Power Quality Improvement and Low Voltage Ride through Capability in Hybrid Wind-PV Farms Grid-Connected Using Dynamic Voltage Restorer

© 2018 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission.This paper proposes the application of a dynamic voltage restorer (DVR) to enhance the power quality and improve the low voltage ride through (LVRT) capability of a three-phase medium-voltage network connected to a hybrid distribution generation system. In this system, the photovoltaic (PV) plant and the wind turbine generator (WTG) are connected to the same point of common coupling (PCC) with a sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up transformer. The PV system is connected to the PCC via a two-stage energy conversion (dc-dc converter and dc-ac inverter). This topology allows, first, the extraction of maximum power based on the incremental inductance technique. Second, it allows the connection of the PV system to the public grid through a step-up transformer. In addition, the DVR based on fuzzy logic controller is connected to the same PCC. Different fault condition scenarios are tested for improving the efficiency and the quality of the power supply and compliance with the requirements of the LVRT grid code. The results of the LVRT capability, voltage stability, active power, reactive power, injected current, and dc link voltage, speed of turbine, and power factor at the PCC are presented with and without the contribution of the DVR system.Peer reviewe

A hybrid multilevel converter for medium and high voltage applications

This paper investigates the suitability of the hybrid multilevel converter for medium and high voltage application. The converter operation, modulation, and capacitor voltage balancing method are described in detail. The ability of the hybrid multilevel converter to operate with different modulation indices and load power factors is investigated. It has been established that the hybrid multilevel converter is capable of operating independent of load power factor. Operation with variable modulation index increases voltage stresses on the converter switches and does not alter the fundamental voltage magnitude as in all known voltage source converter topologies. The viability of the hybrid multilevel converter for medium and high voltage applications is confirmed by simulations

Effective Design of STATCOM Considering Fundamental Frequency Current, Active Harmonic Filtering and Zero Sequence Current

The main objective of this thesis was to investigate the effect of parallel reactive power compensation (RPC) and active harmonic filtering (AHF) operation on a STATCOM design, in terms of needed number of submodules (SMs), DC link voltage capacity, MV busbar voltage, zero sequence current demand, transformer and coupling inductor reactance. To achieve this objective, two design scenarios were carried out. In the first scenario, fundamental reactive current of studied STATCOM was prioritized over its current for active harmonic voltage filtering. In the second scenario, studied STATCOM was required to produce the nominal fundamental reactive power and perform active harmonic voltage filtering simultaneously. The problem was studied in PSCAD based simulation environment. In all simulations, q-component current was supplied manually to enable the RPC operation of studied STATCOM. To enable AHF operation, harmonic current control mode was used, and the reference value of the desired harmonic filtering current was supplied accordingly. However, before proceeding with any simulation, first, the system limitations based on the studied STATCOM technology were studied and adequate majors were placed inside the simulation mode accordingly. Thereafter, simulations providing information on the basic STATCOM design operating in RPC mode only (and without AHF functionality) were carried out so that it can be compared later with the aforementioned scenarios of parallel RPC and AHF operations. In the first design scenario, it was found out that additional AHF operation affects the STAT-COM design in three ways. First was the magnitude of AHF current where an increment in the needed number of SMs w.r.t basic design was noticed with increasing magnitude of AHF current. The second was the phase angle references of AHF current where if phase angle references of AHF current are chosen such that peaks of produced voltage source converter’s (VSC’s) fundamental and harmonic voltages are aligned then the amount of needed SMs to produce the same VSC voltage was increased. But, if phase angle references of AHF current are such that the peaks of VSC voltages are opposite to each other, then fewer SMs are required to produce the same VSC voltage. The third effect on STATCOM design was based on the harmonic order of AHF current produced. It was noticed that when harmonic order of AHF current was high, then the amount of needed SMs to produce the same magnitude of AHF current was increased. In the second design scenario, it was found that maximum fundamental reactive current and maximum filtering current cannot be achieved at the same time with a geometrical summation principle of these currents, but possible with an arithmetical summation principle with a trade-off between optimum utilisation of current capacity and extra hardware cost. Hence, an optimum design to achieve the maximum of RPC and AHF current simultaneously exists between economical (based on the geometrical summation principle) and conservative (based on the arithmetical summation principle) design, but rather close to the economical one. In last, it was also noticed that the maximum demand of zero sequence current occurred when STATCOM was producing fundamental reactive current and negative sequence AHF current simultaneously in the maximum capacitive operation point, with an unbalanced network. And, peaks of positive and negative sequence network voltage and peaks of produced VSC voltages (fundamental and harmonic) were aligned

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Power quality improvement based on hybrid coordinated design of renewable energy sources for DC link channel DSTATCOM

This paper presents a comprehensive analysis of power quality for static synchronous compensator on the distribution power system (DSTATCOM) when a different types of energy sources are used to supply the dc link channel of DSTATCOM. These types of power supplies have a different effect on the compensation of DSTATCOM due to operation nature of these sources. The dynamic response of the DSTATCOM has been investigated that produced by individual and hybrid energy sources to evaluate the influence of these sources in terms of time response, compensation process and reduce the harmonics of current for source. Three cases have been considered in this study. First the photovoltaic (PV) cells alone second the battery storage alone and third a hybrid coordinated design between (PV cells with battery storage) is used. A boost Dc-Dc circuit has been connected to a photovoltaic cell with Maximum Power Point Tracking (MPPT) while a Dc-Dc buck-boost circuit is used with a battery. High coordination between PV and battery circuits in the hybrid system is used in order to improve the performance. A synchronous reference frame (SRF) with unit vector has been used to control the STATCOM circuit. The simulation results show that the hybrid design has the superiority response compared to the individual sources

Power quality improvement using passive shunt filter, TCR and TSC combination

Power system harmonics are a menace to electric power systems with disastrous consequences. The line current harmonics cause increase in losses, instability, and also voltage distortion. With the proliferation of the power electronics converters and increased use of magnetic, power lines have become highly polluted. Both passive and active filters have been used near harmonic producing loads or at the point of common coupling to block current harmonics. Shunt filters still dominate the harmonic compensation at medium/high voltage level, whereas active filters have been proclaimed for low/medium voltage ratings. With diverse applications involving reactive power together with harmonic compensation, passive filters are found suitable [41]. Passive filtering has been preferred for harmonic compensation in distribution systems due to low cost, simplicity, reliability, and control less operation [42]. The uncontrolled ac-dc converter suffers from operating problems of poor power factor, injection of harmonics into the ac mains, variations in dc link voltage of input ac supply, equipment overheating due to harmonic current absorption, voltage distortion due to the voltage drop caused by harmonic currents flowing through system impedances, interference on telephone and communication line etc. The circuit topologies such as passive filters, ac-dc converter, based improved power quality ac-dc converters are designed, modeled and implemented. The main emphasis of this investigation has been on a compactness of configurations, simplicity in control, reduction in rating of components, thus finally leading to saving in overall cost. Based on thesis considerations, a wide range of configurations of power quality mitigators are developed, which is expected to provide detailed exposure to design engineers to choose a particular configuration for a specific application under the given constraints of economy and desired performance. For bidirectional power flow applications, the current source converter is designed and simulated with R-L load. The necessary modeling and simulations are carried out in MATLAB environment using SIMULINK and power system block set toolboxes. The behavior of different configurations of passive tuned filters on power quality is studied. One of the way out to resolve the issue of reactive power would be using filters and TCR, TSC with combination in the power system. Installing a filter for nonlinear loads connected in power system would help in reducing the harmonic effect. The filters are widely used for reduction of harmonics. With the increase of nonlinear loads in the power system, more and more filters are required. The combinations of passive filters with TCR and TSC are also designed and analyzed to improve the power quality at ac mains. This scheme has resulted in improved power quality with overall reduced rating of passive components used in front end ac-dc converters with R-L load

The Modeling and Advanced Controller Design of Wind, PV and Battery Inverters

Renewable energies such as wind power and solar energy have become alternatives to fossil energy due to the improved energy security and sustainability. This trend leads to the rapid growth of wind and Photovoltaic (PV) farm installations worldwide. Power electronic equipments are commonly employed to interface the renewable energy generation with the grid. The intermittent nature of renewable and the large scale utilization of power electronic devices bring forth numerous challenges to system operation and design. Methods for studying and improving the operation of the interconnection of renewable energy such as wind and PV are proposed in this Ph.D. dissertation.;A multi-objective controller including is proposed for PV inverter to perform voltage flicker suppression, harmonic reduction and unbalance compensation. A novel supervisory control scheme is designed to coordinate PV and battery inverters to provide high quality power to the grid. This proposed control scheme provides a comprehensive solution to both active and reactive power issues caused by the intermittency of PV energy. A novel real-time experimental method for connecting physical PV panel and battery storage is proposed, and the proposed coordinated controller is tested in a Hardware in the Loop (HIL) experimental platform based on Real Time Digital Simulator (RTDS).;This work also explores the operation and controller design of a microgrid consisting of a direct drive wind generator and a battery storage system. A Model Predictive Control (MPC) strategy for the AC-DC-AC converter of wind system is derived and implemented to capture the maximum wind energy as well as provide desired reactive power. The MPC increases the accuracy of maximum wind energy capture as well as minimizes the power oscillations caused by varying wind speed. An advanced supervisory controller is presented and employed to ensure the power balance while regulating the PCC bus voltage within acceptable range in both grid-connected and islanded operation.;The high variability and uncertainty of renewable energies introduces unexpected fast power variation and hence the operation conditions continuously change in distribution networks. A three-layers advanced optimization and intelligent control algorithm for a microgrid with multiple renewable resources is proposed. A Dual Heuristic Programming (DHP) based system control layer is used to ensure the dynamic reliability and voltage stability of the entire microgrid as the system operation condition changes. A local layer maximizes the capability of the Photovoltaic (PV), wind power generators and battery systems, and a Model Predictive Control (MPC) based device layer increases the tracking accuracy of the converter control. The detail design of the proposed SWAPSC scheme are presented and tested on an IEEE 13 node feeder with a PV farm, a wind farm and two battery-based energy storage systems

STATCOM Control for Integration of Wind Farm to the Weak Grid

This paper focuses on the STATCOM modeling and nonlinear controller design for fast voltage regulation during the grid disturbance when the wind farm is integrated to a weak grid. A sliding mode inverse controller for the STATCOM connected at the PCC of the wind farm is proposed. It utilizes the inverse system theory to form a pseudo-linear system of the STATCOM. Then the variable structure sliding mode control, with the feature of insensitivity to parameters variation, could be implemented to enhance the system robustness. The comprehensive control scheme could maintain the dc-link voltage of STATCOM and rapidly regulate the ac voltage at PCC to its reference by injecting the reactive current, so as to enhance the voltage stability of wind farm during the transient response. Simulation in PSCAD/EMTDC verified that the STATCOM with the controller proposed can reduce the voltage drop experienced by the wind farm by providing dynamic reactive power support, thus improving the fault ride-through capability of the wind farm.published_or_final_versio