A Sliding Mode approach into Constant Switching Frequency Direct Power Control of a Grid Connected Voltage Source Converter

This paper presents a control method which combines sliding mode approach of direct power control and operates with constant switching frequency. This novel scheme Sliding Mode Constant Switching Frequency Direct Power Control (SM-CSF-DPC) employs a nonlinear sliding mode control (SMC) approach to directly calculate the required converter’s control voltage. The constant switching frequency (CSF) is achieved by using space vector modulation (SVM). In this novel scheme, the extra current control loops are eliminated, which simplifies the system design and enhances the transient performance. The improved strategy is tested on a simulation model of a two level VSC and compared with the conventional switching table direct power control (ST-DPC) strategy. The proposed SM-CSF-DPC methods have very good results both in steady-state and transients. It is shown that the proposed DPC exhibits several features, such as a simple algorithm, constant switching frequency, robust to power step change, step change of referenced DC voltage and is capable of providing enhanced transient performance in case of line voltage sags.