Proceedings of the Estonian Academy of Sciences (Nov 2020)
Multilevel cascaded three-phase inverter with low-voltage ride-through flexible control capability for photovoltaic systems
Abstract
A potential solution for medium and large-scale solar power plants connected to a grid is the multilevel cascade H- bridge (CHB) inverter. Nevertheless, it has not been thoroughly studied how it operates during voltage sags. An easy strategy for controlling the operation of solar grid-connected CHB inverters in periods of unstable voltage sags is presented in this paper. The main contribution of this study is the fact that the proposed strategy is capable of infusing both reactive power, which represents the so-called low-voltage ride-through capability (LVRT), and active power into the grid with either stable or unstable currents, the so-called low-voltage ride-through capability (LVRT), and active power into the grid with either stable or unstable currents, as well as maintaining voltage balance of all DC-link capacitors. To obtain gate signals, phase-shifted sinusoidal pulse width modulation (PWM) technique is applied. Under various unbalanced voltage sags, the performance of the proposed strategy for the operation of a grid-connected CHB converter was illustrated and validated through a computer simulation platform. Moreover, an experimental setup for a 5-level CHB inverter using MOSFET switches with 5 kHz switching frequency was implemented to reveal the effectiveness of the proposed strategy. The Texas instrument DSP C2000 micro-controller TMS320F28335 was used to detect control, modulation and protection functions in real time and simultaneously. The developed system was tested under severe and light unbalance conditions, and the results show that this system can handle a single-phase voltage sag and be used as a practical light unbalance conditions, and the results show that this system can handle a single-phase voltage sag and be used as a practical device for AC grids.
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