AN3095 datasheet(8/55 Pages) STMICROELECTRONICS

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DC-DC converter

AN3095

8/55

Doc ID 16555 Rev 3

DC-DC converter

The dual-stage inverter for grid-connected applications includes a DC-DC converter to

amplify the voltage and a DC-AC inverter to control the current injected into the grid.

Figure 3.

DC-DC and DC-AC converter

The DC-DC converter is depicted in Figure 3 together with the DC-AC converter and LCL

filter. The converter consists of an input capacitor, C1, six switches, M1 - M6, six

freewheeling diodes, two rectifier diodes, D1 and D2, a HF transformer with turns ratio equal

to 1.2 and a DC link capacitor C2.

The transformer provides voltage isolation between the PV array and the grid, improving

overall system safety. Its leakage inductance is used as a power transfer element,

eliminating device overvoltage problems and the need for snubber circuits. Proper phase-

shift control between input bridge legs (M1-M4) and active rectifier legs (M5-M6) allows

transformer current shaping, therefore achieving ZCZVS for all the power devices, as well as

voltage step-up. The adopted phase-shift modulation is shown Figure 4.

Figure 4.

DC-DC converter control signals

The same drive signal used for device M1 also controls M4, as the one controlling M3 is also

used for M2. The effect of the input bridge modulation is to generate a square wave on the

VGSM1

VGSM2

VGSM5

VGSM6

AM05398v1

AN3095 Datasheet(PDF) 8 Page - STMicroelectronics