High Total Harmonic Distortion Research Articles

Leakage current repression and real-time spectrum analysis with chirp Z-transform for a novel high-efficiency PV-based inverter applicable in micro-grids

One of the most critical elements in the connection of photovoltaic (PV)-based systems used to generate electricity from solar energy is the inverter. The harmonic effects of the inverters to be connected to the grid should be as low as possible, and the total harmonic distortion (THD) should be less than 10%. A high THD value will distort the power quality on the grid side. For this reason, the THD value of the inverters in the grid connection approaches must be determined by spectral analysis to ensure that the necessary protection and improvements are made technically. In this study, a novel inverter topology, including six power switches and two power diodes, is presented, and the voltage data obtained from a grid-connected inverter are acquired in real time, and spectrum analysis is performed with the software developed with LabVIEW. The power efficiency of the proposed inverter is compared with conventional inverter types such as HERIC, H5, and H6 inverters. One of the novelty aspects of the proposed inverter topology is forming a proper freewheeling path including switches and diodes in the inverter branches that can provide a separate DC and ac components, and as a result, this prevents the following the PV side leakage currents to the ac grid side. In the spectrum analysis, the chirp Z-transformation (CZT) was used along the contours of the Z-transformation outside the unit circle. Using CZT, the z-transform was calculated for the inverter output voltage along the spiral lines in the z-plane. Besides, spectrum analysis was performed with fast Fourier transform (FFT) and compared with CZT. The results show that the CZT transformation is more efficient than the FFT algorithm and is useful in calculating a subset of FFT for a sequence. The performance of the proposed inverter is compared with conventional topologies. Hardware implementation and the output signals and the leakage current waveforms are also presented.

Fully Integrated Buck and Boost Converter as a High Efficiency, High-Power-Density Off-Line LED Driver

In this article, a high-power-density off-line light-emitting diode (LED) driver is proposed. The proposed ac–dc driver is the novel integrated buck and boost converter (IBBC). Besides the high-power-density, the converter shows a high power factor (PF), and a low total harmonic distortion (THD). The IBBC is a two-stage driver that features just one controlled switch, which leads to high PF and low THD operation ensuring high efficiency, and size and cost reduction. Moreover, the switch current is minimized as it conducts the higher of the buck or boost converter, but not the addition of both as in other integrated converters. Moreover, for a further increase of the power-density, a magnetic integration is made by integrating the two inductors of both the buck and boost converters in one core. Thus, the proposed converter has been named as fully integrated buck and boost converter (FIBBC). In this paper, the IBBC is analyzed, and a design methodology is proposed. Also, this article presents a magnetic analysis of the novel FIBBC. In addition, a comparison between two prototypes is presented, one for the IBBC and another for the FIBBC, both of them supplying an LED luminaire of 46 V/ 0.575 A. The FIBBC shows a high PF equal to 0.994, very small THD of 10%, output current ripple of 6%, and efficiency of 92.62%, which represents a landmark on the efficiency of integrated converters.

Direct Torque Control for Induction Motors Based on Minimum Voltage Vector Error

The traditional direct toque control (TDTC) for induction motors (IM) is afflicted by large torque ripple, high current total harmonic distortion (THD), and variable switching frequency. Recently, some improved direct torque control (DTC) methods have been proposed to address the above problems, but they often suffer from obscure concept, intensive computation, and poor robustness. To further improve the performance, this article proposes a DTC method based on minimum voltage vector (VV) error. The proposed strategy effectively optimizes the duty ratio of fundamental VV to minimize the error between reference VV and final VV imposed on motor terminals. The optimization algorithm dose not increase the system's complexity much and can be intuitively understood by a graphical interpretation. Experiment comparisons between the proposed strategy and some existing DTC methods are conducted on a 0.55-kW IM platform. The proposed DTC method has proven to achieve better steady-state performance, while retaining fast dynamic response of TDTC. Furthermore, the proposed method can obtain almost constant average switching frequency in the entire speed range, especially with rated load, due to the utilization of proportional-integral type torque regulator.

Design and implementation of an improved sinusoidal controller for a two-phase enhanced impedance source boost inverter

This study presents a novel Sinusoidal Pulse Width Modulation (SPWM) model for a two-phase Impedance Source-based Inverter (ZSI) with a hardware prototype implementation. The high-gain feature is investigated based on an innovative mathematical model that involves fewer components and presents efficient performances. The presented topology can be applied broadly in Photo Voltaic systems, Wind Power, Fuel Cell, and Uninterrupted Power Supply topologies due to the ability of wide-range load regulation with higher duty cycles. Through Shoot (TS) and higher Total Harmonic Distortion (THD) problems can be solved by a carefully designed gate-drive circuit and proper switching frequency for the appropriate resistance against the Electromagnetic Interfaces (EMIs). One of the essential specifications of the proposed controller is working with intermediate values of duty cycles for power MOSFETs that can decrease the losses for the inverter. A set of numerical simulation and hardware results are presented for ensuring the proposed claims.

Fluorescence Fiber Based Identification of Partial Discharges in Liquid Nitrogen for High-Temperature Superconducting Power Apparatus

Partial discharge (PD) in liquid nitrogen (LN2) insulation is a key issue in cryogenic or high-temperature superconducting power apparatus. In this letter, we experimentally demonstrate PD identification in LN2 using a fluorescent optical fiber sensor and compare its sensitivity to the conventional ultrahigh frequency (UHF) technique. The Corona inception voltage (CIV) in LN2 is studied under fundamental ac and harmonic ac voltages with different values of total harmonic distortion (THD). It is observed that CIV reduces with the increase in harmonic voltage with higher THD. Phase resolved partial discharge pattern, peak-to-peak voltage, and the energy content due to corona discharges measured by both fluorescence-based and UHF techniques follows the same trend, indicating the viability of the new technique.

Bipolar Phase Shift Modulation Single-Stage Audio Amplifier Employing a Full Bridge Active Clamp for High Efficiency Low Distortion

Two-stage power conversion of class-D amplifier with front-end switching mode power supply affects the power conversion efficiency of audio amplifier system. Single-stage inverter (SSI) developed from cycloconverter can be used as audio amplifier to improve efficiency. However, current commutation of cycloconverter switches challenges for high efficiency and low total harmonic distortion (THD). In this article, a bipolar phase shift modulation (BPSM) SSI is proposed for high efficiency low distortion audio amplification. Full bridge active clamp (FBAC) circuit is used to clamp the voltage across cycloconverter switches and recycle the energy of filter inductor and leakage inductance. By using active clamp, utilization of magnetizing inductance current and optimization of driving sequence of clamp switches, zero voltage switching of the proposed BPSM FBAC-SSI is achieved over wide range. With BPSM and voltage clamp across cycloconverter switches, low THD of output voltage is also achieved. A 200 kHz prototype with 250 W output power is presented to verify the analysis results of the proposed BPSM FBAC-SSI.

Grid integrated photovoltaic system with fuzzy based maximum power point tracking control along with harmonic elimination

ABSTRACTEfficient extraction and conversion of solar power is an important research area in the field of renewable energy integration. Although, literature is enriched with different power extraction, conversion, and harmonics elimination techniques but still there are problems of maximum power point tracking (MPPT) under partial shading conditions, photovoltaic (PV) mismatching, power fluctuation in steady‐state condition, and higher total harmonic distortion (THD) value. The article has two manifolds. First, it proposes a fuzzy embedded MPPT controller to extract the maximum available PV power under time‐varying environmental conditions. For that, it utilizes seven linguistic variables and fuzzy sets along with 49 rules base to have reduced power fluctuation and power losses in a steady‐state condition, and fast tracking under time‐varying temperature and solar irradiance condition. The performance of the proposed fuzzy‐logic control (FLC)‐49 rules base is compared with FLC‐25 rules and perturb & observe based MPPT controllers. Second, for fulfilling the load demands with lower switching losses and THD, particle swarm optimization (PSO) based selective harmonic elimination (SHE) technique is applied on a cascaded half‐bridge multilevel inverter. SHE technique utilizes switching angles, which are found by solving the nonlinear transcendental equations obtained by Fourier series expansion of stepped output voltage waveform. For that, the proposed research preferred meta‐heuristic techniques of PSO over the classical techniques because of their high convergence rate, short run time, less complexity, and ability to obtain lower THD.

Nearest-Level Control Method With Improved Output Quality for Modular Multilevel Converters

Nearest-level control (NLC) is a popular technique used in modular multilevel converters (MMCs) with a large number of submodules (SMs) owing to the NLC's flexibility and ease of implementation. However, in medium-voltage applications, MMCs contain a relatively low number of SMs, and the drawbacks of the NLC methods emerge, wherein the poor quality of output voltages and currents result in high total harmonic distortion, large ripples in SM capacitor voltages, and unsuppressed circulating currents. Several NLC methods have been proposed to handle these problems, but they do not satisfy all the control objectives simultaneously. This paper proposed a modified NLC capable of enhancing the output quality of MMCs with low number of SMs without deteriorating the control objectives. Unlike previously reported NLC methods, instead of directly calculating the numbers of SMs from the upper and lower arm voltage references, the difference and total number of SMs are obtained from the output voltage reference and circulating current control, respectively. Hence, the numbers of SMs in the upper and lower arms are acquired by simply solving a system of first-order two-variable equations. The simulated and experimental results for a single-phase MMC system were used to verify the appropriateness and effectiveness of the proposed modified NLC method.

A Digital Power Factor Controller for Primary-Side-Regulated LED Driver

In this study, a digital primary-side controller for a flyback light-emitting diode driver with superior line regulation, high power factor (PF), and low total harmonic distortion (THD) was proposed. Conventional constant on-time control is hampered by input current distortion, leading to high THD. To achieve high PF and low THD, a digital switching frequency limiter with quasi-resonant control was proposed. In addition, owing to the turn-off delay of the MOSFET and propagation delay of the feedback signals, a primary-side-controlled flyback converter experiences poor line regulation. To achieve superior line regulation, delay compensation was proposed and analyzed. A digital controller was realized using a field-programmable gate array and was applied to an input voltage of 90– $264~V_{\mathrm {ac}}$ and an output current of 1 A in a hardware prototype to verify the feasibility of the proposed control solution. The experimental results indicate that line regulation was within ±3%, PF was higher than 0.95, and THD was lower than 5% at universal input voltage.

Hosting Capacity Enhancement in Distribution System in Highly Trenchant Photo-Voltaic Environment: A Hardware in Loop Approach

The gradual fossil fuel depletion, the exponential increase in load, the environmental, social and political concern has lead to the gradual sprawl of distributed energy resources in the form of microgrid. But disproportionate integration of DERs into the conventional power system may result in the anomalous system behavior causing violation of operational limits i.e., under and overvoltage, thermal overloading, line losses, transformer or feeder overloading, harmonic distortion breaching the standards, mal-operation of the protective devices etc. The key to mitigate these violations is appropriate hosting capacity assessment. This paper proposes the concept of customary hosting capacity and enhanced hosting capacity at all nodes in a network with low voltage level, high voltage level, ampacity and total harmonic distortion as the governing criteria. The analysis is tested on reconfigured IEEE 33 bus distribution system, whose reconfiguration is achieved by particle swarm optimization, keeping loss minimization as the objective function. The attainment of enhanced hosting capacity is significant since it may lead to considerable improvement of voltage in the network, maintaining the line current values very low. The experimentation on reconfigured and base configuration of IEEE 33 bus distribution system is performed in MATLAB and validated in hardware in loop. The results are also compared with existing literature to prove its efficacy.

Investigation and Feasibility Evaluation of Using Nanogrid Technology Integrated Into Road Lighting System

Currently, light-emitting diode (LED) technologies and solar power production are in popular use. This paper proposes the concept of improving conventional road lighting systems using LED technologies and solar energy applications, known as a “nanogrid road lighting system.” The power quality of a nanogrid road lighting system is analyzed in stand-alone and grid-connected operations using an experimental setup. In addition, the IEC 61000-3-2 (2018) Class C standard and power quality control regulations for grid connections are also discussed. The energy storage installed for individual and central systems are analyzed. Moreover, economic comparisons of three kinds of road lighting systems, namely grid-powered high-pressure sodium, LED solar stand-alone, and nanogrid systems, are compared in terms of their individual discounted payback period (DPP), net present value (NPV), and internal rate of return (IRR). The results show that in stand-alone mode, the system can effectively charge its batteries with the maximum power point tracking (MPPT) control and discharge power to supply the road lighting system. In the grid connection mode, the electrical energy produced from the solar power system can be supplied to the electrical grid at all ranges of solar irradiance levels with the MPPT control. However, a high total current harmonic distortion (THDi) flows into the electrical grid when solar irradiance levels are low. Solar road lighting systems installed in a central system have a low initial investment cost, resulting in better economic performance (in terms of DPP, IRR, and NPV). For this reason, using nanogrid road lighting systems shows satisfactory feasibility in terms of power quality and economic performance.

Voltage Regulation in BDC Based on Fuzzy Logic Controller using Solar Power Generation

The PhotoVoltaic (PV) based grid system coupled with Bidirectional DC-DC Converter (BDC) utilize Fuzzy Logic Controller (FLC) for increasing voltage gain and reduce the settling time of DC link voltage than conventional is presented. BDC satisfied the load requirements, and control the power flow from different sources such as PV, grid, and battery. However, problems in conventional system are high Total Harmonic Distortion (THD), DC link voltage gain and settling time of capacitor voltage. The generated power is used for improving the power quality at the output of the inverter using Sliding Mode Controller (SMC). The converter and inverter operate has bidirectional performance and utilize the hybrid power generation as mentioned. The battery can act as a load based on operating modes of BDC and power generation. It provides a comparative analysis of Proportional Integral (PI) and FLC method that is effectively performs harmonic reduction in BDC.

An Analog Optimum Torque Control IC for a 200-W Wind Energy Harvesting System

An optimum torque (OT) control integrated circuit (IC) is implemented for harvesting the most available energy from a wind turbine generator (WTG) in a wind energy harvesting (WEH) system. For maximum power point tracking (MPPT), a rotor speed detector is proposed to obtain the root-mean-square (RMS) value of the WTG output voltage, which is proportional to the rotor speed. Then, three-phase current references are generated by multiplying the RMS value with the three-phase WTG output voltages for regulating the three-phase WTG output currents to achieve OT control. Further, a background calibration circuit is also implemented for adjusting the OT trajectory to maintain high MPPT efficiency. Moreover, to achieve a high power factor and low total current harmonic distortion (THD $_{{i}}$ ), this brief applies three-phase carrier-based current sinusoidal PWM to drive a fully controlled boost rectifier. The chip is fabricated in 0.5- ${ \mu }\text{m}$ CMOS process with a 0.35-mm2 chip area and measured with a WTG test rig designed to emulate the electrical output of a WTG. Measurement shows the proposed IC with fully controlled boost rectifier achieves 96.1% peak power conversion efficiency, 0.99 power factor, and 1.7% minimum THD $_{{i}}$ based on a 200-W WEH system. Compared with prior IC-implemented state-of-the-arts, this brief featuring well-designed circuit linearity has superior power conversion efficiency and THD $_{{i}}$ .

Voltage Control of Isolated Wind Energy Conversion System using Adaptive Voltage Controller for Non-Linear Loads

Electrical energy demand increases day-by-day due to economic growth, technology development and increasing world population. The wind is one of the accessible renewable energy sources to generate electrical energy to meet the increased load demand. When the wind energy conversion system (WECS) is operating as isolated mode, it is more reliable, economical and easy to electrify rural areas. When the WECS is connected to load without controller the output three-phase voltages of the inverter have more transient and steady state errors and higher total harmonic distortion in the voltages and currents. This paper discusses various voltage controllers used in WECS in detail. The proposed WECS is simulated using MATLAB/Simulink with and without adaptive voltage controller for balanced and unbalanced non-linear load conditions. In each case the results have been analyzed and total harmonic distortion is evaluated..

A Modified Asymmetrical Half-Bridge Flyback Converter for Step-Down AC–DC Applications

This article presents a modified asymmetrical half-bridge flyback converter (AHBFC) to fulfill the single-stage step-down ac-dc universal input voltage application. This topology is obtained from the integration of a buck-type power factor correction, an auxiliary energy buffer, and a conventional AHBFC. By sharing common switches and utilizing transformer's leakage inductor, the single-stage circuit can achieve both high power factor (PF) and low total harmonic distortion with the simple constant on-time control while regulating the dc output voltage. In addition, it is able to operate in universal input voltage with low dc link voltage and low output voltage. Moreover, the zero voltage switching and the zero current switching features of the power switches can also be achieved. Detailed analyses and design procedures of the proposed converter are given and verified by the experimental results. Finally, the comparison with reported circuit topologies and power loss analyses verified by experimental results are presented to provide the insight of practical design.

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.

Soft switching flyback inverter for photovoltaic AC module applications

The soft switching flyback inverters still cannot provide high efficiency and low output current total harmonic distortion (THD) in all load ranges. Therefore, a new flyback inverter with soft switching for photovoltaic AC module applications is presented in this study. The introduced inverter is simple and a small auxiliary circuit is added to the conventional topology of the flyback inverter. Since the primary current of the transformer is not affected by the auxiliary branch, the output current THD does not increase. In addition, all of the high-frequency switches of the proposed topology are switched under soft switching condition, which allows high-switching frequency. Hence, high efficiency, as well as compact design, can be achieved in the proposed inverter. Moreover, the voltage overshoot of the main switch during the turn-off process is limited. This effect decreases the conduction losses because the lower voltage rating switch can be used. Furthermore, a new control method is presented, which provides high efficiency in all load ranges. The operations of the introduced flyback inverter and component selection have been discussed in detail. The performance of the proposed inverter with the auxiliary circuit and corresponding controllers are validated with the help of experimental results.

Analysis and Experimentation on a New High Power Factor Off-Line LED Driver Based on Interleaved Integrated Buck Flyback Converter

This paper presents a high power factor (PF), low total harmonic distortion (THD) light-emitting diode (LED) driver with dimming capability. In addition, the proposed technique ensures a high PF and low THD at any dimming level. The driver is implemented by using an interleaved capacitor, which is placed between the rectifier and the integrated buck flyback converter (IBFC). In this way, the line current conduction angle is increased, which in return increases the PF and decreases the THD. The operation of the proposed converter ensures that one diode of the conventional IBFC will not conduct, so that it can be removed. Moreover, owing to the continuous power flow, the proposed technique makes a significant reduction of the converter output ripple. The paper presents a prototype of the proposed converter supplying an LED luminaire of 37 V/ 0.67 A. The prototype shows a high PF of 0.997, small THD of 2.5%, output current ripple of 6%, and an efficiency of 80%.

A Three-Level Universal Electric Vehicle Charger Based on Voltage-Oriented Control and Pulse-Width Modulation

Electric vehicles (EVs) could be used to address the issues of environmental pollution and the depletion of non-renewable energy resources. EVs, which are energized by a battery storage system, are becoming attractive because they keep the environment clean. Furthermore, the cost of EVs is becoming cheaper. Thus, EVs will become a significant load on utility distribution system in the future. EV chargers play a significant role in the expansion of EVs. The input current of an EV charger with a high total harmonic distortion (THD) and a high ripple distortion of the output voltage can impact battery life and battery charging time. Furthermore, the high cost and large size of the chargers are considered other issues in EV development. This work presents the complete design process of a universal EV charger with a special focus on its control algorithms. In this regard, a novel control algorithm based on the integration of voltage-oriented control (VOC) and the sinusoidal pulse-width modulation (SPWM) technique is proposed to ensure effective Levels 1, 2, and 3 battery charging. A simulation of the universal EV charger was conducted and assessed in MATLAB–Simulink. Moreover, a laboratory prototype was constructed with a TMS320F28335 digital signal processor (DSP) programmed as the controller to validate its operation and performance. The findings show that the proposed charger is able to provide a controllable and constant charging voltage for a variety of EVs, with an input current of low total harmonic distortion (THD) and an almost unity power factor.

Double Integrated-Buck Boost Converter versus Double Integrated-Buck Topology for LED Lamps

In this paper a comparative study between two different approaches for LED driving based on the double integrated buck boost and a double integrated Buck converter. It presents a single-stage, single-switch, transformer less ac/dc converter suitable for Led lighting applications. High Brightness Light Emitting Diodes (HB LEDs) can be seriously considered for replacing conventional halogen, incandescent and fluorescent lamps in general illumination including streetlights due to the rapid development in LED technology in recent years. In many offline applications, maintaining a high-power factor and low harmonics are of primary importance. Single stage power factor pre-regulation technology is mainly preferred in cost sensitive applications where power factor regulation is necessary, as adding additional power factor correction controller will surely increase the cost. Here a high-power-factor, long life integrated converter able to supply LED lamps from ac mains is presented. This topology integrates a buck-boost type power-factor correction (PFC) cell with a buck–boost dc/dc converter there by providing the necessary high input power factor and low Total Harmonic Distortion (THD). An isolation transformer increases complexities in the implementation of feedback and control. The proposed topology is non-isolated and hence much simpler in implementation. The main advantage of this converter is that this circuit uses only one controllable switch. The converter is used to provide power factor correction in streetlight application. A Double integrated buck converter finds application in fields of solid-state lighting. Buck Converter is widely used for step down dc-dc conversion when there is no isolation requirement. The narrow duty cycle of the buck converter limits its application for high step-down applications. The double integrated buck converter overcomes its limitation. This converter also provides high power factor and output current regulation. A Double integrated buck converter uses for the offline power supply for LED lighting based on the integration of a buck power factor corrector (PFC) and the tapped buck dc/dc converter having high step-down capability and good output current regulation. Due to the high reliability, the simple structure, and the low component count, the proposed topology effectively results to be very suitable for medium power solid-state lighting applications. From Comparative analysis of two circuits integrated double buck boost converter is found to be more efficient with high power factor and low THD.