Efficient and Power Smoothing Drive-Train Concept for Pumping Kite Generators using Hydraulics

Frédéric Bourgault Principal Scientist New Leaf Management Ltd. 1177 West Hastings Street, Suite 500

Vancouver, BC V6E 2K3 Canada frederic@newleaf.co

www.newleaf.co

new leaf

Efficient and Power Smoothing Drive-Train Concept for Pumping

Kite Generators using Hydraulics

Frédéric Bourgault1_{, Devin Todd}1_{, Jason Beatch}1_{, Mojtaba Kheiri}1,2_{, Luke Damron}1_{, Vahid Saberi Nasrabad}1 1_{New Leaf Management Ltd.}

2_{Concordia University}

A challenge for Pumping Kite Generator (PKG) ground sys-tems is to produce consistent electrical power output to the grid despite the cyclic mechanical power exchange with the kite. Electro-mechanical systems coupled with battery or capacitor accumulators have been proposed for electrical conditioning. However, their economic po-tential is impeded by poor efficiency (especially at part loads), and high accumulator costs. Taking advantage of emerging high efficiency digital hydraulic machines New Leaf has improved on a hydraulic drive-train concept pro-posed by Crosswind Power Systems [1].

The concept introduced in this presentation decouples the winch and generator functions. It consists of high ef-ficiency variable displacement hydraulics (i.e. where one device couples to the winch and another device drives a generator at constant speed) working in conjunction with a hydro-pneumatic accumulator (see Fig. 1). Our presen-tation shall demonstrate that this PKG drive-train config-uration, versus an electro-mechanical analog, can gener-ate consistent electrical power at significantly higher ef-ficiency throughout the whole operational range of wind speed, and especially at part-load. Additionally, the high power density of hydraulic systems may lend themselves to serving fast response grid regulation; and since they do not require inverters, nor gearboxes (i.e. two of the major components responsible for most of the failures in conventional wind turbines), they may demonstrate bet-ter durability than electro-mechanical solutions. They

are also lower-cost than their electrical solution coun-terparts. Moreover, the concept avoids using electro-chemical energy storage with limited usable life. Taken together, a hydraulic-based PKG ground station offers several mechanisms to drive LCOE reductions of PKG sys-tems. PRO= TROVRI PRI= TRIVRI Hydro-Pneumatic Accumulator Pump /M otor M otor Synchronous Generator Pelec_out W inch Drum

Figure 1. PKG hydraulic drive-train concept with hydro-pneumatic accumulator to generate consistent electric power. It uses a large displacement digital hydraulic pump/motor combination to di-rectly drive a winch drum, and a high-speed digital hydraulic motor to spin a synchronous generator at constant speed.

References:

[1] Tattersfield, M.A., Atwater, J.F., Houle, C.P., 2013. Method And System For Harnessing Wind Energy Using Tethered Airfoil. Patent US2013/028537A1.