Weird, the Kitex Channel on Youtube has a live stream going right now…
https://www.youtube.com/channel/UC6drhOIA87c7dLCrbFPr6yA
of a pallet with some reels on it in the corner of a field
?
@aokholm I saw something really interesting i’ your post and actually that is something I want to try for long without having had the time to. You talk about batteryless focus oriented control with capacitors. Did you really manage to do that? How many joule capacity do you have and over what range of voltage? Did you manage to equalize at best power production with power output in order to maintain a rather constant voltage within the DC bus? My first electronician keep telling me it can’t work bit I am not convinced. If really you amange that (and not just a diode bridge passive transformation) I would love to have details
Yeah we managed to do just that. We have a total of ~ 500J in the capacitors (0-41.6V). We are using 16 capacitors in series. Workable energy is (obviously) less. We designed our own little board to hold the capacitors and protection circuit.
Did you manage to equalise at best power production with power output in order to maintain a rather constant voltage within the DC bus?
Perhaps the main difference is that we have pitch regulated turbine ? I wouldn’t attempt it unless I had a much larger capacity or a load resistor if the turbine was stall regulated.
The rotational energy in our rotor is about 100J, realistically you would need at least 2-3 times a much to make an emergency stop? I guess you could model how much buffer you need to run a stall regulated turbine?
I’ve been saying from day one 14 years ago, “Overspeed protection is not the main thing, it’s the ONLY thing”. Wind turbines (the real ones people actually get power from) are categorized by their method of overspeed protection.
The armchair-geniuses of the world know nothing of overspeed protection, because they have never built a turbine that is truly responsive to the wind or a turbine that runs for more than a few minutes before destroying itself, and they give up building anything, but maintain an attitude that they have key insights to improve wind energy, without anything factual to back that up. If your car is not capable of even rolling down the road, you don’t need to even be aware of the need for brakes, as a comparison.
In the case of such a light-duty turbine, obviously (to some) overspeed protection would be even more important, since even what would be considered a normal strong wind for a turbine designed for a windfarm-class wind resource would destroy a light-duty turbine. And as you point out, most people are not going to be camping in a windfarm wind resource (usually anyway). While it’s hard to wrap my brain around exact details from a written description, in general, It sounds like an interesting approach to overspeed protection. Pitch control for small turbines has been tried many times, and somehow never caught on. Seems that the long-term reliability of pitching hubs, including the need for lubrication, has been the challenge. Maybe also the cost, considering the small size of the market.
I don’t understand the whole reply. If you manage FOC with capacitors, you have to equalize production and distribution at high frequency. I don’t understand what the pitch control as to do with that. If you don’t manage to equalize, your DC bus will jump up or down up to a point where your capacitors will fail.
If you do foc, you can tune your production by adjusting regenerative current . of course you can also do it with pitch control but that is far to slow compared to the electronic regulation and far too slow to prevent capacitors from exploding. So to go back to that precise point, you have an ESC such as a VESC I guess ? and then a capacitor bank with some blocking diode ?
In this paper they show that is possible to stabilize the capacitor voltage controlling at a very high frequency. Can’t remember the details, but I guess 100-20000.
I also attempted previously to control (limit) the power production of a vesc at the native 20khz frequency. It’s possible but you could hear audible noise.
Our current setup with the super capacitors only require response time in the order of 10s of hz
We have a ESC such as a VESC connected directly to a capacitor bank made with super capacitors, no blocking diodes
20 Khz is the PWM frequency generation of FOC , typical 10 to 50 Khz. You can’t control bldc this way, that is just the working frequency of the 3 phase bridge. You control the duty cycle. If you go into audible frequency, then you wil ear the motor.
FOC allow to control current and hence speed ( trough current consign via a pid loop ) . so you can control in live the produced power to match the output power. either you do that or maybe you control the pitch angle of the blades . For kiwee we match prod and load but with a rather large joule capacity because it is a battery. if it is capacitor bank, that could be interesting
FOC is done on BLDC motors… But yes in VESC you have several different control regimes available
FOC methods and more traditional BLDC methods
bldc is just 6 step incrementation phases, a really old and basic control far less efficient than foc control. It is almost not used anymore except in old (>20 years ) setups
Doesn’t the number of steps depend on how many pole pairs your motor has?
Absolutely right though @Kitewinder BLDC is dreadful compared to silky smooth FOC
6 steps does not refer to the number of pole pairs in the motors, it is just the order in wich the 6 mosfet ( 3 ups and 3 downs) of the 3 motors legs are switch. pole pair will just affect the number of iterations you will need to do before doing a full rev. same for foc
Wow, pretty good! 