L. Rubino

Buck-boost DC/DC converter for aeronautical applications

In this document a DC/DC converter for power conversion between +28V/+270V voltage levels is presented, and the main characteristics of the converter are discussed. The topological structure is first introduced, outlining the hardware components used and the modular approach. The step-down (or Buck) and step-up (or Boost) modulations are then discussed, focusing on the switching signals to drive the low-voltage and high-voltage bridges of the single modules. The description of the control phase follows, justifying the controller used to steer the output voltage towards the desired value. The firmware realized for the converter management is equipped also with a supervision and protection logic, realized as a composition of finite state machines. Finally, simulative results and real measurements are provided to evidence the correctness of the overall topological choices and of the control system realized for the bidirectional converter, focusing also on the comparison between the expected results and those obtained.

Comparative study of variant topologies for MMC

On the base of the MMC principle, this work considers different topologies of sub module (or elementary converter) which make the High Voltage AC/DC converter more flexible and easy suitable respect to different voltage and current levels. A topological study is consolidated and extended on three different topologies proposed as elementary converter and their employment for the MMC structure is treated. For each cell, topology advantages and limits are discussed in terms of current and voltage. Under SPWM modulation conditions, an analytical approach for the power losses evaluation is proposed for the three topologies used in the MMC structure. A comparison on the efficiency is proposed by fixing the DC voltage and the operating power. By considering the basic topology of the MMC (composed by elementary cells) also an evaluation of the power losses is performed by considering the staircase modulation which is becoming more and more diffused especially for a high number of levels.

Considerations on boost inductor design in back-to-back converters for renewable energy

In this paper, considerations on converter inductor design in PWM back-to-back converter based on Synchronous Active Front End (SAFE) are discussed. This is considered one of the most efficient converter topology that successfully manages the hard trade-off between high power size and power quality requirements at the Point of Common Coupling (PCC). In renewable energy, in wind farm, this trade-off is getting harder due to the increasing size of generators. Despite all converter design parameters influence the performances in terms of harmonic generation, especially the converter inductor assumes a key role. The design of the inductance is carried out evaluating an admissible range according to imposed power quality requirements and power rate desired.

Power losses analysis in AC/DC conversion based on active front end systems

In this paper, a methodology for power losses analysis in Active Front End (AFE) converters based on VSI has been proposed. The interest in these converters topologies in AC/DC conversion, have become more popular in recent years due to its employment in renewable energy applications. Thus, it is interesting to analyze this converters in terms of their thermal behaviors in order to evaluate the system power rate. With this work, an analytical and numerical approach for losses evaluation have been proposed by the authors. Moreover, the use of the AFE in configuration Synchronous (SAFE) has been considered and compared with the base topology.

Evaluation of current harmonic distortion in wind farm application based on Synchronous Active Front End converters

Worldwide, request of renewable energy and power rating of wind farm is strongly increasing in parallel. This, makes more difficult the design of the power electronics converter that interfaces the grid to the renewable energy resource. Synchronous Active Front-End (SAFE) is considered one of the most efficient topology that successfully manages the hard trade-off between high power size and power quality requirements at the Point of Common Coupling (PCC). In this paper the authors present a mathematical approach to estimate the harmonic distortion of converter current at the PCC due to SPWM modulation. This, shows the advantages in terms of current spectrum of the SAFE topology. Moreover, it represents a strong tool in the converter design, as it allows to design converters parameters in order to respect power quality standards requirements. Finally, numerical simulation results validate the study.

Implementation of control and protection logics for a bidirectional DC/DC converter

In this paper, a control strategy for a bidirectional DC/DC power converter is discussed, and the logics to guarantee the operation correctness in various operative modes and for safety requirements are considered. In Buck (or step- down) mode, a voltage PI regulator is proposed, whereas in Boost (or step-up) mode an inner current control loop is introduced to guarantee a more effective current tracking, and to avoid damages due to overcurrents. Furthermore, a Finite State Machine (FSM) approach has been adopted to model the converter behavior and, in particular, to describe the protection logics for both Buck and Boost working modes, along with a special configuration called “Buffer control”, easily described using the FSM approach as composition of states. Numerical simulations results and real measurements show the effectiveness of the control strategy combined with a FSM logic description, rising up as a flexible approach to control a power converter device and to define its behavior in a desired working mode, as for buffer control.

Supervision and control of inverters for ancillary services in MV distribution networks

In this paper, a converter control strategy able to provide ancillary services implemented for the Italian MV distribution Networks has been presented. A three stage system composed by several boost converters, a VSI Active Front End and a transformer has been considered as interface between distribution grid and DERs. The proposed control strategy operates jointly to the DMS. Simulations have been performed and the system seems to work properly, well following DMS reactive power reference and preventing DC bus voltage large variations.

Electrical Power Center with energy management capability for aeronautical applications

This paper focuses on some aspects of the study and development of an Electrical Power Center (EPC) for aeronautical application tested in a flight demo channel up to 15000 ft (4500 m). The studied EPC is composed of several Solid State Power Controllers (SSPCs) each with a dedicated Digital Signal Processing (DSP) for the real time protection. All DSP communicate via CAN BUS with the main computer where are coded the energy management strategies. The paper reports the developed SSPC protection method with several simulation results. The work describe a typical workflow based on requirements analysis, specs derivation, design phase, physical implementation, testing phase, results analysis versus simulations and final equipment validation for flight.

Boost Full Bridge Bidirectional DC/DC Converter for Supervised Aeronautical Applications

The More Electrical Aircraft concept requires electronic devices able to efficiently and safely convert electrical power between different voltage levels. The entire realization of a bidirectional DC/DC converter, from design to validation phase, is here discussed in detail. First, a boost full bridge electrical structure is selected, adopting a Parallel Input Parallel Output (PIPO) interleaving technique and an optimal turns ratio selection for the transformers in order to reduce both weight and size of the equipment. Next, modulation schemes in both step-down and step-up modes are discussed. Successively ad hoc PI regulators for both operative modes are presented. A key idea of the paper is that the converter behavior must be related not only to the control strategy but also to a global supervision logic able to safely conduct the converter operations and to react from external stimuli. Thus, a finite state machine (FSM) approach is employed. An innovative strategy called buffer mode is presented, defined as an intelligent combination of buck and boost modes. Extensive simulations and experimental results are shown, in order to confirm the effectiveness of the proposed approach.

Unified supervised soft start-up and digital PI control for boost full-bridge converters

In this paper, we analyze a simple, yet effective nonlinear digital control approach; regulator behaves like a digital PI controller in steady state and sliding control in start-up phase. The proposed control is useful when the power converter cannot be controlled in start-up phase with control designed at steady state, because becomes instable, but we are interested only performances of converter in steady state. A simple finite state machine (FSM) to switch from a modality to another will be proposed.