Multivariable two-value discrete-time controller restraining load fluctuation

A multivariable discrete-time controller whose manipulated variables take two values, i.e., on and off, is proposed and examined. One of the applications of such a controller is the temperature control of a resistive electric furnace driven by AC voltage with zero-cross switching. The proposed controller is superior to one using the cycle-count method with respect to control performance. However the problem of consuming power fluctuation arises when the control system has multiple variables, as is the case when a furnace has several heaters. One approach to this problem is the use of an ordinal controller with continuous-value manipulated variables and a Δ-Σ modulator which converts some continuous-value signals to two-value ones, thus preserving the lower frequency behavior of the signals considering the total-load fluctuation. This approach is examined in an experimental pilot plant. It is shown that the effectiveness for load restraint is excellent, but that a trade-off appears between load restraint and control performance