Cascaded AC-DC Voltage Control to Provide Reactive Power Support for the PV-Driven Grid-Tied Synchronverter

The objective of this submission is to provide flexible reactive power regulation of a photovoltaic (PV)-driven grid-connected inverter. Here, inverter is realized as a synchronverter by employing frequency regulation using well-established swing equation. However, reactive power regulation is accomplished by employing combined AC-DC voltage control in addition to traditional synchronverter control for ensuring smooth tracking of reactive power. Thus, the PV-driven voltage source converter (VSC) will be injecting available active power as per the prevailing irradiation, temperature, and operator defined reactive power by employing proposed control. The performance of suggested control is evaluated and compared against existing control by considering realistic operational scenarios through a case study. The proposed control will replace the Q-V$$ Q-V $$ regulation loop with the cascaded AC-DC voltage control in which a linear AC voltage controller will act in conjunction with DC-link voltage control for injecting required reactive power. The reference value for AC voltage controller is generated from the active power of photovoltaic (PV)-based source Ppv$$ {P}_{pv} $$ and reference reactive power Qref$$ {Q}_{ref} $$. Then the required DC-link voltage command vdc & lowast;$$ {v}_{dc}<^>{\ast } $$ is thus obtained from the guided terminal voltage |vt & lowast;|$$ \mid {v}_t<^>{\ast}\mid $$ of AC voltage controller according to conventional VSC (voltage source converter) topology. Finally, a cascaded form of AC-DC voltage control is proposed as shown in Figure 2, to achieve desired reactive power injection. The control parameter design for both the methods is carried out based on the time constant or execution time of the individual controllers. The performance of the proposed control is evaluated and compared with existing control by considering operational cases such as change in reference reactive power Qref$$ {Q}_{ref} $$, change in irradiation level, and change in grid voltage vg$$ {v}_g $$, respectively. image