Algorithm for estimation of ship refrigeration unit energy efficiency using full order observers

Abstract

The article considers the construction of an algorithm for estimation the energy efficiency of a ship refrigeration
unit using the minimum required number of sensors. It is established that the existing methods for diagnosing and monitoring the
technical condition of ship refrigeration units are imperfect due to the presence of a large number of sensors and the necessity to
suspend the unit. The choice of the refrigeration coefficient as an indicator of energy efficiency is justified. A method that allows
determining the refrigeration coefficient in real time without the necessity to stop the operation of the ship's refrigeration unit and
use pressure sensors is proposed. For this, the method supposes the calculation of the specific cooling capacity and compressor
compression work, the mechanical power on the shaft and the mass flow rate of the refrigerant. The algorithm for determining the
cooling capacity and compression work using only four temperature sensors is considered. This algorithm supposes the
determination of enthalpies at characteristic points of the refrigeration cycle using the equations of the refrigerant state. A method
for evaluating the mechanical power on the compressor shaft using full order adaptive state observers is proposed. A decision of
using the electromagnetic torque of the compressor motor as a measured quantity is substantiated. A state observer is synthesized
using a modal method based on a linearized model of the electric motor. An expression for calculating the geometric mean root and
elements of the observer matrix is proposed. The resulting observer structure allows constructing it on the basis of a complete
mathematical model of the electric motor and evaluating not only the speed, but also the load torque on the compressor shaft. In the
environment of Matlab / Simulink, a simulation model of the compressor motor state observer is built. The obtained simulation
results confirm the efficiency of the proposed method. An algorithm for determining the electromechanical parameters of a
compressor for a given period of time using three voltage and current sensors is considered. A general algorithm for estimation
energy efficiency, which can be the basis for creating a system for diagnosing and monitoring the technical condition of a ship
refrigeration unit, is constructed