Hossein Ali Mohammadpour

Modeling and Control of Gate-Controlled Series Capacitor Interfaced With a DFIG-Based Wind Farm

This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator (DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations.

High-Impedance Fault Detection in the Distribution Network Using the Time-Frequency-Based Algorithm

A new high-impedance fault (HIF) detection method using time-frequency analysis for feature extraction is proposed. A pattern classifier is trained whose feature set consists of current waveform energy and normalized joint time-frequency moments. The proposed method shows high efficacy in all of the detection criteria defined in this paper. The method is verified using real-world data, acquired from HIF tests on three different materials (concrete, grass, and tree branch) and under two different conditions (wet and dry). Several nonfault events, which often confuse HIF detection systems, were simulated, such as capacitor switching, transformer inrush current, nonlinear loads, and power-electronics sources. A new set of criteria for fault detection is proposed. Using these criteria, the proposed method is evaluated and its performance is compared with the existing methods. These criteria are accuracy, dependability, security, safety, sensibility, cost, objectivity, completeness, and speed. The proposed method is compared with the existing methods, and it is shown to be more reliable and efficient than its existing counterparts. The effect of choice of the pattern classifier on method efficacy is also investigated.

SSR Damping Controller Design and Optimal Placement in Rotor-Side and Grid-Side Converters of Series-Compensated DFIG-Based Wind Farm

This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a 100 MW DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation.

Sub-synchronous resonance analysis in DFIG-based wind farms: Definitions and problem identification — Part I

This paper is part I of a two-paper series (Two-P-S) to review, analyze, and mitigate sub-synchronous resonance (SSR) in series compensated doubly-fed induction generator (DFIG) based wind farms. The IEEE first benchmark model modified to include a 100 MW DFIG-based wind farm is employed as a case study. In this work, MATLAB/SIMULINK is used for eigenvalue analysis and PSCAD/EMTDC for time-domain simulations, respectively. Part I of the Two-P-S focuses mainly on the identification and definition of the main types of the SSR that occur in DFIG wind farms, namely: (1) induction generator effect (SSIGE), (2) torsional interactions (SSTI), and (3) control interactions (SSCI). Regarding the SSIGE, first a simple definition of the SSIGE is given; then, using eigenvalue analysis and time-domain simulations, it is shown that the DFIG wind farm can be highly unstable due to the SSIGE; finally, the impact of wind speed and compensation level variations on the SSIGE is explained. Regarding the SSTI, first a descriptive definition is given; then, the real world possibility of the SSTI in DFIG wind farm is studied; finally, the impact of the stiffness coefficient and compensation level variations on this type of SSR is investigated. Regarding the SSCI, since it may be confused with the SSIGE, a simple definition of the SSCI and its mechanism in DFIG wind farm are presented. In part II of the Two-P-S, three methods to mitigate the SSR in DFIG wind farms will be presented.

SSR analysis of a DFIG-based wind farm interfaced with a gate-controlled series capacitor

This paper investigates the sub-synchronous resonance (SSR) phenomenon in a series compensated doubly-fed induction generator (DFIG) based wind farms. A detailed linear state space model of a fixed-series compensated DFIG wind farm is presented for different operating point conditions. The model of the system includes a wind turbine aerodynamics, a 6th order induction generator, a 3rd order two-mass shaft system, a 4th order series compensated transmission line, an 8th order rotor and generator side converter controllers, and 1st order DC link model. The 22nd order system is modeled in Matlab/Simulink, and modal analysis is performed on the modeled DFIG wind farm, and eigenvalues of the system are calculated. The eigenvalue analysis and time-domain simulation results show that SSR can potentially occur in the fixed-series compensated DFIG-based wind farm even at realistic levels of series compensation. The fixed-series capacitor is replaced with a gate-controlled series capacitor (GCSC), which is a series flexible ac transmission system (FACTS) device composed of a pair of gate-commutated switches in parallel with a capacitor that enables one to control impedance and power flow of transmission lines, for series compensation and SSR damping. The root-locus analysis is employed to design a SSR damping controller (SSRDC) for the GCSC. It is shown than a well-designed SSRDC for the GCSC can alleviate the SSR in DFIG-based wind farms. The IEEE first benchmark model adapted with a DFIG-based wind farm is employed as a case study.

High impedance fault detection in distribution network using time-frequency based algorithm

A new high impedance fault (HIF) detection method using time-frequency analysis for feature extraction is proposed. A pattern classifier is trained whose feature set consists of current waveform energy and normalized joint time-frequency moments. The proposed method shows high efficacy in all the detection criteria defined in this paper. The method is verified using the real-world data, acquired from HIF tests on three different materials (concrete, grass, and tree branch) and under two different conditions (wet, and dry). Several non-fault events, which often confuse HIF detection systems, were simulated, such as capacitor switching, transformer inrush current, non-linear loads, and power electronics sources. A new set of criteria for fault detection is proposed. Using these criteria the proposed method is evaluated and its performance is compared with the existing methods. These criteria are accuracy, dependability, security, safety, sensibility, cost, objectivity, completeness, and speed. The proposed method is compared with the existing methods, and it is shown to be more reliable, and efficient than its existing counterparts. The effect of choice of pattern classifier on method efficacy is also investigated.

Time-Frequency-Based Instantaneous Power Components for Transient Disturbances According to IEEE Standard 1459

IEEE Standard 1459 defines the power components based on the fast Fourier series. However, Fourier series assumes the signal is periodic in nature, and provides erroneous assessment of the power components in the presence of transient signals. Therefore, a new method is proposed for the evaluation of the IEEE Standard 1459 power components based on the time-frequency distribution (TFD) and the cross time-frequency distribution (XTFD) of transient signals. The TFD and XTFD preserve simultaneous time and variable frequency information of transient signals, and estimate the instantaneous power components according to IEEE Standard 1459. Results of computer simulated and real-world power quality disturbance case studies justify the effectiveness of the proposed method for the assessment of instantaneous power components under transient conditions.

Active fault location in distribution network using time-frequency reflectometry

In this work a new single-ended method for fault location in distribution networks is proposed. The method is an active traveling wave fault location, which transmits a Gaussian chirp through the line and applies the cross time-frequency reflectometry in order to find the exact location of the fault with 150 meter tolerance. The method functions in the offline post fault condition, where the system is disconnected. The bandwidth of the proposed method is at least one order of magnitude smaller than its passive counterparts. Furthermore, not only is the method capable of locating the exact distance of the fault away from the relay location, but it also finds the exact line in radial configuration of distribution network. Another characteristics of this method is its immunity to series capacitive compensated transmission line, voltage level, fault phase, fault inception angle, and fault resistance. Another important property of the method is its ability in locating high impedance faults. The method capabilities are verified using PSCAD/EMTDC simulation based on phase-dependent and frequency-dependent models for distribution network lines. An error parameter is defined to compare the method efficiency for different fault types, fault locations, and system configurations.

Sub-synchronous resonance mitigation in wind farms using gate-controlled series capacitor

The increasing deployment of wind power generation is leading to the integration of large wind farms into the power distribution grid. Given the remote geographic location of wind farms, series capacitive compensation is commonly used to ensure stable power transmission over long distances. However, the sub-synchronous resonance (SSR) phenomenon presents potential risks in a series compensated wind farm. Although the SSR problem in traditional power systems is well-known and has been extensively studied in the literature, the SSR problem in series-compensated wind farms requires more study and analysis. This paper investigates the application of the gate-controlled series capacitor (GCSC), a new series FACTS device consisting of a fixed capacitor in parallel with a pair of anti-parallel GTOs, for series compensation in fixed-speed wind turbine generator (FSWTG) systems. The GCSC enables fast control of series impedance of the transmission line, which can be used for SSR damping. The power system studied in this paper is the IEEE First Benchmark Model. Extensive simulations are carried out using PSCAD/EMTDC to validate the result. Simulation results show that the GCSC can effectively damp the SSR in wind farms. Therefore, the GCSC is an effective solution to provide series compensation and SSR damping for the FSWTG.

SSR Damping in Fixed-Speed Wind Farms Using Series FACTS Controllers

Subsynchronous resonance (SSR) damping in fixed-speed wind turbine generator systems (FSWTGS) by using two series flexible ac transmission system (FACTS) devices, the thyristor-controlled series capacitor (TCSC), and gate-controlled series capacitor (GCSC) are studied in this paper. The former is a commercially available series FACTS device, and the latter is the second generation of series FACTS devices using gate turnoff (GTO) or other gate-commuted switches. The GCSC is characterized by a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches enabling rapid control of series impedance of a transmission line. It is shown that the SSR damping with a GCSC is limited to changing the resonance frequency, in comparison with a fixed capacitor, which may not be adequate to damp out the SSR. Therefore, a supplementary SSR damping controller (SSRDC) is designed for the GCSC. Moreover, it is proven that the GCSC equipped with a well-designed SSRDC can effectively damp the SSR in FSWTGS. In order to verify the effectiveness of the GCSC in SSR damping, its performance is compared with the TCSC, which is an existing series FACTS device. In addition, time-frequency analysis (TFA) is employed in order to evaluate and compare the SSR time-varying frequency characteristics of the GCSC and TCSC. The IEEE first benchmark model on SSR is adapted with an integrated FSWTGS to perform studies, and extensive simulations are carried out using PSCAD/EMTDC to validate the result.