|
PSL Projects :
Development of a Digitally-Controlled Fuel-Cell Powered Battery Charging Station
Modern handheld electronic devices such as PDA’s, cellular
phones, portable computers, camcorders, and radios have fueled a great need for
advanced technology rechargeable batteries. The portable, multi-channel
fuel-cell powered battery charging station may provide an appealing solution to
charge the batteries in the field. In this application, power electronics
devices are critical that are expected to condition the power from the fuel cell
power source to the batteries being charged. Digital technology can be applied
in the power electronics control. In the final product, the digital controller
can be realized by a microcontroller-based embedded control system where the
control algorithm coded in high-level language is compiled and exported to.
System Architecture
A PEM fuel cell stack charges up to three lithium-ion battery packs through
separate buck converters. A digital controller is used to coordinate these power
converters. The charging currents and battery voltages are monitored and fed to
the controller. This digital controller calculates the reference charging
current for each channel and the corresponding duty cycle. It also outputs PWM
signals to the switch drivers in these buck converters. By controlling these
buck converters, the charging currents and voltages of the batteries can be
regulated.
A fuel-cell powered battery charging station.
The digital controller is realized by a microcontroller-based embedded control
system. The control algorithm is coded and then downloaded to a dedicated
microcontroller system.
Embedded implementation of the fuel-cell powered battery charger using a microcontroller system.
Methodology
The following design path is adopted for control system development of this
application, where we use three simulation tools: MATLAB/Simulink, Virtual Test
Bed (VTB) and its real-time extension (RT-VTB), and two hardware platforms:
dSPACE controller and microcontroller.
1) Define the high-fidelity system model in Windows version VTB. Design the
digital control algorithm using Simulink. Link the controller model (in Simulink)
to the system model (in VTB) and test the controller with the high-fidelity
system model, interactively tuning the controller when necessary.
2) Use the MATLAB real-time workshop to compile the Simulink file and download
the executive to the dSPACE platform. Test the control algorithm with the real
hardware.
3) Optimize the control for a low-cost platform such as a microcontroller. Code
the control algorithm for the target control hardware (i.e., microcontroller).
Perform real-time processor-in-the-loop (PIL) testing between RT-VTB (system
model) and the microcontroller (control system).
(4) When it is sure that the control algorithm is correct, insert the control
hardware into the hardware of the real system. Test the control algorithm on the
actual hardware.
Four –step design path for digital control of power electronics.
Co-Simulation between VTB and Simulink
System simulations are conducted in Virtual Test Bed (VTB) simulation
environment by embedding the Simulink object of the controller into VTB and
cosimulating interactively with MATLAB.
A virtual-prototype of the fuel-cell powered battery charger in the VTB.
Simulation results.
Rapid Control Prototyping
Experimental tests are performed by compiling the Simulink codes of the controller and downloading to the dSPACE platform to control the actual hardware.
Experiment platform for rapid control prototyping.
Experiment results on the dSPACE platform.
Real-Time Processor-in-the-Loop Testing
The real-time processor-in-the-loop simulation in each time step consists of the
following four parts:
• Take in the analog input from AI channel of the DAQ card.
• Calculate the system state in current step using RT-VTB solver.
• Send out the analog output through AO channel of the DAQ card.
• Calculate the control output for the next step on the microcontroller system.
Configuration of the real-time processor-in-the-loop (PIL) testing system.
During the real-time PIL simulation, the RT-VTB reads the control signals via
the DAQ card and simulates the plant model for one sample interval and exports
data (output of the plant) to the control system under test via the DAQ card.
The microcontroller receives six analog signals from the RTVTB solver. These
signals are converted from analog to digital through the 10 bits ADC. When the
target processor receives signals from the plant model, it executes the control
algorithm described previously for one sample step. The result of the control
calculation sets the duty cycle of a PWM output signal. Since the micro
controller does not have an analog output, the PWM signal is then filtered by
means of a third-order low-pass filter. The controller returns output signals
(output of the controller) computed during this step to the RT-VTB. At this
point, one sample cycle of the simulation is complete and the plant model
proceeds to the next sample interval. The process repeats and the simulation
progresses.
Results of real-time processor-in-the-loop testing.
Hardware Validation
The control algorithm implemented on a dedicated microcontroller can be tested
together with the actual hardware.
Experiment platform for the hardware validation.
<< Back <<
