Simulation of Malfunctions in a Wind System Powered by a DFIG

The paper is about the simulation of malfunctions in an onshore wind energy conversion system powered by a doubly fed induction generator with a two-level power converter, handling only the slip power. These malfunctions are analysed in order to be able to investigate the impact in the wind power system behaviour by comparison before, during and after the malfunctions. The malfunctions considered in the simulation includes are localized in the DC-link of the converter and in the phase change in rectifier

Performance Characteristics of a Cascaded Two-level Converter

A cascaded two-level power converter is proposed which utilizes two six-transistor inverters and is capable of producing voltages which are identical to those of three-level and four-level converters. Since the machine voltages are the same, the converter performance is the same as is verified through laboratory tests. The advantages and disadvantages of the proposed cascaded converter are explored. The proposed converter is simpler to construct and offers more nonredundant switching states per number of active semiconductors than standard multi-level converter

Dynamic and Transient Analysis of LVRT Augmented Grid Tied DFIG based Wind Turbine

This thesis aims to present Low Voltage Ride Through (LVRT) augmentation of the gridtied Doubly Fed Induction Generator (DFIG) based wind turbine. Voltage stability is a critical grid code criterion that must be strictly adhered. A substantial voltage drop happens during a fault or network disruption situation, which must be restored as quickly as possible. According to modern grid code standards, 90 percent of the voltage must be restored to pre-fault levels in 1500 milliseconds. As a result, both dynamic and transient assessments are performed to evaluate the intended power system's LVRT capabilities. In this study, fault analysis including the most severe 3LG fault under transient conditions has been examined in order to evaluate the tuned PI controller scheme and resilience of the developed power system model. PSCAD/EMTDC® v4.5 tool has been used extensively to develop the DFIG wind turbine aerodynamic model, DFIG control scheme and power system model analysis. Simulation results show that tuned Proportional Plus Integral (PI) controllers effectively augment the LVRT functionality by injecting sufficient reactive power into the grid during fault or network disturbance scenarios

Comparison between FS-MPC control strategy for an UPS inverter application in α-β and abc frames

The voltage source inverter (VSI) of an uninterruptible power supply (UPS) is a system where the main objective is to obtain a high quality output sinusoidal voltage with independence on the output load. For this reason, it includes an output LC filter. The presence of the filter increases the complexity of the controller design thus it is necessary to evaluate the performance of the control strategy in terms of the output voltage quality and computational cost of the algorithm. In this paper, both analysis are developed for the finite states model predictive control (FS-MPC) of a VSI performed in the abc and α-βframes. Both algorithms are summarized and compared in order to establish an objective criteria to choose among them when a hardware implementation is developed. Simulation results are presented for both algorithms to validate the analysis

Model predictive control with constant switching frequency using a discrete space vector modulation with virtual state vectors

Finite states model predictive control (FS-MPC) appears as a promising control technique to be applied to power converters in the industry. However, the FS-MPC presents some drawbacks as non constant switching frequency and high sampling frequency. This work proposes a FS-MPC with constant switching frequency and low sampling frequency applying a discrete space vector modulation (DSVM) technique. The real state vectors of the converter are used together with new virtual state vectors forming switching sequences each sampling period. The advantages and disadvantages of the proposed FS-MPC with the DSVM are analysed using a two-level three-phase inverter connected to the grid as setup to introduce the proposed technique. Simulation results are presented, showing that using the proposed technique the switching frequency is fixed and the sampling frequency can be lowered without reducing the quality of the converter behaviour