A Two-stage Single-phase Grid-connected Solar-PV System with Simplified Power Regulation

ABSTRACT:

 This study focuses on the design and development of a simplified active power regulation scheme for a two-stage single-phase grid-connected solar-PV (SPV) system with maximum power point (MPP) estimation. It aims to formulate and test an improvised new control scheme to estimate the real-time MPP of the PV panel and operate only at either the MPP or on the right-hand side (RHS) of the PV characteristics of the panel. A simple active power regulatory control scheme was formulated to provide frequency control services to a single-phase grid without using an energy storage device. The plant operator provides the reserve fraction as the input for the active power regulation controller. At any time, the reserve fraction is used to determine the magnitude of the reference power to be extracted from the PV panel for injection into the grid. A simple PI controller was used to track the calculated reference power. The different modes of operation of the regulatory scheme are presented in detail. All the above control schemes are integrated and implemented through appropriate switching of the DC-DC converter alone. The DC-AC converter maintains the DC link voltage and unity power factor at the single-phase grid terminals. The proposed control schemes were tested on a 250 Wp solar panel feeding power to a 230 V, 50 Hz single-phase grid through a two-stage converter. The entire scheme was modeled using the Matlab/Simulink platform, and the same was validated by hardware experimentation using Chroma Solar Simulator and NI my RIO controller under varied irradiation, temperature, and reserve fractions. The simulation and hardware results are compared and reported.

 KEYWORDS:

1.      Solar photo voltaic (SPV)

2.      Maximum power point (MPP)

3.      Right hand side (RHS)

4.      Power regulation

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Two-stage grid-connected single-phase solar-PV system with control logic

 EXPECTED SIMULATION RESULTS:

 

Fig. 2 Variation in maximum power estimation and grid power under varied irradiation and temperature with zero reserve

 

Fig. 3 Variation in maximum power estimation and grid  power under varied irradiation at constant temperature 25^oC with reserve fraction

Fig. 4 Variation in maximum power estimation and grid power under varied irradiation and temperature with the change in reserve fraction

Fig. 5 Grid injected current corresponding to the various irradiation, temperature, and reserve fraction

 

Fig. 6 Grid voltage in p.u. and grid injected current

 CONCLUSION:

The proposed simplified active power control with reserve fraction over the entire operating range from near-zero to 100 % of the available MPP was tested and reported for various operating conditions. The RHS operating point of the SPV was maintained under all operating conditions with a specified reserve fraction. This was validated by observing the operating voltage of the SPV, along with the results obtained through the solar simulator. Further, the power quality was ensured at the grid terminals in the proposed scheme by maintaining the THD and zero reactive power exchange. The essential findings and results required for supporting the proposed scheme were provided by modeling and simulating a grid-connected 250 Wp solar-PV system. Subsequently, experimental results obtained by implementing a prototype setup with the same specifications in the laboratory helped to validate the effectiveness of the proposed active power regulation scheme.

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