**4. Simulations and experimental acquisitions**

To determine the operation characteristics of the photovoltaic panels and the panel arrays, the built data acquisition system allows to measure the values of current and voltage, to simultaneously trace characteristics (current-voltage, power-voltage, power-charge resistance) - see figures 11 and 12, to present the measured parameters (during the data acquisition) in tables, to save data into files for future processing.

Fig. 11. DC characteristics

For alternative current systems it is necessary to obtain signals with volt-range amplitude to be applied to the input of the data acquisition board. For phase/line voltages there can be used voltage dividers (which do not ensure galvanic isolation) or voltage measurement transformers (ensure galvanic separation). Shunts (current-voltage converters) or current measurement transformers can be used for currents. The use of both voltage dividers and

Today, board level solutions offering 24-bit resolution are now available as, e.g. 6.5 digit DMM boards. On the box side, USB 2.0 is capable of delivering 30 million 16-bit conversions per second and Gigabit Ethernet will handle more than twice that. The internal plug-in slot

The market of data acquisition equipment is very large, different companies propose new solutions. National Instruments offers several hardware platforms for data acquisition. The most readily available platform is the desktop computer, with PCI DAQ boards that plug into any desktop computer. For distributed measurements, the Compact FieldPoint platform delivers modular I/O, embedded operation, and Ethernet communication. For portable or handheld measurements, National Instruments DAQ devices for USB and PCMCIA work with laptops or Windows Mobile PDAs. In addition, National Instruments has launched DAQ devices for PCI Express, the next-generation PC I/O bus, and for PXI Express, the

To determine the operation characteristics of the photovoltaic panels and the panel arrays, the built data acquisition system allows to measure the values of current and voltage, to simultaneously trace characteristics (current-voltage, power-voltage, power-charge resistance) - see figures 11 and 12, to present the measured parameters (during the data

For alternative current systems it is necessary to obtain signals with volt-range amplitude to be applied to the input of the data acquisition board. For phase/line voltages there can be used voltage dividers (which do not ensure galvanic isolation) or voltage measurement transformers (ensure galvanic separation). Shunts (current-voltage converters) or current measurement transformers can be used for currents. The use of both voltage dividers and

data transfer rates have increased 10 fold in recent years.

**4. Simulations and experimental acquisitions** 

acquisition) in tables, to save data into files for future processing.

high-performance PXI bus.

Fig. 11. DC characteristics

shunts must be done by taking into account the current through the voltage divider, the voltage drop on the shunt, the power dissipation, parasite resistances, self-heating effects and dynamic effects. The use of voltage-current measurement transformers guarantees galvanic isolation of the measuring system but it introduces ratio and angle errors and inadequate perturbation transfer.

Fig. 12. Current –voltage characteristics. Experimental acquisition (1,4,5,6,9,11 modules) and simulation (2,3,7,8,10 modules)

Fig. 13. AC Acquisition Instrument (Phase B)

The solution adopted was to use current and voltage transducers based on the Hall Effect. To obtain a good magnetic sensor the magnetic field is concentrated around the transducer, by using a circular core (used as a flux concentrator and made of a material with high magnetic permeability), which ensures both an increase of the magnetic field in the area of the sensor and the independence from the position of the conductor inside the core. Nonlinear behavior of the flux concentrator can be obtained by using an operational amplifier, which injects a compensation current through the reaction loop. Figure 13 presents the front panel of the LabVIEW™ application which acquires and processes data in the AC circuit from the output of the phase B connected inverters.

Figure 14 shows a LabVIEW™ application (Ertugrul, 2002) to determine the characteristics of PV panels, with the possibility of remote monitoring.
