Quality of electricity in power supply of non-traction consumers of railway transport

The article presents the results of the study of the influence of LED lamps with switching power supplies containing power factor correctors on the quality of electricity in the power supply system of non-traction consumers of railway transport. It is noted that the emission of harmonic components of current by electronic loads can cause deviations in the quality of electricity up to the occurrence of emergency situations due to overloads of low (0.4 kV) and medium (6/10 kV) voltage networks. A non-linear electronic load (LED lamp), although equipped with a power factor corrector, causes the generation of a significant level of current harmonics, which significantly affect the operation of the transformer. As a result, the transformer, calculated taking into account the load factor of 0.7 – 0.8, can not be normally operated in the conditions of using electronic load devices. Mathematical modeling of the correction of the modes of the power supply system with nonlinear single-phase loads is performed, provided that the correction devices made on the basis of several condensers and reactors with nonlinear characteristics are used to balance the modes.

An Analysis of Electromagnetic Disturbances from an Electric Vehicle Charging Station

The electric vehicles (EVs) could potentially have a significant impact on power quality parameters and distribution networks as they are non-linear loads and their charging might result in tremendous power demand. When connected to the utility grid, a large number of EV charging stations from different manufacturers might create significant harmonic current emissions, impact the voltage profile, and eventually affect the power quality. Nevertheless, practical examples of disturbances from charging stations have not been made public. This paper aims to clarify the characteristics of conductive disturbances and levels of current harmonics generated by charging station and their severity on the quality of electric energy. The analysis was based on tests of a prototype station of an EV charging station integrated with a LED street light. The tests concern the determination of current harmonics and the values of conductive electromagnetic disturbances in the 150 kHz–30 MHz range. The test results of the prototype charger with observed exceedances of current harmonics (25th–39th range) and conducted interference exceedances are comprehensively described. After applying filtering circuits to the final version of the station, retesting in an accredited laboratory showed qualitative compliance.

INCREASING THE ENERGY EFFICIENCY OF THE AC ELECTRIC LOKOMOTIVE TRACTION DRIVE

The study of the energy characteristics of the active traction converter with pulse-width modulation as part of the traction electric drive of an AC electric locomotive was held during the research. Active traction converter provides pulse-width control of the collector DC traction motors voltage and belongs to the basic AC / DC circuit. The transient process when switching transistor switches is accompanied by significant voltage surge, due to the scattering inductance reaction of the traction transformer. Studies have shown that the diode discharge buffer circuits do not provide discharge of the electromagnetic energy accumulated in the winding of the transformer. An active traction converter control algorithm has been developed, which implies the use of pulse-width and phase regulation of rectified voltage. Switching of transistor switches occurs in the presence of a parallel current circuit. This creates the conditions for the discharge of electromagnetic energy accumulated in the secondary winding circuit of the traction transformer. The developed mathematical model allows to investigate the electromagnetic processes that occur during the switching of transistor switches and to evaluate the energy efficiency of the electric locomotive with active traction converter. In the simulation process, the influence of active traction converter parameters and control algorithms on the power rate of the converter, the total THD distortion rate of current and voltage and the relative values of the rectified voltage were investigated. Measures to increase the power rate and to reduce the emission level of higher current harmonics into the traction network were proposed.

Comparison of Models of Single-Phase Diode Bridge Rectifiers for Their Use in Harmonic Studies with Many Devices

Harmonic modeling of low-voltage networks with many devices requires simple but accurate models. This paper investigates the advantages and drawbacks of such models to predict the current harmonics created by single-phase full-bridge rectifiers. An overview is given of the methods, limiting the focus to harmonic analysis. The error of each method, compared to an accurate numerical simulation model, is quantified in frequency and time domain considering realistic input scenarios, including background voltage distortion and different system impedances. The results of the comparison are used to discuss the applicability of the models depending on the harmonic studies scale and the required level of detail. It is concluded that all models have their applicability, but also limitations. From the simplest and fastest model, which does not require a numerical solution, to the more accurate one that allows discontinuous conduction mode to be included, the trade-off involves accuracy and computational complexity.

Composite Control Strategy of Output Current of LCL Photovoltaic Grid-Connected Inverter

In order to further optimize the output current harmonic suppression effect of photovoltaic grid-connected inverters, a composite control strategy of LCL type photovoltaic grid-connected inverter output current is proposed. This strategy combines proportional complex integral (PCI) control and repetitive control (RC) in parallel, draws a composite control block diagram, introduces a transfer function, and designs PCI and RC control parameters. Prove that the compound control can reduce current harmonics, achieved the purpose of reducing the steady-state error of the fundamental frequency. And adopts a new PCI composite control strategy, which helps to save the cost of the control system. By building the MATLAB/Simulink simulation platform and establishing the PCI+RC composite control model of LCL photovoltaic grid-connected inverter, the comparison of the simulation results shows that compared with the PI+RC control strategy, the total harmonic distortion rate of the grid-connected current is reduced by 25.77. %, significantly improving the quality of grid-connected current.

Mathematical Modeling of Enhanced Whale Optimization Based Power Quality Enhancement Using Unified Power Quality Conditioner for Implantable Biomedical Devices

Implantable biomedical systems that enable the majority of the functions of wireless implantable devices have made significant progress in recent years. Nonetheless, due to limited miniaturization, power distribution limits, and the unavailability of a stable link between implants and external devices, such systems are primarily limited to investigation. Generating electricity from natural sources and human body movement for implantable biomedical devices has emerged as a viable option. Nowadays, energy sources become the emerging use of electricity grid which has formed new challenges for the effectiveness of power quality, efficient energy utilization and voltage stabilization for biomedical applications. Power quality in the implementation of the smart grid in biomedical devices is regarded to be the most problematic. APFs (Active Power Filter) are preferred to reward the related problems, mainly because they can quickly filter out of the PQ and are a dynamic compensation. The UPQC with a PI control unit with DC source to be converted to a three stage inverter based on Enhanced Whale Optimization Algorithm (EWOA) was precisely implemented in the article in order to eliminate voltage and current harmonics inadequate. Similarly, UPQC also used the Enhanced Whale Optimization Algorithm (EWOA). In this approach, UPQC along with EWOA (Enhanced whale optimization) has been introduced for voltage and current harmonics elimination defect specifically. Similarly, EWOA was too implemented with UPQC. UPQC & EWOA conducted a performance estimate by estimating a simulation, results on comparing the parameters of THD levels, load current and voltage. The performance estimate is also used and the results achieved are shown. In order to analyze THD values and validate the system performance, performance estimates are built and compared with THD values, load voltage and current parameters.

Harmonic Suppression Strategy of Photovoltaic Grid Connected Inverter Based on Repetitive and PI Control

To address the serious harmonic problem of grid connected current in photovoltaic grid-connected inverter, a harmonic suppression strategy based on Repetitive and PI control is proposed in this thesis. According to this strategy, the mathematical model of LCL photovoltaic grid-connected inverter is established with the harmonic mechanism analyzed, the repetitive and PI control is added into the current controller, and the capacitive-current feedback is added to enhance the system damping. Furthermore, it puts PI control on the inner loop and the repetitive control on the outer loop to improve the dynamic performance and achieve the harmonic suppression of the system. Moreover, the simulation results show that this method improves the dynamic response ability of the system, and effectively suppress the grid-connected current harmonics as THD of grid-connected current is 19.65% lower than that of PI controller.

Nonlinear load modeling for analysis of non-sinusoidal conditions in electrical networks based on measurements of harmonic parameters

Non-sinusoidal conditions in electrical networks need to be calculated for their control and development of technical measures to maintain harmonic parameters according to the requirements of regulatory documents. These calculations are impossible without electrical network and nonlinear load models that adequately reflect them in computational programs. Nonlinear load models have been developed for a long time. Some studies present general modeling principles and models of various nonlinear devices. Others consider some nonlinear devices as equivalent nonlinear loads connected to low and medium voltage networks. A whole host of high-power nonlinear electrical equipment is connected to high voltage networks. Modeling nonlinear loads connected to these networks is a problem. Research of measured parameters of harmonic conditions in electrical networks has shown that they are random values. The probabilistic nature is determined by the network configuration, a range of network components, the number of nonlinear loads, wave and frequency properties of the network, harmonic source phase currents, voltage at terminals of nonlinear electrical equipment, changes in operating conditions and load power, and many other factors. Nonlinear loads can only be modeled based on the measurements of parameters of harmonic conditions due to their unpredictability. The paper presents an overview of existing methods for modeling nonlinear loads, a methodological approach to modeling nonlinear loads based on measured parameters, an algorithm for modeling harmonics of active and reactive currents, a computational program algorithm designed to identify distribution functions of measured current harmonics, and modeling results for current harmonics of railway transformers supplying power to electric locomotives.