A conventional dynamic voltage restorer with fault current limiting capability

A control strategy has been proposed based on five terminals voltage source converter (VSC)–HVDC typical topological structure of large grid‐connected offshore wind power system, which means that VSCs on the wind farm side are controlled with AC voltage control method and VSCs on the grid side are controlled with DC voltage droop control method. A simulation model has been built on power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) platform, and with it, several simulations have been conducted such as start‐stop of wind farm, power fluctuation and suspension of converter station. In the end, the control strategy is proved out to have coordination control capability and flexibility.

The microgrid containing a large amount of high frequency power switches and nonlinear components has put forward high requirements for power system real-time simulation technology. Multivalued coefficient prestorage can reduce the calculation steps in real-time simulation. In order to reduce the storage pressure of the multivalued coefficients, the whole network is divided into multiple subnetworks that can be simulated in parallel, and only the parameters for computing input variables and internal variables are prestored. The multiport hybrid equivalent is performed to reduce the number of simultaneous network equations. The input variables are tied to state variables of the circuit so that the iterative calculation is limited to the local network. The devised methodology is validated through simulation of a low-voltage microgrid on a field programmable gate array (FPGA)-based real-time digital simulation (FRTDS) platform at a 5 μs time step. Comparison with a power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) model shows that the proposed method is effective.

Enhancement of DFIG-Wind Turbine’s LVRT capability using novel DVR based Odd-nary Cascaded Asymmetric Multi-Level Inverter

The continuity of supply and quality of power supplied to the customers must be uninterrupted from the reliability point of view. The Dynamic Voltage Restorer (DVR) is a custom power device which has an advantage of fast dynamic response and can generate real or reactive power independently. This paper presents the improved topology for DVR by the integration of Proton Exchange Membrane Fuel Cell (PEMFC) with boost converter as a DC input to the DVR. Thus the proposed DVR ensures a constant DCvoltage across the DC link during the process of voltage compensation with active power injection to the grid. The performance of the proposed work is endorsed by comparing the results with conventional DVR and the simulation results are also validated to prove the effectiveness of the proposed work.

In this paper, a comparison of simulation between Power Systems Computer Aided Design (PSCAD) and Real Time Digital Power System Simulator (RTDS) Hardware In-the-Loop (HIL) is presented under the same conditions to express their corresponding results for other researchers reference the differences and choice the suitable testing system. Both RTDS and PSCAD are applied widely and trusted in power electronics researching field. However, RTDS provides a real time simulation process to get close to real experimental results. Further, RTDS support HIL and permit Digital Signal Processor (DSP) control inside simulation components. Therefore, the results differences produced by RTDS and PSCAD becomes one important reference for a system or algorithm. In this study, one power compensator simulation system is built in both PSCAD and RSCAD. The set-up process is introduced, and their simulation results are analyzed.

In the following study a single-phase isolated improved trans-ZS AC-AC converter is analyzed, designed and simulated. This converter is from Z-source family and contains their specific advantages such as inclusive variety of buck-boost output voltage in in-phase or out-of-phase manner. Also, a high frequency transformer (HFT) is utilized in its structure in order to electrical insulation. Therefore, in some applications, for example dynamic voltage restorers (DVRs), there are no need for bulky and lossy grid-coupling transformers. Furthermore, a safe commutation method has been utilized which eliminates the voltage spikes upon power switches. One of the distinct tasks of this paper is to bring all three-winding transformer's conversion ratios into computation as well as extracting all the governing relations of the structure in in-phase and out-of-phase operational states. Finally, the simulation using power systems computer-aided design (PSCAD) software is conducted to confirm the analysis.

Presently, there are mainly two problems that prevent Electric Vehicles (EVs) from becoming popular against the Internal Combustion Engine Vehicles (ICEVs), namely: short range and too long to recharge the battery pack of the EV. Due to this, battery development is a crucial aspect to improve the performance of EVs. This progress requires dependable computer aided designs to model the characteristics of a battery accurately and reliably. This paper uses Power Systems Computer Aided Design (PSCAD) to create an equivalent runtime circuit model to observe the qualities of the Lithium Iron Phosphate battery cell under discharge at different temperatures. The model is a 3-R-C branch runtime equivalent circuit model. In order to find the fixed parameters of the circuit, MATLAB was used to implement basic current voltage characteristics. 3-D tables have been used in PSCAD to implement the State of Charge (SOC) and temperature dependent circuit parameters of the model. Once the simulations for all temperatures were completed, the average marginal error between measured and simulated terminal voltage came to be 2.1%, therefore making PSCAD an accurate simulation tool for modeling equivalent circuits of different batteries.

Background/Objectives: The stability of High-Voltage Direct Current (HVDC) system is improved by optimization of system's control parameters. The simulation model of HVDC network is designed in Power Systems Computer Aided Design (PSCAD) and the Proportional Integral (PI) parameters optimization are achieved by using simplex algorithm. Simulation based evaluation of Integral Time Absolute Error-Objective function (ITAE-OF) is implemented in this paper. Methods/Statistical Analysis: Simulation calculation results are iterated to determine the new values of objective function. The model of three parallel HVDC lines connecting Power system of Central-East China is used as a test network. PI control parameters of San-Chang ±500KV HVDC system line are optimized. Findings: Optimized results have been achieved by evaluating ITAE-OF using transient simulation and converged via Simplex algorithm in PSCAD. The performance of system in steady state behavior as well as in fault condition is improved through optimized control parameters as compared to the initial control parameters, which are presented by plotting graphs. Application/Improvements: The derived equation can be further optimized using the hybrid system.

This paper generalizes the modelling of 132kV transmission line design for the purpose of backflashover simulation using the Electromagnetic Transient Program that is Power System Computer Aided Design (PSCAD) software. Sample of transmission line data was taken from Tenaga National Berhad (TNB) for the purpose of simulation using PSCAD software. Crucial part of the studies include the model of transmission line components such as insulator coordination, tower model, tower footing model and surge arrester. This research will focus on the effect of different position of transmission line surge arrester placement at transmission line to the value of backflashover rate. A model of surge arrester is implemented using PSCAD software and was located across the line insulation, to prevent flashover. The capabilities of arrester in reducing backflashover rate are investigated so that the proper arrester rating can be selected for any system requirement. Results were analyzed and the influence of transmission line surge arrester placement to backflashover rate at transmission line was discussed. Findings from this research can be a significant modelling guideline to the transmission line designers or other researchers to improve the performance of overhead transmission line in term of reducing the backflashover rate.

In line with the latest protection configuration requirements for 35 or 10 kV distribution grids, current differential protection is recommended for distribution lines connected to photovoltaic power sources. However, unlike traditional synchronous generators, photovoltaic power sources provide fault currents with amplitudes typically less than 1.2 to 2 times the rated current, and their phase angles are controlled and capacitive. This often results in the differential current being insufficient to trigger the current differential protection even during internal faults. This paper analyzes the issues with applying traditional current differential protection to photovoltaic power sources connected lines and deduces the threshold for the ratio restraint coefficient. An adaptive protection strategy is proposed, where the restraint coefficient is adjusted based on the amplitude ratios and phase angle differences of the fault currents. This ensures correct operation, particularly in cases of high photovoltaic power sources penetration. The strategy is tested through simulations conducted in Power Systems Computer Aided Design (PSCAD), showing improved sensitivity compared to traditional methods.

Analysis and control of bridge-type fault current limiter integrated with the dynamic voltage restorer

The 3-phase diode bridge rectifier has the least line current distortion among 6-pulse rectifiers; however, its total harmonic distortion (THD) of 31.08% violates power quality standards. This paper reports distortion reduction by lowering magnitudes of harmonics in the line currents using a delta-wye transformer between the 3-phase utility and the diode bridge rectifier. The leakage inductances of the transformer windings provide a filtering effect on the line current harmonics thus providing THD mitigation of utility line currents. The efficacy of the technique is proved by Power System Computer Aided Design (PSCAD) simulations considering the bridge rectifier with and without the delta-wye transformer of vector group Dy1. Experimental results without and with the Dy1 transformer feeding the diode bridge rectifier are presented.

Voltage disturbances which affect the stability of electrical networks are the most important power quality problems. The most known voltage disturbances are voltage sag and swell in distribution systems. Dynamic Voltage Restorer (DVR) is the most effective device to compensate these voltage disturbances among the custom power devices. The basic structure of a conventional DVR consists of an inverter, dc link capacitor, injection transformer and filter. The major component in DVR is inverter that generates controlled voltage to compensate voltage sag/swell and other problems such as flicker, interruption and harmonics. Each inverter implemented in DVR has individual properties such as voltage level, unbalanced compensation capability and/or dc link capacitor requirement. This paper aims a comprehensive review on different inverter topologies according to the number of phases, size, voltage level and structure of DVR. In addition, individual properties of inverters are presented in this study.

A dynamic voltage restorer (DVR) with no energy storage is studied. By using a matrix converter instead of the conventional AC/DC/AC converters, elimination of the DC-link capacitor is possible. The switching algorithm of matrix converter is the space vector modulation. There are different compensation algorithms to control the conventional DVR. These methods have been analyzed in this paper for the proposed matrix-converter-based DVR. A deep analysis through different diagrams would show the advantages or disadvantages of each compensation method. Equations for all methods are derived, and the characteristics of algorithms are compared with each other.

In the present electric power grids, power quality issues are recognized as a crucial concerns and a frequently occurring problem possessing significant costly consequence such as sensitive load tripping and production loss. Consequently, demand for high power quality and voltage stability becomes a pressing issue. Dynamic voltage restorer (DVR), as a custom power device, is one of the most effective solutions for “restoring” the quality of voltage at its load-side terminals when the quality of voltage at its source-side terminals is disturbed. In this paper, a new DVR topology based on double flying capacitor multicell (DFCM) converter for medium-voltage application has been proposed. The advantage of the proposed DVR is that it does not need any line-frequency step-up isolation transformer, which is bulky and costly, to be connected to medium-voltage power grid. The proposed DVR topology obtains the required active power from the energy storage feeding the dc link of the DFCM converter. The pre-sag compensation method, which is explained in detail, is used to restore amplitude and angle of the sensitive load voltage. Moreover, an approach based on d-q synchronous reference frame to determine DVR reference voltages is utilized. The proposed DVR topology is simulated and results to illustrate its performance under various conditions of voltage sag compensation are provided.