What is a Cuk Converter?

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Editorial Team - everything PE

Feb 23, 2022

Cuk converter is a type of DC-DC converter that is used to either step up or step down the DC output voltage. It is the cascaded form of buck and boost converter with an intermediate series-connected capacitor.  This capacitor is the main storage element that transfers energy from the input to the output side, compared to conventional DC-DC converters which use an inductor as a storage element. Cuk converters are ideal for use in the battery management systems of electric vehicles, renewable energy integration that includes systems with solar panels on the input side and hybrid solar-wind energy systems, photovoltaic applications to facilitate regulation and operation at the maximum power point (MPP), high voltage, negative polarity output voltage, and low standby continuous current applications.

Cuk converters are available in two versions: non-isolated Cuk converter and isolated Cuk converter.

Non Isolated Cuk Converter:

In the non-isolated Cuk converter, the input and output circuits share the common ground. The non-isolated Cuk converter topology consists of DC input voltage source Vin, input inductor L1, one controllable switch S, energy transfer capacitor C1, diode D, filter inductor L2, filter capacitor C2, and load resistance R. This converter exchanges energy between the inductor L1, capacitor C1, and inductor L2 to convert input DC voltage to required output voltage level.  A power transistor switch (S1) such as a MOSFET is used to control the amount of energy exchanged.

The output voltage of the non-isolated Cuk converter

where,

Vin - the input DC voltage.

Vo - the average output voltage of the non-isolated Cuk converter.

D is the duty cycle of the switch.

Isolated Cuk Converter:


Isolated Cuk converter is desiged by splitting the intermediate capacitor C1 into two capacitors C2 & C3 and inserting a high-frequency transformer between these two split capacitors. The isolated Cuk converter either steps up or steps down the DC output voltage with zero current ripples. It offers benefits such as reducing device stress on the input side by controlling turns ratio, and providing isolation between input & output circuits, which is necessary for high power applications.