Wind farm dynamic models assessment under weak grid conditions

Abstract

Large-scale integration of wind power is one of the main challenges in today's power systems. Therefore, there is an increased importance to generate more accurate yet simplified wind farm (WF) models. The current modelling techniques of WFs depend on aggregationto reduce the degree of model complexity and computational time. The two techniques of aggregation are adopted in the literature: fully aggregated model (FAM) and multi-machine model where the WF is divided into a number of aggregated models for different sections of the WF. A small-signal model based comparison between the two techniques of aggregation is introduced in this study. The aim is to investigate the impacts of the full aggregation of the wind turbines on the overall system critical modes under weak grid conditions as compared to the multi-machine modelling approach. The comparison is done for different operating conditions (output active and reactive power) of the WF and also under different short-circuit ratios to reveal to what extent the FAM can be relied on to provide an accurate response of large WFs.

Adequacy of the Single-Generator Equivalent Model for Stability Analysis in Wind Farms With VSC-HVDC Systems

“…Assuming that every 40 WTGs present similar dynamic characteristics, the multi-machine model of the wind farm can be divided into two models, each with 100 MW (40 × 2.5 MW) capacity. Such two-machine aggregation can also refer to [24], [47]. In this case, the whole wind farm is modelled by two equivalent WTGs with 100 MW capacity for each, as shown in Fig.…”

“…As a method to represent the wind farm by a single WTG, the capacity-weighted mean value method has been widely used in engineering practice, but the accuracy of this method is questionable [20]- [22]. A drawback of the SEM lies in that the dynamic characteristics within wind farms may be hidden or the dynamic characteristics of certain critical oscillation modes may be misrepresented [23], [24]. When a wind farm is integrated into an AC network, the SEM has been used in many cases to represent the general dynamic behavior of the wind farm at the point of common coupling (PCC) [25]- [27].…”

“…In light of this, the small-signal stability analysis was performed to evaluate the wind farm equivalent models [12], [13], [24], [32]- [39]. To estimate the equivalent parameters of DFIG wind farms, an aggregation technique consisting of a hybrid algorithm was proposed by using the measurement data from phasor measurement units (PMUs) [33].…”

“…To investigate the impact of the SEM on the critical modes under weak grid conditions compared to the MEM, a small-signal based benchmarking between the two equivalent models was presented in [24]. In [38], [39], the oscillation modes comparisons between the detailed model and the SEM in the case of a large number of grid-connected inverters were presented.…”

“…Although there is an adequacy study on the equivalent models for small-signal stability analysis in wind farms directly connected to an AC grid [12], [13], [24], [32]- [37] and grid-connected inverters [38], [39], the accuracy of the SEM has not been studied in the case of the DDWFV. Different from the wind farms directly connected to the AC grid, the oscillation interactions between the grid-side converter (GSC) of the PMSG and the rectifier (REC) of the VSC-HVDC exist in the DDWFV [3].…”