Power quality improvement in distribution system using hybrid AC/DC configuration

The widespread use of power electronic loads which are nonlinear in nature has led to the injection of current and voltage harmonics in low voltage distribution system. As the distribution transformers have to meet the harmonic losses caused due to the nonlinear loads, their power handling capacity is decreased leading to the derating of transformers. This paper investigates the feasibility of reducing harmonic distortion and derating of transformers by employing a hybrid ac-dc distribution system, in which the dc loads are powered by dc supply through a three phase diode bridge rectifier. For this, an in-depth analysis of the harmonic distortions in the power supply of different domestic buildings is performed by real time measurement and the impact of these harmonics on the derating of transformer in a conventional distribution system is evaluated by simulation. The improvement in power quality by dc distribution is demonstrated by simulation and experimental validation.

The input and output impedances in a low voltage distribution system is one of the most important matters for power line communication because from the viewpoint of communication, the attenuation characteristic of the high frequency signals is greatly caused by impedance mismatch during sending and receiving. The frequency range is from 1MHz to 30MHz. Therefore, this paper investigates the input and output impedances in order to understand the characteristic of high frequency signals in the low voltage distribution system between a pole transformer and an end user. For power line communication, the model of Korea's low voltage distribution system is proposed in a residential area and then the low voltage distribution system is set up in a laboratory. In the low voltage distribution system, S parameters are measured by using a network analyzer. Finally, input and output impedances are calculated using S parameters.

This paper proposes a hybrid converter which can offer both AC and DC loads from single DC input. These topologies of the hybrid converter are formed by replacing the control switch of the boost converter with a voltage source inverter. This ensuing hybrid converter needs a lesser number of switches to produce AC and DC loads with more reliability and has shoot-through protection within the inverter operation. Such multiple output converters with higher power process density and dependability are often compatible for systems with both DC and AC loads. This Hybrid converter will overcome the shortage of standard device. We use a solar panel as a source of DC voltage which will be given to a boost converter to increase the DC voltage and is given to a hybrid device. The hybrid device can turn out both AC and DC as output. A suitable pulse width modulation (PWM) technique is used. The validity and effectiveness of the projected device and its control performance are verified by MATLAB Simulink.

High boost DC to AC inverters are used in renewable energy systems like solar PV, fuel cell, wind farm etc and UPS systems to mention a few. High voltage boost, wide output ranges of operation, shoot-through immunity are some of the desired properties of an inverter for a reliable, versatile and low distortion AC inversion. This paper proposes a single-stage, high boost inverter with buck-boost capability which has several distinct advantages over conventional voltage source inverters (VSI) like better EMI noise immunity, wide input and output voltage range of operation, etc. The proposed inverter is named as Current-Fed Switched Inverter (CFSI). A hybrid converter structure of CFSI has been developed which supplies both AC and DC loads, simultaneously, from a single DC supply which makes it suitable for DC Nanogrid application. This paper proposes the operation and control of a CFSI based hybrid converter which regulates the AC and DC bus voltages at their reference values in steady-state or dynamic load change event. The development of the proposed converter from basic current-fed DC/DC topology is discussed. Steady-state analysis of the converter is outlined to establish the relation between DC input and AC output. Small-signal analysis of the converter is done to design the closed loop controller for the converter. An experimental prototype is built to validate the proposed converter with its DSP based closed loop control. The closed loop controller is verified through its low cross regulation and dynamic performance for a 20% step change in either DC or AC load.

Distributed Energy Resources (DERs) installed on low-voltage distribution systems, both utility-owned and nonutility owned may be employed to make improvements to system resiliency and power quality, in addition to simply serving load demand. By selectively dispatching active and reactive power from these existing DERs, improvements in voltage profiles and service availability during adverse events may be achieved. Further benefits can be gained by optimally choosing which DERs to dispatch power from, and the distribution of power from those DERs. For a given operating condition, using Linear Programming methods, optimal power dispatch values for individual DERs can be determined, while considering variables such as voltage gains, losses in the lines and the DERs, and DER reserve capacities. One such optimization technique is developed in this paper, and results from a real-time simulation study on a modified IEEE 13-bus distribution system with three DERs, are being presented. The operation of the optimized DER selection and dispatch algorithm is shown during normal operation of the transmission system when the DERs operate in grid-connected mode. Similar analyses can drive decision making during transmission system failure when the DERs operate in grid-forming or islanded mode.

An approach to the impedance modelling of low-voltage cables in digital twins

In this paper, authors describe the control priority of the system support function installed in the photovoltaic power generator (PV) inverter. The PV inverter is equipped with a system support function as a measure against power quality problems. However, it is not clear which control has priority among these control functions. In particular, it is considered necessary to study in low voltage distribution systems where voltage and frequency problems can occur simultaneously. Therefore, in this paper, authors propose a method for switching the voltage control and frequency control installed in the PV inverter by using the V · f plane centered on the amount of change in voltage and system frequency in a low-voltage distribution system. As a result, it was confirmed that it is effective to control the voltage preferentially in the low voltage distribution system.

This paper presents an experimental study with a pilot hybrid microgrid system that is proposed and implemented in Tagajo campus of Tohoku Gakuin University, Japan. The developed microgrid system is designed to be able to supply power to both DC and AC loads simultaneously by renewable power sources such as PV and wind power generations, etc. Meanwhile, in case that the renewable power is insufficient to supply both these loads, a diesel generator is automatically actuated as backup power source. For the purpose of power balance and voltage stabilization, two types of energy storage devices with different response characteristics and cost, which are secondary battery and EDLC (Electrical Double-layer Capacitor) respectively, are introduced into this system. In this work, a coordinated control strategy for these energy storages were proposed and verified by a series of experimental studies with the developed hybrid microgrid system. The purpose of the experimental study addressed in this paper is to confirm the islanded operation properties of this system for stable power supply to both AC and DC loads, even in case with considerable power fluctuation of renewable sources and significant power change in loads. As a result of this study, it is illustrated that the developed hybrid microgrid and its control systems can work properly and resiliently as being designed.

Lightning surge is one major source that causes failure of power electronic equipments in low-voltage power distribution systems, especially for the equipments with low immunity parameters and high sensitivity to surge. Surge protection device (SPD) is the primary means of surge protection in low-voltage power distribution systems, in this paper, based on the work done before, in use of simulation methods, the protective effect about nine kinds of two-stage cascade SPD is analyzed in low-voltage power distribution systems under the impact of lightning. Finally, in order to protect the power electronic equipments economically and safely, several principles about how to choose SPD coordination are proposed under the circumstances of different length of cable and different type of load.

This novel automated fault isolation system has been developed and integrated into a new customer side distribution system of 415/240V. The distribution system is based on the Tenaga Nasional Berhad (TNB), the Malaysia's power utility company especially the distribution system. Supervisory Control and Data Acquisition (SCADA), Remote Terminal Unit (RTUs) and power line communication (PLC) system have been used and developed for detecting, fault locating, fault isolating, fault segregating and power restoration in terms of hardware and software. Open loop distribution system is the distribution configuration system used as TNB distribution system. It is the first distribution automation system (DAS) based on fault management research work on customer side substation for operating and controlling betweenthe consumer side system and the substation.

It is DC power that Output of renewable energy being recently developed and researched. Also, demand of DC power will expect to proliferate due to increase of digital load. Thus, DC distribution system providing high quality of power and reliability has emerged as a new distribution system. If the conventional distribution systems are substituted by proposed DC distribution system, the output of renewable energy can be connected with distribution systems under minimum power conversion. Therefore, in the event of connection with DC load, it can construct an efficient distribution system. In this paper, the integrated parallel operation of power conversion module for DC distribution system is proposed. Also, this paper proposed modularization of power conversion devices for DC distribution system and power control for parallel operation of large capacity system. DC distribution system consists of three power conversion modules such as AC/DC power conversion module 2 set, ESS module 1 set. DC distribution system controls suitable operation depending on the status of the DC power distribution system and load. Integrated operation of these systems is verified by simulation and experiment results.

Increasing levels of distributed generation (DG), as well as changes in electricity consumption behavior, are reshaping power distribution systems. These changes might place particular stress on the secondary low-voltage (LV) distribution systems not originally designed for bi-directional power flows. Voltage violations, reverse power flow, and congestion are the main arising concerns for distribution system operators (DSOs), while observability in these grids is typically nonexistent or very low. The present paper addresses this issue by developing a method for nodal voltage estimation in unbalanced radial LV grids (at 0.4 kV). The workflow of the proposed method combines a data-driven grey-box modeling approach with generalized additive models (GAMs). Furthermore, the proposed method relies on experimental data from a real-world LV grid in Denmark and uses data input from only one measuring device per feeder. Predictions are evaluated by using a test data set of 31 days, which is more than twice the size of the training data set of 13 days. The prediction results show high accuracy at root mean squared errors (RMSEs) of 0.002–0.0004 p.u. The method also requires a short computation time (14 s for the first stage and 2 s for the second stage) that meets requirements for the practical, real-time monitoring of DSO grids.

This paper discusses the mitigation of power quality disturbance in low voltage distribution system due to voltage swells using one of the powerful power custom devices namely Dynamic Voltage Restorer (DVR). The DVR normally installed between the source voltage and critical or sensitive load. The new configuration of DVR has been proposed using improved d-q-o controller technique‥ The simulations are performed using Matlab/Simulink's SimPower Toolbox. The proposal is then implemented using 5KVA DVR experimental setup. The simulation and experimental results demonstrate the effective dynamic performance of the proposed configuration.

The characteristics of electrical noise and power harmonics from power converters and other harmonic sources, as well as the effects of such noise and harmonics on distribution system equipment and operation are described. Power system surges and their effects on converter equipment are also described. Field tests were conducted on two different distribution systems. Measurements were made of harmonic voltage and current magnitudes, capacitor-switching transients, and impulsive electromagnetic noise in the frequency range of 3 kHz to 300 kHz. Test methodology and instrumentation are described, and the measured results are presented. The implications of this high-frequency noise on power line communication systems are discussed. A computer program was developed to aid in analyzing distribution system response to harmonic sources on the system. Simulations performed for the two distribution systems tested are described, and comparisons between simulation results and measured harmonic magnitudes are presented. The project also addressed methods of controlling harmonics on distribution systems. The different methods for harmonic control, principally the filtering and/or phase cancellation of harmonics, are described.

Voltage regulation mitigation techniques in distribution system with high PV penetration: A review