Abstract
Insufficient frequency regulation capability and system inertia reduction are common problems encountered in a power grid with high wind power penetration, mainly due to the reason that the rotor energy in doubly fed induction generators (DFIGs) is isolated by the grid side converters (GSCs), and also due to the randomness and intermittence of wind power which are not as stable as traditional thermal power sources. In this paper, the frequency inertia response control of a DFIG system under variable wind speeds was investigated. First, a DFIG system topology with rotor-side supercapacitor energy storage system (SCESS-DFIG) was introduced. Then a control strategy for frequency inertia response of SCESS-DFIG power grid under fluctuating wind speed was designed, with two extended state observers (ESOs) which estimate the mechanical power captured by the DFIG and the required inertia response power at the grid frequency drops, respectively. Based on one inconstant wind speed model and the SCESS-DFIG system model adopting the control strategy established, one power grid system consisting of three SCESS-DFIGs with different wind speed trends and a synchronous generator was simulated. The simulation results verified the effectiveness of the SCESS-DFIG system structure and the control strategy proposed.
Highlights
The basis of stable operation of a power grid system is that the balance between the power generation and the load consumption can be maintained in real time
In order to verify the effectiveness of the control strategy proposed in this paper, one simulation model of the SCESS-doubly fed induction generators (DFIGs) grid consisting of wind turbine, DFIG, rotor-side converter (RSC), grid side converters (GSCs), DC/DC converter, and supercapacitor models was constructed in MATLAB/Simulink (2014b, The MathWorks, Natick, MA, USA)
In the grid frequency inertia responses, the influence of wind speed variations on the output power of DFIG was taken into consideration, and one SCESS-DFIG topology and its principle of adjusting the output power was analyzed
Summary
The basis of stable operation of a power grid system is that the balance between the power generation and the load consumption can be maintained in real time. In order to solve the above three problems, a DFIG system topology with rotor-side supercapacitor energy storage system (SCESS-DFIG) was introduced, and extended state observers (ESOs) were built to realize a frequency inertia control strategy for the SCESS-DFIG power grid under wind speed changes. In this control strategy, the instantaneous mechanical power in the wind turbine needs to be captured, but which is a fuzzy variable that cannot be measured directly. The wind speed trends included speed sudden drops, reciprocating speed fluctuation, and sudden speed increases
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