Control Strategy for Renewable Energy System Using Transformerless HERIC Bridge Inverter

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).

Two and three level VSC inverters are the building blocks of most of inverter applications necessitating the employment of appropriate switching techniques that result in harmonic free sinusoidal output. The paper presents the generalized method for harmonic elimination in two and three level voltage sourced converter. The technique used for suppression of selective low-ordered harmonics form the inverter's output voltage waveform is Selective harmonic elimination (SHE). The inverter's output voltage waveform is mathematically modeled using Fourier series that results in the system of nonlinear equations. The non-linear equations are solved for eliminating the specific low order harmonics. The main objective in calculating appropriate switching angle is to minimize the value of Total Harmonic Distortion (THD). To solve the system of non-linear equations numerical method Newton Raphson is applied and appropriate switching angles are calculated. The remaining uneliminated higher order harmonics are eliminated by connecting appropriate value of filter at the output stage of VSC inverter. The model of two level VSC is simulated in SimPowerSystem Matlab tool bar together with the algorithm of Newton Raphson technique. The time domain plot and frequency spectrum of inverter's output waveform is presented in the results section. The results of two and three level VSC inverters are analyzed and debated together with the comparative analysis on the basis of THD. Moreover, a comparison is presented on the basis of IEEE standard Std. 519 and EN 50160.

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.

For medium- and high-power electronic application technologies, the three-level neutral-point-clamped (3L-NPC) inverter is an effective solution and modulation method is one of its research focuses. There are many modulation strategies for the 3L-NPC inverter, among them, the selective harmonic elimination pulse width modulation (SHEPWM) and selective harmonic mitigation pulse width modulation (SHMPWM) techniques are very useful technologies since they have the characteristics of selective harmonics reduction or elimination. In this paper, simulation models of the 3L-NPC inverter with 10kV grid based on total harmonic distortion (THD) using the SHEPWM and SHMPWM techniques are built in MATLAB/SIMULINK. Here, both the SHEPWM and SHMPWM techniques use fifteen switching angles to generate the switching pattern and the solutions of the nonlinear transcendental equations for these two kinds of PWM techniques are obtained by using the fmincon function with THD-based objective function in MATLAB. Finally, the comparative analysis of the SHEPWM and SHMPWM techniques for the 3L-NPC inverter with 10kV grid based on the THD of voltage and current up to the 50th and the 100th is proposed to verify the respective advantages of the SHEPWM and SHMPWM techniques in different harmonic suppression cases.

Selective Harmonic Elimination of Cascaded Multilevel Inverter Using BAT Algorithm

ABSTRACTThe number of bridges, gate drive circuits and dc sources decrease by using asymmetrical is used to solve SHE equations to get the optimal switching angles. Genetic algorithm (GA) is also used to solve these equations to make comparison between Satin bowerbird optimisation (SBO) and GA algorithms. Matlab/Simulink software tool is used to carry out the simulation construction multilevel inverter. The selective harmonic elimination pulse width modulation (SHE-PWM) and sinusoidal pulse width modulation (SPWM) are carried out for a nine levels cascaded H-bridge (CHB) inverter with asymmetrical construction. Comparison between SHE and SPWM is done to get the benefit of SHE over SPWM. The elimination of some lower order harmonics and satisfy fundamental component in output voltage are the major purpose of SHE-PWM. The solving of the non-linear transcendental equations of SHE is the challenge to find out the switching angles, SBO technique.

Selective harmonic elimination (SHE) is a widely used method to minimize the amount of total harmonic distortion (THD) in multilevel inverters. The main challenge associated with SHE method is to solve multiple variable high order nonlinear equations to obtain desired switching angles. To overcome this problem, a new online approach is provided in this paper which does not require solving complex nonlinear equations. In this method, artificial neural networks (ANNs) are used to determine the switching angles to minimize the THD amount of the ac side voltage of an 11-level cascaded Half-bridge (CHB) multilevel inverter. However, unlike offline methods, ANN is updated online, without using any data gained from solving SHE equations. Finally, Simulation results are illustrated and compared with other offline methods.

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 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.

This paper applies the selective harmonic elimination (SHE) technique to determine the switching angles for a multilevel inverter that cooperated with specially connected transformer, zig-zag connection. With the ability to direct controlling harmonics, SHE technique has the adaptability to associate with apparatus which are congenitally immune to specific harmonics, such as the zig-zag connection transformers. In this paper the two sets of primary windings of the transformers are supplied by two 6-switch full-bridge inverters with 30 electrical degrees phase shift. Prohibited by the transformers, harmonics with orders other than 12n±1 (n is positive integral) will not appear in the line-to-line voltage of the secondary side. Then, SHE technique is employed to handle harmonics with orders equal to 12n±1, and controls the amplitude of the fundamental. This paper obtains a set of precise switching angles through off-line calculation and then employs a digital signal processor to implement on-line calculation of the switching angles by an approximate method. Some selected analysis and experimental results are shown in this paper. A small-size prototype is built to verify the validity of the proposed system.

Various factors can cause nonuniform operation problem in photovoltaic (PV) systems such as partial shading (nonuniform insolation), nonuniform ageing, unequal material quality, dust, etc. Nonuniform illuminations are common occurences be faced by PV systems. These cause disproportionate impact on PV system performance. This paper studies switching angles determination of cascaded H-bridge (CHB) inverter under nonuniform conditions to obtain low total harmonic distortions (THDs). So that, no need a bulky filter to meet grid interconnection requirements of PV system integration. The proposed method exploits nonuniform PV voltages by composing voltage levels to produce output voltage waveforms nearly sinusoidal. To realize this is applied CHB inverter topology, selective harmonics elimination (SHE), and Newton Raphson iteration method. By applying generated switching angles, the simulations show the generated output voltages are nearly sinusoidal which characterized by a desired rms fundamental voltages satisfaction, and low THDs as well. To verify the simulations results, the laboratory experimentals were carried out and presented in this paper.

The paper proposes an application of a well-known method of Selective Harmonic Elimination in inverter's output voltage to influence an input traction current spectrum in a DC supplied traction vehicle with asynchronous motors. The aim is to reduce the values of current harmonics in frequency bands that are subject to limitations applicable on Polish railways. This paper introduces the possibility of modifying the method (Selective Harmonics Elimination — SHE) in such a way as to replace elimination of selective harmonics with their reduction (Selective Harmonics Reduction — SHR). Comparative analysis of the effectiveness of both these methods was based on computer simulation results. The important advantage of the SHR method, in comparison with the SHE methods, is the reduction of the required switching angles number with obtaining the aim of the application, i.e. current harmonics amplitudes below the defined limits. Some exemplary results of effectiveness of the proposed method are as well presented and discussed.

Grid interfacing of multi-megawatt photovoltaic inverters is getting a closer attention in recent past. It is always a hard and challenging task for the engineers as there are certain priorities to be taken while interfacingPV cells to grid without which there will bean unsatisfactory operation of the system will taken. Somehow for high power and medium voltage grid invertersthe priorities like IEEE and IEC standards, satisfaction of grid codes and switching losses are to be strictly considered. Mitigation of switching losses is the active area of research for the PV systems. To meet such requirements weare using the traditional and conventional modulation strategy like SHE (Selective Harmonic Elimination). This paper focus on the reduction of switching losses with the help of new implementation technique for SHE that uses the third harmonics to have the switching angles over 90°, which also increases the modulation index. The Selective harmonic elimination strategy can allow the grid connected inverters to operate using a switching frequency less than 1 KHz while it is still able to provide satisfactory operation like simplicity in operation, independent control of active and reactive powers which is not possible in other cases. To validate potential benefits of SHE, it is compared with THI PWM which is controlled with an operating frequency of 2 KHz. Keywords: Grid Interfaced PV Inverters, Pulse Width Modulations (PWMs), Selective Harmonic Elimination (SHE), Switching Losses, THI PWM (Third harmonic injection PWM)

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.

The voltage source inverter (VSI) and Current source inverter (CSI) are two types of traditional power inverter topologies.In this paper selective harmonic elimination (SHE) Algorithm was impelemented to CSI and results has been investigated. Cat swarm (CSO) optimization is a new meta-heuristic algorithm which has been used in order to tuning switching parameters in optimized value.Objective fuction is reduction of total harmonic distortion(THD) in inverters output currents.All of simulation has been carried out in Matlab/Software.