This study proposes a varying phase angle control (VPAC) in isolated bidirectional dc–dc converter (IBDC) for integrating battery storage unit to a DC link in a standalone solar photovoltaic (PV) system. The IBDC is capable of power transfer using high step up/down ratio between DC link and battery. The VPAC control proposed in this study effectively manage the power flow control between the battery storage unit and the solar PV fed DC link by continuously varying the phase angle between high voltage and low voltage (LV) bridge voltage of the IBDC. The solar PV system is incorporated with the maximum power point tracking using DC–DC converter. In order to control the voltage across the AC load a voltage source inverter is used. The study also presents the design aspects of the IBDC converter for the application considered. The performance of the proposed power flow control strategy has been studied through PSCAD/EMTDC simulation and validated using LPC 2148 ARM processor.
Fig. 1 Block diagram for proposed standalone system
(a) Generalised block diagram, (b) Mode 1 operation, (c) Mode 2 operation, (d) Mode 3 operation
EXPECTED SIMULATION RESULTS:
Fig. 2 Simulation results of IBDC
(a) Battery current during change in mode 1 to mode 2, (b) Battery current during change in mode 2 to mode 1, (c) Solar PV power, load power and battery power during change in mode 1 to mode 2, (d) Solar PV power, load power and battery power during change in mode 2 to mode 1
The proposed variable phase angle control of IBDC converter balances the power flow between the solar PV system, battery storage unit and AC load in all the modes. The VPAC algorithm ensures that the, (i) solar PV system delivers maximum demanded power corresponding to the load and battery gets charged/ discharged through the available excess/short power. The governing mathematical formulation of problem reveals the dependency of average battery current on phase angle between the voltages of LV and HV side of the IBDC converter and hence provides a strategy to control the power flow. The analysis presented can be used to design the passive components and switches of the IBDC. From the obtained results, the performance of the proposed VPAC has been established with smooth transition of power flow between the PV fed DC link and the battery through the IBDC converter. The maximum power is extracted from the solar PV and AC load voltage is controlled in all the modes.
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