Unified Damping Assignment Passivity based Controller for Power Conversion Units of Solar Power Plants

In this paper, a unified damping assignment passivity based control scheme (UDA-PBC) is proposed for PV-plants (PV-P) in the form of power conversion unit (PCU) connected to distribution power grids (DPGs). The PCU includes a super-capacitor unit (SCU), bidirectional buck/boost converter interfacing SCU to DC-link capacitor, and grid-side voltage-source converter (VSC) operating in cooperation with SCU. According to the maximum power point tracking (MPPT) algorithm, the boost converter extracts maximum active power from PV-P and feeds the power to the PCU. Then, the PCU using the unified operation of SCU and VSC based on the proposed control scheme damps possible DC-side and AC-side power oscillations and delivers the power smoothly to the DPG. To this end, the model of output filter associated to VSC in synchronous reference frame (SRF), DC-link capacitor, SCU are modeled as a 5-order nonlinear state space equation and represented in the port controlled Hamiltonian (PCH) form. Then, the unified nonlinear control of PCU is designed with the utilization of DA-PBC idea applied to the developed model. In addition to mathematical stability proofs, the effectiveness of the proposed strategy is verified based on a set of time-domain simulations and comparisons with conventional methods.