Total Harmonic Distortion Value Research Articles

Performance evaluation of isolated three-phase voltage source inverter with LC filter adopting different MPC methods under various types of load

As the variety of loads in microgrids continues to grow rapidly, the drawbacks of using conventional voltage and current double closed-loop PI control are becoming increasingly intolerable. These disadvantages include poor static tracking of the output and the need for complicated tuning of optimal PI control parameters. Model predictive control (MPC) is widely studied in recent years and gradually applied to the inverter as a modern control strategy. Currently, the research on MPC mainly focuses on reducing the computational burden of algorithms and improving computing skills. In this paper, the control theory of continuous-control-set model predictive control (CCS-MPC), optimal switching vector model predictive control (OSV-MPC), quasi-sliding mode model predictive control (QS-MPC) and optimal switching sequence model predictive control (OSS-MPC) are elaborated. Also, the disadvantages of adopting conventional voltage and current double closed-loop PI control on microgrids are clarified. Moreover, aiming at evaluating the influence of connecting and/or removing the common loads, such as electric vehicles to the microgrid on the output performance of microgrids in practical engineering applications, single three-phase voltage source inverter with LC filter system with two-phase pure resistance load, three-phase diode rectifier bridge nonlinear load, constant power load and constant current source load applying four different MPC methods, are simulated. The simulation results show that under different types of load, system with nonlinear load applying OSV-MPC method has the biggest value of total harmonic distortion (THD) of the output voltage and the biggest steady state root mean square (RMS) tracking error of the output voltage, which are 1.33% and 2.1 V, respectively. The performances of the output voltage of the system adopting MPC are generally improved compared to the system using conventional voltage and current double close-loop PI control. Regarding the output voltage performance of a system under load step change, a system using the OSS-MPC method with a nonlinear load exhibits the smallest overshoot of the output voltage and the smallest root mean square value of the tracking error (RMSE) between the output voltage and the reference value within 20ms after the load step change. Specifically, the overshoot and RMSE are 2.804 V and 0.810 V, respectively. The simulation results provide valuable guidance for selecting the appropriate model predictive control strategy for microgrid integrating complex loads, such as electric vehicles in practical applications.

Full Grid Voltage Feedforward for Critical Mode LCL-Type Single-Phase Grid-Tied Inverters With Physical Interpretations

Full grid voltage feedforward (GVF) is an effective strategy to suppress the current distortion caused by grid voltage harmonics. However, for critical conduction mode (CRM) grid-tied inverters, the time-varying parts of its control scheme make it impossible to derive its full GVF strategy from the point of view of the transfer function. Hence, this study first analyzes the physical interpretation of the full GVF of conventional LCL-type grid-tied inverters, and then reveals the role of each term from the perspective of the circuit. Then, a full GVF strategy for CRM grid-tied inverters is proposed. The design guidelines, parameter sensitivity, and application limitations of the proposed scheme are analyzed in detail. Finally, a 1-kW single-phase three-level grid-tied inverter was built. Experimental results show that the proposed full GVF can significantly suppress the current distortion caused by the grid voltage harmonics and lower the current total harmonic distortion value by 55% within the full power range.

PENGARUH FILTER AKTIF TERHADAP LOSSES TRANSFORMATOR DI FAKULTAS TEKNIK UNIVERSITAS UDAYANA BUKIT JIMBARAN DENGAN FUZZY LOGIC CONTROLLER MENGGUNAKAN SIMULINK

Harmonics in the electrical system can have a negative impact on the quality of the electrical energy being distributed. Harmonics are phenomena that arise due to the operation of non-linear electrical loads. Thus causing the formation of waves with a frequency that is different from the fundamental frequency. Total harmonic distortion (THD) is the effective value of waves affected by harmonics so that they can affect power losses. This study analyzes the power losses in the KA4214 transformer at the Faculty of Engineering, Udayana University, Bukit Jimbaran. The method used is to carry out simulations and analysis of the results of harmonic measurements carried out in existing conditions using active filters, and using active filters with fuzzy logic controllers and then compared with IEEE 519-2014 standards. The simulation results from using an active filter with a fuzzy logic controller obtained the smallest current THD value of each phase, namely R = 0.28%, S = 0.71% and T = 0.72% with the resulting power losses of 0.0009905 kW.

Power Quality Analysis of Fuzzy DVR based Hybrid Solar PV-PEMFC System Under Severe Disturbance

Hybrid Energy System (HES) is becoming popular as it is identified as the most safe, sustainable, and long-term option for energy management. The grid-connected power network is vulnerable to frequent interruptions, which can lead to instability and a huge blackout. Furthermore, the presence of switching devices in industrial and domestic applications causes disturbances such as voltage swell/sag, waveform distortion, interruptions, impulsive voltage, and so on. Dynamic voltage restorer, known as a modern power compensating device, is cost effective, compact in size and can handle more energy capacity than DTSATCOM and UPFC. Hence for addressing the power quality issues in hybrid solar photovoltaic (PV)-proton exchange membrane fuel cells (PEMFC) system, dynamic voltage restorer (DVR) has been designed in this paper. As the fuzzy logic technique can provide flexible solutions in the case of uncertainty, fuzzy logic-based controller has also been employed with DVR to regulate the firing pulses of a PWM generator. Based on the simulation results obtained using fast fourier transform (FFT) analysis in MATLAB/Simulink, the dynamic performance of HES against the most important contingency condition or three phase faults is analyzed in detail. Further, the impact of DVR on power quality improvement under severe fault has also been demonstrated in this research work. On analyzing the total harmonic distortion (THD) values of HES under heavy disturbances, the fuzzy controlled dynamic voltage regulator (FCDVR) is identified as an efficient control mechanism for enhancing power quality in grid-connected HES.

Hybrid matrix converter for grid connected multiphase wind generation

ABSTRACT This paper presents a novel multiphase hybrid matrix converter topology dedicated to grid-connected five-phase wind generation. The proposed converter, named Five-phase Ultra-Sparse Series Z-source Matrix Converter (FUSSZMC), aims to facilitate the integration of the five-phase wind turbine generators. This is done by taking into account the improvement of the injected power quality and allowing the fixed output converter voltage level to that of the grid, thanks to the use of the series Z-source, under the variable voltage magnitude of the wind turbine generator, which depends on the wind speed. The proposed space vector modulation as a control strategy for FUSSZMC was detailed, where it was demonstrated that a suitable use of both large and small current vectors improves the input current waveforms. The global model of the proposed system was tested by simulation under Matlab/Simpowersys environment. The obtained results demonstrate clearly the advantages of using FUSSZMC and its modulation strategie. These benefits includea good input and output current waveforms, as reflected by the obtained total harmonic distortion (THD) values, that fall within the range prescribed by international standards. Additionally, FUSSZMC is capable of operating with unity input power factor, regulating input voltages and improving the quality of injected power into the grid.

Harmonic Distortion Characteristics Generated by Heating Ventilation Air Conditioning System Case Study in PCR Laboratory

Good power quality is required in health facilities since the increasing use of microprocessor-based equipment. Poor power quality in the electric power system can cause medical equipment in health care centers to malfunction and give incorrect medical diagnoses. Since 2020 we are facing a new type of Virus (Covid-19), this virus requires special laboratory construction with specific air conditioning systems (temperature, humidity, and pressure) to process specimens. This paper presents measurement results of harmonic distortion characteristic by Variable Frequency Drive (VFD) of Heating Ventilation Air Conditioning (HVAC) system in PCR Laboratory at Clinic A. The VFD in this system is used to adjust the rotation of the exhaust fan and outdoor unit. The measured voltage, current and power are used to assess power quality. The main power quality problems found in medical facilities are voltage flicker, neutral currents, and total harmonic distortion (THD) values. The measurement of total harmonic distortion (THD) is used to find the source of the harmonics. Potential problems can be identified within the facility. The results of this study can be used to develop, test, and validate the system that has been used.

MATLAB-Simulink environment based power quality improvement in photovoltaic system using multilevel inverter

Introduction. In this world of technical advancement, conventional resources are at the stage of destruction. To avoid such problems, we are going to use an alternative energy source namely solar by photovoltaic effect. The demand for multilevel inverters increased as they are used for different dynamic (high) voltage and dynamic (high) power appliances as they are capable of producing the output wave shape with low total harmonic distortion. Novelty. A new multilevel inverter is used in adding a (bidirectional) two way switch in between the capacitor and a traditional H-bridge module. This produces a better sine wave. By series connection of these two H-bridge modules, nine levels output voltage including zero is possible. The purpose of the proposed topology is reduction in the number of switches and it gives the good result with comparatively less power loss when it is compared with the other normal basic traditional inverters of the same output quality. Methods. In this paper, sinusoidal pulse width modulation technique is used for the working of the switches in the multilevel inverter. The results are verified by using simulation and also experimental setup is done. From the results it is observed that the proposed topology with reduced number of switches gives lower electromagnetic interference, lower harmonic distortion. Practical value. The total harmonic distortion value in the simulation is 14.4 % and practically it is 13.8 %.

Analysis of total harmonic distortion in single-phase single-stage grid-connected photovoltaic system

<p>This study presents the power quality issue mainly focus the effect of total harmonic distortion (THD) on a grid-connected PV system. Firstly, a grid-connected PV system with a single-phase single-stage has been developed to monitor the output values of voltage and current and also its harmonic distortion behaviours. Maximum power point tracking (MPPT) was implemented since it is proven as the first step for THD reduction because MPPT will extract maximum output power, voltage, and current of the PV system without fluctuation which leads to a low THD level. Furthermore, the employment of a good filter also reduces the THD level in a PV system. Thus, this study will focus on the THD analysis to resolve the power quality problems in the grid-connected PV system. The result shows that the THD value for current, <em>I<sub>THD</sub></em> analysis is more significant than the THD value for voltage, <em>V<sub>THD</sub></em> analysis in the case of grid-connected PV systems operating under different solar irradiances. In a conclusion, the increase in solar irradiance will increase the rated values of generated power and current thus, increasing the performance of THD values.</p>

Dead-Time Compensation in Active NPC Three-Level Inverters Considering Current Ripple

Existence of dead time that makes the ultimate terminal voltage being inconsistent with the modulation voltage, is recognized as the main reason for leading output voltage distortion, as well as the corresponding low-frequency current harmonics through the filter inductance in inverters. The distortion becomes particularly severe in high power-density high efficiency applications where the wide bandgap semiconductors are gradually being adopted, providing higher switching frequency with small junction capacitance. In order to explain this phenomenon, the mechanism of three-phase current distortion in the vicinity of phase current zero-crossing point is thoroughly studied by vector analysis in the space-vector (SV) plane. The relevant factors that lead to the degradation of current quality are also summarized. Improved compensation strategy has been proposed to ameliorate the current distortion. Compared with the conventional method, an additional item for current ripple compensation is introduced, the value of which is obtained by the deadbeat predictive method. This simple scheme avoids the compensation error caused by current ripple and significantly reduces the current total harmonic distortion (THD) value under the case of small inductance. Furthermore, neutral-point (NP) potential balance control is also considered in conjunction with the scheme. Simulations and experiments are carried out in an active NP clamped (ANPC) inverter platform, which demonstrates the validity of theoretical analysis and the proposed method.

Backstepping Control Based on a Third-order Sliding Mode Controller to Regulate the Torque and Flux of Asynchronous Motor Drive

This work represents a new nonlinear control for the asynchronous motor (AM) drive. The designed nonlinear control is based on the combination between the backstepping control (BC) scheme and third-order sliding mod control (TOSMC). In this proposed nonlinear control, the torque and flux are controlled. Also, the torque, current, and flux ripples are minimized by a proposed BC-TOSMC strategy. The proposed BC-TOSMC strategy is more robust compared to the field-oriented control (FOC). The proposed BC-TOSMC strategy of AM drive has been simulated in MATLAB/Simulink software. The comparisons were made between the proposed BC-TOSMC strategy and the FOC strategy under different operating conditions. The results show that the proposed BC-TOSMC strategy minimized the flux, current, and torque ripples of the AM drive compared to the FOC strategy, with a reduction torque ripples ratio of about 57.14%. Also, the total harmonic distortion (THD) values of stator current using the proposed BC-TOSMC strategy and FOC technique are respectively 1.09% and 3.42%. In this case, utilizing the proposed BC-TOSMC strategy, the performance of the AM has improved from the FOC strategy.

Computerised Gate Firing Control for 17-Level MLI using Staircase PWM

A basic 7-level MLI topology is developed and the same is extended to the 9-level then further increased to 17-levels. The developed structure minimizes the component’s count and size to draw out the system economy. Despite the various advantages of MLIs, efficiency and reliability play a major role since the usage of components is higher for getting a low Total Harmonics Distortion (THD) value. This becomes a major challenge incorporated in boosting the efficiency without affecting the THD value. Various parametric observations are done and realized for the designed 9-level and 17-level MLI, being the Total Standing Voltage (TSV), efficiency, cost function per level count, and power loss. The respective parameters are compared with several existing and modern circuits and found to be effective in their performance. A novel single-phase 17-level asymmetrical Multi-Level Inverter (MLI) topology is developed to reduce the number of overall components. The developed topology generates 17-levels by using unequal DC sources. The developed MLI is proved under various tests conducted experimentally for the various loads like resistive, inductive, and combinational loads. A detailed comparison is done on several factors and represented graphically represented. Further, the proposed design provides a less TSV value is 6 Vdc, efficiency is 94.21% and cost factor per level CF/L value for both values of α is 2.01 and 2.05 and devices count with a low THD value 41.4% with respectively.

Novel Integrated NLC-SHE Control Applied in Cascaded Nine-Level H-Bridge Multilevel Inverter and Its Experimental Validation

In this paper, a novel integrated SHE - NLC control is proposed for the mitigation of unwanted lower-order harmonics in the cascaded H-bridge multilevel inverter. The proposed algorithm has been developed by hybridizing the NLC and SHE methods, in an attempt to keep the merits of both the individual control. The switching angles and nearest levels are calculated by applying the Genetic Algorithm (GA). The proposed technique reduces the calculation time and implementation complexity, thus can be a viable alternative to the real time implementation for SHE. Integrated NLC-SHE control is tested by varying the modulation index and load dynamics. This technique resulted in the reduction in Total Harmonic Distortion (THDs) in load voltage and current. Comparative analysis of NLC, SHE and Integrated NLC-SHE technique is also performed on the CHB nine-level inverter. There is significant reduction in voltage and current THD values and power losses. Efficiency of the inverter is increased. The efficacy of the proposed control CHB nine-level is tested on MATLAB Simulink environment and further validated by experimental results.

Neural Network-Based Optimisation of Sinusoidal PWM Controller for VSI-Driven BLDC Motor

Abstract Although increasing the number of switches increases the switch losses, most designed controllers focus on controlling an inverter circuit with more than six switches. The paper aims to address this issue that arises in implementation of the voltage source inverter (VSI) for brushless DC (BLDC) motors. It optimises the sinusoidal pulse width modulation (PWM) controller, minimising total harmonic distortion (THD) while keeping the VSI’s circuit at six switches to avoid increased switching losses. This was achieved by applying an artificial neural network (ANN) to generate a signal, which combines with the already existing reference and carrier signals. The addition of the new signal to the existing signals contributed to generating more pulses compared with the conventional sinusoidal PWM. Simulink was used to design the system and analyse its performance with the conventional and neutral point clamped (NPC) VSI systems. Results indicated that the proposed system performs better when controlled with an LCC filter. Compared with the control experiments, its output waveform has the lowest THD value, which is 6.04%. The switching losses of all the systems were also computed. Results from the computation indicated that the proposed system is capable of reducing the switching losses by 0.6 kW compared with the NPC VSI brushless DC motor (BLDCM) system. BLDCM speed was tested across various conditions; the results are reported in Section 5.

Design Optimization of an Efficient Bicolor LED Driving System

There are some challenges involved in the design of a multicolor LED driver, such as the precise control of color consistency, i.e., maintaining the correlated color temperature (CCT) and luminous intensity. CCT deviation causes a color shift of composite light. This paper approaches the method of nonlinear optimization of the LED currents of two LED sources to achieve the desired CCT. A bicolor blended-shade white LED system is formed by using a warm color LED source of 1000 K CCT and a cool color LED source of 6500 K CCT. By using a nonlinear optimization methodology, the reduced deviation of the blended CCT and optimum LED currents are obtained. The optimized currents in the two LED strings are maintained by the control circuit of the single-ended primary inductor converter (SEPIC). The obtained reduced deviation of the CCT is 43 K, and the precision is 99.15%. Again, harmonics in the input current hamper power quality, i.e., reduce the power factor and increase power loss. This paper proposes the harmonic reduction technique to achieve the lowest value of total harmonic distortion (THD) through the nonlinear parametric optimization of the SEPIC. Measured THD = 4.37%; PF = 0.96; and efficiency = 92.8%. The system stability was determined and found to be satisfactory.

Selection of PI + Notch Voltage Controller Coefficients to Attain Desired Steady-State and Transient Performance in PFC Rectifiers

The well-known trade-off between dc link voltage dynamics and ac-side current quality in power factor correction (PFC) rectifiers limits attainable dc link voltage loop bandwidth. It has been shown that adding a notch filter in series with the typically employed PI or type-II regulator allows improving dc link voltage dynamics without sacrificing total harmonic distortion (THD). However, clear quantitative guidelines for PI + Notch (PI + N) controller design to attain prescribed values of ac-side current THD and dc link voltage undershoot (response to a step-like load power increase) were not established so far. Consequently, analytical expressions linking the coefficients of the PI + N controller with the above-mentioned performance merits for a given value of dc link capacitance are revealed in this article. Corresponding dc link voltage loop gain phase margin and crossover frequency expressions are derived and the feasibility region of the proposed design guidelines is clearly indicated. Simulations and experimental results validate the proposed design methodology.

Guidelines for Voltage Controller Coefficients Design to Attain Prescribed Grid Current THD and DC-Link Voltage Undershoot Values in Power Factor Correction Front Ends

This article establishes analytical guidelines for designing coefficients of proportional integral (PI) controller, typically used as voltage loop compensator of power factor correction rectifiers (PFCRs) operating in continuous conduction mode (CCM), based on two major performance merits (namely, total harmonic distortion (THD) of grid-side current and dc-link voltage deviation upon sudden load increase) and dc-link capacitance-to-rated power ratio. The proposed methodology allows to concretize the commonly used “5–10 Hz crossover frequency, 45°–70° phase margin” rule-of-thumb, typically used in application notes of commercial PFCR controllers. Explicit relationships between voltage loop gain crossover frequency and phase margin as well as settling time of dc-link voltage response to a step load increase to the above-mentioned performance merits are also derived in this article. Provided design guidelines allow to accurately achieve desired values of the two mentioned performance merits and indicate the feasible range of possible dc-link capacitance values. The proposed quantitative design guidelines are well-supported by experiments.

Fast online diagnosis for solid oxide fuel cells: Optimisation of total harmonic distortion tool for real-system application and reactants starvation identification

This study investigates the potential application of total harmonic distortion (THD), as a fast online monitoring tool, to identify the early signs of failure modes in solid oxide fuel cells (SOFC). Indeed, the timely detection and identification of faults is crucial for applying mitigation strategies to avoid irreversible damage and increase the system lifetime. Two of the most common faulty conditions are considered in this work, namely fuel and air starvation. This experimental work aims at progressively triggering these errors in a controlled manner, by following different realistic scenarios, and recording THD values on a frequent basis. Several well-established laboratory monitoring tools, like electrochemical impedance spectroscopy (EIS), complemented by the distribution of relaxation times (DRT) are used to analyse and support the interpretation of the THD measurements. A sensitivity analysis on the THD parameters, namely the signal amplitude and the number of harmonics, is carried out to identify the optimal combination of parameters and achieve the best faults detectability. Finally, the impact of the fuel flow direction and the operating temperature are examined. The results of this work are summarised as practical guidelines to better employ the THD technique to identify the early warning signs of reactants’ starvation.

RF and Shunt Active Power Filters at Multiple Points of Common Couplings of Radial Electrical Systems

This work investigates the effects of RL filters and single-phase Shunt Active Power Filters (SAPFs) on the supply and load current waveforms and their properties. The parameters involved are rms, input Power Factor (PF) and Total Harmonic Distortion (THD). These parameters can describe the quality of any electrical power system, especially PF and THD. This work focuses on implementing both filters in an electrical radial system due to the limited research work. Hence, the effects of utilising both filters in the radial system are studied. In this work, both filters connect at different Points of Common Couplings (PCCs) of a single-phase radial electrical system. The PCCs are located before composite loads (Case 1), before all nonlinear loads (Case 1) and before individual nonlinear loads (Case 3). Both Cases 1 and 2 apply a centralised SAPF, and Case 3 employs individual SAPFs. Matlab/ Simulink simulates all case studies under four operating conditions: (1) without any filters, (2) with SAPFs only, (3) with RL filters only, and (4) with the RL filters and SAPFs. According to the simulation results, the SAPFs require the RF filters to compensate harmonic components effectively. Otherwise, the SAPF’s injection current consists of high current spikes. However, the RF filters may slightly alter the load current waveforms, rms and THD values; the changes are insignificant. Moreover, based on the THD values of the compensated supply current waveform, the centralised SAPFs seem more suitable to be employed in the radial system. By utilising the centralised SAPFs, the THD values of the supply current are lower than using the individual SAPFs. Thus, it can be stated that the centralised SAPFs exhibit better performance. Nevertheless, connecting both filters on the PCCs of all nonlinear loads (Case 2) is suitable to avoid any linear load current waveform deterioration.

Development of an Enhanced Selective Harmonic Elimination for a Single-Phase Multilevel Inverter with Staircase Modulation

A low device switching frequency is recommended for the operation of multilevel inverters (MLIs) to achieve reduced switching losses. Selective harmonic elimination (SHE) and total harmonic distortion (THD) minimization are the two primary switching angle estimation methodologies for low-frequency modulation control. In this regard, a new generalized condition has been developed in this paper for the SHE technique. This original condition will give an output voltage with improved THD in comparison to the conventional SHE technique, while achieving its primary objective of eliminating the specific harmonic content from the output voltage. The proposed condition has been formulated by estimating the error associated with the staircase waveform and the desired sinusoidal output at the fundamental frequency. An infinite harmonic count has been considered for the evaluation of the quality of output, to obtain an accurate THD value without any underestimation. The proposed technique is analyzed, and its critical features are studied in Simulink. The effectiveness of the present work has been also validated by the experimental results.

An improved predictive current control for IM drives

In Finite Control Set-Model Predictive Control (FCS-MPC), the model of the induction machine (IM) is expressed in the α-β or d-q reference frame, and then the back-EMF is estimated based on the applied voltage vectors. In this work, the d-q reference frame is used but unlike the existing method, the estimated back-EMF is calculated by filtering the voltage vectors. Moreover, the work studies the importance of the discretization method on the predictive control behavior of IM. It has been demonstrated that the mentioned enhancements lead to an efficient Total Harmonic Distortion value for stator current (THDi) and torque ripple reduction compared to the conventional methods. The proposed Predictive Current Controller (PCC) has been validated experimentally by using a commercial IM of 7.5[kW] controlled by a dSpace 1103 real-time control board running with sample frequencies from 10[kHz]to 80[kHz]. The test results validate the developed controller’s ability to meet the control objectives in a whole range of speeds, loads, and sampling frequencies.