Load Power Factor Research Articles

An Effective Reactive Power Compensation Method and a Modern Metaheuristic Algorithm for Loss Reduction in Distribution Power Networks

In this paper, a new method of reactive power compensation is proposed for reducing power loss of distribution power networks. The new method is the combination of local compensation at each load and distribution line compensation. In the method, local capacitors at each load are determined to increase power factor of load to an expected value first and then a number of capacitors are placed in distribution lines with two factors, location and capacity by using the three applied methods. Particle swarm optimization (PSO), parasitism predation algorithm (PPA), and tunicate swarm algorithm (TSA) are applied for the proposed method on four distribution systems with 15, 33, 69, and 85 buses. The comparisons of results with previous methods indicate that the three applied methods can reach higher loss reduction for all study cases. TSA can reach loss reduction more effectively than others by 19.4%, 0.5%, 7.9%, and 10.76% for the four distribution systems, respectively. The most important emphasis is that PSO, which was considered to be of low effectiveness in previous studies, can reach much better loss than approximately all previous methods thank to the proposed compensation method. PSO also reached better loss reduction than others by 18.97%, 0.4%, 7.73%, and 10.21%, respectively. Consequently, it is recommended that the proposed compensation method is useful for distribution systems in minimizing total power loss and TSA can be selected a new and powerful method for the problem.

A Novel Method for Winding Faults Diagnostic of Power Transformers Based on Parameter Estimation

This paper presents a parameter estimation based method to diagnose winding deformation and turn‐to‐turn fault of power transformers. First, an estimation model of transformer parameters is built, in which five equations are taken in account including voltage loop equation, active loss equation, input impedance equation, no‐load current equation and no‐load loss equation. Then, particle swarm optimization (PSO) is used to solve the model, and the characteristics of estimation data under winding faults are analyzed. At last, based on the estimation data, random forest (RF) algorithm is employed to classify transformer states and realize fault diagnostic. The simulation results show that the proposed parameter estimation method has high precision and are not affected by the factors including load power factors and the type and degree of winding deformation, and the impact of load rates can be avoided; the fault diagnostic scheme based on RF is quite sensitive and effective. The proposed method eliminates the need of transformer outage, and compared with other methods based on parameter estimation, it can distinguish winding deformation and turn‐to‐turn fault. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Energy efficiency of a 3-level shunt active power filter powered by a fuel-cell / battery DC bus with regulated duty cycles

Introduction. Nowadays, electrical energy is indispensable in industrial, tertiary and domestic appliances. However, its efficiency is becoming affected by the presence of the disturbances that appear in the electrical networks such as harmonics, unbalance, sags/swells, flickers …etc. Indeed, the disturbances cause a decrease in the power factor and an increase in the power losses. In this paper, the harmonic disturbance is considered and a 3-level shunt active power filter powered by a hybrid fuel-cell/battery DC is applied to mitigate current harmonic components from the electrical feeder. Aim. Studying the energy efficiency of a system based on a 3-level shunt active filter powered by a hybrid fuel-cell / battery DC bus. Methodology. It is a matter of finding the suitable formulas that express the efficiency and the relative power losses according to the load factor (which is the ratio between the short-circuit active power and the load active power) and the load power factor. The DC bus energy is controlled using an energy management algorithm that contributes in generating the required reference input currents and output voltages of the fuel-cell and the battery. The DC/DC converters control circuits are performed in a closed loop by means of regulated duty cycles. Results. The simulation results carried-out under MATLAB/Simulink environment show better filtering quality if compared with the case of open loop control of the DC/DC converters and lesser differences between the fuel-cell power, the battery power and their respective reference powers. Which concerns the energy efficiency, the results demonstrate that higher efficiency and lower relative power losses can be achieved only when higher load factor and load power factor are attained. Therefore, the compensating system of the power factor is very important to improve the energy efficiency.

An Enhanced Virtual Space Vector Modulation Scheme of Three-Level NPC Converters for More-Electric-Aircraft Applications

Multilevel converters have been used for aircraft electric starter/generator (ESG) systems due to their high power qualities. One of the desirable topologies is the three-level neutral-point-clamped converter. Our studied ESG system operates at a high speed during its generation mode, which results in high modulation index and puts some specific challenges on neutral-point voltage balance, especially under low power factor load conditions. Moreover, common-mode voltage (CMV) needs to be addressed properly as it leads to irreversible damage of motor shaft bearings, thereby degrading the efficiency and reliability of the entire system. Compared with the conventional nearest-three virtual space vector technique, the proposed modulation scheme employs three adjacent medium vectors to synthesize a new medium vector and two pairs of large vectors to compose new small vectors. This allows the presented modulation scheme to achieve balanced capacitor voltage and reduced CMV at the same time. In addition, the torque ripple of the proposed modulation strategy is thoroughly compared and analyzed. Meanwhile, in order to overcome the heavy computational burden, a fast calculation approach is adopted to simplify the algorithm. Simulation results obtained from Simulink/PLECS and experimental results obtained from a 45 kW, 32 kr/min aircraft ESG system verify the effectiveness of the proposed strategy in more-electric-aircraft applications.

A practical method to assess the potential of energy storage systems to mitigate voltage sags

Energy storage systems (ESS) have attracted significant interest and investments. Despite this interest, industry and utility engineers have not widely considered this technology as a potential solution to improve the power quality supplied for critical loads. This is in part because of the high cost and in part because of the high complexity to assess this type of solution. This paper, therefore, proposes a practical approach to determine whether shunt/series ESS can mitigate voltage sags assuming the availability of system information, as short-circuit impedance and historical voltage sags, and load information. This is done by analyzing a chart obtained analytically, which can be easily constructed based on simple information from the system and load, without resorting to computer simulations. By inspecting this chart, engineers can quickly determine not only the ESS capacity required to mitigate specific sags, but also which is the optimum power factor for operation. Sensitivity studies are provided to reveal key factors affecting ESS capability to mitigate voltage sags and to validate the proposed approach. Results outline that the requirements of shunt ESS depend on the system short-circuit level and X/R ratio, whereas requirements of series ESS depend on the load demand and power factor.

Power/energy loss allocation in deregulated power distribution system with load factor and load power factor variation

Power/energy loss allocation in deregulated power distribution system with load factor and load power factor variation

Photovoltaic Maximum Penetration Limits on Medium Voltage Overhead and Underground Cable Distribution Feeders: A Comparative Study

This paper investigates the maximum photovoltaic (PV) penetration limits on both overhead lines and underground cables medium voltage radial distribution system. The maximum PV penetration limit is estimated considering both bus voltage limit (1.05 p.u.) and feeder current ampacity (1 p.u.). All factors affect the max PV penetration limit are investigated in detail. Substation voltage, load percentage, load power factor, and power system frequency (50 Hz or 60 Hz) are analyzed. The maximum PV penetration limit associated with overhead lines is usually higher than the value associated with the underground cables for high substation voltage (substation voltage = 1.05 and 1.04 p.u.). The maximum PV penetration limit decreases dramatically with low load percentage for both feeder types but still the overhead lines accept PV plant higher than the underground cables. Conversely, the maximum PV penetration increases with load power factor decreasing and the overhead lines capability for hosting PV plant remains higher than the capability of the underground cables. This paper proved that the capability of the 60-Hz power system for hosting the PV plant is higher than the capability of 50 Hz power system. MATLAB software has been employed to obtain all results in this paper. The Newton-Raphson iterative method was the used method to solve the power flow of the investigated systems.

An Optimization Algorithm to Determine Apparent Power of Active Filter

The coal grading plants in Viet Nam extensively apply induction motors. Induction motors consume active and reactive power from the power supply systems. The reactive power flowing through the electrical network creates active power losses. The reactive power received from power utilities reduces the load power factor at the node where coal sorting plants are connected to the supply network. Frequency-controlled induction motors introduce distortions into the electrical network because they are electrical equipment with a nonlinear current-voltage characteristic. Non-sinusoidal current and voltage cause additional losses of active power in the electrical network and electrical equipment, thereby shortening its service life, reducing the reliability of operation, and causing economic damage. Active filters can solve these problems. The paper proposes an optimization algorithm for determining the apparent power of the active filter, which provides the load power factor and power quality indices corresponding to the regulatory documents. The algorithm is used to calculate the apparent power of the active filter for the coal grading plant owned by the Vietnamese company “Cua Ong-Vinacomin."

Islanding Detection Method With Load Power Factor Improvement and High Frequency Transient Suppressing

Reactive power control (RPC) strategy is a promising option for islanding detection in distributed generation (DG) systems. Existing RPC methods have drawbacks of not providing the reactive power to improve the load power factor and are not robust against high-frequency transient disturbances. This paper presents a modified RPC method to overcome these limitations in a 220/380 V distribution network. In this method, the reference of reactive power of the DG is designed to improve the load power factor and ensure a fast islanding detection. In addition, the proposed method incorporates a second decision-making criterion based on discrete wavelet transform (DWT) to avoid false islanding detection due to non-islanding events. The proposed islanding detection method (IDM) is tested under various conditions. Simulation and experimental results show that the proposed IDM can detect islanding rapidly and with zero Non-Detection Zone (NDZ) in the situation of load power factor improvement. Moreover, non-islanding events such as capacitor switching are effectively avoided.

Modeling and Analysis of the Dynamic Response of an Off-Grid Synchronous Generator Driven Micro Hydro Power System

This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed standard IEC limits. The results also expose that the abnormal conditions produced by abrupt changes in load, system faults and severe overload, cause the unwonted variations in the magnitude of generator parameters. Moreover, the study reveals that the system stability significantly enhances when the system is run at full load because the regulation time to fix the variations in the generator parameters; except input mechanical power; decreases, e.g. from 4.1 sec to 0.8 sec for generator voltage, with the increase in the loading from quarter to full load respectively at unity power factor. Further, it is also observed that the regulation time rises, e.g. from 0.8 sec to 1.3 sec for generator voltage, with the reduction in load power factor from unity to 0.8, respectively. Thus, proper protection, to cater for increased fault current at full load and power factor correction must be provided to improve the system stability and protection. Furthermore, it is also concluded that the over loading in any case should be strongly avoided in this type of system and it should never be allowed to exceed 20% of the full load value to avoid system failure

Modeling and Analysis of the Dynamic Response of an Off-Grid Synchronous Generator Driven Micro Hydro Power System

This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed standard IEC limits. The results also expose that the abnormal conditions produced by abrupt changes in load, system faults and severe overload, cause the unwonted variations in the magnitude of generator parameters. Moreover, the study reveals that the system stability significantly enhances when the system is run at full load because the regulation time to fix the variations in the generator parameters; except input mechanical power; decreases, e.g. from 4.1 sec to 0.8 sec for generator voltage, with the increase in the loading from quarter to full load respectively at unity power factor. Further, it is also observed that the regulation time rises, e.g. from 0.8 sec to 1.3 sec for generator voltage, with the reduction in load power factor from unity to 0.8, respectively. Thus, proper protection, to cater for increased fault current at full load and power factor correction must be provided to improve the system stability and protection. Furthermore, it is also concluded that the over loading in any case should be strongly avoided in this type of system and it should never be allowed to exceed 20% of the full load value to avoid system failure

Analysis of the impact of harmonic increase due to penetration of variations in the number of roof PV in the distribution network during the Covid-19 pandemic

The increased penetration of rooftop PV in the distribution network was triggered by the reason for free energy obtained from the sun and an incremental decrease in prices for solar panels. These were bringing it closer to grid parity. However, massive rooftop PVs without storage at medium and low voltages will cause power quality problems, namely increased voltage fluctuation, unbalanced voltage, and harmonics, in addition to active load fluctuations and power factor on nearby buses. The use of an inverter to convert DC to AC will increase the number of non-linear loads on the network so that it will increase the presence of harmonics. In early 2020 the Coronavirus pandemic was spread over the world and brought people to have activities from home. This condition shifts the portion of power consumption for each sector and increases the probability of rooftop PVs usage. This paper analysed the comparison of the use of two inverters with different harmonic characteristics with various levels of rooftop PV penetration in the distribution network. From the simulation results, it can be concluded that the existing harmonic characteristics of the inverter used has a more significant impact than the PV rooftop penetration level on the increase of harmonics in the distribution network.

A boost type switched‐capacitor multi‐level inverter for renewable energy sources with Self‐Voltage balancing of capacitors

This article proposes a single-phase double-source 27-level basic inverter structure based on Switched-Capacitors (SCs) circuit for renewable energy sources. The extendibility, low Blocking Voltage (BV) on semiconductors, step-up capability, and self-voltage balancing of capacitors are the main advantages of the suggested basic structure. Using double H-bridges to generate bi-polar voltage waveform, the blocking voltage on the semiconductors limit to only 0.692 Vo,max. The Average of Normalized Blocking Voltage (ANBV) on semiconductors of basic topology is only about 33.52%. Two extended structures have been presented with higher output voltage steps and boosting factors. The first extended topology composed of two (right and left) Generalized Switched Capacitor based Modules (GSCMs), results in reduced sources (only 2), increased steps, low BV on semiconductors, and boosting factor of 2n (n: number of SC Cells). The second extended topology can be realized by applying more cascaded Switched-Capacitor Modules (SCMs), which benefits from quadruple-gain and increased levels (9m, m: number of cascaded modules). The suggested topologies properly supply the zero or low power-factor load types. The superiority of proposed configurations over recently presented similar structures has been compared and verified. The experimental outcomes of the basic topology have also been provided to validate its correct operation.

Single-Phase Symmetric-Bipolar-Type High-Frequency Isolated Buck-Boost AC–AC Converter With Continuous Input and Output Currents

A single-phase symmetric-bipolar-type high-frequency isolated buck-boost ac–ac (SBT-HFI-BBAC) converter is proposed. The converter is composed of two full-bridge inverter modules, input/output <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filters, and a high-frequency transformer (HFT) with series capacitors. It can provide identical noninverting and inverting buck-boost output voltages with symmetric-bipolar voltage gains of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \pm D/({1 - D})$</tex-math></inline-formula> . The frequency of the output voltage can also be adjusted in discrete steps, similar to single-phase matrix converters (MCs). It supplies continuous input and output currents and works well with nonunity power factor loads. The magnetizing current of the HFT has no line frequency component due to the presence of the series blocking capacitors. Moreover, due to the absence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</i> switches, the converter has a simple commutation process, unlike conventional ac-ac/MCs. Two switching strategies are proposed; Strategy-I with fewer high-frequency switches and Strategy-II with reduced switch currents, providing more flexibility in switch power loss optimization. The proposed SBT-HFI-BBAC converter is well suited for application as a dynamic voltage restorer, compensating a wide range of grid voltage sags and swells, without the need for a low-frequency voltage injection transformer. Its step-changed frequency operation can also find use in various applications, such as high-gain ac–dc converters, traction systems, etc. A comprehensive description of circuit operation is presented along with component design guidelines and appropriate comparisons. Experimental verification results are provided using a 400-W laboratory test circuit.

Evaluation and Analysis of Soft Computing Techniques for Grid Connected Photo Voltaic System to Enhance Power Quality Issues

The major problem in grid connected transmission and distribution networks are the power quality issues due to the unbalance loads. The power quality issues relate to the current and voltage based issues generated at the point of common coupling. Some of the current based power quality issues relate to reactive power extraction, poor zero voltage regulation, harmonics in the load currents undesired neutral current and power factor and. Several DSTATCOM compensation techniques has been introduced for compensation of reactive power and power quality issues in the three phase, four wire system. The proposed system focus on DSTATCOM soft computing techniques such as: Widrow–Hoff least mean square, vectorial filter, discrete adaptive filter and quasi Newton control algorithms. The proposed algorithms controlled the switches pulses to drive the voltage source converter section in the DSTATCOM network thereby mitigating power quality issues and reactive power generation in the grid connected photovoltaic system. The soft computing techniques has maintained constant DC bus capacitor voltage and common coupling voltage along with unity power factor, zero voltage regulation under linear and non-linear load conditions, eliminating the harmonics in the load currents. The proportional integral controller is used for error correction between the reference and capacitor voltage. The novel drift-free maximum power point technique has shown better results under varying temperature and irradiances conditions. The DSTATCOM soft computing techniques has been implemented and simulated in MATLAB/SIMULINK.

On switching transient modeling and analysis of electronic on-load tap-changers based Sen transformer

This paper presents the switching transient model and analysis for an electronic on-load tap-changers (EOLTC) applied to a Sen transformer (ST), including the steady-state voltage and current of the electronic switches, the evaluation of current and voltage transients during the commutation process, and the dimensioning of the EOLTC and voltage spike protection. Firstly, according to the topology of the EOLTC, the steady-state voltage and current models of the EOLTC are established. Secondly, the switching transient model of the EOLTC in overlapping time is derived based on the T-equivalent circuit and Kirchhoff’s voltage law. Finally, the overlap time and voltage spike of the EOLTC are evaluated through the switching transient model, and the voltage spike protection is designed. With the help of MATLAB and PSCAD/EMTDC, two case studies have been carried out on a small-capacity and large-capacity electronic on-load tap-changers based Sen transformer (EST). The influence of different power factors on the overlap time is analyzed. The results show that the load power factor may affect determining the overlap time of the commutation process of the EOLTC. The more the inductive load, the faster the overlap current on the tap-changer rises during the overlap period. Furthermore, it is also verified through the time-domain simulation that the application of high-power EOLTC in the ST can increase the speed of operation of the conventional ST.

Transformer inter‐turn failure detection based on leakage flux and vibration analysis

AbstractInter‐turn winding fault is one of the most critical failures of the transformers. Here, a comprehensive transformer leakage flux analysis under inter‐turn winding fault is presented, and the feasibility and sensitivity of leakage flux‐based fault detection methods are investigated. The leakage flux fault detection strategies are classified into vibration‐based methods and search coil‐based methods. Flux leakage‐based methods have been studied and compared. Moreover, the effects of various important factors, such as fault severity, fault location, load power factor, and loading rate in transformer under inter‐turn faults are studied. Furthermore, two new online methods based on leakage flux and vibration analysis are proposed. In the first method, search coils voltage analysis is used for fault detection. In the second one, the vibration of the transformer is measured using the Digital Accelerometer (ADXL) sensor and compared with the vibration of the normal conditions, and based on the amount of vibration, fault detection is performed. The simulation and experimentation results on 20/0.4 kV, 50 kVA distribution transformer demonstrated that the implementation of leakage flux‐based methods provides valuable information on the transformer behaviour, which can be used to detect transformer winding faults.

Generalized diamond‐type single DC‐source switched‐capacitor based multilevel inverter with step‐up and natural voltage balancing capabilities

This paper proposes a diamond-shaped high step-up switched-capacitor based basic multilevel inverter topology. The basic switched-capacitor (SC) stage consists of 2 active switches, 2 diodes, and 2 capacitors. Using a single DC source with the unfolding circuit (10 switches, 5 capacitors, and 5 diodes) results in the production of 17 voltage-steps at the output with the gain of up to 8 times of the input voltage. By extending the diamond-shaped switched-capacitor stages, higher voltage levels and voltage gains can be possible. The suggested topology employs two half-bridges (instead of a full-bridge) to produce positive, zero, and negative steps, which reduces the Voltage Stress (VS) on two output switches and consequently reduces Total Voltage Stress (TVS). In addition, the natural voltage balancing of capacitors eliminates the need to an additional control circuitry and consequently reduces the total converter size, complexity, and cost. In addition, modularity, scalability, low voltage ripple on capacitors, low total voltage stress, high power quality, and capability of supplying low/medium power factor (R-L) loads are some of the merits of the proposed topology. The low Cost Function (CF) obtained in the comparison section as well as experimental results verifies the advantages of the proposed topology.

Direct Predictive Current Control of a New Five-Level Voltage Source Inverter

This article proposes a direct predictive current control approach to regulate the flying capacitor voltages along with the output currents in a new five-level voltage source inverter under a wide range of output frequencies and load power factors. Also, the proposed approach maintains the flying capacitor voltage ripples well below the desired limits (10%-15%) throughout the operating range. The sampled data model of a new five-level voltage source inverter is developed to predict the future behavior of the control variables such as output current, and flying capacitor voltage and its ripples. A three-objective cost function with reference and predicted control variables is formulated. The cost function is evaluated for all possible switching states, then an optimum switching state which gives the low cost value is selected. The optimum switching state is applied to the converter in one sampling interval. The feasibility of the proposed control method is verified on a new five-level voltage source inverter by using MATLAB/Simulink simulations and experimental studies on a scaled-down laboratory prototype with dSPACE Microlab Box. Furthermore, the performance of the proposed approach is analyzed in terms of voltage and current harmonic distortion, and flying capacitor voltage ripples at different current magnitudes, output frequencies, and load power factors.

Hybrid Reference Current Generation Theory for Solar Fed UPFC System

The extensive usage of power electronic components creates harmonics in the voltage and current, because of which, the quality of delivered power gets affected. Therefore, it is essential to improve the quality of power, as we reveal in this paper. The problems of load voltage, source current, and power factors are mitigated by utilizing the unified power flow controller (UPFC), in which a combination of series and shunt converters are combined through a DC-link capacitor. To retain the link voltage and to maximize the delivered power, a PV module is introduced with a high gain converter, named the switched clamped diode boost (SCDB) converter, in which the grey wolf optimization (GWO) algorithm is instigated for tracking the maximum power. To retain the link-voltage of the capacitor, the artificial neural network (ANN) is implemented. A proper control of UPFC is highly essential, which is achieved by the reference current generation with the aid of a hybrid algorithm. A genetic algorithm, hybridized with the radial basis function neural network (RBFNN), is utilized for the generation of a switching sequence, and the generated pulse has been given to both the series and shunt converters through the PWM generator. Thus, the source current and load voltage harmonics are mitigated with reactive power compensation, which results in attaining a unity power factor. The projected methodology is simulated by MATLAB and it is perceived that the total harmonic distortion (THD) of 0.84% is attained, with almost a unity power factor, and this is validated with FPGA Spartan 6E hardware.