Load Power Factor Research Articles

Artificial Noise Injection and Its Power Loading Methods for Secure Space-Time Line Coded Systems.

In this paper, we consider a space-time line coded (STLC) system having two-transmit and two-receive antennas. To improve the secrecy rate of the STLC system, in which an illegitimate receiver eavesdrops the information delivered from the STLC transmitter to the STLC receiver, we propose an artificial noise (AN) injection method. By exploiting the STLC structure, a novel AN for the STLC is designed and its optimal power loading factor is derived. Numerical results verify that the proposed secure STLC systems with the designed AN injection and the power control method can significantly improve the secrecy rate compared to the conventional STLC systems. It is observed that the proposed method is more effective if there is a significant gap between the main-channel and the eavesdropper-channel gains.

Hierarchical Control of Series-Connected String Converter-Based Islanded Electrical Power System

Cascaded-connected string converter is an effective way to directly interconnect distributed low-voltage dc sources into higher voltage ac grids. When this system is switched to islanding operation, an important task is to obtain decentralized power sharing among power cells according to the corresponding dc source power capacity, and at the same time, maintaining a good regulation of supply voltage quality to local critical loads. In this paper, a hierarchical control approach is proposed to simultaneously realize the abovementioned two tasks. First, the central controller at point of common coupling (PCC) is responsible for supply voltage magnitude and frequency deviation suppression and it also distributes the key control signals to all power cell local controllers with only low bandwidth communications. At the same time, a modified inverse power factor droop regulator with adjustable offset is adopted by each power cell. As the offset is relevant to the PCC load power factor and the state of charges of power cell backstage batteries, it can easily obtain decentralized proportional power sharing. The proposed system and the control strategy are compared with the conventional parallel converters-based system and the potential applications of the system are also given in this paper.

Current Harmonic Reduction Based on Space Vector PWM for DC-Link Capacitors in Three-Phase VSIs Operating Over a Wide Range of Power Factor

This paper proposes a novel space vector pulsewidth modulation (SVPWM) strategy to reduce the switching-frequency-order inverter input current harmonics for a two-level three-phase voltage-source inverter operating over a wide range of the load power factor. The fluctuation of the inverter input current around its average value is minimized by optimization of the utilized voltage space vectors to reduce the inverter input current harmonics, which extends the lifetime of the dc-link electrolytic capacitors. Furthermore, the proposed strategy can be adapted to a motor drive system, where a wide variation of the load power factor is desired, by changing the optimized combinations of the voltage space vectors according to the polarities of the output phase currents. Experiments with the application of the novel SVPWM confirm that the inverter input current harmonics is reduced by up to 29.5% compared to that with the conventional SVPWM strategy. Moreover, the analytical and experimental results confirm that the proposed SVPWM reduces the inverter input current harmonics in both driving mode and regenerative braking mode, as well as with any load power factor.

A Flexible Discontinuous Modulation Scheme With Hybrid Capacitor Voltage Balancing Strategy for Three-Level NPC Traction Inverter

Multilevel inverters are now-a-days being applied in electric vehicles (EV). Considering the dynamic operating conditions of an EV propelled by an induction motor, this paper proposes a flexible discontinuous modulation strategy for three-level neutral-point-clamped (NPC) inverter that can shift modulation pattern seamlessly from sinusoidal pulsewidth modulation (SPWM) to discontinuous PWM (DPWM). The modulation scheme is generalized at each degree of discontinuity to ensure minimum switching losses for variable load power factors. Additionally, a hybrid voltage balancing strategy, which comprises two sets of compensating offset signals with complementary features, has been introduced to mitigate voltage deviation problem at neutral point of the inverter. The unique feature of the proposed hybrid balancing approach is that it generates uniform compensating neutral current regardless of the level of discontinuity. This results in identical and predictable voltage balancing dynamics for the entire modulation transition covering SPWM and DPWM. It has been shown that the proposed hybrid balancing strategy does not lose its unbalance compensation strength even during transition from one modulation pattern to another. The effectiveness of the proposed scheme for wide variations in operating conditions is studied through extensive simulation, and validated in experimentation using a prototype NPC inverter with induction motor loads.

The Influence of Power Quality Indices on Active Power Losses in a Local Distribution Grid

This paper deals with the topic of power quality in a local distribution grid. It is aimed to analyze the individual influences, which aggravate the power quality of the distribution grid. Based on the analysis, the most adverse effects were determined, and they were the voltage drops and supply voltage interruptions, supply voltage unbalance, load power factor, and also higher harmonics. These influences cause the technical losses in a distribution grid, which subsequently have a financial impact not only on the distribution, but also on the transmission of electricity. Only the load voltage unbalance, the load power factor, and the higher harmonics, which mainly cause the technical losses, were analyzed in this paper. The measurement of the influences of the adverse effects was performed on the model of a 22-kV distribution grid. The measurement was performed on the basis of three types of power line conductors and their different lengths, three types of active power consumption, and the different values of these adverse effects. According to this measurement, a simulation in program Matlab-Simulink was created. This simulation represented part of a 22-kV distribution grid, which was influenced by the abovementioned adverse effects. The results of the measurements were compared with the results of the simulation. Based on the evaluation of the technical losses from the measurement and the simulation, the financial losses during a certain period were calculated for the distribution system operators.

Sliding mode control of an active power filter with photovoltaic maximum power tracking

Nowadays, the increase in solar energy installations as a source of energy is growing considerably. The connection to the grid of these installations generally injects all the power obtained from the panel as active power, making zero the reactive power. The same power injection system can be used to achieve a unit power factor if the active filter feature is integrated in it. In this paper, an active power filter (APF) that can control both, the MPP (maximum power point) of a photovoltaic system (PV) and the power factor of a nonlinear load connected to the grid using a three phase DC/AC power inverter with new sliding mode controllers is presented. Perturbation–observation (P&O) is the used MPPT algorithm and three Sliding Mode Controllers (SMC) are used to regulate the DC voltage of the PV and the current d and q components of the active filter using the PQ theory. With a SMC, no exact knowledge of the model parameters is required and it offers good behavior against unmodeled dynamics, insensitivity to parameter variations and good rejection of external disturbances. The space vector pulse wide modulation (SVPWM) of 7 and 5 segments is implemented in order to check the efficiency and grid current ripple. Several experimental tests have been carried in different conditions, concluding that the presented system provides an efficient maximum power tracking and a good power filter characteristic.

Global sensitivity analysis of passive safety systems of FHR by using meta-modeling and sampling methods

Global sensitivity analysis (GSA) aims at quantifying the individual effect of input variables and the main idea is to decompose the variance of a physical model response into fractions that can be attributed to inputs. The Sobol’ indices are obtained by adopting different algorithms analytically. Those methods can be divided into two main parts: the sampling-based method part includes Latin Hypercube Sampling (LHS) and Sobol sequence; the meta-modeling method part includes Polynomial Chaos Expansion (PCE), Stochastic Expansion (SC), and Arbitrary Polynomial Chaos Expansion (APC). This work employs these methods to perform the global sensitivity analysis of Fluoride-salt-cooled, high-temperature reactors (FHRs). The General Flow (GenFlow) code is coupled with DAKOTA or SALib to analyze the loss of force circulation (LOFC) accident of FHR. This study focuses on the effects of five key thermal parameters on safety parameters. It discusses the characteristics of different methods and the accuracy using different orders of the method. Statistical results show that the power load factor would affect safety of FHRs significantly, as it has significant effect on several outputs. The PCE and SC method have significant advantage, as the sensitivity analysis results are obtained from few samples without sacrificing too much accuracy. If the simulation model has jump discontinuities, the results could be significant uncertainty for both meta-based and sampling-based method.

Study on Fast Evaluation Method of the Power Receiving Capability of the Multiple-Section Receiving-End System Considering Voltage Stability Constraint

With the rapid growth of the end-system load, the power system lacks sufficient power supply, and the transient voltage stability after the large disturbance become worse. Considering the lack of quantitative evaluation method of the power receiving capability, a fast evaluation method of the power receiving capability of the multiple-Section receiving-end system considering voltage stability constraint is proposed in this paper. Firstly, an evaluation method of the power receiving capability of the single-section is proposed, which is combined with static voltage stability limit, the amplitude of transient power fluctuations, load power factor, reactive power of receiving-end system, transient voltage stability effect of HVDC. Based on the research of the single-section system, an evaluation method of the power receiving capability of the multiple-Section receiving-end system is proposed, which is utilized the interrelated relations between the average value and standard deviation of the multiple sections. This method can more fully and quickly evaluate the power receiving capability. The results are verified in the Hunan power system. The results show that the proposed method has better engineering applicability and it can be adopted to evaluation method of the power receiving capability of the multiple-section receiving-end system considering voltage stability constraint.

Optimum DG placement for known power injection from utility/substation by a novel zero bus load flow approach

Abstract In this article, a novel analytical approach (named as zero bus load flow (ZBLF)) is proposed for DG placement to the distribution network under the scenario of known power injection from the utility/substation. The study is carried out for deferent load levels and for two different distribution networks (viz. 33- and 69-bus distribution networks). In this work, biomass (working at the power factor same as that of the load power factor) is considered as the DG source. From this study, it may be noticed that, by placing the DG at the selected bus, the active power loss of the network may be reduced even when the power supply from the utility grid is zero. In this paper, a combined approach of ZBLF and symbiotic organism search (SOS) has been proposed for the placement of multiple numbers of DGs for the scenario when the power supply from the utility/substation is known. Both the technical as well as the economic aspects of the DG placement for both the distribution networks are studied and presented in this research paper. DG placement using the proposed method also founds to be economical to the utility.

Improved Fault-Tolerant Method for Modular Multilevel Converters by Combined DC and Neutral-Shift Strategy

In this paper, an improved postfault strategy is introduced for modular multilevel converters, which utilizes the remaining healthy capacity of the converter more efficiently and increases the line voltage amplitude under these circumstances. Previous works proposed to use the neutral point shift in ac side and dc side of the converter simultaneously. This paper adds a comprehensive and coherent formulation, deep analyzation, and experimental validation. The main improvement of the proposed method is maximizing the line voltage amplitude using the optimum dc component and the best neutral point position. Indeed, fewer restrictions in fault numbers, fewer restrictions in load power factor, and fewer nonsolution conditions are among other improvements of a combined dc and neutral-shift method. Comparative simulation and experimental results verify the effectiveness of the proposed method.

A Maximum Power Loading Factor (MPLF) Control Strategy for Distributed Secondary Frequency Regulation of Islanded Microgrid

Microgrids rely on both primary and secondary frequency control techniques to maintain system stability. Secondary frequency control effectively minimizes frequency fluctuations by adjusting the active power reference in each power inverter, but requires complex and costly interequipment communication. In this paper, we propose a distributed secondary frequency control strategy for microgrids containing multiple virtual synchronous generator (VSG) units based on a new maximum power loading factor (MPLF) concept. The MPLF algorithm facilitates power sharing by dynamically identifying the maximum VSG loading factor at each time instance, and then using this value as a unified reference signal for all the VSGs in the microgrid. The active power reference for each VSG will be adjusted based on the unified reference signal, subsequently the secondary frequency control can be realized. The proposed strategy does not require high-bandwidth communication since the MPLF data are transmitted among the VSGs using low-bandwidth communication. We also develop small-signal models for the control architecture to analyze the influence of major proportional–integral control parameters and communication latency. The MPLF control strategy is implemented using custom digital signal processor controllers, and experimentally validated using hardware in loop simulations. Finally, the new control paradigm demonstrates significant tolerance for communication delay or failure, which we purposely introduced in our investigation.

A 5-Level Inverter Scheme Using Single DC Link With Reduced Number of Floating Capacitors and Switches for Open-End IM Drives

This paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n -level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme.

Comparative study of flexibility enhancement technologies for the coal-fired combined heat and power plant

The flexibility enhancement of the coal-fired combined heat and power (CHP) plant can contribute to both renewable energy integration and decarbonization. In this research, we classify the flexibility enhancement technologies into the “power to heat (P2H)” mode and “auxiliary heat source (AHS)” mode based on their principles and operational strategies. Then thermodynamic performances of both modes are compared with the designed heat load and one-day loads. After that, the techno-economic analysis is also conducted. Results show that with the designed heat load, the power load factor range of the CHP plant is extended from 54.87%–78.72% to 25.20%–100% with the AHS mode, and to 0–78.72% with the electric boiler. And compared to integration with the heat-only boiler, the coal consumption of CHP plant can be increased by 2.27% with the thermal energy storage (TES) system (Electric boiler), and reduced by 0.78%, 1.85%, 2.33%, 3.34% with the electric boiler, electric heat pump, TES system (Extraction steam) and waste heat recovery, respectively. The techno-economic analysis indicates that during the heating period, the net annual revenues of the TES system and electric boiler are 2.14 M$ and 1.71 M$ higher than that of the heat-only boiler. This study gives a methodology on choosing the technology to enhance the flexibility for the coal-fired CHP plant.

A Generalized Discontinuous PWM Scheme for Three-Level NPC Traction Inverter With Minimum Switching Loss for Electric Vehicles

A discontinuous pulsewidth modulation (DPWM) strategy for three-level neutral-point-clamped (NPC) traction inverter drive for electric vehicles (EVs) with minimum switching loss for the full power factor (PF) range is developed and presented in this paper. Considering the dynamic loading conditions in an EV propelled by an induction motor (IM), the discontinuous modulation strategy is generalized to obtain minimum switching loss for a wide variations in load PF and modulation depth. The dynamic operating conditions in EV may render frequent unbalances in dc-link capacitor voltages in NPC inverter. It is demonstrated that the addition of an appropriate offset signal with the reference discontinuous signals generates compensating neutral current in the right direction, which can be used to mitigate existing unbalance in two dc-link capacitor voltages. Minimum switching loss at variable PF is attained by positioning the nonswitching clamped regions of the reference auxiliary signals according to the load PF. The effectiveness of the proposed scheme for a wide range of torque/speed variations is studied through simulation by developing a MATLAB/SIMULINK model of an IM traction inverter drive with field-oriented control strategy for closed loop control. Finally, the modulation scheme is validated through experimentation in a small-scale prototype NPC inverter with motor loads.

Power Generation Cost and Quality of Household Electricity Generator as a Back-up for Grid Supply in Nigeria

In this paper operation data were collected to evaluate petrol (PMS) fuel when used as primary source of energy to generate electricity. The analysis highlight cost effectiveness and power quality of this means of generating electricity. For the exercise, a 2 KVA electric power generator was loaded from 800W to 1200W at 100W increment and one hour duration respectively for each load. The Data collected during generator operation include the load current, supplied voltage, power frequency, power factor and power consumed at five minutes interval for each load value. The generated Data were analyzed using mathematical and graphical approach to determine the generated power quality and unit cost of generation. The results, compared with the grid, show that the grid is far more economical and have better power quality.

Power Generation Cost and Quality of Household Electricity Generator as a Back-up for Grid Supply in Nigeria

In this paper operation data were collected to evaluate petrol (PMS) fuel when used as primary source of energy to generate electricity. The analysis highlight cost effectiveness and power quality of this means of generating electricity. For the exercise, a 2 KVA electric power generator was loaded from 800W to 1200W at 100W increment and one hour duration respectively for each load. The Data collected during generator operation include the load current, supplied voltage, power frequency, power factor and power consumed at five minutes interval for each load value. The generated Data were analyzed using mathematical and graphical approach to determine the generated power quality and unit cost of generation. The results, compared with the grid, show that the grid is far more economical and have better power quality.

Determination of PV Hosting Capacity in Rural Distribution Network: A Study Case for Bantul Area

Research on determination of PV hosting capacity in a specified distribution system or feeder is popular recently because of many factors such as, the energy policy from the government, low capital cost of PV panel and the modern society life style. PV hosting capacity determination should consider not only the potential resource and the economic aspect but also the technical consideration based on the static and dynamic performance of the distribution system. In this paper, the PV hosting capacity determination are calculated based on the existing distribution feeder using an iterative method considering the voltage regulation, system power factor and apparatus loading. The result shows that driving the PV location into the center of the load and adjusting the reactive power support by PV producer may increase the hosting capacity size.

GI-Based Control Scheme for Single-Stage Grid Interfaced SECS for Power Quality Improvement

This paper presents an improved generalized integrator (GI)-based control with a frequency locked loop for multifunctional three-phase single-stage grid interfaced solar energy conversion system for power quality enhancement of the distribution network under abnormal grid conditions. The perturb and observe-based maximum power point tracking technique is utilized to obtain peak power from solar photovoltaic array under varying atmospheric conditions. This control scheme provides unity power factor operation, load balancing, harmonics mitigation, and reactive power compensation. The improved GI control algorithm has an advantage of better dc offset and harmonics rejection capabilities as compared to a conventional second-order GI algorithm. To substantiate the control scheme, tests are performed on a paradigm in the research laboratory for manifold operating conditions. Test results show the satisfactory behavior under steady state and dynamic operating scenario such as unbalanced load, solar irradiations variation, voltage sag, and swell and distorted voltage grid. The total harmonic distortions of the grid voltages–currents are achieved within constraints of grid code compliance of an IEEE 519 and 1564 standards.

Analyzing the potential for using active filters to reduce voltage nonsinusoidality in the electric power supply system of a coal open-cut in Vietnam

Coal mining is one of the important economic sectors in Vietnam. Power supply systems of coal mines and open-cuts are complex. They have multiple levels of voltages and different types of loads. New electrical equipment usually works alongside with the equipment that is obsolete and worn-out. Power supply systems of industrial areas of Vietnam where coal is mined are characterized by the low power quality. In Vietnam the indices which characterize the distortion of both voltage and current waveforms have standard values. The article presents the findings upon the analysis of a power supply system of a coal open-cut in Vietnam and the electrical equipment of the coal sorting plant along with the results of the experimental studies of power quality indices and the non-sinusoidal mode parameters. The measurement analysis has shown that the indices of the 5-th and 7-th harmonics of voltage were over the limits. There are interharmonics in voltages and currents. The article analyzes the characteristics of active filters. It is possible to improve the power quality by using an active filter which generates both reactive power to increase the load power factor and harmonic and interharmonic currents to reduce the degree of voltage and current waveform distortion.

An Analysis of the Systematic Error of a Remote Method for a Wattmeter Adjustment Gain Estimation in Smart Grids

Smart energy meters supporting bidirectional data communication enable novel remote error monitoring applications. This research targets characterization of the systematic worst-case error of the previously published remote watthour meter’s gain estimation method based on the comparison of synchronous measurements by the reference and meter under test. To achieve the research aim a methodology based on global maximization of the systematic error objective function assuming the typical low voltage electrical distribution network operation parameters ranges as defined by the standard recommendations for network design. To cross verify the reliability of the assessed solutions the suggested error analysis methodology was implemented utilizing two stochastic global extremum search techniques (genetic algorithms, pattern search) and the third one utilizing nonlinear programming solver. It was determined that the wattmeter adjustment gain worst-case error does not exceed 0.5% if the remote wattmeter monitored load power factor is larger than 0.1 and a network is designed according to the recommendation of the acceptable voltage drop less than 5%. For a load exhibiting power factor larger than cos φ = 0.9 the worst-case error was found to be less than 0.1%. It is concluded therefore that considering the systematic worst-case error the previously suggested remote wattmeter adjustment gain estimation method is suitable for remote error monitoring of Class 2 and Class 1 wattmeters.