Performance Evaluation of Maximum Power
Point Tracking Algorithm with Boost DC-DC
Converter for Solar PV System
Ahteshamul Haque
Department ofElectricalEngineering Jamia Millia Islamia University, New Delhi-25
Abstract
Solar Energy is seen as the most reliable source among renewable energy sources (RES). Solar Photovoltaic (PV) is used to convert solar energy into unregulated electrical energy. Maximum Power Point Tracking (MPPT) algorithm is used to extract maximum power from solar PV. Power electronics DC – DC converter plays a very important role in implementing MPPT algorithm. The objective of this work is to analyze the working of MPPT technique with boost DC – DC converter. The simulation work is done by using PSIM simulation software.
Keywords: MPPT, Solar PV, Power Electronics, Boost Converter, PSIM
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I. INTRODUCTION
Energy Crisis and climate change threats leads the researchers to look for alternate sources of energy [1-3]. The world is virtually on the hunt of promising renewable and sustainable sources of energy. In recent years, renewable energy sources like solar, wind, tidal, have attracted the researchers, as it is limitless, non-pollutant and available free of cost. Solar energy is considered as the most reliable source among RES. Due to technological advancement in power electronics and reduction in the manufacturing cost of PV cell, solar energy is becoming more promising source of energy [4-8]. Solar PV exhibits nonlinear characteristics and its efficiency is also low. It becomes essential to extract maximum power from solar PV under all ambient conditions. MPPT (Maximum Power Point Tracking) algorithm is used to extract maximum power from solar PV [9-10]. The MPPT is implemented in the control circuit of Power electronics converters. A converter without MPPT system only regulates the output voltage of PV module, but it does not ensure that PV system is operating at the maximum power point MPP [11]. The operation of MPPT depends on the type of converter used [12-14]. In this paper a boost dc-dc converter is used and the performance of MPPT is evaluated.
II. SOLAR PV CHARACTERISTIC
Fig. 1: Equivalent model of PV Cell
PV cells are the basic element of solar PV system. Modules are formed using these modules. It is further expanded in the form of arrays as per the power requirements. These PV cells exhibit nonlinear characteristics. The output of the PV cell varies with solar irradiation and with ambient temperature. The equivalent circuit model of PV cell given in Fig (1). The characteristic equation of PV cell based on this model is given by equation 1, 2 and 3 [3].
I = Iph – Ios {exp [(q/AKT) (V + I Rs)] – 1} - (V +I*Rs)/Rp (1)
Ios = Ior exp [q EGO/ Bk ((1/Tr) – (1/T))] [T/Tr]3 (2)
Iph = S [Isc + KI (T- 25)]/100 (3)
Where I am the PV module output current, V is the PV cell output voltage, Rp is the parallel resistor, Rs is the series resistor.
Ios is the PV module reversal saturation current, A, B are ideality factors, T is temperature (oC), k is boltzmann’s constant, Iph is
the light-generated current, q is electronic charge, KI is short-circuit current temperature coefficient at ISC. S is solar irradiation
(W/m2), ISC is short-circuit current at 25oC and 1000 W/m2, EGO is bandgap energy for silicon, Tr is reference temperature and Ior
is saturation current at temperature Tr. The plot of solar PV output power is shown in Fig (2). It can be seen that the power and
current varies non-linearly with the variation in solar irradiation and with ambient temperature.
III. P&O MPPT TECHNIQUE
Perturb and observe (P&O) method is a MPPT scheme proposed by researchers. In perturb and observe method the perturbation is applied either in the reference voltage or in the reference current signal of the solar PV. The flow chart of the P&O method is shown in Fig 3. In this chart Y is shown as the reference signal. It could be either solar PV voltage or current. The main aim is to reach to the MPP. To achieve it the system operating point is changed by applying a small perturbation (∆Y) in solar PV reference signal. After each perturbation the power output is measured. If the value of power measured is more than the previous value then the perturbation in reference signal is continued in the same direction. At any point if the new value of solar PV power is measured less than the previous one then perturbation is to apply in the opposite direction. This process is continued till MPP is reached. In [8] the P&O method uses the solar PV panel current as a reference signal. The issue with this method is it becomes oscillatory around MPP. Table 1 gives the summary of P&O MPPT method.
Table - 1
Summary of the Perturb & Observe MPPT Method Perturbation Change in Power Next Perturbation
Positive Positive Positive Positive Negative Negative
Negative Positive Negative
Negative Negative Negative
IV. BOOST DC – DC CONVERTER
Fig. 4: Schemtaic of Boost DC – DC converter
Table – 2
Parameters of DC-DC BOOST Converter S.No. Name of the Parameter Values
1 Vin VMPP : when MPP is working
2 MOSFET 20A, 600V
3 DIODE 12A, 1000V
4 Lboost 1mH, 15A Saturation
5 Cboost 1000 uF
6 Vo Based on duty cycle expression
7 RLOAD Variable
8 Frequency 20 kHz
9 Power Output 40W
The schematic of boost converter is shown in Fig. 4. The specifications of components are shown in Table I. The boost converter is designed to work in continuous conduction mode. The relationship between boost converter input and output is given by:
Vo = Vin/ (1-D) (4)
V. MPPT WITH BOOST DC-DC CONVERTER
Fig. 5: Block Diagram of Boost DC – DC converter
Fig. 7: Rin Vs Duty Cycle
Rin = Ro (1-D2) (5)
The block diagram of boost dc-dc converter with MPPT is shown in Fig. 5. The MPP zone for boost converter is shown in Fig. 6. The variation of input impedance with duty cycle is shown in Fig. 7. Equation 5 is the relationship between input and out impedances with duty cycle. The MPPT will be working with boost converter between B and C in Fig. 6, where Rload >> RMPP.
The MPPT will not be working between A and B. These zones are decided by equation 5.
VI. RESULT AND DISCUSSION
Fig. 8: MPP Working for BOOST Converter when RLOAD > RMPP.
Fig. 9: MPP Failed for BOOST Converter when RLOAD < RMPP.
0 10 20 30 40
Pmax (W)
0.05 0.1 0.15 0.2
Time (s) 10
20 30 40
Po (W)
34 36 38 40 42 44
Pmax (W)
0.05 0.1 0.15 0.2
Time (s) 0
5 10 15 20
Fig. 8 and 9 are simulation results. Fig. 8 shows that MPPT is working RLOAD > RMPP. The maximum PV power and Load
power is almost same. Fig. 9 shows that MPPT is failed when RLOAD < RMPP. The power is much lower than MPP power of solar
PV. These results shows that entire PV characteristic cannot be MPPT working zone with boost DC – DC converter.
VII.CONCLUSION
The main objective of the paper is to evaluate the performance of MPPT with boost DC – DC converter in terms of MPPT working zone. The MPPT with boost dc-dc converter is analyzed and simulation results are presented. It is evident that MPPT is not function in the entire zone of PV characteristic curve.
ACKNOWLEDGEMENT
The research work of this paper is done by using the instruments purchased under MNRE R&D project sanctioned.
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