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

High Speed DC-DC Converter with Self-Oscillating Control

In order to reduce the overall size of the power conversion device several advanced techniques can be applied. One of the direct ways is increasing switching frequency of DC-DC converter. This leads to decreased size of bulky energy storage components, such as inductors and capacitors. However, a rapid rise of operating frequency brings new challenges. Among those are significant switching and conduction losses, which make using conventional topologies of converters impractical. Therefore, various new topologies should be investigated. This Thesis presents design and simulations of High speed DC-DC converter with self-oscillating control. The design procedure is described in details for discrete implementation on printed-circuit board. The simulation results are analyzed and a few additional recommendations for improving efficiency and performance of circuit are given. The proposed converter consists of cascaded power stage, duty-cycle detector, pulse shaper, and transformer. The primary winding of transformer serves as a filter load coil and secondary supplies feedback signal to the gates of switching transistors by employing duty-cycle detector and pulse shaping circuit. The designed High speed DC-DC converter with self-oscillating control provides an output voltage of 2.34 V while operating at 3.4 MHz switching frequency. The reported efficiency of circuit is 70.35%. The input voltage is 4 V and duty cycle is 58%. The operation of converter is intended for variable supply voltage from 3 V to 5 V. A resonant gate driving technique with respect to the proposed DC-DC converter is also presented in that work. The converter provides 2.30 V of output voltage and efficiency of 72.4%. The operation frequency is 3.35 MHz

Performance Analysis of Photovoltaic Fed Distributed Static Compensator for Power Quality Improvement

Owing to rising demand for electricity, shortage of fossil fuels, reliability issues, high transmission and distribution losses, presently many countries are looking forward to integrate the renewable energy sources into existing electricity grid. This kind of distributed generation provides power at a location close to the residential or commercial consumers with low transmission and distribution costs. Among other micro sources, solar photovoltaic (PV) systems are penetrating rapidly due to its ability to provide necessary dc voltage and decreasing capital cost. On the other hand, the distribution systems are confronting serious power quality issues because of various nonlinear loads and impromptu expansion. The power quality issues incorporate harmonic currents, high reactive power burden, and load unbalance and so on. The custom power device widely used to improve these power quality issues is the distributed static compensator (DSTATCOM). For continuous and effective compensation of power quality issues in a grid connected solar photovoltaic distribution system, the solar inverters are designed to operate as a DSTATCOM thus by increasing the efficiency and reducing the cost of the system. The solar inverters are interfaced with grid through an L-type or LCL-type ac passive filters. Due to the voltage drop across these passive filters a high amount of voltage is maintained across the dc-link of the solar inverter so that the power can flow from PV source to grid and an effective compensation can be achieved. So in the thesis a new topology has been proposed for PV-DSTATCOM to reduce the dc-link voltage which inherently reduces the cost and rating of the solar inverter. The new LCLC-type PV-DSTATCOM is implemented both in simulation and hardware for extensive study. From the obtained results, the LCLC-type PV-DSTATCOM found to be more effective than L-type and LCL-type PV-DSTATCOM. Selection of proper reference compensation current extraction scheme plays the most crucial role in DSTATCOM performance. This thesis describes three time-domain schemes viz. Instantaneous active and reactive power (p-q), modified p-q, and IcosΦ schemes. The objective is to bring down the source current THD below 5%, to satisfy the IEEE-519 Standard recommendations on harmonic limits. Comparative evaluation shows that, IcosΦ scheme is the best PV-DSTATCOM control scheme irrespective of supply and load conditions. In the view of the fact that the filtering parameters of the PV-DSTATCOM and gains of the PI controller are designed using a linearized mathematical model of the system. Such a design may not yield satisfactory results under changing operating conditions due to the complex, nonlinear and time-varying nature of power system networks. To overcome this, evolutionary algorithms have been adopted and an algorithm-specific control parameter independent optimization tool (JAYA) is proposed. The JAYA optimization algorithm overcomes the drawbacks of both grenade explosion method (GEM) and teaching learning based optimization (TLBO), and accelerate the convergence of optimization problem. Extensive simulation studies and real-time investigations are performed for comparative assessment of proposed implementation of GEM, TLBO and JAYA optimization on PV-DSTATCOM. This validates that, the PV-DSTATCOM employing JAYA offers superior harmonic compensation compared to other alternatives, by lowering down the source current THD to drastically small values. Another indispensable aspect of PV-DSTATCOM is that due to parameter variation and nonlinearity present in the system, the reference current generated by the reference compensation current extraction scheme get altered for a changing operating conditions. So a sliding mode controller (SMC) based p-q theory is proposed in the dissertation to reduce these effects. To validate the efficacy of the implemented sliding mode controller for the power quality improvement, the performance of the proposed system with both linear and non-linear controller are observed and compared by taking total harmonic distortion as performance index. From the obtained simulation and experimentation results it is concluded that the SMC based LCLC-type PV-DSTATCOM performs better in all critical operating conditions

Control of Static Converters for Grid-Side and Machine-Side Applications

The research activities summarized in this Ph.D. thesis are mainly referred to the power electronics field, with some extensions related to electric machines and electrical drives. The first chapter focuses on the analysis and control of an unconventional static converter able to extend a common 1-phase mains feeder into a standard 3-phase power supply featuring either a 3-wires or a 4-wires output, the latter including neutral. Such converter exhibits a complete power reversibility and permits to achieve a good power quality level both at the input and the output side. It is proposed as an attractive alternative to conventional solutions possibly available in the market, such as converters for drives supplied by 1-phase mains yet using 3-phase motors, thanks to the following benefits: greater simplicity, lower cost, inherent active-filter-like operation at supply side, low harmonic distortion at load side. Such converter might be then successfully applied in any application requiring a 3-phase standard supply when a 1-phase mains feeder is available. A theoretical analysis of the converter is presented as well as a semi-ideal simulation model implemented referring to different control strategies. Several simulation results are finally reported and commented, confirming the effectiveness of the proposed solution. The second chapter focuses on the real-time control of 3-phase single-dc-bus shunt active filters employed for the parallel compensation of harmonics, reactive components and unbalancing in the currents drawn by a power supply when generic 3-phase non-linear, non-resistive and unbalanced loads are connected. In particular, the specific issues related to applications featuring a high fundamental frequency, such as in aerospace ambit, were addressed, investigating an innovative improved dead beat digital control algorithm. Such solution was proposed and get ready mainly aiming to achieve a rather high bandwidth of the current control loop and a good reference tracking even when the number of commutations per fundamental period that can be used is rather low. In order to probe the performances of the proposed control strategy, a simulation model was first developed and a prototype system was finally get ready. The results obtained from several virtual and experimental tests are reported and commented referring both to standard industrial and much more demanding aerospace operative conditions, thus proving the validity of the proposed solution. The third chapter focuses on the real-time control of 3-phase multilevel shunt active filters employing a multilevel cascaded H-bridges structure, again mainly referring to applications featuring a high fundamental frequency such as in aerospace ambit. In fact, such power structures may permit to improve the equivalent converter performances while keeping at relatively low values the actual switching frequency of the power devices. In particular, the combined application of an innovative modulation technique and of a dead-beat strategy analogous to the one described in the previous chapter was investigated. A theoretical analysis of the proposed control strategy is reported, as well as several experimental results obtained from a prototype system purposely get ready and tested at both industrial and aerospace frequency, highlighting the potential of the proposed solution especially for the latter applications. The experimental activities related to chapters 2 and 3 were developed during a study period spent at the University of Nottingham, UK. The fourth chapter deals with the modeling and control of an innovative rotary-linear brushless machine. In particular, after its ideal analytical modeling and operation principle, its basic control strategy inspired to sinusoidal brushless machines is presented, reporting some simulation results. A more detailed simulation model based on the equivalent magnetic circuit approach is then presented, permitting to approximately take into account several secondary aspects neglected by the simpler basic sinusoidal model while remaining not much computationally intensive as a finite element model would be. Simulation results obtained by such model are reported and commented, highlighting its potential usefulness for both preliminary machine design purposes and for analyzing the operation of a complete drive. Finally, the fifth chapter presents the application of the same intermediate-level modeling approach described in chapter 4 to a consequent-pole brushless machine featuring an unconventional magnet-pole angular width ratio. After some considerations on the specific arrangement examined, which was conceived to achieve a better exploitation of the active materials, a simulation model of the machine is presented and numerical results are reported and commented, highlighting the usefulness of the proposed intermediate-level modeling approach

Flexible Electronics Based on Solution Processable Organic Semiconductors and Colloidal Semiconductor Nanocrystals

Solution-processable semiconductors hold great potential for the large-area, low-cost fabrication of flexible electronics. Recent advances in flexible electronics have introduced new functional devices such as light-weight displays and conformal sensors. However, key challenges remain to develop flexible devices from emerging materials that use simple fabrication processes and have high-performance. In this thesis, we first use a solution-processable organic semiconductor to build field-effect transistors on large-area plastic with mobility of 0.1 cm^2/Vs. Combined with passive components, we are able to build voltage amplifiers to capture few mV amplitude bio-signals. This work provides a proof of concept on applying solution processable materials in flexible circuits. In the second part of the thesis, we introduce colloidal CdSe nanocrystals (NCs) as solution-processable inks of semiconductor thin film devices. By strongly coupling and doping the CdSe NC thin films, we demonstrate high-performance, flexible nanocrystal field-effect transistors (NC-FETs) with mobility greater than 20 cm^2/Vs under 2V supply. Using these NC-FETs as building blocks, we demonstrate the first flexible nanocrystal integrated circuits (NCICs) with switching speed of 600 µsec. To design reliable integrated circuits with low-noise, we characterize the flicker noise amplitude and origin. We find the figure of merit for noise, the Hooge parameter, to be 3 x 10^-2 for CdSe NC-FETs, comparable to other emerging solution processable organic semiconductors and promising for low-noise circuit applications.As most of NCs are reactive and their devices tend to degrade in air, we develop processes that allow manipulation of the NCs in ambient atmosphere without compromising device performance. These processes open up opportunities for NC-based devices to be fabricated over large area using photolithography. By scaling the devices and reducing device parasitics, we are able to fabricate hundreds of NC-FETs on wafer-scale substrates and integrate them as circuits. We demonstrate voltage amplifiers with bandwidths of a few kHz and ring-oscillators with a stage delay of 3 µsec. We also show functional NCICs NOR and NAND logic. This thesis demonstrates the use of colloidal NCs to realize flexible, large-area circuits and the feasibility of more advanced analog and digital NCICs built on flexible substrates for various applications

Design of Power Receiving Units for 6.78MHz Wireless Power Transfer Systems

In the last decade, the wireless power transfer (WPT) technology has been a popular topic in power electronics research and increasingly adopted by consumers. The AirFuel WPT standard utilizes resonant coils to transfer energy at 6.78 MHz, introducing many benefits such as longer charging distance, multi-device charging, and high tolerance of the coil misalignment. However, variations in coil coupling due to the change in receiving coil positions alter the equivalent load reactance, degrading efficiency. In recent studies, active full-bridge rectifiers are employed on WPT receivers because of their superior efficiency, controllability, and ability to compensate for detuned WPT networks. In order to take advantage of those characteristics, the rectifier switching actions must be synchronized with the magnetic field. In the literature, existing solutions for synchronizing the active rectifier in WPT systems are mostly not reliable and bulky, which is not suitable for small receivers. Therefore, a frequency synchronous rectifier with compact on-board control is proposed in this thesis. The rectifier power stage is designed to deliver 40 W to the load while achieving full zero-voltage switching to minimize the loss. The inherent feedback from the power stage dynamics to the sensed signal is analyzed to design stable and robust synchronization control, even at a low power of 0.02 W. The control system is accomplished using commercial components, including a low-cost microcontroller, which eliminates the need for bulky control and external sensing hardware. This high power density design allows the receiver to be integrated into daily consumer electronics such as laptops and monitors. Finally, a wide-range and high v resolution control scheme of the rectifier input phase is proposed to enable the dynamic impedance matching capability, maintaining high system efficiency over wide loading conditions. In addition, to increase the WPT technology adoption to low-power consumer electronics, a small wireless receiver replacing conventional AA batteries is developed. This receiver can supply power to existing AA battery-powered devices while providing the benefit of WPT technologies to consumers

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc