Piggott turbine modelingEstimation of electricity production and blade/tower loads for Hugh Piggott designs, using BEMtheory and simple PMG-battery charging model Hanan Einav Levy
ScopeA BEM code with a battery charging generator model waswritten in matlab (also runs on the open source octave)This presentation shows the basics of the modelAnd comparison to measurementsThe code is open for any one to use!Also, a web page is being written, for allowing non octavesav vy individuals to use this code, for designing andreviewing their Hugh Piggott turbinesThe model is made of t wo parts: BEM - Blade Element Momentum Battery charging PMG model
Part 1 Code algorithm Blade power Geometry and thrust at several coefficientspoint along Chord t wist profile the radius Wind speed RPM range π RPM ·R TSR = Tip Speed Ratio: TSR = 60 V
Part 2 Code algorithm Blade power and thrust coefficients + Generator, Battery & system parameters
Test subject: WindAids’ 4 meter design Are we using the bestgenerator for these blades? How much will we gain by modifying it?
BEM theoryUsing conser vation of momentum/energy/mass on annular rings of flow volume throughthe bladesUsing 2D blade section data - frommeasurements, or simulations (xfoil,JavaFoil )Results: prediction of Shaft power, and bladeloads for every blade RPM and windspeed(usually - the combination of both π RPM ·Rthrough TSR = 60 V ,where R is the bladeradius and V is the wind speed )
Part 2Estimating the Power Curve Balance of power - Blade shaft power = generator shaft power All that’s missing is - a model for the generator shaft power vs. RPM, and generator electrical power vs. RPM
Generator modelAxial flux Permanent Magnet Generator charging a battery Rwire ΔVBR I RPMG rBatt Vd VPMG VBatt
Generator model Axial flux Permanent Magnet Generator charging a battery Rwire ΔVBR IKPMG - Voltage constant RPMG rBatt VdRPMG - stator resistance VPMG VBattmodel parameters can be VPMG = K PMG ·RPMcalculated based on Hugh 120 ⎡ RPM ⎤ K PMG =Piggott’s model (from windpower workshop) 50 ⎢ volt ⎥ ⎣ ⎦Assuming 2 phases activeOr measured from the PMG
Generator model Axial flux Permanent Magnet Generator charging a battery Equations: Rwire ΔVBR I K PMG RPM − Vbatt − ΔVBR RPMGI= Vd rBatt RPMG + Rwire + rbatt VPMG VBattVd = K PMG RPM − I(RPMG + Rwire ) − ΔVBRPbatt = Vd ·IPShaft = K PMG RPM ·I Where Vd was capped according to controller limitation (31V Sources: for a 24V machine) 1 - Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6.685 Electric Machines Class Notes 6: DC (Commutator) and Permanent Magnet Machines 2005 James L. Kirtley Jr. 2 - J. R. Bumby, N. Stannard and R. Martin A Permanent Magnet Generator for Small Scale Wind Turbines
ΔVBR PMG Rwire I RPMG rBatt Vd VPMG VBatt Permanent Magnet GeneratorThe generator model output Example of real PMG numbersMissing: KPMG reduction and RPMG increase at high currents
Estimating the power cur ve - WA4 Putting it togetherComparison to measurements is good (but not enough measurements)
Estimating the power curve - Piggott 3 mComparison to measurements is not very good - Section data from NACA 44XX measurements , resulting in a wrong Cp vs TSR curve
Concluding remarksModel is sufficientlyaccurateCan help decide ifgenerator windingneed changingQuantify how tochange best wind speedefficiency of turbineOr to identify poorblade configuration
Concluding remarksNeeds improvementMany possible measurementerrors Amp/volt measurement wind measurementMany possible modeling errors Generator/Battery/wire resistance Blade profile properties for wooden blades
I’m working on a site for this programAt the moment at It’s at http://gs.playstix.net/piggott/Will include an option to upload your bladegeometry & generator parameters, anduse the code to predict outputs, calibrateto measurements and see how changes ingen. parameters effect performance etc.work is at an early stage… probably upand working by the middle of the yearCode is written in Octave, and is open-source - http://gitorious.org/piggott-turbine-design/piggott-turbine-designThat’s me. Wish I was here in Dakar!