PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 95 NR 8/2019 121 A. M. Shiddiq YUNUS 1 , Makmur SAINI 1 , Ahmed Abu-SIADA 2 , Mohammad A.S. MASOUM 3 State Polytechnic of Ujung Pandang (1), Indonesia Curtin University (2), Australia Utah Valley University, USA doi:10.15199/48.2019.08.27 Impact of SMES Unit on DC-Link Voltage of DFIG during Various Types and Level of Faults Abstract. Wind energy becomes a popular source for renewable energy based power plants since a recent decade ago. Within many types of wind turbine generator (WTG), Doubly Fed Induction Generator currently dominating the market niche by about 64% on all installed capacity all around the world in 2015. A DFIG consists of two converters that linked by a capacitor or so-called as DC link that works to allow the transfer energy from WTG to the grid and vice versa. These converters are very sensitive to any faults particularly when the DC link voltage reach beyond the safety margin, it may be ended with the disconnection of DFIG to avoid any damage on the DFIG's converters. This paper aims to investigate the impact of SMES Unit on DC link voltage of DFIG during various types and levels of faults. The study was conducted through a simulation program and shows that SMES Unit is very effective in reducing the voltage at DC link during grid swell events and slightly affecting the voltage overshoot during grid sag and short circuit events. For the last two cases, the SMES Unit control system is designed to work properly and optimally, therefore, impact of SMES rather insignificant due to the DC link voltages are within the safety margin, however, when DC particularly for the case where the DC link voltage tends to increase and potential to damage the switching parts of DFIG, the SMES Unit could significantly compensate the faults and maintain the voltage within the safety margin. Streszczenie. W artykule analizowany jest wpływ układu SMES (superconducting magnetic energy storage) na pracę układu generatora DFIG typu. DC-link przy różnych typach zakłóceń na przykład zapadów napięcia lub zwarć w sieci. Układy konwerterów w systemie DFIG są bowiem bardzo czułen na przekroczenie przez napięcie marginesu bezpieczeństw co skutkować może odłączeniem generatora. Wpływ układu SMES na pracę generatora DFIG farmy wiatrowej przy różnych rodzajach zakłóceń Keywords: DFIG, WTG, Grid Sag, Grid Swell, Short Circuit Słowa kluczowe: farma wiatrowa, generator DFIG, SMES – superconducting magnetic energy storage Introduction Renewable energy sources become more popular since the last decade due to some efforts on mitigating global warming from the use of conventional energy sources for power plants. One of the popular renewable energy sources is wind energy, where it is reported in JRC Wind Energy Status Report 2016 Edition that there are about 430 GW wind turbine generators have been installed worldwide till 2016. Within all types of wind turbine generators, Doubly Fed Induction Generator (DFIG) become the most type installed worldwide which dominate about 64% of market share in 2015 [1]. This fact is based on the advantages of DFIG in terms of technical aspect where DFIG could supply some amount of reactive power to the grid as it is equipped with power electronics that connected directly to the grid and rotor side. With about 33% capacity of power electronics, the cost of the DFIG system becomes cheaper than its main rival in the same class, Full Converter Wind Turbine Generator (FCWTG) type [2]. A typical model of a DFIG can be seen in Fig 1. Fig.1. Typical Configuration of A DFIG When wind turbines generators (WTGs) connected to the grid, there are some parameters must be complied to avoid the disconnection of WTGs to prevent any damages on the WTGs. For instance, voltage profile at the point of common coupling (PCC), rotors and stators' current, DC- link voltage (for DFIG and FCWTG), etc [3]. A DC link as shown in Fig. 1. is obligated to maintain the transfer energy between the rotor and grid [4]. DC link power electronic that links a grid side converter (GSC) and a rotor side converter (RSC) are very sensitive with any faults, most of the wind turbine generator manufacturers recommended the safety margin voltage level on DC link that allowed the converters standstill is between 0.25%-1.25% [3]. Therefore any voltage profiles of DC-link that violate the safety range, the internal protection of the converters should block the converters and lead to the disconnection of DFIG from the grid. Consequently, many of MWs power from DFIGs undelivered to the grid which means a huge economic loss for WTGs’ owners. In this paper, an investigation is focused on the impact of Superconducting Magnetic Energy Storage (SMES) when connected at PCC on the DC link voltage of DFIGs. The system under study is based on the prior studies in [5, 6, 7]. For comprehension study, three types of faults are applied in this paper: (1) Grid Sag Faults; (2) Grid Swell Faults and (3) Short Circuit. System under Study The system under study is shown in Fig. 2. This system consists of six of 1.5 MW DFIG that is connected through a 30 Km distribution line to a grid. A Superconducting Magnetic Energy Storage (SMES) Unit is connected at Point of Common Coupling (PCC) to improve the DFIGs' Fault Ride Through (FRT) capability. The DFIG itself is based on the typical design as introduced in [8]. The topology of a DFIG, as depicted in Fig. 1, consists of two converters that allow transfer energy from WTG to the grid and vice versa. The two converters namely grid side converter (GSC) and rotor side converter (RSC) are linked with a capacitor that is aimed to maintain the desired level of voltage to allow the energy transfer. The typical generic control system that normally applied in a DC link of DFIG is shown in Fig. 3 [8].