The G83 regs are not my area of expertise, but the way I understand it is that the 180s delay is only req'd after a power outage and not everytime the turbine reaches a cut-in threshold.

For example, on our small turbine systems (Mistrals and Wrens) we generally use Mastervolt Windmaster 500 grid-tie inverters which are G83 certified. The inverter will wait approx 1 second after it receives a cut-in voltage from the turbine before delivering power. This makes it very responsive to gusts etc. This is a default setting and is not changeable in the programming (to my knowledge). However if there is a grid failure, the inverter will wait 180s before reconnecting.

On our larger turbines we generally use Windyboys and we do change the T-start to its minimum value (which from memory is 8s??). This still means that the turbine can accelerate and then deaccelerate during the t-start period and the inverter will miss this potential power generation. However larger turbines are generally used with windyboys and they naturally carry more rotor inertia which tends to lessen the t-start problem. We are looking at an alternative european manufacturer for wind turbine grid-tie inverters above 2.5kw. Windyboy is derived from a PV inverter and has a few shortcomings that do not make it ideal for wind turbines, but this is the case for most inverters at the moment.

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Dave

I have a Proven 6 and Windyboy inverter running. I would be interested to know more about the Windyboy shortcomings with regard to wind turbine service and whether they are the sort of thing that could be resolved via future firmware upgrades.

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jnicolson

We use windyboys for our larger turbine systems. SMA almost have the market cornered in this size range for grid-ties. They also have the advantage of a few years headstart against the other inverter manufacturers.

The problem with most current wind turbine grid-tie inverters is the fact that they are modified from PV grid-ties. When used with PV, the inverters can use an 'active' Maximum Power Point Tracking formula which balances voltage and current to get the maximum output from the PV panels. Unfortunately, because of the fluctuating conditions a turbine operates in, and because of the more complicated generation, this MPPT is not fast enough to keep up with a turbine. Therefore the MPPT has to be cancelled and instead the inverter refers to a pre-programmed 'lookup table' (or graph) to load the turbine. This is different for every different type of turbine. The inverter has to know how much power to pull from the turbine at any given time. If it trys to draw to much power to soon - the turbine will stall. If it doesn't draw enough power, the turbine will overspeed and not generate its full potential.

The other problem with current grid-ties is the lack of internal over-voltage protection. Turbine manufacturers currently have to make a seperate provision for this.

In an ideal world, what I would like to see in a wind turbine grid-tie inverter:

* A MPPT system fast enough to keep up with the changing condition of the turbine and the capability to learn (or auto-tune) to the turbines characteristics.

* Internal over-voltage protection with a modulated output to dump loads if/when an overvoltage situation occurs.

* A cut response of less than 1 second which will help collect the little bit of energy that is available in short gusts.

Cheers,
Dave

With an Eoltec turbine, overvoltage diversion is not required, as the turbine is inherently very well speed controlled due to the centrifugally controlled blade pitch. Unload the turbine, during a grid outage for example, and the turbine only runs slightly faster that in does at full load. Inverter input voltage accordingly doesnt exceed about 430V - Well within the 600V rating of the inverter! However, should you wish to add a diversion load for "belt and braces" you would find that the equipment already has this built in - All you need to add is the diversion load. However, no one actually needs to do this, or has done so, as the turbine controls its speed very closely.

The other beauty about these inverters, is that they come pre-programmed in the box, ready for use. Simply take it out of the box, hang it on the wall, connect the input and output wiring, then switch on the turbine. All the programming is already done, including all G83/G59 settings. Great for installers as it saves time - Great for end users as it means you dont have to fiddle with awkward software, contrary communication settings and "modems" to try and optimise it! Just fit and forget! Its already optimised using firmware intended for a wind turbine rather than PV!

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Bryan Rendall

Does anyone know if the manufacturers supply response characteristics so that a valid comparison can be made between various inverters available - I couldn't find anything other than general statements when comparing various makes; however this could well be due to my very limited knowledge on the subject. Also, how can this be quantified in terms of turbine/inverter performance, e.g. are there data or papers available somewhere to help evaluate this. Are we really talking about small differences in production that are less significant in relation to other factors; a bit like higher efficiency at low wind speeds?

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jnicolson

Jim - The parameters of the inverter, including the response times, are defined by the manufacturers of the turbines, hence you won't find these characteristics from the inverter manufacturers. They are selected to suit the turbine.

Some inverter manufacturers ship the inverters unprogrammed, and the installer then needs to set them up with the parameters provided by the turbine manufacturer. Others, like the Eoltec inverters are shipped pre-programmed. Settings between different turbines can be very different, and this is down to the turbine itself. However, some inverters have more capabilities that others, in that the range of parameters is wider, or there are different types of parameters depending on the firmware.

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Bryan Rendall

So T - start can be set as low as can without breakin G83 regs!
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Stuart