Comparing Proportional Integral and Proportional Resonant Controllers for Improvement, Control and Stability of Multilevel Inverter AC output

Summary

This work considers the replacement of Proportional Integral (PI) controllers with Proportional Resonant (PR)
controllers in the single phase grid-connected inverter and the associated control technique which is always used in the
photovoltaic power conditioning. The proportional integral controller, which had been the conventional control technique
in current controlling system, is identified to function with drawbacks such as: operational losses, harmonics and
distortions of output wave patterns, inability to track sinusoidal current in the reference frame and poor disturbance
rejection capability. Hence, the employment of the Proportional Resonant controller to replace the PI controls technique
and method. When compared with the PI controller, PR controller introduces an infinite gain at the resonant or
fundamental frequency thereby achieving zero steady state error, reduced distortions and improved sinusoidal shaped
output AC wave. An analysis of the PI controller and PR controller is theoretically presented and verified using MATLAB
simulation. Also, pseudo-synchronous d-q and α-β conversions are differently utilized in the current control scheme and
an all pass filter based single phase digital phase-locked loop (PLL) is introduced to identify the phase of the grid voltage,
after which an optimization technique is applied for the enhancement of the current output waveforms. Based on this
theoretical analysis, the control system is implemented and was tested in a 100KW model. Simulation and experimental
verifications proved the high performance and better implementation of the PR controller when compared with the PI
controller current control system.

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