Current Inverter Research Articles

CONTRIBUTION TO THE DESIGN OF INVERTER CONVERTERS FOR HEATING AND WELDING AT HIGHER FREQUENCIES

The paper shows a significant contribution to analytical calculations of half-bridge and full-bridge inverter parameters, aiming to facilitate the operating process itself while designing systems like these. Attempts have been made within the well-known literature to precisely calculate the waveforms of characteristic currents and voltages of the inverter. Due to its complexity, exact explicit analytical forms have yet to be found, but instead, approximate forms were found. Large formulae for inverter currents and voltages prevented them from being used as an inverter project solution. The paper deals with simple analytical dependences for inverters, with a necessary accuracy from the aspect of engineering practice, that can also be directly implemented into calculations for characteristic inverter components and parameters. To confirm the new analytical expressions and method, the paper presents two interesting inverters that can be applied.

Maximizing photovoltaic system power output with a master-slave strategy for parallel inverters

Parallel inverters are commonly used for connecting photovoltaic (PV) and other renewable energy sources to Microgrids (MGs). One of the greatest challenges in MG operation is maximizing the PV system's performance while also enhancing the MG's reliability and efficiency. The PV inverters waste power if the shared load power is less than their maximum output power. When shared load power surpasses the PV inverter's maximum output power, the system may become unstable since PV sources are intermittent. This study proposes a master-slave control system for controlling parallel inverters connected to a PV system. The master inverter is connected to Energy Storage Devices (ESDs) and is responsible for maintaining stable voltage on the load bus. The PV units are connected via slave inverters and are managed using a dual-loop Proportional Integrator Derivative (PID) control approach, with the outer loop maximizing solar panel output. The system is built on a Direct-Quadrature-Zero (d-q-0) inverter architecture, and the controller guarantees that all inverter currents remain in phase to reduce circulating current and enhance overall system efficiency. The simulation model evaluates a system comprising three inverters, with the master inverter powered by ESDs. The PV Units power the other two Slave Inverters. The system is evaluated using four case studies featuring various load and radiation change scenarios. The results demonstrate that the system is highly reliable and operationally efficient, with the absence of circulating currents among the inverters. Moreover, the system is capable of precisely monitoring the MPPs of PV modules with 100% efficiency and a minimal 0.002% fluctuation, while also responding to changes in under 50 ms.

Improved scheme based on memory voltage for transformer differential protection considering the effects of PLL

AbstractThe phase‐locked loop (PLL) is a critical control module applied in the control system of renewable energy sources (RESs) to synchronize with the grid voltage. When a fault occurs, the dynamic response process of the PLL will generate a phase locking error, resulting in a mass of harmonic components in the fault current of the PV inverter, which further poses challenges to transformer differential protection. To address the challenges posed by the phase locking error in practical engineering applications, this paper proposes an improved scheme that uses a digital computer algorithm to record and store the pre‐fault voltage and introduces the limiting coefficient. Firstly, the memory voltage is used to eliminate the phase locking error of the PLL, thereby mitigating harmonic distortion in the fault current of the RESs and ensuring the reliability of the transformer differential protection. In addition, the limiting coefficient is introduced to eliminate the effect of the increased amplitude of the fault current caused by the memory voltage. The voltage reference value of the inverter is multiplied by an appropriate limiting coefficient k and then output to the physical system. Finally, the effectiveness of the proposed scheme is verified by MATLAB/Simulink simulation.

Analysis of harmonics currents in the case of grid connected photovoltaic generator

<p><span lang="EN-US">Nowadays, electrical grid experiences an increase in penetration of single-phase PV generations. Then, it becomes necessary to control this penetration by techniques of synchronization in order to provide electrical energy of good quality to the network. Estimation of the frequency, phase and magnitude of the grid voltage are necessary to correctly synchronizing the PV generator with grid. Connecting a direct current generator to grid via an inverter, requires to fix the performances to improve in the inverter to choose the best-suited topology. This paper describes the control of a non-isolated single-stage single-phase grid-connected inverter fed by a photovoltaic source. In order to define the influence of the three parameters: modulation index, switching frequency and phase shift angle, it is interesting to know the behavior of the system when one of these parameters moves away from its optimal value. Optimal values make it possible to obtain a THD as small as possible to satisfy the international standard. In this work, modulation index and switching frequency are set to their respective optimal values. To study grid current and inverter currents before and after filtering, harmonic analysis is performed for seven shift angles for the same switching frequency (10000 Hz) and modulation index (2.2).</span></p>

Fault compensations in resonant grounded power systems with residual current compensation inverters using an adaptive nonlinear extended state observer‐based model predictive controller

AbstractThis paper proposes a new adaptive nonlinear extended state observer‐based model predictive controller (ANLESO‐MPC) for residual current compensation (RCC) inverters to compensate fault characteristics in resonant grounded power systems (RGPSs). In the proposed scheme, the adaptation feature is used to adapt the adjustable inductor appearing in the dynamical model of RGPSs by satisfying the desired fault current compensation requirement which in turn will ensure the resonance condition. Since the adapted parameter is used in the control signal, the ANLESO‐MPC offers robustness against parameter sensitivity. The neutral voltage is considered as a disturbance and the change in this voltage as an extended state to estimate this disturbance while incorporating the adapted parameter so that the adaptive nonlinear extended state observer (ANLESO) provides robustness against disturbances. Finally, the model predictive controller (MPC) is designed for the RCC inverter utilizing estimated disturbances and adapted parameters to fully achieve the fault current compensation. The performance of the controller is evaluated using simulations in MATLAB/Simulink and OPAL‐RT real‐time platforms under varying fault impedances as the fault characteristics change with variations in the fault impedance. Results are also compared with a conventional MPC where the proposed ANLESO‐MPC seems more effective to compensate fault characteristics.

Analysis of output characteristics of wireless power transfer system based on LCC/S-S hybrid compensation structure

PurposeTo simplify the circuit design and control complexity of the magnetic coupling resonant wireless charging system, the radio energy transmission constant current and constant voltage charging is realized.Design/methodology/approachThe purpose of this study is to simplify the circuit design and control complexity of the magnetic coupling resonance wireless charging system, in order to achieve constant current and constant voltage charging for wireless energy transmission. First, the principle of LCC/S-S compensation structure is analyzed, and the equivalent mathematical model is established; then, the system characteristics under constant current and constant voltage mode are analyzed, and the design method of system parameters is given; finally, a simulation and experimental system is built to verify the correctness and feasibility of the theoretical analysis.FindingsThe results show that the proposed hybrid topology can achieve a constant current output of 2 A and a constant voltage output of 30 V under variable load conditions, and effectively suppress the current distortion problem under light load conditions. The waveform distortion rate of the inverter current is reduced from 33.97% to 10.45%.Originality/valueBy changing the high-order impedance characteristics of the compensation structure, the distortion of the current waveform under light load is suppressed, and the overall stability and efficiency of the system are improved.

A Five-Level Transformer-Less Grid-Tied Inverter Structure With Capacitive Voltage Divider Concept With Leakage Current Elimination

This paper presents a novel single-phase inverter with six switches and five levels that shares a common ground and does not require a transformer. The proposed inverter is intended for use in photovoltaic systems that are connected to the grid. The proposed inverter is derived from the concept of a capacitive voltage divider (CVD) circuit, so that, the leakage current will be eliminated. The CVD circuit produces three levels of output voltages in the proposed inverter. The proposed novel inverter has several significant advantages, such as the elimination of leakage current without the need for additional components, the ability to transfer reactive power fully, and the use of fewer components compared to current five-level transformer-less inverters. Additionally, the voltage stress is evenly distributed across power switches, resulting in higher efficiency. Furthermore, the inverter is designed to automatically balance voltage in capacitors without requiring an additional control system. The proposed inverter achieves these advantages using a suitable switching scheme. The paper also includes an explanation of the proposed circuit, the process for designing minimum capacitors, theoretical loss calculation, and a comparison of features with similar topologies todemonstrate the efficiency of the proposedinverter. Inaddition, a 1 kVA experimental prototype is constructed to showcase the effectiveness of the proposed inverter.

An Adaptive Virtual Impedance Method for Grid-Connected Current Quality Improvement of a Single-Phase Virtual Synchronous Generator under Distorted Grid Voltage.

The proportion of distributed generation systems in power grids is increasing, leading to the gradual emergence of weak grid characteristics. Moreover, using voltage-sourced grid-connected inverters can enhance the stability of a weak grid. However, due to the presence of background harmonics in weak grids, the grid voltage can cause significant distortions in the grid-connected current, which adversely affects the quality of the grid-connected current. This paper begins by briefly introducing the principle of the virtual synchronous generator (VSG). Then, the output current of the voltage source inverter is analyzed to elucidate the mechanism of harmonic current generation. Considering the distortion in the grid-connected current of the voltage source grid-connected inverter caused by background harmonics in the grid voltage, a harmonic current suppression strategy based on an adaptive virtual harmonic resistor is proposed. The proposed strategy employs a signal separation module based on multiple second-order generalized integrators connected through a cross-feedback network. This module effectively separates the fundamental and harmonic currents from the grid-connected current, extracts the amplitudes of the fundamental and harmonic currents through coordinate transformation, and adaptively adjusts the virtual harmonic resistance magnitude through the negative feedback control of the harmonic content (the ratio of the harmonic current amplitude to the fundamental current amplitude). These measures are used to enhance the quality of the grid-connected current. Additionally, the stability of the system is analyzed using the root locus of the open-loop transfer function. Finally, the effectiveness of the proposed method is validated through a combination of MATLAB/Simulink simulations and experimental results.

Sequence-Admittance Measurement Method of Grid-Connected Inverter With Its Control System Disturbance

The impedance or admittance characteristics of the grid-connected inverter play an important role in its stability analysis. The traditional sequence-admittance measurement methods of the grid-connected inverter mostly rely on special admittance measurement equipment or adjacent grid-connected inverters for disturbance injection. Because of high hardware cost or inconvenience, the above methods are not suitable for price-conscious testers to some extent. To address the above issues, this paper proposes a sequence-admittance measurement method of the grid-connected inverter with its control system disturbance. Firstly, the sequence-admittance model of the measured grid-connected inverter when small-disturbance signal is superimposed on its modulation signal is deduced and the system equivalent circuit model is built. Then, the flow chart of the proposed sequence-admittance measurement method is designed. According to the injected small-disturbance signal, the output voltage and inductor current of the grid-connected inverter, the sequence-admittance characteristics in sub/super-synchronous frequency area can be obtained. The measurement process does not need the cooperation of external disturbance source, which saves costs and improves the measurement convenience. Finally, experiments verify the effectiveness of the proposed sequence-admittance measurement method.

Fault Ride Through approach for Grid-Connected Photovoltaic System

This paper presents a fault ride-through approach for grid-connected photovoltaic (PV) systems, aimed at improving the system's response during voltage sags and limiting the maximum inverter current during symmetrical faults. A constant active current reactive power injection approach was developed for low-voltage ride-through (LVRT) operation of grid-connected solar PV inverters in low voltage grids. The method manages the active and reactive power references and satisfies grid code requirements while also addressing tripping problems caused by overcurrent. The approach improves the speed response of the power converters during voltage sags, resulting in better dynamic grid support. The authors evaluated the approach using a 2-kW single-phase grid-connected PV system and demonstrated its ability to inject the required reactive power during a fault to improve the voltage profile and achieve dynamic grid support requirements. The accuracy of the proposed methodology is identified to be 98.3%, and the detection time is reduced by a reasonable margin in accordance with the grid standards. Overall, the fault ride-through approach can enhance the performance and reliability of grid-connected PV systems, particularly in low voltage grids.

Hybrid Switching Control-Based DC to AC Inverter for Microgrid Using Renewable Energy Sources

Hybrid switching control-based direct current (DC) to alternating current (AC) inverter is a method of controlling the flow of power from DC sources such as solar panels or wind turbines to AC loads in a microgrid. In a microgrid, renewable energy sources are often used to supplement traditional sources of energy and improve overall energy efficiency. To simulate micro-grid systems, an effective three-legged IGBT inverter has been developed using Matlab R2016a/Simulink. The inverter switches are controlled by a pulse controller, which creates the switching gate pulses. This work models the output voltage and current waveforms of the three-phase 180° voltage source inverter that supplies nonlinear loads. To lower the total harmonic distortion (THD) of the current and voltage outputs of the three-phase voltage source converter (VSC), a filter circuit and a two-level pulse width modulation (PWM) generator have been presented. This pulse-width modulation generator compares the modulating signal and a high-frequency triangular carrier wave. Sinusoidal pulse width modulation (SPWM) is used for PWM control. Moreover, the hybrid switching control-based DC-to-AC inverter utilizes a combination of pulse width modulation (PWM) and hysteresis current control techniques to maintain a constant AC output voltage and frequency. PWM control is used to regulate the voltage, while hysteresis current control is used to regulate the current. Additionally, an inductor-capacitor-inductor (LCL) filter is used to improve the stability of the power converter by providing a damping effect on the system. Overall, the LCL filter is a versatile and effective tool for improving the performance of power inverters, especially in applications where high efficiency and low harmonic distortion are important. IUBAT Review—A Multidisciplinary Academic Journal, 6 (1): 25-46

Measures to increase the technical resource of electrical equipment of powerful irrigation pump stations

RELEVANCE. At present, unstressed systems for launching high-voltage electric motors have been increasingly used. These systems limit the values of starting currents as well as eliminate alternating oscillations of engine electromagnetic torque. THE PURPOSE. Development of measures to improve the technical resource of electrical equipment of powerful irrigation pumping stations based on the use of soft start systems for high-voltage electric motors. METHODS. In the course of the study, methods for analyzing the technological processes of a pumping station, methods for mathematical and computer modeling of an electric drive were used. RESULTS. Computer models have been developed to study the regime characteristics of asynchronous and synchronous electric drives of pumping stations with direct and soft start of electric motors. A shockless start-up system for high-voltage electric motors of irrigation pumping stations of the first lift based on a current inverter is proposed. CONCLUSION. The reliability and durability of electrical equipment depends primarily on the technical resource, which is determined by a number of factors. The main factors influencing the technical life of the electrical equipment of large irrigation pumping stations are the transient modes that occur when the pumping units are started. The soft start system of high-voltage electric motors of irrigation pumping stations proposed in this article makes it possible to eliminate the negative impact of transient conditions on the operation of electrical equipment and, thereby, increase the technical resource and reliability of the power supply system of the pumping station as a whole.

Reactive Power Flow in Induction Motor Drive With Inverter Output Sinusoidal Filter and Its Influence on Wide Frequency Operation

This paper presents the reactive power flow and its influence on the wide-frequency operation of sinusoidal filter-equipped induction motor (SFE-IM) drives. A sinusoidal filter, placed at the output of a voltage source inverter (VSI) to filter the pulse width modulated (PWM) voltages, unfolds a research opportunity in SFE-IM drives, as the filter capacitors also supply reactive power to the IM. The paper comprehensively investigates this reactive power flow in an SFE-IM system with filter capacitor values designed using two different methods. In continuation, with the designed capacitors, the paper analyzes issues in the wide-frequency operation, such as reactive power imbalance, abnormal escalation in inverter currents, variation in power factor seen by the VSI, and high current stress on DC-bus capacitors and VSI. Furthermore, the analysis formulates the method of filter capacitor selection for the wide-frequency operation of the SFE-IM system in terms of IM and LC filter parameters while resolving the issues mentioned above. The proposed analysis is simulated in MATLAB/Simulink and experimentally validated on a 5 hp IM drive.

Optimized Sampling Mechanism for Full-State Feedback Current Control of LCL-Equipped High-Speed PMSMs for Fuel Cell Air Compressor

In this paper, an optimized sampling mechanism for full-state feedback current control of LCL-equipped high-speed permanent magnet synchronous motor drives is proposed. Firstly, the full-state current control structure is introduced and it indicates that the control performance suffers from the sampling harmonic components caused by the pulse-width modulation. Then the sampled capacitor voltage and the inverter current are analyzed theoretically with different sampling trigger times. Based on the harmonic analysis, an optimized sampling mechanism is developed and the current ripple is much reduced compared with the conventional method. Finally, the effectiveness of the proposed method is validated by the experimental results at 100 kr/min.

A Low Frequency Ripple Current Suppression Strategy for Single-Phase Photovoltaic Grid-Connected Inverter

Due to the absence of the insulated transformer, the non-insulated photovoltaic (PV) inverter possesses excellent properties such as small size, light weight, etc. However, the inherent parasitic capacitance between the PV panels and the ground brings serious leakage current problem, which has been the focus of researchers. Since the instantaneous power of the single-phase inverter results in a ripple current at a double-frequency ripple(100Hz), according to the theorem of conservation of power, the fluctuation of PV panels output voltage leads to a double frequency ripple of input current, which will have a negative influence on the maximum power point tracking in terms of PV panels and reduce the utilization efficiency of solar energy. This paper aims to investigate the suppression of the leakage current of PV single-phase inverters and the double-frequency ripple, the circuit proposed in this paper substitutes a bridge arm of the conventional PV grid-connected inverter with a Boost converter, which can eliminate the leakage current directly. The suppression strategy of double-frequency ripple for the proposed topology is provided as well. By transferring the double-frequency ripple in the DC-link capacitor of the inverter to another capacitor that has no connection to loads, it can suppress the low-frequency ripple current of the input side effectively. The paper verifies the feasibility of the proposed topology and the corresponding control strategy through simulation and experimental results.

Total harmonic distortion reduction based energy harvesting using grid-based three phase system and integral-derivative

Distributed generation (DG) and solar photovoltaic (PV) systems are just two of the many places multilevel inverters have found a home. The total harmonic distortion (THD) of an inverter's output voltage or current is widely regarded as a useful quality indicator. In order to lessen THD while enhancing the performance of the network, the authors of this research presented a unified controller.An integrated controller consisting of PID (Proportional-Integral-Derivative),Fuzzy,and Artificial Neural Network (ANN) controllers is used in the 31-level multilevel inverter to reduce THD in the PV system. The fundamental frequency of the suggested integrated controller is 50 Hz,and the simulation results show that the THD is reduced to 0.94 percent. The proposed controller's performance shown a considerable decrease in 5th order harmonics for the Cascaded H-bridge Multilevel Inverter,as well as an average percentage reduction in line voltage total harmonic distortion of 17.04 compared to the existing approach.

Control of arc suppression devices for reducing powerline bushfires in resonant grounded power distribution networks using global terminal sliding mode controller

AbstractThis paper proposes a global terminal‐sliding mode controller (GT‐SMC) to compensate powerline bushfires due to electric faults in power distribution networks using arc suppression devices (ASDs). A GT‐sliding surface along with a new quick reaching law is used to design the controller. The major control objective is to compensate the fault current caused by single line‐to‐ground (SLG) faults to a value that cannot ignite fires in bushfire prone areas. A T‐type residual current compensator inverter within an ASD is controlled to achieve the goal. An integral‐sliding mode controller (I‐SMC) is also designed using a conventional reaching law for comparing the performance. Simulations studies and processor‐in‐loop implementations are carried out to investigate the ability of the GT‐SMC over an I‐SMC over a range of fault impedance scenarios. Dynamic properties of the voltage and current due to SLG faults along with the current injection by the ASD are analyzed against the standard criteria, to be followed to get rid of powerline bushfires. Results under different operating scenarios indicate that both controllers are capable to maintain standard criteria for preventing powerline bushfires though the GT‐SMC is proven to exhibit superior transient responses to that of the I‐SMC and integral backstepping controller.

An Easily Scalable Dynamic Wireless Power Transfer System for Electric Vehicles

This article deals with a LCC-LCC compensated dynamic wireless power transfer system for electric vehicle charging applications. The presented prototype system allows for a power transfer of about 10 kW at 20 cm coil copper to copper distance. With just one circular pickup coil and a very straightforward control scheme, a new coil arrangement enables a seamless power transfer. Furthermore, the system’s design power level is easily adjustable by the size of the the pickup coil. The hardware architecture as well as the software functionality are described in detail. A 20 m test track was built up according to the outlined principle. By measuring the transmitted power, the efficiency and the interference between the primary segments and its effect on the inverter currents are examined. The results show an effective DC to DC efficiency in the range of 91 to 92% and a power fluctuation of approximately 25%.

Design and control of LCL-type grid-tied PV power conditioning system based on inverter and grid side currents double feedback

ABSTRACT Solar energy as a limitless, clean, and cost-effective energy source could be converted to electrical power by photovoltaic cells. In this paper, a photovoltaic power conditioner, which is connected to the low voltage grid via an LCL filter, is presented. This power conditioning system supplies high-quality current and has high stability against disturbances. Since the generated PV voltage is lower than the grid voltage, a DC-DC converter is utilized. Also, DC voltage is also converted to AC by an LCL-type inverter. To ensure the resonance elimination yielded from the LCL filter, inverter and grid side currents, a double feedback strategy is employed. By considering resonance damping, stability margin, and the grid-connected requirements, a systematic design procedure for the suggested strategy is investigated to ensure the system stability in the low-voltage network. In comparison with the conventional strategies, the suggested strategy gives suitable resonance damping capability, higher marginal stability, and better grid-connected properties. Simulation results of the PV power conditioning system illustrate the accurate performance of the control system, suitable tracking of the PV array maximum power point, and high-quality current injection into the grid.

An Accurate Dead Time Compensation Method for SPWM Voltage Source Inverters

Dead time is generally used to avoid the short circuit of the dc source, which causes harmonics in the output voltage and current of the voltage source inverters (VSIs). Based on an accurate harmonics calculation model of digital sinusoidal pulsewidth modulation, harmonics caused by dead time can be analyzed and calculated accurately. The proposed method obtains the compensation waveforms by the derived calculation module and detailed operation steps and then injects these into the sinusoidal reference voltage to eliminate the corresponding frequency harmonics caused by the dead time effect. The phase delay of the fundamental voltage caused by dead time is also considered. Moreover, this method avoids detecting the current polarity, affecting the compensation effect. Simulation and experimental results of the proposed method are presented to validate the effectiveness.