This paper introduces a residential photovoltaic (PV) energy storage system, in which the PV power is controlled by a dc–dc converter and transferred to a small battery energy storage system (BESS). For managing the power, a pattern of daily operation considering the load characteristic of the homeowner, the generation characteristic of the PV power, and the power leveling demand of the utility is prescribed. The system looks up the pattern to select the operation mode, so that powers from the PV array, the batteries, and the utility are utilized in a cost-effective manner. As for the control of the system, a novel control technique for the maximum power-point tracking (MPPT) of the PV array is proposed, in which the state-averaged model of the dc–dc converter, including the dynamic model of the PV array, is derived. Accordingly, a high-performance discrete MPPT controller that tracks the maximum power point with zero-slope regulation and current-mode control is presented. With proposed arrangements on the control of the BESS and the current-to-power scaling factor setting, the dc–dc converter is capable of combining with the BESS for performing the functions of power conditioning and active power filtering. An experimental 600-W system is implemented, and some simulation and experimental results are provided to demonstrate the effectiveness of the proposed system.
- Active power filtering
- Battery energy storage system
- Maximum power-point tracking
- Power conditioning
Fig. 1. The power circuit of proposed PV energy storage system.
EXPECTED SIMULATION RESULTS:
Fig. 2. Simulated results of MPPT control. (a) An increasing step change in Ip. (b) A decreasing step change in Ip.
Fig. 3. Measured waveforms of , and in MPPT control.
Fig. 4. System operations. (a) Measured waveforms when system is changed from mode 3 to mode 2, where subscripts o;L; and u are used to represent the BESS, the load, and the utility, respectively. (b) Measured real power waveforms in various operation modes.
This paper has proposed a residential PV energy storage system, where the PV power is controlled by a dc–dc converter and transferred to a small BESS. The proposed system, possessing the functions of power conditioner and active power filter, is capable of providing an optimal interface with the utility. The additional PV power makes the system flexible in power usage, so that all powers in the system can be utilized in a cost-effective manner. Some control techniques for realizing the functions of the proposed system, including the MPPT control of the PV array and control of power flows in the system, have been presented. A prototype 600-W system was implemented, and some simulated and experimental results were provided to demonstrate the effectiveness of the proposed system. Although the setup cost of the proposed system is high, such that it is hard to compete with the current utility power, we believe that the capital issue will be resolved if there is a political encouragement in the kilowatt price and the market is large enough.
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