INVERSE CONTROL DESIGN
What is Inverse Control Design
Modern process lines are created in several stages. A preliminary concept of the control system is developed as early as at the design stage. The concept is based on design assumptions and process requirements, and includes selection of measurement signals and location of sensors, selection of the structure and type of control algorithms used, as well as selection and location of actuators to influence the course of the process. Out of necessity, it also takes into account budgetary constraints. Then, for the developed concept of the control system, the hardware configuration is selected and the control software is developed. The last stage is construction of the process line, completed with a start-up of the control system and work in the technological regime. Such a sequence is natural, but it entails inevitable limitations from the point of view of optimal operation of the control system. The concept of the control system, developed at the stage of the process line design, does not always correspond to the current process requirements, during the implementation of the investment project significant changes were made to the process line, which were not reflected in changes to the control system concept, and at the stage of commissioning of the process line there are often significant delays, which make it necessary to limit the time allocated for commissioning of the control system so as to close the entire investment project on time and commission the technological line on time. Consequently, the performance of the finished control system falls short of expectations.
Based on the measurement data collected during the operation of the process line, the quality of operation of the control system is evaluated, taking into account the current process requirements and their potential variability.
This stage makes it possible to identify those parts of the process in which the current control system does not ensure efficient use of energy in the production process and/or leads to unnecessary extension of the production cycle. The audit report also includes suggestions for solving the identified problems.
Based on the control system audit report, the client selects the scope and method of solving the identified problems. In about 80% of cases, a satisfactory improvement can be achieved without additional investment in an expansion of the hardware infrastructure of the control system. It is sufficient to modify the control software so that the control algorithms are better adapted to the process requirements.
Sometimes it happens that the existing infrastructure of the current control system does not allow for the required modifications, e.g. due to limited functionality of the hardware controllers used, bad location of the measurement sensors and/or their insufficient number, and the need to replace the actuator devices (e.g. control valves). In justified cases and with the consent of the client, we recommend such modifications and supervise their implementation.
In particularly justified cases, it may be necessary to change the entire control system concept in order to achieve the intended improvement. With the client’s consent, we recommend such a solution and supervise its implementation. This is a kind of return to the stage of development of the concept of the control system at the time of designing a new process line; however, the introduction of changes in this case results from the actual requirements of the line that is currently in operation and takes into account the actual process limitations.
It is worth noting that the stages of implementation of the ICD method differ in the scope and scale of the modifications made, starting from stage 1, which does not require any interference in the current control system. The established sequence of stages enables flexible adjustment of the offer to the needs and current capabilities of the client. Completion of work at any of the stages makes it possible to start work on subsequent stages at any convenient time. The entire work carried out according to the ICD method can be performed according to any selected time schedule. In particular, the modifications made at any of the stages, from stage 2 to stage 4, can be coordinated with planned technical outages so as not to disrupt the normal production cycle.
