A novel modeling and control method for three-phase PWM converters

The pulse-width modulated (PWM) voltage-source converter (VSC) and current-source converter (CSC) are the building blocks of most of the switch-mode power electronic systems. Irrespective of the converter type, the controller is supposed to fulfill two objectives: (1) real power flow control which leads to the regulation of the DC quantity (DC voltage in VSC and DC current in CSC), and (2) reactive power flow control on the AC-side. The major difficulty in control is caused by the nonlinearities in the converter model. The existing control techniques are based on the design of the PI-controllers without the knowledge of the converter model, linearizing the nonlinear model, or splitting the original system into linear and nonlinear parts and dealing with them separately. In this paper, a power balance equation and nonlinear input transformation are used to derive a linear model from the original nonlinear model. Then, a decoupled state-feedback control method is applied to the new model. The accuracy of the new model and the performance of the applied control method are evaluated using the simulation results obtained from the PSCAD/EMTDC simulation package. It is shown that as a result of using the new model and applying the state-feedback control technique, the dynamics of the system are considerably improved resulting in short response times. It is also shown that the approach taken in modeling and control results in excellent results even at low switching frequencies making the scheme very suitable for high-power applications