Implementation of a multi-level inverter based on selective harmonic elimination and zig-zag connected transformers

This paper presents the multi carrier pulse width modulation (MCPWM) and selective harmonic elimination (SHE) technique for cascade multilevel inverter (CMI) to reduce the total harmonic distortion (THD) of the output voltage waveform. A comparison has been done between the SHE and MCPWM technique to show the advantage of SHE technique over the MCPWM technique. To find the accuracy of total harmonic distortion (THD) between the MCPWM and SHE technique is achieved by comparing the FFT based result for nine level cascade multilevel inverter.

This article presents a hybrid method to solve the selective harmonic elimination (SHE) problem for an adaptive DC bus multilevel inverter (MLI) topology. The proposed hybrid method combines the Grey wolf optimization (GWO) technique and Newton-Raphson (NR) numerical method which drastically minimizes the computational time and further improves the accuracy of the SHE solution. The technique is essentially divided into two stages. In the exploration stage, GWO explores the entire search space of SHE problem and provides initial values of switching angles for a given modulation index with a fast rate of exploration. In the exploitation stage, the NR method uses these initial switching angles as input to iteratively determine the optimum value of the firing angles. This GWO-inspired iterative methodology is implemented on a hybrid MLI topology for photovoltaic (PV) system applications. The performance of proposed SHE method is compared with recently developed metaheuristic SHE techniques based on some key performance indices. From an application point of view, the 11-Level MLI is tested on a PV battery-based stand-alone system to determine the effectiveness of the proposed method in MATLAB/Simulink environment. Finally, a small-scale experimental prototype is developed to validate the proposed method.

Purpose The purpose of this study is to present a new methodology of selective harmonics elimination (SHE) technique suitable for single-phase photovoltaic (PV) tied pulse width modulated (PWM) inverter. Design/methodology/approach In the proposed SHE, switching angles for inverter control are determined offline through numerical techniques and stored in a microcontroller memory as a function of modulation index (md). The methodology uses the solution that leads to a lower change of switching angles from the previous modulation index (md) for storing in the processor memory for multiple solutions. This leads to a smaller number of sections when a piecewise mixed model is considered for storing the entire switching angle curve for the online inverter control. The proposed idea is simulated and experimentally validated on a laboratory prototype of PV (500 W) grid-tied PWM inverter. The control environment is then realized in NI c-RIO 9082. Findings This proposed technique is suitable for limiting voltage total harmonics distortion (THD) in single-phase PV tied grid connected voltage source inverter (VSI). Moreover, it is found that filter (L-C) size requirement is less. Originality/value The proposed SHE with piecewise mixed model technique effectively reduces voltage THD with less filter size (L-C) in a single-phase PV-tied system.

Multilevel inverters (MLIs) are widely recommended for DC to AC power conversion as per the load requirements. The MLIs are preferred over other types of multilevel and conventional converters due to their ability to produce staircase output voltage waveforms with superior harmonics profile. However, the performance of MLIs largely depends on the modulation strategy employed. Among the various modulation techniques, the selective harmonic elimination (SHE) method is more efficient in eliminating low-order harmonics from the voltage waveform produced by MLIs. Proper mitigation of the dominant low-order harmonics results in reduction in switching losses in the semiconductor devices and improves the efficiency of the inverter. However, the analytical solution of the nonlinear SHE equations constitutes the main challenge. Over last few decades, various solving algorithms and techniques such as algebraic methods such as resultant theory, numerical techniques and optimization algorithms have been developed and proposed for selective elimination of unwanted harmonics. This review paper presents the various aspects of the problem formulations for SHE technique. Moreover, the detailed principle operation for five different SHE problem-solving techniques is also discussed in this paper. Solution trajectories corresponding to multiple solutions, PWM waveforms with single and multiple transitions at each voltage level and also for pulse-width-amplitude modulation are evaluated and presented to help the researchers gain better insight into the SHE problem and its solution.

Selective Harmonics Elimination (SHE) technique of power electronic converters can be generally defined as calculation of the optimized switching angles at any desired output (fundamental) voltage component to eliminate a set of preferred lower order harmonic components. This low switching frequency method adds values to Multilevel Inverter (MLI) based systems for the reason that MLI’s have the ability to synthesize waveforms closer to sinusoidal with a better harmonics spectrum. The traditional method for finding the optimized switching angles is by solving the Fourier non-linear transcendental equations of the MLI output voltage and various algorithms like Newton-Raphson (NR) algorithm, Genetic algorithm (GA), Resultant theory, Walsh function etc. are available. This paper proposes a novel approach for performing SHE in MLI working with both equal and unequal dc voltages. The basic principle in which the proposed technique works is a combined effect of equal area criteria and negative harmonics injection techniques. The major advantage is that the proposed methodology comprises of four simple equations for performing SHE instead of solving the complex non-linear transcendental equation. The computational efficiency of this algorithm is evaluated through comparison with traditional NR and GA. In addition, a prototype of three-phase seven-level cascaded MLI is designed through which several informative results are investigated and the effectiveness of the proposed algorithm is proved.

This article proposes a general mathematical solution for a selective harmonic elimination (SHE) technique. The proposed procedure is valid for both symmetrical and unsymmetrical multilevel inverter (MLI) inverter configurations with a wide range of modulation indexes (mi). The proposed procedure eliminates the targeted number of harmonics “ $l$ ” for switching angles $\text {NS}= 2^{l}$ regardless to the MLI output waveform levels. The proposed procedure receives the values and ratios of the dc sources, and then, it calculates the NS values to generate a suitable set of harmonic equations. In this proposed algorithm, the nonlinear transcendental harmonic equations were transformed into a linear system of equations ( $A X=B$ ); the resulting equations can be solved online easily by formulating matrix A and matrix B and then multiplying the inversion of matrix A by matrix B. It has been found that only the last element in matrix B needs to be updated for each change in the modulation index or in the ac output fundamental component, resulting in reduced computation time. The proposed technique generates the switching angles $\alpha _{1}, \alpha _{2}, \ldots, \alpha _{k}$ based on a preset objective functions. The simulation and experimental results in some selected cases are provided to validate the proposed algorithms.

This paper presents, ant colony optimization based hybrid algorithm for selective harmonic elimination in single phase seven level multilevel inverter with reduced switches. For high power and high voltage applications, multilevel structure with selective harmonic elimination (SHE) modulation scheme is used. The output voltage of multilevel inverter contains fundamental component along with harmonics. SHE technique aims to solve non-linear transcendental equations maintaining the fundamental harmonic component to its desired value and to eliminate lower order odd harmonics. Many optimization algorithms have been implemented to solve this problem. But these algorithms are complicated and time consuming. The Newton–Raphson algorithm is also very convergent for solving these non-linear equations. The main disadvantage of this method is, it requires strong initial guess. To overcome these drawbacks, hybrid optimization algorithm is used in this paper. This algorithm is performed in two stages, during first stage ant colony optimization has been run and in second stage the solutions obtained from ACO is used as a initial guess for Newton–Raphson algorithm which confirms the exact converged solution. Thus the drawback of Newton’s method i.e. requirement of good initial guess is overcomed by proposed hybrid algorithm. The MATLAB/SlMULINK software is used for comprehensive simulation of seven-level inverter. Experimental results validate the simulated results.

Multilevel inverters when supplied from equal and constant DC sources does not have a practical sense of applications. For each of the specific harmonic profiles the variation of the DC sources affects the values of the switching angles. This increases the difficulty of the harmonic elimination's equations. This paper presents the application of the cascaded asymmetrical multilevel inverter in the railway traction drive. The total harmonic distortion (THD) reduces with the increase in the voltage level. Various modulation techniques such as Phase Shifted Modulation (PSM), Level Shifted Modulation (LSM) and Selective Harmonic Elimination Techniques (SHE) were implemented in order to find the best modulation techniques among them. Also it is shown that SHE technique resulted in low THD. Thus, an IGBT based-cascaded five level asymmetrical inverters with SHE method has been modelled to lower the supply voltage to a level convenient for the traction induction motors.

specific odd harmonics can be mitigated by operating the semiconductor switches in H-bridge inverters at optimized switching angles of the PWM signals. These switching angles can be achieved by deriving a number of nonlinear equations using Selective Harmonic Elimination Pulse Width Modulation (SHE-PWM) method. Modulation index (m) is a significant parameter used to control the amplitude of the fundamental output voltage of DC-AC inverter. By changing the value of modulation index the Total Harmonics Distortion (THD) also will change. In this paper, the performance of single phase full-bridge inverter using SHE-PWM scheme with varying the modulation index is evaluated. In order to achieve a minimum THD, a different number of nonlinear equations are used to calculate the switching angles. The performance of a single phase unipolar inverter is simulated in Matlab.

This paper proposes two different techniques to optimize the harmonic content in 15-level cascaded H-bridge multi-level inverter (MLI). The proposed techniques are used to determine the switching angle for cascaded H-bridge MLI by solving the non-linear equation using Genetic algorithm (GA) and Newton Raphson (NR) method. Operation for medium voltage and High power converter requires a high-quality waveform with low switching loss. The quality of waveform depends on the number of voltage levels. Higher the voltage level, less will be the harmonics content of different orders. Dominant orders of harmonics have more deteriorating effect in the output wave shape of the inverter. If they are reduced, it will improve the nature of the wave shape. This may be done by applying selective harmonics elimination (SHE) technique. Genetic Algorithm (GA) and Newton-Raphson (NR) techniques have been used in SHE for generating switching pulses for a cascaded multilevel inverter. The simulated results have been presented in this paper indicating the elimination of dominant order of harmonics.

The paper presents non-traditional solutions to the problem of selective harmonic elimination (SHE) in induction motor drives fed by three-phase voltage-source inverter (VSI). The problem is independently solved using genetic algorithms (GA) and particle swarm optimisation (PSO). The inverter switching angles are determined such that the low-order harmonics up to the 17th are eliminated, while the fundamental component is set at a desired value. Findings of the research show that both routines could converge to accurate solutions. PSO outperforms GA in terms of the time of convergence and obtained value of the objective function, while GA is characterised with better robustness. The performance of the VSI-fed induction motor drive is studied under the SHE switching pattern. Results clearly show the merits of applying the SHE technique to the induction motor drive.

Selective harmonic elimination (SHE) technique is used in power inverters to eliminate specific lower-order harmonics by determining optimum switching angles that are used to generate Pulse Width Modulation (PWM) signals for multilevel inverter (MLI) switches. Various optimization algorithms have been developed to determine the optimum switching angles. However, these techniques are still trapped in local optima. This study proposes an opposition-based quantum bat algorithm (OQBA) to determine these optimum switching angles. This algorithm is formulated by utilizing habitual characteristics of bats. It has advanced learning ability that can effectively remove lower-order harmonics from the output voltage of MLI. It can eventually increase the quality of the output voltage along with the efficiency of the MLI. The performance of the algorithm is evaluated with three different case studies involving 7, 11, and 17-level three-phase MLIs. The results are verified using both simulation and experimental studies. The results showed substantial improvement and superiority compared to other available algorithms both in terms of the harmonics reduction of harmonics and finding the correct solutions.

This paper deals with simulation analysis of Selective Harmonic Elimination (SHE) for PV operated Quasi Impedance Source Inverter (q-ZSI) drive system. Electricity generation using Photovoltaic cells is a promising form of sustainable energy. A quasi-Z source inverter (q-ZSI) can minimize the power fluctuations from the electric energy generated by a PV paneL In the existing system, during the discharge of energy stored battery Harmonic Distortion is more. The proposed topology describes an improved ability to compensate power while maintaining a constant dc-link peak voltage with minimum harmonics. It is promising to note that the THD level decreases significantly with the introduction of a closed loop controller with Selective Harmonic Elimination technique. Thus the proposed system provides an efficient means of PV power generation.

This paper reports hardware implementation of three-phase inverter using selective harmonic elimination technique by PIC16F877A microcontroller, whereas the notch angles are calculated through particle swarm optimisation (PSO) technique. This technique is proposed to minimise the overall total harmonic distortion (THD) of the output voltage of PWM inverter and corresponding switching angles are computed. This method is applied for the bipolar switching case, in three-phase inverter for three switching angles and five switching angles. The switching angles are computed to completely eliminate the lower order harmonics.

In this article it proposes a high efficient softswitching scheme based on zero-voltage-switching (ZVS) and zero-current-switching(ZCS) principle operated with a simple auxiliary circuit extended range for the front-end isolated DC-AC-DC-AC high power converter with an three phase three level diode clamped multi-level inverter by using Accelerated Particle Swarm Optimization technique(APSO) with Total Harmonic Distortion(THD), Switching losses, Selective harmonic elimination maintaining with its fundamental values as an objective function. The proposed scheme realize zero-voltage-switching for leading of inverter leg and zero-current switching for lagging leg of inverter. The proposed ZCS scheme is effective by using a simple auxiliary circuit, and it is suitable for applications where low-voltage dc to high-voltage three-phase ac power conversion is required. Output from the inverter applied to three phase three level diode clamped inverter executed with a selective harmonic elimination technique by using APSO and found to be efficiency of inverter is increased with its quality output.