A Grid Connected Single Phase Transformerless Inverter Controlling Two Solar PV Array Operating under Different Atmospheric Conditions

ABSTRACT:

A grid connected single phase transformerless inverter which can operate two serially connected solar photo voltaic (PV) subarrays at their respective maximum power points while each one of them is exposed to different atmospheric conditions is proposed in this paper. As two subarrays are connected in series, the number of serially connected modules within a subarray is reduced to half. Reduction in the number of serially connected PV modules within a subarray leads to an overall improvement in the magnitude of power that can be abstracted from a subarray while the modules of the subarray are exposed to varied atmospheric conditions. The topological structure of the inverter ensures that the common mode voltage does not contain high frequency components, thereby reducing the magnitude of leakage current involved with the solar panels well within the acceptable limit. An in depth analysis of the scheme along with the derivation of its small signal model has been carried out. Detailed simulation studies are performed to verify its effectiveness. A 1 kW laboratory prototype of the scheme has been fabricated. Detailed experimental validations have been carried out utilizing the prototype to confirm the viability of the proposed scheme.

KEYWORDS:

1.      Grid connected single phase transformerless PV inverter

2.      Maximum power extraction

3.      Mismatched operating condition

4.      Serially connected PV subarrays

SOFTWARE: MATLAB/SIMULINK

 PROPOSED CIRCUIT DIAGRAM:

Fig. 1. Combined Half Bridge Inverter with AC Bypass (CHBIAB)

 EXPECTED SIMULATION RESULTS:

Fig.2. Simulated performance: (a) Power output from PV1 and PV2, (b) Voltage output of PV1 and PV2, (c) Output current of PV1 and PV2

Fig. 3. Simulated performance: Grid current and voltage along with their

magnified versions 

Fig. 4. Simulated performance: Output capacitor voltages along with their magnified versions

CONCLUSION:

A grid connected single phase transformerless inverter which can extract maximum power from two subarrays during  mismatched operating condition is presented in this paper. Salient features of the proposed inverter are as follows: i) number of series connected modules is less thereby reducing the effect of shading, ii) two subarrays can be operated at MPP simultaneously, thus it is well suited for PV subarrays operating under mismatched operating condition, iii) decoupled control structure is employed to control the two component half bridges of the inverter, iv) _euro of 96% is achieved which is the highest compared to the topologies dealing with solar PVs experiencing mismatched operating conditions, v) the scheme is realized through single stage of power conversion leading to a considerable reduction in size, weight and volume, vi) simple MPPT algorithm is employed thereby reducing the computational burden of the digital signal processor involved, vii) PV leakage current is limited within the limit specified in the standard, VDE 0126-1-1. The operating principle of the proposed scheme is explained in detail by exploring all the equivalent topological stages. Subsequently the mathematical analysis of the scheme has been carried out and the small signal model of the scheme has been derived. The philosophy of control is described in detail and the configuration of the controller is derived. The design guidelines for selecting the filter components of the inverter are presented. Detailed simulation and experimental studies are carried out to confirm the viability of the proposed scheme.

REFERENCES:

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