Abstract— It is the general trend to increase the electricity production using distributed power system (DPGS), which is based on renewable energy sources such as wind, solar, fuel cell etc.These systems are to be properly controlled in order to provide reliable power to the utility network. For that power electronics converters are used as an interfacing device between DPGS and utility network. In case of unbalanced fault, the major problem in distributed power generation system is the phase unbalance which causes the power quality problem along with grid instability. This paper discuses the implementation of two different controllers namely Proportional – integral (PI) and proportional resonant (PR) controllers in order to obtain the control of grid side converter during single phase to ground fault. The analysis includes the grid current harmonic distortion along with the variation of active and reactive power during the fault condition. The system is simulated using MATLAB software and simulation results demonstrate the effectiveness of both the controller. Keywords — Distributed power generation, Grid converter control, Proportional integral controller, resonant controller, Grid fault, current harmonic distortion. I. INTRODUCTION HE global energy consumption is rising and increasing attention is paid to the alternative methods of electricity generation .The demand for renewable energy consumption is increasing about 30% per year. Due to the low environmental impact of renewable energy source, it becomes attractive for the growing demand. Distributed power generation based on renewable energy sources is experiencing a constant growth. The renewable energy source like wind, photovoltaic, fuel cell gain large acceptance, which are installed along the power system constituting the so called distributed power generation. Power electronics plays an important role in converting the input power which is suitable delivered to the utility network. Introduction of power electronics for DPGS has several advantages such as energy optimal operation by applying 978-1-4577-1510-5/11/$26.00©2011IEEE a control algorithm to extract the maximum available power along with load control, noise reduction, improve power quality and controllable active and reactive power. Power electronics converters are working as interface for easier and flexible grid interconnection. In order to meet the utility network requirement, the power electronics converters are to be controlled during normal and faulty grid condition. The power electronics converter used here is a PWM driven voltage source inverter. The power converter plays an important role in delivering reliable power to the utility network. [1]-[3]. In case of unbalanced grid fault, the major problem in distributed power generation system is the phase unbalance causes the power quality problem along with grid instability. This paper discusses the implementation of two different controllers namely Proportional-Integral (PI) and Proportional Resonant (PR) controllers for grid side converter during single phase to ground fault conditions. The analysis includes the grid current harmonic distortion along with the variation of active and reactive power during the fault condition. The system is simulated using MATLAB software and simulation results demonstrate the effectiveness of both the controllers. II. DPGS STRUCTURE A general structure of distributed generation system is illustrated in fig.1. The input power which is generated from the renewable energy sources is transformed into electricity and delivered to the utility network or to the local load. The system consists of two converters namely input side converter and grid side converter along with input side controller and grid side controller. The major function of input side controller is to extract maximum power from the renewable source and to transmit it to grid side controller. In the event of fault the input side controller also protects the input source. The function of grid side converter is to control the active power generated and the reactive power transfer between DPGS and grid. It also controls the dc-link voltage to ensure high quality of the generated power. One of the important functions of grid side controller is grid synchronization i.e. to synchronize the delivered power with the power system. Grid monitoring is a useful tool for distributed generation system to Analysis of PI and PR Controllers for Distributed Power Generation System under Unbalanced Grid Faults Ashish ranjan Dash, B.Chitti Babu, Memeber, IEEE, K.B.Mohanty, Senior Member, IEEE and Rahul Dubey Department of Electrical Engineering, National Institute of Technology, Rourkela-769008, (ORISSA) E-mail: ashishdashnitrkl@gmail.com, bcbabunitrkl@gmail.com, kbm@nitrkl.ac.in rahul.dubey2011@gmail.com. T