• Energy Research

In this paper a power converter topology where an Unified Power Quality Conditioner (UPQC) is combined with the photovoltaic generators is presented. This topology is based on a dual structure of the classical three-phase two level inverters. Thus, multilevel operation is achieved with the advantages of this type of inverters. Another feature of this structure is the higher reliability of the combined system. In fact, even with a fault in one of the inverters the system can still operate. Voltage and current controllers are also described. The current and voltage controllers are implemented in the synchronous rotating reference frame (dq0-axis). Several results are presented in order to verify the operation of the system under various conditions.

This article deals with fault detection and the classification of incipient and intermittent open-transistor faults in grid-connected three-level T-type inverters. Normally, open-transistor detection algorithms are developed for permanent faults. Nevertheless, the difficulty to detect incipient and intermittent faults is much greater, and appropriate methods are required. This requirement is due to the fact that over time, its repetition may lead to permanent failures that may lead to irreversible degradation. Therefore, the early detection of these failures is very important to ensure the reliability of the system and avoid unscheduled stops. For diagnosing these incipient and intermittent faults, a novel method based on a Walsh transform combined with a multilayer perceptron (MLP)-based classifier is proposed in this paper. This non-classical approach of using the Walsh transform not only allows accurate detections but is also very fast. This last characteristic is very important in these applications due to their practical implementation. The proposed method includes two main steps. First, the acquired AC currents are used by the control system and processed using the Walsh transform. This results in detailed information used to potentially identify open-transistor faults. Then, such information is processed using the MLP to finally determine whether a fault is present or not. Several experiments are conducted with different types of incipient transistor faults to create a relevant dataset.

This paper focuses on the purpose to see if it is possible to increase the earnings associated to the installation of PV systems in people’s homes. In accordance with this, a different way of thinking was adopted, namely the investment in batteries to maximize the energy earnings. The main problem of this classical approach is that the investment in those batteries is important. In this way, a different perspective was taken into account, namely the use of the electrical vehicles. This kind of vehicles is starting to become a real reality. In fact, the selling of these vehicles start to become a solution for the ordinary people, and it is expected in a very near future to be a reality for most of them. Thus, this study presents the use of a storage system based on the vehicle-to-home (V2H) technology for the people’s homes. The V2H availability varies among prosumers profile regarding the daily routines, weather conditions, and business aspects, besides other aspects. These profiles were combined with different power panels with and without injection into the grid. The costs of each configuration considering a residential consumer located in Portugal, as well as, their peak solar hours in a year were estimated. From this study, it will be possible to verify that the obtained economical results show that the usage of V2H as storage system based on batteries for modern homes is very attractive.

The use of a solar photovoltaic (PV) panel simulator can be a valued tool for the design and evaluation of the several components of a photovoltaic system. This simulator is based on power electronic converter controlled in such a way that will behave as a PV panel. Thus, in this paper a PV panel simulator based on a two quadrant DC/DC power converter is proposed. This topology will allow to achieve fast responses, like suddenly changes in the irradiation and temperature. To control the power converter it will be used a fast and robust sliding mode controller. Therefore, with the proposed system I–V curve simulation of a PV panel is obtained. Experimental results from a laboratory prototype are presented in order to confirm the theoretical operation.

The use of distributed architectures for PV panels present several advantages over centralized solutions, such as better harnessing of the generated energy and improved reliability of the system. Therefore, several inverter structures have been proposed to ensure proper operation of distributed architectures and at the same time generate multilevel voltages. A newly proposed structure uses three three-phase two-level inverters. Thus, in this paper a new control system is proposed for grid-connected PV systems with this structure. The proposed control system is based on a sliding mode AC current controller that uses space-vector voltage modulators. The proposed control system is also designed to inject unbalanced power into the grid to provide an ancillary service regarding power unbalances. The proposed controller for the mentioned structure is then tested through several simulations considering different case studies.

In this work it is proposed a switched reluctance machine (SRM) drive supplied by a renewable source (PV array) to operate a water pumping system. To improve the speed of the commutation between phases it is proposed the use of a multilevel converter for the SRM drive. This converter was designed to reduce the number of controlled power semiconductors, reducing the cost of the system. To obtain the maximum power extraction of the PV system is proposed the use of an algorithm based on the product of the time derivative of power with the time derivative of voltage. A control system to ensure the balance between the power generated by the renewable source and the water pumping system is also proposed. The operation and characteristics of the system will be verified by several numerical tests.

Abstract A new non-isolated DC-DC converter for photovoltaic systems is proposed in this paper. This converter topology is characterized by an integration of the classical Boost and Cuk DC-DC converters. The proposed topology requires only a single power semiconductor switch, reduces voltage stress across diodes and power semiconductor switch while providing a continuous input current. Further, this topology allows extending the voltage static gain when compared with the conventional Boost converter. The new converter is regulated by a PWM technique at constant frequency that can be associated to a maximum power point tracking algorithm. Herein, the design considerations of this power converter are presented, and the characteristics of the proposed topology are confirmed by simulations and experiment results from a laboratory prototype.

Pumping systems play a fundamental role in many applications. One of the applications in which these systems are very important is to pump water. However, in the real world context, the use of renewable energies to supply this kind of system becomes essential. Thus, this paper proposes a water pumping system powered by a photovoltaic (PV) generator. In addition, due to its interesting characteristics, such low manufacturing cost, free of rare-earth elements, simple design and robustness for pumping systems, a switched reluctance motor (SRM) is used. The power electronic system to be used in the PV generator and to control the SRM consists of a DC/DC converter with a bipolar output and a multilevel converter. The adopted DC/DC converter uses only one switch, so its topology can be considered as a derivation of the combination of a Zeta converter with a buck–boost converter. Another important aspect is that this converter allows continuous input current, which is desirable for PV panels. The topology selected to control the SRM is a multilevel converter. This proposed topology was adopted with the purpose of reducing the number of power semiconductors. A maximum power point algorithm (MPPT) associated with the DC/DC converter to obtain the maximum power of the PV panels is also proposed. This MPPT will be developed based on the concept of the time derivative of the power and voltage. It will be verified that with the increase in solar irradiance, the generated power will also increase. From this particular case study, it will be verified that changes in the irradiance from 1000 W/m2 to 400 W/m2 will correspond to a change in the motor speed from 1220 rpm to 170 rpm. The characteristics and operation of the proposed system will be verified through several simulation and experimental studies.