Carlos A. García

Energy Management System of Fuel-Cell-Battery Hybrid Tramway

This paper describes the configuration, modeling, and control of a fuel cell (FC)-battery-powered hybrid system for the Metro Centro tramway in Seville, Spain. The proposed hybrid system presents a polymer electrolyte membrane FC as the primary energy source and a nickel-metal hydride cell battery as the secondary energy source, which supplements the output of the FC during tramway acceleration or whenever else needed and cruise and for energy recovery during braking. The tramway presents a traction system which is composed of four traction induction motor drives. The hybrid system also supplies the power for the auxiliary services. The power conditioning system is composed of two converters: 1) a boost-type unidirectional dc/dc converter for the FC and 2) a boost-type bidirectional dc/dc converter for the battery. The energy management system (EMS) of the hybrid tramway determines the reference signals for the electric motor drives, FC, and power converters in order to regulate accurately the power from the two electrical sources. EMS also determines the reference signal for energy dissipation in braking chopper when required during regenerative braking. In this paper, the proposed hybrid system is evaluated for the real driving cycle of the tramway. The results demonstrate the hybrid system capability to meet appropriate driving cycle.

ANFIS-Based Control of a Grid-Connected Hybrid System Integrating Renewable Energies, Hydrogen and Batteries

This paper describes and evaluates an adaptive neuro-fuzzy inference system (ANFIS)-based energy management system (EMS) of a grid-connected hybrid system. It presents a wind turbine (WT) and photovoltaic (PV) solar panels as primary energy sources, and an energy storage system (ESS) based on hydrogen (fuel cell -FC-, hydrogen tank and electrolyzer) and battery. All of the energy sources use dc/dc power converters in order to connect them to a central DC bus. An ANFIS-based supervisory control system determines the power that must be generated by/stored in the hydrogen and battery, taking into account the power demanded by the grid, the available power, the hydrogen tank level and the state-of-charge (SOC) of the battery. Furthermore, an ANFIS-based control is applied to the three-phase inverter, which connects the hybrid system to grid. Otherwise, this new EMS is compared with a classical EMS composed of state-based supervisory control system based on states and inverter control system based on PI controllers. Dynamic simulations demonstrate the right performance of the ANFIS-based EMS for the hybrid system under study and the better performance with respect to the classical EMS.

Reduced model of DFIGs wind farms using aggregation of wind turbines and equivalent wind

In this paper, a new reduced model of wind farms with doubly-fed induction generators wind turbines is proposed for representing all the wind turbines of a wind farm by one single equivalent wind turbine. The simulation results demonstrate the effectiveness of the proposed reduced model to represent the collective response of a wind farm in the point of common coupling to grid during power system dynamic simulations. This model can be used for voltage and angle stability investigations of large power system with an important reduction of the model order and computation time

Control system of doubly fed induction generators based wind turbines with production limits

Doubly fed induction generators based wind turbines are today one of the most widely used generation systems in wind farms due to the ability of variable speed operation and with decoupled control of active and reactive power. Nowadays these wind turbines are operating without generation limits, but the increasing wind power penetration in power systems must lead to that the wind farms have to operate with production limits imposed by the electrical system operators to maintain the stability of the electrical network. In this paper, a new control system of doubly fed induction generators based wind turbines is proposed for the control of active and reactive powers according to the imposed power limitations. This control system presents an active power controller, reactive power controller and pitch angle controller, in order to operate the wind turbine with optimum power efficiency or with limited active power and the demanded reactive power. This generation control provides a better grid integration of doubly fed induction generators

Aggregation of doubly fed induction generators wind turbines under different incoming wind speeds

The increasing wind power penetration in power systems requires the development of adequate wind farms models to be included in power system simulation software in order to represent the behavior of wind farms in power systems. The modeling of wind farms with high number of wind turbines requires the development of a high order model if all the wind turbines are modeled and therefore it is necessary a long simulation time. This paper presents a new way of aggregation of doubly fed induction generators wind turbines under different incoming winds by an equivalent wind turbine to approximate the active and reactive powers of aggregated wind turbines. The proposed aggregation method allows the wind farm to be represented by one single equivalent wind turbine with an important reduction of both model order and simulation time.

Control strategies of a fuel-cell hybrid tramway integrating two dc/dc converters

This paper compares two control strategies of a fuel cell (FC)-battery powered hybrid system integrating two dc/dc converters for the Metro-Centro tramway (400 kW) from Seville, Spain. Besides, modeling of each component is briefly presented. These models have been implemented in MATLAB/SIMULINK environment. A Polymer Electrolyte Membrane (PEM) FC is used in this work. The FC model characteristics are selected from a Nuvera 127 kW PEM FC. Two PEM FCs connected in parallel operate as primary energy source and a group of Ni-MH battery supplements the output of the FC during tramway acceleration or whenever else needed and provides regenerative braking energy recapture capability. Finally, the simulation results of both control configurations (Cascade and States Control Strategies) are presented for the real driving cycle of the tramway. The results demonstrate the hybrid system capability to meet appropriate driving cycle in both cases.

Voltage harmonic compensation control for a stand-alone single phase inverter-based fuel cell

In recent years, Fuel Cells (FC) have gained interest as energy source for stand-alone and grid connected applications, because they are very high-efficiency and multi-fuel power generators that require neither the burning of conventional fuels nor the mechanical equipment of conventional power generators. When FC are used with inverters for supplying AC loads, harmonic distortion in the supply voltage results in increased heating losses in loads, excite resonances and overload customer power factor correction equipment. Sensitivity of customer equipment to voltage distortion may be dependent on both the magnitude of the distortion levels and the specific harmonic components. For these reasons, it is important to keep the voltage harmonics within recommended levels. This paper presents a new method for voltage harmonic compensation of a stand-alone single phase inverter-based FC. The system under study is composed of: 1) Proton- Exchange-Membrane (PEM) FC including a unidirectional DC/DC converter, which converts the DC voltage delivered by the FC to the DC bus voltage; 2) single-phase pulse width modulated (PWM) inverter; 3) transformer; 4) L passive filter; and 5) linear and non-linear loads. The dynamic model of this system and the control applied to the PWM inverter for voltage regulation and harmonic compensation are detailed in this paper. Simulation results show the effectiveness of the purposed method for voltage harmonic compensation to acceptable levels defined in grid codes.

Fuel cell-battery hybrid system for transport applications

This paper presents a fuel cell-battery powered hybrid system for transport applications, more specifically for a tramway. It uses a Polymer Electrolyte Membrane (PEM) fuel cell (FC) as primary energy source and a Ni-MH battery as secondary energy source, which serves as a supplement to the FC during the driving cycle. The hybrid system supplies the power consumption of the auxiliary services and the traction system, which is composed of four traction induction motor drives. The energy management system (EMS) of the hybrid tramway fixes the reference signals for: 1) the FC dc/dc boost converter in order to accurately distribute power between two electrical sources; 2) the electric motor drives; 3) energy dissipation in the braking chopper when required during regenerative braking. The proposed hybrid system is assessed for a real driving cycle. The results show the hybrid system capability to allow the tramway to properly follow the driving cycle.

Comparative Study of the Behavior of a Wind Farm Integrating Three Different FACTS Devices

Improving grid connection of wind farms is a relevant issue to be addressed, especially for fixed-speed wind turbines. Certain elements, such as FACTS (Flexible AC Transmission Systems), are able to perform voltage and reactive power regulation in order to support voltage stability of wind farms, and compensate reactive power consumption from the grid. Several devices are grouped under the name of FACTS, which embrace different technologies and operating principles. Here, three of them are evaluated and compared, namely STATCOM (Static Synchronous Compensator), SVC (Static Var Compensator) and SSSC (Static Synchronous Series Compensator). They have been modeled in MATLAB / Simulink, and simulated under various scenarios, regarding both normal operation and grid fault conditions. Their response is studied together with the case when no FACTS are implemented. Results show that SSSC improves the voltage stability of the wind farm, whereas STATCOM and SVC provide additional reactive power.

Modelling and Control of Wind Parks

Wind parks have experienced a great increase over the last years, from small wind parks with a few wind turbines connected to utility distribution systems, to large wind parks connected to transmission networks that may be considered, from the network system operators point of view, as a single wind power plant with operational capabilities similar to a conventional power plant. In this chapter, three main aspects concern to wind park grid integration are considered: the necessity of suitable wind park models for transient stability studies; the wind park control to fulfill system requirements and the application of special devices to enhance grid integration capabilities.