Optimum harmonic reduction with a wide range of modulation indexes for multilevel converters

Abstract

This paper proposes a novel modulation technique applying in multilevel voltage source converters suitable for high voltage power supplies and flexible ac transmission system (FACTS) devices. The proposed technique can generate output stepped-waveforms with a wide range of modulation indexes and minimized total voltage harmonic distortion. 'The main power devices switch only one time per cycle, suitable for high power applications. For the proposed harmonic reduction technique, the theoretical analysis is presented. By using a systematic method, only the polarities and the number of levels are required to be determined for different modulation levels. Computer simulation results are then provided. To verify the theory and the simulation results, a cascade inverter based hardware prototype including a low cost 8-bit microcontroller and modularized power stage and gate driver circuits, is implemented. Experimental results indicate that the proposed technique is effective for harmonic reduction in multilevel converters, and that both theoretical and simulation results are well validated.

Virtual Group Control Algorithm for Modular Multilevel Converter

“…Therefore, the NLC modulation is used widely in HVDC system because of easier to implement and simple [6]. If the It is important to mention that in DSP(Digital-Signal-Processing) systems, the sampling frequency, , of the reference voltage, , must be considered.…”

“…The AC side dynamics is not affected by subtract the upper and lower arm references according to (4) and (6). As previously described, the and is generated by the current controller and circulating current suppressing controller of the MMC system, respectively.…”

A new approach for selecting the switching states of SVPWM algorithm in multilevel inverter

“…In the SVPWM algorithm, the reference voltage vector is obtained by transforming the output voltages of the three-phase inverter according to Equation (3). If the reference voltage vector U Ã falls in a small triangular region, shown in Figure 4, where u is between 0 and p/3, three adjacent voltage vectors…”

“…All switching states for a (g,h) space vector in sector-I. [3,3,3]). The switching states are used to make a decision of which switch will be on or off in the inverter power circuit.…”

“…The performances of multilevel inverter depend very much on the PWM algorithms. Various multilevel PWM algorithms have been developed and studied [3][4][5][6][7][8][9][10][11][12][13][14]. Among these strategies, there is a general belief that space vector pulse width modulation (SVPWM) is more suitable for digital implementation and switching waveform optimization.…”