AN3095 datasheet(24/55 Pages) STMICROELECTRONICS

24 / 55 page

Schematic description

AN3095

24/55

Doc ID 16555 Rev 3

Schematic description

The power board schematic is shown in Figure 14. The input voltage, produced by the PV

array and comprising between 200 V and 400 V, is fed to the power circuit through

connector J7. The input filter consists of 3 high voltage electrolytic capacitors and two 0.1 µF

polypropylene capacitors connected at the input of the bridge, to reduce the effects of

parasitic inductances due to cables and PCB tracks. Each of the four input power

MOSFETs, STW55NM60ND, are connected in parallel to a STTH30R06, 600 V 30 A ultra-

fast, soft recovery diode. This diode carries only a small amount of current during ZVS

operation of the DC-DC converter due to the relatively lower forward voltage of the MOSFET

body diode.

The power MOSFETs in the active rectifier are connected in parallel to 4.7 nF, 630VDC

polypropylene capacitors used as voltage snubbers to minimize turn-off losses.

The HF transformer is realized using two E70/33/32 cores with N87 ferrite. In a transformer

having only a primary and a secondary winding, the value of the leakage inductance is

determined by the number of turns in each of the two windings and by the spatial

arrangements of these windings. The leakage inductance increases with an increasing

number of turns and with an increasing distance between the windings. However, the spatial

arrangement of the windings cannot be chosen arbitrarily, mainly because of mechanical

restrictions introduced by the core geometry chosen for the specific application. Then, if a

high value of leakage inductance is needed, an additional coil may be added in series to the

primary or a bigger core may be selected for the transformer. The leakage inductance of the

transformer in this application is designed without an additional external coil to achieve a

more compact set-up and lower cost.

A bank of four 330 µF, 500 V electrolytic capacitors, connected in parallel, is placed on the

inverter bus to filter the 100 Hz ripple, together with a 2.2 µF, polypropylene capacitor to

filter the high frequency component generated by the DC-DC converter. The output of the

DC-DC converter is connected to J9, a two-way connector mounted on the PCB in

order to allow the independent operation of both conversion stages. For example, by

connecting an electrical load to J9 and a DC voltage source to J7 the operation of the DC-

DC converter may be evaluated independently from the inverter. In the same way,

connecting a DC voltage source to J9 and disabling the modulation of the DC-DC converter

the operation of the DC-AC inverter may be evaluated both in standalone or grid-connected

operation. In standalone mode of operation the system is controlled in open loop, while in

grid connection mode the system operates with closed loop control.

The full bridge inverter consists of two legs implemented with STGW35HF60WD IGBTs.

A 0.1 µF, 630VDC polypropylene capacitor (CF1, CF2) is connected across each leg. The

mid point of each leg is then reported on J8 to allow the connection of the two 1 mH

inductors used as high frequency filters together with capacitor C1 (Figure 15). This

capacitor, placed on the output sensing and relays board, is connected to the filter inductors

through a two-way connector J7, placed on the same board. The current in the filter inductor

is sensed by means of a Hall effect sensor CS1 and is used as a feedback for the control

algorithm. Also the grid voltage, sensed with LV1, is a feedback for the control algorithm and

is used for current synchronization to obtain unitary power factor.

Hall sensors provide inherent galvanic isolation between the grid and the control circuitry

and are very simple to use, requiring only a +15 V/-15 V supply voltage and a measurement

resistor. Despite these advantages, their cost is higher compared to other sensing solutions.

AN3095 Folha de dados(PDF) 24 Page - STMicroelectronics

AN3095 Folha de dados(HTML) 24 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Folha de dados Download

Ligação URL