Abstract: A method and apparatus for designing perturbation signals to excite a number of input variables of a system, in order to test that system for the purpose of obtaining models for the synthesis of a model-based controller. The method begins with providing input parameters of the system. A plurality of binary multi-frequency (BMF) signals are generated based on these input parameters and the frequency spectra of these BMF signals are calculated. One BMF signal is selected out of the set of BMF signals so that the frequency spectrum of the selected BMF signal most closely matches a desired frequency spectrum specified by the input parameters. The selected BMF signal is used as a first perturbation signal for testing the system. The selected BMF signal is also shifted by predetermined amounts of samples to create delayed copies of the original BMF signal to be used as additional perturbation signals.

Abstract: An exemplary method of improving an initial parametric model of a system by the incorporation of a priori knowledge of the system. The initial parametric model of the system is a model including a plurality of parameters based on analysis of a plurality of input signals and a plurality of output signals. The method includes the steps of determining a set of constraints corresponding to a set of the plurality of parameters and based on the a priori knowledge and then performing a constrained parametric optimization of the system based on the initial parametric model and the set of determined constraints to produce an improved parametric model of the system. The constrained parametric optimization of the initial parametric model does not include the plurality of input signals and the plurality of output signals.

Abstract: A method and apparatus for designing perturbation signals to excite a number of input variables of a system, in order to test that system for the purpose of obtaining models for the synthesis of a model-based controller. The method begins with providing input parameters of the system. A plurality of binary multi-frequency (BMF) signals are generated based on these input parameters and the frequency spectra of these BMF signals are calculated. One BMF signal is selected out of the set of BMF signals so that the frequency spectrum of the selected BMF signal most closely matches a desired frequency spectrum specified by the input parameters. The selected BMF signal is used as a first perturbation signal for testing the system. The selected BMF signal is also shifted by predetermined amounts of samples to create delayed copies of the original BMF signal to be used as additional perturbation signals.

Abstract: A control system for a process of liquefied natural gas production (LNG) from natural gas using a heat exchanger and a closed loop refrigeration cycle employs independent, direct control of both production and temperature by adjusting refrigeration to match a set production. The control system sets and controls LNG production at a required production value, and independently controls LNG temperature by adjusting the refrigeration provided to the natural gas stream. One exemplary method employs compressor speed, for example, as a key manipulated variable (MV) to achieve fast and stable LNG temperature regulation. Other compressor variables rather than speed may be key MVs, depending on the type of MR compressors employed, and may be the guidevane angle in a centrifugal compressor or the stator blade angle in an axial compressor. The second exemplary method employs a ratio of total recirculating refrigerant flow to LNG flow as the key manipulated variable to effectively control the LNG temperature.