# Research on the High Reliable Electromagnetic Stirring Power Supply
## 1 Introduction  
Currently, electromagnetic stirring continuous casting technology has become the most popular and main steelmaking technology. Electromagnetic stirring can make the continuous steel casting process more stable, reduce the rate of breakout, and increase the casting speed of the slab. At the same time, it can improve the quality of the product while increasing the output [1, 2, 3, 4, 5]. The power supply is the key equipment of electromagnetic stirring, and its current waveform quality and response speed directly affect the quality of continuously cast steel [6, 7]. The electromagnetic stirring power supply belongs to the special industrial frequency conversion power supply. At present, the domestic research on electromagnetic stirring for continuous casting mainly concentrates on the stirring form and parameter optimization, but little on the power source. Most of them are modified inverters, lacking a mature power supply. In order to make the stirring uniform and not too violent, the electromagnetic stirring power supply needs to work at a low frequency to obtain a greater penetration depth, stirring force, and higher power factor. Thus, the low-voltage variable frequency power supply is an indispensable and important part of the entire electromagnetic stirring system. It can convert the power frequency of the power grid into alternating current with adjustable frequency to supply power for the electromagnetic stirrer, thereby improving the quality of the cast slab. The stirring force of the electromagnetic stirrer is related to the current of the power supply, and the power supply of the electromagnetic stirrer is required to provide a current with adjustable amplitude, variable frequency, and changeable phase. The electromagnetic stirring power supply for steel continuous casting generally adopts a two-phase quadrature inverter power supply, which outputs two-phase quadrature current to supply for the induction coil, which stimulates the formation of electromagnetic thrust, thereby causing the molten steel to rotate [6; 7; 8]. In the traditional topological structure of the two-phase inverter power supply, the front and rear two-stage structure of the front-stage rectifier, the back-stage inverter is generally adopted. The front stage adopts the uncontrollable rectification method to convert the three-phase alternating current into a stable direct current power source, which seriously pollutes the power grid with a low power factor and a high harmonic content. For the topology of the rear-stage two-phase quadrature inverter, the literatures [9; 10] adopt the structure of two single-phase inverters, and each inverter is connected to a phase electromagnetic stirring roller. This kind of structure has the characteristics of simple control and high DC voltage utilization rate, but it needs 8 Insulated Gate Bipolar Transistors (IGBTs) and the number of components is large. Moreover, there is a certain power loss and high cost. In order to reduce the use of IGBTs and reduce power loss, studies have [11] proposed the use of four power switches to form two bridge arms, each of which forms a half-bridge inverter with a DC side capacitor to form a two-phase quadrature inverter to obtain two-phase quadrature output current. Although the number of components of this structure is reduced, its DC voltage utilization rate is still very low, and the two capacitors on the DC side need to be balanced. In order to bridge the shortcomings, previous studies [12; 13; 14] have used the six power switches to form three bridge arms, of which two switch arms are independent, and the third switch arm became a common arm. Thus, a two-phase quadrature inverter is formed and the two-phase quadrature output current can be obtained by adopting a suitable control method.