.
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine rotor wing strut (2 required)
6 David Parker 11/15/2008
Turbine rotor wing strut
1
1
2
2
3
3
A A
B B
120 degreescenter to center
7.62cm
Radius
43.18cm
3.1
8cm
General Notes1.This strut has a thickness of
0.476cm (3/16 inch). One strut mounts on each end of the rotor axle. The 8 mounting holes are identical (8 mm dia.) and match the mounting holes on the rotor axle flange for M8 mounting bolts.
38
.1cm
±0
.05
cm
41
.91
cm
MATERIAL: 5052 OR 6061 ALUMINUM
34
.29
cm
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine rotor wing strut (2 required)
7 David Parker 11/15/2008
Turbine rotor wing strut
1
1
2
2
3
3
A A
B B
General Notes1.Three thru-holes 6mm
in diameter for M6 bolts.
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine pole mount
11 David Parker 11/20/2008
Turbine pole mount
1
1
2
2
3
3
A A
B B
0.635cm
1.27cm
8cm
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
8cm±0.03cm
Title
Drawing Number
CAD File Name
Drawn By Date
Turbine pole mount3
12 David Parker 11/22/2008
Turbine pole mount3
1
1
2
2
3
3
A A
B B
5.6cm±0.03cm
5cm
2.4cm
3.1cm
3.9cm
5cm
VECTORWORKS EDUCATIONAL VERSION
VECTORWORKS EDUCATIONAL VERSION
52
Appendix D: Electrical Schematics Schematic 1 shows the three phase, two way, six pulse rectifier and the turbine overspeed circuit. Schematic 2 shows the DC-DC Converter and the Maximum Power Point Tracking circuit.
55
Appendix E: PCB Layout
56
Appendix F: PCB BOM
Name Component Package Value Manuf Distrib Distrib Part No Qty
D1 1N5819 DSC On SemiconductorMouser 863-1N5819RLG 1
D2 1N5819 DSC On SemiconductorMouser 863-1N5819RLG 1
D3 1N5822 DSC Vishay Mouser 625-1N5822-E3 1
D4 1N5822 DSC Vishay Mouser 625-1N5822-E3 1
L1 L_15uH DSC 1
Q1 2N4401 DSC Fairchild Mouser 512-2N4401BU 1
Q2 2N4401 DSC Fairchild Mouser 512-2N4401BU 1
QA FDD8453 DSC Fairchild Mouser 512-FDD8453LZ 1
QB FDD8453 DSC Fairchild Mouser 512-FDD8453LZ 1
QC FDD8453 DSC Fairchild Mouser 512-FDD8453LZ 1
QD FDD8453 DSC Fairchild Mouser 512-FDD8453LZ 1
R20 R 0.25W 5% MCF 200R 0.500 200 1
R21 R 0.25W 5% MCF 470KR 0.500 499K 1
R22 R 0.25W 5% MCF 1.0MR 0.500 1.0M 1
R23 R 0.25W 5% MCF 1.0MR 0.500 1.0M 1
R24 R 0.25W 5% MCF 470KR 0.500 499K 1
R25 R 0.25W 5% MCF 470KR 0.500 499K 1
R26 R 0.25W 5% MCF 470KR 0.500 499K 1
R27 R 0.25W 5% MCF 1.0KR 0.500 1.0K 1
R28 R 0.25W 5% MCF 36KR 0.500 36K 1
R29 R 0.25W 5% MCF 7.5KR 0.500 7.15K 1
R30 R 0.25W 5% MCF 100KR 0.500 100K 1
R31 R 0.25W 5% MCF 10R 0.500 10 1
R32 R 0.25W 5% MCF 100KR 0.500 100K 1
R33 R1.0W DSC 1
R34 R1.0W DSC 1
R35 R 0.25W 5% MCF 100R 0.500 100 1
R36 R 0.25W 5% MCF 100R 0.500 100 1
R37 R 0.25W 5% MCF 100KR 0.500 100K 1
U1 LMC6064IN DIP14 1
U2 74VHC4053N DIP16 1
U3 LTC3780EG SM 1
60
Appendix G: Simulation The following figure shows a LTspice simulation of the turbine Overspeed/overvoltage circuit:
61
Appendix H: Turbine photos
Turbine right after initial assembly and balancing
Electronics enclosure and base of tower
62
Open electronics enclosure with diversion load resistor
Disassembled turbine
63
Turbine up and flying
64
Bibliography [1] Boyle, Godfrey. Renewable Energy Power for a Sustainable Future (2nd Edition).Oxford, United Kingdom: Oxford University Press, 2004. [2] Halliday,David, Robert Resnick, Jearl Walker. Fundamentals of Physics (7th Edition). New Jersey: John Wiley & Sons, 2005. [3] Masters, Gilbert M. Renewable and Efficient Electric Power Systems. New Jersey: John Wiley & Sons, 2004. [4] Lenz, Ed. Lenz2 Turbine. 2007. 17 Mar. 2009. http://www.windstuffnow.com/main/lenz2_turbine.htm [5] Nilsson, K.,E. Segergren, M. Leijon. “Simulation of Direct Drive Generators Designed for Underwater Vertical Axis Turbines”. Division for Electricity and Lightning Research Uppsala University, Sweden Fifth European Wave Energy Conference. Cork, Ireland: 17-20 September 2003 [6] Woodward, W Stephen. “Maximum-Power-Point- Tracking Solar Battery Charger.” Electronic Design. 14 Sep. 1998. 7 Jan. 2009. http://electronicdesign.com/Articles/Print.cfm?ArticleID=6262 [7] Woodward, W Stephen. “Solar-array controller needs no multiplier to maximize power.” EDN. 5 Dec. 2008. 7 Jan. 2009. http://www.edn.com/contents/images/6619019.pdf [8] Gitano, Horizon, Soib Taib, and Mohammad Khdeir. “Design and Testing of a Low Cost Peak-Power Tracking Controller for a Fixed Blade 1.2 kVA Wind Turbine.” Electrical Power Quality and Utilisation, Journal Vol. XIV, No. 1, 2008 [9] Vergauwe, Jan, André Martinez and Alberto Ribas. “Optimization of a Wind Turbine using Permanent Magnet Synchronous Generator (PMSG).” INTERNATIONAL CONFERENCE ON RENEWABLE ENERGIES AND POWER QUALITY. 7 April, 2006. 10 Jan. 2009. http://www.icrepq.com/icrepq06/214-vergauwe.pdf
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[10] Charais, John. Maximum Power Solar Converter. 2008. 8 Jan. 2009. http://www.microchip.com/
