Renewable Energy Sources Using Quasi-Z-Source Inverter With Distribution Level Power-Quality Improvement

Quasi-Z-source inverters (QZSI) acquire all the advantages of traditional Z source inverter. The impedance network couples the source and the inverter to achieve voltage boost and inversion in a single stage. By using this new topology, the inverter draws a constant current from the PV array and is capable of handling a wide input voltage range. It also features lower component ratings, reduces switching ripples to the PV panels, causes less EMI problems and reduced source stress compared to the traditional ZSI. The quasi-Z-source inverter (QZSI) is a single stage power converter derived from the Z-source inverter topology, employing an impedance network which couples the source and the inverter to achieve voltage boost and inversion. A new carrier based pulse width modulation (PWM) strategy for the (QZSI) which gives a significantly high voltage gain compared to the traditional PWM techniques is implemented. This technique employs sine wave as both carrier and reference signal, with which the simple boost control for the shoot-through states is integrated to obtain an output voltage boost. The conventional triangular wave carrier used in simple boost control technique is replaced by sine wave, which improves the shoot-through duty ratio for a given modulation index. The conventional perturb and observe maximum power point tracking algorithm is modified for QZSI and used along with the PWM technique for tracking the maximum power from PV. All the simulations are done using MATLAB. Hardware implementation and Microcontroller programming are done in the lab. All of these functions may be accomplished either individually or simultaneously. The combination of grid-interfacing inverter and the 3-phase linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and validated through digital signal processor-based laboratory experimental results.