Real-time Simulation Platform Research Articles

State of charge balancing strategy for energy storage system in islanded DC microgrid based on micro-tuning virtual resistance

For the islanded DC microgrid, the energy storage system (ESS) can be employed to maintain the balance between the power generation and load consumption. In order to avoid the over-charging or over-discharging situation of the certain distributed energy storage unit (DESU), the accurate current sharing strategy considering unmatched line resistances is proposed to balance the state of charge (SoC) among DESUs. The micro-tuning resistance is designed to eliminate the impact of line resistances on SoC balancing and achieves the accurate current sharing without affecting the bus voltage deviation. Then, the DESUs adaptively adjust the virtual resistance according to the SoC or depth of discharge (DoD) during charging and discharging to quickly balance the SoC. Additionally, the stability analysis based on the system characteristic equation is provided to theoretically guarantee the stability operation of the DC microgrid. Finally, the effectiveness of the proposed control strategy is proved by several comprehensive test cases based on real-time digital simulator (RTDS) platform.

Real-Time FPGA/CPU-Based Simulation of a Full-Electric Vehicle Integrated with a High-Fidelity Electric Drive Model

Real-time simulations refer to the simulations of a physical system where model equations for one time-step are solved within the same time period as in reality. An FPGA/CPU-based real-time simulation platform is presented in this paper, with a full-electric vehicle model implemented in a central processing unit (CPU) board and an electric drive model implemented in a field programmable gate arrays (FPGA) board. It has been a challenge to interface two models solved with two different processors. In this paper, one open-loop and three closed-loop interfaces are proposed. Real-time simulation results show that the best method is to transmit electric machine speed from the vehicle model to the electric derive model, with feedback electric machine torque calculated in FPGA. In addition, a virtual vehicle testing tool (CarMaker) is used when building the vehicle model, achieving more accurate modeling of vehicle subsystems. The presented platform can be used to verify advanced vehicle control functions during hardware-in-the-loop (HIL) testing. Vehicle anti-slip control is used as an example here. Finally, experiments were performed by connecting the real-time platform with a back-to-back electric machine test bench. Results of torque, rotor speed, and d&q axis currents are all in good agreement between simulations and experiments.

Digital Twin Envisioned Secure Air-Ground Integrated Networks: A Blockchain-Based Approach

The wide use of unmanned aerial vehicles provides a promising paradigm for improving air-ground services and applications (e.g., urban sensing, disaster relief) in air-ground integrated networks (AGINs). Digital twin (DT), which is an emerging technology that utilizes data, models, and intelligent algorithms to integrate cyber physical networks and digital virtual models, provides a real-time and dynamic simulation platform for strategy optimization and decision making in AGINs. Due to the openness and massive connectivity of AGINs, the security and reliability services in this system become an important issue. In this article, we investigate the DT envisioned secure federated aerial learning for AGINs via an aerial blockchain approach. Specifically, we propose a layered framework of DT envisioned AGINs, which comprises the construction segment, communication segment, aggregation segment, analysis segment, and operation segment. Based on this framework, we offer the applications of the proposed DT envisioned AGINs. To guarantee the security of data transmission in AGINs, we investigate the aerial blockchain-based approach for ensuring data security. Furthermore, we provide a case study of DT envisioned secure federated aerial computing in AGINs to validate the effectiveness of the proposed approach through designing the aerial blockchain and training model.

Design and Verification of an Electro Hydrostatic Brake System

Electro-Hydraulic Actuation is a distributed power telex technology which integrates machine, electricity and liquid as one. A miniaturized Electro-Hydraulic Brake System is designed by introducing Electro-Hydraulic Actuation Technology into aircraft Anti-skid Brake System. It can transmit power by electricity in brake system. Firstly, the mathematical model of the Electro-Hydraulic Braking System is established. Secondly, the semi physical simulation of the hardware in the loop is completed in the real-time simulation platform to verify the anti-skid braking control function of the system, realize the parameter optimization process, and determine the important parameters, so as to provide guidance for the production of the sample. Finally, the correctness and function of the Electro-Hydraulic Brake System are verified by the test on the inertial platform. The results show that the system can achieve the expected anti-skid braking function, and can provide support for subsequent engineering.

A Multi-Frequency DQ Impedance Measurement Algorithm for Single-Phase Vehicle-Grid System in Electrified Railways

Dq impedance measurement is of great importance as a part of the impedance-based analysis. At present, impedance of objects in single-phase vehicle-grid system are mainly obtained by injecting the voltage or current disturbance of one single frequency into the system circularly. However, as the number of measurement frequency points increases, there will produce much time-consuming of measurement. In this paper, a quick dq impedance measurement algorithm for single-phase vehicle-grid system based on multi-frequency sweep is proposed. First, pseudo-random binary sequences (PRBS) and ternary sequences are modified as the driving signals rather than directly injecting into the control link. Then three types of disturbance with specific frequency characteristics are introduced into the system and their parameters setting principle are given for the first time. According to the different characteristics of measurement objects, the proposed algorithms are also different to ensure the maximum specificity and sensitivity. Finally, for different objects in vehicle-grid system like traction network, single-phase converter and dual-interleaved converter, simulation and experimental results based on the hardware in the loop real-time simulation platform both show the correctness of the proposed algorithm, and the possible causes of errors are also analyzed in detail. Moreover, the proposed algorithm makes it possible to quickly measure the dq impedance of the single-phase vehicle-grid system, and the correctness of the theoretical and measured value can be judged and used for the stability analysis of electrical systems.

Real-Time Simulation Modeling Method of Multiphase Converters Based on High-Order Approximation in Micro-grid

As more and more distributed energy resources accessing in a micro-grid, the electromagnetic transient simulation of the whole system becomes extremely complicated due to the increase of multiphase converters. The traditional real-time simulation models of multiphase converters are low in efficiency for their large number of electronic switches and power system nodes. To solve this problem, an efficient real-time simulation modeling method based on high-order approximation is proposed. Starting with the symmetry of structure, the twelve-phase converter and induction motor are equivalent to a three-phase converter and induction motor and thus reducing the order of the model. The switching function model of the three-phase converter is derived, and the mathematical expressions of switching functions are calculated by high-order approximation expansion of the Fourier series; then, the dc input current of the three-phase converter is formulated theoretically. Counteracting the harmonics by means of phase-shifting, the high-order approximation model of the twelve-phase converter is constructed. Finally, the real-time simulation platform and experimental platform of the twelve-phase frequency converter and induction motor are built; the simulation results verify the high efficiency and accuracy of the proposed real-time simulation model compared with traditional models of the multiphase frequency converter.

Power quality assessment and power quality improvement in hospital facility

The power quality (PQ) assessment is carried out at a KIMS hospital facility by conducting the harmonic study as per IEEE3002.8 guidelines. As per PQ data obtained, the hospital facility is experiencing a significant number of PQ disturbances and violating IEEE519 limits for PQ in special application systems. It is found necessary to use a compensator for PQ improvement. A cost-effective compensator, DVR, is designed to improve PQ in the hospital facility. The designed DVR controller model is tested in the RT-LAB hardware-in-the-loop real-time simulation platform using OPAL-RT with multicore FPGA processors to validate the compatibility of the designed controller to be applied for real system implementation. Thus, PQ assessment helps in the appropriate design of compensating controllers to suit practicality. A comparative study of choice of designed DVR controllers such as PI, Fuzzy, ANN, ANFIS-PI optimised and ANFIS-Fuzzy optimised controllers tested in real-time for different cases and for different loading conditions are summarised.

A Framework for Sensitivity Analysis of Real-Time Power Hardware-in-the-Loop (PHIL) Systems

Power hardware-in-the-loop (PHIL) simulation leverages the advanced real-time emulation based technique to carry out in-depth investigations on novel real-world power components. Power amplifiers, sensors, and signal conversion units based power interfaces (PI) incorporate physical hardware systems and real-time simulation platforms into PHIL setups. However, the employment of any interfacing technique inevitably introduces disturbances such as sensor noise, switching harmonics, or quantization noise to PHIL systems. To facilitate quantitatively analyzing and assessing the impact of external disturbances on PHIL simulation systems, a framework for sensitivity analysis of PHIL setups has been developed in this paper. Detailed modelling principles related to the sensitivity analysis of PHIL systems and the inherent relationship between sensitivity transfer functions and stability criteria are elaborated along with theoretical and experimental validation. Based on this concept, accuracy assessment methods are employed in this framework to quantify generic sensitivity criteria. Moreover, physical passive load and converter-based PHIL setups are applied and experimental results are presented to characterize and demonstrate the applicability of the proposed framework.

Differential Power Based Selective Phase Tripping for Fault-resilient Microgrid

Modern fault-resilient microgrids (MGs) require the operation of healthy phases during unbalanced short-circuits to improve the system reliability. This study proposes a differential power based selective phase tripping scheme for MGs consisting of synchronous and inverter-interfaced distributed generators (DGs). First, the differential power is computed using the line-end superimposed voltage and current signals. Subsequently, to make the scheme threshold-free, a power coefficient index is derived and used for identifying faulted phases in an MG. The protection scheme is tested on a standard MG operating in either grid-connected or islanding mode, which is simulated using PSCAD/EMTDC. The efficacy of the scheme is also assessed on the OPAL-RT manufactured real-time digital simulation (RTDS) platform. Further, the performance of the proposed protection scheme is compared with a few existing methods. The results show that the selective tripping of faulted phases in MGs can be achieved quickly and securely using the proposed scheme.

Fault-Tolerant Control and Isolation Method for NPC-Based AFEC Using Series-Connected 10kV SiC MOSFETs

Power Conditioning Systems (PCS) based on three-level converters with series-connected 10kV SiC MOSFETs have gained popularity for medium voltage applications with the increase in distributed energy sources. With the use of Silicon Carbide (SiC), a wide bandgap semiconductor composed of Silicon (Si) and Carbon (C), MOSFET increases in power electronics application due to higher switching frequency operations. A high switching frequency such as 10 kHz or more leads to a reduction in magnetic components’ size and the PCS structure’s size. Therefore, the smaller, modular, and lightweight PCS can be attained for micro-grid integration, EV charging, or high inertia-dominated power grid applications. The three-level NPC (3L-NPC) inverter using series-connected 10kV SiC MOSFET is a suitable topology for coupling the PCS with the medium-voltage utility grid. The converter’s pole sustainability increases with the two series-connected switches, yet the switches are still sensitive and prone to malfunction under various environmental and mechanical causes. Therefore, a meticulous fault isolation and coordination design may be necessary for the front-end converter for possible switch faults in the converter poles. A well-designed fault-tolerant controller may sustain the converter operation under fault conditions while protecting the healthy parts of the converter. Besides, it minimizes the harmful effects of fault on the grid side and increases the system availability. This paper analyzes short and open circuit switch faults that might occur in the PCS. Accordingly, a fault-tolerant method and a fault isolation method are proposed. The proposed methods are verified with Saber™ and the Real-Time Digital Simulator simulation platforms.

FPGA-Based Hardware-in-the-Loop Simulation of User Selection Algorithms for Cooperative Transmission Technology Over LOS Channel on Geosynchronous Satellites

Distributed satellite clusters and cooperative transmission technology have been used to improve the communication capability of the geosynchronous orbit (GEO) satellites in recent years. To validate the effectiveness of distributed cooperative technology, the authors designed an information transmission system using FPGA-based hardware-in-the-loop simulation. The focus of this paper is to complete the implementation of the link layer user selection algorithm to verify that cooperative transmission techniques are feasible. This system uses a Xilinx ML605 FPGA for simulating the synchronization and exchange of data during coordinated transmission in a GEO window. The authors assumed a dual-satellite scenario in the simulation used to validate the efficacy of the satellite system. After testing the system optimized with pipelining technology, the number of clock cycles was reduced by 66%. Furthermore, tests showed the system can process multi-user channel data with signal-to-noise ratios ranging from 110dB to 195dB and could select the optimal channel. Additionally, in a case study with 10 users and 2 collocated satellites, this optimized system’s operation speed is approximately 2000 times faster-after hardware acceleration-than general-purpose processors, which verifies the efficacy of using distributed cooperative transmission algorithms. Because of this, the low-cost, and the low-power features, this system is a promising candidate for an embedded real-time simulation platform for GEO satellites.

A gray-box harmonic resonance frequency identification method of multiple-inverter-fed power system oriented to system designers

This paper presents a gray-box harmonic resonance frequency identification method of multiple-inverter-fed power system, which enables modal analysis oriented to system designers based on only frequency response data provided by diverse vendors or measured by frequency scanning. First, admittance transfer functions of all grid-connected inverters (GCIs) are fitted using Matrix Pencil Method-Vector Fitting (MPM-VF) combined method. Then, node admittance matrix (NAM) is formed according to the topology of whole system. Finally, harmonic resonance frequency along with changes in number of GCIs are identified by NAM-based modal analysis (MA). The proposed gray-box identification method is implemented in a typical multiple-inverter-fed power system. The correctness of harmonic resonance frequency identification results and the effectiveness of the presented method are verified by simulation results obtained in Matlab/Simulink platform and OPAL-RT digital real-time simulation platform. Based on the identification results, a more stable and better power quality multiple-inverter-fed power system can be built by system designers though avoiding the appearance of harmonic sources with corresponding resonance frequency.

Hardware in the Loop Real-time Simulation of Doubly Fed Off-grid Wind Power System

Hardware in the Loop (HIL) semi-physical real-time simulation can shorten the research period and complete the harsh working condition test, which is difficult to be carried out on the physical platform. Taking the off-grid Doubly Fed Induction Generator (DFIG) wind power system as the research object, this paper proposes the bottom modelling method of HIL real-time simulation. Using the Hardware Description Language VERILOG, the bottom real-time models of DFIG, converter and load are designed on Field Programmable Gate Array (FPGA), connected with the real controller, and the HIL real-time simulation platform is constructed. The experiments of conventional working conditions and unbalance load are carried out on the HIL platform and the physical platform. The operation speed of the HIL platform reaches 0.48μs. Compared with the physical platform, the error of HIL platform is between 1.17 ~ 3.29% under various working conditions.

Combined Voltage and Frequency Control for Diverse Standalone Microgrid Networks Using Flexible IDC with Novel FOC: A Real-Time Validation

In this paper, a maiden application of combined voltage and frequency control ensures voltage, frequency, and power regulation in diverse standalone low voltage AC microgrid (MG) networks by combining flexible improved droop control (IDC) with a novel fractional-order controller (FOC) proposed. An effort is made to design an IDC into the control loop based on virtual power, virtual negative resistance, inductance, and FOC to ensure power decupling and compensate voltage source converter (VSC) based distributed generators feeder voltage drop. A maiden proportional fractional integral derivative filter plus double derivative controller is used to precisely monitor VSC voltage and current reference value for reducing the control errors. The controller robustness regarding system parameters uncertainties, unmodeled dynamics, and disturbance in the MG system is ensured by a new memetic salp swarm algorithm by finding optimal controller parameters. Several simulation studies in the MATLAB Simulink environment were conducted to verify the efficacy of the proposed technique. The suggested control methodology is also investigated by hardware in the loop using the OPAL-RT real-time simulator platform to demonstrate the controllers practical functional realization. The findings confirmed the efficacy of the proposed strategy.

High Flexibility Hybrid Architecture Real-Time Simulation Platform Based on Field-Programmable Gate Array (FPGA)

With the expansion of system scale and the reduction in simulation step size, the design of a power system real-time simulation platform faces many difficulties. The interactive operation of real-time simulation presents the characteristics of phased and centralized. This paper proposes selecting the appropriate simulation method for each sub-network according to the system operation requirements, and the sub-network simulation method can be changed with the change in system operation requirements in the simulation process. In order to change the sub-network simulation method in the simulation process, a high flexibility hybrid architecture real-time simulation platform based on FPGA was designed. The main body of the architecture runs in the high control mode of instruction flow and uses instruction flexibility to realize the requirement of changing methods. The algorithm modularity architecture is used as an auxiliary architecture to reduce the instruction cost and increase the computing power. Finally, the hybrid architecture real-time simulation platform was implemented in the Xilinx VC709 board (Xilinx corporation, San Jose, CA, USA), and the verification results show that under the same system scale, the hybrid architecture simulation platform combined with simulation method changing realizes shorter simulation step and complex interactive operation.

Cloud and machine learning experiments applied to the energy management in a microgrid cluster

The way to organize the generation, storage, and management of renewable energy and energy consumption features has taken relevance in recent years due to demands that define the social welfare of this century. Like demand increases, other factors require grid infrastructure improvement, updates, and opening to other technologies that assuage the final customer needs. Precisely, the interest in renewable energy sources, the constant evolution of energy storage technologies, the continuous research involving microgrid management systems, and the evolution of cloud computing technologies and machine learning strategies motivate the development of this article. Tasks associated with a microgrid cluster like the integration of a considerable number of heterogeneous devices, real-time support, information processing, massive storage capabilities, security considerations, and advanced optimization techniques usage could take place in an autonomous and scalable energy management system architecture under a machine learning perspective running in real-time and using Cloud resources. This paper focuses on identifying the elements considered by different authors to define a cloud-based architecture and ensure the appropriately supervised learning functionality under a microgrids cluster environment. Namely, it was necessary to revise and run microgrid simulations, real-time simulation platforms usage, connection to a virtual server for microgrid control and set the energy management system using cloud computing and machine learning. Based on the review and considering the scenarios mentioned, this article presents a scalable and autonomous cloud-based architecture that allows power generation forecast, energy consumption prediction, a real-time energy management system using machine learning techniques.

Research on Risk Assessment of Power Grid Based on Realtime Simulation System

In order to ensure the safe and stable operation of the power system, the importance of power grid calculation in simulation analysis has become more and more prominent. It is particularly important to carry out power system hidden danger investigation and risk assessment for large power grids. This paper builds a "power system full-digital real-time simulation platform" based on ADPSS. Through the modeling of the actual power grid and full fault scanning, the existence and probability of risk, the scope and degree of loss are evaluated and measured, and the operation of the power grid is analyzed. The safety and stability of the power grid, while identifying weak links in the power grid. This assessment method can provide technical support for the investigation and management of hidden dangers in the power grid, and has certain practical significance and positive guidance for the stable operation of the power grid.

Modeling and Control Strategy for Multiterminal Flexible DC Distribution Network with Echelon Utilization Power Battery

With the integration of distributed renewable energy to the distribution network and the development of multiterminal flexible DC transmission technology, multiterminal flexible DC distribution network has broad application prospects. At the same time, with the rapid development of new energy vehicles, the echelon utilization of power battery has become a research hotspot. By analyzing the characteristics of flexible DC distribution network and echelon utilization battery, the structure and control strategy of modular multilevel converter (MMC), DC solid-state transformer, photovoltaic power generation, wind power generation, and echelon utilization battery energy storage system are established, respectively, in this paper. To achieve a DC network connection of various types of power supply and load, this paper proposes a starting method of multiterminal flexible DC distribution network and a cooperative control strategy of the wind-solar-storage system. A six-terminal ring-shape DC distribution network model is built in real-time digital simulation (RTDS) platform. The simulation results show that the modeling methods and control strategies of each component in the real-time simulation model meet the operation requirements of the multiterminal flexible DC distribution network, which provides a reference for the construction and research of the flexible DC distribution network.

Power Hardware-in-the-Loop-Based Performance Analysis of Different Converter Controllers for Fast Active Power Regulation in Low-Inertia Power Systems

Future electrical power systems will be dominated by power electronic converters, which are deployed for the integration of renewable power plants, responsive demand, and different types of storage systems. The stability of such systems will strongly depend on the control strategies attached to the converters. In this context, laboratory-scale setups are becoming the key tools for prototyping and evaluating the performance and robustness of different converter technologies and control strategies. The performance evaluation of control strategies for dynamic frequency support using fast active power regulation (FAPR) requires the urgent development of a suitable power hardware-in-the-loop (PHIL) setup. In this paper, the most prominent emerging types of FAPR are selected and studied: droop-based FAPR, droop derivative-based FAPR, and virtual synchronous power (VSP)-based FAPR. A novel setup for PHIL-based performance evaluation of these strategies is proposed. The setup combines the advanced modeling and simulation functions of a real-time digital simulation platform (RTDS), an external programmable unit to implement the studied FAPR control strategies as digital controllers, and actual hardware. The hardware setup consists of a grid emulator to recreate the dynamic response as seen from the interface bus of the grid side converter of a power electronic-interfaced device (e.g., type-IV wind turbines), and a mockup voltage source converter (VSC, i.e., a device under test (DUT)). The DUT is virtually interfaced to one high-voltage bus of the electromagnetic transient (EMT) representation of a variant of the IEEE 9 bus test system, which has been modified to consider an operating condition with 52% of the total supply provided by wind power generation. The selected and programmed FAPR strategies are applied to the DUT, with the ultimate goal of ascertaining its feasibility and effectiveness with respect to the pure software-based EMT representation performed in real time. Particularly, the time-varying response of the active power injection by each FAPR control strategy and the impact on the instantaneous frequency excursions occurring in the frequency containment periods are analyzed. The performed tests show the degree of improvements on both the rate-of-change-of-frequency (RoCoF) and the maximum frequency excursion (e.g., nadir).

Real-time RMS-EMT co-simulation and its application in HIL testing of protective relays

This work proposes an interfacing technique that uses the built-in three-phase transmission line models available in simulation platforms to perform Root Mean Square (RMS)- Electromagnetic Transient (EMT) real-time, multi-domain and multi-rate co-simulation. The main objective of this paper is to show the application of this kind of simulation in hardware-in-the-loop (HIL) testing of protective relays. Two well-known platforms are considered in this work: OPAL-RT with its ePhasorSim tool is used for RMS simulation, and RTDS is used for EMT simulation. However, the proposed technique is sufficiently general to be applied to other real-time simulation platforms that have similar built-in transmission line models. To convert waveforms to phasors, a non-buffered rapid curve fitting method was implemented to attend to real-time constraints. During the testing phase of this research, tests for the HIL were completed using an actual transmission line protection relay. The presented results of tests highlight the benefits of the proposed interfacing technique.