A. F. Abdou

Improving the low voltage ride through of doubly fed induction generator during intermittent voltage source converter faults

The impact of different voltage source converter (VSC) faults on the low voltage ride through (LVRT) capability of the doubly fed induction generator (DFIG) is also investigated. Faults such as fire-through of the VSC switches and short circuit across the DC-link capacitor are considered in this paper. The impact of internal VSC faults when they occur within the grid side converter (GSC), and rotor side converter is investigated. A proper static synchronous compensator (STATCOM) controller to mitigate the effects of these faults is proposed. The DFIG compliance with numerous and recently released LVRT grid codes under these faults, with and without the STATCOM, is examined and compared. Simulation results indicate that these types of faults have a severe impact on the DFIG voltage profile, especially when these faults occur in the GSC. This is attributed to the fact that the GSC directly regulates the point of common coupling (PCC) voltage. Moreover, the proposed controller is capable of bringing the volt...

Effect of intermittent voltage source converter faults on the overall performance of wind energy conversion system

The doubly fed induction generator (DFIG) is interfaced to the AC network through voltage source converters (VSCs) which are considered to be the core of the DFIG system. This paper investigates the impact of different intermittent VSC faults on the overall performance of a DFIG-based wind energy conversion system (WECS). The fault ride through capability of the DFIG under various VSC faults is also investigated. Faults such as open circuit and short circuit across the switches, when they occur within the grid side converter (GSC) and rotor side converter (RSC), are considered and compared in this paper. Short circuit and open circuit across the DC-link capacitor are also considered in this study as common VSC problems. Simulation results indicate that the short circuit faults have a severe impact on the overall performance of the DFIG, especially when they occur within the GSC. This is attributed to the fact that the GSC directly regulates the point of common coupling voltage. The open circuit faults have less impact on the performance of the DFIG-based WECS. A proper controller along with flexible AC transmission device should be available to compensate the required active and reactive power during these faults. A protection technique is necessary to detect these faults in advance to protect the VSC switches and the machine winding from any catastrophic failure.

Frequency Adaptive CDSC-PLL Using Axis Drift Control Under Adverse Grid Condition

This paper presents a new technique to adapt the cascaded delayed signal cancellation phase-locked loop (CDSC-PLL) using a proposed axis drift control (ADC). When grid frequency changes, the estimated grid angle by PLL drifts with a residual error proportional to the frequency change value thus, the accuracy and performance of the conventional CDSC-PLL is deteriorated which can lead to malfunction of the connected applications. Accordingly, CDSC-PLL type has to be adaptable to frequency changes with high immunity to grid disturbances. Designing frequency adapted CDSC-PLL is complex and needs a dedicated design due to the high nonlinearity introduced by adaptive loops. The ADC is proposed as an online adaptive technique that contains a self-tuned DSC operator to mitigate the grid disturbances and a PI controller to perform the adaptation task. The proposed technique is mathematically analyzed and systematic tuning methods are presented. A new analysis for CDSC under off-nominal sample parameter is presented and verified. The robustness of proposed adaptive controller is investigated under parameters uncertainty and various grid disturbances. The proposed technique is numerically and experimentally verified.

Application of SVC on stabilizing torsional oscillations and improving transient stability

This paper investigates the use of static var compensator (SVC) to stabilize multi-mode torsional oscillations of sub-synchronous resonance (SSR) of a large turbine generator set and to improve the system transient stability. In this context, the study is performed on a detailed nonlinear model for system-1 of the second IEEE benchmark for computer simulation of sub-synchronous resonance using EMTDC/PSCAD. The voltage at the machine terminals along with the generator shaft speed are used to control the number of SVC capacitors which are switched on or off and to generate a proper firing angle for the SVC thyristors to control the reactive power exchange between the AC system and the SVC. Results show that the proposed controller is very effective in damping all SSR modes of the system under study. The proposed controller is efficient, simple, cost effective and easy to implement.

A modified space vector modulation algorithm for a matrix converter with lower total harmonic distortion

This paper proposes a modified symmetric sequence algorithm for indirect space vector modulation to control the voltage and frequency of an R-L Load by using a matrix converter. The modified symmetric sequence algorithm provide lower total harmonic distortion (THD) compared to conventional symmetric sequence. Matrix converter is used rather than AC-DC-AC converter as it eliminates the bulky capacitors, and the displacement factor at its input can be controlled and unity input displacement factor can be achieved. Possibility of bi-directional power flow. Finally, simulation and experimental setup results for different operating points are discussed and the results are consistent with the expected ones.

Application of matrix converter connected to wind energy system

This paper introduces an application of wind energy conversion system (WECs) with matrix converter. Due to the enormous advantage of WECs make it suitable source of energy. When the wind speed changes the generated voltage rms value and frequency will be changes and this will effect on the performance of the load so matrix converter is used to control the voltage and frequency of the load. A self-excited induction generator is utilized as it has many advantages in terms of ease of maintenance, self-protection against short circuits. Matrix converter is used rather than AC-DC-AC converter as it eliminates the bulky capacitors, displacement factor at its input can be controlled.MC is used rather than cycloconverter as it can give a wide range of control of frequency, where output frequency may be greater or equal or less than input frequency. Finally, simulation and experimental set up results for different operating points are displayed which are consistent with the expected results.

Application of UPFC on stabilizing torsional oscillations and improving transient stability

This paper investigates the application of Unified Power Flow Controller (UPFC) to stabilize multi-mode torsional oscillations of sub-synchronous resonance (SSR), and to improve the transient stability during a three phase short circuit fault that may result in oscillatory torques on the generator rotor shaft causing serious damages to the system and may call for the disconnection of a wind farm to avoid any possible damages. Simulation is carried out using MATLAB/Simulink software. Results show that the proposed UPFC controller is very effective in damping all SSR modes of the system under study and in minimizing the potential for the wind farm disconnection during the studied faults. The proposed controller is simple and easy to be implemented.

Improving fault ride through capability of DFIG during RSC flashover fault

Wind power generation is growing rapidly. However, maintaining the wind turbine connection to grid is a real challenge. Recent grid codes require wind turbines to maintain connected to the grid even during fault conditions which increases concerns about its sensitivity to external faults. So, researchers have given attention to investigating the impact of various external faults, and grid disturbances such as voltage sag and short circuit faults, on the fault ride through (FRT) capability of the doubly fed induction generator (DFIG). However, no attention has been given to the impact of internal faults on the dynamic performance of the machine when the fault occurs within the voltage source converters (VSCs) that interface the DFIG with the grid. This paper investigates the impact of the rotor side converter (RSC) IGBT flashover fault on the common coupling (PCC) reactive power and the FRT capability of the DFIG. A proper STATCOM controller to mitigate the effects of the flashover fault on the FRT is proposed. The DFIG compliance with numerous and recently released FRT grid codes under the studied fault, with and without the STATCOM are examined and compared. Furthermore, the capability of a proposed controller to bring the voltage profile at the point of PCC to the nominal steady-state level; maintain the unity power factor operation; and, maintain the connection of the wind turbine to the grid are examined.

Adaptive cascaded delayed signal cancelation PLL based fuzzy controller under grid disturbances

Phase Locked Loop plays a crucial role in synchronizing medium voltage converters. PLL has to precisely and continuously track the grid voltage vector angle and feed it to the converter control loop. Grid disturbances such as voltage dips, harmonics, DC-offset and frequency changes have undesired effects on the estimated angle and as a consequence, the rectifier behavior will be deteriorated. A robust PLL design is essential to provide high immunity to grid disturbances and enable for converter ridging-through during severe disturbances. Using pre-filters to mitigate the grid disturbances slow down the overall system dynamic performance. This paper presents a novel method to ride-through wide range of disturbances by combining an Adaptive Cascaded Delayed Signal Cancellation (CDSC) operator as a pre-filter with a Fuzzy Controller. The obtained results show that the proposed scheme has a great potential for synchronizing high power converters under highly distorted grids.

Wind Energy System with Matrix Converter

Keeping in mind the end goal to address energy issues, considering financial and natural variables, a Wind Energy Conversion System (WECS) is bit-by-bit gaining interest as the suitable source of renewable energy. In this chapter, a direct AC-AC Matrix Converter (MC) is utilized to interface an isolated static load fed from the WECS. Due to the advantage of lower cost, maintenance simplicity and short circuit self-protection, the self-excited induction generator is used to generate electric energy. The MC is used instead of the conventional rectifier-inverter converter because it does not contain the bulky size capacitor, the ability of controlling the input displacement factor and the unity factor can be achieved. Moreover, the MC can be provided in a simple construction, and gives a wide range of output frequency. In comparison with cycloconverter, the MC can give an output frequency that may be equal, less or greater than input frequency. This chapter introduces a modified algorithm for space vector modulation that reduces the total harmonic distortion of the output voltage so the size and cost of the required filter can be reduced. Moreover, a modified open loop control of matrix converter with indirect space vector modulation is introduced to provide constant frequency and output voltage even if the wind speed changed.