Power Factor Control Strategy Research Articles

High Step-Up Resonant DC–DC Converter With Resonant Network for Electrical Collection Systems

Abstract The efficiency of renewable energy electrical collection can be effectively improved by adopting the high voltage direct current (HVDC) electrical collection method. The low-voltage DC power is stepped up to the high-voltage level for HVDC transmission by one-stage step-up type, which can reduce the cost of high-voltage large-capacity DC-DC converters. However, the high cost of DC-DC converters which can achieve high step-up ratio, such as modular multilevel converter (MMC), limits the development of the one-stage step-up type. In this paper, a low-cost DC-DC converter with high step-up ratio which can realize the bidirectional flow of energy is proposed. The total step-up ratio is the product of high-frequency transformer ratio, resonant network gain and step-up ratio of voltage doubler rectifier circuit. Meanwhile, the direct power factor control (DPFC) strategy is proposed based on the idea of controlling active power to achieve the goal of controlling output voltage. Finally, the step-up ratio of the DC-DC converter can reach 160 times, and realize zero-voltage switching (ZVS) turn-on of the switches and zero-current switching (ZCS) turn-off of the diodes.

Control of HVDC Bridges under Light Load Conditions.(Dept.E)

The performance of a HVDC transmission system under light load conditions is investigated. Two types of control schemes are used , namely constant igintion delay and constant power factor. The study has been carried out as a digital simulation. An algorithm is designed to arrive at the results. It has been shown that a reactive power is needed to reduce the over voltages induced across the bridges. This reactive power requires more switching operation in case of ignition delay angle however smaller in magnitude than in case of power factor angle. It has been advised that for reliability of operations , the power factor control scheme is preferable.

A MILP model for optimal renewable wind DG allocation in smart distribution systems considering voltage stability and line loss

This paper introduces a new model for optimal wind distributed generation (WDG) allocation based on mixed integer linear programming (MILP) in todays' smart grids considering on-load tap changing (OLTC) and power factor control (PFC) strategies. The objectives of the proposed optimization model are improving voltage stability and energy loss minimization subject to power flow constraints, line thermal limits, maximum number and size of WDG units, penetration limit, discrete OLTC tap position constraints, and PFC constraints. An efficient voltage phasor-information-based probabilistic voltage stability index (VSI) is extracted to measure the improvement of voltage stability with WDGs. Besides energy losses, reduction index is used to measure the energy loss reduction with the integration of renewable WDGs in the distribution system. An efficient linearized power flow (LPF) model as well as piecewise linearized model of the quadratic terms associated to the PFC constraints are represented to convert the original nonconvex problem into the form of a well-known MILP problem, which guarantees optimal solution and computationally is efficient to be solved using powerful commercial solvers. The effectiveness and validity of proposed model is investigated in compared to the state-of-the-art population-based methods and classical models.

Power Factor Analysis and Maximum Power Factor Control Strategy for Six-Phase DC-Biased Vernier Reluctance Machines

Different from the regular ac machines, the armature winding current waveforms of dc-biased vernier reluctance machines (DC-biased-VRMs) are sinusoidal with dc bias. The power factor (PF) calculation process also shows great difference. This paper intends to analyze the PF theoretically based on the mathematical model. Then, investigate the approach to optimize the PF and the price to pay if measures are taken to further improve the PF. The PF of the DC-biased-VRM is expressed under synchronous rotating frame. A maximum PF control strategy is proposed by adjusting the distribution of three-dimensional dq 0-axis currents. The scale of active power to reactive power is changed, and the PF can be regulated. Experimental results are provided to verify the validity of the theoretical analysis.

Fuzzy 12 sectors improved direct torque control of a DFIG with stator power factor control strategy

Fuzzy 12 sectors improved direct torque control of a DFIG with stator power factor control strategy

Direct torque control-based power factor control of a DFIG

This paper proposes the Direct Torque Control (DTC) of a Wind Energy Conversion System (WECS) based on a Doubly Fed Induction Generator (DFIG) with power factor control strategy. The proposed technique aims at controlling the generator electromagnetic torque and rotor flux while controlling the power factor at the stator terminals. The proposed control is achieved through generating the referential electromagnetic torque from the Maximum Power Point Tracking (MPPT) control so that the maximum power is extracted for each different wind speed, and the referential rotor flux from the reactive power reference.

Comprehensive voltage and power factor control strategy for electric spring

Electric spring (ES) along with the smart load (SL) have recently been used as a smart technology for stabilising distribution networks. ESs are embedded on non-critical (NC) loads in order to protect critical loads against voltage fluctuations. Three different generations of ES have been developed in recent years. A comprehensive control scheme is proposed for the third generation of ES, through which the SL power factor and line voltage can be controlled. In order to control the power factor in steady-state condition, the radial-chordal decomposition (RCD) method, which has been previously used for the second generation, is employed in the closed-loop manner. The proposed controller has also the capability to mitigate the voltage fluctuation in over/under voltage condition. Simulation results show the superiority of this method in voltage control over RCD method. In addition, for a bunch of NC loads, the desired power factor will be reached at the point of common coupling.

A Model Predictive Power Factor Control Scheme With Active Damping Function for Current Source Rectifiers

A model predictive power factor control (MPPFC) scheme is proposed for high-power medium-voltage (MV) current source rectifiers (CSRs). Facing two major issues on input power factor (PF) and LC resonance, the proposed MPPFC uses a novel line reactive power reference estimator to achieve unitary input PF or maximum achievable input PF for a CSR at various operating states, and involves active damping function into itself to mitigate LC resonance at line side. An online capacitance estimation method is associated with the proposed line reactive power reference estimator to guarantee more accurate input PF control, and a novel damping current calculation method, which avoids the use of band-stop filter, is also designed for active damping purpose. In comparison with traditional linear control, the proposed MPPFC not only realizes input PF regulation, but also achieves better steady-state performance on meeting the grid code requirements. In contrast to traditional model predictive control (MPC) for a CSR, the proposed MPPFC achieve more accurate reactive power control. Moreover, it overcomes the challenge on the realization of active damping based on MPC, which extends the application of MPC into high-power MV CSR. Simulation on a high-power CSR (1 MVA/4160 V/139 A) and experiments on a low-power prototype (5 kVA/208 V/13.9 A) are both conducted to verify the effectiveness of MPPFC.

Impacts of Power Factor Control Schemes in Time Series Power Flow Analysis for Centralized PV Plants Using Wavelet Variability Model

This paper presents impacts of three power factor control strategies (fixed power factor, power factor schedule, and power factor function) on the power output of a centralized utility-interactive photovoltaic (PV) plant deployed close to the feeder end and source using the wavelet variability model (WVM) at various penetration levels. The upscaling advantage from a single module and point irradiance sensor to geographic smoothing over the entire PV footprint in WVM is used to simulate effects of a grid-connected large PV system on the IEEE-34 distribution feeder. Also, this study uses high-frequency solar irradiance data (1 s) to show impacts of PV output variability on voltage regulator tap changing operations, feeder voltage, active power profile, and reactive power profile at various penetration levels until the voltage constraint is violated. Results showed that, although variability increases with PV system deployment close to the feeder source and end, it is higher at the feeder end than source.

Novel Simple Reactive Power Control Strategy With DC Capacitor Voltage Control for Active Load Balancer in Three-Phase Four-Wire Distribution Systems

This paper proposes a novel simple reactive power control strategy for the active load balancer (ALB) in three-phase four-wire distribution systems. The proposed reactive power control strategy may be applicable for adjustment of the source-side power factor under the balanced load condition. Only dc capacitor voltage control is used in the proposed control strategy. Therefore, the calculation blocks of the active and reactive components of the load currents are not necessary. The authors, thus, offer the simplest control strategy to control reactive power under the balanced load condition on three-phase four-wire distribution feeders. The basic principle of dc-capacitor-voltage-control-based reactive power control strategy is discussed in detail and then confirmed by digital computer simulation. A prototype experimental system was constructed and tested. Experimental results demonstrate that balanced source currents with reactive power control are achieved on three-phase four-wire distribution feeders. These experimental results also demonstrate that controlling the reactive power reduces the required power rating of the ALB compared with that of the conventional unity power factor control strategy.

PWM 컨버터 차량의 역률 제어를 통한 급전선로의 무효전력 보상

PWM컨버터 차량은 전압벡터제어방식에 의해 부하역률 1.0에 가까운 운전이 가능하므로 기존 저역률의 위상제어방식 차량에 비해 급전선로 전압강하 측면에서 우수한 부하특성을 나타낸다. 그러나 이 경우에도 급 전구간 내의 운전밀도가 높거나 연장급전 구간에서는 선로손실의 증가 및 전압강하 현상이 심각한 수준으로 나타날 수 있다. 본 논문은 PWM컨버터 차량의 역률을 1.0으로 고정하여 운행하는 대신 차량의 운전 조건에 따라 가변적으로 최적 제어함으로써 급전선로의 손실을 최소화 하고 전압 프로파일을 개선하는 방법을 기술하였다. 제시된 방법은 동일 급전구간 내에 운행중인 차량을 대상으로 최대 경사법에 의해 선로의 무효전력손실이 최소화되는 개별 차량의 무효전력 보상량을 결정하게 되며, 이 방법을 표본 계통에 대해 시뮬레이션 한 결과 선로손실의 감소와 함께 전압 프로파일도 상당한 수준으로 개선됨을 알 수 있었다. PWM converter trains exhibit excellent load characteristics in comparison with conventional phase-controlled trains with low power factors, as they can be operated at power factors which are close to unity by means of a voltage vector control method. However, in the case of a high track density or extended feeding, significant line losses and voltage drops can occur. Instead of operating these trains at a fixed unity power factor, this paper suggests a continuous optimal power factor control scheme for each train in an effort to minimize line losses and improve voltage drops according to varying load conditions. The proposed method utilizes the steepest descent algorithm targeting each car in the same feeding section to establish the optimized reactive power compensation levels that can minimize the reactive power loss of the feeder. The results from a simulation of a sample system show that voltage drops can be improved and line losses decreased.

Capability constraints to mitigate voltage fluctuations from DFIG wind farms when delivering ancillary services to the network

Majority of the wind power resources are typically sited at remote locations in power networks and generated power is transmitted through rural transmission corridors to load centres. With increased penetration level of the wind generation there is an increased requirement to provide ancillary services from distributed wind power resources, hence they are operated under different control strategies to provide ancillary services to the network. The control strategies and capability characteristics will significant impact on voltage fluctuations in distribution networks. This paper presents a comparative analysis between different wind generator control strategies (i.e. power factor control strategy, voltage control strategy and reactive power dispatch strategy) on network voltage fluctuations during variable wind conditions while considering extended reactive power capability (i.e. with both generator and power electronic converter reactive power capabilities) for the doubly-fed induction generator (DFIG). Voltage fluctuations are analysed using real wind data measured at a DFIG based wind farm, and the wind farm model was verified against real measurements. Study has shown that voltage fluctuations are exacerbated when wind generator is at mode transition (i.e. from power optimisation mode to power limitation mode). A sensitivity analysis has shown that voltage fluctuations are exacerbated due to the limitations of the reactive power capability of the DFIG, and the operating point of the DFIG power curve irrespective of the control strategy implemented at the wind generator. Furthermore, a mitigation strategy was developed as an integrated control scheme to the main control scheme in order to reduce voltage fluctuations due to wind power variations. However, effectiveness of the mitigation strategy is greatly affected by the reactive power capability of the DFIG, in particular during high wind turbulences.

Power Factor Control in a Wind Energy Conversion System via Synchronous Generator Excitation

This paper proposes a novel control technique to improve the power factor over a wide range of wind speeds in a wind energy conversion system (WECS) using a current source inverter (CSI) and an electrically excited synchronous generator. The system consists of diode rectifier on the generator side, while a pulsewidth modulated CSI is on the grid side. In the proposed control scheme, the generator excitation is controlled with the wind speed to improve the grid power factor, while the control freedoms of the CSI are used to regulate the power output of the WECS to meet maximum power point tracking of wind energy. Theoretical analysis is conducted to investigate the feasibility and limits of this approach. The simulation model for the proposed WECS is developed, and the simulation results confirm the validity of the theoretical analysis. With the proposed power factor control scheme, improvements of grid-side power factor are achieved over a wider range of wind speeds.

Impact on Transient Angle Stability with DFIG-Based Wind Generation Connected to Power System

This paper investigates the impact of wind generation consisting of doubly-fed induction generators (DFIG) on the system angle stability. 3 different factors are considered: the penetration level of wind generation, the connection location of wind generation and the reactive power control strategy that the DFIG utilizes. A modified IEEE-3 machine and 10 bus system has been used as the test network and a number of simulations have been conducted. It shows that the higher the penetration level of the DFIG-based wind generation, the better the system angle stability. Compared with unity power factor control strategy, the system stability is better when the DFIG utilizes constant voltage control strategy. Beside, different connection locations of wind generation also have effects on system stability.

Research on Power Factor Control Strategy of AC-AC Converter Based on Power Balance

Power balance control strategy is applied to a novel AC-AC converter. The simulated model was established based on the power balance. The paper analyzed the input/output characteristics of AC-AC converter under different power factor. The results show that decoupling the active and reactive current, the power factor can be regulated under power balance control, and it is able to avoid the phase-shifting from the input filter. And in inverter stage, the system applies the complex vector model control to obtain the better dynamic performance and stronger robustness.

Comparison of Control Strategies for DSTATCOM in Power Distribution System

In this paper, the perfect harmonic cancellation (PHC), unity power factor (UPF) control strategies of distribution static compensator (DSTATCOM) are compared along with a newly proposed control strategy. In the proposed strategy, to get the best power factor, the conductance factors for the compensated load are evaluated for a specified source current total harmonic distortion (THD) limit. The performance of this method along with perfect harmonic cancellation (PHC) and unity power factor (UPF) strategies is evaluated on a distribution system model developed using PSCAD 4.2.1. In the distribution system, harmonic resonance is one of the prime factors for the harmonic propagation. Hence, in damping the harmonic resonance, selection of an appropriate control strategy for the DSTATCOM is crucial and this is verified with a detailed study. The simulation results are presented to show the performance of these strategies in load compensation and damping the harmonic propagation in the distribution system.

Zero voltage transition isolated PWM push pull boost converter for single stage power factor correction application

Current-fed pulse width modulated (PWM) single stage push pull boost converter is proposed. The converter operates with zero voltage switching (ZVS). A simple auxiliary circuit which includes only one active switch provides ZVS operation to all switches, leading to reduced switching losses in the converter. The converter core can be transparently embedded inside current mode power factor controller. In this paper, operation of the converter core, auxiliary circuits, and design guide lines are presented. Experimental results on a laboratory prototype are presented. In addition, results with the converter core embedded inside power factor control strategies are also shown.

An Input Power Factor Control Strategy for High-Power Current-Source Induction Motor Drive With Active Front-End

This paper proposes an input power factor control strategy for a current-source drive with active front-end. The proposed strategy is realized without modification of the drive's pulsewidth modulation and speed control schemes through the collaborative use of two methods: a modulation index regulation method and a flux adjustment method. Specifically, the modulation index regulation method functions to directly control the dc-link current and voltage, and it can effectively correct a leading input power factor as long as the space vector modulation is used for the inverter. On the other hand, the flux adjustment method can improve the power factor when the power factor is lagging or when the selective harmonic elimination modulation is used for the inverter at high motor speeds. When implemented together, the two methods will complement each other's functionalities and improve the overall compensation performance. Experimental results are obtained from a 600-hp and an 1100-hp drive system.

Power-Factor Compensation for PWM CSR–CSI-Fed High-Power Drive System Using Flux Adjustment

This paper presents a novel power-factor (PF) control strategy for a high-power pulsewidth-modulated current-source rectifier-current-source inverter-fed motor drive system. The PF regulation is realized by adjusting the motor flux in the drive's field-oriented control scheme. The relationship between the motor flux and the drive's input reactive power is first investigated. Based on this analysis, a flux-adjustment PF regulation scheme is proposed. The proposed PF regulation method, together with a properly designed input line capacitor, can ensure a unity PF throughout the whole speed range (including flux-weakening range). Furthermore, unlike all the other PF compensation techniques, the proposed flux-adjustment approach does not require online modulation index control of the rectifier and the inverter, and therefore, offline selective harmonic elimination modulation can be implemented on both the rectifier and the inverter to minimize the line-side and motor-side waveform distortions. Medium-voltage simulation results and experimental results from a low-voltage 30-hp induction motor drive are provided to verify the effectiveness of the PF correction strategy.

A Novel High-Power-Density Three-Level LCC Resonant Converter With Constant-Power-Factor-Control for Charging Applications

This paper proposes a variable-frequency zero-voltage-switching (ZVS) three-level LCC resonant converter that is able to utilize the parasitic components of the high turns-ratio transformer. By applying a three-level structure to the primary side, the voltage stress of the primary switches is half of the input voltage. Low-voltage MOSFETs with better performance can be used in this converter, and zero-current-switching (ZCS) is achieved for rectifier diodes. By applying a magnetic integration technique, only one magnetic component is required in this converter. The power factor concept of resonant converters is proposed and analyzed, and a novel constant power-factor control scheme is proposed. Based on this control strategy, the circulating energy of resonant converters is considerably reduced. High efficiency can be obtained for high-voltage high-power charging applications. The operation principle of the converter is analyzed and verified on a 700-kHz, 3.7-kW prototype, with which a power density of 72 W/inch3 is achieved.