Z Source Inverter Topologies-A Survey

Need for alternative energy sources to satisfy the rising demand in energy consumption elicited the research in the area of power converters/inverters. An increasing interest of using Z source inverter/converter in power generation involving renewable energy sources like wind and solar energy for both off grid and grid tied schemes were originated from 2003. This paper surveys the literature of Z source inverters/converter topologies that were developed over the years

Single Phase Quasi-Z-Source Based Modified Cascaded Multilevel Inverter with Half-Bridge Cell

A new Quasi-Z-Source Modified Cascaded Multilevel Inverter (qZS-MCMLI) with Half-Bridge Cell presents attractive advantages over conventional cascaded MLI with voltage boost ability and reduced switches. The new proposed topology is comprised of cascaded auxiliary units and a full H-bridge inverter, where the auxiliary unit includes half bridge cell with qZS network. With qZS network shoot-through state control, the output voltage amplitude can be boosted, which is not limited to DC source voltage summation similar to conventional cascaded MLI. The performance parameters of qZS-MCMLI with various multicarrier PWM control methods are analysed with simulation results and portrayed here

Finite control set model predictive control for grid-tied quasi-Z-source based multilevel inverter

In this paper, a finite control set Model Predictive Control (MPC) for grid-tie quasi-Z-Source (qZS) based multilevel inverter is proposed. The proposed Power Conditioning System (PCS) consists of a single-phase 2-cell Cascaded H-Bridge (CHB) inverter where each module is fed by a qZS network. The aim of the proposed control technique is to achieve grid-tie current injection, low Total Harmonic Distortion (THD) current, unity power factor, while balancing DC-link voltage for all qZS-CHB inverter modules. The feasibility of this strategy is validated by simulation using Matlab/Simulink environment

A Low-Computational High-Performance Model Predictive Control of Single Phase Battery Assisted Quasi Z-Source PV Inverters

Impedance network inverters are a good alternative for voltage-source and current-source inverters. The shoot-through solution and the boosting capability of such converters make them an excellent solution for photovoltaic (PV) application. Furthermore, energy storage integration in these inverters does not require any additional components in the converter; indeed, a battery can be directly connected in parallel with one of the capacitors of the Z- or quasi Z-network. However, for an optimal control of these converters, complex control and modulation strategies are required. Model Predictive Control (MPC) provides high control performance at the expense of the computational effort. In this paper, a low computational control method where both MPC and proportional resonant (PR) controller are combined, is proposed. This makes the proposed controller perform two iterations only instead of iterating for all the available switching states. As shown in the obtained results, the proposed controller conserves the high performance of the conventional MPC with 50% less computational burden

Grid-tie Quasi Z-Source Inverter-Based Static Synchronous Compensator

This research work proposes intensive study and mathematical modelling analysis of transformer-less quasi Z-source inverter (qZSI) based static synchronous compensator (STATCOM) system. In this work, a single-phase qZSI is acted as a STATCOM system to compensate the grid reactive power at the point of coupling under different loading conditions. A new controller-based lead compensator is developed to achieve fast DC-link voltage balance across each qZS network. Simulation studies are conducted to evaluate the controller’s performance

Performance Characteristics of Multilevel Converter in Grid Connected System with Renewable Energy Resources

The multi-stage cascade converter structure can be fascinating for high-performance solar photovoltaic (PV) systems due to its interchangeability, expansion, and MPPT (Maximum Power Point Tracking) exception. However, power discrepancies in cascaded uniform PV converter modules can cause unstable voltages and system operation. This article highlights the problem, examines the effects of reactive power compensation and optimization on the safety and performance characteristics of the system and proposes a synchronized distribution of active and reactive power in the network in order to reduce this instability. Furthermore, a wind turbine is connected in parallel to the photovoltaic system to increase the reliability of the system. This document presents the standards and specifications of grid-connected photovoltaic inverters and the different topologies of grid-connected photovoltaic inverters. And he also discussed monitoring maximum credit points

Model predictive control of a microgrid with energy-stored quasi-Z-source cascaded H-bridge multilevel inverter and PV systems

This paper presents a new energy management system (EMS) based on model predictive control (MPC) for a microgrid with solar photovoltaic (PV) power plants and a quasi-Z-source cascaded H-bridge multilevel inverter that integrates an energy storage system (ES-qZS-CHBMLI). The system comprises three modules, each with a PV power plant, quasi-impedance network, battery energy storage system (BESS), and voltage source inverter (VSI). Traditional EMS methods focus on distributing the power among the BESSs to balance their state of charge (SOC), operating in charging or discharging mode. The proposed MPC-EMS carries out a multi-objective control for an ES-qZS-CHBMLI topology, which allows an optimized BESS power distribution while meeting the system operator requirements. It prioritizes the charge of the BESS with the lowest SOC and the discharge of the BESS with the highest SOC. Thus, both modes can coexist simultaneously, while ensuring decoupled power control. The MPC-EMS proposed herein is compared with a proportional sharing algorithm based on SOC (SOC-EMS) that pursues the same objectives. The simulation results show an improvement in the control of the power delivered to the grid. The Integral Time Absolute Error, ITAE, achieved with the MPC-EMS for the active and reactive power is 20 % and 4 %, respectively, lower than that obtained with the SOC-EMS. A 1,3 % higher charge for the BESS with the lowest SOC is also registered. Furthermore, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is implemented to validate the simulation result

Power Scheduling Method for Grid Integration of a PV-BESS CHB Inverter With SOC Balancing Capability

The paper deals with a single-phase photovoltaic (PV) inverter based on the Cascaded H-Bridge (CHB) topology for Low Voltage (LV) grid. A distributed architecture of PV sources integrated with battery energy storage systems (BESS) is proposed with the particularity of avoiding the use of dc-dc converters. A method of compensating for the short-term daily variability of PV energy is also presented. The control implements power scheduling to ensure that constant active power is fed into the grid at every predetermined time interval (e.g., every quarter of an hour). Furthermore, a dedicated hybrid modulation scheme based on a sorting algorithm for balancing the state of charge (SOC) of the single cells is proposed. Numerical investigations are carried out on a 19-level CHB inverter implemented in a PLECS®(i.e., the simulation platform for power electronic systems from Plexim) environment to validate the feasibility and effectiveness of the proposed control strategy

A Reduced Power Switches Count Multilevel Converter-Based Photovoltaic System with Integrated Energy Storage

A multilevel topology for photovoltaic (PV) systems with integrated energy storage (ES) is presented in this article. Both PV and ES power cells are connected in series to form a dc link, which is then connected to an H-bridge to convert the dc voltage to an ac one. The main advantage of the proposed converter compared to the cascaded-H-bridge (CHB) converter, as well as compared to the available multilevel topologies, is that fewer semiconductor devices are needed here. As the output voltage levels increase, more switches are saved, which results in a more efficient, cheaper, and smaller converter. So far, there is still no modulation strategy that is designed particularly for PV-fed multilevel converters with built-in ES. The standard modulations are impractical for such an application since they suffer from deficiencies, such as polluted output signals - thus, requiring larger output filter - and overmodulation. A modified modulation strategy for PV+ES multilevel inverters is, therefore, introduced in this article. The proposal has been simulated and experimentally validated to evaluate its effectiveness, where it has been shown that the proposed topology is not exclusively feasible, but also suffers from less conduction and switching loss, achieving higher efficiency with respect to its counterpart CHB. </p