Due to improved efficiency of solar photovoltaic (PV) systems, this article proposes a modified perturb and observe (MPO) maximum power point tracking (MPPT) algorithm. The MPO algorithm in question adopts a tracking approach that divides the power-voltage curve into four operational regions based on the estimated open-circuit voltage. Additionally, this algorithm enhances the maximum power point (MPP) tracking method by reducing unnecessary step-size calculations, focusing only on a 10% section of the power-voltage curve that contains the MPP. Consequently, the two regions located far from the MPP, below 90% of the power-voltage range, utilize a large fixed step-size to ensure swift tracking speed. Furthermore, in the regions close to the MPP, the remaining areas employ a similar tracking strategy as the adaptive P&O algorithm, aiming to achieve minimal steady-state oscillations around the optimal MPP. The performance of the proposed MPO algorithm is demonstrated by validating it against sinusoidal, ramp irradiance, and one-day (10 hr.) irradiance profiles using MATLAB/SIMULINK. The simulation results confirm that the proposed algorithm outperforms recently published techniques in terms of convergence speed, achieving the shortest time of 15 ms, and slightly higher tracking efficiency of the PV system under uniform irradiation, reaching 99.8%.

This paper presents a new symmetrical single-phase nine-level DC-AC converter for the applications of distributed generation systems (DGS). The proposed multilevel inverter (MLI) utilizes four independent DC sources to generate the nine output voltage levels considering a reduced number of switching devices. The proposed inverter consists of main and auxiliary circuits. The main circuit is a single H-bridge circuit, which is responsible for output voltage polarity. The auxiliary circuit consists of a special combination of switching devices, which are used to synthesize the multilevel output voltage. The merits of the proposed MLI are: increased output voltage levels at reduced number of switching devices, low switching loss, low total harmonic distortion (THD), low dv/dt stress on the switches and hence, low ratings of the switching devices, and low cost. The effectiveness of the proposed MLI and its PWM switching pattern has been verified experimentally by using a laboratory prototype controlled by DSPACE-1103.