Large capacity submerged arc furnace's key problems in the design of DC power supply 02

Due to the different materials and manufacturing processes of power electronic devices, their performance indexes are also different. Thyristor is suitable for the occasions with super power and low working frequency. On the one hand, thyristor has high rated parameters, simple control and mature technology; On the other hand, the thyristor has high surge resistance, high current parameters and good overcurrent resistance, which can better meet the operation requirements. Therefore, thyristor is selected as the main power device of the circuit.

In the DC power supply of large capacity submerged arc furnace, the measure of multiple devices in parallel must be adopted to bear the large rectifier arm current. Even if the number of parallel thyristors required by each rectifier arm of 175v / 100kA DC power supply is reduced to 6 through the above main circuit topology, there is still a serious current sharing problem. In the rectifier arm with multiple devices in parallel, if the current sharing coefficient is too low, some devices will not be connected and some devices will be overcurrent. In severe cases, the device will be burned out, resulting in overcurrent of other branches in the rectifier arm, resulting in damage to the whole rectifier arm device. In order to solve this problem, the following measures to optimize the current sharing coefficient are proposed.

Ferrosilicon furnace's appropriate rectifier arm structure shall be adopted

After the general power electronic devices of submerged arc furnace enter the steady-state forward conduction, the on state voltage drop is very low and the corresponding on state resistance is very small. If the configuration of parallel branch bus is unreasonable, the difference of circuit self inductance and mutual inductance will cause the imbalance of current distribution. Therefore, in the case of large working current, due to the influence of branch magnetic field and impedance difference, when the devices at different positions are turned on, the current value flowing is different, which is related to the position of outgoing bus. At present, the bar rectifier arm structure of bus up in and down out (or down in and up out) is the mainstream, but experiments show that this structure has low current sharing coefficient when the number of parallel devices is greater than 4.

In order to obtain better current sharing effect, the rectifier arm is changed to other structures, so that the path of each thyristor in the rectifier arm from AC incoming line to DC output is exactly the same, and the current flowing through each thyristor is decoupled from each other, which can solve the problem of uneven current distribution of each branch caused by the difference between the impedance and magnetic field of each parallel branch caused by the different path from each component to the positive and negative bus. The rectifier arm structure can significantly improve the current sharing effect of each rectifier arm compared with the commonly used straight bar structure, and can achieve theoretical Current sharing.