Modeling and Scaling Feedforwards
Depending on the complexity and precision requirements of the process, the resulting control arrangement can range from simple “Process Value > Controller > Manipulated
Variable control” to a feedforward or cascade control. In this paper I will discuss the considerations when to utilize feedforwards, cascades and the scaling associated with
these control additions.
The areas that will be covered are:
• Why use feed forwards and when feed forwards are useful.
• Simple modeling of feed forwards
• Creating feed forwards from historical data
• More complex modeling of feed forwards
• Advanced modeling
• Cascade Control
1 Simple and Feedforward Control arrangement decisions
1.1 Selection of Simple Control Arrangement
1.1.1 Simple Signal Analysis
For those individuals that analyze control systems in a mathematical fashion, a simple, generic, process diagram reflecting a typical process is shown below.
Figure 1 – Typical Simple Physical Process
This process diagram above indicates a source for the process, a manipulated variable that controls the flow of mass, energy or chemical balance into the system, a process that modifies the source and a measurement of the results requiring control. It should also be noted that there are potential disturbances to the process.
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