Variable Frequency Transformer And Its Application In Power System

Power grid is an important infrastructure of the national economy, and it is an important platform for the carrier of power transmission and the optimal allocation of energy resources.Especially with the accelerated development of clean energy,as well as the popularization and application of power grid intelligent technology,the role of the power grid has become increasingly prominent.As the energy supply and demand in China is typical of the reverse distribution, and energy production is far away from the power load centers, in order to meet the needs of the economic and social development of the growing use of electricity needs for strengthening the power grid interconnection and flexible control,improve the ability of power grid optimal allocation of energy resources more urgent requirements. Variable frequency transformer developed in this context, in the future development of China's power grid can play a positive role.Variable frequency transformer is a tandem type of flexible AC transmission system device, but also a new type of intelligence power grid equipment, has a smooth adjustment transmission power, suppression of the system low frequency oscillation, adjustment of system frequency and other functions, to achieve asynchronous interconnection between different frequency of power grids,and optimize the transmission power and distribution ratio of parallel transmission channels. Is conducive to enhancing the power grid transmission capacity, improve the flexibility of power grid operation control and the security and stability of power system, it can play an important role in building a strong, intelligent and efficient modern large power grid.In this paper, the basic theory of variable frequency transformer is introduced in detail, and the mathematical model of steady-state and transient-state is analyzed,deduce the condition of stable operation of the system and the expression of the required driving torque,and the establishment of a steady trend and electromechanical transient simulation model in PSASP.On this basis,proposed variable frequency transformer control strategy and model,including DC drive system control design, device control design and system control design.According to the steady state power flow equation of the variable frequency transformer,the relation of the transmission power,the equivalent phase shift of the relationship and the trend of steady-state model,completed the flow simulation of variable frequency transformer in power system,description of the variable frequency transformer has a good adaptability in the power system.Also use the variable frequency transformer adjustment function for suppress low frequency power oscillation in interconnected system to simulation,the results show that the damping effect is obvious, and it is beneficial to improve the security and stability level of power grid.Finally, in the power system electromagnetic analysis software PSCAD/EMTDC to establish the variable frequency transformer and the wind power grid interconnection simulation module,by means of frequency adjustment of the variable frequency transformer, the simulation is carried out.the simulation shows that the variable frequency transformer has significant development prospects in wind power grid connection.