Full Converter Research Articles

Performance Analysis of Self-Consumed Solar PV System for A Fully DC Residential House

<p>Malaysia is moving forward by promoting used of renewable energy such as solar PV to the public where it is generated at the distribution voltage level. The fluctuation of fuel prices becomes main concern to the consumers since it affecting the electricity tariff. The objective of this project is to design a self-consumed DC power system for a residential house from renewable energy resource which is solar PV that it will independent from the utility grid. The methodology proposed are configuring daily load demand, sizing PV array and battery bank and simulation of the design system by using PVsyst. Based on solar energy resource, the optimum PV array size is 2.0 kWp while the battery bank size is 700 Ah at 48 V which is designated for 4 days of autonomy. The system could meet 100% of load demand throughout the year with 67.9% of performance ratio. The loss to the system is contributed by the temperature effect to the PV module, unused energy because of battery full capacity, converter and battery efficiencies. Using this concept, the proposed design set-up is expected to benefit the residential consumers in reducing utility electricity consumption up to 2,434 kWh per year and avoiding 1.7 tons of carbon emissions into the environment annually.</p>

Virtual Synchronous Generator Control of Full Converter Wind Turbines With Short-Term Energy Storage

One way to incorporate the increasing amount of wind penetration is to control wind turbines to emulate the behavior of conventional synchronous generators. However, the energy balance is the main issue for the wind turbines to be truly dispatchable by the power system operator such as the generators. This paper presents a comprehensive virtual generator control method for the full converter wind turbine, with a minute-level energy storage in the dc link as the energy buffer. The voltage closed-loop virtual synchronous generator control of the wind turbine allows it to work under both grid-connected and stand-alone condition. Power balance of the wind turbine system is achieved by controlling the rotor speed of the turbine according to the loading condition. With the proposed control, the wind turbine system can enhance the dynamic response, and can be dispatched and regulated by the system operator. The sizing design of the short term energy storage is also discussed in this paper. Experimental results are presented to demonstrate the feasibility and effectiveness of the proposed control method.

ZVS Full Bridge Series Resonant Boost Converter with Series-Connected Transformer

This paper presents a study on a new full bridge series resonant converter (SRC) with wide zero voltage switching (ZVS) range, and higher output voltage. The high frequency transformer is connected in series with the LC series resonant tank. The tank inductance is therefore increased; all switches having the ability to turn on at ZVS, with lower switching frequency than the LC tank resonant frequency. Moreover, the step-up high frequency (HF) transformer design steps are introduced in order to increase the output voltage to overcome the gain limitation of the conventional SRC. Compared to the conventional SRC, the proposed converter has higher energy conversion, able to increase the ZVS range by 36%, and provide much higher output power. Finally, the a laboratory prototypes of the both converters with the same resonant tank parameters and input voltage are examined based on 1 and 2.2 kW power respectively, for veryfing the reliability of the performance and the operation principles of both converters.

Wind Farms Integration in Power System and Frequency Regulation Effects

This paper presents a method for Wind Farms future projects analysis, and integration percentage deduction in Weak Power Systems. In weak power systems, Wind Farms produces two effects: a decreasing primary frequency regulation and power systems global inertia reduction. Wind Farms have no obligations in primary frequency regulation. New Technologies applied in wind farms are Full Converter, which means without rotating masses. These two effects produce a power systems rehabilitee reduction. In this article, a method for weak power systems stability analysis, considering Wind Farms, is proposed. Power flow tool is also applied according to verify transmission system capacity y sufficiency. The proposed method have been validated using a real power system of Bolivia; and analysis of obtained results shows suitable agreement with other analysis performed in power systems of countries of Latino America (LA).

Understanding the Origin of Oscillatory Phenomena Observed Between Wind Farms and HVdc Systems

Field experience has shown that subsynchronous oscillation and harmonic resonance can occur between wind farms (WFs) and high voltage dc (HVdc) systems. The oscillations can appear in the presence of background harmonics due to the interaction between the wind energy conversion system's (WECS's) converter controller, HVdc converter controller, and the impact of the interconnection system impedance. However, the root causes of these oscillations observed in the field are not entirely understood and they can be attributed to various sources within the components and controllers of the interconnected system. This paper explores the possible causes of these oscillations by investigating the impact of controllers and components in the WF and in the voltage-source converter (VSC)-based HVdc transmission system. In order to understand this phenomenon, the impedance of both the WF and the HVdc from the offshore ac collection point is analytically derived to identify potential resonance points. The impedance frequency responses of the WF and the HVdc converter indicate the potential resonance at low frequency. The origin of these oscillations can be attributed to the propagation of the WECS resonance through the WECS full converter dc link and the interaction between the WECS and the HVdc system. Once the source and the load impedance are identified, an impedance-based stability method is adopted in order to determine the stability. In an attempt to improve the oscillatory phenomena, an active damping scheme is implemented on the offshore HVdc rectifier. An analysis and time-domain simulation results with its respective harmonic spectra show that the implemented active damping is very effective in eliminating the oscillations observed in the interconnected system. Moreover, this paper presents the role of the ratio between the bandwidths of the interconnected areas, as having an essential role in the root cause of the instability. The general rule is observed that when the bandwidth of the HVdc rectifier (which is the source) is faster than the bandwidth of the load (WFs inverter); the system operates stably.

Harmonics Reduction in a Wind Energy Conversion System with a Permanent Magnet Synchronous Generator

This paper is mainly doing simulation using Matlab to filter harmonics which are found in a Permanent Magnet Synchronous Generator (PMSG) Wind Energy Conversion System (WECS) connected to a three-phase load through a full converter (AC/DC/AC). Harmonics are caused by the converter system. To reduce these harmonics, an effective filter is needed. There are two types of filters that are usually used, active and passive filters. Among the types of passive filters are band pass which block lower harmonics orders such as 5^th, 7^th, 11^th, and 13^th, and high pass filters which are responsible to filter higher harmonics such as 24^th. So, we use two stages of harmonic filtering. The first stage includes a c- type high pass filter (for lower orders), a double – tuned filter (for 11^th and 13^th) and high pass filter (for higher orders). Secondly, this stage includes a single – tuned filter instead of C- type filter with keeping the other filters. We applied Fast Fourier Transform (FFT) to determine the harmonics and purposes. In this thesis, we investigate and analyse the level of harmonic content of two AC/DC converters working at different wind speeds. Our findings indicate significant improvements in Total Harmonic Distortion (THD) with best results in the second method.

Robust Vector Control of a Very Weak-Grid-Connected Voltage-Source Converter Considering the Phase-Locked Loop Dynamics

Conventional vector-controlled voltage-source converters (VSC) suffer from stability and performance problems when integrated into very weak ac grids (high-impedance grids). This is attributed to the increased coupling between the converter and grid dynamics, via the phase-locked loop (PLL), at the very weak-grid condition. In the current literature, the impact of the PLL is usually ignored when the converter controllers are designed. While this approach can be accepted under stiff grid conditions, it yields unmodeled dynamics that destabilize the converter under weak-grid conditions and high-power injection levels. To overcome this limitation, this paper presents a robust vector-controlled VSC that facilitates full converter power injection at weak and very weak-grid conditions (i.e., when the short-circuit capacity ratio is one). To realize the controller, first, a detailed dynamic model for the ac-bus voltage dynamics, including the PLL dynamics, is developed and validated in this paper. Second, the model is used to optimally design a robust ac-bus voltage controller to stabilize the dynamics under operating point variation and grid impedance uncertainty. Because the developed model includes the PLL dynamics, the developed controller inherently stabilizes the negative impact of the PLL on the converter stability. A theoretical analysis and comparative simulation and experimental results are provided to show the effectiveness of the proposed controller.

Design and Implementation of Space Vector Modulation-Based Sliding Mode Control for Grid-Connected 3L-NPC Inverter

This paper presents a closed-loop space vector modulation (SVM)-based sliding mode controller (SMC) for a three-level grid-connected neutral point clamped (3L-NPC) inverter. The nonlinear SMC based on Gao's reaching law has been designed to control the grid current and inject desired amount of active and reactive power into the network. Due to using single dc source at the NPC inverter dc bus, neutral point voltage is controlled through redundant switching states and instantaneous dc voltage feedback integrated into SVM technique. Meanwhile, there is no external voltage controller involved, thus no associated fine tuning issues are existed. The performance of the proposed hybrid controller to inject a desired active/reactive power to the grid is investigated through external perturbations such as change in the line current amplitude/phase shift, ac voltage fluctuation, as well as dc voltage variation. Full converter state-space model was developed and simulated. Experimental results are provided to verify the fast dynamic performance, low content of line current THD%, and good voltage balancing of dc bus capacitors of the NPC inverter.

A Framework to Analyze the Stochastic Harmonics and Resonance of Wind Energy Grid Interconnection

This paper addresses a modeling and analysis methodology for investigating the stochastic harmonics and resonance concerns of wind power plants (WPPs). Wideband harmonics from modern wind turbines (WTs) are observed to be stochastic, associated with real power production, and they may adversely interact with the grid impedance and cause unexpected harmonic resonance, if not comprehensively addressed in the planning and commissioning of the WPPs. These issues should become more critical as wind penetration levels increase. We thus propose a planning study framework comprising the following functional steps: First, the best fitted probability density functions (PDFs) of the harmonic components of interest in the frequency domain are determined. In operations planning, maximum likelihood estimations (MLEs) followed by a chi-square test are used once field measurements or manufacturers’ data are available. Second, harmonic currents from the WPP are represented by randomly-generating harmonic components based on their PDFs (frequency spectrum) and then synthesized for time domain simulations via inverse Fourier transform. Finally, we conduct a comprehensive assessment by including the impacts of feeder configurations, harmonic filters and the variability of parameters. We demonstrate the efficacy of the proposed study approach for a 100-MW offshore WPP consisting of 20 units of 5-MW full converter turbines, a realistic benchmark system adapted from a WPP under development in Korea and discuss lessons learned through this research.

Stability assessment for transmission systems with large utility‐scale photovoltaic units

Photovoltaic (PV) systems are gradually replacing conventional synchronous generators. However, reduced system inertia and lack of dynamic grid support from PV are the main issues that could have a detrimental impact on the transient response in power systems when critical contingencies arise. In this study, the authors modelled and analysed transient and small-signal stability for a representative transmission system with realistic loading scenarios and high PV penetration levels. First, system eigenvalues were calculated to identify critical modes. Thereafter, the results of the small-signal analysis were further expanded by performing transient simulations after critical contingencies. Such contingencies detrimentally excited the critical modes of the system. To carry out this analysis, they implemented a positive-sequence dynamic model of a utility-scale PV unit (USPVU) in the open programming environment MATLAB/Simulink. This dynamic model is based on a Western Electricity Coordinating Council (WECC) generic model (full converter model), which is suitable for electromechanical transient studies. Also included was the model of the PV array, dc-dc converter, and associated control systems. The most critical factors pertaining to the detrimental or beneficial impact of USPVUs on stability were the unit commitment and dispatch strategy and the protection/control strategy during voltage swell and dip events for equivalent PV penetration and loading scenarios.

Full converter based wind turbine generator system generic modelling: Variations and applicability

Wind energy system integration can lead to adverse effects on modern electric grid so it is imperative to assess their dynamic performance before actual plant startup. Transmission system operators all over the world stress the need for a proper wind turbine generator model for dynamic performance as well as ancillary service assessments. Due to the bulk power system assessment requirements, development of suitable generic modeling has gained high priority. Generic modeling of type 4 full converter wind turbine generator system for application in frequency ancillary service investigations under varying wind speed and varying reference power has been presented in this study. Prevalent generic model, manufacturer specific proprietary generic model along with detailed wind turbine model with synchronous generator is also provided to highlight various modelling framework difference. Descriptions of individual sub models of proposed generic model are presented in detail and performance results are compared and validated with GE’s proprietary generic model and detailed WTG model by means of simulations in the MATLAB® Power System Block set.

Designation and Investigate of a Full-Wave Controller Rectifier (FWCR) for Effect Source Inductance for Full Wave Rectifier

The full wave rectifier with RL load consists of all the SCRs as controlled devices. This full wave converter can operate in quadrants and output voltage can be negative in case of inductive loads. The power factor is poorer than a half converter, as the full bridge converter is primarily used to control the DC motor speed [1].The purpose of this paper is to solve higher ripper power supply in a full wave controlled rectifier using an RL load of 240rms voltage, 50Hz with an attached source inductance, Ls of 10mH value. The average output voltage can be varied from 100–200VDC. The performance of a full wave rectifier with source inductance is to create conduction of four thyristor simultaneously with overlapping angle. The result obtained is with an efficiency of 50.18% at output RL Load.

Design of Full Bridge Buck Converter with a Fly back Snubber for High Power Applications

Design of Full Bridge Buck Converter with a Fly back Snubber for High Power Applications

Critical Clearing Time and Wind Power in Small Isolated Power Systems Considering Inertia Emulation

The stability and security of small and isolated power systems can be compromised when large amounts of wind power enter them. Wind power integration depends on such factors as power generation capacity, conventional generation technology or grid topology. Another issue that can be considered is critical clearing time (CCT). In this paper, wind power and CCT are studied in a small isolated power system. Two types of wind turbines are considered: a squirrel cage induction generator (SCIG) and a full converter. Moreover, the full converter wind turbine’s inertia emulation capability is considered, and its impact on CCT is discussed. Voltage is taken into account because of its importance in power systems of this kind. The study focuses on the small, isolated Lanzarote-Fuerteventura power system, which is expected to be in operation by 2020.

Near-Optimal Algorithm for Group Scheduling in OBS Networks

Group scheduling is an operation whereby control packets arriving in a time slot schedule their bursts simultaneously. Normally, those bursts that are of the same wavelength are scheduled on the same channel. In cases where the support of full wavelength converters is available, such scheduling can be performed on multiple channels for those bursts that are of an arbitrary wavelength. This paper presents a new algorithm for group scheduling on multiple channels. In our approach, to reach a near-optimal schedule, a maximum-weight clique needs to be determined; thus, we propose an additional algorithm for this purpose. Analysis and simulation results indicate that an optimal schedule is almost attainable, while the complexity of computation and that of implementation are reduced.

Potential Evaluation of Hybrid Wind-Diesel System Island Area in Thailand

Some communities in Thailand located on Island with high wind velocities but an unreliable utility supply, will typically install diesel powered generators and wind generators to form a microgrid. Microgrid projects have been developed in many parts of the world, and commercial solutions have started to appear. Such systems face specific design issues, especially when the wind penetration is high enough to affect the operation of the diesel plant. The dynamic behavior of a medium penetration hybrid microgrid is investigated. It consists of a diesel generator set, a wind power generator and several loads. The diesel engine drives a 3x2,000 kW synchronous generator with excitation control. The wind turbine drives a 6x800 kW (full power converter) synchronous generator. The total load of the microgrid is about 4 MW which varies during the day. The excitation controller and speed controller for the diesel’s synchronous generator are designed, as well as the power control of the wind turbine. The system is modeled and simulated using software DIgSILENT PowerFactory. The study evaluates how the power generation is shared between the diesel generator set and the wind generator, the voltage regulation during load connections, and discusses the need of battery energy storage, the system ride-through-fault capability and frequency control. The results of several case studies are presented. The results have shown that the systems are stable under various ratio of PWIND / PLOAD from 10% to 100%, except ratio of PWIND / PLOAD from 110%.

Teaching Sustainable Energy and Power Electronics to Engineering Students in a Laboratory Environment Using Industry-Standard Tools

Power electronics and renewable energy are two important topics for today's power engineering students. In many cases, the two topics are inextricably intertwined. As the renewable energy sector grows, the need for engineers qualified to design such systems grows as well. In order to train such engineers, new courses are needed that highlight the unique engineering challenges presented by renewable energy systems. This paper presents the theory, implementation, and assessment of a new laboratory course designed to teach power electronics and renewable energy to engineering students. A key element of the course is the use of real renewable energy systems in the laboratory setting. Students design, test, and troubleshoot power electronic circuits (such as dc/dc converters and pulse-width-modulated inverters) with tools used widely in industry (such as MATLAB/Simulink and dSPACE digital signal processors). Ten unique experiments are presented, as well as detailed descriptions of two open-ended design projects: a maximum power point tracker for a photovoltaic array and a full converter for a permanent-magnet wind turbine. Results from students' work on the experiments and final projects, as well as an assessment of the effectiveness of the course based on pre- and post-testing, are also presented.

Estimation of the wind turbine yaw error by support vector machines

Wind turbine yaw error information is of high importance in controlling wind turbine power and structural load. Normally used wind vanes are imprecise. In this work, the estimation of yaw error in wind turbines is studied using support vector machines for regression (SVR). As the methodology is data-based, simulated data from a high fidelity aero-elastic model is used for learning. The model simulates a variable speed horizontal-axis wind turbine composed of three blades and a full converter. Both partial load (blade angles fixed at 0 deg) and full load zones (active pitch actuators) are considered. The validation step is done under different conditions of wind shear, speed and direction, giving good estimation results.

Lab Based Analysis of Speed Control of DC Motor by Using Different Semiconductor Power Converters

The flexible control of DC motor has been donated in the extensive use of DC motor in the era of industry, as the increasing usage of semiconductor power converter units. The speed control of DC motor is very sophisticated and specific. The speed of DC motor has been controlled by controlling the armature voltage by using thyristors. The armature voltage is controlled by using the different types of AC to DC semiconductor converters such as half wave converter, semi converter and full wave converter by using thyristor-diodes. This paper shows the experimental comparative analysis of the DC motor speed control by using the different power converter topologies performed at the Quaid-E-Awam University of Engineering Sciences and Technology, Nawabshah lab.

Transient CFD model of full TWC converter

A computational fluid dynamics (CFD) model capable of simulating the cold start transients in a full three way catalytic (TWC) converter is developed by coupling flow and temperature field inside the converter with a detailed chemistry solver. In the proposed model, full TWC chemistry, including oxygen surface coverage based ceria reactions, along with coupled mass transfer is solved using axial integration outside the CFD framework, whereas flow, gas and solid phase energy equations and coverage equations are solved in the CFD framework. The proposed implementation allows direct portability of the kinetics optimized in 1D framework leading to significant reduction in chemistry development time. A CFD converter model developed using the proposed approach leads to 20% reduction in simulation time compared to conventional continuum CFD models. The coupled CFD TWC model is used to predict conversion over the first 150 s of an FTP drive cycle without smoothening the input data.