CLP has its roots in digital control technology which is a demanding one that requires quite some computing power. An electromechanical system will usually include an electrical motor to make things move; control is achieved by controlling the position of the mechanical load, the speed at which it is moving and the electrical currents that are injected in the motor in order to make it move. A control system will therefore also typically include sensors to measure position, speed and electrical currents. The problem that the control system designer will be facing will generally look like this:
The control algorithm will typically include position control, speed control and current control:
• Position control will compare the actual position with the desired position and will provide a reference speed;
• Speed control will compare the actual speed with the reference speed and will provide reference currents;
• Current control will compare the actual currents with the reference currents and will adjust the currents demanded for the motor.
Each control needs to be performed at a minimal frequency in order to achieve stability and precision in terms of control. The most demanding is the current control for which frequencies of up to 20 KHz are not uncommon. Moreover, this control is multidimensional in nature and may require quite some complex processing (transformations, integrators, filters, limiters…). Processing also requires sufficient precision and is inherently floating-point.
Several COTS tools have emerged for model-based designing; Simulink ((© Mathworks) has gradually emerged as a leading industry standard that is widely accepted.