Abstract
It is important to develop modelling tools to predict unstable situations resulting from the interactions between the wind power plant and the weak power system. This paper presents a unified methodology to model and analyse a wind power plant connected to weak grids in the frequency-domain by considering the dynamics of the phase lock loop (PLL) and controller delays, which have been neglected in most of the previous research into modelling of wind power plants to simplify modelling. The presented approach combines both dq and positive/negative sequence domain modelling, where a single wind turbine is modelled in the dq domain but the whole wind power plant connected to the weak grid is analysed in the positive/negative sequence domain. As the proposed modelling of the wind power plant is systematic and modular and based on the decoupled positive/negative sequence impedances, the application of the proposed methodology is relevant for transmission system operators (TSOs) to assess stability easily with a very low compactional burden. In addition, as the analytical dq impedance models of the single wind turbine are provided, the proposed methodology is an optimization design tool permitting wind turbine manufacturers to tune their converter control. As a case study, a 108 MW wind power plant connected to a weak grid was used to study its sensitivity to variations in network short-circuit level, X/R ratio and line series capacitor compensation (Xc/Xg).
Highlights
With the increasing number of solar and wind power plants in the electrical grid, the installation ratio of traditional synchronous generators to the total production capacity is significantly decreasing, which is leading to weak transmission grids [1]
In order to have both the advantages of dq domain and sequence domain modelling, this paper presents a systematic and modular method, where the wind turbine is modelled in the dq domain and where stability analysis of the wind power plant is analysed in the sequence domain
This paper presents a unified impedance-based modelling and analysis tool to predict unstable
Summary
With the increasing number of solar and wind power plants in the electrical grid, the installation ratio of traditional synchronous generators to the total production capacity is significantly decreasing, which is leading to weak transmission grids [1]. State-space and impedance-based modelling have been used in different power electronics-based power systems like microgrids, wind power plants, solar plants, parallel current source converters and voltage source inverters. In addition to state-space modelling, impedance-based modelling is another useful tool for frequency-domain analysis [17] In this method, the grid output impedance (Zs) and the converter input impedance (Zl) are required for stability analysis [5,18]. MWplant wind poweranalysis plant connected to aincluded weak grid is analysed under different literature on wind power stability [24], are to have a more accurate model. The current references (I d ref and Iq ref) are generated from the dc-link voltage and reactive power integral (PI) controllers (Gcc ). The time-delay of the and the discrete control can be modelled by using the Padé approximation [30]
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