SWITCHING LOOKUP TABLE-BASED DIRECT POWER CONTROL OF AC/DC CONVERTERS

Abstract

Traditional diode and thyristor-based line-commutated rectifiers in the grid connected power systems are causing several problems in transmission and distribution systems due to excessive current harmonics and reactive currents injected back into the grid. As a result, line commutated DBRs are being substituted with three-phase PWM VSCs in utility-based applications. The term pulse width modulated voltage source converter (PWM-VSC), which is used in this dissertation, is also known as an AC-DC converter. In the case of an islanded grid structure, which is usually a weak grid that has less inertia compared to a stiff grid. To, operate a multifunctional PWM converter which can replace the passive filters, provide reactive support to the grid etc in such weak grid system where the PCC is not usually at UPF, there is a need to analyse for operating conditions other than UPF. The primary goal of power conversion control in a power electronic system is to develop control techniques with maximum hardware utilization and better power quality. To achieve better power quality, minimisation of harmonic distortions and switching losses is necessary. The Direct Power Control (DPC) is one of the well-known methods in the case of AFE-VSCs, which originates from direct torque control (DTC) of AC machines. Switching lookup table is the vital component of this control technique. Hence, it is extremely important for in depth investigations, analysis of LUTs for better DPC performance. In this report first, existing VOC and DPC schemes are described based on the literature review with more focus on DPC methods. Later, mathematical or power model of 2L-VSC is examined. And finally, three phase 2L-VSC model is created using MATLAB-Simulink and performance study of several switching tables in the existing literature has been done at different power factor conditions. For hardware results and testing dSPACE1104 controller was used and dSPACE ControlDesk software was used for visualization of the results.