Experimental Validation of a quasi Z-Source Modular Multilevel Converter with DC Fault Blocking Capability

This paper considers the design methodology and the modulation of the quasi Z-source modular multilevel converter (qZS-MMC) with half bridge sub-modules and evaluates its performance in voltage boosting mode for medium voltage applications. The qZS-MMC consists of two quasi Z-source networks inserted between the two terminals of the DC input source and the DC-link terminals of a modular multilevel converter (MMC), which allows the generation of an output voltage larger than the input DC voltage. Two modulation schemes have been analysed based on a mathematical derivation for the converter internal voltages, currents, and stored energy. The quasi Z-source circuit is proven to provide the qZS-MMC with half bridge sub-modules to deal with DC-faults. The experimental results validate the performance of the proposed modulation schemes and the DC-fault blocking capability of the qZS MMC. Finally, the losses of the qZS-MMC is compared against a standard MMC using full bridge sub-modules that can also provide DC fault capability. The range in which the qZS-MMC is more efficient has been identified. Furthermore, the qZS-MMC can provide a significant reduction in number of semiconductor power devices with the same performance

Sliding mode controller applied to coupled inductor dual boost inverter

A coupled inductor-dual boost-inverter (CIDBI) with differential structure has been presented to be applied to micro-inverter photovoltaic module system because of its turn ratio of high-voltage level. However, it is hard for CIDBI converter with conventional PI regulator to be designed stable and achieve good dynamic performance, given the fact that it is a high order system. In view of this situation, a sliding mode control (SMC) strategy is introduced in this paper, and two different sliding mode controllers (SMCs) are proposed and adopted in the left and right side of the two Boost sub-circuits respectively to implement corresponding regulation of voltage and current. The schemes of the SMCs have been elaborated in this paper including the establishment of the system variable structure model, the selection of the sliding surface, the determination of the control law, and the presentation of the reaching conditions and sliding domain. Finally, the mathematic analysis and the proposed SMC are verified by the experimental results

New modulation scheme for bidirectional qZS modular multi-level converters

This study proposes a dedicated modulation scheme for a bidirectional quasi-Z-source (qZS) modular multi-level converter. The operation principle and a suitable pulse-width modulation method are proposed. The relation between the modulation index and shoot-through duty ratio is derived. A formula for calculating the required value of qZS capacitance is given. The simulation results presented in the study validate the operation and the performance of the proposed topology

Modelling of reduced electromechanical interaction system for aircraft applications

© 2019 Institution of Engineering and Technology. All rights reserved. Rotational systems such as aircraft engine drivetrains are subject to vibrations that can damage shafts. Torsional vibrations in drivetrains can be excited by the connection of loads to the generator due to electromechanical interaction. This problem is particularly relevant in new aircraft because the drivetrain is flexible and the electrical power system (EPS) load is high. To extend the lifespan of the aircraft engine, the electromechanical interaction must be considered. Since real-time constants of the electrical and mechanical systems have very different magnitudes, the simulation time can be high. Furthermore, highly detailed models of the electrical system have unnecessary complexity for the study of electromechanical interactions. For these reasons, modelling using reduced order systems is fundamental. Past studies of electromechanical interaction in aircraft engines developed models that allow the analysis of the torsional vibration, but these are difficult to implement. In this study, a reduced order electromechanical interaction system for aircraft applications is proposed and validated using experimental results. The proposed system uses a reduced drivetrain, simplified EPS, and sensorless measurement of the vibrations. The excitation of torsional vibrations obtained is compared with past studies to prove that the reduced order system is valid for studying the electromechanical interactions

Analytical modelling and power density optimisation of a single phase dual active bridge for aircraft application

A design procedure for the Dual Active Bridge (DAB) converter is presented, which aims to optimized power density and computational effort. When designing a DAB, the selection of circuit design parameters such as switching frequency, leakage inductance and semiconductor technologies is a complex question when targeting losses and weight minimization of the final design. In this paper, analytical models of the operating waveforms, the losses and the weight of all DAB components are developed. The proposed design algorithm is used for designing a 3kW high frequency DAB for an aircraft DC power system

A leakage-inductance-tolerant commutation strategy for isolated AC/AC converters

This paper proposes a generalised commutation strategy suitable for matrix-based isolated AC/AC conversion stages in Solid State Transformers for use whenever there is nonnegligible leakage inductance in the isolation transformer. The standard 4-step commutation used in matrix converters can no longer be applied when transformer leakage inductance is present, as overrated switching devices or dissipative snubbers would be necessary, reducing the attractiveness of the topologies that include matrix-based isolated AC/AC stages. A case study of a single-phase AC/AC converter has been investigated in detail to demonstrate the application of the proposed commutation method to a topology that has recently been identified as the potential building block for future multi-modular AC/AC converters for grid applications. The proposed leakage-inductance-tolerant commutation strategy is based on the definition of a current decoupling phase in the commutation sequence and only needs suitable timing of the commutation steps, without high bandwidth voltage or current measurements. Matching simulations and experimental results from a 3kW laboratory scale prototype are presented to support the effectiveness of the proposed strategy

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

The More-Electric Aircraft and Beyond

Aviation is a significant contributor to greenhouse gas (GHG) emissions in the transportation sector. As the adoption of electric cars increases and GHG emissions due to other modes of transport decrease, the impact of air travel on environmental pollution has become even more significant. To reduce pollution and maintenance, and ensure cheaper and more convenient flights, industry and academia have directed their efforts toward aircraft electrification. Considering various types of aircraft, several frameworks have been proposed: more-electric aircraft (MEA), hybrid electric aircraft (HEA), and all-electric aircraft (AEA). In the MEA framework, propulsion is generated by a conventional jet engine; however, all secondary systems (hydraulic, pneumatic, and actuation) are electrified. By further increasing electrification, electric motors can provide propulsion with the electric power supplied by the conventional engine (i.e., HEA) or from electrical energy storage (i.e., AEA). Power electronics and electrical machines play a key role in this scenario in which electric power must be efficiently generated, distributed, and consumed to satisfy extremely high requirements of aviation safety. This article provides an overview of recent advancements in aircraft electrification, and trends and future developments referenced to the global aviation roadmap

Transfer function based input impedance determination of triple active bridge converter

The concept of multiport dc-dc converter was proposed to reduce the conversion stages of dc microgrid on more electric aircraft (MEA). The structure of multiport dc-dc converter is basically developed from the dual active bridge (DAB) converter because of its galvanic isolation and bidirectional power flow. A power electronics converter as a key element of the electrical power distribution system may cause stability issues. To address these challenges, the impedance characteristic of the multiport converter will be analyzed. In this paper, a transfer function based small signal model is developed and validated with a switching model, to figure out the characteristic of input impedance of triple active bridge (TAB) converter. Preliminary experimental results are presented to be as a support