Current Inverter Research Articles

Systematic Analysis Based on the Optimal Design of Photovoltaic Inverter Circuit

As a clean and renewable energy source, solar energy is of great significance to reduce greenhouse gas and harmful gas emissions, stabilize energy supply, promote industrial innovation, and help achieve sustainable development and carbon neutrality goals. In this paper, the structure and working principle of photovoltaic cells are introduced, and the characteristics of solar photovoltaic cells and thin film photovoltaic cells are compared and analyzed. Then, the application scenarios of solar photovoltaic power generation and thin film photovoltaic power generation are compared, and the future development direction of photovoltaic cells is prospected. Finally, the structure and working mechanism of the inverter circuit are introduced, some problems in the current photovoltaic inverter circuit are summarized, and then some optimization design of photovoltaic inverter circuit based on the maximum power point tracking technology and leakage current related problems are analyzed, and suggestions on how to optimize the design of photovoltaic inverter circuit are given.

Transient Stability Enhancement of Current Limited-GFM Inverters Based on Varying Virtual Impedance

Transient Stability Enhancement of Current Limited-GFM Inverters Based on Varying Virtual Impedance

High-speed voltage level-up shifter with wide range conversion for system-on-chip applications

Abstract The purpose of this investigation is to demonstrate a level shifter circuit that enhances voltage switching capacity while simultaneously reducing latency by employing a cascaded current mirror, input, and output inverters. We improved our design using multi-threshold complementary metal-oxide semi-conductor (MTCMOS) technology by adding stackable transistors, super-cutoff mechanisms, and cascaded techniques. The level shifting between voltage ranges of 0.3 V and 2.0 V is accomplished by the proposed level shifter. Our design has been fine-tuned to meet the needs of system-on-chip applications by meticulously optimizing performance characteristics like energy usage, latency, and space utilization. The proposed level shifter has an area of 6.936 μm2 and a power consumption of 17 nW, with a delay of 90.64 ps. The proposed work has been done on the Cadence Virtuoso Tool using 45 nm technology. Our suggested level shifter is more effective than earlier methods in terms of latency and conversion range. In addition to delivering considerable reductions in space and power consumption, the suggested design promises a 50-fold increase in operating speed.

Overload mitigation for grid-forming inverters in islanded microgrids with synchronous generators

The prevalence of inverter based resources (IBRs) in microgrid applications continues to increase. However, energy storage remains costly and so parallel operation of IBRs and synchronous generators (SGs) is expected for microgrids requiring sustained, independent operation. Grid-forming (GFM) control for inverters can improve frequency stability in these low inertia environments, but only if poor transient load sharing does not cause the GFM IBRs to exceed current or power limits as demonstrated in recent literature. In this paper, an overload mitigation strategy for GFM IBRs to address the poor transient load sharing problem is proposed. The approach includes several key aspects. First, closed loop control of inverter currents without integrating a phase locked loop is used. Second, the logic of the mitigation strategy is designed to be non-intrusive so that proportional load sharing through GFM operation resumes following the event. Last, the overload mitigation strategy is validated in several simulations with both switching device and average value models of inverters using RTDS. The simulation results demonstrate successful mitigation of overloads and seamless integration of the strategy in-spite of the high level of penetration of IBRs in the study system.

Adaptive Generalized Extended State Observer for a Single Phase PV Grid-connected System Operating Under the Sudanese-Sahelian Climate of Cameroon

Knowing the health of a system allows to guarante its efficiency and sustainability. The state observer is one of several techniques used by authors to estimate system state. This paper focuses on the problem of simultaneous states estimation of DC (Direct Current) and AC (Alternating Current) sides of a single-phase Photovoltaic (PV) grid-connected operating under the Sudanese-Sahelian climate of Cameroon. A generalized extended state observer (GESO) has been designed to simultaneously estimate the three states and the three disturbances of the system. A good estimation of the state and disturbances is achieved by the appropriate choice of the observer gain and the disturbance compensation gain resulting from the correct pole placement. The GESO robustness has been tested by varying the PV voltage and grid voltage. When there are no input fluctuations, the estimation errors of nominal states and disturbances converge to zero. The fluctuation in PV voltage resulting from partial shading has a significant impact on the boost converter current. The boost converter current varies proportionally with the drop in voltage due to partial shading from 55% to 59%. Under the grid voltage fluctuation, the boost converter current remains stable while the DC bus voltage and inverter current are significantly affected. The proposed GESO prove its robustness to perturbations from the PV array and grid side into the Single-Phase PV Grid-connected System. This paper contributes to the study of observers applied to the PV system and points the way to future work on diagnosing faults in PV systems operating in Cameroon's Sudanese-Sahelian climate.

LCL APF control strategy based on model predictive control

In order to further control harmonic current in distribution network, a LCL APF control strategy based on model predictive control is proposed. Firstly, APF mathematical model is established. Then, a multi-objective optimization model predictive control strategy (MPC) is proposed, which comprehensively considers the performance of AC side and DC side of APF. This strategy solves the delay problem existing in the existing MPC strategy: while improving the performance of APF, there is no need to set weight factor; Then, Kalman filter is used to predict the inverter current, thus simplifying the APF measurement system. Finally, the simulation results show that the proposed control strategy can simplify the measurement system and make APF have stronger harmonic suppression ability when it only participates in power conversion and better active filter performance when it participates in harmonic control.

Comprehensive analysis of faults and diagnosis techniques in cascaded multi-level inverters

Reliability is a crucial factor to consider for multi-level inverters (MLIs) used in industrial applications. With the increasing number of power semiconductor devices, the potential for defects to significantly degrade the overall system is heightened. A highly effective fault-detection technique is required to minimize the impact of faults. This paper provides a comprehensive overview of the fundamental principles of multi-level inverters and the various sorts of faults that can occur in multi-level inverters. This study provides a comprehensive analysis of five-level cascaded H-bridge multilevel inverters (MLIs) under both normal and defective conditions. The paper outlines a fault-detection method that utilizes total harmonic distortion and a normalized output voltage factor. In addition, the paper discusses a fault-isolation strategy that relies on reducing amplitude modulation. This method leads to the development of a fault-tolerant inverter. The utilization of level-shifted pulse-width modulation (LSPWM) technology is employed for the purpose of switching operations. LSPWM is the most appropriate technique for MLIs that require a low amount of computational resources. The fault-diagnosis approach given is suitable for MLI-based drives, grid-connected operations, and other applications. This paper presents a comprehensive examination of the 5L-CMLI (5-Level Cascaded Multi-Level Inverter) under various fault scenarios in CMLI. Subsequently, various fault diagnosis approaches will be examined, including their advantages and disadvantages. The paper discusses several defects that can occur in the Insulated Gate Bipolar Transistor (IGBT) of a Current Mode Logic Inverter (CMLI), and also presents a design for a reliable fault diagnosis system. Furthermore, this analysis examines several fault detection strategies in CMLI, categorized according to open-loop and closed-loop dynamic systems fault classifications.

Microstructural Investigation and Mechanical Properties of Resistance Spot Welding Joints of Mild Steel Sheets

Due to its high productivity, low cost, and increased work efficiency, resistance spot welding (RSW) can instantly join two or more steel sheets and it is widely used in the automotive industry and lately in the manufacturing of thin-walled cold-formed steel constructions. However, the RSW of zinc-coated mild steel sheets presents metallurgical challenges, especially when different thickness combinations are used. Therefore, in the present paper a resistance welding machine was used which uses direct current (MFDC) inverter technology combined with SMART AUTOSET technology to weld S250 GD and S350 GD galvanised mild steel sheets with different thicknesses. It is well known that, due to the elevated temperature that occurs during the welding process, followed by rapid cooling, defects such as cracking, porosity, lack of fusion, and an increased amount of brittle phases affect the welding quality. Therefore, the influence of the RSW process parameters established by an automatic sequence on the nugget geometry, microstructure, and mechanical properties was investigated. The phase transformations that took place during the heating-cooling cycle were analysed in detail through metallographic studies. The results showed that the microstructure of the weld nuggets was similar, characterised by columnar grains elongated in the direction of heat evacuation. Nevertheless, there were differences in terms of phase dispersion, defects and mechanical properties that have been linked to the RSW process parameters.

A RANDOMIZED CARRIER-BASED DISCONTINUOUS PULSE WIDTH MODULATION STRATEGY FOR NEUTRAL POINT CLAMPED THREE-LEVEL INVERTER

This article introduces a novel approach called randomized carrier-based discontinuous pulse width modulation (RCDPWM) to address the challenge of mitigating both low-order and high-order harmonics concentrated at the switching frequency and its integer multiples in the output voltage and current of a three-level inverter. The proposed strategy reduces switching losses and a wide dispersion of voltage and current harmonics with significantly smaller amplitudes by integrating features from discontinuous and randomized PWM methods. This characteristic proves beneficial for enhancing efficiency and electromagnetic compatibility. The RCDPWM strategy involves three schemes: two simple schemes (one random parameter), randomized pulse position modulation (RPP-DPWM) and randomized carrier frequency modulation (RCF-DPWM), and a dual scheme combining the two previous ones (RPPRCF-DPWM). Power spectral density (PSD) is used to assess the effectiveness of the proposed strategy in quantitatively analyzing the harmonic dispersion degree. The results demonstrate that the proposed RCDPWM strategy significantly expands harmonic clusters around the switching frequency, reducing its intensity. The spectrum analysis revealed that the RPPRCF-DPWM scheme is the most effective in spreading the output voltage and current spectrum compared to simple schemes (RPP-DPWM and RCF-DPWM).

An Improved Class-E Current Inverter With Two Coupled Inductors for Isolation and Power Scaling Without Affecting Switch Voltage Stress

An Improved Class-E Current Inverter With Two Coupled Inductors for Isolation and Power Scaling Without Affecting Switch Voltage Stress

An Ultra-Low-Voltage Approach to Accurately Set the Quiescent Current of Digital Standard Cells Used for Analog Design and Its Application on an Inverter-Based Operational Transconductance Amplifier

An approach to design analog building blocks based on digital standard cells is presented in this work. By ensuring that every CMOS inverter from a standard-cell library operates with a well-defined quiescent current and output voltage, the suggested method makes it possible to construct analog circuits that are resistant against PVT variations. The method uses the local supply voltages connected to the source terminals of the p-channel and n-channel MOS transistors of the standard-cell inverters as control inputs. It is based on adaptive supply voltage generator (ASVG) reusable blocks, which are comparable to those used in digital applications to handle process variations. All of the standard-cell inverters used for analog functions receive the local supply voltages produced by the ASVGs, which enable setting each cell’s quiescent current to a multiple of a reference current and each cell’s static output voltage to an appropriate reference voltage. Both the complete custom design of the ASVG blocks and a theoretical study of the feedback loop of the ASVG are presented. An application example through the design of a fully synthesizable two-stage operational transconductance amplifier (OTA) is also provided. The TSMC 180 nm CMOS technology has been used to implement both the OTA and the ASV generators. Simulation results have demonstrated that the proposed approach allows to accurately set the quiescent current of standard-cell inverters, dramatically reducing the effect of PVT variations on the pmain performance parameters of the standard-cell-based two-stage OTA.

Control and Stability of Grid-Forming Inverters: A Comprehensive Review

The large integration of inverter-based resources will significantly alter grid dynamics, leading to pronounced stability challenges due to fundamental disparities between inverter-based and traditional energy systems. While grid-following inverters (GFLIs) dominate current inverter configurations, their increased penetration into the grid can result in major stability issues. In contrast, grid-forming inverters (GFMIs) excel over GFLIs by offering features like standalone operation, frequency support, and adaptability in weak grid scenarios. GFMIs, unlike GFLIs, control the AC voltage and frequency at the common coupling point, impacting the inverter dynamic response to grid disturbances and overall stability. Despite the existing literature highlighting differences between GFLIs and GFMIs and their control strategies, a comprehensive review of GFMIs’ stability and the effects of their control schemes on grid stability is lacking. This paper provides an in-depth evaluation of GFMIs’ stability, considering various control schemes and their dynamics. It also explores different types of power system stability, introduces new stability concepts that correspond to power grids with integrated inverters, i.e., resonance and converter-driven stability, and reviews small-signal and transient stability analyses, which are the main two types of GFMI stability studied in the literature. The paper further assesses existing studies on GFMI stability, pinpointing research gaps for future investigations.

An advanced integral sliding mode controller design for residual current compensation inverters in compensated power networks to mitigate powerline bushfire hazards

AbstractThis work deals with designing an advanced integral sliding mode controller (AISMC) for residual current compensation (RCC) inverters connected with arc suppression coils to compensate for power distribution networks where the main idea is to alleviate hazardous circumstances caused by electric faults on powerlines. The key advancement in the proposed AISMC over traditional sliding mode controllers is the utilization of an improved exponential reaching law which ensures the faster convergence of the desired control objective that is the fault current compensation in this particular application. An improved exponential reaching law (IERL) used in this work is a combination of the exponential and constant‐proportional reaching laws (while existing approaches use constant reaching laws) which assists to minimize the current injection error through the RCC inverter in the steady‐state. The integral action in conjunction with the exponential function in the sliding surface, based on which the proposed controller is designed, helps to eliminate the chattering effects in a quickest way that can be evidenced from the settling time and percentage overshoot. The feasibility of the proposed AISMC is theoretically assessed by analyzing the stability using the Lyapunov stability theory. Simulation and processor‐in‐loop results further justify the theoretical foundation by confirming the desired current injection and compensating voltage and current due to the fault. Finally, results are compared with a TIMSC for demonstrating the superiority of the AISMC.

Virtual voltage control to redistribute reactive power of generators in a microgrid

The paper examines a strategy for managing voltage control in a microgrid by redistributing reactive power among its distributed generators. Unlike traditional droop control, the new control approach can provide a more accurate reactive power response based on a virtual impedance that helps calculate a virtual voltage. In addition, this virtual impedance is employed for the current controller inverter to improve the results. The adaptive virtual voltage control works well to provide active and reactive power. The proposed control works effectively by balancing the active and reactive power of the grid and maintains the fundamental frequency. The control technique assists the new microgrid (MG) in adapting the operation effectively and redistributing the active and reactive power.

Control strategy for current limitation and maximum capacity utilization of grid connected PV inverter under unbalanced grid conditions

Under grid voltage sags, over current protection and exploiting the maximum capacity of the inverter are the two main goals of grid-connected PV inverters. To facilitate low-voltage ride-through (LVRT), it is imperative to ensure that inverter currents are sinusoidal and remain within permissible limits throughout the inverter operation. An improved LVRT control strategy for a two-stage three-phase grid-connected PV system is presented here to address these challenges. To provide over current limitation as well as to ensure maximum exploitation of the inverter capacity, a control strategy is proposed, and performance the strategy is evaluated based on the three generation scenarios on a 2-kW grid connected PV system. An active power curtailment (APC) loop is activated only in high power generation scenario to limit the current’s amplitude below the inverter’s rated current. The superior performance of the proposed strategy is established by comparison with two recent LVRT control strategies. The proposed method not only injects necessary active and reactive power but also minimizes overcurrent with increased exploitation of the inverter’s capacity under unbalanced grid voltage sag.

Development of Improved Low-leakage Current H6 Single-Phase Full-Bridge Inverter Topology

Objective: To minimize leakage current in non-isolated photovoltaic grid connected inverters. Methods: The circuit design integrates extra switches and modifies the switch drive signals at the midpoint of the DC bus voltage, altering the common-mode current path. Findings: The proposed topology exhibits significant potential for widespread adoption, finding practical applications in diverse industrial settings as well as in residential use. Novelty: The suggested method implies that the topology presents distinctive or beneficial characteristics in contrast to current solutions, rendering it especially promising for a range of industrial and residential applications. This novelty may arise from enhancements in efficiency, cost-effectiveness, scalability, versatility, or other favorable attributes that distinguish it from traditional approaches. Moreover, Simulation outcomes distinctly demonstrate a noteworthy decrease in leakage current within the refined topology when contrasted with both the H5 topology and the High Efficient and Reliable Inverter Concept (HERIC) topology. This compelling evidence affirms the effectiveness of the proposed configuration in proficiently mitigating leakage current. Keywords: Photovoltaic, Common Mode Voltage, Leakage Current, Grid Connected Inverter

Overlap Time Compensation and Characteristic Analysis for Current Source Photovoltaic Grid-Connected Inverter

In the current source photovoltaic grid-connected system, to prevent the DC-link inductor from incurring an opening circuit fault, it is necessary to include the overlap time in the switching signals. However, current error and serious harmonic distortion in the inverter-side and grid-side currents are generated, which will cause additional losses and reduce the power quality of the grid, so it is important to compensate for the current error caused by the overlap time. In this paper, the relationship between the nonlinear current errors caused by the overlap time and the AC-side voltage is analyzed. Then, the mathematical expression of the low-order harmonics with losses caused by the overlap time is derived. On this basis, a current error compensation method with a discrete filter of AC-side voltage is proposed. Finally, a simulation and experiment are carried out to verify the correctness and effectiveness of the theoretical analysis and compensation scheme presented in this paper. With an overlap time of 3 μs, the THD of the grid-side current decreases from 5.93% to 1.59% after compensation.

An Open-Circuit Fault Diagnosis Method for Three-Level Neutral Point Clamped Inverters Based on Multi-Scale Shuffled Convolutional Neural Network.

This study constructs a power switching device open-circuit fault diagnosis model for a three-level neutral point clamped inverter based on the multi-scale shuffled convolutional neural network (MSSCNN) and extracts and classifies the fault information contained in the output current of inverters. The model employs depthwise separable convolution and channel shuffle techniques to improve diagnostic accuracy and reduce model complexity. The experimental results show that the new model has lower model complexity, better noise resistance and higher average diagnostic accuracy compared with fault diagnosis models based on CNN, ResNet, ShuffleNet V2 and Mobilenet V3 networks.

Development of method for frequency regulation of output current in high-voltage transformerless resonant chargers of capacitive energy storage devices

The object of research is high-voltage systems of electric discharge installations for various technological purposes. The work reports solving the problem of enabling the rate of charging of a capacitive energy storage, set by the requirements of a certain high-voltage technology. The quantitative characteristics of the deviation of the output current of the resonant inverter from the set stabilized value when changing the switching frequency of inverter switches in the range of output voltage change from 0 to 20 kV were determined. Using the Fourier transform of the rectangular input voltage, the frequency regulation possibility of the output current of the charger for capacitive energy storage devices was analyzed. Estimation dependences of the output current of resonant inverter on the load resistance and frequency deviation from resonant frequency were derived. These dependences could be used to implement frequency control over the switching inverter transistors, with the help of which the given effective value of the output current of the resonant inverter is obtained. A method of frequency regulation of the output current in high-voltage transformerless resonant charging devices of capacitive energy storage devices has been developed. Special feature of this method is that it is based on the frequency dependence of reactive resistances of the inductance and capacitance of the resonant circuit connected in series. Owing to that, it makes it possible to adjust the switching frequency of the inverter’s power switches depending on the relative resistance of the load and the specified growth rate of the capacitive energy storage voltage. The results reported here could be used in the design of benches for testing the electrical strength of high-voltage cables, as well as for the construction of high-voltage transformerless chargers in systems of electric discharge impulse processing of materials

Model Predictive Control of Counter-Rotating Motors for Underwater Vehicles Considering Unbalanced Load Variation

The propulsion system for underwater vehicles, driven by a counter-rotating permanent magnet synchronous motor (CRPMSM), can enhance the operational stability and efficiency of the vehicle. Due to the influence of complex underwater flows, the load imbalance of CRPMSM’s dual counter-rotating rotors may lead to severe issues of dual-rotor desynchronization rotation. Combining traditional vector control (VC) with master-slave control strategies can address the desynchronization problem when CRPMSM’s load changes. However, it results in significant speed fluctuations and a long transition time during the transition from load disturbance to synchronous rotation. This paper introduces a model predictive control (MPC) strategy to effectively resolve this issue. The incremental MPC model is established based on the mathematical model of CRPMSM in the dq coordinate system. The predictive control system forecasts the d- and q-axis components of stator currents for the next four control cycles. It selects the optimal control increments to minimize the cost function based on current predictions and different inverter voltage states. The obtained optimal d- and q-axis components of stator voltage are used to control CRPMSM under unbalanced load disturbances. Simulation results demonstrate that, compared to the VC strategy, CRPMSM utilizing the MPC strategy exhibits better dynamic performance with faster speed response and reduced torque fluctuations during load and speed variations.