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Digital control is a branch of control theory that uses digital computers to act as a system. Depending on the requirements, a digital control system can take the form of a microcontroller to an ASIC to a standard desktop computer. Since a digital computer is a discrete system the Laplace transform is replaced with the Z-transform. Also since a digital computer has finite precision (See quantization) extra care is needed to ensure the error in coefficients, A/D conversion, D/A conversion, etc. are not producing undesired or unplanned effects.
The need/use of digital control can readily be understood in the use of feedback. Since the creation of the first digital computer in the early 1940s the price of digital computers has dropped considerably, which has made them key pieces to control systems for several reasons
- Cheap: under $5 for many microcontrollers
- Flexibility: easy to configure and reconfigure through software
- Static operation: digital computers are much less prone to environmental conditions than capacitors, inductors, etc.
- Scaling: programs can scale to the limits of the memory or storage space without extra cost
- Adaptive: parameters of the program can change with time (See adaptive control)
Digital feedback
One usage of a digital control system is as the controller in a feedback system. The rest of the system can either be digital or analog. Some examples of analog systems with a digital feedback controller are:
The typical setup for a digital feedback controller is
- A/D conversion as inputs
- D/A conversion as outputs
- A program that relates the outputs to the inputs
The programs can take numerous forms and perform many functions
- A digital filter for low-pass filtering (analog filters are preferred because digital filters introduce more delay)
- A state space model of a system to act as a state observer
- A telemetry system
See also
"Digital control"