Fundamental switched MW‐size multilevel converter for large‐scale solar PV plant

Abstract

The requirement of high power (MW-size) power conditioning unit (PCU) has increased to minimise the plant balance of system cost due to a continuous increase in solar photovoltaic (PV) plant capacity. Traditionally used high-frequency pulse-width modulated two/three-level PCUs have high device switching losses and lower conversion efficiency and are not suitable for high power PCU application as high switching losses lead to high heat generation within the converter, which is very difficult to manage, and lower conversion efficiency leads to less revenue realisation. In the present work, fundamental switching selective harmonic elimination (SHE) modulated 11-level cascaded H-bridge voltage source converter is utilised for high power MW-size PCU application, as it has lower switching losses, higher conversion efficiency, and higher AC/DC voltage ratio. The PV plant configuration for a 40 MW (AC) capacity is developed in the MATLAB/Simulink environment and implemented in real-time simulator OPAL-RT to validate the design and control. Harmonics, steady-state, and dynamic performances are demonstrated at constant and changing solar irradiance levels. The converter conduction and switching losses and conversion efficiency at different loading conditions are presented. The converter control with the capacitor voltage balancing method for fundamental switched SHE is presented in detail.