A Study on High Efficiency Bidirectional Grid-tied Converters Sung-Ho Lee Department of Electrical Engineering Pohang University of Science and Technology- SOUTH KOREA

A Study on High Efficiency Bidirectional Grid-tied Converters 
Sung-Ho Lee Department of Electrical Engineering Pohang University of Science and Technology
SOUTH KOREA
Thesis for degree of Doctor of Philosophy in the Department of Electrical Engineering.

 ABSTRACT
 This thesis presents three high efficiency grid-tied converter topologies and their respective control algorithms. These converters are applicable to various industrial fields such as energy storage systems (ESS), renewable energy systems, uninterruptible power supply (UPS) systems, and electric vehicles (EV). First, a high efficiency bidirectional grid-tied flyback converter that uses a single power conversion technique and a control system for it are introduced. The proposed converter consists of a bidirectional flyback dc-dc converter and an unfolding circuit. Due to its switching control strategy, the proposed converter performs bidirectional power conversion between the energy storage device and the grid through only single step. From the model analysis, the inherent dynamic characteristics are figured out. Based on the analysis, a control system is developed, which consists of a linear feedback controller with a low pass filter, a repetitive controller, and a feed-forward controller; this overcomes the constrains caused by a right-half-plane zero and a filter resonance and makes the proposed converter achieve the desired control performances and stability. In conclusion, the proposed converter can obtain high efficiency using a single power conversion technique, and the developed control system makes the proposed converter feasible. Second, a high efficiency single-phase bidirectional inverter for a PV energy system integrated with an energy storage system. The proposed single-phase inverter is developed using the transformerless system configuration so that it provides high power conversion efficiency, excellent power density, and low production cost. Using its circuit structure and switching operation, the proposed inverter can suppress the ground leakage current which is considered to be one of the most important design parameters in a transformerless PV system. Therefore, the proposed inverter gives the feasibility for the transforemrless system configuration in a PV energy system integrated with an energy storage system and enhances the overall performance of the bidirectional power converter system. The third is a novel high efficiency three-phase bidirectional grid-tied converter with high power density for high power applications. The proposed converter is composed of the threelevel dc-dc converter and the modified three-phase T-type three-level inverter. The threelevel converter circuit configuration gives smaller passive component size and lower switch voltage stress compared to other two-level grid-tied converters. In addition, due to its novel circuit structure, the proposed converter can use the active and passive components for only two phases of the grid in the inverter stage and eliminate the leakage current problem. Thus, because the proposed converter enables to not only decrease the number of components but also make the transformerless configuration feasible, it provides higher efficiency and higher power density compared to other high power grid-tied converters. All proposed converters are analyzed theoretically, and implemented practically to evaluate their performance. Finally, the experimental results show that the proposed converters improve overall performance such as high power conversion efficiency, power density, and production cost with satisfying the standards for the grid regulations.
LINK
https://www.mediafire.com/file/z79z7ss8hl69w07/A_Study_on_High_Efficiency_Bidirectional_Grid_tied_Converters.pdf/file

APsystems MICROINVERTER Installation Training - FULL VERSION

APsystems YC500 microinverter installation video training series: Complete Series (Parts 1-12) In A Single Video

Electronic Engineering -Circuit theory 1 -Professor Kim, Myung-Sik- Kumoh National Institute of Technology-SOUTH KOREA

Circuit theory 1 is the first major subject of electronic engineering students, and it is the basis of all courses.

POWER ELECTRONICS CIRCUITS- KIM YOUNG-ANYANG UNIVERSITY

POWER ELECTRONICS CIRCUITS- KIM YOUNG-ANYANG UNIVERSITY

LEARN ABOUT FLYBACK CONVERTER IN ISOLATED DC-DC CONVERTER WHERE TRANSFORMER ARE USED.

Modulation Techniques for Leakage Current Reduction in Transformer-less Photovoltaic Inverter Systems- Arsalan Ansari -Department of Electronic Systems Engineering Hanyang University Graduate School

Modulation Techniques for Leakage Current Reduction in Transformer-less Photovoltaic Inverter Systems 
Author : Arsalan Ansari
Thesis Supervisor: Prof. Hee-Jun Kim 
 Thesis for the degree of [Doctor of Philosophy] 
 Department of Electronic Systems Engineering Hanyang University Graduate School

 Abstract 
Energy constitutes a fundamental part in human lives. The well-being and prosperity of the globe is directly linked to energy growth. Overcoming the demand of energy is a key challenge to be solved. Keeping up with pace of energy demand, it requires unprecedented levels of investment and the purist of all economic energy sources. The energy needs are growing and conventional resources are not suitable to compete with the global requirements of energy. Therefore, the trend is to use renewable energies to compensate with the energy requirements. The renewable energies such as photovoltaic (PV) modules, fuel cells and wind turbines are of particular interest due to their tremendous advantages over conventional sources of energy. PV energy is one of the most widely used among all the other forms of renewable energies. This is due to the fact that the PV systems are relatively smaller in size, perform noiseless operation, require simple installation and the possibility to install PV systems closer to the user. The PV energy can either be used independently or can be connected to the utility grid. To connect the PV energy to the grid, the energy conversion device is necessary to convert dc voltage to the ac voltage (inverter). Previ- ously line transformer or a high frequency transformer is used with inverter to provide isolation between PV system and grid. The transformer in the system, however decreases the e ciency, increases the cost and weight and makes the system complex. Therefore, transformer-less inverters are mostly preferred in PV systems due to their high e ciency, low cost, small weight and less complexity. In this thesis a three level transformer-less inverter is used with grid in- teraction. Avoiding a transformer in such systems results in leakage current due to the direct connection between PV panel and utility grid. The high values of the leakage current may be problematic and can cause harmonics and losses in the PV system, electromagnetic interference and even electri- cal safety problems. The major causes of leakage current in transformer-less grid connected PV system are the parasitic capacitance of the PV panel and varying common mode (CM) voltage appearing across the parasitic capaci- tance of PV panel. The leakage current in transformer-less PV system can be reduced either by keeping the CM voltage constant or reducing the am- plitude and frequency of CM voltage. There are many solutions to reduce leakage current within international standards. They include the modi - cation of the inverter topology, by active or passive damping of LCL lter and by improved modulation methods. The modulation methods are most widely used in the industry because there is no need of topological modi ca- tion or extra hardware which increases the cost of the PV system. Various modulation methods to reduce the leakage current in the literature are dis- cussed brie y in this thesis. In most cases space vector based pulse width modulation (SVPWM) methods are used to solve leakage current problems, because three level in- verter has an inherent capability to produce the constant CM voltage by using particular space vectors and thereby eliminating the leakage current in the system. A new simpli ed SVPWM strategy is proposed which is easy to implement as compare to conventional three level SVPWM. The pro- posed SVPWM reduces the leakage current and maintains it within limits as enforced by international standards. The main features of the proposed SVPWM technique are; less computational burden, small leakage current and low THD of phase currents. Detailed theoretical analysis of the pro- posed modulation technique are validated by simulations and experimental demonstration shows the e ectiveness of the proposed SVPWM. A carrier based PWM is also proposed in this thesis to reduce the leak- age current of three level transformer-less PV inverter. The carrier based PWM is very simple since it requires only one carrier to synthesize the output voltage of three level inverter. Due to its carrier based nature this PWM strategy can easily be operated in over-modulation region. Apart from leakage current reduction the proposed PWM is capable of balancing the neutral point (NP) voltage of the three level inverter. Simulation and experiments are carried out for the proposed carrier based PWM to verify the e ectiveness for the leakage current reduction and NP voltage balancing. Finally the proposed PWM techniques are compared with the modula- tion techniques presented in the literature. It is found that the proposed PWM techniques not only suppress the leakage current within allowable limits as described by the international standards but have better spectral performance.
LINK THESIS
https://www.mediafire.com/file/y3c4jhrdvs68bdj/Modulation_Techniques_for_Leakage_Current_Reduction.pdf/file