Typical System Operation
A chopper rectifier system is composed of a step-down power transformer, a bulk dc unregulated diode rectifier, and either a single or multiple chopper circuit(s). With the use of 12-pulse rectification, power factors above 0.92 are achieved without the use of transformer tap changers. Low harmonics that meet the requirements of IEEE 519 [2] can be realized without the use of line filters by selecting a rectifier pulse number compatible with the power system. To produce a 12-pulse chopper rectifier system with the proper voltage, a step-down transformer, typically with a delta primary and wye and delta secondaries, is required. Two diode rectifiers are then utilized to produce two independent bulk dc buses. The two bulk dc buses are fed to chopper sections that are used to draw equal power from each bulk dc bus. The output of each section within the chopper supply is then paralleled at its output or at the load. A chopper section may be composed of multiple paralleled chopper modules to achieve the output current required and also to provide N-1 operation or dynamic derating for greater system reliability. Each chopper section also typically includes a dc-charging circuit. The charging circuit precharges the chopper module input filter capacitors, thereby minimizing inrush currents when the bulk dc bus is energized.