Design and Control of Hydrostatic Continuous Variable Transmission for a Community Wind Turbine

Abstract

This research aims to develop an efficient and reliable hydrostatic drive train (HST) for community wind turbines by implementing an advanced controller to maximize energy capture and stabilize the power grid. An HST is a continuously variable transmission (CVT) consisting of a hydraulic pump driving a variable displacement motor. HSTs are simple, light, cost-effective, and offer high power density. An HST drive train was designed for application in community wind turbines. To validate the performance of the HST, a novel power regenerative test platform was successfully designed, constructed and commissioned. It has two hydrostatic closed loops, coupled to each other. The research platform is capable of generating 100 kW output with only 55 kW of electrical input by taking advantage of power regeneration. The performance of each hydraulic component was measured on the test platform. The test platform is a multi-domain system, consisting of electrical, mechanical and hydraulic components. Using a bond graph-based method, a dynamic model of the system was developed. All possible pairings between inputs and outputs were studied in this multi input and multi output system to select the pair with the strongest coupling. A decentralized controller was later designed to control the rotor speed and pressure of the system. The start-up and shut down algorithms developed, enabled smooth operation of the testbed without a cavitation and pressure spikes. The performance of the HST was validated under various wind profile inputs. A pressure control strategy was developed to maximize power capture. To implement the above controller, one only needs measurement of the rotor speed for the reference command and pressure for tracking. The control law automatically drives the turbine to the optimum point, since the optimal parameters of the turbine are included in the control gain. A hardware-in-the-loop simulation was implemented to mimic the wind turbine environment. The turbine rotor dynamics are emulated on the test platform by implementing a decoupling controller. We examined the results of the HST drive train in transient and steady conditions. The efficiency of the HST wind turbine estimated from these experiments was comparable with that of a conventional turbine. Finally, the feasibility of connecting an HST wind turbine to the grid via a synchronous generator is studied. Furthermore, we investigated the electromechanical dynamics of the synchronous generator and performance of the system under large disturbances in incident wind, through detailed time-domain simulations. We found that the generator terminal voltage and frequency comply with the grid regulation band under all operating conditions. This strategy circumvents the need of expensive power electronics. This research have offered a novel insides of the HST for wind turbine applications. The outcomes of the project will stimulate industry to develop more efficient hydraulic components, system and control for wind applications and contribute to our green economy.