Proportional-Integral-Derivative (PID) control is still widely used in industries because of its simplicity. No need for a plant model. No design to be performed. The user just installs a controller and adjusts 3 gains to get the best achievable performance. While in the past analog circuits such as op-amps together with resistors/capacitors/inductors can be used, most PID controllers nowadays are digital. The analog type has drawbacks that make it become obsolete. Some passive components have aging problem. The circuit parameters and operating points vary with temperature. The PID knobs (variable resistors) are vulnerable to dust and oxidation. All of these affect the performance and service life of controller. A digital PID controller is typically constructed as algorithm running in a microcontroller, an ASIC, or a flexible hardware platform such as FPGA. The PID parameters are kept in system memory and can be adjusted conveniently and accurately by a user.
In this document, PID controller basics and digital implementation on an embedded system are discussed. Examples are provided for microcontroller and FPGA. A section about automatic tuning is included at the end. We assume the reader has some basic understanding of linear controllers as described in our other document.
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