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

Sistema Fotovoltaico Ligado à Rede Usando um Conversor Multinível Quasi-Z do Tipo T

Os inversores quasi-Z de três níveis (qZS) baseados na topologia tipo T são especialmente indicados para uso em sistemas fotovoltaicos conectados à rede. Na verdade, apresentam uma característica importante para este tipo de aplicação, pois apresentam a característica redutor/elevador. Além disso, também é caracterizado por alta confiabilidade e operação multinível. Porém, associados a este conversor, devem ser utilizados controladores que garantam seu melhor desempenho. Neste contexto, esta dissertação irá propor um sistema de controlo global para o inversor trifásico tipo T qZS em um sistema fotovoltaico conectado à rede. Assim, será considerado um algoritmo rastreador de máximo ponto de potência (MPPT) baseado em uma abordagem derivada de tempo integral robusta. Para as correntes de saída será utilizado um controlador de corrente desacoplado no qual será associado um modulador por largura de pulso sinusoidal (SPWM). O desempenho do sistema será verificado e testado por estudos de simulação. Os resultados mostrarão que este sistema fornecerá resultados bem-adaptados para esta aplicação.Three-level quasi-Z-Source (qZS) inverters based on the T-Type topology are especially indicated to be used in grid-connected PV systems. In fact, they present an important feature for this type of application since presents Buck-Boost characteristic. Besides that, is also characterized by high reliability and multilevel operation. However, associated to this converter, it must be used controllers that will ensure their best performance. In this context, this thesis will propose a global control system for the three phase T-Type qZS inverter in a grid-connected PV System. So, it will be considered a MPPT algorithm based on a robust integral time derivative approach. For the output currents will be used a decoupled current controller in which will be associated to a SPWM modulator. The performance of the system will be verified and tested by simulation studies. The results will show that this system will provide results well adapted for this application

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

Quasi impedance source based high power medium voltage converter for grid integration of distributed energy sources

The next generation of Power Electronics systems would need to be able to work at higher power levels, higher switching frequencies, compact size, and higher ambient temperatures, as well as should have improved energy efficiency than existing Silicon (Si) devices. As a result, new wide bandgap semiconductor technologies must be introduced to address Si's physical limitations. Silicon Carbide (SiC) devices are becoming popular because of their outstanding properties that address all the requirements of the next generation Power Electronics system. On the other hand, the converter topology still plays a major role in deciding the overall system performance. Hence the major objective of this dissertation is to devise new multilevel quasi impedance source (qZS) based converter topologies using SiC devices to achieve a compact, highly efficient, and modular solution for grid integration of Solar PV Energy Source to the utility grid. Other objectives include modification in the PWM methods to address the problem of unequal power-sharing in Solar PV multilevel converters. By using qZS as the front-end power converter several different power converter topologies have been developed and presented in this dissertation. The detailed design, modulation, loss analysis, and control have been developed for multi module cascaded structure. Level-shifted PWM technique is developed at first for two cascaded modules which are similar to the standard Phase opposed disposed Pulse width modulation (PODPWM). However, this control method cannot be directly applied to a higher number of modules. For more than two cascaded modules a unified combined hybrid PWM technique is developed and presented. During normal balanced operation, the power among the modules is unequal. To address the unequal power sharing problem, further modification in the PWM technique is done called the Carrier rotation technique. For providing the isolation between the low voltage PV panels and the high voltage AC grid, a modified Inverter topology, and a new modulation technique is developed. The presented technique, however, is limited to a single module, and more research is needed to implement for cascaded structure. Front-end qZS based single-stage DC-AC-DC converter is developed as an alternative of one of the most popular conventional dual active bridge (DAB) converter. The proposed converter offers reduced component count while maintaining the continuous input current. The detailed operation, modulation technique, simulation, and experimental result are presented to show the superiority of the developed qZS Cascaded Multilevel Converter. The developed power converter has strong commercialization potentia