POWER ELECTRONICS - 3

Hello folks,

Today we will discuss about Zeta converter (this is last DC-DC converter we will look up to)

A Zeta converter is a fourth-order DC-DC converter that capable of amplifying and reducing the input voltage levels without inverting the polarities as it includes two capacitors and two inductors as dynamic storage elements. Compared with other converters in the same class, such as Cuk and SEPIC converters, the Zeta converter has received the least attention.

A zeta converter, with regard to energy input, can be seen as buck-boost-buck converter and with regard to the output; it can be seen as boost-buck-boost converter.

Capacitor C1 will be in parallel with C2, so C1 is charged to the output voltage, VOUT, during steady-state CCM. When SW is off, the voltage across L1 must be VOUT since it is in parallel with C2. Since C2 is charged to VOUT, the voltage across Q1 when Q1 is off is VS + VOUT; therefore the voltage across L1a is –VOUT relative to the drain of Q1. When Q1 is on, capacitor C1, charged to VOUT, is connected in series with L1; so the voltage across L1 is +VS, and diode D1 sees VS + VOUT. When SW is on, energy from the input supply is being stored in L1 and C1. L1 also provides IOUT. When SW turns off, L1’s current continues to flow from current provided by C1, and L1 again provides IOUT.

Modes of Operation (shown in figure)

Mode-1:- The first mode is obtained when the switch is ON (closed) and instantaneously, the diode D is OFF. During this period, the current through the inductor L1 and L2 are drawn from the voltage source Vs. This mode is the charging mode.

Mode-2:- The second mode of operation starts when the switch is OFF and the diode D is ON position. This stage or mode of operation is known as the discharging mode since all the energy stored in L2 is now transferred to the load R.

The operational duty ratio is same as that of Sepic converter. At equilibrium, L1 average current equals Iin and L2 average currents equal Iout,  since there is no DC current through the flying capacitor C1 in the circuit. Also there is no DC voltage across either inductor. Therefore, C1 sees ground potential at its left side and VOUT at its right side, resulting in DC voltage across C1 being equal to VOUT.

These are few of the building blocks of advanced DC-DC Converters. Still there is a lot to be explored in the world of Converters and Inverter. You can study them as per your interest

Thank you for your time.