A Study on the Multi-level PV-PCS Using Cascade 3-Phase Transformer Kim, Ki-Seon ; Song, Sung-Geun ; Cho, Su-Eog ; Choi, Joon-Ho ; Kim, Kwang-Heon ; Park, Sung-Jun ;

A Study on the Multi-level PV-PCS Using Cascade 3-Phase Transformer
Kim, Ki-Seon ; Song, Sung-Geun ; Cho, Su-Eog ; Choi, Joon-Ho ; Kim, Kwang-Heon ; Park, Sung-Jun ;


Abstract
The study on the multi-level inverter has been increasingly progressing to reduce the switching loss and improve the THD of output current in photovoltaic inverter. Recently, the main topics of multi-level inverter are to reduce the number of devices maintaining the power quality. Therefore, the novel topology was proposed for these problem which is composed of the isolated H-bridge multi-level inverter using the three phase low frequency transformer. The proposed multi-level inverter may not be need for a independent DC power, diode and capacitor. Specially, It has a advantage in generating high voltage source. The proposed approach is verified through simulation and experiment.

LINK1
http://www.koreascience.or.kr/article/ArticleFullRecord.jsp?cn=DHJGII_2009_v58n12_2359

High power grid-connected PV PCS with power quality improvement and stand-alone operation KIM,JAE HYUNG GRADUATE SCHOOL SUNGKYUNKWAN UNIVERSITY PHOTOVOLTAIC SYSTEM ENGINEERING

High power grid-connected PV PCS with power quality improvement and stand-alone operation
KIM,JAE HYUNG
GRADUATE SCHOOL SUNGKYUNKWAN UNIVERSITY PHOTOVOLTAIC SYSTEM ENGINEERING

ABSTRACT

With the increase of power consumption, the limitation of fossil fuel and global warming, as power generation systems become superannuated, every country has faced several sorts of energy problems. Moreover, since power consumption has increased, not only reserve margin is decreased but also more power plants are required. However, the construction of power plants is restricted since those power facilities are closely related with environmental problems. Consequently, since the use of sensitive loads such as the latest IT products is increased, power quality issue is being magnified as a new controversy. In this research, the power quality improvement function applied to three-phase four-wire H-bridge type photovoltaic power generation system is proposed. When the photovoltaic power generation system is operated in grid-connected mode, grid current distorted by unbalanced load is improved, and the system is operated in stand-alone mode during power failure. Moreover, when the amount of solar radiation is low such as night time, the system is operated as a active power filter and improve the performance of the photovoltaic power generation system. The series dual loop with quasi-resonant proportional controller and 2ndorder deadbeat controller is applied to the system as a controller. Single phase PLL with phase synchronizing function, Goertzel stand-alone detection function with minimized non-detection area and Goertzel power quality control function are proposed. In order to verify the validity of the system performance, simulation and experiment with 100kw H-bridge type three-phase inverter are progressed.

A Study on Improving Efficiency of High-frequency Switching Hybrid Inverter Circuit in Grid-connected Photovoltaic Power Generation Heo, Chan-Yoo Department of Electrical Engineering Graduate School Soongsil University

ABSTRACT
A Study on Improving Efficiency of High-frequency Switching Hybrid Inverter Circuit in Grid-connected Photovoltaic Power Generation Heo, Chan-Yoo Department of Electrical Engineering Graduate School Soongsil University
Supervised by Professor Jeon, Hee-Jong
 The various problems of Energy pluralism by new and renewable energy technique development is in progress mainly from advanced countries due to recent global warming by environmental change and fossil energy resources depletion. And major area of fuel cell, photovoltaic and wind power generation are actively in progress from many types of new and renewable energy. Photovoltaic power system stores the direct current resource generated from photovoltaic module into battery, and converts this into alternating current to use. Photovoltaic power generation uses solar for its energy resource, which does not need fuel, and the equipment has long life since it has no moving parts or heat engine. Also, it is more convenient in operation and maintenance than other existing power generation methods. But, it has higher unit cost than existing power generating methods, and need wide area to install solar cell module to use certain amount of electric power since its energy density is scarce. In addition, it has weak point of close influence by environmental condition such as weather condition. All sections of the photovoltaic power system from raw material to the grid connection are important, but the photovoltaic power inverter, which relates the stable power to the grid or can supply powerto individual load, can be regarded as one of the most important section. The generated power is of no use if the inverter does not make regular output even though a lot of power is generated from the photovoltaic array. The criteria for evaluating the photovoltaic inverter's performance is the power conversion efficiency of the inverter. For domestic photovoltaic power system, the booster converter's efficiency is around 99[%], the inverter efficiency is around 94[%], and studies are in progress to improve inverter efficiency. The Grid connected inverters in photovoltaic PCS(Power Conditioning System) have different efficiency according to their switching methods. 3 Level PWM switching type circuit has half the frequency than the circuit composed of 2 Level PWM, and has improved efficiency because of less switching loss. In general, photovoltaic PCS mainly use IGBT components. But the hybrid circuit composed of MOSFET and IGBT components is considered to improve efficiency even more by improving reverse recovery time and loss by IGBT's tailing current. In this paper, it is intended to prove that the high-frequency switching inverter circuit with MOSFET has improved efficiency than 3 Level circuit with all IGBT components through simulation and 3[kW] PCS hardware.

Non-isolated Single Phase Uninterruptible Power Supply (UPS) System Muhammad Aamir Department of Electronics, Electrical, Control, and Instrumentation Engineering Hanyang University

ABSTRACT
In this thesis, a high performance single phase transformer-less online uninterruptible power supply (UPS) is proposed. The use of the bidirectional buck-boost converter with high conversion ratio not only reduces the number of batteries but also ensures a transformer-less system. The rectifier has capability of power factor correction and provides regulated DC link voltage whereas the inverter provides a regulated sinusoidal output voltage to the load. In order to control the transient effect, efficient control scheme is adopted in the system. The overall efficiency of the system is improved with significant reduction in size and weight of the system due to decrease number of batteries. Qualitative analysis and experimental results obtained with a 500VA prototype shows a normal efficiency of over 94% and an input power factor of over 99%.
LINK
https://copy.com/GDccLCWhNLzUqDJ0

Filtering Methods for DC Link Voltage Control of Common-neutral-type Transformerless Single-phase UPS KIM JI-SU DEPARTAMENT OF ELECTRICAL ENGINEERING GRADUATE SCHOOL KONKUK UNIVERSITY

ABSTRACT

UPS is largely divided into passive-standby, line-interactive, and double-conversion types. Commonly a double-conversion type is used at a site requiring a high reliability. These days, important factors of UPS are high efficiency, low input current distortion, high input power factor, small cabinet size and low price. In this thesis, a common-neutral type transformerless UPS is proposed. A proposed UPS is composed of PFC with 1-switch voltage doubler strategy, half-bridge inverter, separate battery charger and separate battery discharger. PFC with 1-switch voltage doubler strategy and half-bridge inverter are configured as commom-neutral type so that they can convert power without input and output transformer. Therefore input and output transformers can be removed, so the efficiency can be improved and cabinet size can be reduced. Also advantage of PFC with 1-switch voltage doubler strategy and half-bridge inverter is that they need a small number of switching devices so they can simplify driving circuitry and reduce the price. Advantage of separate battery charger and separate battery discharger is that they can make battery voltage lower than DC link voltage so they can reduce the quantity and cost of battery which is an important part of UPS. PI controller was used as voltage controller and current controller of PFC. In order to compensate imbalance of positive and negative DC link voltages, imbalance voltage PI controller was used. In order to compensate leading effect of input current, duty feedforward method was used. Several methods to eliminate 120Hz ripple component in DC voltage feedback were compared with each other. Moving Average resulted in better performance than other methods. Half-bridge was used as inverter circuit. In order to achieve stable static output voltage and improve dynamic characteristic multi-loop control method was used. Finally, the value of proposed UPS was confirmed in the method of simulation and experiment.