A Hysteresis Space Vector PWM for PV Tied Z-Source NPC-MLI With DC-Link Neutral Point Balancing

The Photo-voltaic (PV) tied Z-source Neutral-point clamped multilevel inverter (Z-NPC-MLI) is used in solar grid connected applications due to its single stage conversion and better performance. Though the Z source inverters adaptation is accepted in grid connected technology, the need for suitable controller and PWM scheme are necessary to meet out the performance such as shoot through switching, neutral point balancing, and harmonic reduction. 

The space vector pulse width modulation (SVPWM) strategy is a prominent modulation technique for Z-source NPC-MLIs due to the flexibility to select the appropriate voltage vector. Previous publications have shown the control of a Z-source MLI using the SVPWM with and without modification of shoot through switching. However, the current controller (CC) based SVPWM is not matured, which is the most essential consideration for the grid connected inverter to provide neutral point balancing, shoot through control for low harmonic distortion and a high quality current. With all these aims, this paper presents a PV tied Z-NPC-MLI grid connected system with a unique hysteresis current control SVPWM (HSVM) strategy with neutral point (NP) balancing control and direct current control in the inverter input side. 

Also, the proposed HSVM is assuring the grid connection with high quality voltage and current waveforms. This CC based SVPWM for Z-NPC MLI has been validated through simulation and FPGA based experimental investigations. The results are confirmed the feasibility and reliability of the proposed HSVM for the PV tie grid connected Z- Source NPC-MLI.

INDEX TERMS -Z source MLI, neutral-point clamped inverter, space vector PWM (SVPWM), hysteresis current controller (HCC), neutral point balancing.