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Research Papers

Monitoring Array Output Current and Voltage in Stand Alone Photovoltaics Systems With Pulse Width Modulated Charge Regulators

[+] Author and Article Information
F. J. Muñoz

e-mail: fjmunoz@ujaen.es

M. Fuentes

Grupo IDEA,
Departamento de Ingeniería Electrónica y Automática,
Universidad de Jaén,
Campus las Lagunillas, 23071 Jaén, Spain

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received April 30, 2012; final manuscript received October 20, 2012; published online November 28, 2012. Assoc. Editor: Santiago Silvestre.

J. Sol. Energy Eng 135(2), 021008 (Nov 28, 2012) (9 pages) Paper No: SOL-12-1113; doi: 10.1115/1.4007939 History: Received April 30, 2012; Revised October 20, 2012

Pulse width modulated (PWM) charge regulators are frequently used in stand alone photovoltaic (SAPV) systems. Once the battery has reached the regulating voltage, these electronic devices provide current and voltage pulses to regulate the charge current to the battery. This kind of signals implies rapid variation in the variables and may provide, when being monitored, and if some special considerations are not taken into account, an erroneous measurement of the array output current, the array output voltage and the current to storage. Moreover, this inappropriate monitoring will affect not only to these monitored variables but also may spread over the array output power and most of the derived parameters, providing a mistaken system performance analysis from monitored data. In this way, this paper focus on the different issues that can arise when monitoring the parameters mentioned above in SAPV systems with PWM charge regulators. A comparative study of the two types of sensors (shunt and hall-effect transducer) that can be used to capture either the array output current or the current to storage will be developed. Moreover, it is intended to provide easy monitoring procedures to collect the array output and voltage, the current to storage and the array output power as these variables are the more sensitive to the use of PWM charge regulators. These monitoring requirements may be appropriate under field conditions and may become cost-effective. The solutions given here intends to avoid the complex monitoring system and the high computational cost that may require a simultaneous sampling mode at a relative high sampling frequency to obtain an appropriate monitoring for the modulated signals in SAPV systems with PWM charge regulators.

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References

Figures

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Fig. 1

Parameters to be measured in a stand-alone photovoltaic system

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Fig. 2

Stand alone photovoltaic systems #1 & #2. (a) PV generator and (b) BOS.

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Fig. 3

Array current and voltage in a series charge controller (SAPV system #1) in the PWM stage. (a) Low duty cycle and (b) high duty cycle.

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Fig. 4

Array current and voltage in a shunt charge controller (SAPV system #2) in the PWM stage. (a) Low duty cycle and (b) high duty cycle.

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Fig. 5

Measuring array output current through a DC hall-effect transducer (a) and shunt (b) in SAPV system #1 with a PWM series charge controller.

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Fig. 6

Normalized daily RSMEd and the daily MBEd obtained when comparing a DC hall effect sensor and a shunt to monitor the array output current in SAPV system #1with a series charge regulator. The samples from the DC hall-effect transducer have been taken as reference values and the sampling interval considered is one minute.

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Fig. 7

Measuring battery current through a DC hall-effect transducer (a) and shunt (b) in SAPV system #1 with a PWM series charge controller

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Fig. 8

Normalized daily RSMEd and the MBEd obtained when comparing the DC hall effect sensor and the shunt to monitor the current to storage in SAPV system #1 with a series charge regulator. The samples from DC the hall-effect transducer have been taken as reference values and the sampling interval considered is one minute.

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Fig. 9

Measuring array output current through a DC hall-effect transducer (a) and shunt (b) in SAPV system #2 with a PWM shunt charge controller

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Fig. 10

Normalized daily RSMEd and the daily MBEd obtained when comparing a DC hall effect sensor and a shunt to monitor the array output current in a SAPV system #2 with a shunt charge regulator. The DC hall-effect samples have been taken as reference values and the sampling interval considered is one minute.

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Fig. 11

Normalized daily RSMEd and the daily MBEd obtained when comparing, in a shunt charge regulator (SAPV system #2), the array output current obtained with a DC hall effect sensor and the net array output current estimated from the current to & from storage and the load current. The current to storage has been sensed by a DC hall-effect transducer. Moreover, the net array current has been taken as reference value and the considered sampling interval is one minute.

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Fig. 12

Measuring array voltage through instantaneous (a) and average (b) samples in SAPV system #1 with a series charge controller

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Fig. 13

Measuring array voltage through instantaneous (a) and average (b) samples in SAPV system #2 with a shunt charge controller

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