Switching angle optimization and fault analysis of a multistring-multilevel inverter for renewable-energy-source applications

In this paper,a multistring-multilevel inverter(M-MLI)for renewable-energy-source applications has been proposed with reduced switch count and harmonics along with single-switch fault analysis for various levels.It requires only‘m+1’power switches for‘m’voltage levels.The proposed work achieves the fine-tuning of switching angles using a metaheuristic technique,i.e.the teaching-learning-based optimization algorithm(TLBOA),to mitigate the total harmonic distortion(THD)of the M-MLI.Furthermore,the proposed TLBOA has been compared with conventional modulation techniques such as equal phase(EP),half-equal phase(HEP),near-level control(NLC)and Newton-Raphson(NR)to verify the effectiveness of TLBOA for various voltage levels in terms of%voltage-THD(%V-THD),computational time and methodology.By fine-tuning the switching angles,the%V-THD is improved significantly when compared with EP,HEP,NLC and NR modulation techniques.For an 11-level single-phase M-MLI,the%V-THD using TLBOA at 0.91 modulation index(MI)is 5.051%.The lower-order harmonics,i.e.5,7,11 and 13,are eliminated to improve the power quality.Furthermore,MLIs are often prone to failure,resulting in waveform distortion.The extreme reduction in power quality impacts the load and significant damage is likely.The location of the open-circuit fault to be identified becomes more tedious under the faulty conditions with increased switch counts and voltage levels since the mathematical modelling fails to address the scenario in less computational time.Hence,the machine-learning approach,i.e.support vector machine(SVM)with Bayesian optimization,has been discussed to locate the faulty switch.Finally,the proposed M-MLI configuration has been modelled,simulated and validated using MATLAB®and Simulink®.The results of the M-MLI configuration have been verified for 7,9 and 11 levels using TLBOA along with fault analysis using the SVM approach.

Reliable Phase Selection Method for Transmission Systems Based on Relative Angles Between Sequence Voltages

Fault currents emanating from inverter-based resources(IBRs)are controlled to follow specific references to support the power grid during faults.However,these fault currents differ from the typical fault currents fed by synchronous generators,resulting in an improper operation of conventional phase selection methods(PSMs).In this paper,the relative angles between sequence voltages measured at the relay location are determined analytically in two stages:(1)a short-circuit analysis is performed at the fault location to determine the relative angles between sequence voltages;and(2)an analysis of the impact of transmission line on the phase difference between the sequence voltages of relay and fault is conducted for different IBR controllers.Consequently,new PSM zones based on relative angles between sequence voltages are devised to facilitate accurate PSM regardless of the fault currents,resistances,or locations of IBR.Comprehensive time-domain simulations confirm the accuracy of the proposed PSM with different fault locations,resistances,types,and currents.