Accurate Real-time Simulation Research Articles

Real-time simulation for multi-component biomechanical analysis using localized tissue constraint progressive transfer learning

In virtual surgical training, it is crucial to achieve real-time, high-fidelity simulation of the tissue deformation. The anisotropic and nonlinear characteristics of the organ with multi-component make accurate real-time deformation simulation difficult. A localized tissue constraint progressive transfer learning method is proposed in this paper, where the base-compensated dual-output transfer learning strategy and the localized tissue constraint progressive learning architecture are developed. The proposed strategy enriches the multi-component biomechanical dataset to fully represent complex force-displacement with minimal high-quality data. Meanwhile, the proposed architecture adopts focused and progressive model to accurately describe tissues with varied biomechanical properties rather than singular homogeneous model. We made comparison with 4 state-of-the-art (SOTA) methods in simulating multi-component biomechanical deformations of organs with 100 pairs of testing data. Results show that the accuracy of our method is 50% higher than other methods in different validation matrix. And our method can stably simulate the deformations in 0.005 s per frame, which largely improves the computing efficiency.

Electromagnetic Transient Modeling Method of Photovoltaic Power Station Based on FPGA

The rapid development of renewable energy needs the effective support of simulation technology. Aiming at the shortage of both modeling scale and simulation accuracy of the current large-scale photovoltaic power station, an electromagnetic transient modeling and real-time simulation method suitable for large-scale photovoltaic power stations are proposed. The microsecond accurate real-time simulation of 24 photovoltaic power units is implemented on a single FPGA. Through an equivalent modeling method, the electromagnetic transient model of a photovoltaic power unit including a PV array, DC boost circuit, grid-connected inverter, filter, and grid-side transformer is established. Then, based on the FPGA parallel computing and pipeline time division multiplexing technology, the updating framework of the station collecting network and the power unit is constructed, and the real-time simulation model of the station including 24 photovoltaic power units in 4 sub-stations is built. Finally, the microsecond real-time simulation of the photovoltaic power station is realized through RTRES, a self-developed real-time simulator in China’s Southern Power Grid. The comparison with the detailed PSCAD model shows that the simulation error is within ± 2%, which verifies the correctness of the proposed method and model.

Reduced-order modeling of PEM fuel cell based on POD and PODI: an efficient approach toward combining highest accuracy with real-time performance

The main contribution of this study is developing an efficient reduced-order model for accurate real-time simulation of a proton exchange membrane fuel cell (PEMFC). The basis of reduced space are created by the proper orthogonal decomposition (POD) of the snapshots obtained from the simulation results of the finite-volume method. Another approach is introduced by interpolating between the coefficients of POD, known as PODI method. The developed reduced-order models are examined by simulating the electrochemical behavior of PEMFC for various geometrical parameters and operating conditions, including porosity of catalyst layers, cell temperature, and concentration of inlet oxygen. An extensive eigenvalue analysis of dominant energetic modes shows that the PEMFC can be simulated accurately with very low computational cost. Compared to the finite-volume method (full-order model), speed-up factors of 27 and 67 are achieved by the POD and PODI methods respectively, which can potentially be used for real-time, optimization, and control purposes.

Methods for the Accurate Real-Time Simulation of High-Frequency Power Converters

This article presents general modeling approaches to achieve an accurate real-time simulation (RTS) of high switching frequency converters.The proposed methods are based on the direct mapped method (DMM) and make use of decoupling techniques when appropriate. The DMM links state variables to diode statuses and provides an exact and noniterative solution to network equations. An electric vehicle battery charger test case comprised of a full-bridge rectifier, an interleaved boost, and a three-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> is used to demonstrate the high accuracy achieved by the proposed methods compared to a conventional approach. Field-programmable gate array (FPGA) implementations are proposed and shown to achieve from 75- to 175-ns RTS time steps for this test case circuit, allowing its accurate simulation while switched at 200 kHz. To further validate the effectiveness of the FPGA-based simulator, a resonant boost converter is also implemented and simulated in real time.

Microsecond Enhanced Indirect Model Predictive Control for Dynamic Power Management in MMC Units

The multi-modular converter (MMC) technology is becoming the preferred option for the increased deployment of variable renewable energy sources (RES) into electrical power systems. MMC is known for its reliability and modularity. The fast adjustment of the MMC’s active/reactive powers, within a few milliseconds, constitutes a major research challenge. The solution to this challenge will allow accelerated integration of RES, without creating undesirable stability issues in the future power system. This paper presents a variant of model predictive control (MPC) for the grid-connected MMC. MPC is defined using a Laguerre function to reduce the computational burden. This is achieved by reducing the number of parameters of the MMC cost function. The feasibility and effectiveness of the proposed MPC is verified in the real-time digital simulations. Additionally, in this paper, a comparison between an accurate mathematical and real-time simulation (RSCAD) model of an MMC is given. The comparison is done on the level of small-signal disturbance and a Mean Absolute Error (MAE). In the MMC, active and reactive power controls, AC voltage control, output current control, and circulating current controls are implemented, both using PI and MPC controllers. The MPC’s performance is tested by the small and large disturbance in active and reactive powers, both in an offline and online simulation. In addition, a sensitivity study is performed for different variables of MPC in the offline simulation. Results obtained in the simulations show good correspondence between mathematical and real-time analytical models during the transient and steady-state conditions with low MAE. The results also indicate the superiority of the proposed MPC with the stable and fast active/reactive power support in real-time simulation.

Strategies for choosing an appropriate numerical method for FPGA-based HIL

Hardware-In-the-Loop (HIL) has become a very popular approach for power electronics testing in recent years due to its safety and low cost. Furthermore, the outcome of HIL techniques has improved with the incorporation of Field-Programmable Gate Arrays (FPGAs), which allow faster and more accurate real-time simulations. The use of FPGAs in HIL implies some challenges, like the choice of a relevant numerical method for the implementation. The task is not trivial, because the numerical method should be executed in real time and it should obtain the best trade-off between accuracy and hardware resources using the smallest possible computation time. The HIL performance of four popular numerical methods is evaluated in this paper: 1st order Forward Euler, 2nd order Adams–Bashforth, 2nd order Runge–Kutta, and 4th order Runge–Kutta. Their error results with different simulation time steps and 32- and 64-bit resolutions are calculated. The methods are implemented in FPGA for the simulation of a simple power converter independently and as a part of an HIL system which includes a DAC. The hardware synthesis results are obtained along with the minimum execution time for each method. The results show that even though Runge–Kutta methods get the best accuracy outcome, once accuracy limiting factors in real environments are considered, the simplest methods (1st order Forward Euler and 2nd order Adams–Bashforth) gain the best overall performance considering Cost Performance Indexes.

Real-Time Vehicular Wireless System-Level Simulation

Future automation and control units for advanced driver assistance systems (ADAS) will exchange sensor and kinematic data with nearby vehicles using wireless communication links to improve traffic safety. In this paper we present an accurate real-time system-level simulation for multi-vehicle communication scenarios to support the development and test of connected ADAS systems. The physical and data-link layer are abstracted and provide the frame error rate (FER) to a network simulator. The FER is strongly affected by the non-stationary doubly dispersive fading process of the vehicular radio communication channel. We use a geometry-based stochastic channel model (GSCM) to enable a simplified but still accurate representation of the non-stationary vehicular fading process. The propagation path parameters of the GSCM are used to efficiently compute the time-variant condensed radio channel parameters per stationarity region of each communication link during run-time. Five condensed radio channel parameters mainly determine the FER forming a parameter vector: path loss, root mean square delay spread, Doppler bandwidth, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor, and line-of-sight Doppler shift. We measure the FER for a pre-defined set of discrete grid points of the parameter vector using a channel emulator and a given transmitter-receiver modem pair. The FER data is stored in a table and looked up during run-time of the real-time system-level simulation. We validate our methodology using empirical measurement data from a street crossing scenarios demonstrating a close match in terms of FER between simulation and measurement.

FPGA-Based Submicrosecond-Level Real-Time Simulation of Solid-State Transformer With a Switching Frequency of 50 kHz

The switching frequency of power electronic devices has become much higher than before, which brings great challenges to real-time simulators. The small time step in high switching frequency simulations remarkably increases the difficulty to satisfy the real-time requirement. This article realizes the accurate real-time simulation of a solid-state transformer (SST) with a switching frequency of 50 kHz at the time step of 250 ns on a field-programmable gate array (FPGA)-based platform. The hybrid companion circuit modeling method and the compact-electromagnetic transient program (EMTP) algorithm are proposed in this article to make sure that the simulation loop can complete in less than 1 μs. The hybrid companion circuit modeling method can avoid too many digits used in representing simulation variables. The compact-EMTP algorithm is designed by combining the sequential computation tasks of the traditional EMTP to fully utilize the parallelized hardware structure of the FPGA. Besides, a circuit partition method is adopted to further parallelize the circuit solution of the SST circuit. In these ways, the simulation loop of the SST can be completed in 38 clock cycles (about 237.5 ns). The simulation results show that the real-time simulation waveforms are almost consistent with those of the off-line simulation software. Besides, the hardware-in-the-loop (HIL) simulation can also be performed on this platform to test the control functions of the SST.

A Direct Mapped Method for Accurate Modeling and Real-Time Simulation of High Switching Frequency Resonant Converters

This article presents a direct mapped method (DMM) for real-time simulation of high switching frequency resonant converters. The DMM links state variables to diode statuses and provides an exact and noniterative solution to network equations. The proposed method is implemented on field programmable gate array (FPGA) to simulate an LLC converter with switching frequencies ranging up to 500 kHz. The best reported implementations of DMM achieve a 25-ns simulation time-step for a wide range of clock frequencies, ranging from 40 to 320 MHz.

Distributed Turbulence Model with Rigorous Spatial Cross-Correlation for Simulation of Helicopter Flight in Atmospheric Turbulence

This paper presents a distributed turbulence model with rigorous spatial cross-correlation for helicopter flight simulation in atmospheric turbulence and for future handling-quality analysis. First, digital filters with longitudinal correlations of the von Kármán turbulence are developed to generate discrete turbulence velocity components. Meanwhile, transverse turbulence correlations are considered by relating the filters in different positions with mathematically rigorous spatial cross-correlation. Then, the distributions of the related filters on the transverse plane in front of helicopter and their velocity components in the longitudinal direction of airspeed, as well as turbulence models of helicopter aerodynamic surfaces, are established. Finally, a flight dynamics model coupled with the turbulence model is developed and validated against the flight-test data. The proposed model can achieve accurate real-time simulations of helicopter response to atmospheric turbulence in the frequency range of interest of handling qualities. The effect of transverse turbulence correlations on helicopter frequency response is also analyzed. The results show that the simulation model regardless of transverse turbulence correlations would aggravate the "rotor-to-body attenuation" effect of the main rotor and therefore underpredict the helicopter roll, pitch, and heave rate responses to atmospheric turbulence in the frequency range of interest.

An improved Lagrangian model for the time evolution of nonlinear surface waves

Accurate real-time simulations and forecasting of phase-revolved ocean surface waves require nonlinear effects, both geometrical and kinematic, to be accurately represented. For this purpose, wave models based on a Lagrangian steepness expansion have proved particularly efficient, as compared to those based on Eulerian expansions, as they feature higher-order nonlinearities at a reduced numerical cost. However, while they can accurately model the instantaneous nonlinear wave shape, Lagrangian models developed to date cannot accurately predict the time evolution of even simple periodic waves. Here, we propose a novel and simple method to perform a Lagrangian expansion of surface waves to second order in wave steepness, based on the dynamical system relating particle locations and the Eulerian velocity field. We show that a simple redefinition of reference particles allows us to correct the time evolution of surface waves, through a modified nonlinear dispersion relationship. The resulting expressions of free surface particle locations can then be made numerically efficient by only retaining the most significant contributions to second-order terms, i.e. Stokes drift and mean vertical level. This results in a hybrid model, referred to as the ‘improved choppy wave model’ (ICWM) (with respect to Nouguier et al.’s J. Geophys. Res., vol. 114, 2009, p. C09012), whose performance is numerically assessed for long-crested waves, both periodic and irregular. To do so, ICWM results are compared to those of models based on a high-order spectral method and classical second-order Lagrangian expansions. For irregular waves, two generic types of narrow- and broad-banded wave spectra are considered, for which ICWM is shown to significantly improve wave forecast accuracy as compared to other Lagrangian models; hence, ICWM is well suited to providing accurate and efficient short-term ocean wave forecast (e.g. over a few peak periods). This aspect will be the object of future work.

Evaluation of frequency evaluation index based compensation for benchmark study in real-time hybrid simulation

Abstract Actuator control plays an essential role to achieve stable and accurate real-time hybrid simulation (RTHS) results. Delay compensation is often used to minimize the desynchronization at the interface between numerical and experimental substructures. In this study, a new delay compensation method is proposed for RTHS, which integrates the inverse compensation method (IC) and frequency-domain evaluation index (FEI). Window technique is utilized to enable FEI for calculation of almost instantaneous time delay and the IC parameter is then adjusted accordingly for optimal compensation. The performance of this windowed FEI compensation (WFEI) is evaluated and compared with that of the IC and the adaptive inverse compensation (AIC) through computational simulations of a benchmark model with different initial estimates of time delay. It is demonstrated that the WFEI compensation not only provides accurate actuator control when initial estimated time delay deviates from actual values but also have good robustness under unpredicted uncertainties of the servo-hydraulic system.

Accurate real-time truck simulation via semirecursive formulation and Adams–Bashforth–Moulton algorithm

In this paper, a tailored four-step Adams–Bashforth–Moulton (ABM) algorithm is applied to a semirecursive formulation to perform a real-time simulation of a semitrailer truck. In the ABM algorithm, each integration step involves two function evaluations, namely predictor and corrector. This is fundamentally different when compared to the classic fourth-order Runge–Kutta (RK) integrator approach that contains four function evaluations. A semitrailer truck under investigation is modeled in term of a semirecursive method and simulated by using the presented ABM algorithm. The results show that the four-step ABM method can reduce CPU time almost 50% for solving the truck dynamics with very similar accuracy, in comparison to the fourth-order RK method. The presented ABM algorithm could be used in the semirecursive formulation to carry out accurate real-time simulation of medium-large vehicle systems.

The development of accurate real-time simulation program for reactor

The development of accurate real-time simulation program for reactor

Hybrid modeling of power electronic system for hardware-in-the-loop application

In real-time simulation applications, hardware-in-the-loop (HIL) within nanosecond time step of large size power electronic systems involving high-frequency control strategy is still a big challenge today. In this paper, we propose a new hybrid modeling approach based on a novel nodal analysis and solving method in order to achieve both fast and accurate real-time simulation. The decoupling method allows dealing with circuit element separately regardless the size of power electronic system. After system matrix is obtained, an innovative approach using Cholesky decomposition is proposed. At last, a comparative case study of traction system in the electrical locomotive train is also presented. For this case study, implementations are made on a Field Programmable Gate Arrays (FPGA) Kintex-7 embedded in National Instruments FlexRIO PXIe-7975. Results obtained show that the proposed modeling algorithm can achieve both accuracy and efficiency within a 50ns fixed real-time simulation time step. Besides, the comparison with results obtained from Simpower system in Matlab allows evaluating the accuracy of our proposed modeling approach.

GPU driven finite difference WENO scheme for real time solution of the shallow water equations

The shallow water equations are applicable to many common engineering problems involving modelling of waves dominated by motions in the horizontal directions (e.g. tsunami propagation, dam breaks). As such events pose substantial economic costs, as well as potential loss of life, accurate real-time simulation and visualization methods are of great importance. For this purpose, we propose a new finite difference scheme for the 2D shallow water equations that is specifically formulated to take advantage of modern GPUs. The new scheme is based on the so-called Picard integral formulation of conservation laws combined with Weighted Essentially Non-Oscillatory reconstruction. The emphasis of the work is on third order in space and second order in time solutions (in both single and double precision). Further, the scheme is well-balanced for bathymetry functions that are not surface piercing and can handle wetting and drying in a GPU-friendly manner without resorting to long and specific case-by-case procedures. We also present a fast single kernel GPU implementation with a novel boundary condition application technique that allows for simultaneous real-time visualization and single precision simulations even on large ( > 2000 × 2000) grids on consumer-level hardware - the full kernel source codes are also provided online at https://github.com/pparna/swe_pifweno3.

Real-Time Simulation-Based Multisolver Decoupling Technique for Complex Power-Electronics Circuits

This paper proposes a new method of decoupling and subdividing electrical circuits, containing power-electronics devices, in order to achieve fast and accurate real-time simulation. In this technique, each state variable can be discretized using different discretization methods. Combining implicit and explicit ODE solvers, state-space equations are decoupled while remaining accurate and stable. Unlike most traditional decoupling techniques previously proposed, the proposed one does not require artificial delay or supplementary states to be added in order to decouple the system. Furthermore, this technique is meant to be implemented with commercially available simulation software. By doing so, a large and complex circuit containing several hundreds of state variables can be easily and accurately simulated with minor modification to the existing models. Finally, stability and accuracy of the proposed technique are thoroughly demonstrated in a numerical example during steady state and under faulty conditions.

Real-time simulation dynamics model and solution algorithm for the trolley-hoisting system in container crane simulated training system

The development of simulated training system (simulator) for container crane has made some progress; however, there are still problems in insufficient training function (e.g. the container spreader alignment skill training, one of the most important skill in conventional terminals) and lack of dynamic sense of immersion. In this paper, the technical status of container crane simulator is summarized and the state of art of dynamics model and its solution algorithm for container crane is reviewed. It is pointed out that establishing an accurate real-time simulation dynamics model and studying an efficient algorithm under certain calculation accuracy is the key problem of enhancing immersion, reality and training effect of the simulator. With reasonable simplification and hypothesis, the dynamic equilibrium equations of the trolley-hoisting system are established, further considering the characteristics of the mechanical and electrical transmission system of the crane and also the external mean wind load. Based on the four order Runge-Kutta method by MATLAB programming, the fast solution to the two order ordinary differential equations is realized on personal computer, and the three dimensional (3D) space swing time-history response of the container spreader can be obtained in real-time. The results of numerical calculation are consistent with the actual situation, thus, this study provides a feasible technical route for the real-time dynamics simulation in the container crane simulated training system.

Comparison of delay compensation methods for real-time hybrid simulation using frequency-domain evaluation index

The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods (i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation) are selected and compared experimentally using a frequency evaluation index (FEI) method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer function approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.

Virtual cutting of deformable objects based on efficient topological operations

Virtual cutting of deformable objects is at the core of many applications in interactive simulation and especially in computational medicine. The ability to simulate surgical cuts, dissection, soft tissue tearing or micro-fractures is essential for augmenting the capabilities of existing or future simulation systems. To support such features, we combine a new remeshing algorithm with a fast finite element approach. The proposed method is generic enough to support a large variety of applications. We show the benefits of our approach evaluating the impact of cuts on the number of nodes and the numerical quality of the mesh. These points are crucial to ensure accurate and stable real-time simulations.