Time-domain optimization of current THD for a single-phase three-level inverter modulation

Power electronic converters for medium and high power / voltage applications employ low frequency synchronous fundamental switching to minimize semiconductor switching losses. There are two major approaches to converter switching angles determination - Selective Harmonic Elimination (SHE) and Total Harmonic Distortion (THD) minimization. For the THD minimization, converter switching angles are found to assure minimum THD criterion without taking care of frequency spectrum. For the SHE approach, all degrees of freedom due to available amount of switching angles are spent on elimination of low order harmonics. Recently suggested combined approach suggests spending some degrees of freedom on certain harmonics elimination and the rest for minimizing THD. This generalized problem formulation includes classic minimal THD and SHE problems as special cases. The paper presents comprehensive results on combined SHE and THD minimization for a staircase modulation of a single-phase converter with 5, 6, 7 and 8 switching angles (6, 7, 8 and 9 non-negative voltage levels).

This paper presents a modulation method based on the selective harmonic elimination-pulse width modulation (SHE-PWM) technique. The aim is to determine the optimal switching angles (SA) using the teaching learning-based optimization algorithm (TLBOA), capable of reducing the voltage total harmonic distortion (THD) present in the output waveform of single-phase multi-level inverters (MLIs). The performance of proposed technique has been verified through simulation using Matlab script and Simulink environment. The TLBOA-based SHE-PWM technique is applied to a 17-level inverter to eliminate 5th, 7th, 11th, 13th, 17th, 19th and 23rd harmonics, achieving an improvement of up to 4.31% in the phase voltage THD content in the range of modulation index (MI) 0.5 to 0.95. Furthermore, the superiority of the proposed technique was confirmed by comparison with conventional modulation techniques, which showed that the proposed technique produces lower THD than those used in the equal phase (EP), half-equal phase (HEP), feed forward (FF) and half height (HH) methods.

The preprogrammed pulse width modulation (PWM) method for operating power converters ensures minimum switching loss and at the same time better quality waveform at the output. The Fourier series analysis of the predefined output waveform with the removal of certain low order harmonics yields a set of trigonometric equations in which switching angles are treated as variables. It results in removal of preselected harmonics from the output and control on the fundamental component. The main challenge in implementation of selective harmonics minimization is in solving of these system of highly non linear equations which have different number of solutions for different range of modulation index. The particle swarm optimization technique can be used to obtain switching angles from the system of highly non linear equations by properly formulating an objective function which need to be minimized. The requirement of symmetry constraints on the output waveform can be implemented using penalty function approach. The main advantage of the PSO approach over algebraic and numerical based techniques is that it can be used for computation of large number of switching angles with less dependency on the initial guess of the solution.

Synchronized space vector pulse width modulation (SSVPWM) is widely employed in high‐power AC drive systems. The existing methods are carrier‐based, in which the carrier ratio, position of samples, and switching sequences used to generate every sample for a given SSVPWM are settled, which causes two problems: (i) the control delay changes, and a voltage phase modulation error appears suddenly during transition between different SSVPWMs with different carrier ratios, which causes motor current spikes; (ii) due to the particular switching sequences, some kinds of SSVPWM cannot get into six‐step operation by overmodulation. This paper proposes an improved type of SSVPWM based on switching angles, in which the carrier ratio of a given SSVPWM can change flexibly, and the problems mentioned above can be solved. Theories including switching angle calculation, overmodulation strategy, carrier ratio setting principle, and transition rules between different SSVPWM modes are given in this paper. Meanwhile, the switching angles change linearly with modulation index which makes it easy to implement, and the modulation error in the overmodulation region is effectively limited so that the proposed scheme is suitable in the whole modulation index range. A case study of a 5.5‐kW experimental platform is presented to validate the proposed method. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

The equivalence of space vector pulse width modulation (PWM) and carrier-based PWM through the injection of a common-mode voltage is already known for two-level (first min-max injection) and multilevel (double min-max injection) three-phase converters. However, under regular sampled phase voltage references, these injections do not produce the lowest total harmonic distortion (THD) of the load phase current throughout the linear modulation index range. This paper proposes the use of a similar common-mode injection, called the second min-max injection that achieves the lowest current THD in regions of the modulation index range where the double min-max injection fails to do so. A cascaded H-bridge (CHB) topology is analyzed, and comparison is made between different multicarrier modulation strategies, using simulation results, under different injections for the whole modulation index range. The level-shifted in-phase disposition modulation method is found to produce the lowest load phase current THD with second min-max offset voltage injection for modulation indices below unity. For modulation indices greater than one, the double min-max injection is still considered as optimal.

This study describes the application of a soft computing method – known as differential evolution (DE) to implement the harmonics elimination pulse‐width modulation (HEPWM) for a 15‐level, multi‐level voltage source inverter (MVSI). The main feature of this technique is the wide range of fundamental output voltage that can be achieved, while maintaining a very low total harmonics distortion (below 6%). The fundamental voltage can be controlled very precisely (very small step size) and the trajectories of the HEPWM angles are continuous over the whole range of modulation index – making it very suitable for utility and variable speed drives application. The study details the procedures to obtain the HEPWM angles trajectories, which include the formulation of objective functions, appropriate selection of the DE evolutionary parameters and stopping criterions. The viability of the proposed method is simulated using MATLAB/Simulink and verified by a three‐phase, cascaded‐type MVSI test rig. Experimentally, The HEPWM waveforms are implemented using the Altera field programmable gate array, whereas the 15‐level MVSI is built using metal–oxide semiconductor field effect transistor H‐bridge. Selected results are presented; the simulation and hardware results are found to be in very close agreement with the theoretical predictions.

In this paper, a study has been performed on current source DC-AC boost inverter especially for Photovoltaic (PV) applications. It presents a reactive power control strategy and its effects on the other parameters of the system. It also prescribes a range of modulation index; at which the percentage of Total Harmonic Distortion (THD) is within the suitable limit according to the IEEE standard 519. The reactive power controlling mechanism has been achieved by finding the right combination of bank capacitors placed between the inverter and the load side for different modulation index (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ). Sine Pulse Width Modulation (SPWM) technique has adopted for generating switching signals of the Boost Inverter which controls the output parameters of the inverter. A set of parameters have been studied along with in-depth analysis and simulated which are presented to demonstrate the effectiveness of the proposed control technique.

Low switching frequency operation of multilevel inverter enables it for applications in high power processing needs. The stepped waveform synthesized from multilevel inverter after Fourier series analysis will result in system of nonlinear equations to selectively minimize certain lower-order harmonics from it. These equations are transcendental and exhibits solutions or no solution in certain range of modulation index. In order to obtain continuous solution in entire modulation index range optimization techniques based on meta-heuristic approach is used. In order to achieve better quality waveform at output and selectively removing certain low-order harmonics an ant colony optimization-based technique in continuous mode implementation is proposed in this paper. The simulation and experimental results are provided to confirm the correctness and effectiveness of the method.

In order to minimise the switching losses, low switching frequency pulse width modulation (LSPWM) approach is chosen for medium voltage high power applications. In these techniques, solving a system of non linear transcendental equations is the primary issue to obtain the switching instants to minimize the pre-specified harmonics along with control on the fundamental component. The number of switching angles employed is proportional to the amount of harmonics minimized from the output. Furthermore, the system of equations exhibits multiple solution, no solution or unique solution in different range of modulation index. In this paper, harmonics minimization based on differential evolution in voltage source inverter is proposed to determine the optimum solution in complete linear range of modulation index to minimize lower order harmonics from the output voltage. To validate the proposed concept, a TMS320F2812 DSP based hardware implementation of voltage source inverter developed with intelligent power module (IPM), FSB20CH60B/600V @ 20A is given in the paper.

This paper presents the use of grasshopper optimization algorithm based selective harmonic minimization pulse-width modulation technique for optimizing the switching angles of five-phase nine-level multilevel inverter. The proposed algorithm is able to provide optimum switching angles in a wide range of modulation index. Besides, the switching angles obtained by the proposed algorithm can be used to synthesize an output voltage waveform with desired fundamental component and minimized undesired low order harmonics. MATLAB simulation results show the proposed algorithm can provide a wide modulation index range of optimum solutions. Furthermore, both MATLAB simulation and PSIM experimental results obtained from five-phase nine-level cascaded H-bridge multilevel inverter show good agreement, confirming the validity of switching angles calculated using the proposed algorithm.

In this paper, PSO (Particle Swarm Optimization) based technique is proposed to derive optimized switching angles that minimizes the THD (Total Harmonic Distortion) and reduces the effect of selected low order non-triple harmonics from the output of the multilevel inverter. Conventional harmonic elimination techniques have plenty of limitations, and other heuristic techniques also not provide the satisfactory results. In this paper, single phase symmetrical cascaded H-Bridge 11-Level multilevel inverter is considered, and proposed algorithm is utilized to obtain the optimized switching angles that reduced the effect of 5th, 7th, 11th and 13th non-triplen harmonics from the output voltage of the multilevel inverter. A simulation result indicates that this technique outperforms other methods in terms of minimizing THD and provides high-quality output voltage waveform

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 proposes a family of multiport switched-capacitor multilevel inverter (SCMLI) topologies for high-frequency ac power distribution. It employs asymmetric dc voltage sources with a common ground that makes it ideal to be employed in renewable energy farms and modern electric vehicles. The proposed family of step-up SCMLI attains higher number of output voltage steps with optimum component count in comparison to several existing topologies. The problem of capacitor voltage balancing is solved as the capacitors are inherently charged to a finite voltage every half cycle. In-depth study on two staircase modulation strategies, namely, selective harmonic elimination and minimum total harmonic distortion (THD) scheme is presented with study on the variation of switching angles and THD with modulation indices under both schemes. Working principle and analysis are presented for the proposed family of topologies. Simulation outcomes are validated with experimental results under both the aforementioned modulation schemes with equal and unequal output voltage waveform steps.

To cut down switching losses, the low switching frequency pulse width modulation (LSF-PWM) approach is preferred for medium voltage and high power applications. The major challenge with these strategies is obtaining the switching instants by solving a series of non linear transcendental equations in entire modulation index range. The number of switching angles employed determines how many harmonics are controlled from the output. Furthermore, across various ranges of modulation index, the system of equations reveals several solutions, no solution, or a single solution. The numerical and algebraic techniques does not provide any solution in modulation index range of beyond 0.9 and therefore restricts the maximum achievable output voltage in the entire range. In this paper, minimization of harmonics based on Imperialist Competitive Algorithm in a three phase two-level voltage source inverter is proposed to obtain the optimum solution in the modulation index range of 0.8 to 1. A DSP controller based hardware implementation of a three phase two-level voltage source inverter designed with intelligent power module (IPM) is provided in the research paper to validate the proposed idea.

To reduce the number of sensors in the three-phase current source inverter and lower its cost and size, using a single dc-Link voltage sensor to reconstruct the three-phase ac voltage is a simple and effective solution. However, due to nonideal factors during the sampling process, accurate dc-Link voltage measurement cannot always be achieved, especially at the sector boundaries and low modulation index, where the dwell time of the active vector is short, which leads to voltage reconstruction failure. To address this issue, this article proposes an improved voltage reconstruction method based on virtual space vector modulation. The modulation index is divided into low, medium, and high regions according to constraint conditions. In the low modulation region, the reference current vector is synthesized from virtual vectors constructed from three adjacent active vectors. In the medium region, the virtual vectors are formed by two adjacent active vectors. In the high modulation region, the reference current vector is directly synthesized using three adjacent active vectors. This ensures that the dwell time of the sampled current vectors exceeds the minimum required sampling time. The proposed method reduces the measurement dead zone and can achieve three-phase voltage reconstruction under wide/full modulation index range. In addition, this method can also reduce the amplitude and lower-order harmonics of common-mode voltage. Experimental results validate the effectiveness of the proposed voltage reconstruction method.