Integration of Large Photovoltaic and Wind System by Means of Smart Transformer

Abstract

Large renewable energy systems (RESs), e.g., photovoltaic (PV) and wind turbine (WT) are connected to grid usually weak, with long lines. This degrades power system stability and reliability. Additionally, the magnetic characteristic of conventional power transformer (CPT) implies a slow dynamic and leads to grid current harmonic too high when wind speed is low and irradiance is weak. This paper proposes a parallel connection of a solid-state transformer-based smart transformer and CPT to not only reduce the power rating but also to support the voltage amplitude and improve the grid current quality.

Existing System

Voltage Ride Through Method.

Proposed System

Large photovoltaic and wind systems are connected in rural areas where the grid is weak with long lines. It leads to low grid reliability and stability. Additionally, electromagnetic characteristic of the step-up isolation transformer can significantly degrade the grid power quality in both transient and steady state conditions. The proposed parallel connection of ST and CPT can effectively increase reactive current injection capability and be more effective in supporting MV grid voltage, with respect to a STATCOM of comparable size. The proposed strategy can improve grid current quality during steady state and grid fault conditions. In addition, the parallel structure can significantly reduce the ST power rating requirement.

Architecture

Classic Configuration

ST parallelized with conventional transformer