Abstract
Voltage source inverter (VSI) is a good candidate for grid forming microgrid because it provides constant amplitude, frequency, and sinusoidal shape voltage at point of common coupling (PCC). As the microgrid is separated from utility grid, voltage quality of the PCC is easily affected by the type of load. To ensure power quality in grid operation, a three-phase VSI providing automatic voltage compensation for unbalanced or nonlinear load is presented in this paper. To maintain voltage quality at a certain level, the Fast Fourier Transform (FFT) algorithm is embedded in a proportional-resonant (PR) controller to mitigate the total harmonic distortion (THD) at PCC. In the meantime, any change of voltage magnitude that is caused by the unbalanced load could be reduced as well. To further enhance the transient response with the change of load, a predictive current (PC) controller is integrated into the PR controller. All the control strategies are implemented by digital approach. The effectiveness of proposed controls is verified through experiments on a testbed of the three-phase stand-alone system.
Highlights
The emerging technologies developed for renewable energy resources are making the microgrid operation more resilient in the distribution network
We implemented the Fast Fourier Transform (FFT) and controllers of the three-phase stand-alone voltage source inverter (VSI) using the DSP manufactured by TEXAS INSTRUMENT®
This paper demonstrates a turn key solution for a VSI to compensate unbalanced and nonlinear load conditions in a grid forming microgrid
Summary
The emerging technologies developed for renewable energy resources are making the microgrid operation more resilient in the distribution network. When an outage occurs at the utility grid, the microgrid could quickly switch back to the stand-alone operation for sustaining the electrical power for the loads [1]. Since the DC source cannot directly deliver power to the AC loads, inverters are playing the key role to perform power conversion in between [2–4]. In the grid-connected mode, the voltage at the point of common coupling (PCC) is supported by the utility grid. Without the stiff voltage support by the utility grid, voltage at PCC in the stand-alone operation is heavily affected by the types of loads. The voltage source inverter (VSI) that operates in the grid forming microgrid should be able to maintain quality voltage at PCC [5,6]
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