A Cuk converter has the following parameters: V_d = 12 V, C_1 = C= 250 uF f_x =

Question

A Cuk converter has the following parameters: V_d = 12 V, C_1 = C= 250 uF f_x = 100 kHz, load terminals are maintained at 12V The Cuk converter is to be designed and simulated (using LTSpice). The design specification requires an output voltage of 12V. The input voltage, V_d, is derived from a PV source with a nominal voltage of 12V. The maximum power points at various irradiances are given in Table 1 and this table identifies the range of input voltages and currents that extracts the maximum power from the PV module given a certain irradiance level. So, in this case the converter's input voltage may vary from 9 to 13V. The load connected to the output of the converter should be modelled by a constant voltage source of 12V and the converter controlled such that it extracts the maximum potential P_MPP at each irradiance level (i) Assuming continuous conduction, calculate the required modulation index, D, for each of the irradiance values given in Table 1. ii) Calculate the required values of L_1 and L_2 such that both inductors are on the boundary between CCM and DCM at 25% irradiance when extracting the P_MPP. Sketch the current waveforms at 25% and at 100% irradiance with these values of inductance.

Explanation / Answer

(i)calculate modulation index(m) for each irradiance values: (1).'m' for 100% is v(output)/v(peak) i.e v(output) is 12v which is constant and v(peak) changes.Here v(peak)=13v so, m=12/13=0.92.(2) 'm' for 75% is v0/vp=12/12=1.(3)'m' for 50% is v0/vp=12/11=1.090.(4)'m' for 25% is v0/vp=12/9=1.33.These are the different 'm' values.

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