Low Power Factor Research Articles

유도전동기의 토크 변화시 역률 보상기법에 관한 연구

Induction motors are one of the most commonly used inductive loads in industrial settings. Induction motors may be operated at rated operation, but they are often operated at lower ratings. Induction motors have an inductive load and a power factor of about 0.8 during rated operation, but the power factor drops below this when operating below the rating. A capacitor is attached to the motor terminal to compensate for the low power factor, but the capacity of this capacitor is calculated under the conditions of rated operation of the induction motor and is not suitable for load fluctuations. When the load changes, the current flowing through the stator of induction motor changes, but the excitation current required for magnetization changes very little. When the reactive power required for magnetization of an induction motor is compensated for on behalf of the power source, the power factor can be operated close to 1 even when the motor torque changes.<BR>In this paper, by installing a static synchronous compensator(STATCOM) between the power source and the induction motor side, the reactive power required for magnetization is supplied to the induction motor instead of the power source even when the induction motor torque changes. A control method was presented, and the possibility was analyzed through simulation.

Design and Implementation of Wireless Power Transfer Systems With Improved Capacitor Error Tolerance

Owing to manufacturing defects and aging, compensation capacitors are inevitably prone to errors, leading to the performance deprecation in a wireless power transfer (WPT) system. This paper focuses on the sensitivity analysis of system characteristics to capacitor errors and design methods to improve detuning tolerance. First, the output voltage, power factor, transfer efficiency, and capacitor voltages are derived for LCC-S compensated WPT systems. The worst-case scenarios (i.e., the maximum and minimum values of these indicators) are used to evaluate the effect of capacitor errors. They are calculated under detuned conditions with different inverter quality factors, load quality factors, and the ratios of the primary coils self-inductance to the compensation inductance. Then, the design constraints are summarized to meet the system requirements considering 10% capacitor errors. A simplified and easy-to-follow system design process is proposed and a 22-kW wireless charger for an electric bus is designed. Experimental results show that, compared with the traditional design, the change ratio of the output voltage of the proposed design is reduced from between -40.9% and 13.1% to between -21.5% and 12.4%. The lowest power factor is increased from 0.64 to 0.78, and the maximum drop in transfer efficiency is reduced from 9.9% to 5.9%.

Matlab Simulation for Power Factor Correction

Abstract: Lower in Power Factor of electrical equipments will draws high current from supply power. The effect of this is affected by impedance of electrical equipment. Therefore, the main consideration of this study is how impedance of electrical equipment affects the power factor of electrical loads, and then distributed power as the whole. This study is important to verify the right action to increase low power factor effectively for electrical energy efficiency concern.

Room temperature ferromagnetism and thermoelectric behavior of calcium based spinel chalcogenides CaZ2S4 (Z = Ti, V, Cr, Fe) for spintronic applications

The electronic, magnetic, and thermoelectric properties of CaZ2S4 (Z = Ti, V, Cr, Fe) are explored comprehensively. The stability in the ferromagnetic state (FM) has been ensured by energy released from optimized structures and enthalpy of formation (ΔH). The Heisenberg classical model has been used to calculate Curie temperature (Tc). The band structures (BS), as well as densities of states (DOS), are analyzed to explore half-metallic ferromagnetism and 100% spin polarization. The Δx(pd) (exchange energy) overcome ΔCF (Crystal field energy) because of ferromagnetism prompted by strong hybridization. The negative Δx(pd) and exchange constant N0β reduced exchange energy that satisfies the double exchange model. The thermoelectric properties of the studied compounds are elaborated by estimating electrical conductivity, thermal conductivity, and the Seebeck coefficient. The increase in power factor with the CaFe2S4 has been noted while other spinels have very low power factor.

Reduction of Hf via Hf/Zr Substitution in Mechanically Alloyed (Hf,Ti)CoSb Half-Heusler Solid Solutions

(Hf,Zr,Ti)Co(Sb,Sn) Solid solutions were prepared by mechanical-alloying followed by hot-press method as an attempt to reduce Hf concentration and therefore the material’s cost without negatively affecting the thermoelectric performance. To this end, two different methods were applied: (a) Hf substitution with its lighter and cheaper homologue Zr; and (b) fine tuning of carrier concentration by the substitution of Sb with Sn. The isoelectronic substitution of Hf with Zr was investigated in Hf0.6-xZrxTi0.4CoSb0.8Sn0.2 solid solutions and resulted in lower power factors and ZTs. However, the low thermal conductivity of Hf0.4Zr0.2Ti0.4CoSb0.8Sn0.2 contributed in achieving a relatively good ZT~0.67 at 970 K. The effect of charge carrier concentration was investigated by preparing Hf0.4Zr0.2Ti0.4CoSb1-ySny (y = 0.15–0.25) compounds. Hf0.4Zr0.2Ti0.4CoSb0.83Sn0.17 composition prepared by six hours milling reached the highest ZT of 0.77 at 960 K.

저압 유도발전기에 적용되는 커패시터와 리액터의 동작에 관한 연구

Induction generators are widely used in small hydro or micro hydro power. The induction generator has a low power factor because it is an inductive load and requires reactive power required for the rotating magnetic field. Since this reactive power is not generated by itself, it must be supplied from the power source. Since most of the reactive power is provided from the power supply side, the power factor is lowered. Capacitors are added to the generator terminals to easily compensate for the lowered power factor. Inrush current occurs when an induction generator is connected to the grid. In some cases, a reactor is added to the capacitor as part of a method to reduce this inrush current. The reactor is usually connected to the generator line to reduce the inrush current, but there are cases where it is also attached to the capacitor along with the harmonic current reduction.BRIn this study, changes in inrush current, voltage drop, power and power factor were analyzed depending on whether or not a capacitor was installed and a reactor was installed on the capacitor when the induction generator was started directly and connected to the grid.

Adaptive super-twisting terminal sliding mode control and LVRT capability for switched reluctance generator based wind energy conversion system

Wind Energy Conversion systems (WECS) based on the Switched Reluctance Generator (SRG) devoid of rotor windings and permanent magnets are becoming more and more an attractive generator in wind energy market. Currently, the applicability of this machine in the WECS is now possible thanks to the mitigation of its drawbacks, mainly its high torque fluctuations and its low power factor. In this paper, an Adaptive Super Twisting Terminal Sliding Mode (AST-TSM) control is proposed for SRG-based WECS interfaced to the grid via a full-scale back-to-back converter. The main purpose of the proposed scheme is controlling the generator speed in order to achieve a Maximum Power Point Tracking (MPPT) with better performances. The second issue addressed consists of exploring the Low Voltage Ride Through (LVRT) capability of SRG-based WECS for compliance with recent grid code requirements. In modern grid codes, wind farms are only allowed to be connected to the grid if they have the capacity to remain in service during a short grid disturbance. As a matter of fact, under grid faults, the main tasks of the LVRT method consist in feeding the required reactive power into the grid in order to facilitate the recovery of the grid voltage. In this work, the investigated LVRT scheme, classified as a software method, is responsible for swapping the back-to back converter duties without external devices under grid voltage sags. Thereby, the generated power is stored as kinetic form, preventing strong overvoltage on the DC-bus. The proposed AST-TSM control scheme and the adopted LVRT method are substantiated by simulation results. All simulation case studies show that the AST-TSM control achieves good performance and extreme robustness as compared with the Proportional Integral (PI) and Integral Backstepping (IBC) controllers. Furthermore, the proposed controller is able to improve the suppression of chattering effect when its parameters are adjusted carefully. Also, simulation under grid faults conditions has proven that the LVRT method is effective for SRG-based WECS.

Power Factor Improvement of The Glenmore Sugar Industry Electrical System

AbstractThis study discusses the improvement of the power factor in the Glenmore Sugar Industry electrical system. Low power factor can be caused by variations in inductive loads. This has an impact on large currents and high reactive power so that a black out can occur in the Glenmore Sugar Industry electrical system. Low power factor is corrected with the most effective Costum Power Devices, namely Static Var Compensator (SVC) and Static Synchronous Compensator (STATCOM). The evaluated and corrected load buses are those with low power factor.The simulation results show in the application of SVC for the lowest results, power factor increased from 0.76 to 0.78 with reactive power values in the range from + 1.6 to – 0.64 MVAR. The power factor increased from 0.76 to 0.85 with reactive power values in the range from +4.9 to –1.9 MVAR. And for the highest results, the power factor increased from 0.82 to 0.92 with reactive power values in the range from +3.9 to –1.5 MVAR.The application of STATCOM can increase the power factor with reactive power values in the range from +4.9 to – 0.994 MVAR, +1.6 to -0.32 MVAR and +3.9 to -0.7875 MVAR. Keywords – Power factor, SVC, STATCOM, Reactive power, Industry.

A Multiphase AC–DC Converter With Improved Power Quality for EV Charging Station

This work presents a multiphase ac&#x2013;dc converter-based electric vehicle (EV) charging station that is designed to meet IEEE-519 power-quality (PQ) standard. The proposed EV charging station draws current from the utility grid at low total harmonic distortion (THD) and high power factor (PF), without using PF corrector and active/passive filter circuits. This study evaluates an 18-phase ac&#x2013;dc converter for an EV charging station, which consists of three single-phase multiwinding transformers (MWTs) and diode rectifiers. MWTs are connected to enable direct conversion of a three-phase utility supply into an 18-phase power supply that reduces the measured THD in the input line current. The ac&#x2013;dc conversion stage of the proposed EV charging station is found to be reliable and operates at line-frequency, without the need for high-frequency active switches. For charging an EV in constant current (CC) and constant voltage (CV) mode, a multiphase (interleaved) dc&#x2013;dc converter is used. MATLAB/Simulink environment is used to evaluate the performance of the proposed EV charging station in terms of THD and PF. The results are validated through an on-the-bench prototype hardware setup of the proposed EV charging station.

Study on Analysis and Design of Line-Start Synchronous Reluctance Motor Considering Rotor Slot Opening and Bridges

According to International Electrotechnical Commission (IEC) 60034-1, in industrial applications not only efficiency but also power factors are important performance indexes. When comparing line motor to induction motor (IM), a line-start synchronous reluctance motor (LS-SynRM) has a high efficiency but a low power factor than that of IM. In this article, the analysis and design of LS-SynRM are carried out considering the rotor slot opening and bridges for improving the efficiency and power factor. The reference machine is selected with a 2.2 kW IM, and the performance of the reference model is analyzed based on finite element analysis (FEA). To analyze the effect of rotor slot opening and bridges, an optimal model of LS-SynRM is designed through a two-step design process. First, the design of rotor slot for synchronization is carried out, and second, the design of barriers using the response surface method (RSM) is carried out under the same conditions of the stator size of IM. Based on the basic model, the performances of LS-SynRM are analyzed according to the slot opening and bridges. Furthermore, the parametric analysis is carried out and the final model is designed considering the efficiency and power factor based on the design parameters. Finally, the final model is manufactured, and the experiment is carried out to verify the FEA result.

Study on Multidegree-of-Freedom Ultrasonic Motor Using Vibration Mode Rotation of Metal Spherical Stator

Most of the multidegree-of-freedom ultrasonic motors (MDOF-USMs) use a spherical rotor, and the design of the stator is restricted due to the use of the resonance mode. (1) Therefore, there is almost impossible to freely design the overall shape, resulting in a complicated structure. (2) To solve such an inconvenience, an MDOF-USM using a metal spherical stator was proposed. The vibration mode rotation on the stator was designed by theoretical analysis of spherical vibration and finite element method analysis. Multilayer piezoelectric actuators (MPAs) were embedded in the sphere to excite the vibration mode. Cylindrical projections were attached to the surface of the stator to magnify the vibration displacement and worked as the driving part. Their effects were evaluated using an electronic circuit simulator method of performance analysis. (3) As a result, two types of vibration mode rotation methods for the 3-DOF rotation were confirmed. It was also confirmed that the rotor covering the outside stator rotates around three axes. However, tiny torque, low power factor, and slow speed were obtained. (4) An MDOF-USM using a spherical stator was realized according to the operating principle. However, since the cause of such a low performance is the excitation method of the sphere and the rotor structure, research for improvement is required in the future.

A twelve-switch power conditioner for voltage and current compensation in three-phase four-wire grids

An interesting solution for problems associated with system voltage, such as sags and swells, as well as those associated with current such as low power factor and harmonic distortion is the unified power quality conditioner. However, one of its drawbacks is the high number of semiconductor devices since its conventional topology presents two full-bridge converters connected in a back-to-back configuration. Therefore, this paper proposes a twelve-switch converter topology as a power conditioner for voltage and current compensation in three-phase four-wire grids. The developed topology ally low voltage characteristic of dc bus of a hybrid power filter with a reduced number of semiconductor switches and the capability of homopolar voltage and current compensation through the converter fourth leg for the neutral wire connection. In the twelve-switch converter, there are two sets of three-phase four-wire outputs, each set behaving as an independent converter unit. One of these units is connected in parallel to the load by means of a series LC filter, working as a hybrid power filter and being responsible for the compensation of current harmonics and imbalance. The second converter unit is responsible for compensating harmonics, sags or swells in the grid voltage, in such way that the load receives a sinusoidal voltage waveform. Both converters are controlled in stationary reference frame through proportional-resonant controllers. Experimental results demonstrate the validity and the effectiveness of the proposed topology.

Comparative analysis of unit template, SRF and the modified SRF technique for DSTATCOM-based distribution system

This paper introduces a new hybrid control strategy called the modified synchronous reference frame theory (modified SRF theory) for power quality improvement of a DSTATCOM-based distribution system. This control strategy makes use of both synchronous reference frame (SRF) as well as unit template technique to generate the reference supply currents which are then compared with the sensed supply currents and fed to the hysteresis/PWM current controller to generate the necessary switching signals for switches of the voltage source converter (VSC) of the DSTATCOM for a three-phase, three-wire system. The proposed algorithm eliminates the need of a complex reverse Park's transformation and results in the most efficient harmonic diminution confirming to IEEE-519 standard. The proposed control algorithm is compared with the unit template-based algorithm and the SRF theory to mitigate a variety of problems such as low power factor, voltage regulation, current unbalance and harmonics in the system. The proposed algorithm is proved efficient and reliable when compared with conventional algorithms reported in the literature.

Performance Evaluation of BB-QZSI-Based DSTATCOMUnder Dynamic Load Condition

Abstract This paper presents the shunt compensation performance of quasi-Z-source inverter (QZSI) and back to back connected QZSIs (BB-QZSI) to address the power quality (PQ) issues in the three-phase three-wire power utility network (PUN). Generally, these PQ issues are poor voltage regulation, low power factor (PF), source current distortion, unbalanced voltage, etc. The proposed BBQZSI-based distribution static compensator (DSTATCOM) consists of two QZSIs with a common dc-link capacitor. Because the QZSI could achieve buck/boost conversion as well as DC to AC inversion in a single-stage and the back to back configuration decreases the system down time cost (if a fault occurs in one QZSI the other can continue the shunt compensation). Particularly, icos ϕ control algorithmcontrol algorithm is implemented to generate proper switching pulses for the switches of DSTATCOM. The effectiveness of the BB-QZSI is verified through simulation studies over QZSI using MATLAB/Simulink software satisfying the recommended grid code.

Fair Power Factor Billing Under Unbalanced and Nonsinusoidal Voltage Supply

Utilities apply an additional fee for medium and large customers with low power factors. However, unfair financial charges may occur in installations subjected to voltage unbalance and harmonic distortion. The objective of this paper is to determine the fairest PF definitions and their corresponding measurement algorithms in the case in which a constant impedance load or an induction motor is supplied with unbalanced and nonsinusoidal voltages. Fairness is defined considering that the meter (built based on a particular definition and measurement method) under nonideal supply should lead to very close values as if it was submitted to an ideal balanced sinusoidal supply. We performed computational simulations to emulate several conditions in which a balanced customer (modeled as a constant impedance load or an induction motor) is charged due to a voltage supply no longer balanced and sinusoidal. We also performed experimental tests with an induction motor subjected to a wide range of unbalanced nonsinusoidal supply conditions to ratify the conclusions drawn from the simulations. Based on the simulation results and the experimental tests, we indicate some power factor definitions and measurement methods that are not significantly affected by voltage unbalance and harmonic distortions. These indicated PF definitions provide the fairest billing for conditions with unbalanced nonsinusoidal voltages.

Achieving higher thermoelectric performance of n-type PbTe by adjusting the band structure and enhanced phonon scattering.

Due to the very distinct electronic band structure and lower power factor, the exploration of n-type PbTe as thermoelectric materials has historically fallen behind that of p-type PbTe. In this work, n-type Pb0.97Sb0.03Te-based composites incorporated with Cu12Sb4S13 nanoparticles are synthesized and investigated. Sb doping is utilized to modify its carrier concentration in order to obtain n-type PbTe materials with a high power factor. Then, the incorporation of Cu12Sb4S13 nanoparticles can generate semi-coherent nanophase CuTe, and simultaneously optimize the thermal and electrical properties due to remarkable energy filtering effects and interface scattering in the higher temperature range. Eventually, a peak figure of merit ZT ≈ 1.58 was obtained at 773 K for the sample Pb0.97Sb0.03Te + 1.5 wt% Cu12Sb4S13, indicating that the incorporation of Cu12Sb4S13 in Pb0.97Sb0.03Te is an effective approach to improve its thermoelectric performance.

A Modified Forward PFC Converter for LED Lighting Applications

A modified forward power factor correction (PFC) converter for light-emitting-diode (LED) lighting applications is proposed in this paper. The proposed circuit topology is an integration of a forward converter and a flyback converter with a multi-windings transformer. The flyback converter is operated as an auxiliary voltage source (AVS) connected in series with the rectified ac grid voltage to achieve low harmonic current distortion and high power factor. The magnetizing inductance energy is recycled to charge the capacitor in the AVS. The commonly used constant on-time control and primary side regulation can be easily adopted to control the proposed LED driver. The operation principle of the proposed converter is presented followed by the mathematical derivation of the parameter design. An 80 W prototype converter was built and tested to verify the performance of the proposed PFC converter. Experimental results show that the proposed PFC converter can comply with the IEC 61000-3-2 standard with high efficiency, low current harmonics, and a nearly unity power factor under universal input voltage range.

Enhanced thermoelectric properties of Cu2-xSe by coordinating carrier concentration to reduce thermal conductivity

Cu 2-x Se has been known as an ideal thermoelectric material for application in the middle-high temperature range due to the outstanding electric transmission conductivity and relatively low lattice thermal conductivity. However, its performance is significantly constrained by its high thermal conductivity and thermal stability issues, as well as its difficulty in element doping because of the influence of atomic size and atomic solid solubility. Here, we prominently reduced the thermal conductivity of Cu 2-x Se by addition different amounts of WS 2 to the Cu 2-x Se matrix, and successfully improved the power factor of the material because of the reduction of high Cu defects to coordinate the three mutually coupled parameters. The zT value of the WS 2 -doping Cu 2-x Se sample was eventually enhanced by 56% compared with pristine Cu 2-x Se, and up to ca. 1 at 823 K. Further, we found that the symmetry of the Cu 2-x Se crystal had not been destroyed undergoing the doping of WS 2 into its crystal lattice, and the doped sample showed good thermal stability when cycle test was carried out twice between 315 K and 823 K. Cu 2-x Se were prepared by colloidal synthesis, and it's thermal conductivity was reduced by doping with different amounts of WS 2 into the Cu 2-x Se matrix, and the power factor of the doping material was improved through the reduction of high Cu defects to coordinate the three mutually coupled parameters. The ZT value of the WS 2 -doping Cu 2-x Se sample was eventually enhanced by 56% compared with pristine Cu 2-x Se, and up to ca. 1 at 823 K. • The samples of WS 2 -doping Cu 2-x Se were prepared. • WS 2 -doping Cu 2-x Se had low thermal conductivity and high power factor through the reduction of high carrier concentration. • The zT value of the WS 2 -doping Cu 2-x Se sample was eventually enhanced by 56% compared with pristine Cu 2-x Se, and up to ca. 1 at 823 K.

Transverse Flux Machine—A Review

For applications with high torque demand, gearboxes are commonly used to convert torque and speed in order to receive higher specific values for torque and power. This causes additional losses, cost, inaccuracies, effort, and noise. Eliminating the need of a mechanical gear and the associated disadvantages, Transverse Flux Machines with their high torque density are a very promising alternative. Despite a high torque density and a high efficiency, these types of machines are not commonly used. Due to the complex structure, challenges with mechanical design, and modeling of the machine behavior arise. Additionally, there are high requirements for the inverter due to the low power factor. This paper provides an overview of the state of the art including the potentials and advantages but also the problems and hindrances of these types of machines. Relating to linear and rotary machines from research and industry, the machine is introduced with its history, application and classification. Further, the general technical aspects, the influence of materials for flux guidance, the methods of modeling, methods for a minimization of torque ripples, as well as methods for power factor improvement are presented.

On a Novel Topology of Matrix Converter Applied to Accelerator DC Power Supply

The current topology schemes of heavy ion accelerator power supply have serious pollution to the power grid caused by low power factor of the grid side. Considering the characteristics of adjustable power factor and bidirectional energy transfer of the matrix converter, the possibility of which applied to the accelerator DC power supply is studied and three kinds of backup topology schemes including the preceding regulated matrix rectifier (MR) are proposed in this article. Given the actual situation of accelerator power supply, research has been focused on the modulation strategy suitable for the topology of the preceding regulated MR and simulation validation. Based on simulation of the preceding regulated MR scheme, a matrix power prototype is developed. A power factor tester is utilized to test grid side power factor. According to the experimental results, it is prospectively feasible to apply the preceding regulated MR topology to accelerator DC power supply, with excellent performance of the grid side.