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- Fault-tolerant SRM dive with a diagnosis method based on the entropy feature approachPublication . Fernao Pires, Vitor; Amaral, Tito; Cordeiro, Armando; Foito, Daniel; Pires, Armando J.; Martins, JoaoThe power electronic converter design is essential for the operation of the switched reluctance motor (SRM). Thus, a fault-tolerant power converter is fundamental to ensure high reliability and extend the drive operation. To achieve fault tolerance, fault detection and diagnosis methods are critical in order to identify, as soon as possible, the failure mode of the drive. To provide such capability, it is proposed in this paper a new fault-tolerant power converter scheme combined with a fault detection method regarding the most common power semiconductors failures in SRM drives. The fast and reliable proposed diagnosis method is based on the entropy theory. Based on this theory, normalized indexes (diagnostic variables) are created, which are independent from the load and speed of the motor. Through this method, it is possible to identify the faulty leg, as well as the type of power semiconductor fault. To test and evaluate the proposed solution several laboratory experiments were carried out using a 2 kW four-phase 8 / 6 SRM.
- Compensation of unbalanced low-voltage grids using a photovoltaic generation system with a dual four-leg, two-level inverterPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; J. Pires, A.; Hao, Chen; Martins, Joao; Castro, RuiIn 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.
- Hybrid Sepic-Ćuk DC-DC Converter Associated to a SRM Drive for a Solar PV Powered Water Pumping SystemPublication . Cordeiro, Armando; Chaves, Miguel; Canacsinh, Hiren; Luís, Ricardo; Fernao Pires, Vitor; Foito, Daniel; Pires, A. J.; Martins, JoaoThe present paper describes a solar photovoltaic (SPV) powered water pumping system employing a switched reluctance motor (SRM) and a merged Sepic-Ćuk DC-DC converter. The proposed solution was designed to use efficiently the available solar energy in order to supply water pumping systems. Solutions of this kind assume a special importance in the current scenario of natural and renewable resources optimization. The proposed DC-DC converter operates in continuous conduction mode (CCM), which combined with a maximum power point tracking (MPPT) controller, helps to optimize the power of the solar photovoltaic panel (SPV). The proposed DC-DC topology is characterized by high voltage static gain when compared with the classical boost topology and reduced voltage stress across the power switch and diodes. Several simulation and experimental results are presented in order to confirm the characteristics of the proposed solution for water pumping systems.
- A multilevel fault-tolerant power converter for a switched reluctance machine drivePublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Pires, A. J.; Martins, Joao; Chen, HaoReliability in the electrical drives is becoming an important issue in many applications. In this context, the reliability associated to the switched reluctance machine (SRM) is also an important area of research. One of the major problems, that strongly affect its operation, are drive power semiconductors faults. Typical power converter topologies used in SRM drives cannot handle faults in their power semiconductors. So, this paper presents a power converter topology that provides fault-tolerant capabilities to the drive under a switch fault. This power converter will be used considering that a change in the direction of the current that flows in the SRM windings does not affect the behavior of the machine. Besides that, the proposed power converter will allow to generate multilevel phase voltages in order to apply different voltage levels as function of the SRM speed. A laboratory power converter was developed to test the SRM drive in normal and faulty conditions. From the obtained results it was possible to verify the fault-tolerant capability of the drive under switch faults in different devices and failure modes. It was also possible to confirm the multilevel operation of the drive.
- A multilevel topology based on the T-Type converter for SRM drivesPublication . Fernao Pires, Vitor; Cordeiro, Armando; Pires, A. J.; Martins, João; Chen, HaoMultilevel power converters have been used in SRM drives to improve high speed operating characteristics and reduce switching frequency. Several topologies have been proposed to these drives but it requires an increased number of switches. In this paper it is presented a new multilevel topology for the SRM drives. This topology is based on the T-type structure and characterized by a reduced number of power semiconductors resulting in a low cost, size and weight system. With this topology it is possible to accelerate the magnetization and demagnetization process as well as the efficiency of the system through the reduction of the switching frequency at low speed operation. The characteristics and performance of the proposed topology will be verified through several numerical tests.
- A SRM for a PV powered water pumping system based on a multilevel converter and DC/DC dual output converterPublication . Foito, Daniel; Fernao Pires, Vitor; Cordeiro, Armando; Amaral, Tito; Chaves, Miguel; Pires, Armando; Martins, JoaoThis paper focuses on a proposal for a system based on a photovoltaic (PV) supply for a powered water pumping. The system consists in a switched reluctance machine (SRM) controlled by a multilevel converter and fed by PV panels associated to a DC/DC converter. The multilevel power converter proposed to control the SRM was designed to minimize the switches and to support the balance of the two input capacitors. The DC/DC converter consists in a hybrid solution that merges a Buck-Boost converter with a Sepic converter. They use a topology solution in which the input current presents a reduced ripple and only requires one switch. This DC/DC converter is also characterized by a dual output to adapt to the multilevel converter. The control system and a maximum power point tracking (MPPT) algorithm are also presented. The operation of this system will be verified by tests that are done by computer simulations.
- Three-phase T-type qZ source inverter with control current associated to a vectorial modulator for photovoltaic applicationsPublication . Fernao Pires, Vitor; Foito, D.; Cordeiro, Armando; Martins, JoãoThis 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.
- Combining power electronic converters and automation to simulate solar PV systemsPublication . Cordeiro, Armando; Chaves, Miguel; Gamboa, Paulo; Barata, Filipe; Fonte, Pedro M; Lopes, Hélio; Fernao Pires, Vitor; Foito, Daniel; Amaral, Tito; Martins, JoaoThis paper presents a solar photovoltaic panel simulator system with the ability to perform automatic tests in different condition according to manufacture parameters. This simulator is based on three buck-boost DC-DC converters controlled by a microcontroller and supported by a Programmable Logic Controller which is responsible for the automatic tests. This solution will allow to achieve fast response, like suddenly changes in the irradiation, temperature, or load. To control the power converter, it will be used a fast and robust sliding mode controller. Therefore, with the proposed system is possible to perform the I-V curve simulation of a solar PV panel, evaluate different MPPT algorithms considering different meteorological and load variation. The main advantage of this work is the possibility to evaluate and test several MPPT algorithms and understand the operation and typical operation of solar PV panels in different conditions. Several simulations and experimental results from a laboratory prototype are presented to confirm the theoretical operation.
- PV generators combined with UPQC based on a dual converter structurePublication . Fernao Pires, Vitor; Foito, Daniel; Cordeiro, Armando; Martins, JoaoIn 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.