The paper investigates the current sharing in parallel 3-level Neutral point clamped inverter for islanded AC microgrid application. In Distributed generation, parallel power electronic interface based microgrid suffers from power quality issues due to inaccurate output current sharing. To address the current sharing problem, the paper proposes an improved droop technique that reinforces the droop loop by infusing the incurred voltage drop accountable for inaccurate current sharing at the inverter output. The control based on droop reference is bounded with regard to output current since the output impedance influences the output current of the inverter largely. Besides that, the parallel NPC inverter also suffers from dc link voltage imbalance due to neutral currents. To address these issues a control strategy is proposed in the research work in which the processed DC offset is incorporated into the reinforced droop loop and the generated reference is utilized with feedback control to accurately share the currents under linear and nonlinear load conditions. The effectiveness of devised reinforced droop strategy is realized in MATLAB/Simulink environment and experimental validation is carried out with the field-programmable gate array as hardware interface to the hardware laboratory prototype of parallel NPC inverter.

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Abstract:The action of inverters which are connected in parallel in microgrids is supported on droop process. The actual droop process comprises of rectifying the final voltage frequency and size to obtain self-standing power sharing without control wire interconnections. The actual voltage droop process reveals several drawbacks such as interior multiloop feedback control, frequency and voltage deviations. This paper intends a modern control tactic in microgrid applications by bringing down substantial flux in place of inverter final voltage. Firstly, substantial flux, active and reactive powers are mathematically obtained and a relationship is established between them which are employed to promote a modern flux droop technique. A small signal model is improved in direction to sketch the main parameters which are to be controlled and to study the steadiness as well as the system dynamics. A direct flux control step by step technique is used to adjust the substantial flux agreeing to the droop controller to evade the utility of PI controllers and PWM modulators. The simulation output shows that intended flux droop tactic can obtain reactive and active power shared by decreasing the frequency deviated than actual droop process, which spotlights influential usage in applications of microgrids.