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- PV power conditioning system using a three-phase multilevel pulse width modulation inverter employing cascaded Scott transformersPublication . Fernao Pires, Vitor; Foito, Daniel; Cordeiro, ArmandoVoltage source inverters (VSIs) are power converters that are considered essential in grid connected photovoltaic (PV) generators. There are several types of topologies for these converters. However, from the point of view of high-quality AC output voltage, multilevel inverters are considered the most adequate. Under this context, this study proposes a new structure for the three-phase DC-AC conversion stage for a grid-connected PV system. It consists of two four-leg two-level voltage source inverters that are connected to two PV generators. These inverters are associated with two Scott transformers. The secondary windings of the transformer are connected in a way that allows a series connection. Due to this, a multilevel operation will be achieved. The performance of the proposed power conditioning system will be verified through simulation and experimental results.
- Fault-tolerant three-phase quasi-switched boost inverterPublication . Cordeiro, Armando; Fernao Pires, Vitor; Foito, Daniel; Bondarenko, OleksandrThis paper proposes a fault-tolerant topology based on the three-phase quasi-switched Boost Inverter ( qSBI ). Besides the additional qSBI, the solution also uses non-active power devices to reconfigure the topology and maintain the normal operation in case of an open-circuit failure mode of a power device. The proposed topology presents important features such as boost capability, avoids extra inductors, capacitors or active power devices. Regarding the control solution for this topology, it will be used on a closed-loop current controller at which be associated a vectorial voltage modulator. Since this modulator is also function of the shoot-through will be possible to recover the amplitude voltage space vectors due to failures in power devices. The combination of these elements allows to obtain three-phase balanced AC currents with reduced total harmonic distortion even in fault-tolerant operation mode. The fault tolerance performance of this solution will be confirmed through several simulation results.
- Three-phase multilevel inverter for grid-connected distributed photovoltaic systems based in three three-phase two-level invertersPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, D.; Silva, J. FernandoA multilevel three-phase voltage source inverter (VSI) for distributed grid-connected photovoltaic system is proposed in this paper. This multilevel inverter is based on a new topology using three three-phase two-level VSIs ((TVSI)-V-3) with isolation transformer. The photovoltaic panels are connected at the DC side of each three-phase VSI. The three-phase VSIs AC sides are connected to the three-phase isolation transformer with primary open-end windings, ensuring multilevel operation. The (TVSI)-V-3 can be modulated using existing multilevel Pulse Width Modulation (PWM) schemes. A control system designed to ensure the transfer of the energy generated by the PV generators to the grid is also presented, together with a Phase Disposition PWM (PDPWM) adapted for the multilevel (TVSI)-V-3. Tests of the grid-connected PV multilevel (TVSI)-V-3 will be shown through simulation and experimental results. Several results obtained from experiments confirm the expected characteristics of the multilevel (TVSI)-V-3 photovoltaic system.
- 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.
- Three-level NPC dual-buck inverter designed to safety-critical applicationsPublication . Cordeiro, Armando; Fernao Pires, Vitor; Foito, DanielThis paper presents a three-phase three-level NPC (neutral point-clamped) Dual-Buck inverter topology suitable to increase fault-tolerant capability to safety-critical applications. Using the proposed topology, it is possible to achieve energy processing capability in case of several failure modes. The faulttolerant enhancements are a consequence of appropriate modifications in the control strategy and from redundancy of power devices to maintain the correct operation of the converter. The proposed control strategy adopted in the presented solution can also equalize the capacitor voltages automatically. Some simulation results are included in this study to confirm the validity of the theoretical study.
- Fault tolerant operation of three-phase 3 level T-Type qZS inverters using sliding mode current controllersPublication . Fernao Pires, Vitor; Foito, Daniel; Santos, Natalia; Cordeiro, Armando; Roncero Clemente, Carlos; Silva, J. F.Due to the boost characteristic and the several possible outputs of quasi-Z-source inverters (qZSI), these topologies can be valuable options to operate under fault conditions, provided the controller is able to take advantage of the available output states. Thus, the development of control systems to take advantage of the available outputs is needed. Hence, this paper focuses on the development of a control system to operate a three-phase three-level T-Type qZSI under fault tolerant conditions. The controller is based on a sliding mode current controller associated to a vectorial modulator selecting the available outputs. The proposed strategy for the controller and modulator is presented taking into consideration the normal and fault-tolerant requirements. The strategy also considers the balance of the capacitors under fault tolerant condition. The converter operating in both modes is tested through several simulation studies.
- Multilevel converter fed SRM Drive for Single stage PV array based water pumpingPublication . Fernao Pires, Vitor; Foito, Daniel; Pires, A. J.; Cordeiro, Armando; Martins, J. F.; Chen, HaoIn 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.
- 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.
- A vector voltage modulator for a dual inverter with a floating bridge to operate in normal and fault tolerant modePublication . Fernao Pires, Vitor; Foito, Daniel; Cordeiro, Armando; Silva, J. FernandoThe dual inverter multilevel converter is characterized by a simple structure using two well-known three phase bridge inverters supplied by two independent DC sources. However, it can be supplied only by a single DC source if one of the bridges uses just a floating DC capacitor. In this case the control is more complex since it is also required to ensure the capacitor voltage regulation. Besides this, if a fault in one of the switches is also considered, the operation of the converter in fault operation mode becomes even more complex. This paper presents a vector voltage modulator that in addition to track the reference of the output AC voltages, also allows the capacitor voltage regulation of the floating bridge. The capability of this modulator to operate the converter in fault tolerant mode under an inverter open switch will also be analyzed. This analysis will allow to verify that the proposed control and modulation strategy presents inherent fault tolerant capability to open switch fault, since it does not require any fault detection algorithm or change in the control or modulation strategy. The capability and operation of the proposed vector voltage modulator will be verified through several simulation studies.
- Fault-tolerant multilevel converter to feed a switched reluctance machinePublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Pires, Armando J.The switched reluctance machine (SRM) is one of the most interesting machines, being adopted for many applications. However, this machine requires a power electronic converter that usually is the most fragile element of the system. Thus, in order to ensure high reliability for this system, it is fundamental to design a power electronic converter with fault-tolerant capability. In this context, a new solution is proposed to give this capability to the system. This converter was designed with the purpose to ensure fault-tolerant capability to two types of switch faults, namely open- and short-circuit. Moreover, apart from this feature, the proposed topology is characterized by a multilevel operation that allows improvement of the performance of the SRM, taking into consideration a wide speed range. Although the proposed solution is presented for an 8/6 SRM, it can be used for other configurations. The operation of the proposed topology will be described for the two modes, fault-tolerant and normal operation. Another aspect that is addressed in this paper is the proposal of fault detection and diagnosis method for this fault-tolerant inverter. It was specifically developed for a multilevel SRM drive. The theoretical assumptions will be verified through two different types of tests, firstly by simulation and secondly by experiments with a laboratory prototype.