Multilevel Inverter Using MATLAB

 

MULTI-LEVEL INVERTER

To design and carry Harmonic Analysis of Different Multilevel Inverters.

Software Used: MATLAB R 2018a

Theory:

A multilevel the inverter is a power electronic device which is capable of providing desired alternating voltage level at the output using multiple lower-level DC voltages as input. Mostly a two-level inverter is used in order to generate the AC voltage from DC voltage.

Now a day’s many industrial applications have begun to require high power. Some appliances in the industries, however, require medium or low power for their operation. Using a high-power source for all industrial loads may prove beneficial to some motors requiring high power, while it may damage the other loads. Some medium voltage motor drives and utility applications require medium voltage. The multi-level inverter has been introduced since 1975 as an alternative in high power and medium voltage situations. The Multilevel inverter is like an inverter and it is used for industrial applications as an alternative in high power and medium voltage situations.

The need for the multilevel converter is to give high output power from the medium voltage source. Sources like batteries, supercapacitors, the solar panel are medium voltage sources. The multi-level inverter consists of several switches. In the multi-level inverter, the arrangement switches’ angles are very important.

There are different Types of Multilevel Inverter as shown by the below diagram:

1. Neutral Point Clamped Inverter:

Theory:

The main concept of this inverter is to use diodes and provides the multiple voltage levels through the different phases to the capacitor banks which are in series. A diode transfers a limited amount of voltage, thereby reducing the stress on other electrical devices. The maximum output voltage is half of the input DC voltage. It is the main drawback of the diode clamped multilevel inverter. This problem can be solved by increasing the switches, diodes, capacitors. Due to the capacitor balancing issues, these are limited to the three levels. This type of inverters provides high efficiency because of the fundamental frequency used for all the switching devices and it is a simple method of the back to back power transfer systems.

5 level Diode Clamped (m=5)

IGBT = 2(m)-2

Diode = 2(m)-4

Capacitor = m-1

 

α_i = i*180/m, i=1,2,3……. ((m-1)/2)

α₁=36^o, α₂=72^O, α₃= 108^O, α₄=144^O, α₅=216^O, α₆=252^O, α₇=288^O, α₈=324^O, α₉= 360^O

Components Used:

S. No	Components	Quantity
1.	Dc Source	1
2.	Capacitors	4
3.	IGBT	8
4.	Diodes	6
5.	Load (Resistor)	20Ω

Applications of Diode Clamped Multilevel Inverter:

·        Static var compensation

·        Variable speed motor drives

·        High voltage system interconnections

·        High voltage DC and AC transmission lines

Logic for Output Waveform:

Voltage Level (In Volts)	0	Vdc/4	Vdc/2	Vdc/4	0	-Vdc/4	-Vdc/2	-Vdc/4	0
Time	0.002	0.004	0.006	0.008	0.012	0.014	0.016	0.018	0.02
Angle	36O	72O	108O	144O	216O	252O	288O	324O	360O
T1
T2
T3
T4
T5
T6
T7
T8

Waveform:

FFT Analysis

Conclusion:

1.    As we have made the 5 level Inverter so the 5^th Harmonic has been removed as we can see In FFT Analysis also.

2.    Waveform is approaching to sine as we Increase the level.

2. Capacitor Clamped: 3 level Capacitor Clamped (m=3)

The main concept of this inverter is to use capacitors. It is of a series connection of capacitor clamped switching cells. The capacitors transfer the limited amount of voltage to electrical devices. In this inverter switching states are like in the diode clamped inverter. Clamping diodes are not required in this type of multilevel inverters. The output is half of the input DC voltage. It is a drawback of the flying capacitors multilevel inverter. It also has the switching redundancy within the phase to balance the flying capacitors. It can control both the active and reactive power flow. But due to the high-frequency switching, switching losses will take place.

The parameter employed in these simulation tests were: Vdc=200V, R=5ohms and L=5mH, and switching frequency equal to 500 Hz.

3. H Bridge Inverter:

The combination of capacitors and switches pair is called an H-bridge and gives the separate input DC voltage for each H-bridge. It consists of H-bridge cells and each cell can provide the three different voltages like zero, positive DC, and negative DC voltages.

H bridge Inverter Parameters Used:

Vdc=200V, R=5 Ohms, L=5mH, and switching frequency=1000Hz

 

 

4. Cascaded H Bridge:

The cascaded H-bride multilevel inverter is to use capacitors and switches and requires a smaller number of components in each level. This topology consists of a series of power conversion cells and power can be easily scaled. The combination of capacitors and switches pair is called an H-bridge and gives the separate input DC voltage for each H-bridge. It consists of H-bridge cells and each cell can provide the three different voltages like zero, positive DC, and negative DC voltages. One of the advantages of this type of multi-level inverter is that it needs a smaller number of components compared with diode clamped and flying capacitor inverters. The price and weight of the inverter are less than those of the two inverters. Soft-switching is possible by some of the new switching methods.

Multilevel cascade inverters are used to eliminate the bulky transformer required in case of conventional multi-phase inverters, clamping diodes required in case of diode clamped inverters and flying capacitors required in case of flying capacitor inverters. But these require a large number of isolated voltages to supply each cell.