Two-stage Input-Output Feedback linearization controller for AC-AC converter-based SST

Abstract

Classical transformers are the most important constituent of the power system and act as a passive interface between high voltage and low voltage systems. They have undesirable characteristics such as poor voltage regulation, large size/weight, sensitivity to harmonics, and poor power flow control. Solid-state Transformers (SSTs), are an emerging power electronics-based technology, sought to replace classical transformers after a century. SSTs are equivalent to a classical transformer with embedded desired functionalities. In this paper, three-phase AC-AC converter with capacitor at the DC-link is employed as power electronic interface in MV and LV side of the SST. Input-output feedback linearization (IOFL) controller is used to control the AC-AC based SST in two stages for controlling the external and internal states. AC-AC SST is linearized by the input-output feedback linearization technique where an internal dynamics is observed. IOFL is used to control the internal dynamics and second stage of the controller in the outer loop. Simulation studies are realized to confirm the applicability of IOFL controller and the control method.

Decoupling Control of Cascaded Power Electronic Transformer Based on Feedback Exact Linearization

“…It has been widely applied in DC-DC converters [22], three-phase PWM rectifiers [23,24], active power filters [25], maximum power point tracking of photovoltaic systems [26]. Reference [27] proposed a FEL based nonlinear control for a modular multilevel converter (MMC); Reference [28] presented an application of the FEL technique on the stationary-frame PR grid current control for a CHB rectifier; while References [29] utilize the feedback linearization method for a two-level VSC based AC-AC SST to achieve global asymptotic stability. Both the topologies and control objectives of these references are different compared with the cascaded PET, thus the nonlinear state function models and design process of feedback linearization are different from that of this paper.…”

“…According to (29), one can see that the phase shift function of DAB, Mi, does not contain the ripple voltage term dc v , which means the second-order ripples will not be transferred to the DAB stage by the nonlinear control. However, from (28), as the ripple voltage is contained in the d-axis current reference idref, it will cause odd harmonics of the grid current.…”