Sliding-mode and proportional-resonant based control strategy for three-phase two-leg T-type grid-connected inverters with LCL filter

In this study, sliding-mode and proportional-resonant based control strategy is proposed for three-phase two-leg T-type grid-connected inverter with LCL filter. The sliding surface function is formed by using the inverter current and capacitor voltage errors. When the inverter current and capacitor voltage feedbacks are included into the control loop, the active damping requirement is automatically resolved. The PR controllers are employed in cascaded manner to generate the references for inverter current and capacitor voltage. The use of PR controllers ensures zero steady-state error in the inverter current, capacitor voltage and grid current. In addition, since the proposed three-phase inverter has only two legs, the total switch count is reduced resulting in cheaper and reliable topology. The proposed system is validated through computer simulations which show that proposed control algorithm can achieve the control of grid currents. The total harmonic distortion level of the grid currents is in the limits of international standards

Bulanık Adaptif PI Denetimli Şebeke Etkileşimli Eviricinin Benzetimi

Bu çalışmada gerilim kaynaklı şebeke etkileşimli evirici MATLAB/Simulink'de modellenmiş ve benzetim çalışmaları gerçekleştirilmiştir. Evirici akım kontrollü olarak tasarlanmış ve evirici akımını şekillendiren anahtarlama sinyallerinin üretilmesi için bulanık-PI denetim tekniği kullanılmıştır. Şebeke etkileşimli evirici bünyesinde şebeke frekanslı transformatör ve LC çıkış filtresi bulunmaktadır. Şebeke frekanslı transformatör, şebeke ile yenilenebilir enerji kaynağı arasında elektriksel izolasyonun sağlanmasında kullanılmış ve LC filtre ile de akım dalga şeklindeki PWM anahtarlamadan kaynaklanan yüksek frekanslı bileşenler süzülmüş, çıkış akım THD'si azaltılmıştır. MATLAB/Simulink benzetim çalışmalarından elde edilen sonuçlar evirici çıkış akımının sinüsoidal dalga şeklinde ve şebeke gerilimi ile aynı faz frekansta olduğu, akım harmoniklerinin de uluslararası standartlarda belirtilen sınırlar dâhilinde olduğu görülmüştür

Simulation of Fuzzy Adaptive PI Controlled Grid Interactive Inverter

In this study, a voltage source grid interactive inverter is modeled and simulated in MATLAB/Simulink. Inverter is designed as current controlled and a fuzzy-PI current controller used for the generation of switching pattern to shape the inverter output current. The grid interactive inverter consists of a line frequency transformer and a LC type filter. Galvanic isolation between the grid and renewable energy source is obtained by the line frequency transformer and LC filter is employed to filter the high frequency harmonic components in current waveform due to PWM switching and to reduce the output current THD. Results of the MATLAB/Simulink simulation show that inverter output current is in sinusoidal waveform and in phase with line voltage, and current harmonics are in the limits of international standards

Design and analysis of a wireless power transfer system with alignment errors for electrical vehicle applications

ALTIN, Necmi/0000-0003-3294-9782; ALTIN, Necmi/0000-0003-3294-9782;WOS: 000406726000035In this study, a 15 kW wireless power transfer system with high frequency and large air gap for electrical vehicle battery charge systems is designed and co-simulations with ANSYS-Maxwell and Simplorer software are performed. The air gap between the primary and the secondary windings are determined as 20 cm for the 15 kW wireless power transfer system. Operation of the designed system for different operation conditions such as completely aligned windings (ideal condition) and windings with alignment errors, which can occur because of user error or another reason, are analyzed and obtained results are reported. The resonant frequency of the designed system which has a 60 x 60 cm secondary winding and a 60 x 100 cm primary winding is 17.702 kHz, and the maximum efficiency of the system is obtained as 75.38% for completely aligned windings. The distribution and density of the electromagnetic flux, and variation of efficiency versus load level of the system and responses of the system in case of different alignment errors are also investigated and reported for both ideal operation conditions and in case of alignment errors. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

A Combined Energy Management Algorithm for Wind Turbine/Battery Hybrid System

From an energy management standpoint, natural phenomena such as solar irradiation and wind speed are uncontrolled variables, so the correlation between the energy generated by renewable energy sources and energy demand cannot always be predicted. For this reason, energy storage systems are used to provide more efficient renewable energy systems. In these systems, energy management systems are used to control the energy storage system and establish a balance between the generated power and the power demand. In addition, especially in wind turbines, rapidly varying wind speeds cause wind power fluctuations, which threaten the power system stability, especially at high power levels. Energy storage systems are also used to mitigate the power fluctuations and sustain the power system's stability. In these systems, another controller which controls the energy storage system power to mitigate power fluctuations is required. These two controllers are different from each other. In this study, a combined energy management algorithm is proposed which can perform both as an energy control system and a power fluctuation mitigation system. The proposed controller is tested with wind energy conversion system modeled in MATLAB/Simulink. Simulation results show that the proposed controller acts as an energy management system while, at the same time, mitigating power fluctuations

Overall Efficiency Improvement of a Dual Active Bridge Converter Based on Triple Phase-Shift Control

This paper proposes a control scheme based on an optimal triple phase-shift (TPS) control for dual active bridge (DAB) DC–DC converters to achieve maximum efficiency. This is performed by analyzing, quantifying, and minimizing the total power losses, including the high-frequency transformer (HFT) and primary and secondary power modules of the DAB converter. To analyze the converter, three operating zones were defined according to low, medium, and rated power. To obtain the optimal TPS variables, two optimization techniques were utilized. In local optimization (LO), the offline particle swarm optimization (PSO) method was used, resulting in numerical optimums. This method was used for the low and medium power regions. The Lagrange multiplier (LM) was used for global optimization (GO), resulting in closed-form expressions for rated power. Detailed analyses and experimental results are given to verify the effectiveness of the proposed method. Additionally, obtained results are compared with the traditional single phase-shift (SPS) method, the optimized dual phase-shift (DPS) method, and TPS method with RMS current minimization to better highlight the performance of the proposed approach

Development of a Medium Voltage, High Power, High Frequency Four-Port Solid State Transformer

The power and voltage levels of renewable energy resources is growing with the evolution of the power electronics and switching module technologies. For that, the need for the development of a compact and highly efficient solid-state transformer is becoming a critical task in-order to integrate the current AC grid with the new renewable energy systems. The objective of this paper is to present the design, implementation, and testing of a compact multi-port solid-state transformer for microgrid integration applications. The proposed system has a four-port transformer and four converters connected to the ports. The transformer has four windings integrated on a single common core. Thus, it can integrate different renewable energy resources and energy storage systems. Each port has a rated power of 25kW, and the switching frequency is pushed to 50kHz. The ports are chosen to represent a realistic industrial microgrid model consisting of grid, energy storage system, photovoltaic system, and load. The grid port is designed to operate at 4.16kVAC corresponding to 7.2kV DC bus voltage, while the other three ports operate at 500VDC. Moreover, the grid, energy storage and photovoltaic ports are active ports with dual active bridge topologies, while the load port is a passive port with full bridge rectifier one. The proposed design is first validated with simulation results, and then the proposed transformer is implemented and tested. Experimental results show that the designed system is suitable for 4.16kVAC medium voltage grid integration

Design and loss analysis of LCL filter inductors for two-level and three-level inverters

Grid connected inverters with LCL output filters are widely used in exporting energy generated from renewable energy sources. The LCL filter and inductors used in this filter has important effect on inverter performance. Although it is different in high power levels nowadays, powder cores are commonly used in inductor design in low and medium power levels. In this study, inductors for LCL filter of the grid-connected inverter are designed. The co-simulation studies are performed and performance and losses of the designed filter is analyzed for two-level and three-level inverter topologies. It is seen that, total losses of the LCL filter of three-phase three-level inverter is 35.9% lower than two-level inverter