Germany/TiVA

• converted from dokuwiki-syntax, pad at apollo.open-resource.org, WIP, authors: chrono, Alex Shure.

TiVA

The Tiny Vertical Axis Wind Turbine is a general prototype model and testing platform for a larger wind turbine, and also the prototype for the Apollo-NG Zephyr Wind-Park Construction Kit.

Part of the modular wind turbine system is this downscaled VAWT, with tiny dimensions. With these inexpensive, small prototypes we can have a fast prototyping and research pace. A successfull design may then be scaled up.

Prototyping

Gathering the material for the first prototypes. Do you have something available for this project? Please add yourself to this list and describe the parts, tools or experience you have to share.

TODO: post a list with all the parts needed for one TiVA.

NICE TO HAVE and still searching for this project: Someone with the ability to establish FEM simulations of different rotor type models and mechanics to analyze stress points in the mechanics and to optimize the rotors performance.

Alex Shure

As I work at etemu.com, I have access to an electronic lab and some parts which could come in handy for a TiVA prototype. --Alex Shure 13:23, 3 April 2012 (CEST)

• 16 high power RGB common anode LEDs
• 6 AA NiMH cells, 2950 mAh
• 1 battery holder for 4 AA cells
• 4 MSP430 dev kits with debugging and hardware flash emulation.
• 1 Arduino Duemilanove, Atmega168
• 1 Arduino UNO, Atmega328, Atmega8U2
• 11 NRF24L01+ 2.4 GHz wireless transceiver modules
• 8 LM2596 DC/DC step-down buck converter modules, while a simple drag-based turbine with no optimization nor special aerodynamics may have an efficiency of about 20%.

h_1=0.32 m
d_1=0.32 m
A_1=0.1024 m^2

h_2=0.48 m
d_2=0.32 m
A_2=0.1536 m^2

	m/s	km/h	P_{0.1024m^2}[W]	P_{0.1536m^2}[W]
	1.8	6.5	0.35	0.5
	4.5	16.00	5.5	8.2
	6.25	22.50	15	22.6
	8.0	29	32	48

	m/s	P_{0.1024m^2} [W]	P_{\rho=0.2}	P_{\rho=0.3}
	1.8	0.35	0.07	0.1
	4.5	5.5	1.1	1.65
	6.25	15	3	4.5
	8.0	32	6.4	9.6

	m/s	P_{0.1536m^2} [W]	P_{\rho=0.2}	P_{\rho=0.3}
	1.8	0.5	0.1	0.15
	4.5	8.2	1.65	2.5
	6.25	22.6	4.5	6.8
	8.0	48	9.6	14.4

• Assuming a bad (20%) or decent (30%) turbine design \rho_{turbine}=0.26
• A rather bad permanent magnet alternator with \rho_{alternator}=0.75;
• A normal synchronous rectifier with superb-by-design perfomance of \rho_{rect}=0.98;
• A buck-boost inverter with a good performance of \rho_{rect}=0.85;

<m>\rho_{overall}=0.25*0.75*0.98*0.85=0.16</m>

Conclusion: A 0.32 x 0.32 drag-only VAWT generates about P_{mech} = 0.1...10 W and in average German wind conditions (3 - 4 m/s??) about 0.5 - 1 W. If we have a good alternator (which will be easier at this size because of the high rpm) and a synchronous rectifier (rectifier not necessary if buck/boost power supply doesn't need DC, are there suitable packages for this mode?), most of the power will be available as an input for a buck/boost converter, which can operate reasonably well at these small power ratings. Chrono developed a PDU (power distribution unit) which contains low power buck-boost inverters maybe a small scale version can be powered directly by this wind turbine, generating only 5 V and 3.3 V, omitting the 12 V.

Alex Shure: I would go for a 0.32 x 0.48 m^2 VAWT and I guess the overall efficiency will be about 0.08 - 0.1.

Assuming a worst-case average electrical power of 1 W after rectifying and regulating, one can still charge a cheap 4-pack of NiCd/NiMH (4 x 1.3 V = 5.2 V) which provides power for the system and for high power demands, e.g. activating the LED pattern at night. Charging all of the cells with 1 W from 0 % to 100 % takes (4 * 4 Wh) / 1 W = 16 h. At a wind speed of 8 m/s = 28,8 km/h and P_{el} = 48 W * 0.16 = 7.68 W, the batteries will be fully charged in just (4 * 4 Wh) / 7.68 W = 2 h 5 min.

One AA cell contains 1.3 V x 2500 mAh = 3.25 Wh of stored energy. We don't fully discharge the batteries, thus only 3 Wh will be used. However, taking charging and internal resistance losses and a safety margin into account, we need about 4 Wh of energy to store and retrieve about 3 Wh of energy.

4 AA cells equal 4 x 3 Wh = 12 Wh of energy. Without simultaneous recharging, this is enough to provide:

• five hours of one hp-LED shining at full brightness in white color or
• ten days of one hp-LED flashing at full brightness with one color at a duty cycle of 10%, e.g. on for one second and off for nine seconds.
• one MSP430G2231IPN14 16bit micro controller working for ages, at as low as 2V, it may consume 1 mW = 1/1000 W. Typical no-load best-case values from the MSP430 datasheet:

0.1 µA RAM retention
0.4 µA Standby mode (VLO)
0.7 µA real-time clock mode
220 µA / MIPS active

Excellent values! An 8-bit Arduino looks pretty old school against these numbers. ;-)

>lx: I have 6 MSP430 in a DIP form factor in my lab and 3 spare ti MSP430 Launchpad proto boards with onboard hardware emulator and debugger. (...)
>>Chrono: (...) I'd really recommend staying on avr for bigger projects since many people can do arduino now, so they won't have to much trouble with pure avr. Another arch always reduces the amount of people who can deal with it yet :(
>(...) I don't have the tools for AVR, except an Arduino. So no debugging, HV-programming or hardware emulation. The full dev kit for an MSP430 is dirt cheap at $4.30, including two MSP430s in DIPs, a hardware emulator, spy-by-wire, debugging etc.
I agree with the Arudino-publicity argument, and I would always try to incorporate an Arduino, as it is the most simple and comprehensing development tool there is for beginners. However, the ti.MSP430s are relatively new. A downside is their not-so-easy dev environment. Eclipse or IAR or propietary, free software from ti can be used. I have not yet experimented with it, but I have Arduino experience. It would be new for the both of us.

pro MSP430, con Arduino:

• the price! can be bought with a programmer for $4.30 vs Arduino $25 or a third-party Arduino for maybe $18. This is a serious difference.
• even the single MCUs are cheaper, also, the AtMegas for an Arduino bootloader are hard to get.
• less external parts for operation at high speeds, Arduino/atmega168 and 328 need an external oscillator to operate at full speed (16 Mhz)
• runs stable over a wide range of input voltage down to 1.8V
• an excellent sleep mode with RAM retention at only 0.1µA and great power efficiency. 220µA in full operation mode is an excellent figure for off-grid low energy applications. Almost no load to the turbine. Can also be powered by a "Joule Thief" and a single old AA battery, or just two old AA cells in series (3V). That should last for ages, at a constant current of 0.25 mA and an old battery of 1000 mAh, the unit will still run for 180 days, and the MSP430 can be operated with a supply voltage as low as 1.8V.

con MSP430:

• less memory, but this depends on the package, (there are top-end msp430 processors which cost less than $1 vs an ever-expensive-avr)
• less libraries available, smaller community

At a small production run of 10 TIVAs and the demand for USB ISP, Arduino vs MSP430 would equal 10*$25 = $250.00 vs 10*$4.30 = 43.00 (!)

A nice solution: => Write clean C-code and let it be compatible with MSP430 and AVR compilers. Some Arduino projects were easily ported to the MSP430.

In realtime without battery backup, the hp-LED may be pulsed at full power and 10% duty cycle at quite low wind speeds and 100% at >6.25 m/s.

Base mount

<m>F_{pole} = \frac{1}{2} \times \rho \times C_d \times A_{wind} \times v_{wind}^2</m>

|<m>\rho</m>|Density of air = about 1.2 Kg/m³| |<m>C_d</m>|Coefficient of drag = 1.0 (cylinder Re > 100)| |<m>A_{wind}</m>|Area of turbine| |<m>v_{wind}</m>| Wind speed in m/s|

controlled parallel-serial generator switching system

Draft for a closed control loop:

example values: V_out = 16V V_sys = variable, depending on load V_gen = variable, depending on wind input and switching and system voltage

1. watchdog V_out. if V_sys less than Vout, then
2. serialize the windings,
   1. still to little voltage? -> if generator-coil-form-1 and many points are broken out of the coil, then serialize them in a pattern to gain more voltage
   2. too much voltage? nevermind, either wait for a small period of time because the rotor has a mass and stores kinetic energy, which first has to be converted by the "new serial-wound-generator". the speed will drop eventually and the voltage will stabilize itself, OR
   3. rapidly switch between parallel and serial modes (if the load, e.g. the synchronous rectifier, can cope with the spikes (inductive..) and has appropiate switiching abilities) and thus form an sort of automatic pulse width modulated, regulated, operation mode.
3. if V_sys + Vdelta,hysteresis >Vout, then
4. switch to parallel mode

other cases:

• any of the voltages exceed e.g. 56V: emergency mode:
• either make the generator windings float or short them.

!! shorting may not be an option. only with temperature control of the generator and the semiconductors due to the heat generated at a shortcut.!!

• If all batteries are loaded and the current user power consumption level is minimal, the power surplus of the turbine should be fed into high power LEDs, pointing upwards from the base, lighting the turbine. This adds to protect the system of an unbalanced situation, when more power is generated than reasonably consume- or storable and at the same time to signal, that we still have more energy to share, inviting people to join, in a friendly and beautiful manner.

• In general, LEDs should also be incorporated at the controller: the controller should have a mosfet-switched control output, one 3W RGB led should display the wind speed or the battery voltage.. (on a scale from red to green and strobe patterns)

• 'high-tech' electronic idea: dual rotor on single pole design, counterrotating, brushless royer converter, doubled rpm, less poles, switching power supply is already build in due to the royer converter, coil-in-coil, core coupling, voltage output may be quite high from the start. lower electrical efficiency? downside: needs IP67 protected circuits on both the rotor and the stator of the royer converter. upside: output voltage could be regulated on-board. also, input voltage may be very low depending on the setup.
• variation: a rotor with lift-type wings on top and a rotor with drag-type wings at the bottom. thus the lower rotor gains speed at lower wind speeds but has a top end speed of approx. lift-type/2, while the lift-type wing still accelerates in high wind speed conditions.

Modular Rectifier Options

Controlled - 4 MOSFET Rectifier

active synchronous rectifier
German: "gesteuerter Synchrongleichrichter"
Examples, Schematics & Links to concept

Schotky-Rectifier

Examples, Schematics & Links to concept

TiVA applications

I would like to deploy 1-3 of these tiny turbines at a nearby off-grid mountain bike downhill track, for which I am developing a MCU equipped timekeeping system. I hope to gain the interest for renewable energy / wind turbines of any passenger who rides or cheers there at a race and of course to supply the small timekeeping nodes with 5 V @ 21 mA. --Alex Shure 13:31, 3 April 2012 (CEST)