Three-level Inverter Controlled by means of Vector Hysteresis Current Control. Application to Back to Back Structure

The studied application is a back to back power electronic structure feeding a three-phase load. The line side converter is a two-level PWM rectifier controlled by a current hysteresis controller in the abc reference frame. It regulates the dc voltage and enables a unit power factor. The load side converter is a three-level voltage source inverter (VSI), which is controlled by means of a novel vector hysteresis current control (V.H.C.C). The proposed V.H.C.C, which is based on error square areas, controls the three-phase load AC currents. In addition, it regulates the neutral point voltage using the redundant inverter switching states. The three load current errors are gathered into a single space vector quantity. In this case, the magnitude of the error vector is limited within boundary areas of a square shape. The control scheme is based on the detection of areas and sectors, in which the vector tip of the current error can be located. Then it applies an appropriate voltage vector among the 27 voltage vectors. Simple look-up tables are required for the detection of areas and sectors, and also for the vector selection. The proposed V.H.C.C can be extended to further multilevel inverters.