Analytical Multiloop Control for Multivariable Systems with Time Delays

In this paper, a new design method with performance improvements of multiloop controllers for multivariable systems is proposed. Precise expression is developed to show the relationship between the dynamic- and steady-state characteristics of the multiloop control system and its parameters. First, an equivalent transfer function (ETF) is introduced to decompose the multivariable system, based on which the multiloop controller parameters are calculated. According to the ETF matrix property, an analytical expression for the PI controller for multivariable systems is derived in terms of substituting the ETF matrix for the inverse open-loop transfer function. In the proposed controller design method, no approximation of the inverse of the process model is needed, implying that this method can be applied to some multivariable systems with high dimensions. The simulation results obtained from several examples demonstrate the effectiveness of the proposed method.

Double Sliding-Surface Multiloop Control Reducing Semiconductor Voltage Stress on the Boost Inverter

Sliding-mode control (SMC) has been successfully applied to boost inverters, which solves the tracking problem of imposing sinusoidal behavior to the output voltage despite the coupled or decoupled operation of both boost cells in the converter. Most of the results reported in the literature were obtained using the conventional cascade-control structure involving outer loops that generate references for one or two sliding surfaces defined using linear combinations of inductor currents and capacitor voltages. As expected, all proposed methods share the inherent robustness and insensitivity to the uncertainties of SMC, which are the reasons why one of the few comparison criteria between them is the simplicity of their implementation that is evaluated according to the required measurements and mathematical operations. Furthermore, the slight differences between the obtained dynamic performances do not allow a clear distinction of the best solution. This study presents a new SMC approach applied to a boost inverter in which two boost cells are independently commutated. Each of these boost cells integrates an outer loop, enforcing the tracking of harmonic-enriched waveforms to the capacitor voltage. Although this approach increases by two the number of measurements and requires multiloop controllers, it allows effective alleviation of the semiconductor voltage stress by reducing the required voltage gain. A complete analytical study using harmonic balance technique allows deducing a simplified model allowing to obtain a PI controller valid into to the whole set of operation conditions. The several simulation results completely verified the potential of the control proposal and the accuracy of the employed methods.

Determination and use of feasible operation region in flash distillation control

Flash distillation is essentially a single stage mass transfer operation. The flash distillation operation is used in this work to highlight the importance of identifying the zone where a system has an appropriate behavior. In this sense, this paper presents a discussion about the use of the feasible operation region (FOR) in the design of process control structures. For this reason, three control structures are presented. The first one is the traditional one, a PID multiloop control structure. The second structure uses the FOR graphically in order to determine a better operation point and improve the control response. Finally, the third structure uses the FOR numerically for guiding the controller using a modified control structure. The improvement of the closed loop operation of the flash using the last control structure is notorious when compared with the traditional control structure.

Multi-Loop PID Controller Design for MIMO Processes Based on SIMC Fractional Order Filter

This paper presents a multiloop control for the different dimensional multivariable processes which are having the strong interrelation amid its variables. The objective of this discussion is to enhance the overall performance of the system by reducing the effects of interrelation of process variables. The prerequisite for design of multi loop control is to determine the best pair of controlled variables. In this paper the pair of variables is identified by using the relative gains of the process variables. Based on these, the pair of possible control loops is identified and their FOPDT models are approximated. Then to improve the servo operation (for set point changes in input) the PID controller parameters are calculated for these models using Simplified IMC tuning formulas. To minimize the effects of interrelations fractional order filter is used. With this combination, the overall objective of the control system is fulfilled i.e., tracking the set point and lessening the interaction. To show the effectiveness, the two examples are considered with different dimension, interaction and controller is designed. The results show that the SIMC algorithm improved the performance of the system.