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3.0 - 4.2 kW brochure (pdf)




3.0 - 4.2 kW manual (pdf)

 


6 kW brochure (pdf)

 


6 kW manual (pdf)

 


Wind interface brochure (pdf)

 


Wind interface manual (pdf)

 


AuroraInstaller manual (pdf)

AuroraInstaller software (zip)
 


Overvoltage protection (pdf)

 


Dual-inverter wiring (pdf)

 

Power-One Wind Turbine Grid-Tie Inverters

Similar to its line of PV inverters, Power-One also makes true MPPT inverters for wind turbines. These grid-tie inverters use a table to relate either voltage or frequency to the inverter's output power, ensuring the correct load on the wind turbine for optimal energy production at any wind speed. The Power-One Aurora wind inverters are available in 3kW, 3.6kW, 4.2kW and 6kW output power. Multiple inverters can be stacked to provide additional inverter power as needed for larger wind turbines.

If you are looking for the Power-One solar inverters - Click Here!

An optional 3-phase rectifier box is also available, the PVI-WIND-BOX, to create DC for input into the inverter. The same box can also generate the frequency signal that can be used by the MPPT table, and it can switch on a diversion load to keep the turbine voltage under control. The wind inverters share many of the same electrical and physical attributes as the solar inverters listed above, in addition the following is worth mentioning:

  • 16-point true MPPT table. Unlike other wind inverters that use just two or three points to do a crude approximation, the Aurora has a full 16 points to build a smooth MPPT curve. The inverter can use either DC voltage, or the AC frequency in the MPPT table to relate this to grid output power. Frequency is the best method, since this is directly proportional to turbine RPM, which in turn is proportional to tip-speed-ratio (TSR). The ultimate function of the MPPT table is to load the wind turbine just right to keep it running at the optimal TSR for maximum energy extraction. We can assist you to determine the MPPT table for your wind turbine.
     

  • An incredibly wide MPPT range of 50 Volt through 580 Volt DC! Thanks to its very wide MPPT range it is easy to make the Aurora inverter work with a large number of different wind turbines. Full output power is available from 180 through 530 Volt.
     

  • Ultimate efficiency. The same CEC weighted 96% efficiency as the solar inverters, UL1741 and CSA C-22.2 listing, 5 year warranty (10 years optional), IP65 housing for outside installation etc.

 

Important Notes For Those Considering The Power-One Aurora Wind Inverters

Please realize that the Aurora wind inverters, while they work very, very well, are not exactly plug-and-play boxes. They need an MPPT table to work properly, and unless you buy the inverter from the wind turbine manufacturer it will arrive empty (if you have an MPPT table we will be happy to load it into the inverter before shipping, just let us know). It is your responsibility to make sure the inverter has a proper MPPT table loaded into it, suitable for your wind turbine. It will not work without it!

Also keep in mind that the Aurora wind inverters expect DC on their input. Most wind turbines supply 3-phase AC, and this will not work directly (despite the obvious, we have had people try it)! If your turbine produces AC you can use the PVI-WIND-BOX from Power-One (which we can supply) to convert it to DC, or you can use your own solution. As long as there is reasonably smooth DC going into the inverter.

If you use your own rectifier or controller (as opposed to the PVI-WIND-BOX), make sure there is an overcurrent protection device in the form of a DC rated fuse or breaker in the DC path of the inverter. While this is common sense, surprisingly few third-party controllers contain overcurrent protection. If the rectifier fails it will send AC into the inverter. The inverter has some protection for AC on its input, by using a diode that will short-circuit the input if the polarity is wrong. That diode will only handle a limited current though before it blows, and when it does, that is the end of the inverter. Size the overcurrent protection such that regular use will not exceed 75% of the fuse or breaker rated value.

The Aurora inverters, wind and solar, are transformerless. While that makes them very efficient (no transformer losses), it requires that their DC inputs 'float' with respect to ground. That means the alternator of the wind turbine, nor the rectifier, can reference ground (their housings should still be grounded, but the wiring cannot be grounded). Especially if you are supplying your own rectifier solution this can be an issue, and you have to make sure it complies.

The Aurora inverters are pretty hardy boxes; it is really, really hard to kill them (we have tried). They also have extensive on-board diagnostics that will tell you when something is wrong. However, the one sure-fire way to kill an Aurora is by exceeding the 600V input limit. Doing so will with certainty let the magic smoke out, and the inverter will not work again. What is more, this will log an event in the permanent memory of the unit, and repairs will not be covered by warranty. It is your responsibility to make sure your wind turbine will never, ever, deliver more than 600V DC to the inverter (in fact, it is a good idea to stay below 500V just to have a margin of safety). If you are uncertain your turbine will stay under 600V, even if there is no load, we have a suggested circuit using a measurement relay that can protect your inverter.

Please take a moment to understand the above before you place an order for an Aurora wind inverter.

 

Wind Inverter Pricing

 

 

MPPT for Wind Turbines

Maximum Power Point Tracking (MPPT) has been used for photovoltaic (solar) energy for a long time. It is more recent for wind turbines. What MPPT does is to always load the wind turbine just right, so it delivers the most energy at any wind speed.

When the wind blows through the turbine it will produce a certain amount of torque on the blades. For each wind speed there is a specific rotor RPM where this torque will be at its maximum; speed up the blades at that wind speed (higher RPM) and drag will increase so less torque is available, slow down the blades (lower RPM) and blade lift will decrease, resulting in less torque. It helps to think of this point of maximum torque as the best lift-to-drag ratio for the blades, even if this is not completely correct it is close enough. In real life the wind speed is not constant, but changes continuously, and with it the best rotor RPM for maximum torque will change as well. What is important to remember is that there is an optimum RPM for each wind speed, and that is where we want to run the wind turbine to achieve MPPT.

Another way to think about the best power point for a wind turbine rotor is with the use of the Tip Speed Ratio (TSR) concept. The TSR is the number you get when dividing the speed at which the rotor blade tips travel, by the speed of the wind. For most wind turbines the TSR is in the range of 5 ... 10, and it is frequently used with wind turbines because it carries lots of information in a single number: A high TSR means a noisy wind turbine, with tips traveling at great speeds, resulting in high wear as well. Usually the efficiency of high TSR machines is not great, because the blades are working in the higher-drag end of their range. Its usefulness for MPPT comes from the way airfoils work: The point where the airfoil works best, the best lift-to-drag ratio if you will, is at a certain angle of the blade to the wind, the angle-of-attack (AOA) of the airfoil. This AOA actually stays almost constant over a wide range of wind speeds (this is not entirely true; the Reynolds number is a factor and it changes as the wind speed changes, but for our purposes we can assume the best AOA is the same at all wind speeds). To keep the AOA constant as the wind speed changes, means that the tip speed of the blade has to change proportionally with the wind speed. Double the wind speed, double the tip speed, and the resulting AOA stays the same. Remember that the TSR is tip speed divided by wind speed, and if those two numbers change in proportion to each other that means the TSR needs to be constant over a range of wind speeds for the best power point!

The way MPPT is done by the inverter is by loading up the rotor in such a way that at each wind speed the rotor torque is at its optimum. Since power is torque times RPM, what the inverter really needs to know to track the maximum power point is how much power to extract from the rotor for each rotor RPM. The inverter does not have direct access to the rotor RPM, so it uses a different parameter that is proportional to it. Rotor RPM corresponds directly with the frequency of the voltage coming off the AC alternator of the turbine, and the Aurora inverters can use this. It also corresponds closely, not quite directly but the difference is small, to the alternator's voltage. The Aurora inverters can also use the voltage of the alternator after rectifying it to DC. Programmed into the inverter is a table that has a number of points linking frequency or voltage versus inverter output power. The inverter will use these points (up to 16 points the Aurora inverters) to create a curve by interpolating between points as needed. That is the MPPT table, and MPPT curve, which is different for each brand and type of wind turbine.

When the wind is blowing the turbine's rotor will spin, and the inverter will load the rotor according to the MPPT table it has. That load on the alternator results in a torque on the blades, and if that torque matches the torque the wind exerts on the blades the rotor will not speed up or slow down.  The other side of this is that if the inverter load is not enough to match the blade torque, the blades will speed up and rotor RPM will increase, the voltage will increase, and the inverter will increase the load according to the MPPT table until the blades stop speeding up (and vice-versa). The net-result is that at each wind speed the rotor will continuously reach equilibrium, where the alternator torque (created by the inverter load) matches rotor torque, and the turbine will automagically gravitate to this RPM. If the wind picks up the rotor torque will exceed the inverter torque, and the RPM will increase. The inverter sees this and increases the load accordingly, until a new equilibrium RPM is reached. If the MPPT table was made in such a way that this equilibrium RPM is the point of maximum torque for a wide range of wind speeds we will truly be tracking the maximum power point and get the most energy out of the wind turbine. Another way of saying the same is that the MPPT table should be such that the TSR of the wind turbine is kept at its optimum regardless of wind speed. That is what MPPT does: Load the turbine such that it is always running at its most efficient, extracting the maximum amount of power from it, at any wind speed.

Deriving a working MPPT curve for a new wind turbine is not rocket science (luckily!). In fact, just by using the rotor diameter, voltage characteristics of the alternator, and a guess of its efficiency, it would be possible to get a curve that works, at least well enough to get started. To make something a bit more precise it is good to measure at least one point high up on the power curve, and one at the lower end. While power in the wind follows a cube relationship with wind speed (and RPM of the alternator, since RPM has to vary linearly with wind speed to keep the TSR constant), most wind turbines are not efficient enough to follow a cube relationship for output power vs. voltage or frequency. In practise, most turbines end up with an MPPT curve that is between a square and a cube relationship (the more efficient ones are closer to a cube). MS-Excel can greatly help, due to its graphing ability and build-in functions that can map a smooth curve through a few points. Luckily, the efficiency of most wind turbine airfoils does not change all that much even if the TSR is off from its best value by quite a bit. That means the MPPT table can be off considerably, without noticing much difference in energy production.

To work properly the Aurora wind inverters need an MPPT table that is specific for the wind turbine that you hook up to the inverter. The MPPT table is simply a list of numbers, it can be as little as two points (though we suggest a minimum of 3 points) to a full 16 points. Power-One makes the AuroraInstaller program available to load the MPPT table into the inverter. AuroraInstaller can also read the table that is in the inverter, or modify it. The process is very easy and the AuroraInstaller manual describes it in detail. Of course, we are here to help you with this if needed.

 

Aurora Wind Inverter FAQ

Issue: Inverter never switches off, even when the wind turbine is not spinning, and shows 60 or more Volt on its input.

Solution: This is caused by stray voltage, possibly capacitive coupling into the turbine wiring, that gets rectified and charges the input capacitors of the inverter. When the inverter is not exporting power to the grid the load on the input may be too low to discharge the input capacitors, and make the voltage drop low enough for the inverter to shut off. The PVI-WIND-BOX has resistors build into it, that serve to discharge the inverter input, but if you use your own rectifier you may have to add a 100 kOhm / 5 Watt resistor over the positive and negative DC inputs of the inverter.

 

 

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