Harmonic Elimination Pulse Width Modulation Research Articles

Selective voltage harmonic elimination in PWM inverter using bacterial foraging algorithm

Pulse width modulation (PWM) techniques are increasingly employed in power electronic circuits. Among the various PWM methods used, selective harmonic elimination PWM (SHEPWM) method is popular and it is widely accepted for its better harmonic elimination capability and its ability to maintain output voltage regulation. However, in this method difficulty persists in the identification of switching instants as it involves non-linear transcendental equations for obtaining the desired solution. In this paper, bacterial foraging algorithm (BFA) method is proposed for switching angle selection in PWM inverter. The problem of voltage harmonic elimination together with output voltage regulation is drafted as an optimization task and the solution is sought through the proposed method. Extensive simulations are carried out using MATLAB/SIMULINK environment under various operating points with different switching pulses per half cycle. To demonstrate the superiority of the proposed method, BFA results are compared with other existing techniques such as Genetic Algorithm and Particle Swarm Optimization method. Further, the obtained simulation results are validated through experimental findings.

SHE–PWM Cascaded Multilevel Inverter With Adjustable DC Voltage Levels Control for STATCOM Applications

This paper presents a new multilevel selective harmonic elimination pulse-width modulation (MSHE-PWM) technique for transformerless static synchronous compensator (STATCOM) system employing cascaded H-bridge inverter (CHI) configuration. The proposed MSHE-PWM method optimizes both the dc-voltage levels and the switching angles, enabling more harmonics to be eliminated without affecting the structure of the inverter circuit. The method provides constant switching angles and linear pattern of dc-voltage levels over the modulation index range. This in turns eliminates the tedious steps required for manipulating the offline calculated switching angles and therefore, easing the implementation of the MSHE-PWM for dynamic systems. Although the method relies on the availability of the variable dc-voltage levels which can be obtained by various topologies, however, the rapid growth and development in the field of power semiconductor devices led to produce high-efficiency dc-dc converters with a relatively high-voltage capacity and for simplicity, a buck dc-dc converter is considered in this paper. Current and voltage closed loop controllers are implemented for both the STATCOM and the buck converter to meet the reactive power demand at different loading conditions. The technique is further compared with an equivalent conventional carrier-based pulse-width modulation to illustrate its enhanced characteristics. The effectiveness and the theoretical analysis of the proposed approach are verified through both simulation and experimental studies.

Selective Harmonic Elimination PWM Technique with Walsh Functions for Nine-Level Cascade Inverter

This paper presents a nine-level cascade inverter and gives its mathematical model of SHEPWM with Walsh functions. Based on the model, the solutions of the switching angles in the full range of fundamental voltage are calculated and listed, which is beneficial to the application of the nine-level cascade inverter.

Design and Real-Time Implementation of SHEPWM in Single-Phase Inverter Using Generalized Hopfield Neural Network

In this paper, a real-time implementation of selective harmonic elimination pulsewidth modulation (SHEPWM) using generalized Hopfield neural network (GHNN) as applied to the single-phase inverter is designed and discussed. Finding the location of the switching instants in the case of SHEPWM involves the solution of a set of nonlinear algebraic transcendental equations. The problem is redrafted as an optimization problem, and it is solved by using GHNN. Though, in principle, then number of harmonics can be eliminated using the presented methodology, this paper tries for the case of the elimination of the 5th-, 7th-, 11th-, and 13th-order harmonics while retaining the desired fundamental. An energy function is formulated for this problem and the set of ordinary differential equations (ODEs) describing the behavior of GHNN is obtained. A program in KEIL C was developed to solve these systems of ODEs by the Runge-Kutta fourth-order method to give the switching instants for continuously varying modulation indexes (M). A MATLAB simulation was carried out, and an experimental setup was also constructed in order to validate the simulated results. The fast Fourier transform analysis of the simulated output voltage waveform and the experimental output voltage waveform confirms the effectiveness of the proposed method. Hence, the proposed method proves that it is much applicable in the industrial applications by virtue of its suitability in real-time applications.

Theoretical Considerations for Single-Phase Interleaved Converters Operated With SHE-PWM

This letter defines selective harmonic elimination pulse width modulation (SHE-PWM) formulations for single-phase, interleaved converters. Through precalculated solutions, interleaved converters work at the same operating point while eliminating multiple low-order harmonics. It is shown that multiple continuous solutions can be acquired for three-level interleaved waveforms. Extending the method to multiple levels further complicates the problem and reduces both the number and continuity of the solutions. Searching for solutions when the maximum possible number of harmonics, that can be minimized using this PWM method, is reduced confirms that such compromise can provide additional solutions with a minimal effect on the waveform's harmonic distortion. The SHE-PWM considerations are verified with simulations and experimental results.

Enriching Electric Power Quality by using Bee Algorithm in Shunt Active Filters

The application of soft computing technique is growing fast in the area of power electronics and drives. The Bee optimization technique is considered as a new technique for power-quality (PQ) devices. The main objective of this paper is to present the Bee optimization method and Multiple Synchronous Reference Frame (MSRF) Theory in cascaded multilevel inverter for harmonic elimination. The foremost aim in Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) strategy is eliminating low-order harmonics, while the fundamental component is satisfied. In this paper, the Bee algorithm (BA) and MSRF theory is applied to a 9-level cascaded multilevel inverter using MATLAB software. The BA is based on the food foraging manners of a swarm of honeybees and it performs a neighborhood search joint with a random search. This method has higher accuracy and possibility of convergence. Simulation results prove supremacy of BA over MSRF theory in attaining perfect overall minima and higher convergence rate. Finally their results are compared and verified for a distorted three phase power system utility.

Application of differential evolution for cascaded multilevel VSI with harmonics elimination PWM switching

Harmonic elimination pulse width modulation (HEPWM) method has been widely applied to multilevel voltage source inverter (MVSI) to remove low frequency harmonics from its output voltage. However, the computation of the HEPWM switching angles for MVSI is very challenging due to several constraints, namely angle sequencing, very tight angular spacing and the numerous possibilities of angles distribution ratio. Realizing the potential of Differential Evolution (DE) to handle complex problems, this work proposes its application to solve the HEPWM problem for cascaded MVSI. Its emphasis is on improving the availability of HEPWM for higher output voltage by extending the maximum range of modulation index (M). It also removes the discontinuities in the switching angles and reduces the number of distribution ratio required to obtain the required solution. Compared to the most advanced (similar) work, i.e., 7-level MVSI with seventeen switching angles, DE covers a wider range of M; the maximum achievable M is 2.80. Furthermore, it exhibits very low second order distortion factor (DF2): for the worst case, the value of DF2 is 0.0014%. To verify the viability of the proposed algorithm, simulation is carried out and hardware prototype is constructed. Both results show very good agreement with the theoretical prediction.

Improved Method for Paralleling Reduced Switch VSI Modules: Harmonic Content and Circulating Current

A new zero-sequence circulating current (ZSCC) reduction method for multimodule voltage source inverters (MVSIs) consisting of P three-phase inverters that are connected in parallel is proposed in this paper. Four-switch inverter modules are used instead of the conventional six-switch modules to reduce the cost. In this paper, the effectiveness of the proposed ZSCC reduction method is studied using selective harmonic elimination pulse width modulation. The proposed ZSCC reduction method can remove about P times the number of harmonics using the same switching frequency as compared to more conventional methods, as explained later in this paper. The concepts discussed in the paper are confirmed with results obtained from an MVSI experimental prototype.

Harmonics Reduction in Cascade H-Bridge Multilevel Inverters Using GA and PSO

This paper presents the mitigation of total harmonic distortions (THD) in cascade H-bridge multilevel inverter. Selective harmonic elimination pulse width modulation (SHE- PWM) switching method is used to calculate the values of switching angles from the solution of non-linear transcendental equations. These non-linear complex equations is minimized by the using of particle swarm optimization (PSO) and genetic algorithm (GA) techniques, and also have been compared the simulating and analyzing results related to harmonics.

A review of soft computing methods for harmonics elimination PWM for inverters in renewable energy conversion systems

For a renewable energy (RE) system, an inverter is normally required to condition the dc power to ac, so that it could be connected to the electrical grid. At the heart of the inverter is the modulation strategy that synthesized the ac waveform by chopping the dc voltage using power electronics switches. Among the numerous modulation techniques, the harmonics elimination PWM (HEPWM) is preferable due to its superior harmonics profile; the elimination of low order harmonics results in reduced switching losses, hence improved inverter efficiency. However, the non-linear and transcendental nature of the HEPWM equations poses a challenge for the conventional computational methods (mostly calculus-based). With the advent of low cost and powerful computers, the soft computing (SC) approach seems to be a better approach and well suited to handle the complexity of the HEPWM problem. This review paper attempts to summarize the operation of the nine SC methods, as well as highlighting their advantages and limitations. Furthermore, the work also presents a critical evaluation on the performance of the three prominent SC techniques, namely, the Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and Differential Evolution (DE). It is envisaged that the information gathered in this single reference will be useful for researchers, designers and practitioners that utilize HEPWM to design energy conversion system.

Genetic Algorithm based Approach for Reduction of Total Harmonic Distortion in Photo Voltaic Inverter

paper, a genetic algorithm (GA) optimization technique is applied to cascaded multilevel photo voltaic inverter to remove pre specified order of harmonics and to reduce THD. Genetic Algorithm is developed as the preferred solution algorithm of specific harmonic elimination (PWM-SHE) switching pattern. This paper describes an efficient genetic algorithm that reduces significantly the computational burden resulting in fast convergence. An 11-level and 7-level inverter is preferred as a case study, and optimum switching angles are determined to eliminate low order harmonics and to reduce THD. Comparison has been done between the 7-level and 11-level with respect to the consideration of THD. Simulation results validate purpose method. Keywordsalgorithm, photo voltaic inverter, Selective harmonic elimination pulse width modulation (SHEPWM), Total harmonic distortion

Optimal selective harmonic elimination for cascaded H‐bridge‐based multilevel rectifiers

In medium-voltage medium- and high-power converters, it is of great importance to reach high-quality waveforms with low switching frequency. In active rectifiers, both converter's ac-side harmonics and grid preexisting distortions affect the quality of the input current, which according to the existing standards is restricted from both the individual harmonics amplitude and total harmonic distortion point of view. The well known selective harmonic elimination pulse-width modulation technique is able to completely eliminate certain harmonics from the ac-side voltage of the converter, and as a result increases the quality of the input current. In this study, an optimal selective harmonic elimination control strategy is introduced for cascaded H-bridge (CHB) rectifiers. By fully manipulating the ac-side waveform of the rectifier, maximum number of harmonics is eliminated for a specific number of switching transitions. Moreover, this method can be easily extended for any number of H-bridge cells and it uses only one lookup table for the whole interval of modulation index. Also using an effective voltage balancing technique, dc-link voltages are balanced to the reference value and the rectifier does not encounter any difficulty under equal or nonequal loads conditions. Using this method, the size of the bulky line-side filters can be reduced which leads to lower overall cost of implementation. To prove the feasibility of the proposed scheme, simulation and experimental results for a seven-level CHB-based rectifier are reported.

Improved SHEPWM Strategy By The Robustness Optimization Algorithm In Multilevel Inverters With Equal DC Sources

A multilevel Inverters have many advantages such as reduced Harmonics, no need for a transformer, cost and loss reduction. In this paper the multilevel inverter with equal DC sources is used for THD optimization. Different modulation methods have been proposed to control the multilevel inverters. This paper focuses on the Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) technique in multilevel inverter with equal DC sources. In the SHEPWM technique for multilevel inverters, in order to eliminate N-1 non-triplen odd harmonics of the AC-side voltage and to regulate the output line voltage amplitude, N switching angles need to be determined. Therefore a set of N non-linear transcendental equations must be solved to find the desired switching angles for any value of the modulation index. In this paper a new robustness optimization algorithm is presented to elimination of selective low order harmonics (LOH) in the output line voltage of the multilevel inverter based on the Multi Population Particle Swarm Optimization (MPPSO) algorithm. The switching angles are computed by a MPPSO algorithm to eliminate of LOH with high accuracy and determine the fundamental component to the desired value simultaneously. The proposed algorithm can generate stepped voltage waveforms with a wide range of modulation indices. The performance of the proposed algorithm for a seven-level cascaded H-bridge converter, based on simulation studies, is evaluated. MATLAB software is used for programming and simulation.

On re-examining symmetry of two-level selective harmonic elimination PWM: Novel formulations, solutions and performance evaluation

This paper analyzes the half-wave symmetrical two-level SHE-PWM, proposes two formulations of the SHE-PWM waveform with multiple solutions and evaluates the solutions for different cases of eliminated harmonics. Previous work on SHE-PWM focused on algorithms for calculating the solutions and only considered the quarter-wave symmetry in the formulation. In this paper two different formulations to the problem are considered and solutions for a number of eliminated harmonics are presented. The different formulations increase the solution space of the problem and the number of acquired solutions. A comparison of the solutions in terms of harmonic performance is also presented. When compared with the quarter-wave symmetrical solutions, certain half-wave symmetrical solutions exhibit better performance and additional benefits can be acquired for two-level converters operated under SHE-PWM techniques. The HW symmetrical solutions are experimentally verified on a laboratory setup in order to confirm the validity of the solutions sets.

Hybrid Seven-Level Cascaded Active Neutral-Point-Clamped-Based Multilevel Converter Under SHE-PWM

This paper presents the hybrid seven-level cascaded active neutral-point-clamped (ANPC)-based multilevel converter. The converter topology is the cascaded connection of a three-level ANPC converter and an H-bridge per phase. The voltage of the H-bridge is actively maintained to the required level through selection of the switching states of the converter. The topology is operated under selective harmonic elimination pulsewidth modulation (SHE-PWM), maintaining the switching frequency of the converter to a minimum. The operating principles, voltage balancing methods, and limitations of the converter are analyzed together with extensive simulation results of the topology. Experimental results from a low-power laboratory prototype are presented that verify the operation of the hybrid converter under SHE-PWM.

Selective Harmonic Elimination PWM for Cascaded Multilevel Inverter Based Genetic Algorithm and Newton Raphson: a Comparison Study

The Selective Harmonic Elimination Pulse Width Modulation technique (SHEPWM) is widely used for eliminating pre-selected lower order harmonics in multilevel inverters (MLI) output voltage with controlling the fundamental voltage component. The problem of roots solving of the set of transcendental nonlinear harmonic equations derived by Fourier analysis is addressed in many recent researches. The Newton Raphson (NR) method is limited used in case of multilevel inverter controlled by SHEPWM, due to the transcendental nature of the system set of equations and dependency of roots initial values. Modern optimization techniques such as Genetic Algorithm (GA) optimization are widely used in case of MLI controlled by SHEPWM. The main problem when using GA is how to find the switching angle patterns for a wide range of the modulation index (M). Which they eliminate pre-selected lower order harmonics and controlling the fundamental voltage component with minimum Total Harmonic Distortion (THD). In this paper a comprehensive study to obtain the required switching patterns which satisfy elimination pre-selected lower order harmonics at minimum THD from cascaded MLI output voltage controlled by SHEPWM was performed. The performance of cascaded multilevel inverter controlled by SHEPWM is compared based on calculating the required switching patterns using NR and GA methods. A significant improve in the obtained solution sets in a wide range of M in GA is achieved. In particular, it is shown that there are new solution sets which haven't been previously reported in literatures. Selected simulation and experimental results for 5, 7, 9 and 11 MLIs were reported to verify and to validate the theoretical findings.

Neural Network Based Pipelined-Parallel Generation of PWM Signals Suitable to Drive Three Single Phase UPS-ENG

A reliable technique has been proposed to generate a real time pulse width modulation (PWM) signals in order to drive three – single phase uninterruptible power supply (UPS). The PWM patterns have been generated using field programmable gate array (FPGA) and based on selective harmonic elimination method. These patterns are used to drive the six of switching power transistors of the voltage source inverter to produce three – single phase UPS. In order to solve the problem of the complexity of the nonlinear transcendental equations, an intermediate steps have been taken, using artificial neural network (ANN). This will overcome the problem of the off line solution and therefore obtaining the required data to solve the obstacle solution from off line to on line. Therefore, the trained ANN is implemented in a parallel hardware by using FPGA. The benefits of using FPGA to perform ANN are promising and the technique becomes very attractive. It allows a real time, simple, fast, reliable and efficient design with low hardware costs. Finally generating selective harmonic elimination pulse width modulation (SHEPWM) patterns as a real time signals are become visible. Keywords: Field programmable gate array, Selective harmonic elimination pulsewave modulation, Neural networks

Optimum control of total harmonic distortion in field programmable gate array-based cascaded multilevel inverter

Nowadays high quality power is essential for medical, research and industrial applications to produce good quality results and analysis. In this work an attempt has been made to improve the power quality by minimizing the harmonic content in the output voltage of a cascaded multilevel inverter using the selective harmonic elimination pulse width modulation technique. Sinusoidal PWM technique is used to generate the switching signals. A single phase nine-level cascaded multilevel inverter with identical DC supply is designed to reduce the harmonic components of the output voltage. Particle swarm optimization technique is applied to determine the optimum switching angles, thereby reducing some higher-order harmonics while maintaining the required fundamental voltage. This generalized technique can be extended to multilevel inverters with any number of levels. The total harmonic distortion is measured accordingly for different modulation indices. A prototype model of a field programmable gate array-based nine-level inverter has been designed, fabricated and tested. The results are presented and analyzed and hence the hardware results are verified with the simulation results.

On the improved computational speed and convergence of the Newton Raphson iteration method for selective harmonics elimination PWM applied to cascaded multilevel inverter with equal and non‐equal DC sources

PurposeThis paper proposes an improved algorithm to compute selective harmonics elimination pulse width modulation (SHEPWM) angles, based on the Newton‐Raphson (NR) iteration for cascaded multilevel inverter (CMI).Design/methodology/approachNewton Raphson (NR) is a very popular numerical method for transcendental equations that lack analytical solutions. It has been successfully used to compute the angles for selective harmonics elimination pulse width modulation (SHEPWM) schemes. Despite its effectiveness, NR has not been used for SHEPWM with cascaded multilevel inverter (CMI) structure with equal and non‐equal DC voltage sources. It is known that for CMI, inappropriate selection of initial angles causes long‐iteration time and possibly non‐convergence takes place. The computational difficulty is compounded by the fact that the SHEPWM switching angles need to be correctly sequenced, i.e. each angle must be assigned to the correct output voltage level of the CMI. In this work, an attempt is made to reduce the iteration time and to resolve the non‐convergence problem. The main idea is to relax the switching angle constraint by placing the switching angle sequencing outside the main loop of NR iteration. This allows for the program to run more freely and able to generate more possible solutions for the switching angles. Then these angles are selected to fulfill the requirements of multilevel sequencing. The performance of the proposed technique will be compared with the standard NR for CMI with equal and non‐equal DC sources. The latter case is quite common for CMI with renewable energy applications because the sources normally have different voltage levels.FindingsUsing MATLAB simulation, it will be shown that using this scheme, accurate SHEPWM angles can be achieved for a wide range of fundamental components. Furthermore, significant reduction in iteration time to compute the SHEPWM switching angles is achieved.Originality/valueThis paper proposes an improved algorithm to compute SHEPWM angles based on NR iteration.

Optimised active harmonic elimination technique for three‐level T‐type inverters

This study develops a pulse-width modulation (PWM) method that is referred the optimised active harmonic elimination (AHE) technique to eliminate more harmonics with minimum switching frequency for three-level T-type converter (3 L-T2C) based on the fundamental frequency switching control method. First, Homotopy algorithm is applied to non-linear transcendental equations to eliminate low-order harmonics and to determine switching angle sets for selective harmonic elimination PWM in 3 L-T2C. The characteristics of the multiple solutions in terms of harmonic distribution, and total harmonic distortion (THD) are investigated. Then a detailed analysis of optimised AHE-PWM technique is presented to cancel more harmonics in 3 L-T2C using harmonic compensation strategy. A switching angle solution set that gives the lowest THD for optimised AHE-PWM is derived and the effectiveness of the control method is verified through extensive simulation studies. Finally, selected experimental results are reported to verify and validate the theoretical and simulation findings.