A Buck & Boost based Grid Connected PV Inverter Maximizing Power Yield from Two PV Arrays in Mismatched Environmental Conditions

ABSTRACT:

A single phase grid connected transformerless photo voltaic (PV) inverter which can operate either in buck or in boost mode, and can extract maximum power simultaneously from two serially connected subarrays while each of the subarray is facing different environmental conditions, is presented in this paper. As the inverter can operate in buck as well as in boost mode depending on the requirement, the constraint on the minimum number of serially connected solar PV modules that is required to form a subarray is greatly reduced. As a result power yield from each of the subarray increases when they are exposed to different environmental conditions. The topological configuration of the inverter and its control strategy are designed so that the high frequency components are not present in the common mode voltage thereby restricting the magnitude of the leakage current associated with the PV arrays within the specified limit. Further, high operating efficiency is achieved throughout its operating range. A detailed analysis of the system leading to the development of its mathematical model is carried out. The viability of the scheme is confirmed by performing detailed simulation studies. A 1.5 kW laboratory prototype is developed, and detailed experimental studies are carried out to corroborate the validity of the scheme.

KEYWORDS:

1.      Grid connection

2.      Single phase

3.      Transformerless

4.      Buck & Boost based PV inverter

5.      Maximum power point

6.      Mismatched environmental condition

7.      Series connected module

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Dual Buck & Boost based Inverter (DBBI)

EXPECTED SIMULATION RESULTS

Fig. 2. Simulated waveform: Variation in (a) p_pv1 and p_pv2, (b) v_pv1 and

v_pv2, (c) i_pv1 and i_pv2 during entire range of operation

Fig.3. Simulated waveform: v_g and i_g and their magnified views

Fig. 4. Simulated waveform: i_L1 and i_L2 and their magnified views

Fig. 5. Simulated waveform: v_co1 and v_co2 and their magnified views

CONCLUSION:

A single phase grid connected transformerless buck and boost based PV inverter which can operate two subarrays at their respective MPP was proposed in this paper. The attractive features of this inverter were i) effect of mismatched environmental conditions on the PV array could be dealt with A single phase grid connected  transformerless buck and boost based PV inverter which can operate two subarrays at their respective MPP was proposed in this paper. The attractive features of this inverter were i) effect of mismatched environmental conditions on the PV array could be dealt with in an effective way, ii) operating efficiency achieved, _euro = 97.02% was high, iii) decoupled control of component converters was possible, iv) simple MPPT algorithm was employed to ensure MPP operation for the component converters, v) leakage current associated with the PV arrays was within the limit mentioned in VDE 0126-1-1. Mathematical analysis of the proposed inverter leading to the development of its small signal model was carried out. The criterion to select the values of the output filter components was presented. The scheme was validated by carrying out detailed simulation studies and subsequently the viability of the scheme was ascertained by carrying out thorough experimental studies on a 1.5 kW prototype of the inverter fabricated for the purpose.

REFERENCES:

[1] T. Shimizu, O. Hashimoto, and G. Kimura, “A novel high-performance utility-interactive photovoltaic inverter system,” IEEE Trans. Power Electron., vol. 18, no. 2, pp. 704-711, Mar. 2003.

[2] S. V. Araujo, P. Zacharias, and R. Mallwitz, “Highly efficient singlephase transformerless inverters for grid-connected photovoltaic systems,” IEEE Trans. Ind. Electron., vol. 57, no. 9, pp. 3118-3128, Sep. 2010.

[3] B. Ji, J. Wang, and J. Zhao, “High-efficiency single-phase transformerless PV H6 inverter with hybrid modulation method,” IEEE Trans. Ind.Electron., vol. 60, no. 5, pp. 2104-2115, May 2013.

[4] R. Gonzalez, E. Gubia, J. Lopez, and L. Marroyo, “Transformerless single phase multilevel-based photovoltaic inverter,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2694-2702, Jul. 2008.

[5] H. Xiao and S. Xie, “Transformerless split-inductor neutral point clamped three-level PV grid-connected inverter,” IEEE Trans. Power Electron., vol. 27, no. 4, pp. 1799-1808, Apr. 2012.