Design and implementation of decoupled periodic control scheme for a laboratory-based quadruple-tank process

It is well known that linear time-invariant controllers fail to provide desired robustness margins (e.g. gain margin, phase margin) for plants with non-minimum phase zeros. Attempts have been made in literature to alleviate this problem using high-frequency periodic controllers. But because of high frequency in nature, real-time implementation of these controllers is very challenging. In fact, no practical applications of such controllers for multivariable plants have been reported in literature till date. This article considers a laboratory-based, two-input–two-output, quadruple-tank process with a non-minimum phase zero for real-time implementation of the above periodic controller. To design the controller, first, a minimal pre-compensator is used to decouple the plant in open loop. Then the resulting single-input–single-output units are compensated using periodic controllers. It is shown through simulations and real-time experiments that owing to arbitrary loop-zero placement capability of periodic controllers, the above decoupled periodic control scheme provides much improved robustness against multi-channel output gain variations as compared to its linear time-invariant counterpart. It is also shown that in spite of this improved robustness, the nominal performances such as tracking and disturbance attenuation remain almost the same. A comparison with [Formula: see text]-linear time-invariant controllers is also carried out to show superiority of the proposed scheme.

Analiza vremena ispitivanja i greške očitavanja pametnih brojila električne energije u zavisnosti od njihovog podešenja

The time of checking the registers of smart meters of accuracy class 0.2 S for indirect measurement of active electricity via instrument transformers, during the first, extraordinary or periodic control and verification has been significantly increased according to the latest Rules on meters of active electrical energy of accuracy class 0.2 S from December 23, 2016. This is especially pronounced when the meter is set to show the measured value of electrical energy in kWh on the secondary side of instrument transformers with the often used meter of active electrical energy of accuracy class 0.2 S, rated phase voltage 110 / √3 V and for the rated current 1 A. In that way, the total time as well as the costs of testing such meters has increased a lot. In addition, with electricity meters set in this way with a resolution of three decimal places and a unit in kWh, there is an additional error when reading the measured value of active electrical energy and especially when calculating the energy loss of active electrical energy. A more acceptable approach to setting such meters will be considered.