Three phase inverter with droop control

Abstract

Due to the recent increase in the number of distributed energy resources (DERs) installed to the main grid, the concept of microgrids is becoming more popular. The aim of the microgrid is to integrate these DERs into a single subsystem such that they operate at their maximum efficiency. In order to connect these distributed generations to the microgrid, a number of power electronic converters are required. Since most modern equipment operates using alternating current, one of the most common converters is the inverter. An example of a popular inverter application is within solar panels, since these convert direct current into alternating current signals. This dissertation focuses on the study of a droop controlled three phase inverter within an AC microgrid. The project was divided into three stages. Primarily, the system modelling was designed. Various simulations were then carried out in order to verify the design. These simulations investigated the three phase inverter switching, the output waveforms with and without LCL filter, the nested current and voltage control loops implemented using vector control and lastly the primary control loop using the droop technique. The second stage encompassed the design of the hardware interface for the three phase inverter. This included the LCL filter, multiple sensing boards, a gate drive interface board and a signal conditioning with protection board. The final stage subsequently consisted of sensor calibration and protection tests which were carried out in order to ensure the correct operation of the hardware interface. A digital signal controller was used to apply the appropriate three phase inverter switching and test the system. The nested current and voltage control loops were also implemented on hardware. The results show that readings from both the simulation design and experimental setup were close to the theoretical values. Correct dynamic response of controllers resulted in the desired output waveforms with zero steady state errors.