Enhancement of LVRT Ability of DFIG Wind Turbine by an Improved Protection Scheme with a Modified Advanced Nonlinear Control Loop

Abstract

One of the problems with the doubly-fed induction generator (DFIG) is its high vulnerability to network perturbations, notably voltage dips, because of its stator windings being coupled directly to the network. As the DFIG’s stator and rotor are electromagnetically mated, the stator current peak occurs during a voltage dip causing an inrush current to the critical converter back-to-back and an overload of the DC-link capacitor. For this purpose, a series of researchers have achieved a linear and non-linear controller with a crowbar-based protection scheme. With this type of protection, the Rotor Side Converter (RSC) is disconnected momentarily, and consequently, its control of both the active and reactive output power of the stator is totally lost, leading to incorrect power quality at the point of common coupling (PCC). In this document, a robust nonlinear controller by Advanced Backstepping with Integral Action Control (ABIAC) is initially employed to monitor the rotor and the network side converters under normal network operations. In the presence of a network fault, an improved protection scheme (IPS) is tacked on to the robust nonlinear control to help enforce the behavior of the DFIG system to be able to overcome the fault. The IPS, which is formed by a crowbar and an RL series circuit, is typically located in the space between the rotor coils and the RSC converter. Compared to a standard crowbar, the developed scheme is successful to limit the rotor transient current and DC-link voltage, also an RSC disengagement to rotor windings can be prevented during the fault. Furthermore, the controllers of both the RSC and the Network Side Converter (NSC) are modified to boost the supply voltage at the PCC. A comparative study is also performed between the IPS without and with modification of the reactive power control loops. The simulation results mean that with the modified controllers during the fault, the amount of reactive power sustainment with ABIAC at the PCC is optimized to 17.5 MVAr instead of 15 MVAr with proportional-integral control (PIC). Therefore, the voltage at the PCC is fort increased in order to comply with the voltage requirements of the farm and absolutely to maintain the connection to the network in case of voltage dip.

A New Short-Circuit Current Calculation and Fault Analysis Method Suitable for Doubly Fed Wind Farm Groups

“…As the stator flux orientation control strategy is adopted on the rotor side of the DFIG group, ψ sd = ψ s = u s /jω s , ψ s is the amplitude of the stator flux. Formula (3) can be rewritten as follows: (14) According to Equations ( 13) and (14), the relationship between rotor flux and DFIG output active power, reactive power, and pre-fault voltage at the initial time of fault can be expressed as follows:…”

“…The converter of the DFIG cannot simply be blocked using crowbar during the fault period, and the rotor excitation needs to be adjusted through the LVRT control strategy to output reactive current [13]. In this case, the output short-circuit current of the DFIG is affected by the converter control characteristics [14]. Therefore, it is necessary to consider the low-voltage crossing control strategy and the control characteristics of the converter when calculating the short-circuit current [15].…”

Enhancing the control of doubly fed induction generators using artificial neural networks in the presence of real wind profiles

“…Additionally, the ability to limit the rise in global temperature to 1.5°C and achieve the CO2 reduction targets by 2050 may rely on the widespread adoption of renewable energy sources (RESs) coupled with increased electrification [ 2 ]. In light of advancements in technology, wind energy has emerged as one of the most promising renewable energy sources worldwide, primarily due to its remarkable efficiency and adaptable control capabilities [ 3 ].…”

Heat transfer characteristics in Williamson fluid flow in a vertical channel with chemical reaction and entropy production

“…Entropy, a key thermodynamic irreversibility parameter, occurs in the second law of thermodynamics. The analysis of entropy production makes a significant contribution to thermal systems design decisions and thus supports in optimization of cost and energy in science and engineering areas like the cooling of electronic devices, heat exchangers, energy storage systems (Yessef et al [51], Chojaa et al [52], Loulijat et al [53], and Hamid et al [54]), etc. Bejan [55,56] presented pioneering work on entropy production and its optimization.…”