Hydraulic Control Technology Trends Can Impeller MPPT

Tidal current energy is a clean and renewable energy source, and the studyand utilization of the tidal current energy has great significance for easingenergy crisis and developing uninhabited islands. In order to solve the problemof low energy capturing efficiency that is usually encountered in running thehorizontal axis turbine of tidal current power generation system at low currentspeed, a variable pump countertorque reference value model was establishedbased on the maximal power tracking theory and the torque equilibriumequation between the turbine and the variable pump. On the basis, a maximalturbine power control system including constant pressure control, indirect speedcontrol, pressure feedback, and torque control was designed. In the conditionthat the tidal current speed is unknown, the constant pressure control subsystemcan be used to stabilize the pressure of the hydraulic system. In the subsystem,the countertorque of the variable pump and the pressure of the hydraulic systemare taken as feedbacks, and the initial value of the output regulating device ofthe variable pump was set up before the main controller starts to regulate theoutput of the variable pump. Thus, no matter how the speed of the turbinechanges, the initial value of the variable pump output would make the turbinerunning under the desired torque. On this basis, the direct torque closed loopcontrol is added in the system, and the compensation value for the output of thevariable pump is given by the main controller. By regulating the output of thepump in a small range through the control system, the countertorque of thepump and the turbine speed are under control and follow the desired value,ensuring the turbine running at the optimal tip speed ratio, and then, realizingthe maximal power control for the turbine.The performance of the designedcontrol system was numerically simulated by means of the Automation Studiosoftware tool, a hydraulic type tidal current power generation system was builtup, in which the energy capturing turbine with8kW rated power was installed.With this power generation system, a series of sea tests were conducted. Testresults showed that the control system ran steadily, the power capturing coefficient of the turbine was about0.35and0.33in numerical simulation andsea tests respectively. Comparing with the results obtained without any controlaction, the power capturing efficiency of the turbine was increased about0.03and0.05, indicating that the efficiency was effectively increased and theeffectiveness and reliability of the control system was verified.