Aurora inverters with a 17.5 Jake?

[Jerry Giesler]

I have been on the phone and the internet with a number of people these last few days looking for an alternative to the Mastermind Controller for my Jake. Initially, I thought that using Windy Boys might be the ticket after reading an article about Victor Creazzi who did just that with a smaller 10kw Jake in Colorado. I had a good conversation with him yesterday about it. Then I talked to Emile at ARE and he e-mailed me back after he talked to Robert about our conversation. Robert suggested that the Aurora inverter may be a better option. Emile also gave me a link to Power One concerning the Aurora inverter. I talked to a gal named Jenny Ong at Power One and I asked her if the Aurora inverters can be stacked since they are only rated at 6000 watts. She said that you would have to use an isolation transformer. I don't understand how that works, but then, I'm not an electrical engineer. I have studied the info that I can find on the net about the Aurora inverters and that led me to this forum. I see that they use a "Wind Interface Box" in conjuction with the inverter. I am starting this thread to see if anyone here has any thoughts, insight, or comments as to the viability of using the Aurora inverters paired up to the Jacobs machines.

[Rob Beckers]

Hi Jerry,

As you've probably read on the forum I use the Aurora inverters with the Scirocco wind turbine, and I'm a Power-One dealer. Before the 6kW Aurora came along, we used to stack two 3.6kW inverters together, with the isolation transformer Jenny mentioned. Never tried that with a pair of 6kWs, but it should work just the same. I've attached Power-One's own PDF on stacking inverters. The downside of the transformer is that you will be loosing a certain amount of power all the time (transformers have standby losses).

The PVI-WIND-INTERFACE box does two things: It rectifies the 3-phase AC coming from the wind turbine. The Aurora inverter is DC only. It also has an overvoltage sensor and a very large IGBT that switches the wind turbine to a (break) load for a certain amount of time in case overvoltage (>530V DC) is detected. The largest PVI-WIND box made by Power-One is 7200 Watt. I would have to verify with my tech contacts, but it is likely OK to use a separate PVI-WIND box with each inverter. Alternatively you can use your own rectifier. You have to make absolutely dead sure that the DC voltage never goes above 600V DC, or you'll have two very expensive paper weights. From what I've heard the inverter will log this event, so the factory can tell in case you claim it died unexpectedly under warranty.

Why did Robert suggest not to use WindyBoys? Last time I talked to him he was no great fan of Power-One. If I remember right they use a pair of WindyBoys with their 10kW turbine. The Auroras are nice in that they have a real power curve that can be programmed. The WindyBoy has only a 2 or 3 point curve, depending on the model. I've not done the calculation myself, through Robert tells me that doesn't make much difference in produced energy (the 2 or 3 point curve will not be as good a match to the wind turbine's power curve). What is the voltage range of your Jake?

Either way, you have to have a power curve of the Jake. Of course, it can be fun all by itself to play with that and optimize production. The Auroras can use either USB or RS485 to set the curve, the software runs on Windows (I'm using XP). Hope this helps!

-RoB-

[Rob Beckers]

Re-reading this, I may have misunderstood: My initial thought was that your Jake is 10 kW. If I understand this right, yours is 17.5 kW? So that would mean 3 sets of PVI-WIND and PVI-6000 inverters. Should still work just the same as described. It'll cost you about $14K in inverters though, plus 2 isolation transformers (6.5 or 7 kVA units, big ones!).

If you want to be really smart about this, you'd put a contactor/relais on the grid side to disconnect the inverters with the transformers when the turbine is not producing energy, saving energy otherwise lost on the transformer standby power (they loose about 1 - 2% of rated power continuously, or 150 - 300 Watt continuously in your case). Unless the wind is always blowing where you are. It'll add a bit because the contacter needs power to work, but it'll save transformer losses when there's no wind to offset them. The Aurora has a set of relais contacts and they can be switched to activate when the unit is producing power. I'd have to ask my tech contacts to make sure, though I believe that they can be used for this purpose.

It may even be possible to stagger the inverters, so the first inverter is used up to 6 kW, then the next one switches on from 6 .. 12 kW, and so on. I'd have to take a closer look at the MPPT parameters, though I believe it's possible to stagger the inverter cut-in voltages in a way that makes this happen. Inverters are more efficient when used at a higher percentage of their rated power. Also, every time the inverter itself gets fired up in the Aurora it uses 200 Watt idle power (from the grid side, unless the wind side is producing enough to offset it). So the fewer inverters are active the less idle power is used.

By the way, the Aurora itself gets powered by the wind turbine. It doesn't need the grid to power up. In fact, I never even bother to hook up the grid side when I program them. I just put power on the wind side. Following from this, the unit also switches itself off when the wind turbine output falls below a set voltage for a set time, saving power.

-RoB-

[Jerry Giesler]

Rob,
Thanks for responding. First, yes my machine is a 17.5. As far as why Robert thought that the Aurora would be a better choice, I think is because the Windy Boy inverter has a low end voltage of 150 or 200 volts. The Jake puts out a range of about 40-190 volts give or take of wild 3 phase. Victor, the fellow I mentioned in the earlier post reconnected the leads on the alternator to increase the output voltage on the 10kw he worked on. That enabled him to get the output voltage of the alternator in the range that would work with a Windy Boy.
You mentioned something about running the Auroras stacked so that one would be fully utilized before the next one kicked in. Would you still need an isolation transformer with that setup? Another question I have as far as this isolation transformer goes is, where does it go in the system, before or after the current is rectified? In other words, are you talking a single phase or a 3 phase transformer. Sorry if this is a stupid question, it's just that I still don't understand the purpose of the isolation transformer.

Jerry

[Jerry Giesler]

Rob,
I looked at the file you posted and I see where the transformer goes and that they are single phase, however, I still do not understand their purpose.

Jerry

[Rob Beckers]

Hi Jerry,

The Aurora output is split-phase, 240V (yeah, that's still single phase, but I wanted to point out it's not 120V). Do you need 3-phase coupling to the grid? The power level, 17.5 kW, is low enough that split-phase shouldn't be a problem.

The transformer is needed because the Aurora inverters do not have galvanic separation between their input (the turbine) and output (split-phase grid). When you have two inverters they would 'fight' each other if you hooked them up directly, because there would be a DC voltage difference from inverter to inverter. Even if both are producing almost the same 240V output waveform. Without the transformer you'd get a current from inverter to inverter, possibly a large one, that would at the very least eat up energy you could otherwise use and quite possibly do damage. The transformer blocks the DC voltage difference between inverters, and that makes them get along. Any time two inverters that don't have galvanic separation between input and output get hooked together, and they work from the same source (ie. the same wind turbine in this case), you need an isolation transformer. Regardless of how they are used, stacked or otherwise.

The range of 40 - 190 V 3-phase works out to about 70 - 340 V DC, into the inverters. The MPPT window of the Aurora is 50 - 580 V, with 180 - 530 V for full power (below 180V you're limited in current, so it can't reach a full 6kW output). I'd have to take a closer look at the low end, but it looks like that would work out OK.

It is strange that the Jake puts out such a low voltage, given the large power. At 17.5 kW that makes 53 Ampere per phase, at 190V. That makes for some pretty hefty wiring, in fact, it would be better to put the inverter(s) right next to the tower since the 240V wiring would be cheaper to run. I would also invest in some really serious lightning arrestors (http://www.solacity.com/Lightning.htm) in that case, since there is no lengthy wiring to take some of the sting of a direct hit off the wires.

Just to re-iterate though, that you will need a power curve for the Jake that has at the very least voltage vs. output power, and better yet, RPM/frequency vs. output power.

-RoB-

[Jerry Giesler]

Hi Rob,

Thanks for all of the info so far. I understand the isolation transformer issue now. I am connected to 240 single phase by the way. I have a fair amount to think about. I am going to try to get some info on the power curve for the 17.5 Jake. I would still need to have some kind of a field controller. I'm wondering if it would work to use the rectifier portion of the Mastermind controller that I currently have instead of using the wind interface boxes. I'm still weighing the pros & cons between the Windy Boys and the Aurora inverters. I don't need isolation transformers if I use the Windy Boys but I would have to get my voltage up (this may be possible by reconnecting the leads on the alternator, I don't have that info yet). The Aurora's curve can be programmed finer plus the voltage may not be an issue.

The goal is to have a system that is robust, efficient, and of reasonable cost.

I think that Victor Creazzi may have some insight on a field controller and I have some ideas of my own which I may bounce off of my electrical engineer here at the shop.

Any other brainstorming that you come up with is welcomed,
Jerry

[Rob Beckers]

What do you mean by a "field controller"? What does it do?
By the way, the PVI-WIND boxes do a few things besides rectifying 3-phase AC: They also provide overvoltage protection (not a big issue in your case I suppose, given the very low voltage of the Jake), and they provide a frequency signal that the Aurora inverter can use for the MPPT table. It doesn't have to use frequency for MPPT, instead it can use DC voltage. However, frequency is a much more precise measure for determining optimal power from the turbine (compared to using voltage).

So the Windyboys can be stacked without using a transformer? That would mean they have a transformer inside (probably running at a high frequency, so it can be kept small). The reason the Auroras don't have a build-in transformer is because it makes the inverter a few percent more efficient. Then there's the thing that it saves money for the manufacturer, I suppose that was more important to them than the extra efficiency... ;)

-RoB-

[Jerry Giesler]

The field controller is part of the Mastermind controller that I have been using. The Mastermind controller does numerous functions. I don't profess to be an expert, however I have a fairly good understanding of what it does. My turbine has 5 wires running from the alternator to the controller. 3 wires are heavy gauge wire which carry the generated power from the alternator to the controller. 2 wires are lighter gauge wires which carry a variable DC current to the field windings in the alternator to excite the field. The amount of current sent to the field determines the amount of load on the turbine. There is a field control circuit in the Mastermind controller which is designed to properly load the turbine at any given RPM.

The 3 wires go to a rectifier in the controller and then though a choke which is a heavy device resembling a transformer which I believe it is. They just call it a choke. From there the current goes to a pair of SCR's which are used to convert the Dc to 240 AC. This is a very simplified explanation as there is a lot of electronics involved to synchronize to the grid with special circuitry to provide safety for over/under voltage, frequency and to shut down in case of grid failure. When it works it usually works well. The electronics seem to be a bit prone to failure though, at least in my experience. The other issue is that this controller is older technology and is not certified or compliant to UL1741. Using SCR's to make AC results in a rough looking sine wave or, more accurately, a modified square wave. This hasn't created any problems for me and it certainly wouldn't for the grid because the juice has to go through a step down transformer before it gets to the grid. Never the less, that's a big issue right now for anyone wanting to grid connect a larger Jacobs machine, new or used.

Here is a link to a description that one Jacobs dealer wrote to explain the operation of the alternator.

http://www.baywinds.com/new/Thorough%20Explanation%20of%20Alternator.htm

I hope this explains it to you,
Jerry

[Jerry Giesler]

Rob,

I neglected to mention that there is a sixth wire running from the alternator to the controller which is a heavy gauge ground wire.

Jerry

[Rob Beckers]

Interesting type of alternator. Sounds like something similar to a car alternator where field windings provide the magnetic field. I would have to take a much closer look at the circuitry, however, very much in general: Yeah, it looks like you should be able to use part of the Jake controller. Keep the rectifier and control part (you need the control part of it will never produce energy), get rid of the inverter part. Then go straight from DC after the rectifier of the Jake controller into the Aurora inverter (or Windyboy). Take a look though that there is decent filtering of the DC in the Jake controller. The Aurora and Windyboy expect fairly clean DC on their input and the PVI-WIND box has lots of capacitors in it for that purpose.

-RoB-