| Photovoltaic (PV) generation is one of the most widely-used renewable energies because of its easy installation and flexible operation modes. The key technology in the operation of PV system is the control for power converters. This work is combined with two main parts: PV control under normal operation conditions and the control under unbalanced voltage.;In the first part, different mainly-used control strategies (grid-forming, grid-feeding and grid-supporting) are presented. These control strategies are used in PV systems with different functions. And the main control methods (MPPT and Droop control) related to grid-feeding and grid-forming converters are introduced. In addition, PV systems with these control strategies are combined together to form a much more economical microgrid. The operation of the microgrid in a sunny day time is simulated in Simulink.;In the second part, control strategies under unbalanced voltage are introduced. Under unbalanced voltage, converters with recent conventional control technologies can hardly operate well and there will be several defects in power quality, such as current harmonics and power fluctuation. Firstly, different controllers are compared with each other. Then another topic of the power quality under unbalanced voltage which is the way to calculate the current reference is introduced. Two coefficients are brought in to the current reference. By tuning theses coefficients continuously, relatively low current harmonics are injected into the output current and the power fluctuation can be suppressed in a compromise way. This control model is built and simulated in PSCAD/EMTDC. |
