Improving the Dynamic Response of PI Voltage Modulated-Direct Power Controlled Grid-tied VSIs

The alternative method of the voltage modulated-direct power control (VM-DPC) approach, is used as the basis for a novel controller design that effectively achieves accurate power regulation of grid-tied voltage source inverters (VSI). The proposed control schemes realize PI-type active and reactive power regulators which are substantially stabilized by introducing suitable damping terms in their structure. To avoid steady state errors, an appropriate adaptation mechanism is proposed which eliminates the damping terms in steady-state, while simultaneously it enables them to act exclusively during transient periods. Contrary to the conventional approach, the whole design does not require the use of a fast phase locked loop (PLL) mechanism and does not depend on any system parameters, since it does not include the commonly employed feed-forward decoupling terms in its structure and hence it displays significant robustness properties. These properties are also enhanced particularly against dc voltage variations since a division by the dc voltage state is not further needed. The theoretical analysis of the resulting closed-loop system is performed on the full nonlinear model. Stability properties are extracted by exploiting some critical structure characteristics, whereas suitable nonlinear analysis tools are used to establish stability and convergence properties under some mild conditions. Finally, the theoretical results that guarantee enhanced dynamic behavior of the system are validated by conducting a detailed simulation procedure.