1426 PIERS Proceedings, Marrakesh, MOROCCO, March 20–23, 2011 Comparison of Different Filter Types for Grid Connected Inverter Jiri Lettl, Jan Bauer, and Libor Linhart Department of Electric Drives and Traction, Faculty of Electrical Engineering Czech Technical University in Prague, Technicka 2, 166 27 Prague 6, Czech Republic Abstract— The acquisition of the electrical energy from renewable sources is very trendy in these days. That is also why the applications for renewable energy generation undergo rapid development. As the greatest weakness of renewable sources can be assumed the instability and dependence of energy amount, that they deliver. In order to stabilize the energy output and to give it some defined shape and value, the power converter must be connected to the output of the solar panel. For this purpose of application is the most suitable choice voltage source inverter (VSI). In order to suppress or reduce negative effects the filter is connected between the converter and the network. The filter must be designed precisely, because it must have sufficient attenuation at the inverter’s switching frequency and it must not bring oscillations to the whole system. This paper deals with design and simulation of such a filter type. Simulation models of the systems inverter-filter were made. 1. INTRODUCTION The amount of the energy from renewable energy sources, as solar energy or wind turbine energy, that is delivered to supply network, significantly rises. That is why the grid friendly interface between the supply grid and the energy source is needed. The quality of generated energy is crucial, because non-sinusoidal currents delivered to the grid can cause additional non-sinusoidal voltage drop across the line impedances and therefore increase of the voltage distortions delivered to the load. Next problem is that the energy supplied by these sources does not have constant value, but fluctuates according to the surrounding conditions (intensity of sun rays, water flow, etc.). These sources are supplemented by additional converters as voltage source inverters (VSI). This converter is then controlled by a modern sophisticated control algorithm such as PWM which ensures nearly sinusoidal current generation. This solution is illustrated in Fig. 1. The power from some renewable energy source is delivered to the DC-link and the output of the inverter is filtered in order to obtain low current distortion. 2. FILTER TOPOLOGIES The output filter reduces the harmonics in generated current caused by semiconductor switching. There are several types of filters. The simplest variant is filter inductor connected to the inverter’s output. But also combinations with capacitors like LC or LCL can be used. These possible topologies are shown in Fig. 2. Inverter C 1 DC link L i Lg Cf R sd S 1 S 2 S 4 S 3 L-C-L filter UCf UDC Controller I o ICf S O L A R A R R A Y D I S T R I B U T I O N N E T W O R K Figure 1: Block diagram of the VSI.