Performance analysis of solar PV based DC optimizer distributed system with simplified MPPT method
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The proposed work focuses on the design and development of solar photovoltaic (PV) based DC optimizer distributed the system to enable individual maximum power point tracking (MPPT) in solar panels. This DC optimizer distributed system avoids mismatch losses and hot spots in solar PV panels during partial shadow conditions. A novel PI controller based fractional open circuit voltage MPPT method to extract the maximum power has been designed and discussed in this work. The entire system has been designed and modeled in MATLAB/Simulink and the same has been validated in hardware experimentation under varying environmental conditions. The results prove that the proposed system has fast voltage and current settling time with minimum oscillation and is cost-effective as it uses only a voltage sensor eliminating the use of the current sensor.
KeywordsSolar PV grid-connected system DC optimizer MPPT
Nowadays, solar power is one of the most significant energy sources among all renewable sources due to the elimination of greenhouse gas emissions effect, avoid usage of fossil fuels and high accessibility of solar irradiation . However, the environmental conditions such as solar-irradiation and temperature highly impact on the power generation efficiency in the solar PV systems . To improve the power generation efficiency in solar-PV power plants nowadays the research focuses on MPPT and new topology of power converters . Solar PV power plants are conventionally configured central inverter and string inverters . In general, the solar photovoltaic based large-scale energy system the solar PV panels are regularly associated in arrangement of series and parallel combinations, in the event that shadow falls on the specific solar PV panel which causes the bungled I–V characteristics, a hot spot in shadow panel and decrease in maximum power point . The causes of partial shading are clouds, buildings and, trees, dirt accumulation. Due to partial shading, the multiple peaks happen in the series-connected module since it reduces the converter efficiency . To avoid the mismatch losses in the large-scale solar PV energy system bypass diode utilized in parallel with each submodule. Subsequently, bypass diodes are solved the mismatch losses in solar panels to some extent and prevent PV hot spotting. Nevertheless, PV modules incapable of function at their individual MPP . To fathom the above-mentioned drawbacks like mismatch losses, end of bypass diodes and panel-level MPPT this paper focuses on power optimizer topology.
The Power optimizer is a DC/DC converter integrated with each solar-PV modules, that tries to capture MPPT and reduce losses  . The PV-battery series inverter architecture proposed in  used for the partial-power processing universal dc–dc optimizer to have flexible battery current control and extended PV MPPT control range. A dc optimizer modeled in  with DC–DC isolated boost converter. A step-down partial power optimizer structure proposed in  for PV series-connected optimizer system. DC Power Optimizer for PV Modules Using SEPIC Converter proposed in .
The authors  have been proposed the DC- optimizer distributed system in large scale grid-connected sun powered PV plants further this system allows better data gathering and protection of power sources.
In order to maximize the energy in solar PV based power plant the Maximum power point tracking is employed. The MPPT is classified into three groups (1) direct method (P&O, incremental conduction) (2) indirect method (Fractional short circuit current, open-circuit voltage) (3) self-computing method . The Perturb and observation(P&O) algorithm proposed in  to achieve maximum power point form the solar PV panel. To implement this MPPT scheme requires two sensors which sense the voltage and current when a rapid change in irradiation causes the oscillation in MPPT. As compared to the P&O method, the incremental conductance method is accurate and less oscillation, but the computation complexity is high in . The authors of  and  has been proposed the fractional open circuit and short circuit methods. To implement both algorithms is very simple, and it delivered a moderate level of accuracy. The multiple peaks in the PV curve cause the power losses the conventional MPPT techniques are wrongly identified local peak as global. To capture global MPPT a tracking loop based on a fuzzy logic controller (FLC) with scanning and storing algorithms used . The paper  has been proposed DC optimizer system implemented based on incremental conductance method MPPT method which gives 95% efficiency to get MPP power voltage and current sensors are required. SEPIC converter-based DC–DC converter is used in DC optimizer type PV distributed system proposed in  Further, in this system PI controller is produced PWM pulses to operate SEPIC converter corresponding to measure radiation and temperature sensors.
The uniqueness of the work is to design and development a DC optimizer distributed system, for grid-connected, single-phase solar PV systems. Further, to obtain MPPT for various environmental conditions efficient and simplified MPPT scheme has been proposed to suit the grid-connected application. Whereas in the conventional fractional open circuit voltage (FOCV) algorithm a single PI control is added for improvement in the MPPT scheme. To implement this algorithm (PI-FOCV) only voltage sensor information is enough. Hence, the current sensor has been eliminated due to this the overall power plant cost reduced. In this paper, the overall proposed system has been designed for 240 Wp capacity and the same has been modeled in MATLAB/Simulink and experimentally.
2 Proposed DC optimizer distributed system with PI FOCV algorithm
2.1 Design and fabrication details of boost-converter
Whereas VS is the dc voltage, L represents inductor, D is a power diode, C represents the capacitor, S denoted as MOSFET switch the capacitor and Vo is the voltage output across the resistive load, R.
In this scheme, Boost Converter is operated as in DCM mode and the design equations are as follows.
Solar-PV panel specifications
Open circuit voltage
Short circuit current
Diode quality factor
3 PI-FOCV MPPT technique
The Proportional segment of the PI controller has an effect on the transient response whereas an integral segment impacts the steady-state response. Further, the transfer function of the proposed system has been derived to tune the PI controller gains value using the Ziegler Nichols tuning strategy in which Kp value has been considered very small compared to Ki value for maintaining a system as stable with minimizing errors. Also, this tuning technique doesn’t require entire knowledge about the overall plant transfer function.
In this algorithm initially, real-time solar panel voltage is detected by a voltage sensor. Further, real-time solar PV voltage is compared with set voltage (Vmp). Hence, a gotten blunder from the comparator is bolstered to the PI controller and the same error has processed. To find the present duty value named (k) the processed error signal (Vp) processed by the PI controller is subtracted from the previous duty cycle value after scaling (Ve) suitably. Finally, the pulse of duty d(k) is then fed to the power switch to obtain MPPT under certain environmental conditions.
4 Results and discussions
Boost converter parameters
Actual value in SI units
4.1 Simulation studies
Individual solar PV panels value of Vmp, Imp, VDC, and IDC
Solar PV panel
4.2 Experimental studies
A 240 Wp solar panel DC optimizer distributed system has been modeled and experimentally verified to deliver the maximum power to the single-phase grid. A novel PI controller based Fractional Open Circuit Voltage (FOCV) algorithm to extract the maximum power effectively with a reduction in the current sensor has been discussed. The PI Controller based Fractional Open Circuit Voltage is tuned by the simple Ziegler Nichols method. The simulation and experimental results show that the overall system can operate at any environmental conditions. The maximum power point settles fast and this method avoids the current sensors used in the conventional MPPT method thus reducing the overall cost of DC optimizer based distributed system. It is found that the proposed controller is robust against the different environmental conditions.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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