In the last article, multilevel inverters topologies have been well discussed. Now that you know them, their design and their applications, let’s see what Nasir has to say about some of the most important ones.
One of the basic and well-known topologies among all multilevel inverters is Cascaded H-Bridge Multilevel Inverter. It can be used for both single and three phase conversion. It uses H-Bridge including switches and diodes.
At least three voltage levels are required for a multilevel inverter. This can be accomplished by a single H-Bridge unit in Cascaded H-Bridge Multilevel Inverter. To keep the discussion snappy and clear I will go with the major points of this topology and also its advantages and disadvantages compared to other topologies.
Features of Cascaded H-Bridge Multilevel Inverter
- Each H-Bridge Cell consists of four switches and four diodes as shown in the picture.
- Like every H-Bridge, different combinations of switch positions determine different voltages such as V+, V- and 0.
- Two switching combinations are present for 0 volts.
- S1 and S2 are connected to positive voltage and S3 and S4 are connected to negative voltage.
Single Phase Multilevel Inverter
- The number of output levels from a multilevel inverter depends upon the number of separate DC sources attached to it.
- The relation is m=2s+1
- All the outputs from H-Bridges should be quarter symmetric to generate a sin like wave.
- No even harmonics are present.
Three-Phase Multilevel Inverter
- Three-phase Multilevel Inverter is simply like three single phase inverters connected in wye configuration. Three H-Bridges are connected together.
- Delta configuration can also be used.
- Maximum number of line voltages is 2m+1 where m=no. of phase voltages.
- Triple harmonics are eliminated themselves.
Real Time Switching
In ideal cases the switching time is considered zero and the switching devices turn on and off as soon as you command. But in real time application, switching time is an important phenomenon. To avoid this Blanking time is introduced. The switch turns off just immediately, but the other switch turns on after a certain delay.
Separate DC Source
One of the major issues with Cascaded H-Bridge Multilevel Inverters is that we need separate DC sources with each leg. Well it might look that separate DC source will create a mess or increase the components, but it is fairly necessary. Because same DC sources can give multiple configurations that result in short circuit.
However this issue has also been resolved. Now lesser number of DC sources can be used and SDC topology has also been proposed.
Advantages of Cascaded H-Bridge Multilevel Inverter
As the name suggests this multilevel inverter uses full H-Bridges connected is series to produce inverted AC from separate DC sources. These DC sources can be any natural resource such as sunlight or wind energy or anything.
- It does not need any capacitors or diodes for clamping.
- The wave is quite sinusoidal in nature even if you don’t filter it.
This was all about cascaded H-Bridge multi -level inverters. Due to their advantages they are often used now-a-days. More of the inverters types are still there which are extensively used and will be discussed in the upcoming tutorials. So keep visiting to know more about them and their uses and advantages as well.