A multi-port power conversion system for the more electric aircraft

In more electric aircraft (MEA) weight reduction and energy efficiency constitute the key figures. Additionally, the safety and continuity of operation of its electrical power distribution system (EPDS) is of critical importance. These sets of desired features are in disagreement with each other, because higher redundancy, needed to guarantee the safety of operation, implies additional weight. In fact, EPDS is usually divided into isolated sections, which need to be sized for the worst-case scenario. Several concepts of EPDS have been investigated, aiming at enabling the power exchange among separate sections, which allows better optimization for power and weight of the whole system. In this paper, an approach based on the widespread use of multi-port power converters for both DC/DC and DC/AC stages is proposed. System integration of these two is proposed as a multiport power conversion system (MPCS), which allows a ring power distribution while galvanic isolation is still maintained, even in fault conditions. Thus, redundancy of MEA is established by no significant weight increase. A machine design analysis shows how the segmented machine could offer superior performance to the traditional one with same weight. Simulation and experimental verifications show the system feasibility in both normal and fault operations

Design of power converters with embedded energy storage for hybrid DC-AC applications

The high penetration of renewable energies into power systems is leading to a revolution in the structure of modern power grids. In this context, the present thesis investigates the design of power electronics converters with extended capabilities due to the embedding of energy storage within the topologies. Thus, the research objective is to propose power converters with capabilities of integrating energy storage technologies to provide further services required for the operation of hybrid dc-ac systems. The thesis contains two parts, first part shows the work developed for low- and medium-power applications, while the second part describes the investigation performed for high-power systems. The first part of this thesis explains the design and operation of a three-port dc-dc-ac converter developed for integrating energy storage into hybrid dc-ac applications. The topology is based on a conventional two-level dc-ac converter, and it uses a single power conversion stage to control the power flow between three ports, minimising the required components. Simulation and experimental results validate the operation of the proposal, showing that a multi-variable control system allows exploiting the degrees of freedom to manage power interactions of multiple elements without needing extra power converters. Furthermore, a comparative analysis is carried on to showcase the advantages and limitations of the proposal as opposed to state-of-the-art solutions in the same context. The study concludes that the proposed topology is suitable for low- and medium-power systems with bidirectional power flow capabilities among all ports and limited voltage boost needs. Simulation analysis shows that efficiencies up to 95.94% can be reached for a 3 kW design, which compares to efficiencies of similar state-of-the-art topologies. Moreover, the operation is also validated in a reduced-scale prototype allowing to test the multi-variable control scheme in a real-time implementation. The second part of the thesis focuses on the design and operation of a Modular Multilevel Converter (MMC) topology with integrated energy storage using new parallel branches in the phases of the converter. This topology allows the integration of partially-rated Energy Storage Systems(ESS) to decouple the ac and dc sides of a High Voltage Direct Current~(HVDC) substation. Thus, it enables the provision of ancillary services such as fast frequency response, black-start capabilities and load-levelling, which are required by modern hybrid dc-ac power grids. Results show that the proposal allows the addition of up to 37% power from the ESS considering similarly rated power semiconductors in a simulated 1 GW MMC substation. Analysis shows that extra device losses remain under 1% for an additional +-10% of ESS power on top of the nominal substation-rated power. Furthermore, a laboratory-scale experimental rig was built to demonstrate the operation of the proposed design. In conclusion, two different topologies are proposed and analysed for integrating energy storage into hybrid dc-ac applications depending on the power rating required. The study is supported by simulation and experimental results obtained during the project to validate both proposals

Isolated Single-stage Power Electronic Building Blocks Using Medium Voltage Series-stacked Wide-bandgap Switches

The demand for efficient power conversion systems that can process the energy at high power and voltage levels is increasing every day. These systems are to be used in microgrid applications. Wide-bandgap semiconductor devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) are very promising candidates due to their lower conduction and switching losses compared to the state-of-the-art Silicon (Si) devices. The main challenge for these devices is that their breakdown voltages are relatively lower compared to their Si counterpart. In addition, the high frequency operation of the wide-bandgap devices are impeded in many cases by the magnetic core losses of the magnetic coupling components (i.e. coupled inductors and/or high frequency transformers) utilized in the power converter circuit. Six new dc-dc converter topologies are propose. The converters have reduced voltage stresses on the switches. Three of them are unidirectional step-up converters with universal input voltage which make them excellent candidates for photovoltaic and fuel cell applications. The other three converters are bidirectional dc-dc converters with wide voltage conversion ratios. These converters are very good candidates for the applications that require bidirectional power flow capability. In addition, the wide voltage conversion ratios of these converters can be utilized for applications such as energy storage systems with wide voltage swings

Efficient, High Power Density, Modular Wide Band-gap Based Converters for Medium Voltage Application

Recent advances in semiconductor technology have accelerated developments in medium-voltage direct-current (MVDC) power system transmission and distribution. A DC-DC converter is widely considered to be the most important technology for future DC networks. Wide band-gap (WBG) power devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) have paved the way for improving the efficiency and power density of power converters by means of higher switching frequencies with lower conduction and switching losses compared to their Silicon (Si) counterparts. However, due to rapid variation of the voltage and current, di/dt and dv/dt, to fully utilize the advantages of the Wide-bandgap semiconductors, more focus is needed to design the printed circuit boards (PCB) in terms of minimizing the parasitic components, which impacts efficiency. The aim of this dissertation is to study the technical challenges associated with the implementation of WBG devices and propose different power converter topologies for MVDC applications. Ship power system with MVDC distribution is attracting widespread interest due to higher reliability and reduced fuel consumption. Also, since the charging time is a barrier for adopting the electric vehicles, increasing the voltage level of the dc bus to achieve the fast charging is considered to be the most important solution to address this concern. Moreover, raising the voltage level reduces the size and cost of cables in the car. Employing MVDC system in the power grid offers secure, flexible and efficient power flow. It is shown that to reach optimal performance in terms of low package inductance and high slew rate of switches, designing a PCB with low common source inductance, power loop inductance, and gate-driver loop are essential. Compared with traditional power converters, the proposed circuits can reduce the voltage stress on switches and diodes, as well as the input current ripple. A lower voltage stress allows the designer to employ the switches and diodes with lower on-resistance RDS(ON) and forward voltage drop, respectively. Consequently, more efficient power conversion system can be achieved. Moreover, the proposed converters offer a high voltage gain that helps the power switches with smaller duty-cycle, which leads to lower current and voltage stress across them. To verify the proposed concept and prove the correctness of the theoretical analysis, the laboratory prototype of the converters using WBG devices were implemented. The proposed converters can provide energy conversion with an efficiency of 97% feeding the nominal load, which is 2% more than the efficiency of the-state-of-the-art converters. Besides the efficiency, shrinking the current ripple leads to 50% size reduction of the input filter inductors

A Survey: Space Vector PWM (SVPWM) in 3φ Voltage Source Inverter (VSI)

Since last decades, the pulse width modulation (PWM) techniques have been an intensive research subject. Also, different kinds of methodologies have been presented on inverter switching losses, inverter output current/ voltage total harmonic distortion (THD), inverter maximum output of DC bus voltage. The Sinusoidal PWM is generally used to control the inverter output voltage and it helps to maintains drive performance. The recent years have seen digital modulation mechanisms based on theory of space vector i.e. Space vector PWM (SVPWM). The SVPWM mechanism offers the enhanced amplitude modulation indexes (MI) than sinusoidal PWM along with the reduction in the harmonics of inverter output voltage and reduced communication losses. Currently, the digital control mechanisms have got more attention than the analog counterparts, as the performance and reliability of microprocessors has increased. Most of the SVPWM mechanisms are performed by using the analog or digital circuits like microcontrollers and DSPs. From the recent study, analysis gives that use of Field Programmable Gate Arrays (FPGA) can offer more efficient and faster solutions. This paper discusses the numerous existing research aspects of FPGA realization for voltage source inverter (VSI) along with the future line of research

Reconfiguration of Multilevel Inverter with Trapezoidal Pulse Width Modulation

This paper presents different multi-carrier unipolar trapezoidal pulse width modulation strategies for a reduced switch asymmetrical multilevel inverter. The different strategies are phase disposition, alternative phase opposition and disposition, and carrier overlapping and variable frequency that involve triangular waves as carriers with a unipolar trapezoidal wave as a reference. The reduced switch, asymmetrical multilevel inverter operation was examined for generating the seven-level output voltage using Matlab/Simulink 2009b and the results were verified with a real-time laboratory-based experimental setup using a field-programmable gate array. Different parameter analyses, such as total harmonic distortion, fundamental root mean square voltage, and distortion factor, were analyzed with different modulation indices to investigate the performance of the selected topology. Unipolar trapezoidal pulse width modulation provides a higher root mean square voltage value.publishedVersio

Design and implementation of a dual-input single-output photovoltaic converter

In many solar inverters, a dc/dc converter is mainly located between the solar arrays and the inverter. This study presents an enhanced maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems that drives solar array voltages to track a reference value and decreases fluctuations and oscillations in PV voltage. Different from the previously presented methods, a novel MPPT method is proposed that ensures tracking accuracy by considering output voltage in addition to input voltage and currents. The proposed method detects dI/dV variations, compares the output voltage with the desired reference to shift operation mode and refreshes step size. The digital filtering, enhanced PI, and perturb-and-observe (P&O) tracking features of the proposed MPPT method make it robust to mitigate source fluctuations and sensitivity to partial shading based oscillations. In order to validate the success of the proposed method, a test rig has been installed with dual boost converters. The performance improvements have been verified by both simulation and experimental results that are compared to InCon and P&O MPPT methods. It is also confirmed by experimental results that the proposed MPPT method provides robust control capability in terms of tracking the reference voltage and rejecting the effects of various shading situations on solar arrays

Current fed multilevel converters for high current power applications

Phd ThesisThe majority of the worldwide installed power inverters today are voltage source inverters followed by current source inverters where the concluding decision lies with the performance of the applications besides the usual economic reasons. Recent active development in the current source inverter areas has seen the emerging of various generalized multilevel current source inverter topologies analogous to the existing multilevel voltage source inverter families. To date, the multilevel current source inverter families have been classified principally by the physical appearance of their basic structures and also by the number of current sources employed. The existing multilevel current source inverter topologies are unpopular for present applications due to reasons such as big sizes, high control complexity and low reliability; which circumstances are often associated to massive component counts and multiple requirements of current sources. Therefore, this research has been focused on the single-phase single-source generalized multilevel current source inverter for this apparent advantage; where this thesis proposed a novel generalized multilevel current-source inverter topology with the lowest component utilization while employing just a single current source. In addition, the proposed topology can conveniently achieved dc current balance with a simple low frequency switching strategy for the five- and nine-level current outputs. From comparison analysis, the proposed topology has significantly less number of components employed compared to the nearest topology, which implies low implementation cost. The experimental results verify the characteristics and performances of the proposed topology acquired by computer simulations.ministry of education, Malaysia and also to my employer the University Malaysia Pahang (UMP) for the financial suppor