Reactive Power Changes Research Articles

A Novel Integrated Method for Harmonic Suppression and Reactive Power Compensation in Distribution Network

Aiming at the serious harmonic pollution and the low power factor in the distribution network of industrial enterprises, this paper develops an integrated method for harmonic suppression and reactive power compensation suitable for the distribution network of industrial enterprises. The integrated method realizes the dual functions of harmonic filtering and reactive power compensation, and filters out the harmonic current to get a symmetrical current waveform while ensuring safe operation of the power compensator. In addition, it solves the problems of high harmonic content, small power factor in the distribution network, and device burnout caused by direct input of reactive power compensator. The main contributions of this paper are as follows: (1) According to the demand for the integration of harmonic suppression and reactive power compensation, the steps of integrated method for harmonic suppression and reactive power compensationare proposed, and then the methods for harmonic filtering and reactive power compensation are investigated; (2) a method for designing the capacity of a filter capacitor and the rated parameter of an electromagnetic coupling reactance converter is proposed, and an optimization simulation system is constructed to design the parameters of the filter; (3) a simulation system is developed, followed by parameter design and simulation analysis of harmonic filtering subsystem (HFSS), reactive power compensation subsystem (RPCSS) and the integrated system of harmonic suppression and reactive power compensation. Simulation results verify that the HFSS is put into operation first and then switched off later to ensure the normal operation of other equipment in the distribution network. After the treatment, the power factor, harmonic current content and total distortion rate all meet the national standards. The integrated method can dynamically track harmonics and reactive power changes, filter out harmonics, improve power factor and the symmetry level of the power source, and ensure the normal operation of other equipment in the distribution network. The research results lay a certain theoretical and technical foundation for the harmonic filtering and reactive power compensation theory, technology and its device innovation to achieve effective suppression of power harmonics and reactive power compensation.

A Feature Extraction Method for Non-intrusive Load Identification

When some household appliances are running, the electrical quantities such as active power and reactive power will change slowly for a long time, which will affect the feature extraction of event-based non-intrusive load identification, resulting in low accuracy of load identification results. In view of this situation, a feature extraction method is proposed. Its core idea is that there is a certain law in the change of active power and reactive power in a very short time, and the curve can be fitted to speculate the values of these electrical quantities in the next time, so as to eliminate the influence. Based on this, a feature extraction method applied to non-intrusive load identification is realized. The test results show that this method can effectively improve the accuracy of non-intrusive load identification feature extraction data, and has good application value.

An Alternative Low-Cost Embedded NILM System for Household Energy Conservation with a Low Sampling Rate

The measurement of the energy consumption of electrical appliances, where the meter is installed at a single point on the main input circuit of the building, is called non-intrusive load monitoring (NILM). The NILM method can distinguish the loads that are currently active and break down how the loads consume electricity. A microcontroller with embedded software was selected to read the data into the NILM method process at a low sampling rate every 1 s or 1 Hz. The measured data and the data obtained by the NILM algorithm were displayed via an internet platform. This article presents an alternative low-cost embedded NILM system for household energy conservation with a low sampling rate, which could identify electrical appliances such as an air conditioner, refrigerator, television, electric kettle, electric iron, microwave oven, rice cooker, and washing machine. Four features of symmetry pattern were extracted, containing information on the value of active power change, the value of reactive power change, the number of intersection points between the active power data and the reference line, and an estimation of an equation for the starting characteristics of the electrical equipment. The proposed NILM system was tested in a selected test house that used a single-phase power system. A typical meter was also installed to compare the results with the proposed NILM. The validity of the tests was checked for 1 month in 3 houses to analyze the results. The proposed method was able to detect 91.3% of total events. The accuracy of the average ability of the system to disaggregate devices was 0.897. The accuracy value for total power consumption was 0.927. The continuous data recording of the NILM method provides information on the behavior of electrical appliances that can be used for maintenance and warnings.

Hybrid islanding detection technique for distribution network considering the dynamic behavior of power and load

AbstractNowadays, distributed generation (DG) has become an indispensable part for meeting the growing power demand in electrical power generation and distribution. However, one of the drawbacks of DG is unintentional islanding phenomena, which has become a safety issue for both human and equipment connected to the system. To prevent this hazardous condition, according to IEEE 1547 standards, this islanding condition must be detected within 2 s. This paper proposed an approach to develop a hybrid islanding detection method (IDM) to prevent the damages caused by this islanding condition. The proposed hybrid IDM is a combination of three different IDMs, two passive and one active; that is, rate of change of active power (ROCOAP) and rate of change of reactive power (ROCORP) are passive IDMs where load connecting strategy (LCS) is active. To differentiate islanding conditions with similar occurrences, different case studies are taken into account with photovoltaic (PV) and synchronous generator (SG) working as distributed generators on PSCAD/EMTDC platform. The simulation results confirm that proposed IDM is more favorable compared to other IDMs due to simplicity and fast islanding detection time when its performance is tested on the 11‐kV Malaysian distribution system for various cases.

Complex use of smart grid technology in railway traction networks

The goal is to develop a methodology for modeling electric power supply systems for railways equipped with a complex of devices implemented using smart grid technologies. The results obtained showed that a reliable and high-quality electric power supply for traction of trains and non-traction consumers could be implemented on the basis of the integrated use of Smart Grid active elements, such as a phase converter, an active harmonic conditioner, a controlled reactive power source and a distributed generation plant. On the basis of computer simulation, it has been established that in the absence of reactive power sources, noticeable voltage fluctuations are observed on the 10 kV buses of a non-traction consumer. The asymmetry approaches the limit of normally permissible values; turning off the active filter leads to an increase in the total voltage harmonic distortion up to 16%; in the presence of the whole complex of active devices, high quality of electricity is achieved. The phase number converter is robust and has low sensitivity to parameter setting errors; voltage deviations caused by a limited range of changes in reactive power in its source are short-term and do not exceed values acceptable for practice. Thus, on the basis of Smart Grid technologies, it is possible to implement the connection of distributed generation plants directly to the traction network using a device for transducing the number of phases, formed according to the inverted Steinmetz’s circuit. Elimination of harmonic distortions created by rectifier electric locomotives is carried out by means of an active conditioner of higher harmonics. A controlled reactive power source can be used to maintain voltage levels.

WITHDRAWN: Critical bus ranking constrained optimal allocation of PMUs for network observability

The paper presents critical bus ranking to allocate Phasor Measurement Units (PMUs) in network considering Integer Linear Programming (ILP). A Reactive Load Sensitive Index (RLSI) is proposed which depends upon reactive power change at load to find critical buses. Contingency cases like PMU loss or N-1 outages are chosen for PMU placement (OPP). Zero Injection (ZI) model is formulated to further minimize allocations in network for OPP. ZI modeling for normal and outage conditions is formulated and compared. Performance of observability of network is checked with Complete Network Observability Index (CNOI) approach. IEEE 14, 30 and 57-bus test cases are programmed for proposed method in MATLAB and are compared with existing techniques to present its efficacy.

Fuzzy logic control of active and reactive power for a grid-connected photovoltaic system using a three-level neutral-point-clamped inverter

This paper aims to present a fuzzy logic control (FLC) of active and reactive power for a grid-connected photovoltaic system. The PV system is connected to the grid utility using a three-level neutral point clamped inverter (3L-NPC) and LCL filter. Two control strategies, fuzzy logic control, and conventional PI control are applied. The design of the two control strategies is based on calculating the instantaneous active and reactive power from the measured grid voltages and currents to allow the system to have a dynamic robustness performance against a sudden change in reactive power and satisfactory active power tracking under rapid solar radiation changes. The control strategies can transfer the total active power generated by the PV array to the grid utility with high power quality and a unity power factor. The simulation results using the Matlab-Simulink environment show that the FLC strategy has a better dynamic performance with less settling time, and overshoot compared to the conventional PI control.

Active power filter for reactive power compensation for the powerful sounding pulses shapers

The expediency of using a power active filter in the mode of reactive power compensation of the supply network for the powerful sounding pulses shaper power supply system of the Institute of ionosphere NAS and MES of Ukraine is shown. An analysis of the literature has been carried out, which shows the effectiveness of solving the problem of reactive power compensation, filtering higher harmonics of the power supply network using active filtering of higher harmonics of current or voltage using an additional energy source to obtain a compensating signal in the form of current or voltage. The choice of the power circuit for constructing a power active filter has been made. A voltage inverter on IGBT transistors is used as a power active filter. The basic principles of operation of the power active filter control system are described, which are based on the p-q theory of power and provide for the calculation of instantaneous values ​​of the task currents for each phase of a three-phase power supply system. The work of the Matlab-model of the power supply system of the shaper is shown, the oscillograms of the main energy characteristics of the shaper are given. As a result of using a power active filter, the current of the supply network becomes close to sinusoidal, and the power factor tends to 1. A positive effect on the efficiency of the shaper when the power active filter is included in the supply network is noted, which is due to the efficiency of compensation of the reactive power consumed by the shaper from the supply network. The simulation results are presented, in particular, graphs of reactive power change at the point of connecting the power active filter to the supply network, at different levels of reactive power consumption by the shaper. The results obtained confirmed the possibility of using a power active filter in the mode of reactive power compensation of the supply network when solving the problems of improving the electromagnetic compatibility of powerful sounding pulses shapers with the supply network, reducing losses and increasing the reliability of the shapers. Keywords: active power filter, reactive power control, control systems

Исследование энергетических характеристик устройства компенсации реактивной мощности с регулируемой индуктивностью в электротяговой сети на экспериментальной установке

Objective: Checking the theoretical provisions of the possibility of controlling the reactive power of an adjustable inductance compensating device. Testing and optimizing the algorithm of the reactive power regulating device. Assessing energy effi ciency of the device. Checking stability of the device in transient modes. Suggesting methods to improve stability of the system. Conducting a harmonic analysis of current and voltage curves obtained as a result of physical modeling, developing ways to suppress higher current and voltage harmonic. Methods: The scheme of the experimental setup was built, the electrical element base was selected, the measuring instruments used were determined, the experimental stand was assembled. Curves of changes in current, voltage, active and reactive power were taken on the physical model for operating modes without a compensating device, with an unregulated and adjustable compensating device. The change in current for critical transients is analyzed. To evaluate the fi ltering of higher harmonics of current and voltage by a compensating device, oscillograms were taken in operating mode with a load and after adding a diode bridge to the electric locomotive circuit, and their harmonic analysis was performed. Results: The adjustable device provides reactive power compensation in the load range of no less than 90 %. Additional measures are required to lower the active resistance of the compensating device reactor. The use of a reactor connected in series with a capacitor reduces the switching current and overvoltage in the device. The compensating device can operate in the mode of a broadband fi lter of higher harmonics. Practical importance: A physical model of an alternating current traction network with a reactive power compensating device and a controlled variable inductance has been created, which makes it possible to analyze both instantaneous and long-term processes in the traction network.

Hybrid LCC-AAC HVDC transmission system

A hybrid HVDC transmission system based on a line-commutated converter (LCC) and an alternate arm converter (AAC) is developed in this article. The basic operation principles and control methods of the proposed LCC-AAC hybrid HVDC system are demonstrated following with appropriate system design and parameter selection. In addition, this paper proposes a set of control schemes for riding through ac faults and handling dc fault. The operation and performance of both converters in such a hybrid HVDC configuration are verified through a detailed set of results based on a 3000 MVA LCC-AAC hybrid HVDC system including steady state operation, ac-grid harmonics & dc-side ripple analysis, reference tracking (active power change at LCC station, reactive power change at AAC station) and system performance under ac-grid faults without blocking converter at both terminals of the HVDC system. Also, the response of the hybrid system under dc fault presents potential dc fault handling capability compared with the hybrid system based on LCC and modular multilevel converter (MMC) with half-bridge submodules (HBSMs). The hybrid LCC-AAC HVDC transmission system lays preliminary steps for research on complex mixed converter multiterminal dc configurations in future dc super grids.

The Role of Mathematical Model of Energy Storage by Power Systems Computer Aided Design / Electromagnetic Transients including DC in Power Energy Security Control

In order to discuss the application of energy storage system in power energy control, in this study, the energy storage system in small wind power generation system is taken as the research object, and the converter mathematical model in the energy storage system is built. Meanwhile, in the control state of grid-connected operation, the energy storage system is analyzed and a Power Systems Computer Aided Design / Electromagnetic Transients including Direct Current (PSCAD/EMTDC) simulation model based on Power Quality (PQ) control and Space Vector Pulse Width Modulation (SVPWM) mode is built. And when Insulated Gate Bipolar Transistor (IGBT) fails on the upper bridge arm of A-phase Alternating Current (AC) converter in the energy storage system, the changes of AC voltage, AC current, active power, and reactive power in the system and simulated. The results show that the simulation model of energy storage system established by PSCAD/EMTDC is feasible under the PQ control of grid-connected operation. In addition, fault analysis shows that the current conduction of A phase is delayed in the negative half wave, and there is a positive Direct Current (DC) bias, but the distortion of current of B phase and C phase is not significant. And the active power and reactive power remain within the set reference range. Therefore, it is possible to determine the failure of the converter IGBT of the energy storage system by whether or not the three-phase current on the AC side of the energy storage system has a DC offset. This study aims to provide theoretical basis for the follow-up fault diagnosis and system protection of the energy storage system.

Heuristic Coordinated Voltage Control Schemes in Distribution Network with Distributed Generations

The voltage and reactive power control (Volt/VAR Control, VVC) in distribution networks has become a challenging issue with the increasing utilization of distributed generations (DGs). In this paper, a heuristic-based coordinated voltage control scheme that considers distribution voltage control devices, i.e., on-load tap changers (OLTC) and step voltage regulators (SVR), as well as reactive power control devices, i.e., DGs, are proposed. Conventional voltage control methods using non-linear node voltage equations require complex computation. In this paper, the formulation of simplified node voltage equations accounting for changes in tap position of distribution voltage control devices and reactive power changes of reactive power control devices are presented. A heuristic coordinated voltage control scheme using the proposed simplified node voltage equations is proposed. A coordinated voltage control scheme to achieve voltage control for nominal voltage and conservative voltage reduction (CVR) is presented. The results of the proposed schemes are compared with the results from the quadratic optimization method to confirm that the proposed schemes yields suitably similar results. Furthermore, a tap scheduling method is proposed to reduce the number of tap changes while controlling network voltage. The tap position is readjusted using a voltage control performance index (PI). Simulation results confirm that when using this method the number of tap changes is reduced. The proposed scheme not only produces reasonable performance in terms of control voltage of networks but also reduces the number of tap changes made by OLTC. The proposed control method is an alternative candidate for a system to be applied to practical distribution networks due to its simplified calculations and robust performance.

Control Design of Automatic Voltage Regulator to Improve the Voltage Stability at Sengkang Power Plant, South Sulawesi Indonesia

The change in voltage at the generator terminal is highly correlated with the change in reactive power at the center load. There are several reactive power sources in the power system including those from field amplifiers that are controlled by equipment called Automatic Voltage Regulators (AVR). Changes in reactive power in the system will change the voltage profile including the voltage at the generator terminal. To maintain the voltage level on the generator terminal, the AVR must be adjusted properly. Determination of the value of the amplifier gain on the AVR largely determines the performance of the AVR in stabilizing the voltage. Wind Turbine penetration greatly affects the system voltage. This research is to see the impact of voltage changes due to wind turbine penetration in sulseltrabar interconnection systems. Determination of AVR gain is generated from the Routh-Hurwitz equation. Furthermore, in this study PID control will be applied to increase the AVR output response. Determination of the correct Kp, Ki and Kd constants is obtained with the help of a MATLAB simulation model. The simulation shows that using a PID controller, the overshoot and settling times obtained are better. The maximum exceeded voltage is 1 per unit and the settling time is 10.15 seconds.

Research on restraining low voltage of distribution power network using STATCOM

In order to solve the problem of low voltage in distribution power network, this paper proposes a novel static synchronous compensator (STATCOM) based on modular multilevel converter. When the bus voltage of distribution power network changes rapidly, The MMC-STATCOM can quickly provide reactive voltage support and maintain the stability of bus voltage. Firstly, this paper introduces the operating principle of the MMC-STATCOM, and then propose three-level control strategies including device-level-, converter-level- and system level-control. Finally, based on the data of a power station in the distribution network, Simulation is carried out in the power system analysis and synthesis program (PSASP). The simulation results show that the MMC-STATCOM control function is reasonable and can respond quickly to the system reactive power change. It can effectively realize the voltage support and ensure the safe and stable operation of the power network.

Performance Evaluation of Power Swing Blocking in Compensated Transmission Lines

Traditional and modern compensation devices can increase power flow limit and enhance voltage drop in transmission lines. However, these systems can cause to malfunction of distance relays utilized to protect transmission lines. While compensation devices can effect distance relay operation, some disturbances like power swings are significant risk to ability of distance relays to distinguish faults. Power swing blocking (PSB) methods are used to discriminate faults from power swings. This study focuses on efficiency of conventional PSB methods when transmission lines are compensated with various compensation devices such as series capacitor (SC), thyristor-controlled series capacitor (TCSC) and static VAR compensator (SVC). A test system is simulated on PSCAD under various operating conditions. Conventional PSB methods (swing center voltage, reactive power change and change rate of impedance) are tested under these scenarios. The study revealed that compensation devices significantly affect the accuracy of PSB algorithms, therefore it is recommended to develop an adaptive PSB method to block power swing in the case of various operating conditions.

Constant Power Factor Mode of Grid-Connected Photovoltaic Inverter for Harmonics Distortion Assessment

The increased active power injection of the grid-connected Photovoltaic (PV) inverters has led to some challenges in the power quality issues. The PV inverters have been recommended in the technical standard requirements in order to control the reactive power supply into the grid. The purpose of this study is to investigate the correlation of the power factors to total harmonics distortion in a 30 kWp grid-connected PV inverter using two different operating modes. This research presents analyses of the statistical results of power quality parameters such as the changes in relative and reactive power, THD on current and voltage, and harmonic components of current and inverter voltage at different loads. The power quality parameters is assessed by using the Var regulation based on a constant power factor (CPF) and compared with the Var regulation based on changes in grid voltage (Q(U)). The unity and non-unity PF is simulated with high and low capacitive level. The results showed that THDi and THDv were less than 5% when the inverter approached nominal power. The non-unity PF constant inverter produces lower harmonic distortion than the unity PF. The simulation results found that the harmonic component of the current increased by more than 7% in the 7th order when the active power was less than 9% of the nominal power. However, reactive power regulation is proportionally constrained to prevent overvoltage of the inverter. The presented results are useful in fulfilling the technical requirements associated with the operating mode of the grid-connected PV inverters.

Analysis of Wind Farm Synchronization Impacted by Short Circuit of Grid Fault

In order to improve operational stability of the island system after grid faults of local weak connection, a wind farm and grid power system model composed of doubly-fed induction generator is built. This paper studies the impact of faults on the wind farm output and the grid bus after the wind farm is connected to the grid, and sets three-phase short-circuit fault in wind farm synchronization. Moreover, we analysed voltage fluctuation of the wind farm connected to the grid and voltage fluctuation of grid bus, as well as changes in output frequency, active power and reactive power of the wind farm. The microgrid voltage and frequency changes are studied in island operation when the fault is removed. The research results lay the foundation for island operation when fault occurs after wind turbine is connected to the grid.

Generator Performance in Steam Power Plant

This paper presents generator performance in a steam power plant. Location of this research is steam power plant, PT Paiton Unit 7, on Jalan Surabaya - Situbondo km 141, Binor, Paiton, Probolinggo, East Java, Indonesia. In the steam power plant, PT Paiton Unit 7 is used synchronous generators. The generator is said to be synchronous if it meets the requirements, among others, the phase sequence must be the same, the voltage must be the same, the frequency must be the same, and the phase angle must be the same.The performance of the generator can be known by looking at changes in active power, changes in output voltage, changes in output current, changes in reactive power in MVAR, changes in apparent power in MVA, changes in power factor, changes in frequency, changes in efficiency and percentage of the supply voltage.

D-STATCON model for voltage sag mitigation

<span>Development of a FACTS device model for mitigating voltage sag is presented. It deals with a static synchronous condenser (STATCON) to be used in the AC distribution networks. Simulation with the help of a commercial software Matlab/Simulink was explored to investigate its characteristics and performance during the voltage sag occurrence. The considered main cause of voltage sag was the starting of high capacity asynchronous motor. A voltage source inverter based on the phase-controlled thyristor components was implemented in this application to compensate the change in reactive power of the system. The concerns have been put on the influence of initial operation point and DC capacitance. The study results show the capability of D-STATCON model to reduce the consequence of voltage sag following the starting of high-power asynchronous motor in the distribution network. A fast response of the condenser work confirmed the desired performance.</span>

Islanding Detection of Synchronous Generator-Based DGs using Rate of Change of Reactive Power

The question of the islanding operation of distributed generations (DGs) and that of the current inadmissible networking policy of islanding operations sets a demanding task for an efficient islanding detection, preferably from a single place, using either passive or active islanding-detection method. Islanding detection shall be faster than the fast automatic reclosing of the connected transmission line connected to the DG unit. This paper deals with the detection method of islanded operation mode for the large power synchronous generator-based DGs in bio-mass power plants. The proposed method has been applied to a practical 10-MW bio-mass power plant and experimentally tested to verify the simulation results. The rate of change of reactive power ( dQ/dt >) criterion is derived as a yardstick for islanding detection. The practical power plant model has been implemented to be simulated in DIgSILENT PowerFactory and MATLAB/Simulink software environments. Offline digital time-domain simulations and experimental tests on a practical bio-mass power plant reveals that the proposed method efficiently, and authentically detects islanding phenomena with high accuracy, low detection time, very small number of non-detected zones and, with almost zero power balance ( ΔP = 0).