Low Voltage Ride-through Capability Enhancement of Doubly Fed Induction Generator Based Wind Turbines under Voltage Dips

Abstract

Based on the advantages of doubly fed induction generator (DFIG)-based wind turbine (WT). This paper proposes a new control strategy to improve the ride-through capability of DFIG-based WTs in the event of a grid fault. The proposed method is performed by using the DFIG converters control and the addition of the damping resistances connected to the DC circuit, to follow the requirements defined by the grid codes. The proposed ride-through solution limits the peak values of the DC link voltage, the rotor inrush current, electromagnetic torque and DFIG transient response at the times of occurrence and clearing the fault. The proposed solution is simulated and compared with the crowbar solution using MATLAB/Simulink environment. Keyword:Damping INTRODUCTIONWind energy is gaining increasing importance throughout the world. This fast development of wind energy technology has large implications for a number of people and institutions. As WTs become larger and level of penetration becomes higher in electrical power systems, grid operators have modified the grid codes. According to these new grid codes, WTs must remain connected to the grid and supply reactive power to guarantee the grid voltage during the grid faults. This ability of WTs is called the fault ride through (FRT) capability [1], and more specifically for voltage dips, low voltage ride through (LVRT) capability [2], [3]. Nowadays, DFIG is the most used generator for WTs due to the advantages of variable-speed ability, higher energy capture, improved power quality and using converters rated for partial-scale converters [4]. On the other hand, because the stator of the DFIG is directly connected to the grid, it is very sensitive to the grid disturbances, particularly voltage dips [5]- [12]. The transients voltages on rotor side during grid faults, are higher than the stator side, and thus the rotor side converter (RSC) and intermediate DC circuit are particularly susceptible to be destructed due to voltage transients. Also, the voltage sag at the stator terminals due to the grid faults causes the rotor over-currents, DC-link over voltage and torque oscillations that could lead to destruction of the power converter and mechanical parts. So, without a proper control strategy, the DFIG is unable to stay connected to the grid during the grid faults [5]. Likewise, the DFIG system is not controlled during the critical time of grid faults and the system cannot support the grid. Previous approaches of researches have been presented to address DFIG FRT issues. The most common FRT solution is to short circuit the rotor windings with the crowbar circuit [6]- [7]. When the rotor over-current is detected, The crowbar circuit short circuits the rotor windings when the rotor overcurrent is detected, which isolates the

Improved crowbar protection technique for DFIG using fuzzy logic

“…The fuzzy rules in sugeno  ISSN: 2088-8694 system is presented in two models as decribed in [26]. Each rule of sugeno fuzzy inference operates in zeroorder methods as in ( 4) with (𝑝 𝑖 = 𝑞 𝑖 = 0), while 𝑧 𝑖 is constant, or first-order method as in (5). Rule i:…”

“…𝐼𝐹 𝑥 is 𝐴 𝑗 𝑎𝑛𝑑 𝑦 𝑖𝑠 𝐵 𝑘 𝑇𝐻𝐸𝑁 𝑧 𝑖 = 𝑝 𝑖 𝑥 + 𝑞 𝑖 𝑦 + 𝑟 𝑖 (5) where 𝐴 𝑗 and 𝐵 𝑘 are the fuzzy sets for inputs 𝑥 and 𝑦, 𝑗 and 𝑘 are the membership functions that defined the input, 𝑧 𝑖 represent an output (consequent function) and it is a linear or constant consequent function, 𝑝 𝑖 , 𝑞 𝑖 and 𝑟 𝑖 are the consequent parameters and finally, 𝑖 indicates the number of rules. The third step, the interface engine, calculates the output value for each rule defined in the previous step.…”

“…Furthermore, the second category is external retrofit techniques, which add protective devices to the DFIG system and advanced control strategies, such as rotor-side and stator-side external retrofit techniques, limiting the DC-link and rotor overvoltage and overcurrent, also to remain the stator current and stator voltage on an acceptable level. In light of these findings, different device topologies using protective circuits and storage methods such as damping resistances [5], DC-Chopper, series dynamic braking resistor [6] energy storage system (ESS) [7], [8] are discussed in many types of research. A combination of parallel crowbars and DC Chopper is presented in [9] to reduce the overcurrent in rotor converts and control the DC-link.…”