MPC Type



Cycle Time



Application



MPC.Micro



1 sec or more



FC, TC, PC,  LC



MPC.Mini



1 min or more



Quality Control



MPC.Meta



2 min or more



Throughput Optimal



MPC.Net



30 min or more



Product Value Chain Optimal


Preemptive Constraints Resolution

By design, the slower MPC.* inherits the related faster MPC.* in accordance with the process characteristics. The MPC.* will always honor the constraints of the inherited faster cycle time MPCs. The MPC.* are designed with set cycle times, however, the unified MPC framework supports preemptive control actions based on the process situations exceptions.

Each of the MPC type above runs normally as per its cycle time, however, at any run time, if necessary  it can invoke preemptively slower cycle time MPCs for its constraints resolution. The  related slower MPCs can be invoked progressively. MPCs within each type follow the underlying process dynamics.

This makes the process control system to operate reliably and robustly under varying process conditions. The preemption control capabilities permits Unified MPC to apply a range and severity of control actions as warranted by the process situations that would include local to global as well as immediate to postponed control actions.

Process Situational Awareness Control Actions

The measured/unmeasured disturbances effects happening at any part of the process are first absorbed locally at the fastest cycle time and the uncompensated effects are propagated downstream for compensation in accordance with the process situational awareness. The propagation compensation can result in control actions downstream and/or upstream of the disturbance location.

For small magnitude disturbances, the downstream MPCs are not normally invoked preemptively, but for large magnitude disturbances or in an abnormal process situation, the disturbance effects are preemptively compensated  commensurately.

In order to maintain dynamic stability, at their normal cycle time run, each of the MPC.* are validated for dynamic stability of the related lower level MPC.*. If any of the lower level MPC.* is detected to be unstable, it is put into AutoHold mode internally. Under AutoHold mode, the MPC is constrained by the variance limits.  The AutoHold mode permits the MPC to stabilize without being moved around by any other MPC. In effect, the AutoHold mode creates a zone of minimal external changes whilst letting the MPC regain its stability. That is to say normal external control actions are  constricted to let the MPC regain stability. In fact, the operator can put any of the MPC or the entire MPC.* into AutoHold mode at any time as well. For instance, during a thunderstorm, the operator can put the entire MPC.Net in AutoHold after having reduced the throughput in preparation of the impending thunderstorm.

The multi-frequency architecture of the unified MPC provides extraordinary capabilities for the operator to run any of the  MPCs in any desired mode of MAN, AUTO, and CAS and including in OFF mode for engineering maintenance without any loss of operability.

The cycle times in the table above are representative, they can all be adjusted in accordance with the fastest and slowest dynamics of the process.

MPC.Micro will relate to PID as external controller for steady state control only or can be replaced with an equivalent dynamic control as well.

Home WhitePaper Applications UpgradeMPC UMPCSoftware Contact Us

An existing MPC can be upgraded for robust performance with the following seven steps migration path:


Embed Regulatory Controllers As Appropriate


Identify missing models from previous plant test data


In Accordance with Various Holdups in the process


Monitor model mismatch error

Re-identify models as necessary

Result:


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