Energetica India nº91 July August 2020

WIND POWER Anticipating complex network issues through the use of advanced simulation models The increase in share of wind energy in the transmission networks, has brought about the challenge of integration with the electrical grid. An accurate modeling of the converter control loops and its interaction with the grid becomes indispensable in order to overcome this challenge. Introduction Wind energy penetration in the transmission networks has been steadily increasing during the last decades. This situa- tion causes integration problems with the electrical grid. Regarding the power converter, these problems can be clas- sified as follows: Working with very low SCR or quality factor grids: the reso - nance frequency of the harmonic filter decreases and can de - stabilize the current control loop. Sub-synchronous resonances: when series capacitors used in long transmission lines interact with the converter control loops, resonances at low frequencies appear. Parallel resonances: the use of capacitor banks on a wind farm level can have an influence on the system stability. An accurate modeling of the converter control loops and its interaction with the grid becomes indispensable in order to overcome these challenges. Using SIL and HIL systems meet this requirement, but these systems are time-consuming. The modeling of the control loops, grid, and generator systems as linear time-invariant (LTI) models, instead, allows high agility to run parameter sweeps and test new algorithms. The LTI model allows to express the whole system (grid + con- trol + generator) as one state-space matrix. The stability and dynamic behaviour of the system can be obtained easily from the LTI model. The non-linearities of the system (converter switching, non-lin - ear control algorithms…) must be linearized or eliminated. Results The following workflow is proposed to anticipate grid interac - tion problems: • Characterization of all possible casuistic of a grid: param - eter variations (e.g. number of turbines connected), network branches connected or disconnected, capacitor banks con- nected or disconnected. • Generation of LTI models of all possible grid, generator and control algorithm casuistics to analyze the control loops be- havior and obtain the set of parameters or new algorithms to assure the good performance, • Validation of the solution using SiL and HiL systems. Generation of LTI models LTI model of a certain grid, LTI model of a certain converter control option and LTI model of a certain generator are com - bined to form an LTI model associated to a particular grid, con - trol and generator combination. Figure 1. Generation of LTI models workflow Validation of LTI modelling Despite simplifications (no switching and dead-time, lineariza - tion of non-linearities), the LTI model replicates with sufficient precision the current response measured in real test-bench. X. JUANKORENA, D. VELASCO, I. ESANDI and E. BURGUETE Ingeteam Power Technology, Sarriguren, Spain 38 energetica INDIA- July-Aug_2020