A Photovoltaic Tied Three-Phase Transformerless DC-MLI Control Switching to Accomplish the Grid Connected Solutions : A Photovoltaic Tied Three-Phase Transformerless DC-MLI Control Switching to Accomplish the Grid Connected Solutions

Abstract

Due to their superior performance over other inverter topologies, photovoltaic (PV) tied Z-source Diode-Clamped (DC) multilevel inverter (MLI) topologies are widely employed for high-power medium voltage grid linked applications. Due to its single stage power conversion, Z-source DC-MLI (ZsDCMLI) is employed in solar grid linked applications where it outperforms traditional inverters. Despite the fact that Z source inverters are accepted in grid connected technologies, a sufficient controller to meet the grid/standalone standards is required. The MLI are used in most of the power electronic industries for its better harmonics performance, lower switching stress, lower losses etc. For increasing the AC output voltage, the Z-source converter circuitry uses two identical structures: X-shaped capacitance and inductance, and an impedance network connected between the DC input source and the inverter circuit [1]. The DCMLI is a topology from the MLI family that can accommodate all of the circuit and operation features of a traditional two-level inverter. The preceding literature review gives an overview of the work that has been done on space vector PWM development and implementation. It, on the other hand, lacks a thorough understanding of Z-source MLI Space vector modulation (SVM) development and implementation. Because of the adequate voltage vector selection opportunity, the SVM is a popular modulation technique for Z-source NPC-MLIs. The control of a Z-source MLI inverter with and without modification of shoot through switching has been demonstrated in previous papers. However, no attempt is made to use a current controller (CC) to implement SVPWM, which is the most important factor for a grid-connected inverter to offer minimal harmonic distortion and good quality current [2]. The grid-connected CCs should operate using a direct control method based on the grid reference. Researchers have proposed alternative PV powered transformerless (TL) inverters for grid connected power systems in both three and single phases to tackle the transformer dependency issue [3]. Many single phase TL inverter topologies have been developed, with the goal of simply reducing leakage current by adding extra power switches to the main inverter circuitry. The study in three-phase networks is entirely focused on PWM and current control design algorithms [4],[5]. In terms of reducing harmonic content output waveforms and suppressing common mode voltage (CMV), Z source MLIs are a better choice for PV applications than two-level VSIs.

      In this paper a PWM method proposes for the performance enhancement of PV-tied Z-NPC-MLI grid-connected system with a unique hysteresis current control SVPWM (HSVM) technique and neutral point (NP) balancing control to achieve all of these goals. The suggested current control provides good direct current control with neutral point balancing on the inverter input side. As a result, the suggested CC ensures a high-quality current and voltage waveforms for utility grid. The HCC and SVPWM adaptations to the Z-MLI for NP balancing were described in the article. MATLAB/Simulink software is used to model and verify the proposed system. The validation of the laboratory prototype 2-kWp solar panels attached grid linked three-phase three-level Z-NPC-MLI is done using a Xilinx family SPARTAN-6 controller. The feasibility and reliability of the suggested CC for the PV tie grid linked Z- Source MLI were proven by simulation and experimental results. The CC can be used with other MLI topologies as well.