Minimum Total Harmonic Distortion Research Articles

A new design algorithm for hybrid active power filter

The correct determination of the parameters of Hybrid Active Power Filter (HAPF) plays a decisive role in its performance. Therefore, this paper proposes a new design algorithm for HAPF based on the Social Spider Algorithm (SSA). This algorithm has the advantage that it is possible to determine the parameters of both the power circuit part and the control circuit part of HAPF. The achieved results are multi-purpose, such as: minimum total harmonic distortion of the supply current and source voltage, the maximum reactive power compensation into the system and satisfy many constraints such as: system stability, resonance conditions of the branches and the limits of the parameters. Compared to traditional design method using the Particle Swarm Optimization algorithm, the proposed algorithm shows the advantages of smaller total harmonic distortion of supply current and source voltage, and higher reactive power compensation into the grid while still meeting the constraints.

A Passivity-Based Control of Euler–Lagrange Model for Suppressing Voltage Low-Frequency Oscillation in High-Speed Railway

The traction network voltage low-frequency oscillation (LFO) in high-speed railways easily leads to the traction blockade of electric multiple units (EMUs), which seriously affects the normal operation of high-speed railways. A passivity-based control (PBC) strategy for single-phase EMUs rectifier is proposed in this paper. First, for the single-phase EMU rectifier, the Euler–Lagrange (EL) mathematical model in dq frame is built, which can realize the decoupling of active power and reactive power. Second, according to the unique characteristics of the rectifier, it is proven that the rectifier is strictly passive, which is the premise of PBC controller design. Third, using the deduced EL mathematical model and the passivity of rectifier, the PBC controller for the single-phase rectifier of EMUs is designed using the damping injecting method. Next, compared with dq current control and interconnection and damping assignment PBC (IDA-PBC), it can be verified that the PBC controller has better dynamic and static characteristics, and can significantly suppress the voltage LFO of traction network. In these strategies listed in this paper, using the PBC, the single-phase rectifier input current has minimal total harmonic distortion, and the dc-link voltage has minimal oscillation. Finally, the dSPACE semiphysical experiment platform of the cascade system of EMUs and traction network is built. Simulation results are validated by the dSPACE semiphysical experiments, which indicate that the PBC has the better inhibitory effect for LFO as compared with that of the IDA-PBC and dq current control in single-phase EMUs rectifier.

Improved hyper-spherical search algorithm for voltage total harmonic distortion minimization in 27-level inverter

Multi-level inverters (MLIs) have become popular in different applications such as industrial power control systems and distributed generations. There are different forms of MLIs. The cascaded MLIs (CMLIs) have some special advantages among them such as more different output voltage levels using the same number of components and higher power quality. In this paper, a 27-level inverter switching algorithm considering total harmonic distortion (THD) minimization is investigated. Switching angles of the inverter switches are achieved by minimizing a THD-based objective function . In order to minimize the THD-based objective function, the hyper-spherical search (HSS) algorithm, as a novel optimization algorithm, is improved and the results of improved HSS (IHSS) are compared with HSS algorithm and other five evolutionary algorithms to show the advantages of IHSS algorithm.

Sliding mode control for a grid connected PV-system using interpolation polynomial MPPT approach

In this paper, two controllers are proposed to optimize the photovoltaic (PV) energy injected into three phase grid. The first controller is used to predict the DC voltage that allows the three-phase inverter to track the maximum power point of photovoltaic generator under unbalanced climatic conditions and variable load. This new controller uses a multivariate polynomial interpolation based on the Lagrange’s theory. The second controller is based on the robust Sliding Mode Control (SMC). It is used to control the active and reactive powers injected into the network in order to achieve the maximum active power into grid with high efficiency and minimum total harmonic distortion using the same three-phase inverter. The control strategies efficiency is confirmed by simulations and experimental results. In addition, in order to validate the choice of control strategies, a comparative study was carried out.

Bat Algorithm Based Selective Harmonic Elimination PWM for an Eleven Level Inverter

Multilevel inverters are the vital drives in industry and new energy power schemes. Selective Harmonic Elimination (SHE) based inverters are the best choice for attaining the preferred fundamental component as well as for harmonic free electrical applications. Since the SHE-PWM methodology has non-linear and transcendental equations, finding the appropriate switching angles for this are so difficult. In this paper, Bat Algorithm (BA) is proposed to solve the switching angles for an eleven level inverter with dissimilar dc sources. This proposed algorithm is validated with thorough simulation for finding its viability and efficiency. The attained results prove that Bat algorithm is very effective than Genetic algorithm (GA) and Flower Pollination Algorithm (FPA) in removing the selective harmonics and in turn that leads to the minimization of Total Harmonic Distortion (THD) in the voltage output.

Multilevel inverter with MPWM-LFT switching strategy for voltage THD minimization

<span>This paper presents a proposed modified pulse width modulation – low frequency triangular (MPWM-LFT) switching strategy for minimization of voltage THD with implementation of asymmetric multilevel inverter (AMLI) topology on the reduced number of switching devices (RNSD) circuit structure. Principally, MPWM-LFT able to produce optimum angle of the output voltage level in order to minimize total harmonic distortion (THD). In this study, 5-level reduced number of switching devices circuit structure is selected as a circuit configuration for asymmetric (7-level structure) multilevel inverter. For switching strategy, MPWM used low switching frequency in producing signal and needs higher output voltage levels to achieve low total harmonic distortion. In contrast, sinusoidal pulse width modulation used high switching frequency in order to minimize total harmonic distortion. By optimizing angle at the output voltage using MPWM-LFT switching strategy, the voltage THD is lower as compared to MPWM and SPWM switching strategies. MPWM-LFT switching strategy obtains 11.6% of voltage THD for the 7-level asymmetric topology as compared to MPWM and SPWM switching strategies with the voltage THD are 21.5% and 17.5% respectively from the experimental works.</span>

Investigations on shunt active power filter in a PV-wind-FC based hybrid renewable energy system to improve power quality using hardware-in-the-loop testing platform

The current power distribution system involves usage of nonlinear loads that cause power quality problems. Further, the penetration of renewable energy sources is increasing in the power networks to satisfy the consistently rising energy demand, which changes the traditional network plan and control drastically. This paper presents an intelligently controlled hybrid energy system (HES) integrated with shunt active power filter (SAPF) to address the power quality problems. Renewable sources like-Wind, PV and fuel cell (FC) are integrated into HES and are regulated using artificial intelligence techniques that are also implemented for maximum power point tracking (MPPT) in both PV and wind energy systems. The dynamic performance of SAPF is optimized using fuzzy logic, neural network and adaptive neuro-fuzzy inference system (ANFIS) based control algorithms. These controllers provide the smooth DC-link voltage and minimize the total harmonic distortion (THD) produced by the balanced/unbalanced and nonlinear loads. Comparison of these reveal that the ANFIS based algorithm provides minimum THD. The system is tested in real-time using hardware-in-the-loop (HIL) setup. The control schemes are executed on FPGA based OPAL-RT4510computational engine with microsecond step.

Minimizing Total Harmonic Distortion of a Two-Level Voltage Source Inverter Using Optimal Third Harmonic Injection

Full time-domain analysis of the impact of third-harmonic injection (THI) on the output phase voltage waveform of a two-level voltage source inverter is presented, and the total harmonic distortion (THD) performance of different pulsewidth modulation (PWM) methods is provided. Two well-known third harmonic injection PWM (THIPWM) schemes are adopted from the literature: THIPWM6 and THIPWM4, where the THI amplitude is one-sixth and one-fourth the amplitude of the sine-wave, respectively. In this article, three analysis-derived developments are provided. Global optimal THIPWM ensures minimum THD in all linear region, unlike other THIPWM schemes. A unique THI-level is selected for each modulation index from the proposed curve or the compacted lookup table. The best suboptimal THIPWM method is provided that employs a linear injection applied over the linear modulation. To achieve better THD performance and to satisfy different operation criteria, several suboptimal THIPWM methods are proposed. Comparisons between these schemes must define performance indices, and this is carried out using various objective functions, such as the sum of squared error and area under the curve. The impact on extending the linear region is also presented. This study examines when THIPWM is useful and which injection level is best. Experimental verifications support the presented analysis.

A Control Strategies of PV System based on VOC, SMC and MPC Algorithms

Objectives: Due to the stochastic behavior of the climatic conditions, a comparative study of grid- connected PV inverter based on Voltage Oriented Control (VOC), Sliding Mode Control (SMC) and the proposed Model Predictive Control (MPC) method is required to enhance the power quality that is affected by the weather fluctuations, and to ensure unremitting operation at the maximum power point in order to inject to grid the totality of the generated electrical energy. Methodology: The PV power extracted from the PV array is fed to grid via a three phase inverter interface by maintaining constant DC-link voltage. To evaluate the MPC algorithm efficiency for controlling this power inverter, it\'s necessary to compare its performances to already studied techniques. Comparative case studies often introduce qualitative criteria such as waveforms, current Total Harmonic Distortion (THD), power distortion and switching frequency. Findings: The simulation results under Psim environment prove the MPC-based algorithm robustness to control the photovoltaic inverter, particularly, the lower overshoots, the accuracy and the minimum current THD. Improvement: The obtained Psim simulations validate the effectiveness of the proposed MPC method against parameter variations. Keywords: Grid, PV System, MPC, VOC, SMC

THD minimization for Z-source-based inverters with a novel sinusoidal PWMswitching method

This paper presents a modified sinusoidal pulse width modulation (SPWM) switching method for one-phase and investigated two-phase impedance-source inverter structures. The proposed structure generates pulses for a quasi- Z-source converter and this block produces a unilateral voltage sine wave in the block's output. This signal is applied to the inverter as its input wave. For this purpose, the novel SPWM method is proposed for power switches while being switched complementarily. Two power switches are used in the structure to generate the pure sinusoidal output voltage and to minimize total harmonic distortion (THD), which is an essential parameter in inverter design. The results show that the proposed method generates the pure sinusoidal voltage and current signals for resistive and inductive loads and pure voltage and improved current waves for capacitive loads in comparison with existing techniques, since the THD of the output voltage and current signals is strongly affected by the dynamic loads. This method leads to final cost improvement and reduction of the size of the system with fewer number of components, which are essential parameters for renewable energy resource applications. A mathematical model is validated with the 2017a version of MATLAB/Simulink and 1.51% and 1.33% THD values are reported for low and high power loads, respectively, in the one-phase structure and 0.95% and 0.87% in the two-phase system. Finally, a 120 W prototype has been implemented and tested. A sine-wave with 620 Vac peak to peak amplitude and 50 Hz frequency has been gained in the inverter?s output and the quality of the voltage and current waveforms has been evaluated for different two 1.8 k$\Omega$ and 600 $\Omega$ resistive loads in the one-phase structure. Experimental results confirm all mathematical and simulation results.

Distortion-Free Instantaneous Multifrequency Saturator for THD Current Reduction

The importance of distributed generation and renewable energies inclusion has led to obtain the maximum from power converters, in terms of total harmonic distortion (THD) reduction and power injection. The reachable operating point is associated with the inverter output voltage, which is limited by the input dc voltage. Some capabilities, such as reactive power injection, require a high-voltage margin. Furthermore, in modern applications, the combination with harmonic capabilities for THD reduction can increase the required voltage leading to extra harmonic pollution. In this paper, a distortion-free instantaneous multifrequency saturator (DFIMS) is proposed, which delivers the maximum power in a multifrequency environment, conditioned to the minimum current THD. This novel saturator instantaneously calculates a trajectory that avoids overmodulation at every time step. Simulation and experimental results state the benefits of proposed procedures.

A novel optimization harmonic elimination technique for cascaded multilevel inverter

The main goal of utilizing Selective Harmonic Elimination (SHE) techniques in Multilevel Inverters (MLI) is to produce a high-quality output voltage signal with a minimum Total Harmonic Distortion (THD). By calculating N switching angles, SHE technique can eliminate (N-1) low order odd harmonics of the output voltage waveform. To optimized and obtained these switching angles, N of nonlinear equations should be solved using a numerical method. Modulation index (m) and duty cycle play a big role in selective harmonic elimination technique to obtain a minimum harmonic distortion and desired fundamental component voltage. In this paper, a novel Optimization Harmonic Elimination Technique (OHET) based on SHE scheme is proposed to re-mitigate Total Harmonic Distortion. The performance of seven-level H-bridge cascade inverter is evaluated using PSIM and validated experimentally by developing a purposely built microcontroller-based printed circuit board.

Family of Multiport Switched-Capacitor Multilevel Inverters for High-Frequency AC Power Distribution

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.

Application of Evolutionary Algorithms for Harmonic Profile Optimization in Symmetric Multilevel Inverter used in Medical Electronic Equipments

Background: Inverters are finding applications in electrical field where conversion from Direct Current (DC) to Alternate Current (AC) has become an inevitable option. The need of Multi Level Inverter (MLI) is to provide a high output power from medium voltage source. High power quality is the very basic important requirement for MLI used in medical electronic equipment. Harmonic elimination in MLI is a challenging one and is solved by optimum switching of power electronic switches present in the MLI topology. Methods: Several control strategies have been proposed for harmonic elimination in multilevel inverters. Newton-Raphson method is the conventional and iterative based method to obtain optimum switching angle to minimize the Total Harmonic Distortion (THD). But it requires an initial guess of switching angles which is very close to the exact solution. To overcome this, harmonic elimination is converted into an optimization task and is solved by using evolutionary algorithms such as Genetic Algorithms (GA) and Particle Swarm Optimization (PSO). GA and PSO offer optimum switching angles to minimize THD and used to increase the robustness of the system. Results: The performance of proposed symmetric 21 level multilevel inverter with GA and PSO techniques are analysed and the objective of minimum THD is obtained by using MATLABSIMULINK software.In experimental setup, FPGA controller has been used to generate the Pulse Width Modulation (PWM) control signals according to the proposed soft computing based switching strategy. The experimental result is used to verify the ability of the proposed system for the generation of desired output voltage with minimum THD. Conclusion: The proposed symmetric MLI with evolutionary algorithm based switching is a good choice for medical electronic equipment used in hospital to obtain quality power with minimum THD.

Control of Cascaded H-Bridge Multilevel Inverter Based on Optimum Regulation of Switching Angles, and the FPGA Implementation

A new concept in control of cascaded H-Bridge multi-level inverters is proposed in this paper. According to this concept, switching angles are considered to be independent from the fundamental voltage. A polynomial term is presented to show the relation between switching angles and DC voltages. Based on this concept, Total Harmonic Distortion (THD) calculations are updated and proved to be independent from the fundamental voltage. Thus, once calculated for minimum THD, the switching pattern can be used for any required level of output voltage. To examine the effectiveness of the proposed method, it is applied in control of an eleven level inverter. The simulation results are demonstrated and verified through experiments with a setup controlled by Xilinx SPARTAN3 family FPGA (XC3S400-PQG208).

Swarm Optimization-Based Modified Selective Harmonic Elimination PWM Technique Application in Symmetrical H-Bridge Type Multilevel Inverters

The problem of elimination of harmonics and the need of a large number of switches in multilevel inverters (MLIs) have been a hot topic of research over the last decades. In this paper, a new variant swarm optimization (SO) based selective harmonic elimination (SHE) technique is described to minimize harmonics in MLIs, which is a complex optimization problem involving non-linear transcendental equation. Optimum switching angles are calculated by the proposed algorithms considering minimum total harmonic distortion (THD) and the best results are taken for controlling the operation of MLIs. The performance of the proposed algorithm is compared with the genetic algorithm (GA). Conventional MLIs have some disadvantages such as the requirement of a large number of circuit components, complex control, and voltage balancing problems. A novel seven-level reduced switch multilevel inverter (RS MLI) is proposed in this paper to recoup the need of a large number of switches. Matlab/Simulink software is used for the simulation of two symmetrical topologies, i.e., a seven-level cascaded H-bridge multilevel inverter (CHB MLI) and a seven-level (RS MLI). Simulation results are validated by developing a prototype of both MLIs. The enhancement of the output voltage waveform confirms the effectiveness of the proposed SO SHE approach.

On PWM Strategies and Current THD for Single- and Three-Phase Cascade H-Bridge Inverters with Non-Equal DC Sources

Cascade H-bridge (CHB) inverter is an attractive choice for integration of DC sources of different nature, e.g., for distributed generation with energy storage, photovoltaic generation, etc. In general, non-equal DC voltage sources can affect the total harmonic distortion (THD) of the CHB by introducing undesirable low-frequency subharmonics. This paper investigates different level-shifted (LS) and phase-shifted (PS) pulse width modulation (PWM) strategies for single- and three-phase cascade H-bridge inverters with non-equal DC sources from the load current THD minimization perspective. The best current quality is provided by LS PWM, as reported in the literature. The paper provides a simple time domain explanation of LS PWM superiority. However, PS PWM may be a preferable choice for practical applications due to fair power and loss sharing across individual H-bridges. The paper explains how to obtain the best current quality by PS PWM carriers’ order arrangement (DC sources switching sequence selection).

Hardware in the loop implementation of wavelet based strategy in shunt active power filter to mitigate power quality issues

This paper presents a Wavelet Transform (WT) based control algorithm for a shunt active power filter (SAPF), mainly to mitigate harmonic distortions in power distribution system modeling. Wavelet transforms are being used extensively for signal analysis and processing for fast and accurate identification of transients in power systems. In this work, SAPF has been modeled with a three-phase voltage source inverter using WT based schemes, resulting in minimizing of harmonic distortions and improvement in power factor for balanced, unbalanced & nonlinear loads. The system response for different types of WTs is compared and it is found that Haar WT provides minimum Total Harmonic Distortion (THD) and maximum power factor. OPAL-RT 4510 controller with microsecond step on its FPGA based computational engine is used for Hardware in the loop testing (HIL).

Direct Model Predictive Control of Novel H-Bridge Multilevel Inverter Based Grid-Connected Photovoltaic System

In this paper, a direct model predictive control (DMPC) for the novel H-Bridge multilevel inverter topology-based grid-connected photovoltaic system (GCPS) is presented. The DMPC has several advantages over the conventional control techniques, including optimality, ability to handle multiple control goals, and direct manipulation of semiconductor switches instead of the modulator. The main control goals in the GCPS are to extract the maximum energy from the photovoltaic (PV) system and inject the current into the grid with minimum total harmonic distortion (THD) or close to unity power factor. The DMPC performs well in terms of these control goals. The entire GCPS with the proposed controller is simulated in Simulink MATLAB and the results are compared with the existing GCPSs in the literature. The usage of less number of semiconductor switches while keeping the same number of output voltage levels made the proposed GCPS efficient, less costly, and simpler in design. Moreover, its voltage and current THD are comparable with the systems existing in the literature.

CMOS Realization of OTRA Based Electronically Controllable Square Wave Generator Enhancing Linearity with Minimum Total Harmonic Distortion and Power Consumption

CMOS Realization of OTRA Based Electronically Controllable Square Wave Generator Enhancing Linearity with Minimum Total Harmonic Distortion and Power Consumption