Elimination of the Voltage Oscillation Influence in the 3-Level VSI Drive Using Sliding Mode Control Technique

Today the three-level voltage-source inverters (3LVSI) are active used in the AC drive thanks to their merits as output signal quality improvements and a lower common mode voltage for semiconductor switches. However, their increased control complexity is the main barrier on the way to their extensive use. The cause is from one side a nonlinear feature of control plant that is a series coupling of two non-linear objects: a switched converter and ACmotor, and from another one a big set of 3LVSI output voltages. The sliding mode control (SMC) is one of the possible control solutions that gives the possibilities to design AC drive with the high dynamic feature in combination with robustness against disturbances and plant parameter variations. SMC does feasible overcoming one of the main problems of 3LVSI, namely the lower-frequency voltage oscillations that appear in the input DC-line voltage after the rectification of the industrial three-phase voltage and in the neutral point under some operating conditions. SMC based on the two-step control design procedure that takes into account the operation features of 3LVSI is designed. The original control algorithm includes a choice condition for 3LVSI input DC-line voltage and a switch table for the 3LVSI semiconductor switches. In its frame a choice condition for the input DC-line voltage based on the boundary conditions of both voltage oscillations is obtained. The performance of the considered control structure has been examined by simulation.