Z- source based DC-DC converter

Hi folks.

Lets start or MISO systems' discussion with a trending technology - Z source impedance network. This was proposed in 2002 and up till now, it is utilized in almost every possible power conversion circuit. 

We start our discussion with the simplest application i.e. DC-DC converter. Z source based DC-DC converter can reduce in-rush and harmonic current, provide larger range of output dc voltage and improve reliability. It can operate in voltage-fed and current-fed when the place of the source and load is exchanged each other (bidirectional operation), and it can be perform buck-boost function in these two conditions.

The figure shows voltage fed Z source based DC-DC converter.

It has two operating states named shoot through and non shoot through states. 
The Z-network of the Z-source dc-dc converter is  symmetrical, that is, the inductors L1 and L2 and capacitors C1 and C2 have the same inductance (L) and capacitance (C), respectively.

so we have, 

In non shoot through state , the switch S1 (or diode forward biased, you can say) is turned on and S2 turned off. The dc source charges the z-network capacitors, while the inductors discharge and transfer energy to the load. 

                                

The interval of the converter operating in this state is (1-D)T, where D is the duty ratio of switch S2, and T is the switching cycle then one has,

In the shoot through state (remember this name, its very important),  the switch S2 is turned on and S1 turned off (diode reverse biased by capacitor voltage to protect source from short circuiting- very important function of diode) . The z-network capacitors discharge, while the inductors charge and store energy to release and transfer to the load. 

The interval of the converter operating in this state is DT, one has,

Where Vi is the value of the dc voltage source. 

The average voltage of the inductors over one switching period (T) in steady state should be zero. (ref = volt-sec balance theory - inductor and capacitor basics we talked about) 

so we have, 

So, this is how it works. It has large number of applications. A friend of mine used it in MPPT (maximum power point tracking) of solar system. I used quasi Z and Extended quasi Z source for the same application. We both are working on Z source inverter as our project and its not as easy as it seems..! 

In the upcoming session we will talk about MISO systems that I have proposed through my papers. Please feel free to leave a comment or you can mail me your opinions on nachiketa1010@gmail.com. You can also mail me topics of your interest or any other useful information that you want to share.