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- Input output linearization and PI controllers for AC-AC matrix converter based dynamic voltage restorers with flywheel energy storage: a comparisonPublication . Gamboa, Paulo; Silva, J. Fernando; Pinto, Sonia; Margato, ElmanoThis paper presents the theoretical development and performance of novel Input-Output Linearization (IOL) AC voltage controllers applied to Dynamic Voltage Restorers (DVR) with Flywheel Energy Storage (FES). IOL performance is compared to decoupled proportional integral (PI) controllers, both relying on a backward Euler predictive current controlled AC-AC matrix converter. The critical load AC decoupled voltage control using IOL or PI is detailed as well as the backward Euler predictive current control. The matrix input and output current tracking control uses a backward Euler predictive current control minimizing a weighted cost functional. The stable backward Euler matrix vector estimation enables the AC-AC matrix to perform as a current tracking converter. Experimental results are obtained using a laboratory level DVR fitted with FES device made from a vertical axis rotating seamless steel hollow cylinder (flywheel) storing kinetic energy. The flywheel is coupled to a Permanent Magnet Synchronous Machine (PMSM) motor/generator, which is driven by the AC-AC matrix converter. The DVR was tested to mitigate voltage sags in isolated neutral critical loads, using IOL and PI controllers. The DVR is able to compensate the critical load voltage without noticeable delays, voltage undershoots or overshoots, overcoming the input/output coupling problem of matrix converters. IOL controller proves to be faster and more aggressive than the PI controller, which is softer introducing less voltage distortion.
- A buck-boost converter with extended duty-cycle range in the buck voltage region for renewable energy sourcesPublication . Monteiro, Joaquim; Fernao Pires, Vitor; Foito, Daniel; Cordeiro, Armando; J. F. Silva, Fernando Silva, Fernando A Silva, J. Fernando Silva, J F A Silva, Fernando Silva José; Pinto, SoniaBuck-boost DC-DC converters are useful as DC grid interfaces for renewable energy resources. In the classical buck-boost converter, output voltages smaller than the input voltage (the buck region) are observed for duty cycles between 0 and 0.5. Several recent buck-boost converters have been designed to present higher voltage gains. Nevertheless, those topologies show a reduced duty-cycle range, leading to output voltages in the buck region, and thus require the use of very low duty cycles to achieve the lower range of buck output voltages. In this work, we propose a new buck-boost DC-DC converter that privileges the buck region through the extension of the duty-cycle range, enabling buck operation. In fact, the converter proposed here allows output voltages below the input voltage even with duty cycles higher than 0.6. We present the analysis, design, and testing of the extended buck-boost DC-DC converter. Several tests were conducted to illustrate the characteristics of the extended buck-boost DC-DC converter. Test results were obtained using both simulation software and a laboratory prototype.
- A Novel Multilevel T-Type Indirect Matrix Converter for Three-phase Open-end AC LoadsPublication . Bento, Alexandre; Luís, Ricardo; Pinto, Sonia; Silva, J. FernandoIn this work a novel topology featuring an Indirect Matrix Converter (IMC) supplying a three-phase openend load is proposed to allow multiple levels of voltage while reducing common mode voltages (CMV) at load terminals. The topology features a T-Type three phase inverter connected to the grid neutral terminal, allowing phase to phase or phase to neutral voltages to be supplied to the load. A comparison with the already known IMC open-end load scheme, based on two voltage source inverters (VSI), is performed achieving promising results in terms of Common Mode Voltage reduction at the load terminals, while achieving current waveforms with lower distortion. The improvement of CMV waveforms is useful for motor drives, reducing drive bearing currents and increasing overall lifespan.
- Diagnosing Power Transistor Faults in Multilevel T-Type Based Nine Switch Inverter Using Center of Mass IndexesPublication . Monteiro, Joaquim; Amaral, Tito; Silva, J. Fernando; Pinto, Sonia; Fernao Pires, VitorNine-switch voltage source inverters (NSVSI) are DC-AC converters that utilize a reduced number of switches, making them advantageous for dual or six-phase motors. To enhance the quality of the output voltage and provide fault tolerant capability, NSVSI topologies, like the T-Type-based NSVSI, have been modified to operate as multilevel converters. However, to ensure fault-tolerant capability, a fault diagnosis algorithm for power transistors must be developed. Therefore, this paper proposes a novel fault detection and diagnosis algorithm to identify faulty transistors in a multilevel T-Type-based NSVSI. This method is based on the development of specific indices derived from the center of mass of the output currents. The proposed technique offers a fast and reliable solution, demonstrating robustness under various load conditions. The effectiveness of this method will be validated through a series of simulation tests.