Closed-Loop Control and Performance Evaluation of Reduced Part Count Multilevel Inverter Interfacing Grid-Connected PV System

Multilevel inverters (MLIs) have drawn a tremendous attention in power sector. Application of MLI has grown extensively to improve the power quality and efficiency of the photovoltaic (PV) system. For an MLI interfacing PV system, the size, cost and voltage stress are the key constraints of the MLI that need to be minimized. This paper presents a novel reduced part count MLI interfacing single-stage grid-tied PV system along with a closed-loop control strategy. The proposed MLI consists of n repeating units and a level boosting circuit (LBC) that assists to generate 4n+7 voltage levels instead of 2n+3 levels. Three different algorithms are proposed for suitable selection of dc-link voltages to further enhance the levels. Comparative analysis is carried out to confirm the superiority of developed MLI. The workability of the proposed MLI is investigated with a 1.3 kW PV system. The closed-loop control strategy ensures the maximum power tracking, dc-link voltage balancing, satisfactory operation of the MLI and injection of clean sinusoidal grid current under any dynamic changes. Comprehensive simulation analysis is carried out considering a 15-level MLI structure. The practicality of the topological advancement for PV system is further confirmed by experimental tests under different dynamic conditions.publishedVersio

A single-source switched-capacitor based step-up multilevel inverter with reduced components

Switched-capacitor based multilevel inverters (SC MLIs) have received a great deal of interest that reduces the dc source requirement and improves the power quality. However, multiple dc sources and requirement of a large number of switches to generate a high-quality boost output are the fundamental issues in the SC MLIs. This paper presents a stepup 17-level SC MLI using reduced number of switches, three capacitors and a single dc source. The steady-state voltage across the capacitors is maintained in the ratio 1:2:0.5 that contributes to quadruple boosting ability without using any auxiliary capacitor voltage balancing circuit. Besides, lower switch count in the conduction path and operation of 50 % of the switches at fundamental frequency ensures total power loss reduction in the proposed circuit. A comparative assessment with recently developed 17-level MLIs in terms of the number of components, gain, stress and cost factor elucidates the advantages of the proposed MLI. After a detailed circuit analysis and loss evaluation, simulations are performed to verify the step-up and inherent balancing features of the proposed MLI. Further, using both the fundamental frequency and high-frequency switching techniques, extensive experimental test results are presented under different transient conditions to validate the operational feasibility of the 17-level prototype

Recently Developed Reduced Switch Multilevel Inverter for Renewable Energy Integration and Drives Application: Topologies, Comprehensive Analysis and Comparative Evaluation

Recently, multilevel inverters (MLIs) have gained lots of interest in industry and academia, as they are changing into a viable technology for numerous applications, such as renewable power conversion system and drives. For these high power and high/medium voltage applications, MLIs are widely used as one of the advanced power converter topologies. To produce high-quality output without the need for a large number of switches, development of reduced switch MLI (RS MLI) topologies has been a major focus of current research. Therefore, this review paper focuses on a number of recently developed MLIs used in various applications. To assist with advanced current research in this field and in the selection of suitable inverter for various applications, significant understanding on these topologies is clearly summarized based on the three categories, i.e., symmetrical, asymmetrical, and modified topologies. This review paper also includes a comparison based on important performance parameters, detailed technical challenges, current focus, and future development trends. By a suitable combination of switches, the MLI produces a staircase output with low harmonic distortion. For a better understanding of the working principle, a single-phase RS MLI topology is experimentally illustrated for different level generation using both fundamental and high switching frequency techniques which will help the readers to gain the utmost knowledge for advance research

Single-stage PV System With Multi-Objective Predictive Control Approach

Model predictive control (MPC) as a current controller has gained attention in a grid-connected power electronic converter system. The multi-objective predictive control is in greater demand when the photovoltaic (PV) sources are integrated with the utility grid since the inverter alone must ensure all of the control objectives such as grid current following, constant power factor operation and accurate maximum power point tracking (MPPT) performance. In this regard, this paper aims to implement the multi-objective Finite Set Control (FCS) - MPC for a single-stage grid-connected PV system considering the two-stage system is less cost-effective, more loss and less reliable. Moreover, the classical MPPT fails to extract the maximum power under fluctuating and shaded environmental condition. Therefore, an improved MPPT algorithm is proposed in this work which is again combined with the multi-objective FCS-MPC to ensure the extraction of the maximum power from the PV and good transient performance of the grid-side voltage and current. Two different approaches for the dc-voltage tracking are compared, one is implemented with an outer-loop proportional integral controller and the second one is implemented directly in the MPC objective function. The output findings clearly show the single-stage PV system with the proposed control can ensure a fast and accurate maximum power tracking and maintenance of stable output signal throughout all the transient conditions

Single-stage Grid-Connected PV System with Finite Control Set Model Predictive Control and an Improved Maximum Power Point Tracking

The single-stage grid-connected photovoltaic (PV) topology has drawn attention in the recent years as it can reduce the overall losses and installation costs. However, an efficient control is necessary to operate such a system satisfactorily. This paper presents a new control approach for single-stage grid-connected PV systems. The proposed controller is a combination of a finite control set model predictive control (FCS-MPC) and a maximum power point tracking (MPPT) algorithm, which ensures the extraction of maximum power from the PV panels and good transient performance of the output voltage and current. The disadvantages of classical MPPT algorithms in tracking the global maximum power point under fluctuating environmental conditions are avoided by including additional constraints in the cost function of the FCS-MPC. The effectiveness of the proposed controller is shown by a comparative study with the standard two-stage PV configuration. Further, the controller performance is tested for the partial shading in PV. The results show that the single-stage PV system with the proposed control can effectively extract the maximum power from the PV system and maintain a stable output signal through all the transient condition. Finally, experimental results are presented to validate the effectiveness of the proposed algorithm