Real-time Simulation Platform Research Articles

The Simulator of China General Nuclear Power Group (CGNPC) Delingha 50 MW Parabolic Trough Solar Thermal Power Plant

CGN Delingha 50MW parabolic trough solar power plant is China's first commercial trough solar power station. There are 190 heat collecting loops in the solar field of the power plant. Due to the mutual coupling of heat collecting loops layout location, environmental conditions, medium flow, working medium physical property changes and other factors, the hydrodynamic characteristics of the solar field are complex. In practical operation, balancing the flow of the heat absorbing medium in each loop of the large-scale trough solar thermal power plant and stabilizing the outlet medium temperature are difficult problems. Taking CGN Delingha 50MW parabolic trough solar power plant as the research object, this paper adopts the idea of modular modeling to establish the mathematical model of the main equipment in different systems of the power plant, to build the dynamic model of its solar field, steam generation system, heat storage system and steam turbine system. Based on the parallel computing function of the real-time dynamic simulation platform STAR-90, the real-time coupling calculation between different systems is realized. The error of the built model in steady-state is less than 2%, and the dynamic results of the model are in good agreement with the actual operation data. The modeling method in this paper is universal and can be a reference for dynamic modeling of other large-scale trough solar thermal power plants.

Towards a concurrency platform for scalable multi-axial real-time hybrid simulation

Multi-axial real-time hybrid simulation (maRTHS) uses multiple hydraulic actuators to apply loads and deform experimental substructures, enacting both translational and rotational motion. This allows for an increased level of realism in seismic testing. However, this also demands the implementation of multiple-input, multiple-output control strategies with complex nonlinear behaviors. To realize true real-time hybrid simulation at the necessary sub-millisecond timescales, computational platforms will need to support these complexities at scale, while still providing deadline assurance. This paper presents initial work towards supporting (and is influenced by the need for) envisioned larger-scale future experiments based on the current maRTHS benchmark: it discusses aspects of hardware, operating system kernels, runtime middleware, and scheduling theory that may be leveraged or developed to meet those goals. This work aims to create new concurrency platforms capable of managing task scheduling and adaptive event handling for computationally intensive numerical simulation and control models like those for the maRTHS benchmark problem. These should support real-time behavior at millisecond timescales, even for large complex structures with thousands of degrees of freedom. Temporal guarantees should be maintained across behavioral and computational mode changes, e.g., linear to nonlinear control. Pursuant to this goal, preliminary scalability analysis is conducted towards designing future maRTHS experiments. The results demonstrate that the increased capabilities of modern hardware architectures are able to handle larger finite element models compared to prior work, while imposing the same latency constraints. However, the results also illustrate a subtle challenge: with larger numbers of CPU cores, thread coordination incurs more overhead. These results provide insight into the computational requirements to support envisioned future experiments that will take the maRTHS benchmark problem to nine stories and beyond in scale. In particular, this paper (1) re-evaluates scalability of prior work on current platform hardware, and (2) assesses the resource demands of a basic smaller scale model from which to gauge the projected scalability of the new maRTHS benchmark as ever larger and more complex models are integrated within it.

Positive sequence component based directional relaying for lines integrated with solar photovoltaic plant

Different fault current characteristics of converter interfaced solar photovoltaic plants as compared to the synchronous generator based sources impose challenges to the commonly used directional relaying methods. In this work, the issues with phasor based directional relay algorithms are analysed for the solar plant connected lines. A directional relaying method is proposed for such connectivity using the phase angle difference between positive sequence voltage and the line current measured at the local bus relay. Using PSCAD/EMTDC simulations the proposed method is tested for solar plant connected 39 bus system and validated using field data. The accuracy of the proposed method is also evaluated on a real-time simulation platform. Comparative analysis with the conventional directional relaying methods reveals the superiority of the proposed method.

DC fault current clearance coordinated control strategy for DC grid with hybrid MMC

For DC grid based on the hybrid modular multilevel converter (MMC), the traditional DC fault current clearance scheme takes a long time and greatly affects the active power transmission. A novel DC fault current clearance coordinated control strategy is proposed, which can quickly interrupt the fault current and reduce the impact of DC fault on the DC grid and AC system. For fault-line connected MMC (FLMMC), a negative DC voltage control is employed, which can improve the current attenuation speed and ensure reliable fault isolation. For non-fault-line connected MMC (NFLMMC), the active current-limiting control (ACLC) based on the virtual reactor is adopted, which can reduce the current flow to the fault location and further shorten fault isolation time. To reduce the impact on the AC system during the DC fault, a short-time active power support control is designed. Finally, a four-terminal DC grid simulation model is built based on the RT-LAB OP5600 real-time digital simulation platform. The simulation results show that the proposed coordinated control strategy for the DC grid can quickly clear DC fault current, shorten DC fault isolation time, and strengthen active power support capability.

Error analysis and improved method of time-domain distance protection for wind power transmission lines

Time-domain distance protection has a good transient performance and operation speed when applied to wind power transmission lines. In this paper, the error analysis and improved method of phase-to-phase time-domain distance protection are investigated. Firstly, based on the time-domain mathematical model, the location error caused by fault resistance is analyzed, and then the algorithmic convergence and accuracy of conventional phase-to-phase distance relay are evaluated. To solve the computational non-convergence problem, an improved phase-to-phase distance relay is proposed, in which the instantaneous negative-sequence current is used to improve the location accuracy, especially during the fault transient stage of wind farms. In order to avoid the protection overreach problem, the threshold selection method is designed based on the maximum allowable error of the calculated distance. According to the proposed method, the corresponding protection device is developed. And the hardware-in-the-loop (HIL) test system is built based on the real-time digital simulation (RTDS) platform. Extensive experimental tests are carried out, to verify the feasibility and superiority of the proposed time-domain distance protection.

Real-time Assessment of Ride-through Capability of Grid-tied Converter in Renewable Power Applications

This paper presents a comprehensive strategy for controlling grid-tied converters, with the primary goal of seamlessly integrating renewable power sources into the grid while ensuring stability and reliability. The control strategy is designed to achieve unity power factor operation under normal grid conditions, while also adhering to ride-through requirements to withstand voltage dips. Using the Typhoon HIL604 real-time simulation platform, extensive testing of the grid-tied converter is conducted to validate its performance. The results of the performance assessment are thoroughly analyzed and presented to exemplify the efficacy of the proposed control strategy. Notably, the paper emphasizes the converter's operation at unity power factor during normal grid conditions, indicating maximized active power delivery to the grid. Furthermore, the grid-tied converter demonstrates impressive ride-through capability during symmetrical voltage dip, achieved through the dynamic adjustment of grid current references to maintain grid stability. This research contributes to the advancement of grid-tied converter control strategies, offering insights into enhancing the integration of renewable power sources into the power grid while upholding system reliability and stability. Overall, this research offers valuable insights into the practical implementation of grid-tied converters for renewable power integration. It presents a comprehensive control strategy that not only enhances the integration of renewable power sources into the power grid but also prioritizes system reliability and stability.

Coordinated Control of Intentional Islanding and Phase Sequence Exchange for Enhancing Transient Stability of Isolated Power Grid

An isolated power grid (IPG) is electrically weakly connected to the utility power grid, and intentional controlled islanding (ICI) can secure IPG from external faults. Phase Sequence Exchange (PSE) is a recently developed emergency control technology in which power electronic devices are used to switch the three-phase sequence, thereby reducing the power angle of the generator by 120° and preventing the system from losing stability. This paper proposed a coordinated control scheme for PSE and ICI. After the system is disturbed, the local measurement of the interconnection line between IPG and the utility grid is used to assess the system's stability. PSE is adopted to adjust the power flow direction to reduce the transient energy of IPG. At the same time, using the internal measurement of IPG, the transient energy of IPG is calculated in real-time, and the critical energy is rolling refreshed based on offline information. After PSE reduces the energy of IPG to lower than the critical energy, IPG is safely disconnected from the utility grid. The proposed scheme needless to adjust the internal generator or load of IPG and is verified on the real-time digital simulator (RTDS) platform with a PSE prototype.

Entirely Coupled Recurrent Neural Network-Based Backstepping Control for Global Stability of Power System Networks

In an interconnected power system network, global performance is affected by various unknown power system parameters subjected to system uncertainties. These unknown parameters in the control expression deteriorate the performance of the power system network. Therefore, these terms associated with the control expression must be estimated precisely. This paper proposes an adaptive backstepping scheme using an entirely coupled recurrent neural network (ECRNN) to estimate these control terms. Three continuous differentiable functions are used to design control input, virtual signals, and adaptive control laws to achieve global performance. The objective of ECRNN is to reduce the control complexity by estimating the associated nonlinear term in the control expression. It will facilitate the complex formulation of the controller and improve system performance. The robust functional estimation ability of ECRNN will make the system immune to uncertainties that may appear due to external disturbances. In ECRNN, feedback loops are added to each neuron layer to achieve additional estimation accuracy. The proposed adaptive law enhances the online weight update speed and accuracy. Verification of the proposed scheme is carried out in MATLAB/Simulink. It is also verified in the real-time digital simulator (RTDS) platform using the IEEE standard New England 39-bus, 10-machine power system model. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper is motivated by the existing limitations in the global performance of a multimachine power system network due to uncertainty in the system parameters. Uncertainties in the power system network primarily appeared due to penetration of renewable power sources, load uncertainty, or occurrence of an uncertain fault in the network. As power system networks are complex nonlinear interconnected systems, these perturbations in the generator states may cause economic losses, load demand uncertainty, or electric scarcity. Thus, a control scheme is required to address the global performance of such networks. This article proposes uniform ultimate bounded stability of synchronous generators in a multimachine power system network with a robust ECRNN-based backstepping control design. The other available technique has not adequately addressed the global performance under uncertainties. The efficacy of the proposed scheme is verified in a real-time environment via a real-time digital simulator which may be a feasible solution for designing excitation control for the synchronous machine in an extensive industrial network.

Asynchronous co-simulation of photovoltaic power generation system based on FPGA-CPU

In order to realize the real-time electromagnetic transient simulation of grid-connected photovoltaic power generation system with small time step, a heterogeneous multiplexed parallel real-time simulation method based on field programmable gate array (FPGA) and central processor is studied. According to the simulation accuracy requirements of the high and low frequency decoupling module, a differentiated simulation step size is used to solve the problem, and a 1us/50us FPGA-CPU multi-rate real-time simulation platform is constructed, in which the FPGA simulation part meets the real-time requirements of small-step transient simulation through the optimization of the response matching method and the EMTP algorithm, the offline simulation results are compared with Simulink, and the model before and after optimization is analyzed, the real-time electromagnetic transient simulation results are compared with Simulink, and the model before and after optimization is analyzed. By comparing the offline simulation results with Simulink and analyzing the FPGA resource consumption before and after model optimization, the accuracy and real-time performance of the co-simulation method for real-time simulation of grid-connected photovoltaic systems are verified.

A privacy-preserving anomaly diagnosis scheme for AC microgrids

The integration of cyber infrastructure in renewable energy source based AC microgrids (MGs) raises concerns about potential cyber attacks on such systems. An adversary can fabricate the information being exchanged between system components, which may cause false tripping of the installed protection devices. This creates the need for an anomaly diagnosis scheme that can distinguish between faults and cyber attacks to attain a reliable and secure system under large signal disturbances. This work presents a machine learning-based anomaly diagnosis scheme which characterizes these anomalies. The scheme uses the well-known XGBoost approach, and requires local measurements (such as, active power, reactive power, and frequency) of inverter-interfaced distributed energy resources (IIDERs). Since such measurements may be difficult for participants in a system to share across organizational boundaries due to commercial or regulatory concerns, the proposed approach obfuscates the measurements by additive noise while preserving detection accuracy. This scheme was tested on an AC MG network with four IIDERs, modeled on a real-time simulation platform in an OPAL-RT environment. The results validate the effectiveness and accuracy of the proposed scheme under different conditions.

An novel oscillation suppression strategy for permanent magnetic synchronous generator based on grid-forming control

With the increase of permeability of renewable energy and power electronic equipment, the inertia and damping parameters of the direct-drive wind turbine based on grid-forming control have a large impact on the system stability, and the system oscillation will be triggered when the parameters are not set properly. In this paper, the problem is addressed by establishing the small-signal model of two permanent magnetic synchronous generators connected to the grid in detail, analyzing the influence of the active control parameters on the system stability through the root locus of the dominant characteristic root, and proposing the adaptive control of damping and inertia to suppress the system oscillations. Finally, a real-time simulation platform for grid-connected wind turbine systems was built, and the experimental results verify the correctness of the small-signal modelling for stability analysis of grid-forming wind turbines established in this paper.

Nonintrusive Condition Monitoring of FCEV Using System-Level Digital Twin Model

High maintenance costs and short lifecycles are two main issues in fuel cell electric vehicle (FCEV) development. With the development of digital technology, the concept of digital twins provides new opportunities for monitoring and predicting the behavior of FCEV. However, the constitution of the digital model of FCEV faces many challenges caused by the multi-physical domain. In this paper, a digital model is built for condition monitoring of FCEV in both short-term and long-term. The built model reflects the interaction of multi-physicals domains by representing the FCEV using the energetic macroscopic representation (EMR) method. Moreover, by considering different road condition, the effect of different driving modes can be shown through the energy flow between the battery and the fuel cell. And the model can give a visible reflection of the electric, magnetic, mechanical, and chemical inside the vehicle. To further investigate the effect of all the above factors on the long-term operation status, the echo state network (ESN) is used to predict the degradation phenomenon of the proton exchange membrane fuel cells (PEMFC), which is used for prognostic purposes. At last, the digital twin test bench is shown with a real-time simulation platform of the OPAL-RT.

A robust damping control for battery energy storage integrated power systems to mitigate inter-area oscillations

This paper presents the effect of a Battery Energy Storage System (BESS) on the power system inter-area oscillations under changing load conditions. The dynamic interaction between the BESS control modes and synchronous generators, along with BESS control parameters, influence the damping of prominent inter-area oscillations under different loading conditions. Furthermore, H∞ mixed sensitivity scheme-based Wide-Area Damping Controller (WADC) is proposed for BESS. This controller is designed using the Linear Matrix Inequality (LMI) framework to mitigate the prominent inter-area oscillation of the power system. Sensitivity to control parameter variation and the geometric measure of the observability are utilized to select the location and feedback signal for the WADC. The performance of the proposed WADC is compared with an Energy Storage System-based stabilizer and WADC proposed in an existing work on a modified New England ten-machine benchmark system. The Real-Time Digital Simulator (RTDS) platform is used to assess the real-time viability of the proposed WADC. The simulation results demonstrate that the proposed WADC can effectively diminish several inter-area modes. Additionally, it offers robust performance under varying load conditions, contingencies and with communication delays in feedback signals. The proposed controller is also effective under the system integrated with Doubly Fed Induction Generator-based Wind Turbine System.

A novel power control scheme for distributed DFIG based on cooperation of hybrid energy storage system and grid-side converter

Due to the uncertainty of wind energy, the wind power is difficult to be dispatched and may cause the voltage fluctuations for distributed network. Therefore, a novel power control scheme is proposed to manage the output power of the distributed doubly-fed induction generator (DFIG) by cooperating the hybrid energy storage system (HESS). In the proposed scheme, the grid-side converter of DFIG is controlled to manage overall output power of the DFIG/HESS hybrid system in accordance to the power dispatching command. The HESS is utilized to deal with the power difference between DFIG generation power and the power dispatching command. The HESS is embedded in the DC-link bus of DFIG and is composed of superconducting magnetic energy storage and batteries. Additionally, in order to avoid HESS from overcharging and over-discharging, the pitch angle control and power dispatching command are adjusted by considering the state of charge (SOC) of HESS. Finally, the simulation model of distributed DFIG and HESS is built on the real-time digital simulation (RTDS) platform, and the simulation results validate the effectiveness and reliability of the proposed power control scheme.

Advanced Frequency Control Technique Using GTO with Balloon Effect for Microgrids with Photovoltaic Source to Lower Harmful Emissions and Protect Environment

Renewable energy (RE) resources such as wind and PV solar power are crucial for transitioning to carbon-free and sustainable energy systems, especially for agricultural and domestic applications in the desert and rural areas. However, implementing RE resources may lead to frequency penetrations, especially in isolated microgrids (µGs). This study proposes an adaptive load frequency control (LFC) technique for power systems. An integral controller can be tuned online using an artificial gorilla troops optimization algorithm (GTO), which is supported using a balloon effect (BE) identifier. Adaptive control is used to control the system frequency in case of variable loads and fluctuation due to 6 MW photovoltaic (PV). Three other optimization methods have been compared with the GTO + BE technique, namely the Grey Wolf Optimization method (GWO), the standard artificial gorilla troops optimization (GTO) and the Jaya technique. Digital simulation tests approved the efficiency of (GTO + BE) during system difficulties such as load disturbance and system parameter variations. In addition, the same test conditions have been repeated using a real-time simulation platform. The real-time simulation results supported the digital outcomes.

Fixed time adaptive fault tolerant sliding mode control of PEMFC air supply system

Guaranteeing rapid management of oxygen excess ratio (OER) for proton exchange membrane fuel cells (PEMFC) under load variations is a challenge with practical significance. To improve the controller response of PEMFC air supply system, a fixed time fault-tolerant control strategy is proposed in this paper. A fixed convergence time of PEMFC air supply control system is quantified and guaranteed by the proposed method and the control response can be accelerated by reducing the setting time. The contributions of this paper is fourfold. Firstly, the manifold leakage fault is estimated by fixed time fault observer, which can improve the real-time fault tracking performance of the control system. Secondly, a hierarchical fixed time sliding mode controller is proposed to regulate the OER rapidly. Furthermore, a novel adaptive term is employed to reduce the effects of the chattering from fault observer in the outer loop. Finally, the effectiveness of the proposed method is verified on a real-time PEMFC simulation platform. Experimental results on a Hardware-in-the-loop (HIL) platform show that the proposed fixed time fault tolerant control strategy has the characteristics of fast response and high robustness.

Analytical voltage sensitivity-based distributed Volt/Var control for mitigating voltage-violations in low-voltage distribution networks

Integrating solar photovoltaic system in low-voltage distribution networks leads to significant voltage violations. This issue can be alleviated using the cutting-edge control techniques (Volt/Var control, Volt/Watt control, etc.) of smart inverters. Moreover, the smart inverters absorb/inject the necessary amount of reactive power from/into the substation to alleviate the over/under voltages. This increases the reactive power burden on the substation and deteriorates its power factor. Therefore, this paper proposes a novel distributed Volt/Var control technique to reduce the dependency on substations for reactive power support and improve its power factor. The proposed technique is based on analytical voltage sensitivity analysis. By developing suitable relations, the feeder nodes are categorized into two groups, one operating in lagging mode, while the other in leading mode. This ensures proper utilization of reactive power capability of the inverters. An IEEE 13-node low voltage distribution network with the solar photovoltaic system at different load conditions is used to test the proposed and other existing Volt/Var control techniques. Compared to other distributed Volt/Var control techniques, the proposed method requires a minimum reactive power support to regulate the feeder voltage. Additionally, the obtained results by the proposed method are closer to those by the optimal reactive power support approach using GAMS software and are validated on a real-time digital simulator platform.

Real-time simulation for detailed wind turbine model based on heterogeneous computing

The deployment of sophisticated and costly large-capacity wind turbines continues to rise. It is urgent for precise real-time simulation to accurately identify and address potential problems. However, the existing solutions, which joint various simulation platforms, suffer from the disadvantages of complex architecture and high cost. This paper proposes a CPU-FPGA heterogeneous computing-based real-time simulation platform for detailed wind turbine model (DWTM). DWTM encompasses the turbine model (covering the inflow wind, aerodynamic, and mechanical dynamic), the electrical model (covering the electromagnetic transient), and the control system. The real-time operating system is introduced to guarantee the real-time performance of the turbine model and control system in the CPU. FPGA is used to perform real-time electrical model calculation. Furthermore, a general FPGA solver for electromagnetic transients is designed. It can accommodate various circuit topologies without the need for recompiling the FPGA code. Finally, the real-time simulation performance and accuracy are verified. The coupled dynamics between the turbine and electrical models are investigated under multiple power grid and wind conditions.

ECS-Grid: Data-Oriented Real-Time Simulation Platform for Cyber-Physical Power Systems

ECS-Grid is the first data-oriented real-time electromagnetic transient simulation platform for cyber-physical power systems (CPPS). Traditional simulation tools are constrained by object-oriented programming (OOP) architecture, which is now a significant obstruction to creating a comprehensive cyber-physical simulation. Therefore, the proposed ECS-Grid platform follows a new data-oriented paradigm based on an Entity-Component-System (ECS) framework, which delivers higher flexibility, extensibility, scalability, and performance to support cyber-physical system research. ECS-Grid proposes a layer of virtual intelligent electronic devices (vIEDs) to model IEDs in CPPSs. The vIEDs directly talk to physical components and communicate asynchronously with cyber services via the proposed high-performance JSON-like binary protocol. Tests with the islanding and the man-in-the-middle cyber attack scenarios on a 711-node AC-DC microgrid cluster based on a modified CIGRE 15-Bus system are performed and give accurate results. A faster-than-real-time performance is achieved on the 10th Gen Intel <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> Core <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> i7 computer, and real-time performance is achieved on distributed embedded NVIDIA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> Jetson platform. The ECS-Grid design and test results demonstrate the potential of the ECS data-oriented paradigm and may inspire the renovation of industrial simulation software.

Performance Analysis of 9, 11, 13, and 15 – Level Back-to-Back Connected Modular Multilevel Converters fed Doubly Fed Induction Machine

In this paper, back-to-back Modular Multilevel Converters are used to feed the Doubly Fed Induction Machine. The MMC with 9, 11, 13, and 15 – Level output voltages are generated and fed to the DFIM and the performance of the DFIM is analyzed, when the machine is working as Doubly Fed Induction Generator (DFIG) and when the machine is working as Doubly Fed Induction Motor. The performance of the DFIG is analyzed in terms of power factor at Grid Side Converter (GSC) for different levels of operation of MMC. The results show that the power factor is maintained near to unity power factor at grid side. The performance of the Doubly Fed Induction Motor is analyzed in terms of variation of the load torque being applied to motor. The results show that there is clear variation of the speed for two different load conditions. The work is carried out by using Typhoon HIL Real-Time Simulation platform, i.e., both Software and Hardware.