Combined constant speed control method for a wind generator equipped with hydraulic energy storage

Abstract

A wind generator equipped with hydraulic energy storage (WG-HES) uses hydraulic transmission systems instead of gearbox transmissions, thus eliminating high-power converters and reducing the tower-top cabin weight. When there is no wind or the wind speed is extremely low, the pressured oil released by accumulators is used to drive a motor to operate at a constant speed, thereby generating constant-frequency power. However, few studies have examined the constant speed control characteristics for generating electricity using only an accumulator group. In this study, a combined constant speed (CCS) proportional-integral-derivative (PID) control method based on "variable displacement and throttling" is proposed, which includes two closed loops and one regulating loop. First, a simulation model of the CCS PID control method for a variable motor was established in the Simcenter Amesim program. The influence of different PID parameters on the anti-interference ability of the constant speed control of the motor was analyzed under a given load step. Then, we obtained the range of control parameter values and a set of optimal values. Second, the effectiveness of the CCS control method and the accuracy of the simulation results were verified on a 600-kW WG-HES system prototype. The results verified that the CCS control method has good anti-interference ability and can meet the requirements of constant speed control for a variable motor under the best PID parameters. These results can provide a basis for developing control strategies for WG-HESs when there is no wind or at low wind speeds. KEYWORDS accumulator-controlled hydraulic motor, anti-interference, combined constant speed control, hydraulic energy storage | INTRODUCTIONRenewable energy is becoming increasingly prominent owing to the rising insufficiency of fossil fuels to meet the demands of the growing global population. 1-5 Solangi et al. revealed that wind energy is the most feasible renewable energy resource for electricity generation, 6 and the proportion of wind energy in the energy market is increasing continuously. 7 Significant advances in wind turbine manufacturing have enabled lowering the production costs of devices for harvesting wind energy, and the application range of wind power generation equipment has broadened. 8,9 Conventional wind turbines use gears and gearboxes to transfer energy. However, such systems have a high risk of failure and heavy cabins, both of which result in high maintenance costs. 1,10,11 Therefore, direct-drive wind turbines were developed, but these systems require a large-

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