Inverted Model Research Articles

Comparison and Selection of Grid-Tied Inverter Models for Accurate and Efficient EMT Simulations

This article compares five modeling methods of grid-tied inverters for the electromagnetic transient simulation of power system, clarifies their differences, and discusses the suitable model for each simulation purpose. The comparison was made under the same conditions between the conventional switching model, and four simplified models—voltage interpolation, average-value, controlled current-injection, and simplified current-injection model. The comparison of the simulated waveforms clarifies the behaviors that can be simulated and cannot be simulated by each simplified model. The comparison of the computing time reveals the significant decrease of the computing time by selecting the proper simplified modeling method. Based on these comparisons, this article discusses the selection of the modeling methods for each simulation purpose to perform simulations accurately and efficiently.

An improved method of phase-locked loop grid-connected inverter based on capacitor voltage full feedforward

Different from the conventional grid voltage feedforward, the capacitive voltage type full feedforward will not amplify high frequency harmonics, and it can eliminate the capacitor current control and simplify the controller design. However, when the grid impedance is relatively large, the phase-locked loop may increase the current harmonics of the grid-connected inverter, leading to system instability. Therefore, this paper establishes the output impedance model of the grid-connected inverter with full feedforward capacitor voltage including phase-locked loop, and then proposes an improved strategy for adding a low-pass filter in the traditional phase-locked loop, and parameterizes it *Design, so as to achieve the purpose of improving the output impedance phase of the inverter. Finally, the simulation verifies that the inverter using the improved phase-locked loop can effectively improve the quality of the grid current and improve the stability of the inverter system in a weak grid.

Level-Shift PWM Control of a Single-Phase Full H-Bridge Inverter for Grid Interconnection, Applied to Ocean Current Power Generation

A small prototype of a 5-level single-phase full H-bridge inverter for ocean current applications is presented. The inverter was designed applying level-shift control in pulse-width modulation (LS-PWM), and experimental tests were conducted using a variety of modulation subschemes, including in-phase disposition (IPD), alternate-phase opposition–disposition (APOD), and phase opposition–disposition (POD). The test results were examined for harmonic content and voltage total harmonic distortion (THDV). The results suggest that the inverter presents a viable solution with significant potential for the development of a larger three-phase inverter model that can be used to connect ocean current power sources to the electrical grid.

4D inversion of resistivity monitoring data with adaptive time domain regularization

The time-lapse or 4D inversion aims to image significant underground changes and efficiently suppress inversion artefacts. However, the inverted model changes are frequently over-smoothed along the time-axis. Particularly in cases where models have poor resolution, even significant model changes are severely blurred or blunted in the reconstructed image. In this study, we developed a new 4D inversion algorithm that automatically determines time domain (TD) regularization based on model changes and the resolution to achieve a more accurate interpretation of resistivity monitoring data. By assigning a smaller TD constraint to model parameters with poor resolution, model changes at depth can be imaged if the models are significantly changed over time. Moreover, TD regularization was adaptively adjusted according to the TD error roughness, which can effectively control model smoothness. We conducted inversion experiments on synthetic and field data to test the performance of the proposed inversion algorithm. The inversion results for synthetic data demonstrated that the 4D inversion with adaptive TD regularization yields the model change that is most similar to the true change, among various options of TD regularization. The adaptive 4D inversion confirmed its capability to clearly image widespread and locally confined model changes. Model changes with poor resolution could likewise be imaged. Finally, the applicability of the proposed 4D inversion algorithm was demonstrated with real resistivity monitoring data collected for leakage detection at an embankment dam in Korea.

An Invertible Dynamic Graph Convolutional Network for Multi-Center ASD Classification.

Autism Spectrum Disorder (ASD) is one common developmental disorder with great variations in symptoms and severity, making the diagnosis of ASD a challenging task. Existing deep learning models using brain connectivity features to classify ASD still suffer from degraded performance for multi-center data due to limited feature representation ability and insufficient interpretability. Given that Graph Convolutional Network (GCN) has demonstrated superiority in learning discriminative representations of brain connectivity networks, in this paper, we propose an invertible dynamic GCN model to identify ASD and investigate the alterations of connectivity patterns associated with the disease. In order to select explainable features from the model, invertible blocks are introduced in the whole network, and we are able to reconstruct the input dynamic features from the network's output. A pre-screening of connectivity features is adopted to reduce the redundancy of the input information, and a fully-connected layer is added to perform classification. The experimental results on 867 subjects show that our proposed method achieves superior disease classification performance. It provides an interpretable deep learning model for brain connectivity analysis and is of great potential in studying brain-related disorders.

Joint Control Strategy of Microgrid Inverter Based on Optimal Control and Residual Dynamic Compensation

With the continuous development of microgrid, the inverter under traditional PID control is difficult to meet the power quality requirements of microgrid. In order to improve the anti-interference ability and transient response speed of the output voltage of Isolated AC microgrid inverter, a dynamic compensation control structure combining linear quadratic optimal control and disturbance residual generator is proposed in this paper. Firstly, the quadratic optimal controller is established based on the inverter model. Secondly, the residual generator is established to observe the residual value of the disturbed system. Then, the dynamic compensation controller is designed according to the superposition principle, and a control signal opposite to the influence caused by the disturbance is output at the output of the controller. The disturbance signals can cancel each other without knowing the specific disturbance form. Finally, the experiments of load switching, three-phase imbalance and nonlinear load are designed on MATLAB/Simulink simulation software to verify the effectiveness of the control strategy proposed in this paper.

Mathematical Model of Frequency Inverter with Autonomous Voltage Inverter

An analytical analysis of the processes occurring in the systems of an electric drive with a frequency converter, which are characterized by discrete, nonlinear properties, is practically impossible. This predetermines the need to use methods of mathematical modeling and mathematical experiment to study the properties of such systems. Purpose of the work: building a model of a frequency converter with formalization in the form of mathematical relationships of the relationships between the variables characterizing its functioning, based on the analysis of physical processes in each of its elements. Mathematical models of each element must be represented by structural diagrams, which are subsequently combined into a common block diagram of the frequency converter in accordance with the method of structural modeling. Research methods: to solve the set tasks, the methods of the theory of electronics and electrical engineering, induction devices and the concept of switching functions were used. Software implementations of the proposed mathematical models and numerical studies of the processes reproduced by them were performed in the MATLAB computing environment (SIMULINK application software package). Results: the method of structural modeling made it possible to create a fairly universal and flexible version of a complete mathematical model of a frequency converter, due to the possibility of a fairly simple inclusion in it of various options for mathematical models of elements included in a specific real frequency converter. In this case, the resulting model preserves the topology of a real frequency converter and the observability of all its real physical variables. The use of the theory of induction devices and the concept of switching functions made it possible, on a single methodological basis, to create physically and mathematically grounded mathematical models of all the main elements of the frequency converter. The constructed model makes it possible to clarify the relationship between the physical variables of the individual elements of the frequency converter and their mutual influence

Hamilton-Based Stability Criterion and Attraction Region Estimation for Grid-Tied Inverters Under Large-Signal Disturbances

As the crucial interface of renewable energy integration, the stable operation of power converters under grid faults and external disturbances has become much more important. However, synchronization instability of grid-tied inverters has been found caused by the phase-locked loop (PLL) under some critical operating conditions, such as the grid voltage sag, current surge, and transmission line faults. Due to the strong nonlinearity, transient stability analysis of inverters with PLL becomes much more complicated under large-signal perturbations and weak grid conditions. In this article, the large-signal synchronization stability of grid-tied inverters is investigated from the energy perspective. Based on the structural resemblance between the PLL and synchronous generator, the energy function is constructed to establish a port-Hamiltonian model for the grid-tied inverter. For the nonlinear inverter system, an explicit Hamilton-based stability criterion is developed for grid-tied converters according to the concept of dissipativity and LaSalle’s theorem. Moreover, the analytical stability boundary is acquired based on the proposed stability criterion and attraction region estimation, covering both controller parameters and grid parameters. To verify the effectiveness of the proposed analysis approach, extensive simulation and experimental results are presented. Compared with the conventional large-signal methods, the proposed Hamilton-based approach has explicit physical meaning and high accuracy.

Power system solution based on root matching method in FPGA environments

Digital electromagnetic transient simulation is an important means to analyze the operation, planning and control of power systems. Numerical integration algorithm is the core of electromagnetic transient simulation analysis. By analyzing the existing electromagnetic transient simulation methods of power systems, it is difficult to solve the numerical oscillation and decoupling problems, and the root matching method is proposed to solve such problems. From the perspectives of basic component modeling methods and basic simulation algorithms, the disadvantages of mainstream algorithms in solving electromagnetic oscillations are analyzed. Combining the calculation and simulation features in FPGA, the three-phase two-level inverter model of the power system built is verified.

보일러 시스템에 적용한 송풍기 개발에 관한 연구

In this paper, a blower with BLDC(Brushless Direct Current, BLDC) moter was developed and applied to the boiler system to linearly control the amount of air with respect to the amount of gas in order to optimize combustion in the boiler system to meet the user’s convenience and eco-friendly needs. The proposed blower structure analysis, controller modeling for controlling the amount of air in the blower, inverter modeling, and BLDC modeling were presented, and blower prototype was actually manufactured and applied to linearly control the boiler system. In the future, it is thought that additional research is needed so that the linear control of the boiler system can be controlled more broadly and more linearly.

Quantitative analysis of DC–DC converter models: a statistical perspective based on solar photovoltaic power storage

Abstract Photovoltaic (PV) systems have paved their way into general households due to their high efficiency, low deployment cost and huge power savings. These advantages combined with Government incentives further assist in wide-scale adoptability of the solar powered systems. PV systems generate direct current (DC) outputs, which needs to be converted into alternating current (AC) via inverters. The efficiency of inverter design decides the overall efficiency of the PV system, which allows effective utilization of the solar power for feeding to grid or for local usage. In order to design effective inverter models, a large number of electrical configurations are designed by researchers over the years. These include, stand-alone inverters, grid-tie inverters, battery backup inverters and hybrid inverters, each of which are further divided into multiple sub-categories. Each of these sub-categories have a different application, for instance, string-converters are used for moderate power applications up-to 150k W, while central converters are used for high power applications above 80k W, etc. Apart from power capabilities, these designs vary in terms of efficiency of conversion, usability, cost, etc. Due to so many parametric variations, effective selection of these converters for a given PV application becomes ambiguous. In order to reduce this ambiguity, the underlying text statistically evaluates performance of some of the most efficient PV converter models, and compares them on the basis of power capabilities, accuracy of conversion, converter used, control model used, etc. This review will assist researchers and system designers to select the best suited models for their given applications, and thus reduce the time needed for efficient PV inverter system design. This text also recommends future research which can be adopted for improving efficiency of these systems.

Design of FPGA-Based SHE and SPWM Digital Switching Controllers for 21-Level Cascaded H-Bridge Multilevel Inverter Model.

Multilevel inverters are a type of power electronic circuit that converts direct current (DC) to alternating current (AC) for use in high-voltage and high-power applications. Many recent studies on multilevel inverters have used field-programmable gate arrays (FPGAs) as a switching controller device to overcome the limitations of microcontrollers or DSPs, such as limited sampling rate, low execution speed, and a limited number of IO pins. However, the design techniques of most existing FPGA-based switching controllers require large amounts of memory (RAM) for storage of sampled data points as well as complex controller architectures to generate the output gating pulses. Therefore, in this paper, we propose two types of FPGA-based digital switching controllers, namely selective harmonic elimination (SHE) and sinusoidal pulse width modulation (SPWM), for a 21-level multilevel inverter. Both switching controllers were designed with minimal hardware complexity and logic utilisation. The designed SHE switching controller mainly consists of a four-bit finite state machine (FSM) and a 13-bit counter, while the SPWM switching controller employs a simple iterative CORDIC algorithm with a small amount of data storage requirement, a six-bit up-down counter, and a few adders. Initially, both digital switching controllers (SHE and SPWM) were designed using the hardware description language (HDL) in Verilog codes and functionally verified using the developed testbenches. The designed digital switching controllers were then synthesised and downloaded to the Intel FPGA (DE2-115) board for real-time verification purposes. For system-level verification, both switching controllers were tested on five cascaded H-Bridge circuits for a 21-level multilevel inverter model using the HDL co-simulation method in MATLAB Simulink. From the synthesised logic gates, it was found that the designed SHE and SPWM switching controllers require only 186 and 369 logic elements (LEs), respectively, which is less than 1% of the total LEs in an FPGA (Cyclone IV E) chip. The execution speed of the SHE switching controller implemented in the FPGA (Cyclone IV E) chip was found to be a maximum of 99.97% faster when compared with the microcontroller (PIC16F877A). The THD percentage of the 21-level SHE digital switching controller (3.91%) was found to be 37% less than that of the SPWM digital switching controller (6.17%). In conclusion, the proposed simplified design architectures of SHE and SPWM digital switching controllers have been proven to not only require minimal logic resources, achieve high processing speeds, and function correctly when tested on a real-time FPGA board, but also generate the desired 21-level stepped sine-wave output voltage (±360 VPP) at a frequency of 50 Hz with low THD percentages when tested on a 21-level cascaded H-Bridge multilevel inverter model.

Estimating the Shear-Wave Velocities of Shallow Sediments in the Yellow Sea Using Ocean-Bottom-Seismometer Multicomponent Scholte-Wave Data

Scholte-wave dispersion analysis is effective at imaging the relatively low shear-wave velocity of shallow marine sediments in marginal seas. The combination of a four-component ocean-bottom-seismometer (OBS) and a towed air-gun source can economically and effectively acquire the marine dispersive seismic data. Extracting higher-order dispersive Scholte wave modes is the most critical problem in the dispersion analysis method. The extremely low shear-wave velocity and severe attenuation in the top hundreds of meters of marginal sea sediment provide an uneven dispersive energy distribution for the four components of the Scholte wave data. The fundamental mode dispersive energy dominates in the vertical component and higher-order modes dominate in the horizontal component. We developed the method of the four-component OBS Scholte velocity-spectra stacking, which can effectively, rapidly, and robustly extract higher-order modes. We imaged the shear-wave velocity structure of complicated shallow marine sediment in the North Yellow Sea using an active OBS seismic profile with a large-volume air-gun array. The fourth higher-order Scholte wave mode can be imaged with the four-component velocity-spectra stacking method with a lower frequency range of 1.0–7.0 Hz. Only the second-order mode can be recognized from the dispersion energy image of the single vertical component. The joint inversion of multimode dispersion curves can provide more accuracy and deeper constraints for the inverted model; thus, the constraint depth with five modes increases by a factor of 1.9 compared with single fundamental mode inversion. The inverted profile suggests a low shear-wave velocity of 123–670 m/s and strong lateral variations within 350 m. The main regional geological structures are shown by the inverted shear-wave velocity structure.

High Performance Single and Double Loop Digital and Hybrid PID-Type Control for DC/AC Voltage Source Inverters

The concept of hybrid control has been introduced, in which the analog implementation of the control algorithm is combined with a digital algorithm for determining the PWM duty cycle. Single-loop PD and PID control systems are compared to a double-loop architecture with additional capacitor current sensing for both digital and hybrid controller realizations. The performance is measured as the THD value under resistor-capacitor rectifier load. It has been shown that a properly constructed continuous-time model of a digital controller with a PWM power converter behaves like the actual discrete-time system, which allows for a simple controller analysis and design. The role of a PWM type for capacitor current feedback is emphasized. The simulation models of a real inverter are presented, which are used to tune the controllers and to evaluate the control performance for both rectifier and abruptly changing resistive load. The obtained solutions achieve the THD values comparable to the VSI without load. The results are contrasted with the control methods based on resonant filters.

Analysis of Some Power Quality Parameters at the Points of Common Coupling of Photovoltaic Plants Based on Data Measured by Inverters

With the increasing implementation of renewable energies, the impact that this type of installation can have on the electricity supply grid is of great importance. In this context, the aim of this work is to analyse how the production and injection of electricity generated by a series of small photovoltaic (PV) installations influence some parameters of the electricity grid in the low-voltage (LV) distribution networks to which they are connected, by analysing the basic data provided by the inverters of these installations. The presence of a slight rise in the grid voltage values in the Point of Common Coupling (PCC) as the production of the PV plants increases has been verified, with maximum slopes between 0.95 and 0.00027 V/kW, but which do not result in voltage values close to the limits set by the regulations. In addition to assessing this impact, the results obtained made it possible to determine the hosting capacity that the networks into which these installations inject their energy would have for this type of installation so as not to have a detrimental effect on the voltage values of the grid. The possible influence of the production of PV installations on the voltage imbalance between phases or on the frequency of the grid has also been analysed in this work. Although the values recorded by the inverters have limitations in their measurements that do not make them valid for assessing events such as the presence of harmonics or flickers, they do allow a first analysis to be made of the influence of PV plant production on some grid parameters, without the need to incorporate additional measurement systems in these renewable installations. However, it is important to be aware of the limitations of the measurements of this equipment and, as far as possible, to choose inverter models that carry out this type of measurement as completely as possible.

Secondary frequency regulation and stabilization method of islanded droop inverters based on integral leading compensator

The microgrid multi-parallel inverters system with droop control strategy will produce microgrid frequency static error due to the reference power mismatch. In order to eliminate the frequency static error caused by droop control as well as enhance the stability of multi droop inverters system, a secondary frequency regulation and stabilization method for multi-parallel droop inverters system based on island operation of the frequency static error integral lead compensator is proposed. The proposed method includes no communication link among inverters. Through the state space modeling of the multi-parallel drooping inverter microgrid system based on the component connection method (CCM), the state space model of multi parallel inverters is established. Parameter design and analysis are carried out accordingly. The state space model of the load is also established with transfer function-state space mapping method as a comparison. The method proposed in this paper can effectively enhance the small signal stability of the system while realizing the frequency error-free operation of multiple parallel droop inverters. To verify the method proposed in this paper, MATLAB/Simulink simulation is conducted to compare the proposed method with the method based on communication consensus algorithm and proves the effectiveness of the proposed method and at the same time.

Power inverters for solar panels

Wind turbines have a lifespan of 15-20 years on average. They have high initial costs and a lot of moving parts, which leads to a lot of wear and tear, decreased efficiency, and high maintenance needs over time. Solar energy, on the other hand, is now the most abundant and reliable source of renewable energy. This research has been aimed at building a solar panel-based electrical system suited for rural locations. A model of a power inverter has been created in this paper which accepts DC input from a basic solar panel and outputs 150 Volts, which has been proven to be excellent for satisfying lighting needs in rural areas.

Near-Surface Characterization Using High-Speed Train Seismic Data Recorded by a Distributed Acoustic Sensing Array

A high-speed train can be regarded as a moving seismic source when it travels along a railway. Seismic waves from such sources have strong energy and can be used for near-surface characterization, safety monitoring of high-speed railways, and detection of urban underground spaces. Distributed acoustic sensing (DAS) is a newly developed seismic acquisition technology. It has attracted widespread attention due to its advantages of low cost, high sensitivity, high efficiency, and dense sampling. This study investigated near-surface characterization using high-speed train seismic data recorded by DAS. The data were processed to obtain surface waves by seismic interferometry. Thereafter, the extracted surface waves were inverted to obtain the near-surface shear-wave velocity model using a multichannel analysis method. The inverted model is consistent with the subsurface geology of the study area. Our results demonstrate the effectiveness and reliability of DAS-based acquisition and data analysis in near-surface characterization using the high-speed train type of moving sources.

Forward Modeling Steady-State Free Precession in Surface NMR

In efforts to map water at depth, steady-state free-precession (SSFP) sequences promise to rapidly increase data acquisition rates in the practice of surface nuclear magnetic resonance (NMR). Unlike conventional surface NMR excitation schemes, pulses in SSFP are transmitted so frequently that the nuclear magnetization of hydrogen in water can not return to its natural alignment with the earth’s ambient magnetic field, and instead achieve a steady-state; a dynamic equilibrium between pulses. Unfortunately, the traditional formulations of SSFP sequences and the full surface NMR forward models are not immediately compatible with each other. Firstly, the traditional analysis of SSFP sequences assume that relaxation during pulse (RDP) effects are negligible, which is not always valid in surface NMR. Secondly, even for single pulse measurements, the surface NMR forward model can be computationally demanding; this challenge scales with the number of pulses. Here we investigate the incorporation of RDP effects on the dynamic equilibrium of SSFP measurements. This is then incorporated into the full surface NMR forward model by deriving analytical expressions to directly predict processed surface NMR data. The model is validated by jointly inverting an extensive and diverse suite of SSFP measurements; 12 distinct sequences each with 16 pulse moments. The inverted model has a data misfit of 0.99 and is consistent with models derived from standard NMR data. The ability of our forward model to reproduce diverse signals and jointly invert them is a strong indication of its validity.

Modeling H-bridge inverter based on PI control and its nonlinear dynamic behaviour

In the H-bridge inverter, the control and circuit topology parameters are the key factors affecting its dynamic stability, and the changes of each parameter have different effects on the stability of the system. This paper takes the current-controlled first-order H-bridge passive inverter based on PI control as the research object. Firstly, based on the different modal of the circuit, an accurate discrete iterative mapping model of the H-bridge inverter is derived according to the stroboscopic mapping principle. Then iterate through the above iterative formula, after retaining the data of the current peak value, the dynamic bifurcation diagram on the control parameters of the system is obtained, with the bifurcation behavior and stable working area of the system being analysed when the control parameters change, and verified by the current folding diagram the correctness of the analysis. Finally, according to the same method, the influence of other parameters on the system stability is studied. The research results show that when different parameters change, there are critical maximum or minimum values to keep the system running stably.