Power Converter Topologies for Multiphase Drive Applications

The yet growing demand for higher demanding industrial applications and the global concern about harmful emissions in the atmosphere have increased the interest for new developments in electric machines and power converters. To meet these new requirements, multiphase machines have become a very attractive solution, offering potential advantages over three-phase classical solutions. Multiphase machine’s power demand can be split over more than three phases, thus reducing the electric field stress on each winding (protecting the insulation system) and the requirements on maximum power ratings, for semiconductor devices. Moreover, only two degrees of freedom (i.e. two independently controllable currents) are required for independent flux and torque control. Due to the previous facts, the use of multiphase drives has become very attractive for applications and developments in areas such as electric ship propulsion, more-electric aircraft, electric and hybrid electric road vehicles, electric locomotive traction and in renewable electric energy generation. As a consequence of this multiphase drive tendency, the development of power converter topologies, capable of dealing with high power ratings and handling multiphase winding distributions, has encourage the development of new converter topologies, control strategies and mathematical tools, to face this new challenge

DC-Link Control Schemes in Multilevel Converters for WECS

The introduction of renewable energy resources since the late 1990s as an alternative to fossil energies has impact the development of wind energy and its integration to the grid. From the early 2000s, the wind energy has positioned itself as the most grown-up energy market in the world. This fact has introduced the need to deal with increasing power demands with limited generation capabilities, in terms of generator power density, for low rotation speeds and medium voltage generation within a grid interconnection in high voltage, and other grid code demands, like THD, power factor regulation, and the requirement of continuous operation under faulty condition. Until today, this issue has been solved using classical power converter topologies, using three-level voltage source converters (3LVSC) or multilevel configurations, such as neutral point clamped and cascaded H-Bridge topologies. In this chapter, the main advantages and drawbacks of classical multilevel converter topologies are analyzed, in terms of their DC-link voltage stability capability and different approaches to DC-link control and to new converter topologies, derived from classical topologies, are presented and compared with simulation results

Particle Dark Matter Physics: An Update

This write--up gives a rather elementary introduction into particle physics aspects of the cosmological Dark Matter puzzle. A fairly comprehensive list of possible candidates is given; in each case the production mechanism and possible ways to detect them (if any) are described. I then describe detection of the in my view most promising candidates, weakly interacting massive particles or WIMPs, in slightly more detail. The main emphasis will be on recent developments.Comment: Invited talk at the 5th Workshop on Particle Physics Phenomenology, Pune, India, January 1998; 21 pages, LaTeX with equation.st

Surface runoff and accelerated erosion in a peri‑urban wellhead area in southeastern Brazil

Degradation of hydrological conditions can adversely impact water resource quality and quantity. This degradation can generate social and economic losses, including losses for users outside the basin area. Therefore, studies focusing on surface runof and accelerated erosion processes are needed to enable interventions that address degradation-induced challenges. In the present study, the surface runof and accelerated erosion potential of the Feijão River basin were presented in charts at a 1:50,000 scale. The Feijão River basin has an area of 243.16 km2 and is used as the main water source for the city of São Carlos, Brazil. Geoenvironmental attributes, such as substrate, climate, relief, soil, water bodies and land cover and use, were integrated and assessed in a GIS environment, using a multicriteria analysis and weighted sum tool. The results show that a large part of the area (86.12% of the basin) exhibits a low surface runof potential and a moderate accelerated erosion potential. Accelerated erosive processes are triggered by changes in soil cover and have a direct relationship with the removal of existing vegetation and implementation of anthropogenic activities. In this case, as well as for most of the areas in southeastern Brazil, extensive grazing followed by sugar cane cultivation was the main driving force of erosion, acting as trigger for accelerated erosive processes at the water source area

Evaluation of the Emission Impact of Cold-Ironing Power Systems, Using a Bi-Directional Power Flow Control Strategy

Even though cold ironing is not a new technology applied to reduce the impact of emissions from ships at berth, commonly used arrangements for shore-side power substations only allow a unidirectional power flow, from port to ship side. Although these applications have a positive contribution to port community health and global reduction of greenhouse gases (GHG), especially when the energy is supplied from renewable sources, emissions during loading/unloading operations are directly related to the operating profiles of auxiliary engines of a ship. The present work evaluates a ship’s emission impact when applying cold-ironing technology using a bi-directional power flow control strategy while at berth, thus optimizing the auxiliary engine operating profile and enabling regeneration into the port installations. The methodology applied considers the establishment of the operational profile of the ship, the adaptation and use of carbon intensity indicators (CII) used by the International Maritime Organization (IMO) to evaluate the impact of shipping, and the strategy considering the capacities of the ship to obtain and provide electric power from and to the port when at berth. Results show that the strategy can be applied to any ship with a high demand for electric power while at berth, and that the adaptation and use of different CIIs allows operational profiles of electric power generation on board to be optimized and to reduce emission generation, which affects port community health

Model Predictive Control Scheme of a Four-Level Quasi-Nested Converter Fed AC-Drive, with dc-Link Voltage-Drift Compensation

In this paper, a Model Predictive Control (MPC) strategy is introduced for its application in a four-level quasi-nested topology, feeding an Interior Permanent Magnet Synchronous Machine (IPMSM) AC-drive. The proposed control strategy is capable to synthesize the required output space vectors to ensure perfect tracking of the AC-drive speed reference under different loading conditions, while also ensuring voltage balance between the dc-link capacitors. The proposed converter topology is based on a reduced number of components compared to other mature converter topologies, such as the neutral-point clamped converter (NPC) or the active neutral-point clamped converter (ANPC) topologies, when compared in terms of the number of output voltage levels, since this quasi-nested topology does not require passive clamping devices such as diodes or active switches. Moreover, no floating dc-link capacitors with asymmetrical voltage levels are employed, thus simplifying the dc-link capacitor voltage balance mechanism. This work presents the switching operation principles and MPC control law when supplying an IPMSM AC-drive load are addressed in detail. Simulation and validation results using a Hardware in the Loop (HIL) prototype under different operation conditions are presented in order to validate the proposed converter topology and control strategy

Four-Level Quasi-Nested Inverter Topology for Single-Phase Applications

In this paper, a novel four-level single-phase multilevel converter is introduced, consisting of six active switches arranged in a quasi-nested configuration. The proposed topology synthesizes its output voltage levels with respect to a floating neutral point, using four cascaded capacitors with identical voltage levels. The proposed converter contains a reduced number of components compared to the neutral point clamped (NPC) or active-NPC topologies (ANPC) for the same number of output voltage levels, since it does not require diode or active switch clamping to a neutral point. Moreover, no floating capacitors with asymmetric voltage levels are employed, thereby simplifying the capacitor voltage balancing. The switching operation principles, modulation technique and control scheme for supplying a single-phase resistive-inductive load are addressed in detail. The proposed four-level inverter allows generating an additional output voltage level with the same semiconductor count as conventional three-level inverters such as NPC and ANPC which allows a superior waveform quality, with a THDv reduction of 32.69% in comparison the clamped inverters. Experimental tests carried out in a laboratory-scale setup verify the feasibility of the proposed topology

Four-Level Quasi-Nested Inverter Topology for Single-Phase Applications

In this paper, a novel four-level single-phase multilevel converter is introduced, consisting of six active switches arranged in a quasi-nested configuration. The proposed topology synthesizes its output voltage levels with respect to a floating neutral point, using four cascaded capacitors with identical voltage levels. The proposed converter contains a reduced number of components compared to the neutral point clamped (NPC) or active-NPC topologies (ANPC) for the same number of output voltage levels, since it does not require diode or active switch clamping to a neutral point. Moreover, no floating capacitors with asymmetric voltage levels are employed, thereby simplifying the capacitor voltage balancing. The switching operation principles, modulation technique and control scheme for supplying a single-phase resistive-inductive load are addressed in detail. The proposed four-level inverter allows generating an additional output voltage level with the same semiconductor count as conventional three-level inverters such as NPC and ANPC which allows a superior waveform quality, with a THDv reduction of 32.69% in comparison the clamped inverters. Experimental tests carried out in a laboratory-scale setup verify the feasibility of the proposed topology

Optimization of the Emissions Profile of a Marine Propulsion System Using a Shaft Generator with Optimum Tracking-Based Control Scheme

Nowadays, marine propulsion systems based on thermal machines that operate under the diesel cycle have positioned themselves as one of the main options for this type of applications. The main comparative advantages of diesel engines, compared to other propulsion systems based on thermal cycle engines, are the low specific fuel consumption of residual fuels, and their higher thermal efficiency. However, its main disadvantage lies in the emissions produced by the combustion of the residual fuels, such as carbon dioxide (CO2), sulfur oxide (SOx), and nitrogen oxide (NOx). These emissions are directly related to the operating conditions of the propulsion system. Over the last decade, the International Maritime Organization (IMO) has adopted a series of regulations to reduce CO2 emissions based on the introduction of an Energy Efficiency Design Index (EEDI) and an Energy Efficiency Operational Indicator (EEOI). In this context, adding a Shaft Generator (SG) to the propulsion system favoring lower EEDI and EEOI values. The present work proposes a selective control system and optimization scheme that allows operating the shaft generator in Power Take Off (PTO) or Power Take In (PTI) mode, ensuring that the main engine operates, always, at the optimum fuel efficiency point, thus ensuring minimum CO2 emissions