Research On Marine Combined Electrical Power Plant And Electric Network Power Quality

The most important goals in the development of shipbuilding industry are the improvement of the ship operational safety, as well as the energy source utilization rate. Marine electrical power system is one of the most important systems in a ship and has close relationship with almost all the systems in the ship. And it influences the operational safety and economical efficiency of the ship directly. The energy saving and improvement of operational reliability of marine electrical power system includes two aspects, they are, the energy saving and improvement of operational reliability of marine electrical power station and that of marine electric network.The subject of the dissertation is concentrated on how to save energy consumption and to improve operational reliability of the two component parts of a marine electrical power system - electrical power station and electric network. The method of application of marine combined electrical power plant to the electrical power station, together with the application of combined active power factor correction circuit and series active power filter aided by shunt passive power filter to the electric network, is brought forward. Based on the simulation experimental results, the marine electrical power system achieves a significant production of saving energy consumption and improving system operational reliability when the aforementioned method is applied.The dissertation consists of six parts. Except that the first chapter introduces the purpose of the research in the dissertation and the main contribution of the dissertation, and the second chapter gives the summing-up of the dissertation, the other four chapters are all the research content of the dissertation.In chapter two, the composition of a marine electrical power system is introduced. Then method of improvement of energy consumption and reliability of traditional marine electrical power plant is discussed. Afterwards, a number of relevant precision auto-control methods are described in multi-aspect of the operation of marine electrical power plant. The emphasis of chapter two is laid on the analysis of the combined generation system which acts as the marine electrical power supplier in order to further the efforts in saving fuel oil consumption and keeping continuity of electrical power supply, as well as promoting safety of ship. The combined generation system consists of diesel generators, exhaust gas turbo-generator and SCR shaft generator. The latter two generation sets are applied to ocean ships as effective means of saving fuel oil consumption. In this subpart, mathematical models of the aforementioned generation systems are established according to the analysis of their dynamic operational characteristics. These models are detailed - the mathematical model of rotation speed regulation of exhaust gas turbo-generator according to the load variation of the generator, and both the mathematical model of field current regulation process while the output power of the SCR shaft generator is rated and the mathematical model of the inverse angle regulation process while the output power of the SCR shaft generator declines linearly. Then, relevant simulation experiments of the generation systems have been done, and the experimental results show that the established mathematical models are reasonable. It is analyzed that application of the combined generation system is in a position to contribute to save fuel oil consumption in ships more significantly. Simultaneously, its contributions to keeping continuity of electrical power supply since it makes sure that the electrical power supply is uninterrupted during transforming one type of generator to another type of generator. Furthermore, it promotes safety of ship when main engine works under fault conditions. This solution is considered to be promising in shipbuilding industry.In chapter three, the necessity of improvement of marine power quality is discussed considering the influence of those phenomena on economical operation of ship and reliability of marine systems. Firstly, the criteria of electrical power quality are listed. After the description of the state of art the power quality parameters measurement and power quality improvement technology, theoretical basis of electrical power quality analysis is discussed, which includes definitions of power quality parameters, Fourier transform and wavelet transform in frequency domain and instantaneous reactive power theory in time domain. Afterwards, theoretical basis of power quality improvement is discussed too, which includes two aspects - adoption of impulse controllers of alternating current power and application of power filters, while rather typical trend of development of the first choice is pulse width modulation technology of cascade multilevel converter, and that of the second choice is technology of active power filter. Finally, certain criteria on marine electrical power quality that issued by China Classification Society and other main classification societies in the world are specified. And the key technology which is required in dealing with marine electrical power quality is set forth.In chapter four, a shunt active power filtering system is established based on a physical simulation experimental system of a low capacity marine electrical power network, which is designed to suppress the electric network harmonics, and simultaneously, to elevate its power factor. In the physical simulation system, a transform is applied to form an isolated small capacity electric network, and the model of nonlinear load is obtained through adoption of a full controlled three-phase power electronic bridge followed by a resistor- inductance load. The designed filtering system contains both real time measurement unit of electric network parameters and power filtering unit. In the measurement unit, an analog anti-aliasing low-pass filter is applied to its input module; a piece of data signal processor is applied for data processing; a liquid crystal display screen is designed for display of data and waveform. Moreover, the anti-interference design of hardware is suggested and the error analysis of the system is also introduced. In the filtering unit, a set of power version DSP equipped with three-phase IGBT-bridge is adopted, and the output strategy adopts the control of space vector pulse width modulation. Based on the analysis of relevant experimental results, the designed system testifies its feasibility.In chapter five, in order to design a suitable circuit for marine electric networks to improve power quality, the parameter selection method of reactive power filter and the control system design of active power filter and active power factor correction circuit are analyzed at first. Then, the models of reactive power filter, the series active power filter and the active power factor correction circuit are established respectively, and their operational properties are analyzed accordingly. The most important part of this chapter is that a new filtering and power factor correction circuit is designed. This circuit is called combined active power factor correction circuit (APFCC) and series active power filter (SAPF) aided by shunt passive power filter (PF). The new solution is designed in order for a marine electrical power network to simultaneously suppress harmonics and elevate power factor to improve the efficiency of power transmission in the electrical power network and reduce the volume of generators. Based on the analytic results of the comparison of three types of circuit topology, a proper type of topology is selected for realization in a simulation experiment which is carried out in the environment of Matlab. Experimental results show that the suggestion of applying the designed hybrid circuit to marine electrical power networks is feasible.The innovations of the dissertation are as follows.(1) The mathematical model of the marine multi-mode power station which consists of three types of generation sets is established and the relevant simulation experiments are fulfilled. And its merits in saving fuel oil consumption and keeping continuity of electrical power supply, as well as promoting safety of ship, are analyzed. The research unifies the three types of ship generation sets in combined operation. This theory is verified in practice by the multi-mode marine simulators established in Guangzhou Maritime Academy and Jiangsu University of Science and Technology respectively.(2) Filtering and power factor correction technology is researched in order to improve harmonic pollution and low power factor of marine electric network. For the first time, a hybrid circuit which combines the series circuit and shunt circuit is designed for marine use. The hybrid circuit is different from the nowadays applied filtering circuits. Furthermore, since current harmonics has rather significant influence on operational reliability and energy consumption of a ship, and the research on current harmonics is very few before (that is, only voltage harmonics is analyzed when voltage source is concerned), the dissertation has analyzed in details the formation and influence of current harmonics in theory. And the hybrid filtering and power factor correction circuit designed in the dissertation is proved to be with better properties in fulfilling filtering than traditional shunt systems.(3) An electrical power parameter measurement and power filtering system is developed based on a physical simulation experimental system of a low capacity marine electrical power network. The experimental results show that the established system has good property in anti-aliasing, and moreover, its properties in speedability and veracity are able to meet the requirements of a ship electric network.