Single phase precharge control method for active front end rectifier

Active front end rectifiers (AFE) are widely used in various industrial area applications. In these types of systems, AC pre-charge circuit, output LCL filter and power module switches are the three most critical power segments. AC pre-charge circuit design is often related to an overall high component volume and cost. Many manufacturers adopt mechanical contactors or breakers between the utility connection point and the rectifier in order to ensure a smooth pre-charge of the DC bus capacitors. Since these mechanical components are typically associated with lower reliability and increased size, the power density and lifetime of the whole system gets affected significantly. This paper proposes a simple solid state pre-charge circuit for AFE rectifiers. Solid state pre-charge circuit offers a fairly simple control while reducing the inrush current for both LCL filter and DC bus capacitors. This method also demonstrates the following advantages: 1) increased lifetime, 2) smaller foot print 3) lower cost. Basic operating theory and circuit analysis along with simulation and experimental results are presented in the paper to demonstrate the effectiveness of the proposed method.