PhD Thesis - Cranfield University

Chapter 6
Velocity (km/h)
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Segment 1 (20secs)
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Control System Architecture
Segment 2 (20secs) Segment 3 (20secs) Segment 4 (20secs)
Time (s)
Figure 6.5 Developed test profiles
The control system is designed around the National Instruments Compact Field Point (CFP)
architecture. This system was chosen due to its robust operating condition tolerance and
flexibility of developing real-time control process treads. To facilitate online monitoring of
the vehicle during test runs, a wireless link was added to transmit system parameters to a Lab
View visualisation environment running on a remote PC. The power and energy
management framework described in Chapter 5 was implemented with LabView® -7 and
hosted in the CFP real time controller.
Acquisition of data and process input variables was accomplished via the CFP voltage,
current and counter/timer input modules. The analog and digital output modules fascinated
controller commands. The four PWM signals required for the operation of the Power
Electronics Shell was derived external to the CFP. Four independent programmable
controllers (PIC) were designed to convert the duty cycle values generated via the CFP
analog (0-5V) output module to four 20kHz fixed frequency – variable duty ratio PWM
signals. Four enable signals were also made available as outputs of the CFP for each PWM
channel. This provided a method to synchronize the PWMs as well as to feed an interlock
circuit that prevents cross conduction of the power electronic switches. Optical isolation
between the PWM signals and the power electronics drive circuitry was designed into the
system. Details of this are to be found in the Appendix section.
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