Combined Control of the Air-Cooling Unit of Oil

The air-cooling units of oil are widely used in the oil systems of gas compressors. They are designed to maintain at their outlet a certain temperature of the oil pumped through hydrostatic bearings of superchargers and powerful synchronous motors. The air-cooling unit includes fans driven by asynchronous motors. In order to save electric power, air-cooling units are supplied with frequency converters and control systems closed by the oil temperature sensor. A feature of functioning feature of the air-cooling unit is a wide range of variations of the ambient air temperatures. Therefore, most of the known control systems for such devices require changing the settings of the controllers depending on the season, which is produced by the operating personnel of the compressor station. The purpose of this study is to synthesize a combined control system for an air-cooling unit of oil. To achieve this goal, a single-loop control system, closed by an oil temperature sensor, is equipped with an air temperature sensor that directly affects the output signal of the temperature controller. The transfer functions of all elements of the control system of the air-cooling units of oil are given, and the main constant times and the range of their changes in dependence of the cooling air temperature are determined. A proportional-differential link was used to compensate for the inertia of the oil temperature sensor in the feedback circuit. To give the control system the properties of astaticism, it was proposed to use a proportional-integral controller in a straight circuit. Analytical expressions are found that allow one to correctly select the settings of the temperature controller, which remain unchanged in all operation modes of the device. To ensure exceptional simplicity, it was proposed to carry out a technical implementation of the control system of the air-cooling unit of oil on a frequency converter that incorporates free functional blocks and that use the so-called BICO programming technology. A computer simulation of the control system of the air-cooling unit of oil was carried out at two boundary values of the ambient temperature. It is shown that the time of the step response varies slightly from the average value with a significant variation in the parameters of the control object.