Steady-state bumpless transfer under controller uncertainty using the state/output feedback topology

Decentralized compensation of controller uncertainty in the steady‐state bumpless transfer under the state/output feedback

“…In [8,9], moreover, a significant controller uncertainty is also found in megawatt/throttle pressure control of a boiler/turbine unit. This controller uncertainty is shown to give rise to the divergence of the output of the offline controller from that of the online one under the topology of [6], thereby precluding controller transfer.…”

“…This controller uncertainty is shown to give rise to the divergence of the output of the offline controller from that of the online one under the topology of [6], thereby precluding controller transfer. Analysis of this problem carried out in [9] demonstrates that this convergence loss arises due to the use of the nominal state of the offline controller, in lieu of its true state, by the transfer operator. To address this problem, the concept of full information set for bumpless transfer under controller uncertainty is introduced in [9] and this set is shown to consist of the nominal state and the actual output of the offline controller along with the actual input and output of the online controller.…”

“…Analysis of this problem carried out in [9] demonstrates that this convergence loss arises due to the use of the nominal state of the offline controller, in lieu of its true state, by the transfer operator. To address this problem, the concept of full information set for bumpless transfer under controller uncertainty is introduced in [9] and this set is shown to consist of the nominal state and the actual output of the offline controller along with the actual input and output of the online controller. This observation resulted in a novel state/output feedback bumpless transfer topology and the corresponding design technique, developed in [8,9] and demonstrated therein to solve the problem of high-quality steady-state bumpless transfer from the industry standard low-order nonlinear multi-loop proportional integral derivative (PID)-based controllers to modern MIMO robust controllers in the megawatt/throttle pressure control of a boiler/turbine unit.…”

“…The topology of [9] consists of two feedback loops: the inner loop that employees the nominal state of the offline controller and is designed using the technique of [6], and the outer loop that compensates for the controller/model mismatch by employing the offline controller output. A block diagram showing the outer loop is given in Figure 1, where e and u are online controller input and output, respectively, K and denote the mismatch compensator and its output, u is the offline controller output, and G 1 and G 2 represent, respectively, the transfer functions from the input e of the online controller and the output of the mismatch compensator to the output u of the offline controller.…”

“…The transparency of the transfer operator implementation and tuning in industrial MIMO applications dictates that the mismatch compensator structure be the simplest possible, preferably diagonal and consisting of decoupled scalar PID-type controllers. In [8,9] G 2 is numerically found to have a diagonal steady-state structure for a given specific boiler/turbine controller. This, in turn, is determined to be sufficient for the existence of the stabilizing decentralized mismatch compensator, and the procedure based on loop shaping and convex programming is developed in [8,9] to compute the required compensator parameter values.…”