Single-carrier phase-disposition PWM techniques for multiple interleaved voltage-source converter legs

Interleaved converter legs are typically modulated with individual carriers per leg and phase-shifted PWM (PS-PWM) as it facilitates current balancing amongst the legs. Phase-disposition PWM (PD-PWM), despite the better harmonic performance, cannot be directly used due to the resulting current imbalance that may damage the converter. This paper addresses the current sharing issue and proposes a single-carrier PD-PWM technique for multiple leg two-level converters based on a hierarchy scheme derived from current sorting algorithms. An extension of the proposed algorithm through a switching state feedback loop, limiting the average switching frequency, is also developed. In both cases, the load current is shared amongst the legs and the high-quality of the output voltages and currents is maintained while the circulating currents amongst the converter legs are kept to a minimum. Simulation results demonstrate the method for multiple interleaved legs as well as its current sharing capabilities for high-power applications. Experimental results from a low-power laboratory prototype validate the operation of the proposed approach.Peer ReviewedPostprint (published version

Digital Control of Power Converters and Drives for Hybrid Traction and Wireless Charging

In the last years environmental issues and constant increase of fuel and energy cost have been incentivizing the development of low emission and high efficiency systems, either in traction field or in distributed generation systems from renewable energy sources. In the automotive industry, alternative solutions to the standard internal combustion engine (ICE) adopted in the conventional vehicles have been developed, i.e. fuel cell electric vehicles (FCEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEV) or pure electric vehicles (EVs), also referred as battery powered electric vehicles (BEV). Both academic and industry researchers all over the world are still facing several technical development areas concerning HEV components, system topologies, power converters and control strategies. Efficiency, lifetime, stability and volume issues have moved the attention on a number of bidirectional conversion solutions, both for the energy transfer to/from the storage element and to/from the electric machine side. Moreover, along with the fast growing interest in EVs and PHEVs, wireless charging, as a new way of charging batteries, has drawn the attention of researchers, car manufacturers, and customers recently. Compared to conductive power transfer (usually plug-in), wireless power transfer (WPT) is more convenient, weather proof, and electric shock protected. However, there is still more research work needs to be done to optimize efficiency, cost, increase misalignment tolerance, and reduce size of the WPT chargers. The proposed dissertation describes the work from 2012 to 2014, during the PhD course at the Electric Drives Laboratory of the University of Udine and during my six months visiting scholarship at the University of Michigan in Dearborn. The topics studied are related to power conversion and digital control of converters and drives suitable for hybrid/electric traction, generation from renewable energy sources and wireless charging applications. From the theoretical point of view, multilevel and multiphase DC/AC and DC/DC converters are discussed here, focusing on design issues, optimization (especially from the efficiency point-of-view) and advantages. Some novel modulation algorithms for the neutral-point clamped three-level inverter are presented here as well as a new multiphase proposal for a three-level buck converter. In addition, a new active torque damping technique in order to reduce torque oscillations in internal combustion engines is proposed here. Mainly, two practical implementations are considered in this dissertation, i.e. an original two-stage bi-directional converter for mild hybrid traction and a wireless charger for electric vehicles fast charge

Improved Predictive Control in Multi-Modular Matrix Converter for Six-Phase Generation Systems

Distributed generation systems are emerging as a good solution as part of the response to the world’s growing energy demand. In this context multi-phase wind generation systems are a feasible option. These systems consist of renewable AC sources which requires efficient and controlled power conversion stages. This work proposes a novel predictive current control strategy that takes advantage of a multi-modular matrix converter topology in the power stage of a six-phase generation system. The proposed method uses a coupling signal between the modules to decrease the error and the total harmonic distortion compared to independent control of each module. Experimental results validate the new control strategy showing the improvement regarding the target parameters

Decentralized and adaptive selective harmonic elimination strategies for the control of multilevel converters

Este trabajo consta de dos secciones relevantes. La primera sección propone un control descentralizado para los convertidores multi-nivel. Para el diseño del mismo se plantea un modelo generalizado de los convertidores multi-celulares, basándose en los modelos de los convertidores de capacitores flotantes, convertidor multi-nivel de puentes H en cascada y convertidor de multi-phase Buck. Con ese modelo generalizado se plantea el control que consta de 3 partes: Un sistema de derivación, un control de balance de las celdas de los convertidores y un regulador de la variable de salida. El trabajo presenta resultados de simulación y experimentación con los convertidores de capacitores flotantes y de puentes H en cascada, perturbando el voltaje de entrada, insertando una celda y perturbando la resistencia de carga, obteniéndose resultados favorables y en concordancia entre la teoría, la simulación y la experimentación. La segunda parte de la tesis consiste en un controlador para un inversor multi-nivel simétrico de puentes H en cascada de 9 niveles con la modulación de Eliminación Selectiva de Armónicos. Este controlador regula la componente fundamental y elimina las armónicas 3,5 y 7 cuando existen perturbaciones en las fuentes de entrada o cambios en la resistencia de carga. Este controlador es validado tanto en simulación como en experimentación con dos tests, insertando una carga de 200 W y cambiando una fuente de entrada. obteniéndose resultados favorables y en concordancia entre simulación y experimentación. Finalmente, conclusiones y trabajos futuros son detallados.Doctor en IngenieríaDoctorad

EFFICIENCY AND RELIABILITY ENHANCEMENT OF MULTIPHASE SYNCHRONOUS MOTOR DRIVES

Multiphase electric machines are attractive in comparison with three-phase ones due to advantages such as fault-tolerant nature, smaller rating per phase and lower torque ripple. More specifically, the machines with multiple three-phase windings are particularly convenient, because they are suitable for standard off-the-shelf three-phase dc/ac converter modules. For instance, they are becoming a serious option for applications such as electric vehicles and wind turbines. On the other hand, in these applications, operation at low power is often required for long time intervals; hence, improving the efficiency under such conditions is highly desired and could save a significant amount of energy in the long term. This dissertation proposes a method to enhance the efficiency of electric drives based on multiple three-phase windings at light load. The number of active legs is selected depending on the required torque at each instant. To ensure that the overall efficiency is effectively optimized, not only the converter losses, but also the stator copper losses, are taken into account. Experimental results verify the theoretical outcomes. Surface-mounted permanent-magnet synchronous motors (SPMSMs) require a position measurement to ensure a high-performance control. To avoid the cost and maintenance associated to position sensors, sensorless methods are often preferred. The approaches based on high-frequency signal injection are currently a well-established solution to obtain an accurate position estimation in SPMSMs. These techniques can be roughly divided into two groups: those based on sinusoidal or on square-wave high-frequency signals. The main drawback of the former is the limitation on the response speed, due to the presence of several low-pass filters (LPFs). On the other hand, the latter methods are sensitive to deadtime effects, and high-frequency closed-loop current control is required to overcome it. This dissertation proposes to improve the sensorless strategies based on sinusoidal high-frequency injection by simplifying the scheme employed to extract the information about the position error. Namely, two LPFs and several multiplications are removed. Such simplification does not only reduce the computational complexity, but also permits to obtain a faster response to the changes in the angle/speed, and hence, a faster closed-loop control. Experimental results based on a SPMSM prove the enhanced functionality of the proposed method with respect to the previous ones based on high-frequency sinusoidal signal injection

Design And Implementation Of Co-Operative Control Strategy For Hybrid AC/DC Microgrids

This thesis is mainly divided in two major sections: 1) Modelling and control of AC microgrid, DC microgrid, Hybrid AC/DC microgrid using distributed co-operative control, and 2) Development of a four bus laboratory prototype of an AC microgrid system. At first, a distributed cooperative control (DCC) for a DC microgrid considering the state-of-charge (SoC) of the batteries in a typical plug-in-electric-vehicle (PEV) is developed. In DC microgrids, this methodology is developed to assist the load sharing amongst the distributed generation units (DGs), according to their ratings with improved voltage regulation. Subsequently, a DCC based control algorithm for AC microgrid is also investigated to improve the performance of AC microgrid in terms of power sharing among the DGs, voltage regulation and frequency deviation. The results validate the advantages of the proposed methodology as compared to traditional droop control of AC microgrid. The DCC-based control methodology for AC microgrid and DC microgrid are further expanded to develop a DCC-based power management algorithm for hybrid AC/DC microgrid. The developed algorithm for hybrid microgrid controls the power flow through the interfacing converter (IC) between the AC and DC microgrids. This will facilitate the power sharing between the DGs according to their power ratings. Moreover, it enables the fixed scheduled power delivery at different operating conditions, while maintaining good voltage regulation and improved frequency profile. The second section provides a detailed explanation and step-by-step design and development of an AC/DC microgrid testbed. Controllers for the three-phase inverters are designed and tested on different generation units along with their corresponding inductor-capacitor-inductor (LCL) filters to eliminate the switching frequency harmonics. Electric power distribution line models are developed to form the microgrid network topology. Voltage and current sensors are placed in the proper positions to achieve a full visibility over the microgrid. A running average filter (RAF) based enhanced phase-locked-loop (EPLL) is designed and implemented to extract frequency and phase angle information. A PLL-based synchronizing scheme is also developed to synchronize the DGs to the microgrid. The developed laboratory prototype runs on dSpace platform for real time data acquisition, communication and controller implementation

Determination and dynamic compensation of fictitious power in electric power systems

D.Ing. (Electrical & Electronic Engineering)Please refer to full text to view abstrac