Design and analysis of a Medium Voltage DC wind farm with a transformer-less wind turbine generator
In recent years, the interest in offshore wind farms has been increased significantly. One of the reasons of this development is the less perceived environmental cost of an offshore wind farm with respect to an in-land one, especially for new installations where big turbines are preferred. However, they have also the advantage of an increased and more constant wind speed, leading to higher and more constant production of electrical power. For these kinds of wind farms a pure DC system could be an interesting and cost effective solution. This paper describes an innovative Medium Voltage Direct Current electrical grid system (MVDC) for wind farms, based on transformer-less wind turbines. An accurate analysis is presented and the proposed solution has been validated through a simulation and experimental phase performed on a low voltage prototype.
Reduction of motor overvoltage fed by PWM AC drives using a universal model
An induction motor model construction and the validation of the model response to a filtering technique is analyzed in this paper. The filter is connected to the rotating machine terminals in order to suppress overvoltages due to the long cables and high frequency pulses of the inverter. With the help of high frequency measurements made by the authors on a 1.1kW induction motor, an accurate simulation with Matlab Simulink™ based on differential mode analysis, is made. The simulation shows realistic results for the determination of the filter parameters among different values of rise time and cable length.
MVDC connection of offshore wind farms to the transmission system
This paper describes an innovative Medium Voltage Direct Current electrical grid system (MVDC) for wind farms, based on transformer-less wind turbines, equipped with modular, multilevel converter (M2LC). A comparison between this MVDC system and a traditional MVAC one has been done using EECC (Electrical Energy Conversion Cost) index in order to evaluate the competitiveness of this solution for an offshore wind farm in the Mediterranean Sea.
Design and application of a Linux Real Time board for distributed power generation
The use of distributed energy resources is increasing and represents a valid answer to environmental problems and to the significant costs of more traditional energy sources. The need of developing distributed energy systems is strictly related to the need of flexible and scalable high level controller, able to manage control references in order to optimise global system efficiency. This paper proposes a solution based on Real Time Linux environment, which can be applied both to single source system and to multi-source ones. A soft PLC emulator together with other software tools are provided to help application development process. The proposed control board has been developed for wind turbine applications and has been preliminary tested.
Design and development of a 7kW polymer electrolyte membrane fuel cell stack for UPS application
This work presents the PEMFC stack design methodology developed at CNR-ITAE, in the frame of a collaboration with an industrial partner, Electro Power Systems (EPS), operating in the Uninterruptable Power Supply (UPS) market. A detailed description of the design procedure of a 7 kW PEMFC stack is reported, starting from technical requirements of the UPS system to experimental tests. Bipolar plate layout, active area surface and shape, maximum (OCV) and minimum voltage, maximum cooling circuit pressure drop, maximum cathodic flow-field pressure drop, were the main constraint that influenced the constructive solutions. The electrochemical performances of Gore Primea 5621 MEA with SGL Sigracet GDL were chosen as reference to select the appropriate operating point in terms of current density and single cell voltage. A current density of 800 mA/cm2 was imposed as operating point of the stack, subsequently main stack parameters were calculated. Three different cathodic flow fields, that were designed to fulfill UPS system requirements, were tested in a single cell arrangement, to find the best gas flow path in terms of compromise between cell performance and pressure drop. Also a specific study was dedicated to the selection of gasket material to find the best compromise between cell performance and limited mechanical stress. The assembled 70 cells unit was tested in a test bench simulating the power system. Preliminary tests of the full unit yielded to a power of 6.2kW at 36 V.
Hybrid PV-CHP distributed system: Design aspects and realization
The use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover, their intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper discusses a full experience in the realization of a hybrid plant which uses an internal combustion engine with cogeneration/trigeneration functionalities and solar source, installed in Delebio, Italy. System design aspects, with particular attention to the possible topologies and power flow control strategies are analyzed. After the analysis of design aspects, some simulations are presented to validate the proposed solution and finally experimental results of the real plant are reported.
Hardware in the Loop (HIL) test bench for small-scale Distributed Generation systems
The test procedure of electrical drives for Distributed Generation (DG) systems generally requires the installation of dedicated prototypes on site: this is an expensive, time and power consuming procedure. In recent years, the availability of high performance calculation platforms has made possible to perform these tests using Hardware in the Loop (HIL) test benches before the plant installation. A HIL environment allows reducing costs and saving time because an implementation error can be easily identified and it is possible to test fault conditions in a safety way. This paper presents a general HIL test bench for DG electrical drive testing. Experimental results emulating different DG sources and plant have been provided to validate the approach.
GreenShelter for telecom applications. A new generation of shelters for telecom applications integrating fuel cell electric backup and a new cooling approach
A new generation of shelter for telecom application has been designed and manufactured. The basic approach was to overcome the limit of the current technology regarding cooling needs and energy consumption as well as maintenance costs and backup autonomy. In this perspective the following elements have been considered: to implement an active cooling with very low energy consumption or passive cooling, to backup the apparatus with fuel cell based power system, to integrate as much as possible both the technologies. Shelter cooling without air conditioning is possible with free-cooling and phase changing materials (PCM). Fuel cell based power systems give advantages in terms of wide range of accepted working temperature (from -5°C to 45 °C) and very low maintenance needs. The fuel cell based power systems have been tested by several different Telecom operators but up to now very small activities have been performed for a complete integration into the shelter. In this application a 3 kW power system provides 24 hours of autonomy to all the equipments installed in the shelter. To accomplish to a complete integration work a new generation of power system has been generated: the new release consist in a 19’’ core component equipped with fuel cell, power management and control system and a separated thermal split to dissipate the heat generated during the working time (backup). The result is a new generation of shelter with very interesting specifications. Experimental tests on the manufactured GreenShelter are in progress. Preliminary results confirm that in the same conditions of temperature and heat dissipation, the energetic gain of the GreenShelter solution can be up to 70% with respect to a traditional shelter with air conditioning. Not less important, the gain in terms of CapEx and OpEx could assest around 10% and 50-70%, respectively.
Advanced control strategy for PQ improvement in PV systems without energy storage device
The use of distributed generating systems based on renewable energy sources has experienced a significant development in the last years. This paper focuses its attention on those based on photovoltaic systems. The intrinsic intermittent nature of this kind of renewable source implies the use of storage to accommodate fluctuations. The present paper proposes a hybrid solution in which photovoltaic source and gas engine are both present without storage device. With this configuration a new control technique can be used to maximizes system efficiency in both grid connection and stand alone operation mode.
A novel small-scale variable speed hydropower emulator using an inverter-controlled induction motor
The test procedure of an electrical drive control generally requires connecting the control to the power converter, the motor and the load. This is an expensive, time and power consuming procedure especially when it is necessary to test new control algorithms or architectures as often happen in renewable energy generation power plants. This paper introduces a low power emulator of a Small Hydropower generator used to develop and test the power quality functions of a universal digital controller for distributed generation systems.
Fuel Cell based Power System for Backup applications: Telecom Italia and other field test results
Fuel cell power system are currently under test by several different Telecommunication operators worldwide for backup applications. Compared to traditional systems (battery based ups, genset), the PEM fuel cell based power systems have both benefits (higher efficiency and better environmental impact) and drawbacks (higher cost, hydrogen supply need). In this paper a 7 kW fuel cell power system is described and the experimental data related to telecommunication and AC field tests are reported. The field test demonstrated a very good system performance either in terms of power delivery and reliability.
Universal digital controller for power quality and distributed generation systems
The paper introduces a complete study of a flexible digital control device for a very large number of low voltage power systems with functions of power quality (PQ) and/or distributed generation (DG). The novel aspect of the device is its hardware and software architecture: a modular and object oriented approach allows a high ability in adaptation to different power system topologies. In this work the authors have investigated various DG systems (wind turbine, photovoltaic generators, gas powered generating set) and different functionalities of the grid interface inverter (grid connected or stand alone operation mode). The proposed control strategy allows the definition of the power flows in order to optimize the energy source exploitation.