Research Of Critical Technology On Flexible Power Conditioner Using Flywheel Energy Storage

The Flexible Power Conditioner (FPC) incorporates the functions of the synchronous condenser and flywheel energy storage. It is made up of a doubly-fed induction machine connected with flywheel, a back-to-back converter for AC excitation and an excitation vector control system. The advantage of FPC is its capacity of controlling both active and reactive power, and it have the storage, generate and synchronous condenser operating mode.So it can be used to improve the stability of power system.Additional advantage of the FPC over the other storage system is that it is suitable for power compensation of low frequence, large capacity and long time.The principle, modeling, and applications in power system of the FPC have been discussed in this dissertation.The dissertation consists of six main chapters as follows:The background of this project is introduced.The energy storage technology and its applications in power system have been discussed. And then, the structure and principle of the FPC are introduced and the key technologies are discussed.The mathematic model of the FPC is discussed.The steady state equivalent-circuit model of DFIG is established and the energy floating of FPC is discussed. Based on the analysis above, the operation of the FPC is analyzed.For this basis, the vector excitation control strategy of the FPC will be discussed detailedly in the next chapter.The vector excitation control strategy of the FPC is researched.The mathematic models and control strategies of a back-to-back converter is discussed. The simulation model of FPC on EMTDC/PSCAD environments is established. At last, simulation results show the effectiveness of the proposed scheme.The control strategy of the FPC during the grid voltage drop is researched.For the grid side converter, the control strategy based on the load current feed-forward is presented to suppress fluctuation of DC capacitor voltage.For the rotor side converter, firstly, the transient flux and rotor voltage from the rotor open model is analyzed.Then, basing on the establishing of the transient model which considering rotor current, we get a conclusion that the transient flux of stator side is the reason of the over-current on rotor side.Based on the conclusion of the transient analysis, a new excitation control strategy was adopted in this paper.To guarantee the safety of the rotor side converter, using the virtual impedance control strategy to suppress the rotor over-current, it can expand the operating range of doubly-fed generator during the grid voltage drop.At last, simulation shows the effectiveness of the proposed scheme.The application of FPC in damping out power system oscillations is discussed.The principle of FPC on damping out power oscillation is analyzed theoretically.It is found that variation of the active power where the FPC is applied is the best signal used for FPC to damp out power system oscillations.The simulation model of FPC used to damp out power system oscillation is carried out and very encouraging results are obtained.At last, it designs and implements a laboratory platform of FPC system with DFIG which main part is a set of a back-to-back converter which is made up of the grid-side converter and rotor-side converter. A lot of experiment items are performed on this platform, which including the grid-side converter control and the rotor-side converter control.Another experiment test of the FPC prototype is used to damp out power system oscillation is carried out in a power system dynamic simulation laboratory environment.The experimental results testify the validity of the theory and the control strategy proposed in this dissertation.