Three-Phase T-Type qZ Source Inverter With Control Current Associated to a Vectorial Modulator for Photovoltaic Applications V. Fernão Pires ESTSetúbal, Polytechnic Institute of Setúbal INESC-ID Lisboa Setúbal, Portugal vitor.pires@estsetubal.ips.pt D. Foito ESTSetúbal, Polytechnic Institute of Setúbal Setúbal, Portugal daniel.foito@estsetubal.ips.pt A. Cordeiro ISEL – Polytechnic Institute of Lisboa Lisboa, Portugal acordeiro@deea.isel.ipl.pt J. F. Martins CTS/UNINOVA FCT/UNL Caparica, Portugal jf.martins@fct.unl.pt Abstract—This paper presents a fast and robust control system for a three-phase quasi-Z-source inverter (qZSI) connected to the grid. The topology combines two quasi-Z-source networks with a T-type inverter allowing to obtain AC voltages with multilevel characteristics and properties of the referred networks. To control this system a closed-loop current controller for the AC currents is proposed. The controller is based on a vectorial modulator associated to the shoot-through states. The DC-link voltage is maintained stable at the reference value by adjusting the shoot-through duty cycle. The controller is characterized by fast transient response and robustness to parameter and load variations. In order to confirm the desired characteristics and performance of the converter and control system several simulation tests were performed. Keywords—T-Type converter; qZ voltage source inverter; current controller; shoot-through states. I. INTRODUCTION Renewable energy sources play a fundamental role in the actual context. Such energy sources generally require power electronic converters associated to these systems to obtain the maximum power as well as an appropriate interconnection with the electrical grid. Due to the different characteristics and specificities of the several renewable sources and applications, the choice of the power converter topology and associated control system must be done very carefully. One of the specificities that are usually required by photovoltaic sources connected to the electrical grid is the requirement of a power converter with voltage boost characteristics. In order to fulfill this requirement there are different solutions, most of them based on single or double stage conversion [1-3]. In single stage conversion it can be used a low frequency transformer between the inverter and the grid [4-6]. Another solution is based on the application of several photovoltaic panels associated to a multilevel inverter such as the cascaded H-bridge [7-9]. Besides the capability to extend the AC voltage this last solution also provides the advantages of multilevel converters. Regarding double stage conversion, one of the most common solutions is based on two converters, a DC/DC converter and DC/AC converter. The DC/DC stage normally uses a Boost type DC/DC converter or a topology with a high frequency transformer associated to a maximum power point tracking algorithm [10-12]. Other types of power converters can be used on photovoltaic grid-connected systems. One interesting solutions that has been proposed and studied in the last years is through the integration of a qZSI connected to the grid. This converter combines a qZ-source network with a classical voltage source inverter. One of the main characteristics of this converter that makes it suitable for this kind of application is the Boost feature provided by the special shoot-through state. Furthermore, the shoot-through state provides additional protection to short-circuit failure of power devices. Thus, many works related with single and three-phase qZSI and respective control system were proposed for this type of application [13- 16]. Due to the characteristics of these converters, they were also expanded to multilevel applications. In this context, several works have been focused in the quasi-Z neutral-point- clamped converter [17-19]. Regarding control strategies, several solutions have been applied, such as, sinusoidal pulse- width modulation (SPWM) or the space vector modulation techniques. Other solutions based on current controller have also been proposed. A hysteresis current control for Z and quasi-Z voltage source inverters was also proposed [20,21]. However, this technique was also applied to the two-level single-phase inverter. Another proposed multilevel qZSI solution for photovoltaic applications is based on the cascaded H-bridge inverter topology [22,23]. Recently the use of a multilevel qZSI based on the T-type inverter was also proposed [24]. To control this converter was proposed sinusoidal pulse- width modulation. This paper proposes a fast and robust closed-loop control solution for a three-phase multilevel qZSI topology based on the T-type inverter. The proposed solution allows to control the AC currents through a multilevel hysteretic current controller and vectorial modulator combined with the shoot-through state to provide the necessary step-up voltage. This modulator was also developed in order to maintain the stability of DC voltages. Several simulation testes will be performed in order 978-1-XXXX-XXXX-X/16/$31.00 ©2016 IEEE 656