In recent years, multilevel inverters have grown in popularity in medium and high power applications. There are several advantages of multilevel inverters over two-level inverters, such as higher quality output, lower device rating, etc. In this article, we will learn what are the advantages and disadvantages of multilevel inverter.
What are multilevel inverters?
A multilevel inverter is a power electronic circuit that utilizes a combination of multiple DC sources and a number of low-rated power semiconductor switches to synthesize a stepped voltage waveform for achieving higher power levels. For the purpose of multiple input DC sources, a variety of energy sources including batteries, capacitors, fuel cells, and solar PV panels may be utilized.
Problems associated with two level inverters
In the case of medium and high power level applications, two-level square wave and PWM inverters have the following drawbacks.
1. To achieve the necessary voltage or current, they require devices with high power ratings, which are often not available, and therefore many devices must be connected in series or parallel to achieve the needed voltage or current.
2. A further issue with these inverters is the poor power quality output and the need for filtering before the load is applied. Hence the size and cost of the filter increase.
These issues are solved with the use of multilevel inverters.
Advantages and Disadvantages of Multilevel Inverter
Advantages of multilevel inverter
Multilevel inverters have the following advantages over two-level inverters
1. Voltage derivatives (dv/dt) on semiconductor switches have been reduced as a result of dividing voltage stresses across switches at different levels.
2. Due to the multiple level output waveform, the power quality is improved (low THD output).
3. In solar PV and electric drive applications, it is possible to avoid or lower common-mode voltages by utilizing appropriate switching methods.
4. It can operate with low or fundamental switching frequency. High levels of efficiency are achieved through switching at the fundamental frequency, which reduces switching and conduction losses.
5. It has the ability to operate without transformers.
6. A fault-tolerant operation is possible using redundant switching states and suitable control schemes.
7. It is common for multilevel inverters to have a modular structure. Due to its modularity, the system offers greater voltage and current capabilities.
8. Electromagnetic interference is reduced as a result of a reduction in dv/dt.
9. There is very little distortion in the input current.
Disadvantages of multilevel inverter
Multilevel inverters have the following disadvantages
1. There has been a significant increase in the number of switching devices. This increases the complexity and cost of the circuit. There have also been instances where reliability has been affected.
2. Due to the many switches in multilevel inverters, multiple gate pulses must be generated, which again requires the use of advanced PWM-based digital signal processors.
3. There are some multilevel inverter topologies that require more than one isolated DC supply. This is a significant issue because the cost of the system increases. The unavailability of DC supply is also a concern.
4. Multi-winding transformers are often required in order to make multiple DC sources. Therefore, the system becomes even more expensive.
Despite these disadvantages, multilevel inverters are very advantageous due to their high efficiency, low filter requirements, and ease of implementation with low-rating switching devices. There are no other alternatives to multilevel inverters if that is your requirement.