Continuous and discrete variable-structure controls for parallel three-phase boost rectifier

We describe three nonlinear control schemes for a parallel three-phase boost rectifier consisting of two modules. The basic idea, however, can be extended to a system with N modules. All of the control schemes are developed in a synchronous frame. Moreover, each of the closed-loop power-converter modules operates asynchronously without any communication with the other module. Based on the dynamical equations of the parallel converter, we find that independent control of both of the modules on the DQ axes is not necessary and possible. Consequently, we develop control schemes that stabilize the dq axes and limit the zero-axis disturbance by preventing the flow of the pure zero-sequence current. One of the control schemes is developed purely in the discrete domain. It combines the space-vector modulation scheme with a variable-structure control, thereby keeping the switching frequency constant and achieving satisfactory dynamic performance. The performances of the other control schemes are also satisfactory.