Since the coils are not overlapped nor magnetically linked, as they are in a car alternator, the difference between 1 and 3 phase's specific efficiency is minimal, if not more dependent upon the specific variations, not topology.
MPPT as far as i know needs some "intelligence", whether it be an analog circuit, or a 50 cent 8 bit micro controller.
If you are suggesting using silicon controlled rectifiers (SCRs) to control the output voltage, then the alternator will need to be rated significantly higher. Reason is, I^2R losses are increased during voltage reduction. At the cut in speed, the conduction angle will be the highest, As the wind increases, the conduction angle must decrease, to avoid a stall. What happens next depends on the alternator's resistance, and the blade's output power curve.[ Parent ]
I don't know that I'd use SCRs. I'd probably try an NPN junction power transistor with its emitter terminal in series with the positive terminal of the battery. The base voltage would be held down until that part of the pulse cycle was reached for conduction to occur. The transistor would either be cut-off where essentially no emitter current flows or hard on where the collector to emitter voltage is small, around 0.3 volts. With 10 amps through the transistor when on the power dissipated in the transistor would be 3 watts or less. Obviously, other circuitry is needed to track the turbine's power curve and determine the on time. That's where the challenge is, but such circuitry need not consume much power either.GeoM[ Parent ]
If you can find me anything other than a mosfet that will drop less than .8 volt, please, I'm all ears. (btw this voltage don't matter too much, since you got rid of the diode(s))
If I understand you correctly, then naturally commutated scr rectification is still more eff if it is three phase, at the turbine, on the tower. all it takes is 3 diodes, 3 scrs, 3 capacitors, and 3 variable resistors.
what you want is on page 13 of this pdf: http://www2.ing.puc.cl/power/paperspdf/dixon/21.pdf
and there is a bunch more here: http://www2.ing.puc.cl/power/publications/electronics.htm
I hope that is of some help. post a schematic please. [ Parent ]
http://www.fieldlines.com/story/2006/4/21/16237/9933
The arguments that I give show that for the same investment in magnets you can get considerably more power out. That is where "the rubber hits the road" as I see it.
The junction transistors that I have known and loved all had a saturation (hard on) value of Vce in the 0.3 volt range. This is true whether they were PNP or NPN.
To a certain extent an argument of SCRs versus Transistors is pointless. You still need to control the on or conducting time and relate that to the power output characteristics of the wind turbine so as not to drive it into stall at any point along the power curve. Both the single phase and 3 phase alternator output current have the basic frequency information built in due to the ripple. You can pick that off by bleeding some current through a 100 - 500 microfarad blocking capacitor to a suitable resistor. From there you can process the information any way you see fit. You might need to add a resistor in series with the battery, although with a transistor in the off state in series with the battery you might not need to to get the basic information.
By the way, if the SCRs would work as you describe, why are people even bothering with the bulky and expensive buck converters? GeoM[ Parent ]
The reason SCRs are not used is due to increased copper losses as the conduction angle decreases. If Scrs are used to reduce the voltage by 50% and 66%, but the average rectified current into the battery remains the same, then I^2R losses in the coil are going double, triple, respectivly.
Buck regulators maintain a full 120 degrees of conduction in a 3 phase rectifier. In addition to this, if a buck regulator is used on a single phase unfiltered rectifier, than the conduction angle can be increased further, up to say about 150/160 degrees, at a dc output of 1/4 of the ac peak voltage. (on a sinewave machine) PMA's oftem produce trapezoidal waveforms, and that won't be a significant difference. [ Parent ]
