V. Fernao Pires

Bio: V. Fernao Pires is an academic researcher from INESC-ID. The author has contributed to research in topics: Inverter & Fault (power engineering). The author has an hindex of 18, co-authored 154 publications receiving 1457 citations. Previous affiliations of V. Fernao Pires include Technical University of Lisbon & University of Lisbon.

Compensation of Unbalanced Low-Voltage Grids Using a Photovoltaic Generation System with a Dual Four-Leg, Two-Level Inverter

Abstract: In this paper, a grid-connected photovoltaic (PV) generation system is proposed with the purpose of providing support to low-voltage grids, namely through the elimination or attenuation of the grid imbalances. This compensation must consider the load types, which can be either linear or non-linear, and whether the reactive power and current harmonics generated by the non-linear loads need to be compensated in addition to the unbalanced active power. This must be well considered, since the compensation of all aspects requires oversized PV inverters. Thus, the different unbalanced compensation schemes are addressed. Several schemes for the generation of the inverter current references taking into consideration the compensation and load type are presented. For this PV generation system, a dual four-leg, two-level inverter is proposed. It provides full unbalanced compensation owing to the fourth leg of the inverter and also extends the AC voltage, which is important when this compensation is required. To control this inverter, a control scheme for the inverter that considers several compensation factors is proposed. A vector voltage modulator associated with the controller is another aspect that is addressed in the paper. This modulator considers the balance between the DC voltages of the inverters. Several compensation schemes are verified through computational tests. The results validate the effectiveness of the proposed PV generation system.

Impact of photovoltaic systems with ancillary services in low voltage grids

Abstract: Photovoltaic systems (PV) are now playing an important role in low voltage (LV) grids. Due to this there are impacts in these grids that previously were not expected. Usually these systems are connected to the grid with the goal of transferring the maximum power generated by the solar panel to the grid. However, the power inverter can be controlled in order to also provide ancillary services (AS). In this context this paper presents a study of the impact of PV with AS in LV grids. In this study it will be proposed the injection of the active power in an unbalanced way, taking into consideration the characteristics of the grid. It will also be considered the PV plants providing a reactive power AS. The impact of these AS in a LV grid will be analyzed.

Conversion structure based on a dual T-type three-level inverter for grid connected photovoltaic applications

Abstract: A conversion structure based on a multilevel inverter for grid connected photovoltaic applications is presented. The structure includes two T-type three-level inverter, which are connected to grid by a three-phase transformer with the open winding configuration on inverters side. It also includes two insolated strings of PV panels that are feeding each one of the T-type inverters. The obtained multilevel inverter allows obtaining fifty seven different voltage vectors. To control the dual T-type three-level inverter is used a sliding mode controller and a vectorial modulator. The proposed structure is analyzed and verified by numerical simulations. From the obtained results it is possible to confirm the effectiveness of the proposed structure.

Grid-Connected PV System Using a T-Type qZS Inverter with an Integral Time Derivative Approach to Ensure MPP and Decoupled Current Control

Abstract: 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 paper 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.

Multi-level conversion : high voltage choppers and voltage-source inverters

Abstract: The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<>

Recent Advances in the Design, Modeling, and Control of Multiphase Machines—Part II

Abstract: The main objective of this two-part state-of-the-art paper called “Recent Advances in the Design, Modeling, and Control of Multiphase Machines” is to present latest contributions in the multiphase machines' field. The first part of this paper focuses on the recent progress in the design, modeling, and control, whereas the drive is in healthy operation. This second part presents relevant contributions in two not analyzed fields. The first is in relation with the use of the additional degrees of freedom of multiphase machines and the exploitation of their fault-tolerant capabilities without adding extra hardware. The second one analyzes multiphase generation, particularly in grid-connected wind energy conversion systems and stand-alone applications. Recent progresses are shown and open challenges and future research directions are discussed.

Overview of Control Systems for the Operation of DFIGs in Wind Energy Applications

Abstract: Doubly fed induction generators (DFIGs), often organized in wind parks, are the most important generators used for variable-speed wind energy generation. This paper reviews the control systems for the operation of DFIGs and brushless DFIGs in wind energy applications. Control systems for stand-alone operation, connection to balanced or unbalanced grids, sensorless control, and frequency support from DFIGs and low-voltage ride-through issues are discussed.