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Hybrid System Operation with an On/Off Charge Controller: Hybrid Test Bench Results

Michael M.D. Ross
RER Renewable Energy Research

Full Text Report
Link to CETC-Varennes

Acknowledgements:

Research conducted on behalf of the Photovoltaics and Hybrid Systems Program at the CETC-Varennes (Natural Resources Canada) with partial funding from the Panel on Energy Research and Development (PERD).

Citation:

Ross, Michael M. D. Hybrid System Operation with an On/Off Charge Controller: Hybrid Test Bench Results. Report to CETC-Varennes (Natural Resources Canada). Montreal, Qc: RER Renewable Energy Research, 2005.

Summary:

This document reports on a five-week test run on the hybrid system test bench of the Photovoltaic and Hybrid Systems Group at the CANMET Energy Technology Centre—Varennes. During the test, a photovoltaic array and a genset provided power to a DC load, with energy surpluses and deficits being accommodated by a battery. Overcharging of the battery was avoided by interrupting and reconnecting the charge current on the basis of voltage thresholds, that is, “on/off” charge control.

The test investigated the ability of on/off charge regulation to fully charge the battery. It found that with relative dimensions of batteries and photovoltaic arrays in Canadian hybrid systems, simple on/off charging is not appropriate, and will be unable to fully charge the batteries even when sufficient sunlight is available. On/off charge control may be appropriate for Canadian PV-only systems, in which the battery is relatively large compared with the maximum array charge current. On/off charge control of multiple, independently switched sub-arrays may be an appropriate charging method for hybrid systems, however.

Measurements at a frequency of one hertz were used to track battery voltage and current during on/off charge regulation. Two different reconnect voltage thresholds and several different load currents were used. Both were found to significantly affect the behaviour of the system. The conclusion that the voltage reconnect threshold is a key variable in the efficacy of on/off charge regulation, drawn in previous studies found in the literature, was supported by the behaviour observed here.