Tuning of Weighing Factors by Direct Pole-Placement for Model Predictive Current Controlled Grid-Tied Converters with an LCL Filter

Abstract

The inductive-capacitive-inductive (LCL) filter is a popular choice for harmonic attenuation in voltage source converters (VSCs) in kW range systems. The filter provides a high damping attenuation of −60 dB/decade above the resonance frequency at the cost of a higher order plant, complex parameter design, and, increased vulnerability to un-modeled disturbances. The model predictive control (MPC) technique is well suited for regulation of LCL connected converters, as several state-variables need to be simultaneously regulated to maintain stability. However, the tuning of weighting factors (WFs) within the cost function is not trivial, and in most cases employs a trial-and-error procedure. This paper presents an analytical procedure for tuning of weighting factors for fixed switching frequency model predictive current controlled VSCs. The method is based on deriving closed-form expressions of WFs in terms of closed-loop poles and system parameters. This approach, thus, removes the ambiguous trial and error procedure associated with the tuning of WFs and provides accurate closed-loop response based on desired control requirements. The presented method is verified through hardware-in-the-loop (HIL) simulations by deploying the controller on a TMS320F28379D DSP.