control system based on IGBT

On basis of IGBT control technology, a novel neutral grounding impedance optimal control system is proposed in this paper. The method is implemented by passive IGBT circuit to compensate the capacitive current in distribution network. When the operation of distribution network is normal, the IGBT circuit is off, the power frequency overvoltage will not be produced; when the single-phase grounding fault occurs, the IGBT circuit is on, the arc-suppression coil is put into operation, then through the corresponding control strategy of the IGBT on-off control, the grounding fault current can be fully compensated, fault arc can be extinguished instantaneously. The theory analysis and the MATLAB simulation results show that the proposed method has quick speed, wide adjustment range and low cost, the inductor- current can be adjusted continuously, the grounding fault current can be compensated effectively. At present, in 3-35KV distribution network, neutral point is mainly designed to use inefficient grounding. With rapid development of power system and increasing of its capacity ,great changes occurring on main connection of power system ,power cables sharply increasing and the proportion became larger and larger and the increasing of line-to-ground capacitance current, when single-phase grounding fault occurs, it is difficult to extinguish the arc fault and can produce over- voltage which is 3.5-4.76 times as large as the phase voltage, so that it may threaten system equipments with fragile insulation and cause chain accidents. Therefore, the new arc- suppression optimal control system is necessary to be installed in order to compensate the capacitive current to ground and reduce the probability of failure. According to recent research on arc suppression coil automatic tracing compensate device. From the different ways to change the inductance, the arc suppression coil generally can be divided into different categories such as: air-gap adjustable type, Multi-tap type, magnetic valve type, dc additional magnetic type, adjustable capacitive-based type, high short- circuit impedance transformer and so on. The flux-controllable arc-suppression systems based on the principle of magnetic flux adjust the primary side equivalent reactance of the arc suppression by changing the duty cycle and make the reactance. But the compensation accuracy of this device is bad; it can not compensate the capacitive current, neither the active current. And its groups of IGBT parallel structure leads to the question of high engineering cost. The control theory based on IGBT arc-suppression compensates the fault current to extinguish the arc by detecting the unbalanced voltage and control the conduction of IGBT. The control system adopt the PWM control technique to compensate the capacitive current is faster than before and will not arise differential problems. The two methods of control compensation based on the active IGBT control theory and increase the cost. The paper proposed a new type of neutral grounding impedance control system based on passive IGBT. It ensures the displacement voltage of neutral grounding point within the allowed range of operation procedure in the power systems. The rapid compensation make the residual current of the ground-fault point close to zero and extinguish the fault arc efficiently, then reduce the reduce the probability of ground failure and improve the reliability of the power distribution system.