Lagging Power Factor Research Articles

A Constant DC-Capacitor Voltage Control Based Strategy for Current Balancer in Single-Phase Three-Wire Distribution Systems

This paper proposes a constant dc-capacitor voltage control based strategy for a current balancer in single-phase three-wire distribution systems. The proposed control strategy only uses the constant dc-capacitor voltage control block commonly used in active power conditioners to calculate the compensation current. No calculation blocks to obtain the reactive and unbalanced-active components are necessary. Thus, we provide the simplest possible control strategy for the current balancer. The basic principle of the proposed control method is discussed in detail then its validity is confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that balanced source currents with a power factor of unity are obtained on the secondary side of a pole-mounted distribution transformer while retaining unbalanced load current conditions with a lagging power factor.

A Novel VSI- and CSI-Fed Active–Reactive Induction Motor Drive with Sinusoidal Voltages and Currents

Till date load-commutated inverter (LCI)-fed synchronous motor drive configuration is popular in high power applications (>;10 MW). The leading power factor operation of synchronous motor by excitation control offers this simple and rugged drive structure. On the contrary, LCI-fed induction motor drive is absent as it always draws lagging power factor current. Therefore, complicated commutation circuit is required to switch off thyristors for a current source inverter (CSI)-driven induction motor. It poses the major hindrance to scale up the power rating of CSI-fed induction motor drive. A new power topology for LCI-fed induction motor drive for medium-voltage drive application is proposed. A new induction machine (active-reactive induction machine) with two sets of three-phase winding is introduced as a drive motor. The proposed power configuration ensures sinusoidal voltage and current at the motor terminals. The total drive power is shared among a thyristor-based LCI, an insulated gate bipolar transistor (IGBT)-based two-level voltage source inverter (VSI), and a three-level VSI. The benefits of SCRs and IGBTs are explored in the proposed drive. Experimental results from a prototype drive verify the basic concepts of the drive.

Lessons Learned From the Generator Loss of Field at a Cogeneration Thermal Power Plant in Taiwan

The contribution of this paper is that we present experiences from dealing with practical issues related to synchronous machine stability events. We describe and analyze the scenarios of generator loss-of-field occurring two times at a cogeneration thermal power plant in Taiwan in the years 2003 and 2005. Since the total production loss from both events was quite large, some improvements have been implemented to prevent the recurrence of similar events in the future. They consist of installing the sequence of events recorder at the generator output terminal, regulating the generator lagging power factor operation from 0.95-0.99 to 0.91, adjusting the tap position to decrease the secondary voltage of the 161 kV/161 kV interconnecting transformer, operating the phase-leading capacitors attached with a multi-stage chain cut-off control unit, and running two or three generators in automatic voltage regulation mode instead of automatic power factor regulation mode. Although similar events occurred twice at the same power plant in 2006, the generating units were capable of continuous stable operation which had effectively verified the improvements of operational changes. In conclusion, we suggest that the operating modes of generators in a cogeneration plant should reexamine constantly as well as monitor power quality of different end-user sectors continuously in order to ensure the security of power-system operation.

변압기 기반 3상 전압변동발생기의 전압강하 특성해석

본 논문에서는 변압기 기반 전압변동 발생기의 직렬변압기에 의한 전압강하 특성을 분석하였다. 전압변동 발생기의 회로구성 방식에는 여러 가지가 있으나 본 논문에서는 비교적 비용이 저렴하고 신뢰도가 높은 직렬변압기를 사용한 방식에 대해 다루고자 한다. 직렬변압기에 의한 전압강하는 변압기의 %Z와 부하용량 및 부하역률에 의해 결정된다. 직렬변압기의 설계가 잘못되면 전압강하가 심각하게 발생하여 제대로 된 성능을 확보할 수 없다. 본 논문에서는 10kVA급 전압변동 발생기에 대해 %Z가 4%인 직렬변압기를 사용한 경우 부하역률에 따른 전압강하를 분석하였으며 지상 부하일수록 전압강하가 증가하고 역률이 0.85 지상인 경우 전압강하가 4% 발생함을 시뮬레이션 및 실험을 통하여 확인하였다. A voltage drop characteristics of a transformer-based voltage disturbance generator with series transformers is analysed. It is well known that a voltage disturbance generator with series transformer is cost-effective and reliable compared with other types. The voltage drop depends on the %Z of the transformer, power rating, and output power factor. A wrong design of the transformer results in a severe voltage drop, which can not guarantee the proper performance of the generator. The voltage drop is analysed under the condition of 10kVA output power rating and 4% of %Z with the variation of power factor. It is found through simulations and experiments that the drop increases as the power factor decreases in lagging mode, and the drop is 4% of the rated voltage in case of 0.85 lagging power factor.

3-D Electromagnetic Force Distribution in the End Region of Turbogenerator

The paper deals with detailed investigation of the electromagnetic forces in the end zone of turbine generator. The electromagnetic field is analyzed using 3-D FEM computation. The regions of interest are the stator and rotor end cores including the zone of the teeth and the end windings. The dynamic behavior of the local electromagnetic force densities is studied in accordance with the working mode. Two modes at the leading and at the lagging power factor are considered. Comparison between the ratio of the local electromechanical loads under considered modes and the relevant loads at the rated mode is discussed and appropriate conclusions are drawn. Calculations are implemented on a 200 MW turbine generator.

Power Factor Correction for Thyristor Equipment in Glass Industry

Thyristor power controllers are now widely used in the glass industry for controlling furnace temperature. While offering a number of operational advantages, they operate at lagging power factors which require correction for minimum power cost. Harmonic resonance with the utility feed, however, complicate the use of capacitor banks. The nature of harmonic problems is described and the use of inductors to tune capacitor banks below any possible harmonic frequency is demonstrated.The Information Manager Vol. 8 (1) 2008: pp. 22-26

수용가에 설치된 캐패시터 뱅크의 역률개선 및 고조파 저감에 관한 연구

Most power system loads and delivery apparatus are inductive in nature and therefore operate at a lagging power factor. Applying capacitor banks to a customer will result in a power factor correction and other benefits such as VAR support, increased voltage, reduced power losses, and reduced billing charges. Also there can be power quality problems as a result of adding capacitor banks. The most common are harmonics. This paper provides an in depth analysis on the power factor correction and harmonics reduction of capacitor bank installed at a customer. The EDSA program was used as a simulation tool for the case study.

DSP microcontroller‐based fuzzy control of a DC/DC parallel resonant converter using phase‐shift PWM technique

Purpose – To analyze the operating performance of an ac‐dc‐ac‐dc PWM parallel resonant converter operating at lagging power factor mode controlled based on fuzzy logic control method.Design/methodology/approach – A range of published works relevant to dc‐ac‐dc converters and their control methods based on PWM technique are evaluated and their limitations in converter output voltage control are indicated in the first section of this paper. The Simulink model and different stages of the converter are described in the second section. In Section 3, the general mathematical model of the system is derived and the phase‐shift PWM switching technique is explained. The equivalent circuit of the high‐voltage high‐frequency transformer used in the converter and the effects of the transformer parameters on the converter operation are presented in Section 4. In Section 5, fuzzy logic control and the basic concepts of this method are described and its application to the proposed converter output voltage control is expl...

Steady‐state modeling of a phase‐shift PWM parallel resonant converter

PurposeTo derive an analytical model for a dc‐ac‐dc parallel resonant converter operating in lagging power factor mode based on the steady‐state operation conditions and considering the effects of a high‐frequency transformer.Design/methodology/approachA range of published works relevant to dc‐ac‐dc converters and their control methods based on pulse‐width‐modulation technique are evaluated and their limitations in output measurement of higher output voltage converters are indicated. The circuit diagram of the converter is described and the general mathematical model of the system is obtained by deriving and combining the mathematical models of the different converter blocks existing in the system. The derived mathematical model is used to study the steady‐state and transient performance of the converter. The deriving procedure of the analytical model for a parallel resonant converter is extensively given and the analytical model obtained is verified by simulation results achieved using MATLAB/SIMULINK and the program written by the authors.FindingsThe paper suggests an analytical model for dc‐ac‐dc parallel resonant converters. The model can be used in the output voltage estimation of a converter in terms of its phase‐shift angle and the dc‐link voltage.Research limitations/implicationsThe resources in the library of the authors' university and also the English resources relative to dc‐ac‐dc converters reachable through the internet were researched.Practical implicationsThe analytical model suggested can be used in estimating the output voltage of the converters used in high‐voltage applications or where there are difficulties in employing sensors in measurement of the output voltage due to high price or implementation problems.Originality/valueThe originality of the paper is to present an analytical model for dc‐ac‐dc parallel resonant converters. Using this model makes it possible to estimate the output voltage of the converter using the dc‐link voltage and the phase‐shift angle. The proposed model provides researchers to regulate the output voltage of the converters using feed‐forward control technique.

Some Aspects of Modeling and Simulation Techniques for Harmonic Reductions of Power Electronic Inverters

Power electronic converters suffer from certain irregularities usually at the load side as well as on the mains. One of the major effects of such irregularities, are the introduction of harmonics, which has the detrimental effects on the system. There is a need to reduce and suppress them, so that the system performance can be improved. Some of the main sources are the ac-to-ac, dc-to-dc, ac-to-dc, dc-to-ac converters, etc. As the conventional converters have the drawbacks of a high-value of lower-order harmonics produced at the input and at the output side, the larger switching angles leads to lagging power factor. This paper aims at developing an efficient method of modeling and simulation of harmonic reduction by PWM (Pulse Width Modulation) via “Phase Displacement Control” method. Actually bipolar and unipolar voltage notches are introduced at the output side of the power electronic inverter circuit for the suppression of harmonics. Different schemes are available in the literature for the elimination of harmonics up to 2nd order by the above method. This paper develops the methods of harmonic reduction up to 4th order and also uses the concepts of “Artificial Intelligence Search” techniques as per the complexity of the problem. The analysis is done and the expressions are derived, to obtain suitable switching angles. But due to necessity of tackling the mathematical restrictions in numerical algorithms developed for suppression of a number of harmonics more than two, some constraint equations have been developed from the power system interaction viewpoint. Such interaction finally leads to the choice for a compromising value of capacitor. Thus finally, the present work acts like a bridge between “Power Electronics” and “Power System”.

Low-harmonic resonant CLL-type AC/DC converter

A new resonant AC/DC converter is presented. It has been shown that the series parallel CLL topology is particularly useful in resonant rectifier applications. The transformer may be designed to replace one or both the inductances used in the resonant network. The converter is operated only in the lagging power factor mode. Dispensing with the need of an external device snubber. Such a converter is analysed and simulation results are obtained by using MATLAB. Two new control strategies are proposed. Both control schemes are implemented and compared. Scheme 1 requires reduced hardware and no current sensor, but scheme 2 uses a current sensor and an additional PI controller. Scheme 2 performs better than scheme 1 in terms of total harmonic distortion (THD) of the converter input current. A laboratory prototype has been fabricated and excellent performances have been confirmed.

A Low Harmonic High Power Factor Half Bridge Resonant AC/DC Converter

A new resonant rectifier is introduced in this paper. Due to the suitability of operation in the lagging power factor mode, the series parallel CLL topology is utilized. The converter has been analyzed and simulation results have been obtained by using MATLAB. Control requirements have been identified and two new control schemes have been developed. The first scheme does not require any current sensor to improve the current drawn from the supply. The technique is to use a PI controller to maintain the output voltage constant, with an additional gain proportional to the rectified AC input voltage to create a fixed frequency modulation to improve the input current waveform. The second scheme uses a current sensor and forces both the output voltage and the input current to follow the corresponding desired references using two PI controllers. A laboratory prototype has been fabricated to realize the proposed converter topology along with the control schemes and satisfactory results have been found.

Development and performance testing of a 200 kVA damperless superconducting generator

A 200 kVA, 3000 RPM superconducting generator has been developed and tested. The rotor has been wound with superconducting wire of Nb-Ti alloy. A closed-circuit liquid helium system has been designed and installed for cooling the superconducting windings. The stator carries the air-gap type armature windings and a laminated-iron flux-shield. A new concept in the design of superconducting generators with high short-circuit ratio (more than 5) has been introduced. This eliminates the requirement of an electromagnetic damper and quick response excitation system. The generator has been comprehensively tested in the superconducting state. Open-circuit and sustained short-circuit tests, three-phase sudden short-circuit tests, synchronization with the grid and parallel operation with power systems have been conducted. The synchronous machine was operated up to its rated kVA in the four quadrants-as a generator and as a condenser with leading and lagging power factors. A few special tests on superconducting generators, which were not reported earlier, such as direct-online starting of a 20 hp squirrel-cage induction motor and negative phase sequence tests have also been performed successfully. Test results and conclusions are given.

Analysis and design of a fixed-frequency LCL-type series-resonant converter with capacitive output filter

A fixed-frequency modified (LCL-type) series-resonant converter which uses a capacitive output filter is analysed using the Fourier series approach. Based on the analysis a simple design procedure is given. Detailed SPICE simulation results are presented for the designed converter to evaluate its performance for varying input supply voltage and for load variation. Experimental results obtained from a MOSFET based 500 W, 115 V output converter are presented to verify the analysis. The converter operates in lagging power factor mode for a very wide variation in the load and the supply voltage and is suitable for high voltage output applications.

A three-phase series-parallel resonant converter-analysis, design, simulation, and experimental results

A three-phase DC-to-DC series-parallel resonant converter is proposed and its operating modes for a 180/spl deg/ wide gating pulse scheme are explained. A detailed analysis of the converter using a constant current model and the Fourier series approach is presented. Based on the analysis, design curves are obtained and a design example of a 1-kW converter is given. SPICE simulation results for the designed converter and experimental results for a 500-W converter are presented to verify the performance of the proposed converter for varying load conditions. The converter operates in lagging power factor (PF) mode for the entire load range and requires a narrow variation in switching frequency, to adequately regulate the output power.

A fixed-frequency modified series-resonant converter: analysis, design, and experimental results

It is shown that a fixed-frequency modified (LCL-type) series-resonant converter operates in five different modes with variations in the load current and the supply voltage. The converter is analyzed using the state-space approach for these operating modes. Both the general solutions and the steady-state solutions are obtained. Based on the analysis, design curves are obtained and a simple design procedure is illustrated using a design example. Detailed experimental results obtained from a MOSFET-based 500 W converter are presented to verify the analysis. It is shown that using a proper design, the converter operates only in modes 2 and 3, ensuring a lagging power factor mode of operation for very wide variations in the load and supply voltage. >

Analysis and design of (LC)(LC)-type series-parallel resonant converter

A series-parallel resonant converter employing (LC)(LC)-type tank circuit operating in lagging power factor (PF) mode is presented and analyzed using complex ac circuit analysis. Design curves are obtained and the converter is optimized under certain constraints. Detailed Space Integrated Control Experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load conditions. Results obtained from an experimental converter are also presented. The results obtained from the theory, SPICE simulation, and the experimental converter are compared. The proposed converter has high efficiency from full load to very light load (<10%). Switching frequency variation required for a wide change in the load (near load open circuit to full load) is narrow compared with the series resonant converter (SRC).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A fixed frequency LCL-Type series resonant converter

A fixed frequency LCL-type series resonant converter (SRC) which uses an inductive output filter is proposed. Steady-state analysis of the converter is presented using complex ac circuit analysis. Based on the analysis, a simple design procedure is given. Detailed space integrated control experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load and supply voltage conditions. Also, detailed experimental results obtained from a metal-oxide-semiconductor field-effect transistor (MOSFET) based 500 W converter are presented to verify the analysis and SPICE simulation results. The results obtained from the analysis, SPICE simulation and the experimental converter are compared. The proposed converter requires a narrow variation in pulsewidth while maintaining lagging power factor mode of operation for a very wide variation in the load as well as supply voltage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power system applications for PASC converter systems

This paper shows, using EMTP computer simulations, some preliminary results of applying pulse amplitude synthesis and control (PASC) technology to single-source voltage converter systems. The method can be applied to any single terminal pair source with appropriate modifications in power extraction interface and computer control program to match source and load impedance characteristics. The PASC realization as discussed employs banks of transformers, one bank per phase, in which the primaries are connected in parallel through a switch matrix to the DC source. Two opposite polarity primaries per transformer are pulsed alternatively in time to produce an oscillatory sinusoidal output waveform. PASC conversion system capabilities to produce both leading and lagging power factor power output in single-phase and three-phase /spl Delta/ or Y configurations are illustrated. EMTP simulations are used to demonstrate the converter capabilities. Also included are discussions regarding harmonics and potential control strategies to adapt the converter to an application or to minimize harmonics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Some limitations in the use of discharge lamps

Fluorescent lamp technology is quite old. Inductive ballasts used with discharge lamps operate at a low lagging power factor (p.f.) with associated power losses. This introduces a heavy reactive KVA burden in the power system.