ABSTRACT:
This report 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 fullbridge
DC to DC boost converter for the fuel cell and a bidirectional full-bridge DC to
DC buck/boost converter for the battery. Third, for a three-phase DC to AC inverter
without or with a delta/Y transformer, a discrete-time state space circuit model is given and
two discrete-time feedback controllers are designed: voltage controller in the outer loop
and current controller in the inner loop. 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. To demonstrate the proposed circuit
models and control strategies, simulation test-beds using Matlab/Simulink are constructed
for each configuration of the fuel cell based DGS with a three-phase AC 120 V (L-N)/60
Hz/50 kVA and various simulation results are presented.
In Topology 2, this report presents system modeling, modified space vector PWM
implementation (MSVPWM) and design of a closed-loop controller of the Z-source
converter which utilizes L and C components and shoot-through zero vectors 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 (SVPWM)
technique is modified to realize the shoot-through zero vectors that boost the DC-link
voltage. Also, three discrete-time feedback controllers are designed: a discrete-time
optimal voltage controller, a discrete-time sliding mode current controller, and a discretetime
PI DC-link voltage controller. Furthermore, an asymptotic observer is used to reduce
the number of sensors and enhance the reliability of the system. To demonstrate the
analyzed circuit model and proposed control strategy, various simulation results using
Matlab/Simulink are presented under both light/heavy loads and linear/nonlinear loads
for a three-phase AC 208 V (L-L)/60 Hz/10 kVA.
If your company is a member of the Mechatronic Laboratory, please send the request to receive a copy of any technical report. If you are not a member please send a request to Ali Keyhani, Department of Electrical Engineering, Mechatronics Program at the following address: Ali Keyhani, Ohio State University, Electrical Engineering Department, Mechatronics Systems Laboratory, 2015 Neil Ave., 205 Dereese Lab., Columbus, OH 43210.