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

A survey on capacitor voltage control in neutral-point-clamped multilevel converters

Neutral-point-clamped multilevel converters are currently a suitable solution for a wide range of applications. It is well known that the capacitor voltage balance is a major issue for this topology. In this paper, a brief summary of the basic topologies, modulations, and features of neutral-point-clamped multilevel converters is presented, prior to a detailed description and analysis of the capacitor voltage balance behavior. Then, the most relevant methods to manage the capacitor voltage balance are presented and discussed, including operation in the overmodulation region, at low frequency-modulation indexes, with different numbers of AC phases, and with different numbers of levels. Both open- and closed-loop methods are discussed. Some methods based on adding external circuitry are also presented and analyzed. Although the focus of the paper is mainly DC–AC conversion, the techniques for capacitor voltage balance in DC–DC conversion are discussed as well. Finally, the paper concludes with some application examples benefiting from the presented techniques.Peer ReviewedPostprint (published version

Optimized Modulation and Thermal Management for Modular Power Converters

The transition to a more and more decentralized power generation based on renewable energy generation is accompanied by high challenges. Modular power converters play a central role in facing these challenges, not only for grid integration but also to provide flexible services, highly efficient power transmission and safe storage integration. These goals are the key elements in becoming independent from fossil and nuclear power plants in near future. Even if the costs for renewable energy power plants like wind or photovoltaic systems are already competitive to conventional solutions, more flexible operation and further reduction in costs are required for faster global transformation towards sustainable energy systems. The further optimization of modular power converters can be seen as an ideal way to achieve these ambitious goals. It is therefore chosen as the focus of this work

Hybrid Active PWM Strategy with Dual-Mode Modulation Waves of Three-Level T-type Converter for Aircraft Turboelectric Propulsion Systems

Turboelectric propulsion is emerging as an enabling technology for the future aviation industry, aiming to reduce its carbon footprint. To provide electrified thrust for aircraft, the converter-fed motor drive system is a promising solution for the energy conversion between an onboard dc distribution bus and a high-speed electric machine. However, the neutral-point potential fluctuation and even drifting can be an outstanding issue when employing three-level neutral-point-clamped (3L-NPC) topologies, which puts the converter output performance and the lifespan of capacitors at risk. To address these problems, in this paper, a new hybrid active pulse-width-modulation (PWM) strategy is proposed for the studied airborne electric propulsion systems. With the versatile dual-mode modulation signals, not only can the proposed PWM algorithm keep capacitor voltages balanced at the entire range of operating points but also switching losses can be lowered with the help of discontinuous pulse trains during the cruise. Moreover, the computational burden rendered by a short switching cycle is reduced by the sextant coordinate-based analytical derivation. The effectiveness of the presented modulation technique are validated through simulation results from a Simulink/PLECS model and experimental results obtained from a 200 kVA silicon-carbide (SiC) based T-type 3L-NPC prototype with a variable output fundamental frequency

Hybrid modulation technique with dc-bus voltage control for multiphase NPC converters

The paper presents a novel Carrier-Based Pulse Width Modulation (CBPWM) technique for multiphase Neutral Point Clamped (NPC) converters. The technique is aimed to actively control the Neutral Point (NP) potential while supplying the desired set of line-to-line voltages to the load. Standard techniques are either based on the sole Common Mode Voltage Injection (CMI) or on the sole Multi-Step (MS) switching mode; contrarily, the proposed algorithm combines these two approaches to take advantage of their main benefits. The technique performs well for each number of phases, for each modulation index and for each type of load. It can control in closed-loop the NP voltage to any desirable value with a reduced number of switching transitions. The proposed approach has been experimentally validated and compared with other carrier-based algorithms

Emerging Power Electronics Technologies for Sustainable Energy Conversion

This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches

Emerging Power Electronics Technologies for Sustainable Energy Conversion

This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches