Thiago Morais Parreiras

Hundreds kW Charging Stations for e-Buses Operating Under Regular Ultra-Fast Charging

A natural evolution for public transportation vehicles is to develop towards the electric driven buses (e-buses). Batteries weight and volume is still an issue for passenger electric cars. However, the urban bus has interesting characteristics as predefined routes and stops which allow an optimized onboard storage capacity and strategies of Regular Ultra Fast Charging (R-UFC). This way, some hundreds kW charging stations (UFC-Station) may be installed next to the bus boarding stations for providing the R-UFC in e-bus. This paper proposes a power architecture for UFC-stations using the new True Unit Power Factor (TUPF) Rectifier as a charger front-end and interleaved dc-dc converters as charger output. Both technologies contribute significantly to the reduction of filter components and assure high power quality standards. The proposed TUPF rectifier eliminates all harmonic order up to 50th, operates with low switching frequency and does not use sinusoidal filter. The UFC-stations are explained and evaluated based on computer simulations of a 400 kW application.

Forward dual-active-bridge solid state transformer for a SiC-based cascated multilevel converter cell in solar applications

Central inverters based on conventional topologies are the current preferred solution in solar farms because of their low cost and simplicity. However, such topologies have some disadvantages as poor maximum power tracking, use of bulky filters and low frequency transformers. A good alternative in this case is the SiC-based Cascaded Multilevel Converter (CMC), which provides a distributed MPPT control with reduced footprint and high flexibility. Each cell of a CMC usually has as an intermediate stage a solid-state transformer based on a Dual-Active-Bridge (DAB) DC-DC Converter. Due to the unidirectional power flow characteristic of the photovoltaic application and aiming further reduction in the converter footprint, this work proposes a Forward Dual-Active-Bridge (F-DAB) topology, which reduces the number of active switches. This paper shows through analytical, simulation and experimental results that the cell using an F-DAB is superior to other unidirectional topologies in two aspects: greater power density with the available power modules and simplicity of control.

Control of a SiC-based Cascaded Multilevel Converter cell for solar applications

Central inverters based on conventional topologies are the current preferred solution in solar farms because of their low cost and simplicity. However, such topologies have some disadvantages: poor Maximum Power Point Tracking (MPPT), and the use of bulky filters and Low Frequency (LF) transformers. An attractive alternative in this case is the Cascaded Multilevel Converter (CMC), which can provide a distributed MPPT control, allied with overall reduced footprint and high flexibility. A CMC cell using silicon carbide devices has been proposed and designed in previous works to incorporate three main functions: MPPT control of a Photovoltaic (PV) array, galvanic isolation through a Solid-State Transformer (SST) and control of grid power flow. This work proposes a closed-loop control strategy for each stage of the CMC cell and shows its validation thorough simulations. Experimental results are performed and presented in a single-phase 6.2 kW prototype cell. These results lead to the conclusion that the applied control techniques are suitable to the PV application.

True Unit Power Factor Active Front End for High-Capacity Belt-Conveyor Systems

Belt conveyors in mining industry constitute an efficient and economical way for minerals and heavy-load transportation from mines to their destination. The ongoing desire to further extend the length, speed, and capacity of the conveyors has led to the increasing size of the conveyor-drive systems. More and more frequently, high-capacity belt conveyors are efficiently driven employing medium-voltage power converters connected with large induction motors. Power converters in the megawatt (MW) range are often used, increasing the power-quality issues in the grid system. This work proposes a new true unit power factor active front end for regenerative multimotor conveyor-drive systems. The proposed solution eliminates all the current harmonics in the range considered by the international standards without using sinusoidal filters. Three-winding conventional transformer and well-established medium-voltage power converters are considered to ensure the robustness and simplicity requirements.

The True Unity Power Factor converter — A practical filterless solution for sinusoidal currents

High power conversion entails the necessity of converters interfacing with the grid which have both low losses and low harmonic content. For this purpose several topologies have been proposed, but, due to the restriction imposed on the switching frequency, these topologies often make use of complex multi winding transformers or large sinusoidal filters. These features increase cost, losses and reduce reliability of the converters. This paper proposes a new solution called True Unity Power Factor (TUPF) converter, which makes use of a well selected PWM pattern, a simple three winding transformer and two or three level active rectifier topologies. As the name implies, this converter is capable of delivering a true unity power factor conversion and accomplish these task keeping a low enough switching frequency without using any capacitive filter element. This paper shows the mains elements of the TUPF concept, some applicable regenerative or non-regenerative topologies, simulation and experimental results.

True unit power factor active front end for high capacity belt conveyor systems

Belt conveyors in mining industry constitute an efficient and economical way for minerals and heavy-load transportation from mines to their destination. The ongoing desire to further extend the length, speed, and capacity of the conveyors has led to the increasing size of the conveyor-drive systems. More and more frequently, high-capacity belt conveyors are efficiently driven employing medium-voltage power converters connected with large induction motors. Power converters in the megawatt (MW) range are often used, increasing the power-quality issues in the grid system. This work proposes a new true unit power factor active front end for regenerative multimotor conveyor-drive systems. The proposed solution eliminates all the current harmonics in the range considered by the international standards without using sinusoidal filters. Three-winding conventional transformer and well-established medium-voltage power converters are considered to ensure the robustness and simplicity requirements.

Common-Mode Overvoltage Mitigation in a Medium-Voltage Pump Motor Transformerless Drive in a Mining Plant

Mining process requires several types of mining pumps to transfer a fluid from one point to another in the process. In the majority of applications, those pumps are driven by variable speed motor drives in order to improve the energy efficiency of the overall system. Large pumps, ranging from hundreds of kW to a few MW, usually demand medium voltage converters. Transformerless converters reduce the footprint required for the installation, but produce additional concerns related to the common-mode voltages applied to the system and motor. The absence of an isolation transformer along with the use of PWM rectifiers are the root causes of this issue. This concern increase when long cables are needed to connect the converter to the motor. This paper presents an application where 3L NPC transformerless medium voltage converters were applied to drive motor pumps in a mining plant. The passive filter techniques used to address the common-mode voltage issue were analyzed through simulations and compared with the field results.

Common-mode overvoltage mitigation in a medium voltage pump motor transformerless drive in a mining plant

The mining process requires different types of pumps to transfer fluids from one point to another. In the majority of applications, those pumps are driven by variable speed motor drives in order to improve the energy efficiency of the overall system. Large pumps, ranging from hundreds of kW to a few MW, usually demand medium-voltage converters. Transformerless converters reduce the footprint required for the installation, but give rise to additional concerns related to the common-mode voltages applied to the system and motor. The absence of an isolation transformer along with the use of pulse-width modulated rectifiers are the root causes of this issue. This concern increases when long cables are needed to connect the converter to the motor. This paper presents an application where three-level neutral point clamped transformerless medium-voltage converters are applied to drive motor pumps in a mining plant. The passive filtering techniques used to address the common-mode voltage issues are analyzed through simulations. The proposed solutions are field tested with successful results.