THD Of Output Voltage Research Articles

A Power Boosting Method for Wireless Power Transfer Systems Based on a Multilevel Inverter and Dual-Resonant Network

With the deepening of research on wireless power transfer (WPT) technology, there is an urgent need to improve the output power of WPT systems. Therefore, this paper proposes a power boosting method based on a multilevel inverter and dual-resonant network. The system adopts a five-level inverter whose output voltage contains rich fundamental and harmonic components. The transmitting side adopts a dual-resonant compensation network, and, through its parameter configuration, the system can be in a resonant state at both the fundamental and third harmonic frequencies. The receiving side adopts two receiving channels which can simultaneously receive power at both frequencies, thus boosting the output power. Firstly, the overall structure and operating principle of the system are introduced. Then, the relationship between the system output power and efficiency with the inverter modulation parameters is obtained and the strategy for selecting the optimal operating points of the inverter is designed by comprehensively considering the THD of the inverter output voltage and the efficiency of the system. Furthermore, the proposed system is simulated in a Matlab/Simulink platform. Finally, an experimental setup is created to verify the proposed method. The results show that, compared with the single-channel WPT system, the proposed method can enhance the output power from 160 W to 310 W with a boosting coefficient of nearly double and with the highest efficiency exceeding 92%.

A simple 60‐pulse voltage source inverter using voltage reinjection strategy to improve voltage harmonics for high‐power local loads

AbstractThe voltage reinjection strategy is an effective solution to improve the voltage quality of the voltage source inverters for high‐power applications. In this article, the fundamentals of voltage reinjection strategy are analyzed to reduce voltage harmonics of the output voltage. Then, a novel voltage reinjection circuit is proposed which can generate a 5‐level voltage to be injected on the voltages of the DC sources. The reinjected voltage can create a 60‐pulse voltage waveform for a three‐phase load. Turn ratio optimization of the reinjection transformer has a significant effect on the improvement of the harmonic situation of the output voltage. Furthermore, the proposed reinjection circuit provides ZVS conditions for the main switches to reduce switching losses considerably. The simulation results indicate that the proposed reinjection circuit can reduce the output voltage THD to 3.16% without any type of filter or modulation, and the load variation does not have a considerable effect on the voltage quality. The experimental results approve the analytical trend and simulation process and also confirm the reinjection circuit performance. According to the results, the proposed method has generated a semi‐sinusoidal voltage waveform with in the laboratory.

The Influence of Switching Frequency on Control in Voltage Source Inverters

This paper aims to show how the switching frequency influences the properties of the digitally controlled voltage source inverter (VSI). The measurements of the Bode plots of the inverter are shown and discussed to present the existing signal delays and power conversion efficiency, depending on the switching/sampling frequency. Two types of controllers are presented, Single-Input–Single-Output (SISO) and Multi-Input–Single-Output (MISO), and adequate prediction units (the Smith Predictor for SISO—Coefficient Diagram Method and the full-state Luenberger Observer for MISO—Passivity Based Control) were used to compensate for the delays. It will be shown by comparing the THD of the VSI output voltage that prediction is useful with low VSI switching frequency (about 10 kHz) but is not important for the middle switching frequencies (about 25 kHz) or the high switching frequency (>50 kHz). This paper shows that increasing the switching frequency simplifies digital control without reasonably decreasing efficiency. The theoretical considerations, the Matlab/Simulink 2021b simulations, the final experimental laboratory verification are presented.

A novel nine‐level inverter, applicable in air plane ground power unit

AbstractIn this study, a novel nine‐level inverter using one voltage source, 10 unidirectional and one bidirectional power switches, and two capacitors has been proposed to utilize in ground power units (GPUs). Selective harmonic elimination method has been applied to reduce the output voltage's THD to less than 3% with 115/200 V and 400 Hz. The proposed converter utilized a lower number of devices to output a nine‐level staircase in comparison to existing converters. Also, the proposed converter uses inherent self‐voltage balancing for capacitors' voltage. So, the control algorithm gets simpler. In this study, the topology analysis, modulation algorithm, capacitor calculation, loss, efficiency, and performance analysis of the proposed topology have been presented. The proposed circuit has been compared to recently published papers in terms of efficiency, switch, capacitor, diode, and source numbers. The theoretical and experimental performance of the topology has been verified by simulation on PSCAD and PSIM software and 350 W experimental setup.

A seven‐level switched‐capacitor based transformerless inverter with modified PWM strategy to enhance the performance of grid‐connected PV systems

AbstractAmong different types of transformerless photovoltaic inverters, multi‐level inverters based on switched‐capacitors (SC) are the burning topic of recent decades due to their potential advantages, such as, single source requirement, voltage boosting capability, and high power density. However, for a seven level output voltage, a conventional SC based inverter architecture uses more than two units of SC, a large amount of power switches, which then lead to capacitor voltage balancing problems. This paper presents a seven‐level switched‐capacitor transformerless inverter (SCTI), which is structured with only two SC units, ten power switches, and a single DC source. The proposed SCTI ensures voltage boosting capability, self‐voltage balancing, and low power semiconductor losses. Apart from these, a modified sinusoidal pulse width modulation (MSPWM) is also proposed in this work, which guarantees better thermal performance and low inverter output voltage THD for the proposed SCTI. The proposed SCTI along with the MSPWM is simulated in MATLAB/Simulink and PLECS computer simulation environments. A reduced scale laboratory prototype is also built and tested to ensure the feasibility of the proposed SCTI.

A Novel Single-Phase Five-Level Current-Source Inverter Topology

Recent technological advances have renewed the research interest in current-source inverters (CSIs). Nonetheless, CSI research still falls behind its voltage-source counterpart with regards to topologies, modulation, and control. Acknowledging the above, this paper presents a novel single-phase five-level CSI topology. The proposed circuit utilises eight switches and two inductors for the generation of five distinct output levels while maintaining low output voltage THD and dv/dt. Furthermore, by offsetting the inductor currents from a binary 1:2 to a trinary 1:3 ratio, the proposed inverter can generate seven current levels at its output. The inverter offers built-in short-circuit protection and can boost a low input DC voltage to a higher peak AC output voltage. These merits, alongside an electrolytic-capacitor-free design, simple current balancing mechanism, and fault-tolerant characteristics, make it a promising candidate for PV module-integrated inverter (MII) systems. The current topology utilises two inductors but is fully functional with single-inductor operation. The paper provides a functional analysis of the inverter topology alongside the inverter switching states and corresponding conduction paths. A detailed analysis of the inductor current dynamics as well as a current-balancing algorithm for dual- and single-inductor operations are given. The theoretical analysis of the proposed circuit and its functional operation are verified using simulations and experimental results carried out on a laboratory prototype.

Modelling for Multiport Converter-based Hybrid Power supply for Renewable Energy Source Application

This research work deals with the design, modeling and technical evaluation of multiport modular converter based hybrid Power supply using solar PV for small village. The village’s maximum power demand is 50kvA, consisting of demands of twenty (20) households. The first converter in the proposed multiport system is a high frequency isolated DC-DC converter fed with HVDC link yielding an output voltage of 700vDC. The isolated DC-DC converter uses a medium frequency transformer with primary and secondary side converters in input-series output-parallel (ISOP) configuration. Also, the output of first converter is connected to a solar PV and battery system through a buck-boost converter. The second converter in the system is solar PV fed three phase modular inverter designed to have output AC line voltage of 0.415 kV. The three phase inverter is based on modular multilevel converter (MMC) with interleaved modulation techniques. A silicon carbide power MOSFETs, with model numbers CPM3-10000-0270(CREE) and SD11703 (Solitron) are used as a building blocks for isolated DC-DC converter. On the other hand, SiC -MOSFET with part number SCT3017AL (RHOM) is used as basic building block for modular inverter. A solar PV module with open circuit voltage of 85V and maximum power rating of 415W is used to feed the inverter. Different scenarios such as changes in load and changes in solar irradiance are used for critically evaluating the performances of the system under question. The output voltage THD, current distortions, changes in the converter output voltage, current magnitude and converter efficiency are used for performance evaluation of the system under consideration. Simulink/ PLECS (Piecewise Linear Electrical Circuit Simulation) combo simulation platform is used to model and simulate the system in question. Simulation results showed that the proposed multiport converter system can be a viable alternative to low frequency distribution transformer.
 Keywords: Multiport converter, MMC, DC-DC converter, Hybrid power Supply, Solar PV.

Application of soft computing algorithms for hybrid modular multilevel inverters

This study utilized Harris Hawk optimization to analyze the harmonic distortions of a symmetric capacitor based multilevel converter. The proposed multilevel converter uses identical and symmetric DC sources in its input. The proposed topology for a multilevel converter uses fewer switches than typical cascaded designs. It can output 9-level outputs and can be scaled up to higher levels. The proposed multilevel converter can be improved by implementing a low frequency pulse width modulation technique to reduce the stress on the switches. The optimization of the switching angles using Harris Hawk was able to solve the non-linear aspects of the Selective Harmonic Elimination Pulse Width Modulation. The output voltage's THD was compared with that of other optimization methods, such as ant colony and particle swarm. The comparison shows that the output THD of the Harris Hawk optimizer is lower than that of other methods, which is about 5 %, according to the standards of IEEE-519.

A Fifteen-Level Reduced Switch Count Multilevel Inverter with Multicarrier PWM

A multilevel inverter performs a major role in increasing the range of the level of output voltage without the use of a transformer in the power sector. Here an asymmetrical 15-level multilevel inverter fed from three unequal voltage sources has been proposed. The various modes of the conduction of the eight switches with the switching pattern are discussed with the circuit’s operation. The performance of the circuit is analysed using various techniques under MC-PWM methodologies such as Phase disposition (PD) PWM, Alternate POD (APOD) PWM, and Phase Opposition Disposition (POD) PWM. Key Finding: The logical expression used for generating the pulse pattern of the above techniques using the level shifting PWM technique to reduce the harmonics is performed, simulated, and compared by implementing three techniques for linear and non-linear load. The performance in terms of THD of output voltage under various modulation indexes is compared for various Llvel-shifting techniques. The performance of this 15L-MLI is simulated using MATLAB/Simulink and implemented in a prototype hardware model.

THD Reduction of Improved Single Source MLI Using Upgraded Black Widow Optimization Algorithm

An upgraded Black Widow Optimization algorithm for obtaining the ideal switching angles of a reduced structure multilevel inverter is proposed in this paper with minimum voltage THD. The conventional BWO algorithm has been modified and proposed to solve the THD minimization problem with faster convergence rate, lesser tuning variables, and lesser number of equations than the other existing nature inspired algorithms. The reduced structure MLI is designed with three asymmetrical DC voltage sources of ratio 1 : 2 : 4 to generate 15-level output voltage which requires reduced number of switching devices in comparison with the existing topologies of equivalent voltage level. The asymmetrical DC voltage sources to the MLI are derived from a single DC voltage source using a multisecondary winding DC-DC converter in order to provide the isolation between the load side and source side. The proposed modified BWO algorithm reduces the complexity of solving the nonlinear equations to achieve the best result by avoiding the local optima. To verify the effectiveness of the upgraded BWO algorithm, the optimization problem for three phase fifteen level MLI has been solved using the genetic algorithm, BFO algorithm, and PSO algorithm. The results for the above three applied algorithms are compared with the upgraded BWO and presented. The proposed algorithm has minimized the output voltage THD to 1.83% at 0.88 modulation index. The developed scheme has been corroborated with the help of MATLAB simulation and the results have been verified through a hardware model developed in laboratory.

A double T‐type H‐bridge reduced switch multilevel inverter for a wide range of DC voltage variations

AbstractRenewable energy sources are subject to input source uncertainties, which can negatively impact output voltage THD. Having a high number of voltage levels in multilevel inverters (MLIs) with minimum components is cost‐effective. This paper proposes a new structure, Double T‐type H‐bridge (DTH) module, that can produce 9, 13, 17, 19, 21, and 25 levels using reduced components. Switching patterns in MLIs refer to the way in which the power switches are controlled to generate the desired output voltage waveform. As a result, having more switching patterns make the converter flexible to produce voltage levels in the face of input source uncertainties. The DTH structure provides new switching patterns, making it possible to produce levels when the difference of capacitor voltage is negative in a positive cycle or vice versa. This paper presents a new algorithm based on nearest level control to order voltage levels in ascending order, which improves output THD significantly. This topology brings a lower switching state that is linked to switching losses directly compared to the topologies with the same number of power switches. The DTH module's performance is evaluated through graphical analysis, simulations, and experimental results in symmetrical, asymmetrical, and load change conditions.

Performance of an OVT inverter reliant on the switching frequency of the filtering inverter

The paper presents an inverter based on the orthogonal space vectors theory (OVT inverter) and its performance. The OVT inverter consists of two constituent twolevel 3-phase inverters: the main inverter (MI) and the auxiliary one (AI). The MI is controlled in a simple way to generate the stepped output voltage and the AI works as an active filter limiting the higher harmonics in the OVT output voltage. The filtering process is formed by the use of the orthogonal space vector theory. The output voltage of the OVT inverter takes the shape of a stepped voltage comparable to the voltage generated by multilevel inverters. The AI operates as a very effective active power filter (APF) of the OVT inverter output voltage. The AI power is significantly lower in comparison to the MI power nevertheless its switching frequency affects the OVT performance. The article describes studies in which the impact of changes in the switching frequency filter inverter on the operation of the orthogonal inverter and the output voltage THD. Increasing the filter inverter switching frequency improved performance and reduced the transformer size, which acts as a summing node.

A Single Phase GaN GITs-Based Bidirectional Multilevel Inverter for High Voltage Grid Tied Photovoltaic Power System

— In this article, a performance comparison has been conducted between Si MOSFETs, SiC MOSFETs, and Gallium nitride (GaN) GITs in single phase BSNPC inverter. The PSpice study shows that the All GaN GITs BSNPC inverter has the highest efficiency of 98.97% compared to all other power devices used in the simulations. Due to a low dead time of 50 ns, the THD in output voltage for the All GaN GITs BSNPC inverter has decreased by 10% compared to the All Si MOSFETs BSNPC inverter and by 0.5% compared to the All SiC MOSFETs BSNPC inverter. The operation of GaN GITs at 200 kHz resulted in a 63% reduction in output filter size compared to the operation at 10 kHz. The Gate Drive circuit for GaN GITs and its complete design is presented. The All GaN GITs BSNPC inverter laboratory prototype study shows that at 16 kHz, 700 W the maximum efficiency of 99.4% is achieved whereas at 64 kHz, 350 W the lowest efficiency of 98.7% is achieved. The performance of the two GaN GITs connected in series to make a single series bidirectional switch is very reliable and robust. When the switching frequency is increased from 16 kHz to 64 kHz at 700 W output power, the reduction in the output filter size is 35%. The reduction in THD in the output voltage is 8.3% for the GaN GITs when operated at 150 ns dead time compared to 1 μs dead time.

A Complete Online Solution of Harmonic Elimination PWM Method Using Modified-Equilibrium Optimizer-Levenberg- Marquardt Algorithm

This paper proposes a novel online solution, i.e. Modified-Equilibrium Optimizer-Levenberg-Marquardt (M-EO-LM) algorithm, for the symmetric and asymmetric harmonic elimination pulse width modulation (HEPWM) methods of the modular multilevel cascaded converters. A detailed comparison of the proposed M-EO-LM algorithm with nine state-of-the-art algorithms is also presented for twenty-nine unimodal, multimodal and composite benchmark test functions. M-EO-LM has proven its effectiveness by outperforming these algorithms. EO algorithm is first introduced for the solution of HEPWM method. Its comparison with several state-of-the-art algorithms depicts its superiority; but it gets stuck in the local minima. Modified-EO (M-EO) solves the problem by enhancing its exploration ability, and is then attached to a rapid calculus-based LM method to form the novel M-EO-LM algorithm. M-EO-LM algorithm initiates the solution process by solving the HEPWM equations for nine angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N=9$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.78\leq M\leq 6.86$ </tex-math></inline-formula> ) offline in only two iterations, depicting its remarkable convergence ability. Solution angles are then divided into several groups, serving as the search space for the online M-EO-LM algorithm. A comparison between HEPWM and nearest level modulation methods based on the output voltage THD values is provided to report the maximum number of solvable HEPWM angles for a complete online solution. These angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N=8$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.78\leq M&lt; 5.18$ </tex-math></inline-formula> ) are then solved online using the M-EO-LM algorithm. Comparing the computational times of the proposed online algorithm with differential evolution-Newton Raphson algorithm proves the rapid solution behavior of the M-EO-LM algorithm, validated through the simulation and real-time experimental results.

Design and investigation of a triple boost multilevel inverter with self‐balanced switched capacitors and reduced voltage stress

AbstractMultilevel inverters (MLI) play a key role in various medium voltage and high power industrial applications. This paper proposes a triple boost multilevel inverter (TBMLI) comprising switched capacitors. The special features of the proposed circuit are three times boosted output voltage, reduced voltage stress on switches, and the presence of a single dc source. Moreover, the self‐balancing in the capacitors voltage which eliminates the need of auxiliary control circuitry and reduced number of overall components also add to the salient qualities of proposed MLI. The simulation has been done using MATLAB/Simulink, whereas the loss analysis, describing the distribution of the various power loss, has been completed with the help of PLECS software. The proposed topology has a maximum efficiency of 98.3%, whereas the THD in output voltage is 13.65%. The proposed MLI is experimentally investigated to see its performance. A comparison has been conducted to assess the proposed MLI on various parameters.

A new level Increased NLM method of modular multi-level converters for reducing THD of output voltage

ABSTRACT This paper proposes a new modified level, increased nearest level modulation (NLM) method to improve the THD quality and enhance the quality of output voltage of modular multilevel converters (MMCs). Offshore wind farm links need connections from onshore national grids, and this paper is consistent with higher level voltage generation techniques by using MMC. By changing the on-number sub-modules (SM) at the middle position after using the round function, the generated gate logic by using the proposed method maintains a fixed magnitude value of phase voltage with a maximal number of (2 N + 1) levels, where N is the number of sub-modules per arm. The proposed method maintains the advantages of the conventional NLM such as simple implementation and low switching loss and avoids the disadvantages of the existing NLM method such as capacitor voltage ripple, peak value of arm inductor voltage, complexity in topology, etc. Both the advantages and disadvantages of the proposed and the conventional schemes are also studied, and an illustrated comparison shows the THD result differences for four methods. The system is simulated using MATLAB-Simulink to validate the feasibility of the proposed scheme and carried out by a hardware-in-the-loop simulation (HILS) system. By reviewing the simulation and experimental results, it was found that the proposed scheme improves the output voltage and THD quality.

Implementation Analysis of Solar PV Based SEPIC Inverter System

For welfare of environment, world needs to use more and more renewable energy system not only at the level of industrial but also for domestic load system. Due to much installation cost involving in a solar PV cell/panel based system there is a need of better mechanisms to get maximum utilization and benefits from the system with reliable operation, especially in the case of microgeneration power plant to full fill the minimum desired requirements of domestic appliances to achieved reliable operation. Mostly available PV based inverter system having problem of low output voltage generation and THD producing issue, which needs to a requirements of extra circuit to the control THD and boost up the level of output voltage. In this paper, solar PV based closed loop SEPIC converter by PWM technique to maintain a step up constant dc output voltage with no polarity reversal, low ripple in output and minimizing the requirement of additional filter circuit and fed to single phase inverter. This paper has been focused for the overall single phase PV based SEPIC inverter system implementation, performances and simulated on MATLAB/SPS software to provide low losses, 2% minimum THD and reliable operation in compare with single phase PV based Cuk inverter is used for DC-AC conversion system to compatible with domestic load appliances.

Modified Selective Harmonics Mitigation PWM for a Switched Diode Multilevel Inverter

A modified selective harmonic mitigation (SHM) technique for multilevel inverters considering the RMS output voltage magnitude is presented. The harmonic contents in the output voltage of these inverters must satisfy the specified grid code requirement standards. In conventional SHM techniques, the firing angles of the multilevel inverters have been derived by taking into account grid code harmonic reduction standards. When the multi-level inverters are driven with these firing pulses generated, it results in reduction of the magnitude of the inverter output voltage. In order to overcome this issue of output voltage reduction, the modified SHM optimization problem includes another constraint on the RMS output voltage limits, which results in different set of firing angles. This facilitates the use of firing angles, which takes into account the grid code standards of harmonic mitigation without compromising the value of the RMS output voltage of the inverters. The proposal has been simulated and validated in MATLAB Simulink and the experimental results are obtained for a single-phase seven level inverter with Silicon made semiconductor switches. By using the proposed method, output voltage THD (upto 40th harmonics were considered) of 5.9% was obtained, which is well below the harmonic standards specified by EN 50160.

Study of a method to reduce the harmonics of the output voltage of medium frequency power supply

Since the electrical equipment with nonlinear load began to be used, the harmonic suppression technology has become the focus of research. In this paper, a robust multi resonance servo control method is proposed and applied to the medium frequency power supply. The method can not only perform the closed-loop system stability and asymptotic tracking, but also make the power supply output possess the advantage of rapid dynamic response, and low-order strong harmonic suppression. First, this paper presents a mathematical model, analyzes the time-domain robust control - linear matrix inequality and regional D stability and turns the analysis of the problem of robust control problem to a one of linear matrix inequality (LMI) convex optimization problem through the augmentation of system matrix dimension. Then, the YALMIP toolbox is used to solve for the status feedback gain matrix. Finally the whole system is simulated and tested. The results show that the designed controller makes the dynamic recovery time of the closed-loop system less than 5ms, and the output voltage THD is reduced to less than 4.5% with the nonlinear load.

An Efficiency Analysis of 27 Level Single-Phase Asymmetric Inverter without Regeneration

For medium voltage applications, multilevel inverters are used. One of its classic topologies is the Cascaded H-Bridge, which requires isolated DC voltages to work. Depending on the DC voltage ratio used in the Cascaded H-bridge can be classified into symmetric and asymmetric. In comparison between symmetric and asymmetric inverters, the latter can generate an AC output voltage with more output voltage levels. DC voltage ratio most documented are binary and trinary. The last can generate an AC voltage of 3n = 27 levels is obtained, using n = 3 inverters in cascade and NLM modulation, which generates a flow power of the load to the inverters (regeneration). This work analyzes the semiconductor losses (switching and conduction) and the THD of the AC output voltage in function of index modulation, considering a non-regenerative modulation technique for a 27-level single-phase asymmetric inverter. To confirm the theoretical analyzes, simulation and experimental results are shown.