This paper presents the control strategy for a three phase LCL-filter type based grid connected inverter system for photovoltaic (PV) applications. The control strategy proposed in the paper involves the independent control of active and reactive power injected into the grid during steady state and transient conditions. In addition to that, a comparative study between active and passive damping configurations for LCL type filter resonance damping is also analyzed. The control strategy implemented on a three-phase grid connected PV inverter is studied and verified by computer simulation based on MATLAB Simulink and the results are analyzed for effectiveness of the study.
1. Renewable Energy Source (RES)
3. Proportional-Resonant (PR) Controller
4. Active damping
5. Passive damping
Fig.1. Schematic diagram of grid-connected inverter system with LCL filter
Fig.2. Over all control strategy of Grid-connected PWM VSI
EXPECTED SIMULATION RESULTS:
Fig.3. Simulation results for active damping method under steady state condition (a) grid voltage and grid Current waveforms (b) d and q-axis grid currents (c) response of active and reactive Power (d) response of dc-link voltage (e) THD of grid current.
Fig.4. Simulation results for passive damping method under steady state condition (a) grid voltage and grid Current waveforms (b) d and q-axis grid currents (c) response of active and reactive Power (d) response of dc-link voltage (e) THD of grid current.
Fig.5. Simulation results for active damping method during step change in the input PV power (a) step change in the input PV power (b) d and q-axis grid currents (c) response of dc-link voltage (d) THD of grid current
Fig.6. Simulation results for passive damping method during step change in the input PV power (a) d and q-axis grid currents (b) response of dc-link voltage (c) THD of grid current.
The paper discusses the control strategy for gridconnected PWM VSI with LCL-type filter. The advantage feature of PR controller is the possibility of implementing harmonic compensator without interfering with control dynamics, achieving a high quality delivered current are explored. In addition, a comparative study has been made between active and passive damping methods to damp-out the LCL-filter resonance. From the above said discussions, it is found that active damping method is better than passive damping method to inject sinusoidal current into the grid with less THD. Also it ensures zero steady state error with stable response. In addition to that, passive damping method involves extra cost and losses due to additional circuit components. Nevertheless, active damping method difficult to implement, but overall performance of grid-connected PWM VSI is improved with higher efficiency
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