Transient Performance Enhancement of Tank Circuited 3-Pole PV Based DC Microgrid with Limit-Based P & O MPPT Algorithm

Abstract

This paper presents a limit-based approach in improving transient performance of tank-circuited 3-Pole PV Based DC Microgrid (3-PPDM) during zero to non-zero insolation transition of the solar irradiance profile. This approach is necessitated due to the transient behavior of the microgrid during the above-mentioned transition that results into huge voltage sag which appears to violate the conditions set for desirable operation of the dc loads. The tank-circuited 3-PPDM is conceived to mimic, under set conditions, operational feature of grid-connected three-phase ac microgrid where transformer is not required at distribution level for the provision of different voltage levels (phase and line) operation within the ac microgrid. 3-PPDM is developed with PV Based DC Microgrid connected to ac grid via single stage dc link and 3-Level Voltage Source Converter (3L-VSC). The dc loads are directly connected to the dc link and operated at high and low voltage levels without the employment of dc-dc converters. These voltage levels are established via the support of the three poles created by two serially connected centre-tapped capacitors meant primarily for improving the harmonic performance of the 3L-VSC. The observed huge voltage sag is technically linked to abrupt change in the high dc link reference voltage of the dc link PI controller during zero irradiance to low voltage of the PV power optimizer at the transition point. Subsequently, a limit-based perturb and observe maximum power point tracking (P&O MPPT) technique was employed as corrective measure. The concept of the technique is to determine the transition point and assign suitable pre-determined value that is within the technical constraint of the microgrid as the reference voltage of the dc link. The simulation results of this approach prove the efficacy of the techniques as the set conditions are successfully met within considerable time, leading to an improvement in the transient performance of the microgrid.