계통 연계형 인버터의 최적화된 LCL-필터 설계 기법- Optimization Design Method for LCL-filter in Grid-connected Inverter Systems -AUTHOR Seong Soo Park -Department of Space Survey Information Technology Ajou University--Dissertation for doctoral degree in engineering

 Optimization Design Method for LCL-filter in Grid-connected Inverter Systems

ABSTRACT 

Autrhor Seong Soo Park -Department of Space Survey Information Technology Ajou University

 Dissertation for doctoral degree in engineering 

This study proposes an optimized design method of LCL filter in grid connected inverter system using various pulse width modulation (PWM) methods. Recently, many contries around the world are implementing low carbon policies to prevent glob al warming. Importance of new renewable energy such as photovoltaic power , fuel cells and wind power generation is coming to the fore significantly . And also many countries are interested in the development of smart grid technology because it is necessary to develop a technology which connect s distributed power sources to power systems in order to introduce renewable energy. The Smart Grid means operating an effective power network by combining ICT (Information and Communication Te chnologies) with existing power grids. As the photovoltaic power generation and fuel cell power generation are DC power generation units , they are used in conjunction with the power grid like as electrical power system with converting DC to AC using inverter The harmonics is caused by switching control of the inverter and these harmonic components should be compiled with standard of IEEE (IEEE 519, IEEE 1547.2) and also THD (Total Harmonics Distortion) of output current should be limited to within 5 % based on this standard . For this reason, it is necessary to reduce harmonics by using filters at input and output sides of the inverter. In the past, L filter was used mainly , but drawback is increasing volume and weakness of dynamic characteristic as L filter capacity is increased. Therefore, recently LC filter or LCL filter are mainly used and various studies in terms of the filter design are under progressing. LCL filter has a combined structure with L filter and LC filter of inverter and has same characteristics with the third order low pass filter, furthermore same level of harmonics can be reduced with using only small capacity compared with L filter. However, there are some disadvantages that design is complicated and unwilling resonance might be happened. This paper proposes on optimized design method of the LCL filter based on the inverter topologies and switching methods. There is no different of design value from others in the low range of voltage modulating factor but the higher tolerance is happened, the bigger voltage modulating factor is incresead, This paper shows optimized design method related to this improvements. The simulations are carried out to verify the effectiveness of the proposed methods: 3 phase 2 level, 3 level topologies and SVPWM, DPWM switching methods for the grid connected inverter. Moreover, 3kW experimental setups are used to identify the feasibility of their methods.

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