Wind Inverters – Using Frequency Power Curves

Wind Inverter Power Table

The typical power table for a wind turbine is exponential. As speed rises, power available rises exponentially

Wind Inverters

increase the power harvested from the turbine as the turbine speed increases. Usually this is calculated from voltage, but using frequency to estimate the power from RPM can be a lot more accurate. The speed to power ratio has an exponential increase – at low speeds, only a minimal amount of power is harvested.

Most wind turbines have been configured for voltage based power curves. As the turbine speeds up, voltage rises, and this is used to determine the power harvested. SMA Windy Boy and many other inverters only allowed for this type of power curve. This is because most wind inverters were initially designed as solar inverters, and subsequently modified to allow a power curve to be entered as a table in the inverter’s firmware.

Power One was the first company to mass produce inverters which could take a frequency signal to read in the RPM of the turbine. This is a much more accurate way to determine the power available from the turbine. Turbine voltage often lags behind the RPM and vice-versa. As a turbine accelerates, the voltage will rise rapidly, then inverter will respond to the rising voltage by harvesting more power, but that will cause the turbine voltage to drop, and the inverter will momentarily be over-taxing the turbine, which slows down, causing the voltage to drop again.

We would recommend using frequency to determine available power where possible. We can assist you in this work. The Aurora / Power One wind interface has a frequency output which can send an RPM signal to one or more inverters.