An Analytical Design Approach for Inverter Output Impedance in Parallel Operation of Micro Source Inverters

This paper proposes an analytical framework to design an inverter output impedance in microgrid applications to meet the requirements of proportional load sharing and low total harmonic distortion in the output voltage. In the proposed work, an integral controller is designed in order to make the overall impedance of an inverter to be capacitive in nature. The optimum design of overall capacitive impedance at the harmonic frequencies ensures low THD levels in the output voltage without affecting proportional load sharing, which is determined by an inverter impedance at fundamental frequency component. The output impedance design decouples to meet different requirements at the same time. The focus is also laid on inherent limitations of conventional droop control of inverters and its remedial measures through bolting regulator on its control loop. A multilevel VRI topology is proposed and its parameters/coefficients are optimized. Small signal stability analysis is performed to ensure steady state stable operation. The load voltage THD is evaluated through FFT tool for parallelly operated C inverters feeding a nonlinear load to prove the effectiveness of the proposed design through time domain simulations.