Nearest level control for improving total harmonic distortion in a 13-level three-phase multilevel inverter

This paper introduces a novel 49 Level (49-L) inverter topology designed to overcome the limitations of traditional inverters in photovoltaic (PV) renewable energy systems. This design focuses on minimizing component count and total standing voltage (TSV) at high output levels, making it versatile for various applications. The proposed inverter incorporates a modified packed H-Bridge unit and basic units to optimize component usage and reduce switch voltage stress. Mathematical formulations for calculating switching angles are provided, simplifying switching signal generation and reducing processing requirements. The 49-level inverter undergoes rigorous testing under different load conditions, with analysis emphasizing key performance metrics such as total harmonic distortion (THD), switch voltage stress, TSV, and efficiency. Its suitability for PV system integration - particularly in standalone systems - is demonstrated, highlighting its potential for renewable energy applications. The obtained results unveil that the proposed inverter achieves low THD for voltage and current, meeting IEEE 519 standards. The voltage THD is found to be at the value of 1.66% under all loads. The current THD is found to be at 1.66% under resistive load and ranges from 0.11% to 0.14% under RL loads. Moreover, the inverter's efficiency - depending on load conditions - is found to range from 96% to 98%. Additionally, the proposed inverter performs well under dynamic conditions, with smooth transitions during changes in irradiation levels and load types. Furthermore, this topology is the most cost-effective compared to other recent multilevel inverter (MLI) designs. Finally, the proposed 49-level inverter offers a promising solution for PV renewable energy systems, delivering high power quality, efficiency, and flexibility.

One of the main advantages of multi-level inverters (MLI) is their ability to achieve high power quality and high efficiency power conversion. With the emergence of wide-band-gap (WBG) devices, the tendency has grown towards using high switching frequencies to improve converters’ output power quality and minimize switching harmonic filters footprint. While high-frequency switching finds significant success in low and medium-power applications, it is not the best practice to reduce the filter size when applied to medium voltage (MV) high power (HP) inverters implemented with high voltage levels. In this paper, we show that the least filtering requirements for MV HP higher level inverters is achieved using the modulation strategy with the least switching, i.e., the staircase modulation. The paper compares the harmonic filter requirements and power losses for low-frequency and high-frequency pulse-width-modulated MLI. The analysis shows that low-frequency switching not only achieves the lowest losses, but also produces the lowest line-to-line voltage total harmonic distortion (THD), which allows eliminating both voltage and current harmonic filters in higher level inverters. Simulation results are provided to verify the theoretical analysis on the THD, and experiments on a 1 kW, 600Vdc MLI are presented to compare efficiency for low- and high-frequency modulation.

Abstract: The conventional two-level inverter is most commonly used for AC drive systems. The inverter produces harmonics, which will cause heating of the power electronic devices as well as load and deteriorate the life of it. Thus, anyhow harmonics should be suppressed or removed, the most common or well-known method to filter out harmonics are introduction of various filters between inverter and load according to requirements. The filters are mainly designed with L and C connection in different ways, the use of filters become more bulky and costly. To design accurate desired response filters are complex. These issues of filters for the high voltage ratings and higher power applications can be solved by multilevel (ML) inverters topology. In this paper cascaded 5-level and 7-level single phase inverter is being compared with conventional 2-level single phase inverter through proposed simulation model. MLI using cascaded H-Bridge is more advantageous than conventional 2-level such as reduced dv/dt stress improves the EMC problem. Multilevel inverters are more reliable than two-level inverters at lower speed. Voltage rating of each cell in cascaded H-Bridge inverter topology are of low values to obtain 230 AC output MLI is mostly used for stored power in batteries and fuel cell. The inverter can generate different level stepped staircase output voltages at load side to produce more sinusoidal voltage signals and to reduce the THD value. THD value of MLI using cascaded H-Bridge topology reduces on increasing number of levels. Keywords: Total harmonic distortion (THD), electromagnetic compatibility (EMC), and multilevel inverter (MLI) Cite this Article Vijay Shankar, Ankur Kumar, A.N. Tiwari. Harmonics Analysis of Single Phase VSI with 5-level and 7-level Inverter. Recent Trends in Electronics & Communication Systems. 2019; 6(1): 16–23p.

This research compared the performance of PWM (Pulse Width Modulation) inverter and multilevel inverter in terms of their output voltage and current total harmonic distortion (THD). The inverters were designed to have the output voltage of 220 V at 50 Hz. The input voltage for both inverters are 400 VDC. For PWM inverter, the PWM technique utilized was sinusoidal PWM (SPWM) and for multilevel converter, the number of voltage level is five with diode-clamped topology. The study included circuit implementation, analysis, and THD calculation, all of which were carried out through simulation using PSpice software. In controlling the SPWM inverter output, the adjusted parameters included amplitude modulation ratio, frequency modulation ratio, and filter components’ parameters. On the other hand, the firing angles of the switching components were designated as controlling parameters in multilevel inverter. From the study, it was found that the best THD values of the designed SPWM inverter are 4.2% (voltage) and 1.7% (current), while those of multilevel inverter are 27% and 11%, for voltage and current, respectively. Thus, it can be concluded that SPWM inverter is better than 5-level inverter for the application in solar panel due to its lower THD. In our study, 5-level inverter did not satisfy the THD requirement specified in IEEE 512-1992, i.e. 5%.

Multi-level inverter used in applications that require high power. The important factor in multi-level inverter is Total Harmonic Distortion (THD). This study discuss nine level cascaded H-bridge multilevel inverter. Also, proposed the effects of using filter on waveform and Total Harmonic Distortion (THD) of output voltage and current. Discussed LC low pass filter and sinusoidal pulse width modulation as control technique of switches. Comparison THD of nine level cascaded H-bridge multilevel inverter with and without filter. The proposed level and filter are design and simulate by MATLAB 2010 Version 7.11.0. The simulation results show the effects of using filter on THD and waveform of output voltage and current. Different methods for choosing filter value are used to illustrate the filter effect.

It is suggested to build a 9-level pencil-shaped (PS) inverter with a minimum of two DC supplies. Low component multilevel inverters (MLIs) employ extra conducting switches in addition to the DC supply. • This suggested MLI is more effective since it uses fewer power electronic switches. The architecture enables a higher voltage level inverter with a modular design that uses fewer DC supplies and does it appropriately without the need for an additional H-bridge circuit. Additionally, a control plan is suggested for distributing loads equally in a nine-level architecture. • The potential for equitable load distribution in higher-level designs and fundamental frequency switching of switches carrying larger voltage strains are also being looked into. Through simulations and experimental experiments, several notions are validated. The simplified formulae for the suggested inverter parameters are built to determine their optimal capabilities. • Additionally, an optimal PSMLI design is created using the expanded model of the suggested architecture to reduce the inverter's total standing voltage (TSV). Comparison studies are provided to support the proposed inverter and show its benefits over recent MLIs of comparable sorts. • Through accurate simulation and lab tests, the MLI was able to achieve a greater efficiency of 95.54%. The improved 17-level version of PSMLI, on the other hand, achieved IEEE 519 standard performance with total harmonic distortions (THD) of just 5.15%. Key Word: Multi-level inverter, power electronics, switched capacitor, voltage boost, nearest level control.

This paper proposes an offset voltage control scheme for the modular multilevel converter (MMC) operated in nearest level control (NLC) to improve the total harmonic distortion (THD) of AC phase voltages. The offset (neutral-to-zero-point) voltage is adjusted so that the magnitude of each AC pole voltage maintains constant value with N + 1 level in the range of whole modulation index (MI). The validity of the proposed scheme was confirmed by computer simulations for the MMC with 22.9 kV/25 MVA and experimental works for the scaled MMC with 380 V/10 kVA. It was confirmed that the proposed control scheme can generate linearly variable AC phase voltages with improved THD in the over-modulation region as well as the normal-modulation region.

In this paper, a new 23-level inverter topology has been proposed with two different modulation schemes, viz., Nearest Level Control (NLC) and Unipolar Phase Disposition (UPD) techniques. It comprises six unidirectional switches, three bidirectional switches, and five DC sources. A backend H-bridge is not needed to produce negative voltage levels because all levels are naturally produced. The main advantage of this topology is that in every state, only three switches are in conduction mode, and the rest are in the OFF state. Here, switching losses are significantly reduced due to the NLC technique's fundamental switching frequency, which is also particularly appropriate for a wide range of levels. Similarly, the UPD technique is a high switching frequency technique and because of absolute function, the number of carrier count can be reduced by half as compared with the conventional In-Phase Disposition (IPD) technique. Finally, with a step-change in input dc voltage, the proposed topology has been tested with two different control schemes and validated through MATLAB/Simulink platform.KeywordsMultilevel DC link inverterNearest level controlUnipolar phase disposition

In this paper, a new switching strategy is proposed for a multi-level STATCOM system. An efficient approach in reducing the harmonic contents of the inverter's output voltage is total harmonic distortion (THD) minimization. In multilevel inverters with fundamental frequency switching strategy (each switch turning on and off once per output cycle), the switching angles can be selected such that the output THD is minimized. In three phase multilevel inverters, the optimization algorithm is commonly applied to the phase voltage of the inverter. This results in the minimum THD in phase voltage, but not necessarily in the line to line minimum THD. In this paper, THD minimization process is directly applied to the line to line voltage of the inverter, and a new control strategy of multilevel STATCOM is proposed. The proposed method will be implemented, in RTDS and the closed loop operation of multi-level STATCOM will be explored.

This paper analyzes the Total Harmonic Distortion (THD) performance of a single phase 5-level CHB MLI. The multi level inverter is simulated using the carrier overlapping APOD Pulse Width Modulation (PWM) switching control technique. The total harmonic distortion (THD) of the output voltage is observed for the PWM control technique at varying modulation index of 0.7-1.0. The performance of a 5-level CHB MLI is simulated using MATLAB/SIMULINK. It is observed that the carrier overlapping APODPWM provides output with relatively low THD.

Progress in efficiency improvement has been main a matter in grid tie inverters. The employment of multilevel inverters in energy conversion promises a better power quality and lower switching losses than ordinary two-level inverters even in low voltage grid. This paper presents the implementation of several control schemes (Vector Oriented Control, Hysteresis Control) and modulation techniques (Pulse-width Modulation, Nearest Level Control) for a 17 level cascaded H-bridge grid tie inverter for a battery energy storage system. For this purpose, the different physical models distinguished in control and modulation schemes were implemented in Simulink® and Simscape™. On the merits of simulations it is concluded, that the phase shifted modulation technique gives less total harmonic distortion in current and the nearest level control gives lower switching losses when compared to other studied techniques in strong and weak grid tie inverters.

<span>In this paper, modified multilevel inverter, via addition of an auxiliary bidirectional switch, based on Newton Raphson (NR) and Particle Swarm Optimization (PSO) techniques is presented. The NR and PSO techniques were employed for selective harmonics elimination (SHE) solution in a modified Cascaded H Bridge Multilevel inverter (CHB-MLI). The Selective Harmonic Elimination Pulse-Width Modulation (SHE-PWM) is a powerful technique for harmonic minimization in multilevel inverter. The NR and PSO techniques were used to determine the switching angles by solving the non-linear equations of the output voltage waveform of the modified CHB-MLI in order to control the fundamental component and eliminate some low order harmonics. The proposed NR and PSO techniques are capable to minimize the Total Harmonic Distortion (THD) of the output voltage of the modified inverter within allowable limits. This paper aims to modeling and simulation by MATLAB of the modified topology of the CHB-MLI for a single-phase prototype for 13-levels. The inverter offers less THD and greater efficiency using PSO control algorithm compared with the NR algorithm. <br https://server9.kproxy.com/servlet/redirect.srv/sruj/snbzofspy/skvyzff/p1/> The performance of the proposed controllers based on NR and PSO techniques is verified through simulation.</span>

In this paper, a novel integrated SHE - NLC control is proposed for the mitigation of unwanted lower-order harmonics in the cascaded H-bridge multilevel inverter. The proposed algorithm has been developed by hybridizing the NLC and SHE methods, in an attempt to keep the merits of both the individual control. The switching angles and nearest levels are calculated by applying the Genetic Algorithm (GA). The proposed technique reduces the calculation time and implementation complexity, thus can be a viable alternative to the real time implementation for SHE. Integrated NLC-SHE control is tested by varying the modulation index and load dynamics. This technique resulted in the reduction in Total Harmonic Distortion (THDs) in load voltage and current. Comparative analysis of NLC, SHE and Integrated NLC-SHE technique is also performed on the CHB nine-level inverter. There is significant reduction in voltage and current THD values and power losses. Efficiency of the inverter is increased. The efficacy of the proposed control CHB nine-level is tested on MATLAB Simulink environment and further validated by experimental results.

Researchers in the field of multilevel inverters (MLI) have recently been focused on decreasing the number of power switches while maintaining a higher-level AC (Alternating current) output voltage waveform with a very lower total harmonic distortion (THD) value. To generate a nine-level output waveform, this article introduces the new topology of an asymmetrical cascaded auxiliary module multilevel inverter (ACAM-MLI). Twelve switches and four DC sources are needed by a traditional cascaded H-Bridge inverter to provide the same output voltage but the proposed inverter requires eight switched and a single DC source. The nearest level control (NLC)-PWM is applied to the proposed topology, and the results are compared to those obtained using a conventional seven-level full bridge cascaded multilevel inverter. To test the performance of the ACAM-MLI, inverter implemented on MATLAB 2023a and results presented at different load conditions.

Asymmetric Cascaded H-bridge (ACHB) level inverters can output more voltage waveforms with fewer cascaded units while ensuring the quality of output voltage waveforms, so they have attracted more and more attention. Taking the topology of Type-III asymmetric CHB multilevel inverters as the research object, a Modified Hybrid Frequency Pulse Width Modulation (MHF-PWM) strategy is proposed in this paper. This modulation strategy overcomes the local overshoot of low-voltage unit in the presence of traditional Hybrid Frequency Pulse Width Modulation (HF-PWM), thus completely eliminating the low frequency harmonics in the output voltage waveform of Type-III ACHB nine-level inverters, and the Total Harmonic Distortion (THD) of output line voltage of the modulation strategy is lower than that of PS-PWM strategy in the whole modulation degree, which effectively improves the quality waveform of the output line voltage. At the same time, the strategy can also improve the problems of current backflow and energy feedback caused by the high-voltage unit pouring current to the low-voltage unit, thereby reducing the imbalance of the output power of the high-voltage and low-voltage units. Finally, the Matlab/Simulink simulation model and experimental platform are established to verify the validity and practicality of the modulation strategy.