Analysis, design, and experimental evaluation of power calculation in digital droop-controlled parallel microgrid inverters

Parallel operation of distributed generation is an important topic for microgrids, which can provide a highly reliableelectric supply service and good power quality to end customers when the utility is unavailable. However, there is a well-knownlimitation: the power sharing accuracy between distributed generators in a parallel operation. Frequency and voltage droop is awell-established control method for improving power sharing performance. In this method, the active and reactive power calculationsare used to adjust the frequency and amplitude of the output voltage. This paper describes the digital implementation of adroop method, and analyzes the influence of power calculation on droop method performance. According to the analysis, theperformance of droop control in a digital control system is limited by the accuracy and speed of the power calculation method. Wepropose an improved power calculation method based on p-q theory to improve the performance of the droop control method, andwe compare our new method with two traditional power calculation methods. Finally, simulation results and experimental resultsfrom a three single-phase 1-kW-inverter system are presented, which validate the performance of our proposed method