The influence of control laws of frequency-regulated electric motors on electric ships’ maneuvering characteristics

Abstract

Relevance. In shipbuilding, there have been trends in the use of electric motion. The most important advantages of electric vessels are the high maneuverability, which contributes to the safety of maneuvering operations. Electric propelling power plants (EPPP) are most often built on the basis of asynchronous frequency-controlled electric motors (EM). More and more attention is being paid to electric vessels with a unified electric power system. Electric propelling plant (EPP) is the largest power consumer. The transient modes of its operation significantly affect the parameters of the electric power of the ship network, which raises the requirements for the quality of transient processes in the EPP. On this basis, both the indicators of maneuverability and the quality of electric power of the ship network should be the quality indicators of the control of the EPP on maneuvers. Status of the issue under consideration. Three laws of control of frequency-regulated electric motors are used in the theory of electric motion: at a constant moment; at constant power; at quadratic load. For a real engine, deep frequency control according to one of these laws is not possible, since the motor overload capacity will either be lowered at low frequencies or overestimated in nominal mode. Constant overload capability can only be ensured if there is a variable correlation between voltage and frequency. In the case of frequency control of electric ships’ electric motors, the task becomes more difficult, since a set of indicators characterizing the ship's maneuvering characteristics, transient processes in the EPPP and the parameters of electric power of the ship network should be chosen as the criteria of regulation quality. This leads to the need to clarify the control laws. The purpose of the work is the search for frequency control laws of electric motors that are able to provide better maneuverability of electric vessels. Research results. A structural diagram of EPPP as part of an electric ship’s propulsive complex has been made. A mathematical model of transient operation modes has been worked out on its basis. An algorithm and a package of application programs for calculating the basic mode indices of the complex have been developed. The estimation procedure of the basic indicators of quality of maneuver operation performance is worked out. The model and method of calculation make it possible to study the influence of EM control laws on the electric ships’ maneuvering characteristics, on transient processes in the EPPP and on the parameters of electric power of the ship network. The research was carried out on the example of the science-research vessel MV SANCO STAR. Maneuver modes for various control laws are calculated and the performance indicators of maneuver operations are evaluated. A comparative analysis of the results made it possible to find the best EM control laws on maneuvers. Conclusions. With respect to electric vessels with frequency-controlled electric motors, the proportional control law has significant advantages over other control laws. At the same time, increasing the supply voltage of the EM in transient modes opens the possibility of increasing the efficiency of performing maneuver operations. It is recommended to form the control laws of the EM voltage as analytical dependencies, in which the correlation between the relative voltage and the relative frequency changes gradually depending on the depth of regulation. Specific analytical dependencies are obtained from the results of optimization calculations of control laws.