Efficacy of Smart PV Inverter as a Strategic Mitigator of Network Harmonic Resonance and a Suppressor of Temporary Overvoltage Phenomenon in Distribution Systems

The research work explores the design of Smart PV inverters in terms of modelling and investigates the efficacy of a Smart PV inverter as a strategic mitigator of network harmonic resonance phenomenon and a suppressor of Temporary Overvoltage (TOV) in distribution systems. The new application and the control strategy of Smart PV inverters can also be extended to SmartPark-Plug in Electric Vehicles as the grid becomes smarter. As the grid is becoming smarter, more challenges are encountered with the integration of PV plants in distribution systems. Smart PV inverters nowadays are equipped with specialized controllers for exchanging reactive power with the grid based on the available capacity of the inverter, after the real power generation. Although present investigators are researching on several applications of Smart PV inverters, none of the research-work in real time and in documentation have addressed the benefits of employing Smart PV inverters to mitigate network resonances. U.S based standard IEEE 519 for power quality describes the network resonance as a major contributor that has an impact on the harmonic levels. This dissertation proposes a new application for the first time in utilizing a Smart PV inverter to act as a virtual detuner in mitigating network resonance. As a part of the Smart PV inverter design, the LCL filter plays a vital role on network harmonic resonance and further has a direct impact on the stability of the controller and rest of the distribution system. Temporary Overvoltage (TOV) phenomenon is more pronounced especially during unbalanced faults like single line to ground faults (SLGF) in the presence of PV. Such an abnormal incident can damage the customer loads. IEEE 142-“Effective grounding” technique is employed to design the grounding scheme for synchronous based generators. The utilities have been trying to make a PV system comply with IEEE 142 standard as well. Several utilities are still employing the same grounding schemes even now. The attempt has resulted in diminishing the efficacy of protection schemes. Further, millions of dollars and power has been wasted by the utilities. As a result, the concept of effective grounding for PV system has become a challenge when utilities try to mitigate TOV. With an intention of economical aspects in distribution systems planning, this dissertation also proposes a new application and a novel control scheme for utilizing Smart PV/Smart Park inverters to mitigate TOV in distribution systems for the first time. In other words, this novel application can serve as an effective and supporting schema towards ineffective grounding systems. PSCAD/EMTDC has been used throughout the course of research. The idea of Smart inverters serving as a virtual detuner in mitigating network harmonic resonance and as a TOV suppressor in distribution systems has been devised based on the basic principle of VAR injection and absorption with a new control strategy respectively. This research would further serve as a pioneering approach for researchers and planning engineers working in distribution systems

An Extensive Review of Multilevel Inverters Based on Their Multifaceted Structural Configuration, Triggering Methods and Applications

Power electronic converters are used to transform one form of energy to another. They are classified into four types depending upon the nature of the input and output voltages. The inverter is one among those types; it converts direct electrical current into alternating electrical current at desired frequency. Conventional types of inverters are capable of producing voltage at the output terminal that can only switch between two levels. The range of output voltage generated at the output is low when they are used for high power applications. To improve the voltage profile and efficiency of the overall system, multilevel inverters (MLIs) are introduced. In multilevel inverters the voltage at the output terminal is generated from several DC voltage levels fed at its input. The generated output is more appropriate to a sine wave and the dv/dt rating is also less leading to the reduction in EMI. Though they possess many advantages compared to the conventional inverters, the structural complexity and triggering techniques involved in designing multilevel inverters are high. Many studies are being carried out in defining new topologies of MLI with reduced switch as well as with the implementation of different PWM techniques. This paper will provide an extensive review on variety of MLI configurations based on the parameters such as the number of switches, switching techniques, symmetric, asymmetric, hybrid topologies, configurations based on applications, THD and power quality

Novel Exertion of Intelligent Static Compensator Based Smart Inverters for Ancillary Services in a Distribution Utility Network-Review

Integration of distributed energy resources (DER) has always posed a challenge. Smart inverters have started playing a crucial role in efficient integration of DERs. With the basic functionalities of traditional inverters in place, smart inverters can provide grids with related ancillary services either from the customer side or from the utility as well. The ancillary/augmented service from smart inverters includes the concept of reactive power exchange with the grid. Such grid support functions includes the functionalities of photovoltaic/plug in electric vehicles (PV/PEV) inverters as a static synchronous compensators (STATCOMs) by performing virtual detuning, temporary over voltage (TOV) mitigation, voltage regulation, frequency support and ride through capabilities. As the penetration levels of DERs have gone up, the need for such ancillary services has grown as well. This paper is organized in such a way that it will serve as a benchmark for smart inverter technologies in the form of a review. It includes several domains involving the applications, advanced and coordinated control, topologies and many more aspects that are associated with smart inverters based on reactive power compensation schemes for ancillary services. Apart from that, the applications those are associated with smart inverters in the smart grid domain are also highlighted in this paper

Hall-Sensor-Based Position Detection for Quick Reversal of Speed Control in a BLDC Motor Drive System for Industrial Applications

This paper proposes the novel idea of eliminating the front-end converters used indirect current (DC) bus voltage variation, thereby allowing for control of the speed of the brushless direct current (BLDC) motors in the two-quadrant operation of a permanent magnet brushless direct current (PMBLDC) motor, which is required for multiple bi-directional hot roughing steel rolling mills. The first phase of steel rolling, the manufacture of plates, strips etc., using hot slabs from the continuous casting stage, is carried out for thickness reduction, before the same is sent to the finishing mill for further mechanical processing. The hot roughing process involves applying high, compressive pressure, using a hydraulically operated mechanism, through a pair of backup rolls and work rolls for rolling. Overall, the processes consist of multiple passes of forward and reverse rolling at increasing roll speeds. The rolling process was modeled, taking into account parameters like roller dimensions, angle and length of contact, and rolling force, at various temperatures, using actual data obtained from a steel mill. From this data, speed and torque profiles at the motor shaft, covering the entire rolling process, were created. A profile-based feedback controller is proposed for setting the six-pulse inverter frequency and parameters of the pulse width modulated (PWM) waveform for current control, based on Hall sensor position, and the same is implemented for closed loop operation of the brushless direct current motor drive system. The performance enhancement of the two different controllers was also evaluated, during the rolling of 1005 hot rolled (HR) steel, and was taken into consideration in the research analysis. The entire process was simulated in the MATLAB/Simulink platform, and the results verify the suitability of an entire-drive system for industrial steel rolling applications

Dynamic Voltage Stability Assessment in Remote Island Power System with Renewable Energy Resources and Virtual Synchronous Generator

Increasing the proportion of renewable energy generations in remote island power systems is becoming essential for realizing decarbonized society. However, since inverter-connected renewable energies have different generation characteristics from conventional generators, the massive penetration can adversely affect system stability. In particular, fault events in such weak remote systems can cause fast voltage collapse, and there is a need to assess dynamic voltage stability. This study attempts dynamic voltage stability assessment using the critical boundary index (CBI) and investigates the impact of the virtual synchronous generator (VSG) on dynamic voltage stability. A remote island power system and VSG are modeled, and time-domain simulations are conducted with case studies of fault events. The simulation results show the potential of CBI to use for dynamic voltage stability assessment. Furthermore, the VSG can provide suitable power output during fault events and improve dynamic voltage stability

A virtual synchronous generator control method for remote island power system considering dynamic voltage stability

Remote island power systems are difficult to install renewable energy sources (RES) because of the small system capacity and the large impact of intermittency of RES. Virtual synchronous generators (VSG) can equip inverters with the inertia of synchronous generators and can suppress frequency and voltage fluctuations. This paper proposes a VSG control method for dynamic voltage stability in remote island power systems. In conventional VSG control methods, the command of active and reactive power is determined by the Droop characteristics of frequency and transmission line voltage. However, the command are not based on dynamic voltage stability indices. Therefore, the compensation amount of active and reactive power is inappropriate. The proposed method determines the command of active and reactive power based on dynamic voltage stability indices. The dynamic voltage stability index considers the critical boundary index (CBI). The CBI is defined as the distance between the operating point of active and reactive power flowing through a transmission line and the stability limit curve calculated from the power flow between two bus lines. The proposed method improves dynamic voltage stability by determining power command so that the operating points of active and reactive power are closer to the origin direction. Simulation verification is performed for load increase and three-phase ground fault. In the three-phase ground-fault simulation, FRT requirements are considered to verify continued operation and the case of gate blocking. The conventional Droop control and the proposed method are compared for the case of continued operation with FRT requirements during load increase and ground fault. Simulation verification results show that the proposed method improves the dynamic voltage stability compared to the conventional method. Furthermore, it is shown that the proposed method is capable of stable continuous operation of the system even after a transmission line failure considering the FRT requirement

Feasible Evaluation and Implementation of Shunt Active Filter for Harmonic Mitigation in Induction Heating System

This paper proposes a shunt active filter (SAF) for harmonic mitigation and reactive power compensation in an induction heating (IH) system. The high-frequency switching in the resonant inverter of the IH system generates a considerable number of high-frequency harmonics. The latter flow back to the supply side and causes a wide variety of problems. The predominant ones are the deterioration of the power quality, distortion in the grid voltage, and malfunctioning of the protective equipment. These harmonics need to be attenuated as per the IEEE 519-1992 and IEEE 519-2014 standards. To overcome these problems, an SAF based on the modified version of instantaneous power theory was placed between the power supply and the IH equipment. Moreover, the proposed model could work in unbalanced and non-sinusoidal input voltage conditions, as well as dynamic conditions with changing reference currents. The feasibility of the proposed SAF-based IH system was verified by a series of simulation results and a comparative analysis of the THD of the input currents. The power quality issues were successfully addressed, which signifies the ability and effectiveness of the proposed model to mitigate the problems caused by harmonics and enhance the power factors

Technical and Economic Analysis of an HVDC Transmission System for Renewable Energy Connection in Afghanistan

Aged and insufficient domestic power plants and insecure, unreliable and expensive power imports pose significant challenges for the power sector of Afghanistan. On the other hand, due to the absence of a suitable transmission grid, the internal renewable energy resources are not adequately developed, despite their abundant resource potential throughout the country. This paper proposes a voltage source converter (VSC)-based high-voltage direct current (HVDC) transmission link to connect the Herat province in the west, which has huge solar and wind energy potential, to Kabul, the capital of the country and the main load center. A techno-economic analysis of this HVDC against high-voltage alternating current (HVAC) technology was performed to determine the suitability and effectiveness of the proposed transmission system. The active, reactive and corona losses were calculated as the technical parameters and the discounted cash flow (DCF) method was deployed to economically compare both technologies. The outcomes of the paper disclose that the implementation of this transmission project is techno-economically feasible, and can result in the energy security and economic stability of the country

Feasible Evaluation and Implementation of Shunt Active Filter for Harmonic Mitigation in Induction Heating System

This paper proposes a shunt active filter (SAF) for harmonic mitigation and reactive power compensation in an induction heating (IH) system. The high-frequency switching in the resonant inverter of the IH system generates a considerable number of high-frequency harmonics. The latter flow back to the supply side and causes a wide variety of problems. The predominant ones are the deterioration of the power quality, distortion in the grid voltage, and malfunctioning of the protective equipment. These harmonics need to be attenuated as per the IEEE 519-1992 and IEEE 519-2014 standards. To overcome these problems, an SAF based on the modified version of instantaneous power theory was placed between the power supply and the IH equipment. Moreover, the proposed model could work in unbalanced and non-sinusoidal input voltage conditions, as well as dynamic conditions with changing reference currents. The feasibility of the proposed SAF-based IH system was verified by a series of simulation results and a comparative analysis of the THD of the input currents. The power quality issues were successfully addressed, which signifies the ability and effectiveness of the proposed model to mitigate the problems caused by harmonics and enhance the power factors

An Experimental Investigation and Feasibility Analysis of a Novel Modified Vienna Rectifier for Harmonic Mitigation in an Induction Heating System

This paper presents a novel single-phase modified Vienna rectifier (MVR) for the harmonic mitigation and power factor improvement of an induction heating (IH) system. The latter employs a high-frequency resonant inverter that is responsible for the generation of high-frequency harmonics, which, in turn, deteriorates the power quality. This mitigation must be done in accordance with harmonic regulations such as IEEE Std. 519-2014,IEC-555, and EN 61000-3-2, etc. Consequently, an MVR is placed between the power supply and the IH system. The proposed novel MVR topology overcomes the limitations of conventional Vienna rectifiers, such as their unbalanced voltage across output capacitors, high ripple at the output DC bus, and high THD in the supply current, etc. The efficacy of the proposed model has been verified by a series of simulations in PSIM. It is followed by a hardware validation using an Arduino Uno ATmega328 digital controller on a 1.2 kW experimental prototype of the IH system. The simulation and experimental results of the power quality indices comply with the IEEE-519 standards