Advantages Of Multilevel Inverter

Abstract

The use of multilevel inverters is increasing in the field of renewable energy, FACTS devices and machine drive

applications. The multilevel inverters have many advantages than two level inverters. The power rating of the switches,

the total harmonic distortion, electromagnetic interference and switching losses are less in a multilevel inverter than a

two level inverter. The main disadvantage of the multilevel inverter is that it requires more number of control switches

and so the control of the switches becomes complex. This inturn reflects on the cost of the inverter. This paper

describes a topology to reduce the complexity of the control of a multilevel inverter and to reduce the overall cost of

the inverter. The complexity

The smaller common mode voltage can furthur be reduced by using advantage

modulation strategies such as that proposed in [14]. Input current drawn will of low distortion. The switching

losses in multilevel inverters are due to low switching frequency.

There are basically three types of multilevel inverters. They are diode clamped multilevel inverter or

neutral clamped multilevel inverter, flying capacitor or capacitor clamped multilevel inverter and cascaded

H-bridge multilevel inverter with seperate dc sources [15]. Neutral point converter was proposed by Nabae,

Takahashi, and Akagi in 1981. The proposed topology was a three level diode clamped inverter [5]. In the

1990s, seeral researchers published articles that have reported esperimental results for four-,five- and sex- level diode-clamped converters for uses such as static var compensation, variable speed motor drives, and

high voltage system interconnections [16–29]. The disadvantages of these converters are, the real power

flow is difficult for a single inverter because the ntermediate dc levels will tend to overcharge or discharge

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without precise monitoring and control. The numbers of clamping diodes required is quadratically

Flying-Capacitor

Multilevel inverter was first introduced by a flying-capacitor-based inverter in 1992 [30]. This is similar to a

diode clamped inverter except this uses capacitors instead of clamping diodes. The major advantage of flying

capacitor inverter is that it has phase redundancies which will allow the choice of charging and discharging

specific capacitors and can be incorporated in the control system for balancing the voltage across the various

levels [2] [3] [31]. The disadvantages of the topology are the control is complicated to track the voltage

levels for all of the capacitors. Precharging all the capacitors to the same voltage level and start-up are

complex. Switching ultilization and efficiency are poor for real power transmission. The large number of

capacitors are expensive as well as bulky than clamping diodes.Packing is also more difficult in inverters

with a high number of levels. Cascaded h-bridge inverters employes h-bridge circuits connected in series

to generate required level generations. They are employed for applications such as static var