Selection of the Best Topology

On the basis of the analysis developed in Chap. 7, the considered DC/DC converter topologies, i. e., the buck converter, the boost converter, and the buck-boost con­verter, are all, in principle, possible candidates to be used for the power amplifier stage of a PV emulator.

Anyway, the following practical considerations suggest the employment, when possible, of the buck topology.

• The DC voltage level for supplying the PV emulator can be easily obtained by the grid voltage through a simple bridge rectifier both in the case of single-phase grid and three-phase grid. In this last case, the obtained DC voltage of about

Table 8.1 Main features under standard test conditions (stc) of the PV plant for the emulator design

Parameter

Symbol

Value

Number of assemblies

Np

2

Number of modules per assembly

Ns

6

Peak power

Ppv

1450 W

Open circuit voltage

Voc

228.6 V

Short-circuit current

/sc

9.2 A

Maximum power voltage

VMP

186 V

Maximum power current

/MP

8 A

500 V is suitable to be reduced, via the buck converter, to the rated voltage of a common PV plant of a power up to tens of kW.

• The use of a buck topology permits a simpler control implementation, because the corresponding transfer functions are not dependent on the operating point, for a given electrical load, as illustrated in Table 7.2.

With reference to the first aspect, it is worth observing that the boost converter does not permit to obtain an output voltage less than the supply voltage; this means that operating conditions close to the short circuit are not reproducible.

Furthermore, high output voltages imply high input currents. This last disad­vantage is also present in the buck-boost scheme, which, however, allows low voltages to be reproduced.

Regarding to the second aspect, it should be noted that both the boost and the buck-boost converters, show a nonlinear dependence on the duty cycle and the load value as well, thus making difficult a fixed parameter control strategy.

Updated: August 20, 2015 — 6:43 am