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Creators/Authors contains: "Balda, Juan Carlos"

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  1. This paper presents the design of a three-phase three-limb high-efficiency medium-voltage medium-frequency transformer with an integrated leakage layer using ribbon-based nanocrystalline cores for three-phase grid-connected applications. The design methodology is based on a custom-core approach developed by a series of design equations that allow the user to select a design that best fits the transformer specifications. A 150kVA 10-kHz 5-kV-to-400-V three-phase three-limb transformer is designed to validate the proposed design method. In addition, a series of experimental characterisation tests are conducted to measure the performance of the design according do the theoretical performance.
  2. This work presents the modeling and characterization of 10-kV SiC MOSFET modules used for medium-voltage distribution system applications. In addition to the nonlinear junction capacitances of the devices, the model includes the non-linearities present at steady-state like transfer characteristics and the behavior in the Ohmic region, which allows to increase the accuracy of the SiC MOSFET model. Furthermore, the parasitic inductances in the circuit (such as the source inductance shared by the power stage and driver loop and the drain inductance) are considered in the model since it has been demonstrated previously that it influences the total losses. By using the proposed model, the calculated voltage and current transients show a good match with the experimental results.
  3. Inherent current imbalances are often present in electric distribution systems due to the increase of singlephase generation in the form of renewables and the existence of single-phase loads. The continued expansion of non-linear load usage is also increasing the levels of harmonics through the power transformers servicing these distribution systems. The issues that arise from these operating conditions are widely known and standard solutions used by utilities are as well. However, they are often bulky and do not provide a level of control or versatility appropriate for these challenges. This paper gives an overview of many of the problems that are faced on distribution systems and how an active shunt compensator may be used to mitigate or eliminate them.
  4. Microgrid are gaining popularity due to several advantages like potential for fuel savings and resiliency in case of grid catastrophic failures. In a microgrid, many energy sources like wind and solar farms are connected to the grid through inverters with different power ratings and LCL filter parameters. The inverters incorporated in these systems might have a different frequency response and stability ranges than those inverters with identical LCL filter values. This paper establishes the model and analyzes the stability of a system with multiple paralleled- and grid-connected inverters with different LCL filter paramenters using the grid-side currents as feedback signals. The analysis results showed that a method similar to the interactive and common current analysis technique used on inverters with identical LCL filters can be implemented on a system with different LCL filers to calculate the maximum values of the inverters’ current controller gains without having to derive the complicated equations of the MIMO system.
  5. Distributed generation is gaining greater penetration levels in distribution grids due to government incentives for integrating distributed energy resources (DERs) and DER cost reductions. The frequency response of a grid-connected single inverter changes as other inverters are connected in parallel due to the couplings among grid inductance and/or inverter output filters. The selection of the inverter- or grid-side currents as feedback control signals is then not trivial because each one has tradeoffs. This paper analyses the system stability for multiple parallel- and grid-connected inverters using the inverter- or gridside currents as feedback signals. Modeling of both feedback signals is performed using the current separation technique. Moreover, the stability range for different conditions including active damping is analyzed through the root locus technique. The grid-side current has a wider range of stability, but the inverterside current allows for higher values of the proportional gain near the critical frequency and no extra sensors are needed since measurement of the inverter current is needed for protection in high-power applications.
  6. The analysis of a shoot-through-proof converter topology designed to eliminate the need for a dead time between switching transitions is presented. Shoot-through-proof is done by splitting each leg of a normal converter and inserting an inductor to limit the current during transitions. Matlab/Simulink™ simulations based on a 10-kVA laboratory test setup, which was built to validate the proposed ideas, are used to evaluate the system performance. In particular, simulations were used to predict losses associated with the topology and reduce the harmonics injected by the converter. The control system was implemented in a TMS320F28335 DSP, and the results of both the simulations and prototype testing showed very good agreement.