Download Impact of Switching Harmonics on Capacitor Cells

Impact of Switching Harmonics on Capacitor Cells Balancing in
Phase-Shifted PWM Based Cascaded H-Bridge STATCOM
Abstract
The purpose of this paper is to investigate the impact of switching harmonics on the
instantaneous power distribution in the cells of a cascaded H-Bridge based STATCOM when
using Phase-Shifted PWM. The case of high and low switching frequency for the converter cells
are investigated and the interaction between voltage and current harmonics is analyzed. It is
shown that in both cases, this interaction results in an uneven power distribution among the cells
in the same phase leg, leading to drifting of the dc-capacitor voltages and thereby the need for
proper stabilization control loops. It is also shown that the selected frequency modulation ratio
affects the active power distribution among the cells. In particular, the selection of a non-integer
frequency modulation ratio helps in providing a more uniform power distribution among cells of
the same phase leg, thus contributing to the capacitors balancing.
Existing method:
The existing method describes in the recent years, both manufacturers and researches have paid
high effort to improve the control and the modulation of this converter topology. For the latter,
Phase-Shifted Pulse Width Modulation (PS-PWM) has been extensively investigated in the
literature. However, not sufficient attention has been given to the investigation of the different
harmonic components that are generated when using PS-PWM and their impact on the system
performance, in particular in case of non-ideal conditions of the system.
Proposed method:
The proposed method describes about the investigation of the impact of switching harmonics and
the selection of a non-integer frequency modulation ratio on the voltage capacitor balancing
when using PS-PWM, with focus on CHBSTATCOM applications. Configurations where the
STATCOM is equipped with a low or a high number of cells, leading to the selection of a low or
high switching frequency, respectively, are considered. It is shown that the interaction between
Further Details Contact: A Vinay 9030333433, 08772261612
Email: [email protected] | www.takeoffprojects.com
the carrier side-band harmonics of the cell voltage and the baseband harmonics of the current, as
well as poor cancellation of carrier side-band harmonics due to non-ideal conditions, lead to nonuniform power distribution among cells.
Block diagram:
Fig. 1. CHB converter.
Advantages:
 Output voltages levels are doubled the number of sources
 Manufacturing can be done easily and quickly
 Packaging and Layout is modularized.
Applications
Cascaded H Bridge Multilevel Inverters are mostly used in renewable resources’ of energy and
battery based applications.
Extension:
Here we used conventional PI controller in controlling of the circuit so in place of that we eplace
that one with modern controller of fuzzy logic controller because of the drawbacks of the
conventional PI controller.
Further Details Contact: A Vinay 9030333433, 08772261612
Email: [email protected] | www.takeoffprojects.com
Further Details Contact: A Vinay 9030333433, 08772261612
Email: [email protected] | www.takeoffprojects.com