Topology And Simulation Of A PWM-Controlled Fault Current Limiter

The expansion of the modern power system results in the fast increase of the fault current level of the system. Fault Current Limiter (FCL) is a good key to this problem as a new protective device. In this paper, a PWM-Controlled Fault Current Limiter is proposed. It is composed of a limiting reactor and a compensator capacitor, which is in parallel with a pulse width modulation (PWM) switched reactor. A variable reactance can be realized by duty ratio control. Then the FCL can attain to the goal of controllable limiting fault current and controllable series compensation.First, the topology of PWM-FCL is proposed based on the analysis of others' s research. Then the operation principle of the device is introduced to the readers and the definition of the limiting rate of the fault current and the compensation degree of the series reactance is done. In this section, the author designs the snubber circuit and the gate drive circuit of the GTO.Second, PWM-FCLs are separately installed in the transmission line and the feeders where a short circuit fault may occur. MATLAB is used to simulate this process. The obtained results show that the PWM-FCL can limit the fault current quickly, and the unfaulted phase(s) and unfaulted line(s) will keep stable operation state when an asymmetry fault occurs. In addition, it will limit the expected voltage sag during the fault and improve the system power quality.Next, the PWM-FCL's merit of producing low harmonics and fast responseowing to PWM is demonstrated in theory and simulation. And a simulation and academic analysis proved the fact that PWM-FCL could restrain the spread of the harmonic within the distribution network.Finally, how the PWM-FCL contributes to the system stability, three-phase load unsymmetry and the transmission capacity is discussed. And how to decide a reasonable compensation rate of the PWM-FCL is also proposed.