Active Hybrid DC Circuit Breaker With Controlled Superimposed Current

With the load centers and power resources distributing in faraway areas which leads to unbalanced situation, interconnecting regional power systems and constructing Ultra High Voltage Direct Current(UHVDC) project is considered as a promising option to solve the contradiction. Flexible HVDC technology has been widely used in the world nowadays, HVDC circuit breaker, whose main role is to change the operating mode of DC system, clear failure of the DC side, is important in HVDC. The research on hybrid DC circuit breaker which combines the advantages of mechanical and solid-state DC circuit breaker is of great value.Firstly, the fundamental mechanisms of different methods to interrupt DC are presented. An active DC circuit breaker interrupting DC circuit by superposing oscillation current is simulated on the basis of Mayr arc model. Simulation results reveal that traditional DC circuit breaker lead to increased positive amplitude of the superimposed current while a current zero crossing is produced. It may cause damage to the switch contacts and it’s uncontrollable. It can not suppress the arc effectively or make appropriate adjustments for different DC to interrupt.Considering the shortcomings of traditional DC breaker, this paper presents an active hybrid DC circuit breaker with controlled superimposed current. By producing a particular current with controllable magnitude and asymmetrical waveforms, the positive amplitude of the superimposed current is reduced while an artificial current zero crossing is generated, thus decreacing damage to the switch contacts. Moreover, the topology and working principle of voltage-source hybrid DC circuit breaker is presented in this paper with its simulation model established. Based on the scheme of voltage-source hybrid DC circuit breaker a improved scheme have been proposed. By simulation software, the current-source hybrid DC circuit breaker and voltage-source hybrid DC circuit breaker have been modeled and compared due to their interrupting effects, simulation studies were analyzed in detail too.Finally, the proposed hybrid DC circuit breaker is applied to the DC system model, simulations are studied on line-to-ground faults. The simulations of unipolar blocking and DC circuit breaker clearing DC line faults are conducted to verify the feasibility of the proposed design scheme in HVDC System. Results has shown that the established hybrid DC circuit breaker model is able to quickly cut off the fault line, thus protecting the DC grid.