Abstract
In the power system, the filter is often used to eliminate harmonics or noise. There are many types of filters, such as L filters, LC filters, and LCL filters. We use LCL filter to effectively eliminate harmonics, but its disadvantage is that the control would be more complicated. Usually, we use the single-chip like DSP to achieve our control to our system. However, it may result in a time delay because of the signal sampling and conversion, which would deteriorate the power quality. In order to solve the situation, we can use observer into our control loop. It can not only reduce the number of sensors, but also improve the quality of electricity and system instability caused by a time delay. In this thesis we use Simulink to construct a single-phase converter which is connected to a grid via an LCL filter. We also simulated the situation that the time delay of the signal occurs, and then put the observer into our control loop. We can check that whether the unstable waveform caused by time delay can be improved when the observer is used.