Modeling and control of fuel cell based distributed generation systems
This dissertation presents circuit models and control algorithms of fuel cell based distributed generation systems (DGS) for two DGS topologies. In the first topology, each DGS unit utilizes a battery in parallel to the fuel cell in a standalone AC power plant and a grid-interconnection. In the second topology, a Z-source converter, which employs both the L and C passive components and shoot-through zero vectors instead of the conventional DC/DC boost power converter in order to step up the DC-link voltage, is adopted for a standalone AC power supply.
In Topology 1, two applications are studied: a standalone power generation (Single DGS Unit and Two DGS Units) and a grid-interconnection. First, dynamic model of the fuel cell is given based on electrochemical process. Second, two full-bridge DC to DC converters are adopted and their controllers are designed: an unidirectional converter for the fuel cell and a bidirectional converter for the battery. Third, for a three-phase DC to AC inverter without or with a ?/Y transformer, a discrete-time state space circuit model is given and two discrete-time feedback controllers are designed for voltage control and current control. And last, for load sharing of two DGS units and power flow control of two DGS units or the DGS connected to the grid, real and reactive power controllers are proposed. Particularly, for the grid-connected DGS application, a synchronization issue between an islanding mode and a paralleling mode to the grid is investigated, and two case studies are performed.
In Topology 2, this dissertation presents system modeling, modified space vector PWM implementation and design of a closed-loop controller of the Z-source converter for the standalone AC power generation. The fuel cell system is modeled by an electrical R-C circuit in order to include slow dynamics of the fuel cells and a voltage-current characteristic of a cell is also considered. A discrete-time state space model is derived to implement digital control and a space vector pulse-width modulation technique is modified to realize the shoot-through zero vectors that boost the DC-link voltage. Also, three discrete-time feedback controllers and an asymptotic observer are designed.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:distributed generation systems fuel cell dynamic modeling standalone grid interconnection isolated full bridge dc to power converter three phase inverter space vector pwm z source digital control
Date of Publication:01/01/2005