Dear all,
Please help me in designing digital current controller for boost converter. I have designed the controller in analog domain and now want to make a digital controller. Please help me in this, and provide me the related literature and other relevant material so that I could understand the philosophy of controller design in digital domain.
The best way to make the current controller pulse width modulation (PWM), which allows you to vary the duty cycle of the waveform and thus can control the current used. The most basic form is 555 or Arduino microcontrollers or arduino
These are three excelent books on the subject:
1) K. J. Astrom and B. Wittenmark,"Computer-Controlled Systems: Theory and Design 3rd Edition"
2) K. Ogata, "Discrete-Time Control Systems (2nd Edition)"
3) G. F. Franklin, J.D. Powell, M. L. Workman, "Digital Control of Dynamic Systems (3rd Edition)"
It's highly recommend the reading of at least one of them. But, in short words, you can approximate the analog control law by using the trapezoidal discretization rule with a sampling period of at least 1/20 times the time constant of the fastest mode of the system composed by the actuator, plant and sensor units (this is a very simplistic view of the process).
The overall strategy, is to take the S Plane Transfer Function describing the analog controller's Control Law, and map the LHS of the S Plane into the Z Plane by discretizing the S Plane s = jω parameters as described by Trevor. The Z Transform converts a discrete time signal consisting of a sequence of real or complex numbers, into a complex frequency domain representation.
Z Transform Control Law theory includes analyses techniques to help find the Residue, Z Plane Poles and Z Plane Zeros. One analysis technique involving Poles is to determine the stability of the digital system's Control Law; such a system is stable in the Z Plane if all its Poles lie within the unit circle of the Z Plane.
In general terms, the LHS of the S Plane is mapped within the Unit Circle of the Z Plane, and the RHS of the S Plane is mapped outside of the Unit Circle in the Z Plane. The S Plane boundary between the LHS and RHS is mapped on the Z Plane's Unit Circle.
I have uploaded a pdf by Dr. David Corrigan from Trinity College in Dublin, describing some of my above comments in more detail, from the URL:
http://www.mee.tcd.ie/~corrigad/3c1/DSP2_2012_students.pdf
The above pdf may be a reasonable introduction to the topic of substituting a digital controller for an analog or S Domain Control Law; for further information I'd recommend consulting the list of text books listed by Trevor.
I'm not sure if Trevor's recommended texts include mathematical proofs for Z Domain theory; one of the foundations of Z Domain mathematics is the Cauchy Integral Formula. There is a textbook that covers this topic:
Churchill R.V., Brown J.W., "Complex Variables and Applications"
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