Real-time Digital Simulator Platform Research Articles

A Fault Detection and Classification Scheme for Unified Power Flow Controller Compensated Transmission Lines Connecting Wind Farms

In recent years, there is an increasing trend of integrating large capacity offshore wind farms into power grids through UPFC compensated TLs for accommodating large flow of power. The nonlinear fluctuations of output power due to unpredictable variation of wind speed and the different operating modes of the UPFC greatly affect the performance of the conventional distance relaying-based TL protection scheme. This article investigates the impact of such TLs on distance relay performance and proposes a two criteria-based new fault detection and classification scheme. The method utilizes the sign of the change in the magnitude of positive-sequence current at both ends of the line for fault detection and the transient monitor index derived from the locally measured three-phase current for fault classification. The performance of the proposed scheme is evaluated on different fault and nonfault transients generated on two standard test systems through EMTDC/PSCAD during different operating modes of UPFC and at different wind speed. The performance of the proposed scheme is further validated through dSPACE DS 1103-based real-time digital simulation platform. Finally, the comparative assessment results with some important existing methods justify the effectiveness of the proposed method.

An Improvized Coordinated Voltage Control Scheme for Better Utilization of Regulating Devices During Various Operating Conditions of a Distribution System

Currently, in the literature, the slow responding device like on-load tap changer transformer (OLTC) is better operated by introducing the time delay in the operation of fast-acting converters. Although the literature also indicates an improvement in the transient condition, it keeps the converters idle during the waiting period. Henceforth, there is a lot of scope for improving the reactive power reserve. In this article, we propose a coordinated voltage control (CVC) scheme that employs a unique approach where the converters are allowed to absorb reactive power (of a specific voltage range from the grid) during the waiting period. A modified IEEE 33-bus distribution system is modeled in the real-time digital simulator platform and the simulation results are compared with the existing and without CVC schemes. The simulation results justify the effectiveness of the proposed CVC scheme in terms of improving the reactive power reserve and voltage profile up to 100%/164% and 0.0093 pu/0.014 pu against existing/without CVC scheme, respectively. Furthermore, the postfault voltage recovery time in the case of proposed CVC is decreased by 20 ms/28 ms with respect to the existing/without CVC schemes. These results imply that the proposed CVC scheme performs better in all the operating conditions of the grid.

Assessing the Performance of ROCOF Relay for Anti-Islanding Protection of Distributed Generation Under Subcritical Region of Power Imbalance

In practice, the load-curve and distributed generation (DG) penetration level determines the power imbalance level that a network can experience if islanding occurs. Therefore, with the prior knowledge of load-curve and DG penetration level, the setpoint of rate-of-change-of-frequency (ROCOF) relays can be adjusted so as to make them suitable for a real network. This paper first investigates the subcritical power imbalance region of ROCOF relays through analytical formulation followed by extensive simulation study in order to establish the maximum boundary limit of ROCOF's nondetection zone (NDZ) under all possible deficit/excess of active and/or reactive power imbalance scenarios. Second, ROCOF's reliability (assessed by detection rate and false alarm rate) is expressed analytically and then, validated numerically by simulating a test network of Australia in MATLAB and OPAL-RT real-time digital simulation platform. Finally, ROCOF's performance is assessed through receiver operating characteristics curves and a detailed reliability study under variable setpoints and detection time of the relays; the assessment considers the number of islanding events associated with the time-wise percentage of power imbalance level computed from the net load demand and variable DG penetration in a real network. All these test results demonstrate a clear operational guideline for ROCOF relay.

Fast adaptive autoreclosing technique for series compensated transmission lines

Auto-reclosing renders fast restoration of the line for arcing faults which constitutes almost 80% of transmission line faults and thus improves system stability. Existing methods, using harmonics of voltage and current, have drawbacks in series-compensation environments because of associated dynamics and control mechanisms. This research work proposes a technique for adaptive autoreclosing in case of line-to-ground faults for series compensated transmission line. A technique is devised that utilises the cumulative sum of energy (CSE) calculated using the fast sparse S-transform coefficients to derive an index (PI) which discriminates between permanent and transient faults. Another extinction index (EI) is computed using CSE during the secondary arc to identify the arc extinction. This parameter is employed to alter the dead time set for the recloser and thus reclosing during fault process is avoided. The performance validation on the real-time digital simulator platform for both single- and double-circuit line with shunt compensation and neutral reactor, enhances the applicability of the proposed protection scheme for adaptive autoreclosing.

Bidirectional boost converter for high‐power transmission between energy storage battery and DC microgrid

When the energy storage battery (ESB) is introduced into the DC microgrid, the DC microgrid can perform demand side management well. To achieve flexible charge and discharge controls of the ESB, the grid-connected device of the ESB needs to have a bidirectional power transmission control function with constant power. Based on this, this Letter first designs circuit topology of bidirectional boost converter for high-power transmission between the ESB and the DC microgrid. Secondly, the control system based on the staggered timing trigger mechanism is developed, and the working process of the converter in the forward and reverse transmission of power is analysed. Finally, the bidirectional boost converter and its control system are verified by real-time digital simulator platform. Simulation results show that the proposed converter and its control system can realise stable high-power bidirectional transmission between the ESB and the DC microgrid, and achieve accurate tracking of the power reference value.

Detection and switching control scheme of unintentional islanding for ‘hand‐in‐hand’ DC distribution network

With the large-scale access to distributed generation and energy storage (ES), the rapid growth of DC loads, and the development of power electronics technology, the DC distribution network is becoming a new type of high-reliability power supply. Detection and switching control of islanding is important to ensure the stability and robustness of the DC distribution network. In this study, first, for a ‘hand-in-hand’ DC distribution network, an unintentional islanding detection method, which is a combination of the main criterion based on switch status and an auxiliary criterion based on no-current and difference-voltage criteria, is proposed. Second, an unintentional islanding control strategy based on the coordination of the switching strategy of ES controller and DC solid-state transformer is proposed. Finally, the proposed detection and switching control scheme is validated through simulations using the real-time digital simulator platform. Simulation results indicate that the proposed scheme for the DC distribution network can accurately identify an island, and effectively switch control mode to achieve stable islanding control.

Rapid Prototyping of a Hybrid PV–Wind Generation System Implemented in a Real-Time Digital Simulation Platform and Arduino

The growing penetration of generation systems based on renewable energy in electric power systems is undeniable. These generation systems have many benefits, but also many challenges from the technical point of view. One of the biggest problems in the case of solar photovoltaic (PV) and wind energy is the intermittency of the raw material, thus hybrid generation systems that contain both sources are being used to complement electric power generation. To analyze the problems of this type of hybrid generation systems, it is necessary to develop models and test systems that allows to study their dynamic behavior. Reported in this paper is the implementation of a full hybrid PV–wind generation system model in a real-time digital simulation platform, and the development of the electronic converter controls. These controllers were implemented in digital devices (Arduino Due) and connected to the simulation platform to test their performance in real-time. In addition, the procedure followed for the development and implementation of the controllers is presented. The proposed test system can be used in renewable energy integration studies and the development of new control strategies.

Modelling and simulation of AC–DC hybrid distribution network based on flexible DC interconnection

AC and DC hybrid distribution network detailed modelling and multi-operation conditions of the simulation analysis will effectively support the distribution network project reliable and stable operation. However, at present, large-scale system-level simulation of AC–DC hybrid distribution network based on flexible DC is the lack of timeliness and practicability. Based on the real-time digital simulation platform RT-LAB, ACDC distribution network model is established, which includes ±20 kV flexible DC interconnection system, distributed photovoltaic, wind power, energy storage system, electric vehicle and the corresponding converter control detailed modelling. In view of the limitation of the balance of energy storage system, the flexible DC interconnection is applied to active distribution network, which can provide power supply when the power gap occurs. The conditions of consumptive mode by the energy storage system, power supply through flexible DC interconnection from external power grid were simulated and analysed. The model verifies the validity of the system application in distribution network. This study provides preliminary design reference for active distribution network construction.

Power system stabiliser PSS4B‐W parameters optimisation and RTDS test verification

This study introduces the mathematical model of a new type of power system stabiliser PSS4B-W. The concept of crossbreed in genetic algorithm is introduced to particle swarm optimisation algorithm and applied to PSS4B-W parameter optimisation. With a PCS-9410 excitation regulator, the semi-physical simulation system is constituted on a real time digital simulator (RTDS) platform. By measuring the excitation system phase frequency characteristic without compensation, the PSS4B-W parameter optimisation is converted to a set of parameters optimisation process with inequality constraint. In the RTDS platform, the time-domain dynamic response of without PSS, adding PSS2B and PSS4B-W, is compared and analysed. Simulation results show that the optimised PSS4B-W can provide effective damping in different frequency bands, and have good inverse-regulation suppression effect.

Modeling and Simulation of Single-stage Photovoltaic Power Supply in Double dq Coordinate System

In order to study the fault characteristics of a distributed power supply, a photovoltaic power supply model that satisfies grid-connected standards needs to be built first. In this paper, for the single-stage photovoltaic power supply, the mathematical model of the grid-connected inverter in the positive and negative-sequence synchronous rotating coordinate system is firstly set up from its topological structure, and then the expression of the output power of the inverter is deduced. In order to suppress the current distortion caused by voltage asymmetry at the grid point, a control strategy in the dual dq coordinate system is presented by controlling the positive and negative sequence components simultaneously by introducing the control factor K. Finally, simulation analysis was performed on the RTDS real-time digital simulation platform under normal operation and fault conditions. The results prove that the bill of lading-type photovoltaic power supply model meets the distributed photovoltaic power grid-connected standards and can be applied to the analysis and application of engineering projects. Introduction With the rapid development of new energy

Experimental assessment of maximum power extraction from solar panel with different converter topologies

The solar power plants are playing a significant role in energy market due to its eco-friendly nature, low operational, and maintenance cost. The efficiency of these plants depends mainly on load impedance, topology of converters, and maximum power point tracking algorithms. In this work, effect of operating point (load line selection) on the performance of maximum power point tracking for different DC-DC converter topologies has been studied and experimentally validated. Further, the operating constraints of buck, boost, and buck-boost modes of converter operation in terms of load impedance are presented. The performance of different maximum power point tracking algorithms under load and solar irradiance change has been investigated for all converter topologies discussed. The modified model of photovoltaic module has been presented for simulation study under different solar irradiance and load variations that can be easily implemented on Real Time Digital Simulator platform unlike conventional models.

Supervising zone‐3 operation of the distance relay using synchronised phasor measurements

The study presents a new protection scheme to enhance the zone-3 operation of the distance relay. The proposed scheme develops an index based on the rate of change of active power and angle derived from synchronised phasor measurement units (PMUs). It is found that it clearly distinguishes faults from several stressed conditions those are likely to occur, and takes necessary action. The proposed scheme is developed and validated for a modified Western System Coordinating Council 9-bus, 3-machine system and New England 39-bus system with different fault scenarios on a MATLAB/Simulink platform. Further to test the robustness, the proposed method is tested on a real-time digital simulator platform using phasors received from gigabit transceiver network PMUs. Extensive performance testing for faulted as well as stressed conditions such as stable power swing, load encroachment and voltage stressed conditions indicate that the proposed scheme is highly reliable in enhancing the zone-3 operation of distance relay.

Variational Mode Decomposition and Decision Tree Based Detection and Classification of Power Quality Disturbances in Grid-Connected Distributed Generation System

This paper presents a variational mode decomposition (VMD) and decision tree based detection and classification method of single and mixed power quality (PQ) disturbances in grid-connected distributed generation system. Applicability of VMD technique is investigated for discrimination of stationary PQ disturbances (such as harmonics, interharmonics, and flicker), non-stationary events (e.g., transients) and noise. Studies indicate usefulness of VMD for accurate estimation of phasor quantities such as amplitude, phase angle, and frequency and other describing features. Features namely, mode central frequencies, relative mode energy ratios, zero crossings, and instantaneous amplitude (IA) are extracted for classification of single and mixed PQ disturbances using a decision tree algorithm. A set of synthetic test signals, disturbance signals obtained from real events as well as signals generated from real time digital simulator platform are used to test effectiveness of proposed method, under various system operating scenarios and noise levels. Proposed method is found to be capable of accurate detection, estimation, localization, and classification of all kinds of PQ disturbances in both noisy and noise-free cases.

Transient Stability Enhancement Using a Wide-Area Controlled SVC: An HIL Validation Approach

This paper presents a control scheme of a wide-area controlled static VAr compensator (WAC-SVC) and its real-time implementation in a hardware-in-the-loop (HIL) simulation scheme with three control objectives: (1) to increase the critical clearing time, (2) to damp the power oscillations, and (3) to minimize the maximum line current. The proposed control scheme considers a correction strategy to compensate the delays up to 200 ms. In addition to this, a generator tripping scheme based on synchrophasor measurements to determine the proximity to the loss of synchronism is proposed. A delay compensation algorithm based on polynomial approximations is also developed. The proposed WAC-SVC is experimentally validated using a Real-Time Digital Simulator platform (RTDS), industrial communication protocols, a commercial device for PMU-based control implementations, and digital relays with PMU capability. The real-time simulation results confirm its effectiveness and feasibility in real industrial applications. Furthermore, practical guidelines to implement this kind of control schemes are provided.

A Novel Decentralized Coordinated Voltage Control Scheme for Distribution System With DC Microgrid

This paper proposes a novel decentralized coordinated voltage control (CVC) scheme for a distribution system consisting of dc microgrid (DCMG), doubly fed induction generator-based wind system, on-load tap changer (OLTC), and DSTATCOM. The proposed scheme considers the response time of various voltage regulating devices and assigns a master/slave role based on the operating conditions of the grid and availability of the device. This paper offers a distinctive solution to optimally utilize the voltage regulating devices which do not take part in the contingency situation such as OLTC and DCMG converter in order to achieve the following objectives: 1) A better voltage regulation and increased reactive power reserve during normal operating conditions of the grid. 2) To improve the transient performance of the system in terms of reduction in postfault voltage recovery time. Two modified IEEE 33 bus systems are implemented in a real-time digital simulator platform to test the effectiveness of the proposed CVC scheme. Furthermore, power hardware in loop (PHIL) experimentation is conducted with a reduced scale DCMG hardware setup to test the stability, feasibility, and practicability of the proposed scheme. The simulation and PHIL results demonstrate that the proposed CVC scheme provides a better solution compared to existing work by fulfilling the set objectives.

The Coordinated Control of Wind-Diesel Hybrid Micro-Grid Based on Sliding Mode Method and Load Estimation

In order to reduce the frequency deviation resulting from renewable energy fluctuation and load variance, the coordination control strategy for isolated wind-diesel hybrid micro-grid is proposed by taking advantage of smart neural network observer and sliding mode method. For diesel generator system side, the sliding mode load frequency control including load variance is designed to regulate the output power. For the wind turbine generator system side, the sliding mode pitch angle control considering load variance is constructed to smooth the wind turbine generator output power fluctuation. Furthermore, the different coordinated strategies are proposed to realize the plug and play for the hybrid micro-grid, it is easy to see that the control accuracy can be improved by the designed neural network adaptive observer and considering the load variation. The effectiveness of the proposed control strategy is validated through real time digital simulator platform under different operation condition.

Improved Control Strategy for Bidirectional Single Phase AC-DC Converter in Hybrid AC/DC Microgrid

This paper presents the improved control strategy with optimal switching scheme to improve the bidirectional converter's power flow control capability and to allow for different modes of operation in hybrid AC/DC microgrid. Also, this improved control strategy eliminates the need of PI controller for independent reactive power control. With the improvements in digital controllers, it is possible to implement complex control circuitry easily. The performance of bidirectional converter with improved control strategy is verified first in simulation environment and then on lab scale experimental set-up with the control circuit is implemented using hardware in loop in the real-time digital simulation platform. The simulation and experimental results for all the cases show that the controller is highly capable for power transfer between AC and DC grid with very fast response and also control reactive power without additional PI controller. Also, it maintains the current total harmonic distortion (THD) within standard limits.

An enhanced fault detection and location estimation method for TCSC compensated line connecting wind farm

The paper presents a new approach to enhance the fault detection, and location determination based on travelling waves using Fast Discrete S-transform (FDST) for TCSC compensated lines connecting to wind farm. The FDST is applied to the modal components of measured currents at each terminal to detect the arrival time of the first travelling wave (transient) produced by the fault. The proposed method includes detecting the terminal with fastest arrival time of wave to identify the faulted section and estimate the fault location by using proper distance index. The simulation results have demonstrated good performance of the proposed scheme under different fault locations, fault resistances, fault inception angles, fault types, faulted sections, variations in TCSC parameters and changing wind speeds. The performance validation on the real-time digital simulator (RTDS) platform enhances the applicability of the proposed protection scheme for the TCSC based compensated line integrated with wind farm. The performance comparison with the conventional travelling wave fault location algorithms using Continuous Wavelet Transform (CWT) shows potential ability of the proposed method.

A New Wide-Area Backup Protection Scheme for Series-Compensated Transmission System

This paper presents a new wide-area backup protection scheme based on the phase angle of positive-sequence integrated impedance (PAPSII). The proposed scheme uses phasor measurement units (PMUs) that comply with standard C37.118.1-2011 for retrieving the phasor information. The PMUs provide the positive-sequence phasor information of the voltage and current signals at each and every bus of a system to a phasor data concentrator (PDC). The positive-sequence integrated impedance of each line of the system is extracted, and the PAPSII of each line is continuously monitored at the PDC. The values of the PAPSII help in identifying the faulted line of the power transmission system. The proposed scheme is extensively tested for different types of fault scenarios on a three-machine nine-bus power transmission network on a real-time digital simulator platform. Critical issues such as voltage inversion, current inversion, load encroachment, and the power swing are addressed in the proposed scheme. The test results indicate that the proposed scheme can overcome the limitations of existing backup protection schemes and can provide a reliable protection measure.

Multivalued Coefficient Prestorage and Block Parallel Method for Real-Time Simulation of Microgrid on FRTDS

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.