O. Bobrov^{1}
The on-off pressure control system is widely used in reciprocating compressor units. The normal operation of consumers of compressed air is ensured by maintaining the pressure in the system in a predetermined interval (Pmin ÷ Pmax).
Improving the energy efficiency of the “electrical network - compressor - pneumatic network” system as a whole can be achieved by performing a “floating” upper pressure level. In [1], a profitability criterion was introduced for a control system and determining the value of the upper pressure level in one cycle of pumping the pressure release - efficiency. The rationale for this energy indicator is based on elucidating the relationships between different indicators of the elements of the entire system, determining the most significant, in terms of energy losses, elements of the electromechanical system, as well as the relationship between them.
To solve the previously formulated optimization problem [2], a digital mathematical model is developed. When creating the model, the assumptions described in [3] were taken into account, taking into account the purpose of the simulation — obtaining the optimal value of the maximum upper level of pressure in the pneumatic system corresponding to the maximum of the objective function for various fixed compressed air flow rates by the pneumatic receivers. The obtained values can be implemented in the control system for the production of compressed air with a certain accuracy (up to 10% of the calculated values). Consider the obtained simulation results for electromechanical systems with a nominal range of capacities of air piston compressors with an asynchronous squirrel-cage rotor motor - 2.5; 5; 10; 11; 12; 20; 24; 27, m^{3} / min. In the process, electromechanical systems were selected whose parameters are similar to the parameters of the base model, taking into account the rated performance of the compressors.
According to the method described in [4], tests were carried out to determine the actual performance of compressors and the loss of compressed air in the pneumatic system.
Based on the need for a comparative analysis of the results, the initial parameter, the flow rate of compressed air consumed by the pneumatic receivers, was set for all complexes in relative values reduced to the nominal capacity of air compressors. The need to pre-set certain discrete values of the flow rate of compressed air arises because Q_{potr} is an independent parameter, since it is determined by the operating modes of the pneumatic receivers and is not controlled by the control system of the piston compressor unit. The highest compressed air flow rate for all electromechanical systems is limited to 55% —the lowest maximum compressed air flow rate of the complexes under consideration. When modeling the parameters of their operating mode, fixed values of the flow rate of compressed air consumed by the pneumatic receivers for a duration of one hour were sequentially set.
It should be noted that for other values of the considered parameters, the simulation results may differ from those presented. However, in general terms, the relationship between the flow rate of compressed air Qpotr and the energy savings will be similar. Three options for the consumption of electric energy were calculated: with the classic on-off control of the performance of an air piston compressor, with on-off control of the productivity with an optimal upper pressure level without restrictions on the number of starts and on-off performance control with an optimal upper pressure level with a limit on the number of starts per hour of a drive induction motor. When comparing the first and second control options, it is clear that the saving of electric energy consumed by the considered complexes exists for all given values of the compressed air consumption consumed by the pneumatic receivers, and can reach 13.5%.
However, when considering the first and third options, the savings will not be so significant, especially at low flow rates of compressed air. This is due to the influence of the limit on the number of starts per hour of the asynchronous drive. Therefore, the proposed power management system is most effective at high flow rates of compressed air. Taking into account the simulation results in the absence of a limit on the number of starts in the power management of air piston compressors with an asynchronous squirrel-cage rotor drive at the design stage of such complexes will increase the passport number of starts per hour, and thereby significantly increase the potential savings in electric energy.
c