Research On DC Bus Stability Control Of Marine Electric Propulsion System And LVRT Technology

With the development of power electronics technology, improvement of motor controltechnology and wide application of computer, the research on Marine Integrated Full ElectricPropulsion (IFEP) system in developed countries like Great Britain and the United States hasmade a great breakthrough and applied to many types of ships since the eighties of the lastcentury. Future direction of development of marine power system is IFEP, as the ship withIFEP is helpful for simplification of the whole ship design, optimization of the power systemand enhances the marine stealth performance. Meanwhile, the IFEP can also provide powerassurance for future ship-borne high-energy weapons. The U.S. Navy has proposed a powernetwork topology which has many advantages called Multi Zonal Medium Voltage DC(MVDC) Shipboard Power System (SPS) for the next generation of their surface combatants.In this dissertation, the following issues in the marine integrated full electric propulsionsystem are studied:First of all, a simulation model based on MATLAB of marine electric propulsion systemincluding AC source, diode rectifier, DC bus, DC bus filter, propulsion frequency converter,propulsion motor and propulsion propeller has been built. The mutual influence between shipmaneuvering motion and propulsion system was considered. The effection of wave wasintroduced which is working on the propulsion system by influencing performance ofpropeller. The simulation model can be used as a research propulsion system by the fullelectric propulsion of ships sailing in the waves. A power-speed combined control methodwas studied to restrain propulsion system power fluctuations when ship sailing in waves.In the next place, Several power electronic cascade system stability analysis methodbased on impedance analysis were introduced for research on the stability of DC bus withinDC Zonal Distribution Systems (DC ZEDS). The input impedance and output impedance ofthe DC bus filter–propeller inverter–motor system were derived. The filter parametersinfluence over the DC bus output impedance was analyzed, Another method can be used foranalysis of the DC bus stability was applied with the Hurwitz Criterion, which was muchsimple and intuitive than classical impedance method, a new active damping control methodwas derived based on this criterion, this method was able to guarantee the stability of the DCbus when the DC bus filter capacitor cannot meet the system stability requirements.At last, the method can improve the low voltage ride through (LVRT) capability of thepropulsion system was studied, several reasons caused voltage drop of the ship electric propulsion system was analyzed, the weakening control method was established for keep thepropulsion motor running during the voltage drop, weakening control method widely used atpresent based on stator voltage control was analyzed after the target of weakening control indifferent regions was distinguished. Furthermore, one SVPWM field weakening controlmethod which was superior to those methods based on stator voltage control was appliedconsidered the choice of the maximum stator q-axis current in non-ideal rotor magnetic field.The results showed that this method has strong adaptability for voltage drop of DC bus andcan make full use of the remaining DC bus transmission capacity. In the next, the impedanceanalysis method was applied for analysis of the influence of asynchronous motor flux on DCbus stability. The field weakening control method was used in conjunction with activedamping control method to enhance the low voltage ride through capability of propulsionsystem and increase the stability of the DC bus.