AN3095 datasheet(17/55 Pages) STMICROELECTRONICS

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AN3095

DC-DC converter design

Doc ID 16555 Rev 3

17/55

where:

Parray is the PV field maximum output power,

ΔV

array is the allowable peak-to-peak voltage

ripple at the input of the array, fs is the switching frequency and Vinmin is the minimum

operating value for the input voltage. Assuming 90 % efficiency for the converter and 0.1 %

of admissible peak-to-peak ripple voltage the input capacitance value is:

Equation 20

Three 330 µF, 450 V electrolytic capacitors are connected in parallel at the input of the

converter to limit the effect of the high frequency ripple on the PV generator.

●

Output capacitor value:

In a similar way the value of the C2 bus capacitor may be calculated, taking the fact that the

ripple is sinusoidal at twice the grid frequency into account:

Equation 21

where the peak-to-peak voltage of 9 V corresponds to a voltage ripple of 1 % of the nominal

bus voltage and the grid frequency is 50 Hz.

●

HF transformer design:

The design is based on the core geometry method. The transformer specifications are

shown in Table 4:

Table 4.

HF transformer specifications

Specification

Symbol

Value

Nominal input voltage

Vin

300 V

Maximum input voltage

Vinmax

400 V

Minimum input voltage

Vinmin

200 V

Input current

Iin

27 A

Nominal output voltage

Vout

450 V

Output current

Iout

22.5 A

Switching frequency

35 kHz

Efficiency

99 %

Regulation

0.15

Max operating flux density

0.15 T

Window utilization

0.3

Duty cycle

Dmax

0.5

Maximum temperature rise

70 °C

200

35000

3333

Vin

min

array

450

3000

bus

grid

out

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