Seong-Soo Park, “계통 연계형 인버터의 최적화된 LCL-필터 설계 기법,” 아주대학교 공학박사 학위 논문, 2018. > Paper

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 global warming. 

Importance of new renewable energy such as photo voltaic power, fuel cell sand 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 connects 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 Technologies) with existing power 

grids. As the photo voltaic 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 filter sat 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.