A compensation method for averaged models of PWM converters in large-time-step simulations

The control systems, devices and phenomena are modelled in Transient Analysis of Control Systems (TACS), while the transient phenomena of the electric power systems are simulated in Electromagnetic Transients Program (EMTP). However, TACS and EMTP are solved separately with one-time-step error at the interface. This provides an efficient time-step solution, but numerical stability and accuracy problems associated with the one-time-step error may occur. In this paper, the accuracy of the averaged model (AVM) of pulse width modulation (PWM) converters in transient simulations with large time steps is analyzed. The control system of AVM is implemented in TACS, the electronic circuits of converters are modeled in EMTP. A proportional-derivative (PD) controller is used to compensate the time delay between TACS and EMTP. Large-time-step simulations are so supported, and the accuracy of AVM is improved with large-time-steps. Test cases including a two-level three-phase ac-dc converter are simulated to demonstrate the efficiency and accuracy of the proposed method.