08-10-2012, 01:29 PM
A Bridged New Five-Level Inverter for DC–AC Conversion With Reduced Harmonics
A Bridged New Five-Level Inverter.ppt (Size: 224.5 KB / Downloads: 77)
ABSTRACT
Multilevel converters offer high power capability, Associated with lower output harmonics and lower commutation losses.
The new topology produces a significant reduction in the number of power devices and capacitors required to implement a multilevel output. The new topology is used in the design of a five-level inverter.
The new topology achieves a 37.5% reduction in the number of main power switches required.
Additionally, the dedicated modulator circuit required for multilevel inverter operation is implemented using a FPGA circuit, reducing overall system cost and complexity.
INTRODUCTION
The different topologies presented in the literature as multilevel converters it reduce the commutation frequency applied to the power components, reduction in the voltages applied to the main power switches, enabling operation at higher load voltages and transient voltages automatically limited.
The main disadvantage associated with the multilevel configurations is their circuit complexity, requiring a high number of power switches and they also require a great number of auxiliary dc levels.
As a contribution to solve these twin problems, this work proposes a new converter topology, presented as a block diagram in Fig. 1.
PROPOSED INVERTER CIRCUIT
Single-phase five level H-bridge is formed by the four main power devices, Disp1 to Disp4.
A capacitor voltage divider, formed by C1 and
C2 provides a half supply voltage point, node An The auxiliary switch, formed by the controlled switch Disp5 and the four diodes, D5 to D8, connects
The center point of the left hand half-bridge to node A.
The new topology achieves a 37.5% reduction in the number of main power switches required.
The auxiliary switch voltage and current ratings are lower than the ones required by the main controlled switches.
The new configuration reduces the number of diodes by 60% and the number of capacitors by 50% when compared with the diode clamped configuration.
ANALYSIS OF TOTAL HARMONIC DISTORTION:
The graph gives the variation of Modulation index, Ma with Amplitude of total Harmonic Distortion. From the graph it is clear that the THD of the proposed inverter has lower values than those of conventional inverter.
With the growth of modulation index Ma≤1.0 in the linear region, THD of the proposed inverter will slightly increase. This is because that the larger the value of Ma being increased, the smaller the regions of half level of dc bus voltage are reduced.
ADVANTAGES OF MULTILEVEL INVERTER
The voltage capacity of the existing devices can be increased many times without the complications of static and dynamic voltage sharing that occur in series-connected devices.
Spectral performance of multilevel waveforms is superior to that of their two- level counterparts.
Multilevel waveforms naturally limit the problems of large voltage transients that occur due to the reflections on cables, which can damage the motor windings and cause other problems.
CONCLUSION
Multilevel inverters have become an effective and practical solution for increasing power and reducing harmonics of ac waveforms.
Its operated at very high modulation frequencies, producing a very clean output.
This configuration reduced circuit complexity will be adequate for low-medium power applications.
The modulator circuit implemented using a FGPA IC is able to generate all the control signals required to operate the five-level converter, controlling both the commutation sequences and the output amplitude by pulse width modulation.
The combined use of these two technologies may lead to the design of multilevel converters at a cost competitive with that of standard two-level converters.