Real-time Digital Simulation System Research Articles

Pilot protection method of half-wavelength AC transmission lines based on random matrix theory

The fault characteristics of ultra-high voltage (UHV) half-wavelength (HWL) transmission lines exhibit significant differences from those of conventional transmission lines, which renders the conventional relay protection method unsuitable for ensuring the protection of HWL. To solve this problem, a pilot protection method of HWTL based on random matrix theory was proposed. Voltage and current fault components obtained at the protection installation on both sides of the line were used as the input of the random matrix to form the singular value equivalent matrix, and the eigenvalues of the random matrix at both ends were calculated. The faults inside and outside the area were determined according to the distribution of the eigenvalues in the circular plane area. The protection scheme avoids the data synchronization problem at both ends of the line. Real time digital simulation system (RTDS) simulation revealed that the proposed protection method can protect the full length of the line, is suitable for various fault types and fault conditions, and exhibits excellent resistance to transition resistance.

Implementation of Control Standardization Based on HCM5000G DC Control and Protection Platform

This paper introduces the whole construction of the control standardization simulation system based on the HCM5000G DC control and protection platform, which can meet the requirements of engineering design and various control performance indexes by adopting the standardization design of the self-control and localization platform. In this paper, the construction principle of the standardized control system and the optimization strategy of the control structure are discussed in detail, and the engineering simulation model is realized by using the real-time digital simulation system with the layered and distributed standardized interface design, which provides an important reference for the future large-scale application of the control and protection of DC Engineering.

Research on Modeling Method for Excitation System of One Million-Kilowatt Unit in Nuclear Power Plant based on Real-Time Digital Simulation System

The excitation system is an important link between the generator set and the power grid. It is not only the key system to stabilize the operation of the generator set but also an important element related to the network. The accurate modeling and testing of the excitation system clarify and analyze the characteristics of the system. The traditional simulation software can only simulate the excitation system without the ability to test the control device and protection equipment. However, the real-time digital simulation system (RTDS) can realize real-time closed-loop tests of the hardware, which provides a new means for the excitation system analysis. This paper builds a detailed excitation system model of nuclear power units based on RTDS. The under-excitation limitation model is proposed based on the actual test data. Furthermore, the stability of the stator current limitation is improved by adding restriction conditions. Finally, the excitation system model is validated based on the measured data.

A Decentralized Fault Section Location Method Using Autoencoder and Feature Fusion in Resonant Grounding Distribution Systems

In industrial applications, the existing fault location methods of resonant grounding distribution systems suffer from low accuracy due to excessive dependence on communication, lack of field data, difficulty in artificial feature extraction and threshold setting, etc. To address these problems, this study proposes a decentralized fault section location method, which is implemented by the primary and secondary fusion intelligent switch (PSFIS) with two preloaded algorithms: autoencoder (AE) and backpropagation neural network. The relation between the transient zero-sequence current and the derivative of the transient zero-sequence voltage in each section is analyzed, and its features are extracted adaptively by using AE, without acquiring network parameters or setting thresholds. The current and voltage data are processed locally at PSFISs throughout the whole procedure, making it is insusceptible to communication failure or delay. The feasibility and effectiveness of the approach are investigated in PSCAD/EMTDC and real-time digital simulation system, which is then validated by field data. Compared with other methods, the experiment results indicate that the proposed method performs well in various scenarios with strong robustness to harsh on-site environment and roughness of data.

A novel distance protection scheme using single‐ended transient voltage based on generalized S transform

Concerning the distance protection steady-state over-reach or under-reach caused by the transition resistance, a novel distance protection scheme based on transient information is proposed. First, multiple fault features are extracted using the Generalized Stockwell Transform (GST), and a criterion for identifying low-resistance and high-resistance ground faults is constructed. Then, a GST coefficient matrix is established for the single-ended transient voltage of the line, the attenuation coefficient and delay coefficient are derived by the least-squares method and the beat phenomenon, and the transition resistance is calculated. On this basis, adjust the operation boundary in the +R axis direction of the operation zone according to the transition resistance value. Finally, test results on real-time digital simulation system (RTDS) demonstrate that the protection scheme operates reliably in different fault cases and is highly immune to fault resistance. Compared with the traditional distance protection scheme, this scheme performs better when the transition resistance is large.

Longitudinal Protection Method Based on Voltage Wave Comparison in AC/DC Hybrid System

When a fault occurs on the tie line of ac/dc hybrid system, the change rule of electrical quantity on the inverter side is different from that of infinite ac power source. Sensitivity and reliability of the traditional relay protection methods will be affected. A longitudinal protection method for ac/dc hybrid system based on voltage wave similarity comparison is proposed. The protection compares the similarity of the measuring voltage wave and the calculated reference voltage wave, and determines the fault location roughly. By comparing the judgment results of voltage similarity between both ends of line, a reliable judgment can be made to distinguish between internal and external faults. In order to improve the reliability of voltage wave similarity comparison, dynamic time warping method is used to overcome the influence caused by phase error, and Pearson correlation coefficient method is used to judge the similarity of voltage wave. The simulation results of real time digital simulation system (RTDS) show that the proposed method can identify the fault which occurs on the tie line of ac/dc hybrid system accurately which has high reliability and good applicability.

An optimal phase control method for the suppression of phase sequence exchange impulse current and voltage

Phase sequence exchange (PSE) is an emerging emergency control method for power systems. However, PSE will generate impulse current and voltage. In this research, to suppress the impulse of PSE, a phase control method for zero-current opening and equal-voltage closing is adopted, and verified via both physics and experiments. First, an equivalent circuit is established, and the differential equations are solved to validate that this phase control method is the optimal method for the suppression of the impulse current and voltage in PSE. Then, the action sequence scheme and calculation method of the phase control method are advanced. Finally, based on the real-time digital simulation system (RTDS), a PSE prototype was used to carry out impact experiments. The results verify that the performance of the optimal method is the best compared to those of other control methods, the requirement for the sampling frequency is low, and there is almost no additional cost. In the two experiments, the first peak of the impulse current was found to be reduced by 47.49% and 33.28% on average, respectively, and the first peak of the impulse voltage was found to be reduced by 14.89% and 44.10% on average, respectively.

Performance test of small-current grounding line selection device based on the real-time digital simulation system

Single phase grounding fault is the most common fault type in small-current grounding distribution network, but the small-current grounding line selection device put into operation on site is often difficult to meet the application requirements, affecting the rapid and accurate treatment of grounding fault. Considering that there are many small-current grounding line selection manufacturers and various device forms, it is difficult to intuitively evaluate the line selection performance of different devices and make horizontal comparison, and there is no supporting basis for the selection and application of on-site line selection devices. Therefore, based on the real-time digital simulation system (RTDS), this paper establishes a test platform for small-current grounding line selection device. Based on the constructed test platform, four line selection devices form different manufacturers are tested in parallel, the performance of the devices is compared, and the influencing factors affecting the accuracy of line selection results are analyzed. The conclusions of this paper can provide strong support for the pilot application of small-current line selection devices.

Fault Detection System for 500 kV AC Fault Current Limiter Based on High-Coupled Split Reactor

Aiming at the problem of limiting high short-circuit current in 500 kV AC power grid, we develop an economical-type fault current limiter (FCL) based on high-coupled split reactor (HCSR), namely, HCSR-FCL. This paper addresses designing the early fault detection system of HCSR-FCL. Firstly, it introduces the working principles of HCSR-FCL and gives the system design of HCSR-FCL control system. Subsequently, it discusses the real-time requirement of the HCSR-FCL control system, and apply an early short-circuit fault detection algorithm based on the ratio of the summation of squared three-phase currents (SSC). Then, it gives implementation of the applied algorithm, and also designs the hardware of fault detection unit. Finally, simulation verification on RTDS (real-time digital simulation system) platform is given. Experimental results show that the designed system can detect short-circuit fault rapidly and robustly. When short-circuit occurs, the control system designed can output control signals, which enables the FCL into operation quickly.

Improvement and Dynamic Simulation Test of the Power Electronic Device Applied to Phase Sequence Exchange Technology

Phase sequence exchange (PSE) is a recently developed emergency control technology. PSE uses power electronic devices to switch the three-phase sequence, which reduces the power angle of the generator by 120° and prevents the system from losing stability. In this work, the structure of the PSE device is improved. Based on the original nine solid-state circuit breakers (SSCBs), three mechanical circuit breakers (MCBs) are added. Normally, the current flows through the MCBs, which greatly reduces the conduction loss of the PSE device. Once the generator is identified as being out-of-step, the MCBs quickly open to transfer the current to the SSCBs. When the power angle threshold of the PSE is reached, the SSCBs are switched to complete PSE. In this article, the transient characteristics of the current transfer and PSE processes are analyzed. Based on the real time digital simulation system (RTDS) platform, dynamic simulation tests of the improved PSE prototype are carried out under different conditions. Experiments and calculations demonstrate that the improved PSE device can meet the technical requirements of PSE, and that the conduction power loss is reduced by 96% on average.

5G Communication Based Distributed Fault Recovery Scheme of Active Distribution Network

As more and more distributed power sources are connected to low and medium voltage distribution networks, the traditional single-ended passive distribution networks have evolved into multi- terminal, multi-source active distribution networks. When distributed generations with high permeability are connected to a distribution network, the structure and power flow of this network will change significantly, thus the original fault detection method and reclosing scheme may be challenged, which may cause incorrect action of protection or failure of reclosing. On basis of that, this paper proposes an active distribution network fault recovery scheme based on 5G wireless communication, in which the topology recognition technology and smart terminal units with peer-to-peer communication capability are applied. To prove the method’s feasibility, delay of 5G communication is analysed and tested online. In addition, a model of 10 kV active distribution network is built on Real Time Digital Simulation system. Principle investigation and simulation indicate that the proposed scheme can adapt to the change of network structure and implement the fault self-healing quickly.

Voltage Support under Grid Faults with Inherent Current Limitation for Three-Phase Droop-Controlled Inverters

A novel nonlinear current-limiting controller for three-phase grid-tied droop-controlled inverters that is capable of offering voltage support during balanced and unbalanced grid voltage drops is proposed in this paper. The proposed controller introduces a unified structure under both normal and abnormal grid conditions operating as a droop controller or following the recent fault-ride-through requirement to provide voltage support. In the case of unbalanced faults, the inverter can further inject or absorb the required negative sequence real and reactive power to eliminate the negative sequence voltage at the point of common coupling (PCC) whilst ensuring at all times boundedness for the grid current. To accomplish this task, a novel and easily implementable method for dividing the available current into the two sequences (positive and negative) is proposed, suitably adapting the proposed controller parameters. Furthermore, nonlinear input-to-state stability theory is used to guarantee that the total grid current remains limited below its given maximum value under both normal and abnormal grid conditions. Asymptotic stability for any equilibrium point of the closed-loop system in the bounded operating range is also analytically proven for first time using interconnected-systems stability analysis irrespective of the system parameters. The proposed control concept is verified using an OPAL-RT real-time digital simulation system for a three-phase inverter connected to the grid.

Research on application of FDNE based on RTDS and comparison analysis of fault transient of Shanghai Sijing power grid

As a most widely applied real-time digital simulation system, real time digital simulation (RTDS) is however quite limited on scale of simulation by the number of hardware purchased. Through frequency-dependent network equivalent (FDNE), scale of simulation of RTDS could be largely increased by frequency equivalent on limited hardware. Based on basic principles of FDNE, function limitations and problem are analysed, taking the Shanghai Sijing district power grid as an example; detailed simulation model and FDNE equivalent module are built, transient characteristics under faults before and after FDNE equivalent are analysed. Furthermore, the fault characteristics of high-voltage direct current (HVDC)-Sijing power grid is also studied, which provides a realistic means for real-time digital simulation of AC–HVDC hybrid power grid with limited hardware of RTDS.

Harmonic Analyzing of the Double PWM Converter in DFIG Based on Mathematical Model

Harmonic pollution of double fed induction generators (DFIGs) has become a vital concern for its undesirable effects on power quality issues of wind generation systems and grid-connected system, and the double pulse width modulation (PWM)converter is one of the main harmonic sources in DFIGs. Thus the harmonic analysis of the converter in DFIGs is a necessary step to evaluate their harmonic pollution of DFIGs. This paper proposes a detailed harmonic modeling method to discuss the main harmonic components in a converter. In general the harmonic modeling could be divided into the low-order harmonic part (up to 30th order) and the high-order harmonic part (greater than order 30) parts in general. The low-order harmonics are produced by the circuit topology and control algorithm, and the harmonic component will be different if the control strategy changes. The high-order harmonics are produced by the modulation of the switching function to the dc variable. In this paper, the low-order harmonic modeling is established according to the directions of power flow under the vector control (VC), and the high-order harmonic modeling is established by the switching function of space vector PWM and dc currents. Meanwhile, the simulations of harmonic a components in a converter are accomplished in a real time digital simulation system. The results indicate that the proposed modeling could effectively show the harmonics distribution of the converter in DFIGs.

A Novel Cloud-Based Platform for Implementation of Oblivious Power Routing for Clusters of Microgrids

There has been an increasing demand for connectivity of the clusters of microgrids to increase their flexibility and security. This paper presents a framework for implementation, simulation, and evaluation of a novel power routing algorithm for clusters of microgrids. The presumed cluster is composed of multiple direct current (dc) microgrids connected together through multi-terminal dc system in a meshed network. In this structure, the energy is redirected from the microgrid with excessive power generation capacity to the microgrid which has power shortage to supply its internal loads. The key contribution of this paper is that each microgrid in the cluster is unaware of the current state and other flows of the cluster. In this approach, the optimal power flow problem is solved for the system while managing congestion and mitigating power losses. The proposed methodology works for both radial and non-radial networks regardless of the network topology, scale, and number of microgrids involved in the cluster. Therefore, it is also well suited for large-scale optimal power routing problems that will emerge in the future clusters of microgrids. The effectiveness of the proposed algorithm is verified by MATLAB simulation. We also present a comprehensive cloud-based platform for further implementation of the proposed algorithm on the OPAL-RT real-time digital simulation system. The communication paths between the microgrids and the cloud environment can be emulated by OMNeT++.

Design and tuning of wind power plant voltage controller with embedded application of wind turbines and STATCOMs

This study addresses a detailed design and tuning of a wind power plant voltage control with reactive power contribution of wind turbines and static synchronous compensators (STATCOMs). First, small-signal models of a single wind turbine and STATCOM are derived by using the state-space approach. A complete phasor model of the entire wind power plant is constructed, being appropriate for voltage control assessment. An exemplary wind power plant located in the United Kingdom and the corresponding grid code requirements are used as a base case. The final design and tuning process of the voltage controller results in a guidance, proposed for this particular control architecture. It provides qualitative outcomes regarding the parametrisation of each individual control loop and how to adjust the voltage controller depending on different grid stiffnesses of the wind power plant connection. The performance of the voltage controller is analysed by means of a real-time digital simulation system. The impact of discretising the controller being initially developed in continuous-time domain is shown by various study cases.

Energy Management System for Stand-Alone Wind-Powered-Desalination Microgrid

An energy management system for stand-alone microgrid consisting of a wind turbine (WT) generator, a diesel generator, an energy storage system (ESS), and a sea water desalination system is proposed in this paper. The coordinated control of the distributed generations and ESS is researched with two operation modes. Then, a real-time rolling horizon energy management method is presented based on hour-ahead wind speed forecast. The operation mode of the microgrid system and the reference output power of WT generator are determined according to the forecasted wind speed and state of charge of the ESS, which can achieve the goal of maximizing utilization of wind energy and minimizing utilization of diesel generator on the basis of system stable operation. The proposed energy management method has been tested on the real-time digital simulator system. The results clearly verify the effectiveness of the proposed method.

Automatic Decoupling System: Preventing the Uncontrolled Shutdown of a Petrochemical Plant

This article is a case study of a dual-primary redundant automatic decoupling system (ADS) for a critical petrochemical process. GPIC selected a new dual-primary redundant ADS to island its system from the external system disturbances. The operation of an as-built ADS was validated against a real-time digital simulation system. Real-time system modeling made it possible to validate the decoupling system operation for various system disturbances and select the set points accordingly. After installation, the new ADS has successfully islanded the GPIC system several times. IE E I n

Method of Reactive Power and Voltage Optimization Control Based on RTDS

Automatic voltage control (AVC) system has been widely used in power systems at home and abroad, with some problems in applications. This paper proposes a closed-loop testing method based on real time digital simulation system (RTDS) and reactive optimization procedures to simulate the actual AVC operation mode, we can obtain an optimal control which is different from the actual AVC system, it can be used as the actual AVC system judgment to evaluate the action effectiveness and the advantages/disadvantages of the actual AVC system compared with optimal results. Finally, the simulation tests show that RTDS-based reactive power and voltage optimization control method is good so that it can be regard as reference to evaluate the control effectiveness of the actual AVC system action.

A Method of Automatic Voltage Optimization Control Based on Real Time Digital Simulation

With the development of smart grid, regional grid automatic voltage control (AVC) system has been widely used in power systems, but the effect is uneven, and there are not relating tools to evaluate its performance. The paper proposes a Closed-loop test method combining Real Time Digital Simulation system (RTDS) with reactive optimization procedures to simulate and optimization the status of actual grid. An optimal control scheme of the actual grid from the new method can be used to judge the advantages and disadvantages of actual AVC system. Simulation tests show online RTDS-based power system reactive power and voltage control simulation is good. It can be regard as reference to evaluate the control effectiveness of the actual AVC system.