Abstract
Wind has been admitted as one of the most promising renewable energy resources in multinational regionalization policies. However, the intermittent wind energy volatility and the weak coupling between traditional wind generators and the power grid all influence the electrical grid frequency stability. The hydrostatic transmission wind turbine (HWT) is taken as the research object, and the hydraulic energy storage system (HESS) is introduced into HWT to improve the frequency regulation capability. First, the mathematical models of rotor, hydraulic power main transmission system, and the excitation synchronous generator are established. Then, the HWT frequency modulation characteristics are analyzed under different amplitude of load frequency fluctuation. In view of the HWT limited frequency modulation capability, the frequency modulation control strategy based on virtual inertia compensation is proposed with the HESS. Under the condition of maximum power point tracking, the effectiveness is verified. The simulation and experimental results show that the control strategy has a good control effect, and the HESS dynamic response characteristic satisfies the wind power–frequency regulation. The research results will be helpful to make wind power become grid-friendly power and solve the problem of electrical grid low frequency stability.
Highlights
Wind energy is a vast renewable energy resource being increasingly tapped by wind turbines which are growing in number and size
The hydrostatic transmission wind turbine (HWT) with hydraulic energy storage system (HESS) is taken as the research object, the frequency modulation (FM) requirements and the working principle of the HWT are analyzed, and the HWT FM controller is proposed
(3) The HWT frequency modulation control strategy based on virtual inertia is obtained
Summary
Wind energy is a vast renewable energy resource being increasingly tapped by wind turbines which are growing in number and size. Combining energy storage device with wind farm, a hierarchical model predictive control method of wind turbine and energy storage system under black start was proposed in Ref. 20, and frequency modulation and frequency recovery at grid side were realized. For a doubly fed wind turbine, a primary frequency control strategy based on variable power point tracking and super-capacitor energy storage was proposed in Ref. 22, and the optimal configuration of energy storage device capacity was comprehensively considered to realize the frequency modulation control under high wind energy utilization. The original hydraulic system functions and control strategies of HWT remain unchanged, and the working conditions of the variable pump/motor are adjusted to realize the dynamic adjustment of the generator output active power and compensate for the power grid load frequency fluctuation. Where q is the air density (kg/m3), A is the swept area of the rotor blade (m2), and v is the wind speed (m/s)
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