Mathematical approach to THD optimisation in multilevel convertors

Abstract

The paper is related to the problem of generating the high quality AC voltage waveforms using multilevel converters. This technique can be applied especially in the distributed power energy systems with renewable DC voltage sources like photovoltaic farms and fuel cells. A novel approach to the synthesis of AC voltage waveforms, considering minimising of THD by use of analytical methods like Fourier transform is presented. The analysis of the obtained waveforms is presented as well as examples of chosen parameter optimisation. The meaning of the THD factor from the construction point of view is analysed and a new bandwidth factor THD B , containing more information about the frequency range of harmonic components is proposed in the paper.

Cascaded Multilevel Converter as a Voltage Compensator

“…The cascade inverter allows for the generation of stepped output voltage [9,10]. If the PWM method is not applied the instantaneous value of the output voltage is = ( ).…”

“…The final stepped voltage waveform depends on the ratio of voltages U5/ U4. The authors of work [9,10], analysing the symmetrical three-phase cascade inverter (with equal voltage sharing in DC link circuits and without auxiliary DC converters as in the presented construction), pointed out the possibility of lowering the carrier frequency in proportion to the number of component inverters by using an unipolar sine-wave PWM modulation with a phase shift. An example of the voltage stepped waveforms in case the ratio U5/ U4 is ½ is presented in Fig.…”

A Case Study on High Power Compensator of the Power Grid Irregularities for Industrial Appliances

“…The main difference between the wavelet transform described in [8] and DFT is that the first one operates in the time domain while the FFT in the frequency domain and uses variable window sizes to capture voltage changes. But practical implementation to the detection process is still difficult [11].…”

A Novel Approach to GSA, GA and Wavelet Transform to Design Fuzzy Logic Controller for 1ϕ Multilevel Inverter

“…Wavelet Transform is based on these small wavelets and allows to analyze the signals in different time scale, with different resolutions [20], [21]. It provides both time and frequency analysis of signal simultaneously.…”

“…Over a period of time, GSA has undergone major changes in the basic algorithm and has been adapted for specific applications in varied fields of science [18]- [19]. Another approach used in this paper for harmonic reduction is Waveform synthesis, which is based on wavelets transform, it is a useful mathematical tool for designing multilevel inverter structures and control strategies, features of wavelets such as dilation and translation allow them to be used not only for analysis of processes consisting in decomposition but also in composition of signals and structures in power electronics [20]- [21].…”