Hi Doug,
I think that the gist of the invention is in its title:
A METHOD AND APPARATUS TO COUNTERACTS SLOWDOWN IN AIRBORNE WIND ENERGY
The paragraphs 28-33 can bring some clear up about the purpose:
[0028] In light wind conditions, gravity induced speed change adds to the problem of keeping the kite airborne. This in turn increases the cut-in wind speed necessary for operation of the power plant, relative to a kite flying at substantially constant speed. This is shown in figure 2 . The cut-in wind speed of the uncompensated system is at approximately 10 m/s while the cut-in wind speed of the compensated systems compensated as disclosed herein is only around 6-7 m/s. This difference is expected to increase with scale.
[0029] If the kite is travelling faster relative to the nominal path, it should be depowered by reducing lift and/or adding drag to slow it down to allow it to obtain the speed according to the nominal path. Such a high speed may be affected by the kite flying in a flight direction component toward the ground (see also figs. 6 and 7 ).
[0030] The reason why the kite should slow down may be one or more of the following:
to protect the structural integrity of the kite
to protect the structural integrity of the tether
to protect the power electronics from high currents, high power, high temperatures etc.
to protect the tether from high current and/or temperature
to protect the winch from high torque, power or temperature[0031] A kite flying in a flight direction having component away from the ground needs to counter act gravity to gain altitude. If no counter measures are taken, the kite will slow down. Being slowed down by gravity typically leads to less power being harvested from the surrounding wind. If the kite should be slowed down intentionally, this also causes less power to be harvested from the surrounding wind.
[0032] The invention aims to use a one or more of six measures to counteract gravity induced speed changes thereby indirectly reduce speed variation(s) of the kite during production.
[0033] The reduction of speed variation can be described in term of “instil” kinetic energy into the kite". Within the concept of instil kinetic energy is considered that the kinetic energy can be increased or decreased. That is, instil can also refer to removal kinetic energy since such a removal is instil with opposite sign.
Some means are envisaged. An interesting embodiment is provided:
[0038] When using direct thrust e.g. with propellers and/or RAT, the invention suggests in some embodiments adding energy storage on the kite to store energy harvested in the down stroke such that it might later provide thrust in the upstroke. The amount of energy stored in this manner may advantageously be a substantial portion of the change in gravitational potential energy between the kite at its highest point on the nominal path and its lowest point.
If we remember, Makani wing had a problem by going down at high speed, leading to high kinetic energy towards the ground (I mentioned it somewhere), then going up with difficulty and slowly, and even with the help of generators as motors.
The invention intends to overcome this issue, among other purposes. At least that’s what I think I understood after a first reading.