Investigation of Cascaded Multilevel Inverter Based SAF with Alternative Configurations Under Ideal and Nonideal Grid Voltage Conditions

Abstract

Issue of harmonics is a greater apprehension as it severely affects the power quality of the supply and utility. Increased use of nonlinear loads in medium and high power application causes a shocking intensification of harmonic pollution, which results in several negative consequences. As a result, the performance analysis of power conditioning devices has become very crucial in the design and engineering process. Over the years, active power filter (APF) gains much more attention due to its significant harmonics elimination standard in AC power network and provides a wider perspective to researchers and application engineers dealing with power quality issues. Among the various power conditioning devices, shunt active filter (SAF) gains popularity for significant harmonic elimination during extremely non-linear load conditions. The conventional SAF configurations are based on two-level inverters. The power managing ability of these inverters is low, so it is not an appropriate choice for high power application, hence limited to low power applications. However, Multilevel Inverter (MLI) operates in lesser switching frequency and the harmonic elimination capability is quite high compared to these two-level inverters. So MLIs are preferable to operate as a SAF and extend effective performance in high power applications. Among the different topologies of multilevel inverters, cascaded H-bridge multilevel inverter (CHBMLI) have several advantages but its major drawback is handling of separate DC sources for each module. So with more number of individual DC sources, the control complexity with increasing sensors becomes difficult to handle. However, the above-mentioned problems can be effectively eradicated if CHBMLI operates with a single DC source. In the present work, the drawback of conventional CHBMLI is eradicated by introducing a cascaded MLI adopting cascaded transformers which operates with single DC source. The proposed cascaded MLI is investigated under various PWM techniques to show its effectiveness. The purpose of the research is to introduce an alternative approach to limit harmonics by proposing effective method yet developing the appropriate mathematical models and then validating models with the simulations and experiments. So, the ultimate goal is to investigate the performance of the proposed cascaded MLI based shunt active filter and to mitigate the control problems associated with it under ideal and nonideal source voltage condition. During unbalanced and distorted input condition many control technique fails to generate a significant reference current to achieve proper compensation. Since these control techniques are sensitive to frequency deviation and imbalance, significant harmonic elimination cannot be achieved. So in order to deal with these issues, different harmonic extraction control techniques are compared and alternative control techniques are proposed and its performance is also analysed in the present work. The performance of the proposed SAF is investigated using 𝑖𝑑−𝑖𝑞 control technique and a comparative evaluation is carried out by applying carrier based PWM and SVM technique. A comparison is carried out between the previously addressed 𝑖𝑑−𝑖𝑞 control, improved 𝑝−𝑞 control and PHC control technique under balanced, unbalanced and distorted source voltage condition. Further, a real time empirical mode decomposition (RT-EMD) based control technique and a novel spline EMD based control technique is adopted for effective mitigation of system harmonics under ideal and nonideal supply voltage conditions. The significance of the proposed control technique is evaluated in steady state and transient condition with ideal and nonideal source voltage condition. Finally, the proposed hardware setup is also verified under steady-state, transient and load unbalanced conditions under ideal and nonideal input voltage condition adopting different control technique.