Research On Energy Storage Protection For LVRT Of Direct Driven Permanent Magnet Wind Turbine System

At present, wind power is the fastest developing renewable energy, with the expansion of wind power energy on the grid, it brings a number of related technical subjects to be solved, and one of the most representative subject is Low voltage ride through technology, however, our country is relatively late in this area, and the related literatures are almost based on unloading protection, which would have resulted in a waste of energy sources. Besides, the efficiency of the system is relatively low. Therefore, in order to save the energy, the paper has improved the control strategy, and then made a study about energy storage protection for low voltage ride through.The paper firstly analyzes the development and the existing problems of low voltage ride through technology at home and abroad; Then introduced the model of energy storage system based on super-capacitor, and the topology of wind power systems for energy storage protection, finally this paper selected the uncontrolled rectifier topology, and made a analysis of the three storage protection circuit and its principles.Secondly, the paper made an analytical and research of MPPT algorithm based on non-controlled rectifier, and summarized a power-speed bias controlled algorithm to achieve the function; Thirdly, the paper derived voltage space vector modulation algorithm, and established the simulation circuit model using the M-S function; Then, created a mathematical model of the network-side converter, and took the voltage loop and inner current closed-loop control strategy to achieve unity power factor control objectives.Finally, the paper studied the control algorithm on a basis of the storage protection for low voltage ride through, analyzed and proposed a kind of coordinated control algorithms between multi-variable to achieve a better control to change the operational status of the energy storage system, all that was achieved by a DC-DC converter between the DC-line and the energy storage system, which provided a channel for voltage conversion and energy ransmission. At the end, the paper completed simulation about low voltage ride through using the improved multi-variable coordinated algorithms to control the operating status of the DC-DC converter for charging and discharging.In order to simplify the simulation model, the paper studies the low voltage ride through capability just based on a constant wind speed, and then examined the effect of the balance of power based on the energy storage system in the low voltage ride through times. With the theory research the paper has built the modeling and simulation of the whole circuit based on MATLAB/SIMULINK simulation software, the system proposed in this paper can realize the expected control objectives, and finally verified its correctness.