In previous posts here and here, I discussed the General Electric Company’s (GE) two wind turbine patent actions against Mitsubishi, one in the U.S. International Trade Commission (ITC) and the other in federal court in the Southern District of Texas. 

Last month GE added a third case to the mix when it sued Mitsubishi for infringement of two patents relating to a wind turbine base frame and zero voltage ride through (ZVRT) technology. 

Filed in the Northern District of Texas in Dallas, the complaint (gecomplaint.pdf) identifies Mitsubishi’s 2.4 megawatt wind turbine as the allegedly infringing product.

The patents-in-suit are U.S. Patent Nos. 6,879,055 (‘055 Patent) and 7,629,705 (‘705 Patent).  The ‘055 Patent is directed to a two-part base frame for arranging a drive train on the tower of a wind turbine.

The upper part (6) of the base frame carries the drive train, and the lower part (16) of the base frame has an azimuthal drive device (23), which rotates azimuthally to adjust the rotor axis as a function of wind direction. 

The connection point (15) that joins the upper and lower parts of the base frame extends along a horizontal cross-section having a larger dimension in the direction of the rotor axis than in the perpendicular direction. 

According to the ‘055 Patent, this construction of the connection point (15) is favorable for absorption of stress from the rotor.  The two-part design also makes transport and assembly of the base frame easier.

The ‘705 Patent, which issued in December 2009, relates to methods of facilitating zero voltage ride through so the turbine can remain online during voltage dips down to zero volts. 

As the ‘705 Patent explains, some gearless direct drive wind turbine generators include power converters, and both the generators and the converters are susceptible to grid voltage fluctuations. 

The patented methods mitigate wind turbine generator trips during events in which voltage amplitude decreases to zero volts, as opposed to known low voltage ride through methods that can handle less extreme voltage drops.

The patented systems and methods include a phase-locked loop (PLL) regulator to receive voltage measurement signals from a plurality of voltage transducers.  The PLL regulator includes a PLL that receives the sinusoidal voltage measurement signals.

If a voltage amplitude is outside a pre-determined range, an algorithm within the PLL generates a control signal and the PLL regulator changes to a different mode or state of operation.  A plurality of states of operation are possible, with varying parameters such as gain constants.

According to the ‘705 Patent:

the plurality of states of operation facilitate zero voltage ride through (ZVRT) as well as other grid faults while also facilitating normal operation   

This lawsuit comes shortly after the ITC terminated GE’s complaint against Mitsubishi.  GE’s infringement suit in the Southern District of Texas has been stayed pending a final determination of the ITC case.

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