Research On Non-Minimum Phase Suppression Of Γ-Source DC Circuit Breaker

DC system has no natural zero-crossing point,and DC circuit breakers have become a key technology for the promotion and application of DC systems.The Γ-source DC circuit breaker(ΓDCCB)uses the shoot-through mode of operation to break short-circuit faults.As a new type of micro-level self-shutdown solid-state circuit breaker,it solves the problem of non-common ground,power circulation,load mutation error action and input resonance of traditional Z-source circuit breakers.However,ΓDCCB is a non-minimum phase system,the undershoot affects the safety of hardware,the voltage fluctuation affects the transient performance.Therefore,ΓDCCB non-minimum phase problem is studied in this paper to optimize the performance of the DC circuit breaker.In this paper,the undershoot of capacitor voltage in short circuit shutdown process ofΓDCCB is studied,and it can be seen that ΓDCCB is a non-minimum phase system by means of average PWM switch modeling method.In this paper,the suppression of non-minimum phase characteristic of ΓDCCB is studied by the following three methods.Firstly,from the perspective of parameters,the small signal modeling of ΓDCCB is carried out,the peak value and peak time of undershoot are derived according to the transfer function from control to capacitor voltage.By constraining and designing the parameters which affect the peak value and peak time of undershoot,the inductance and capacitance selection basis that can restrain the negative voltage is obtained,so as to realize the inhibition of negative voltage.Then,from the perspective of energy,two fully controlled switches and an energy absorption loop are introduced to improve the topology.After the thyristor is closed,the connection between the capacitor and the short circuit is cut off.The remaining energy of the capacitor is dissipated in the energy absorption loop,and the undershoot is eliminated through the energy transfer of capacitor.Finally,from the perspective of control,fractional order control is used to reduce the zero point of the right half plane of the non-minimum phase system to fractional order,so that the frequency of the zero point of the right half plane in the s-plane is increased.At the same time,the traditional PID control is added to realize the suppression of undershoot.Finally,the experimental prototype of ΓDCCB is built in this paper,and the above-mentioned function of circuit breaker is verified by simulation and experiment.The experimental results show that the undershoot of ΓDCCB can be suppressed by the proposed parameter suppression scheme and be eliminated by the improved topology based on energy transfer and fractional order control method,which shows the feasibility and effectiveness of the proposed scheme for non-minimum phase suppression of circuit breakers.