This example shows the operation of a non-isolated Cuk converter.
The non-isolated Cuk converter is a DC/DC power converter that, like a buck-boost converter, can produce an output voltage (Vout) magnitude that is either greater or less than the input voltage (Vin) magnitude. However, it is an inverter converter, so the output voltage is of opposite polarity with respect to the input voltage. In the Cuk converter topology, the capacitor C1 acts as the primary means of storing and transferring energy from the input to the output. The advantage of this converter is that both the input current (IL1) and the current feeding the output stage (IL2) are reasonably ripple-free (unlike the buck-boost converter where both these currents are highly discontinuous). Assuming a constant voltage across C1, the theoretical transfer function of the Cuk converter is:
where is the duty cycle.
In this example, the converter is feeding a 50-W load from a 12 V source and the PWM frequency is set to 50 kHz.
Run the simulation and observe waveforms on Scope. Verify that the mean value of the load voltage (Vout) is very close to the theoretical value of: Vout = -0.294/ (1 - 0.294) * 12 = -5 V.
Ned Mohan, Tore M. Undeland, Power Electronics: Converters, Applications, and Design, John Wiley & Sons.