Enhancing Doubly Fed Induction Generator Low-Voltage Ride-Through Capability Using Dynamic Voltage Restorer with Adaptive Noise Cancellation Technique

Some of the major challenges facing micro-grids (MGs) during their connection with the utility grid are maintaining power system stability and reliability. One term that is frequently discussed in literature is the low-voltage ride-through (LVRT) capability, as it is required by the utility grid to maintain its proper operation and system stability. Furthermore, due to their inherent advantages, doubly fed induction generators (DFIGs) have been widely installed on many wind farms. However, grid voltage dips and distortion have a negative impact on the operation of the DFIG. A dynamic voltage restorer (DVR) is a commonly used device that can enhance the LVRT capability of DFIG compared to shunt capacitors and static synchronous compensator (STATCOM). DVR implements a series compensation during fault conditions by injecting the proper voltage at the point of common coupling (PCC) in order to preserve stable terminal voltage. In this paper, we propose a DVR control method based on the adaptive noise cancelation (ANC) technique to compensate for both voltage variation and harmonic mitigation at DFIG terminals. Additionally, we propose an online control of the DC side voltage of the DVR using pulse width modulation (PWM) rectifier to reduce both the size of the storage element and the solid-state switches of the DVR, aiming to reduce its overall cost. A thorough analysis of the operation and response of the proposed DVR is performed using MATLAB/SIMULINK under different operating conditions of the grid. The simulation results verify the superiority and robustness of the proposed technique to enhance the LVRT capability of the DFIG during system transients and faults.

A Distributed Control Scheme Using SiC-Based Low Voltage Ride-Through Compensator for Wind Turbine Generators

As the penetration of renewable energy power generation, such as wind power generation, increases low-voltage ride-through (LVRT), control is necessary during grid faults to support wind turbine generators (WTGs) in compensating reactive current to restore nominal grid voltages, and maintain a desired system stability. In contrast to the commonly used centralized LVRT controller, this study proposes a distributed control scheme using a LVRT compensator (LVRTC) capable of simultaneously performing reactive current compensation for doubly-fed induction generator (DFIG)-, or permanent magnet synchronous generator (PMSG)-based WTGs. The proposed LVRTC using silicon carbide (SiC)-based inverters can achieve better system efficiency, and increase system reliability. The proposed LVRTC adopts a digital control scheme and dq-axis current decoupling algorithm to realize simultaneous active/reactive power control features. Theoretical analysis, derivation of mathematical models, and design of the control scheme are initially conducted, and simulation is then performed in a computer software environment to validate the feasibility of the system. Finally, a 2 kVA small-scale hardware system with TI’s digital signal processor (DSP) as the control core is implemented for experimental verification. Results from simulation and implementation are in close agreement, and validate the feasibility and effectiveness of the proposed control scheme.

A Novel Control Method of Low-voltage-ride-through Technique for Asymmetrical Hybrid Energy Storage System

Low-voltage-ride-through (LVRT) capability is an important criterion for the stability of cascaded multilevel energy storage system (ESS). Based on asymmetrical hybrid ESS, a coordinated operating method is proposed to maintain the phase angle of positive-sequence-voltage of battery cells and capacitor cells. To deal with the asymmetrical chains among three phases, its influence on the power distribution is eliminated by modifying the command of battery cells, then the traditional zero-sequence-voltage injection is feasible for asymmetrical situations. Proposed methods can stabilize the dc-side voltage of capacitor cells, maintaining the output current. Finally, the correctness and effectiveness of proposed methods are proved by experiment.

Control of a Variable-Impedance Fault Current Limiter to Assist Low-Voltage Ride-Through of Doubly Fed Induction Generators

A fault current limiter (FCL) may be applied to assist the low-voltage ride-through (LVRT) of a doubly fed induction generator (DFIG). FCLs with fixed impedance, lack the flexibility to adjust their impedance to adapt to different LVRT scenarios. The direct switch-in and -out of the fixed-impedance FCL yields transient electromagnetic oscillations in the DFIG, which need to be addressed. In this paper, a variable-impedance FCL is implemented at the stator side of the DFIG to assist its LVRT, and a novel methodology is proposed to control the impedance of the FCL, with which the stator current oscillation is effectively constrained and the smooth switch-out of the FCL is realized to avoid continued active power consumption of the FCL and to restore the DFIG to its pre-fault working condition. Analysis of the LVRT transient is carried out, which lays the foundation for the control methodology to determine the impedance of the FCL based on calculation of the optimization goal. The feasibility and effectiveness of the control to the variable-impedance FCL are verified by the numerical analysis results, which compare the LVRT simulation results with the application of the fixed-impedance and the variable-impedance FCLs.