10-04-2015, 01:46 PM
Implementation of super lift luo converter with mppt and voltage balancing control for photovoltaic-fed converter
Mrs.P.Kalaiselvi1 Mrs.K.V.Dhamaraiselvi2
Email id : kalaiselvi9894[at]gmail.com: Dhamaraieee[at]velsuniv.org
Department of EEE, Vels university school of engineering, Chennai, India
ABSTRACT
In the existing system photovoltaic converter fed system , photovoltaic voltage and current Need to be sensed to execute maximum Power point tracking (MPPT) control. For the proposed system using super lift luo converter, to achieve MPPT control , both the capacitor voltages need to be sensed and an additional voltage balancing control loop is required to balance the capacitor voltages.The positive output elementary super lift Luo converter is a new series of DC-DC converters possessing high-voltage transfer gain, high power density, high efficiency , reduced ripple Voltage and current. These converters are widely used in computer peripheral equipment , industrial applications and switch mode power supply , especially for high voltage-voltage projects. In this project, the voltage balancing Control is obtained by Sensing only the inductor current
KEYWORD: Maximum power point tracking, voltage balancing control loop, Super lift luo converter
I.INTRODUCTION
Solar Energy is the ultimate sources of energy, which is naturally replenished in a short time period of time, this is called “Renewable Energy” or “Sustainable Energy” Thus the efficiency of solar cells mainly depends on many factors such as temperature, insolation, direct sunlight, and so on. That ambient temperature can reduce the photovoltaic (PV) array output power. In addressing the poor efficiency of PV systems, among many methods is proposed, among which is a new concept called Maximum power point tracking .MPPT works , let assume your battery is low at 12 volts.,A MPPT takes that 17.6 volts at 7.4 Amps and converts it down, so that what the battery gets now 10.8 amps at 12 volts now you still have almost 130 watts and everyone is happy.
The super lift luo converter have the advantages of high-voltage transfer gain ,high power density, high efficiency, reduced ripple voltage and current. These converters are most widely used in computer peripheral equipment, industrial applications and switch mode power supply, especially for high voltage-voltage projects. In this project, the voltage the voltage balancing control is obtained by sensing only inductor current.
The PV-fed converter, sensing both PV current and voltage is required to achieve the maximum power point tracking (MPPT) control. Additionally, for super lift luo-type converter, sensing additional capacitor voltages is also required to detect the voltage imbalance and force both capacitor voltages to be balanced.
To overcome the voltage imbalance in the output side we execute the method of using voltage balancing control loop this is the proposed technique in this project. This means that sensing only PV current (ie., the inductor current) is able to achieve both MPPT function and the voltage balancing function. Finally both the MPPT and voltage balancing control can be achieved only by the use of proposed sampling system (ie.,by sampling the inductor current values . And so the simulation and experimental results are provided to verify the proposed method.
II.SUPER LIFT LUO CONVERTER
Luo Converters
Luo converters are new series of DC/DC converters developed by Fang Lin Luo. They are made of a simple structure and cheap topology. Luo claims
That these converters have superior performance in terms of high voltage gain and minimum output ripple. The converters are developed based on two techniques, the voltage-lift technique and the super-lift technique. Luo converters are primarily used to step-up (boost) DC voltage but some circuits (such as the voltage Luo converters are primarily used to step-up (boost) DC voltage but some circuits (such as the voltage-lift elementary) can also be used to step-down voltage, similar to the buck-boost converter. In existing system three level boost type converter is used to over come the number of switches we prefer super lift luo converter. Because switching stress loss is mainly reduced.
(fig.1 proposed circuit of super lift luo converter with MPPT and voltage balancing control loop)
The super-lift technique is a major breakthrough in DC/DC conversion. . Compared with the voltage-lift technique, its voltage transfer gain is much larger. The super-lift technique implements an output voltage increasing in geometric progression. This means that with the addition of the nth stage, the gain of the converter is equal to the super-lift elementary circuit raised to the nth power. The super lift luo converter have the advantages of high-voltage transfer gain , high power density, high efficiency, reduced ripple voltage and current. These converters are most widely used in computer peripheral equipment, industrial applications and switch mode power supply, especially for high voltage-voltage projects.
A. Modes operation:
Fig . 2 proposed circuit of super lift luo converter when the switch is ON.
Mode:1 When the switch is ON the inductor L1 is connected across the supply with C1 in parallel is charged. Then C1 will get discharge so the D1, D2 will not conduct.
Fig .3 2 proposed circuit of super lift luo converter when the switch is OFF.
Mode:2 When the switch turns off, current across the L1 start decreasing at same time voltage across the C1 increases and the diode D1 and D2 starts conducting and C2 maintains the output filter. It is done during the continu-ous conduction mode.
B. Super-Lift Technique
Geometric Progression:
The main advantage of the super-lift converters is their ability to reach very high gains using geometric progression .The voltage transfer gain
duty ratio and the average inductor current value is follow
Since the average inductor current value is
is therefore obtained by the proposed sampling method PPV can be rewritten as
Hence the DC- bus voltage Vdc is well regulated,
Gain for the Super-Lift elementary circuit with n additional stages Study of the above formulae shows the high gains that are possible with multiple stage super-lift converters, this is because n is a power (instead as in voltage-lift where n is a multiple). For this reason the super-lift technique is very powerful and if implemented correctly could be applied to many industry applications.
III.PROPOSED MPPT AND VOLTAGE BALANCING CONTROL LOOP
MPPT or Maximum power point tracking is algorithm that included in charge controllers used for extracting maximum available power from PV module under certain conditions. The voltage at which PV module can produce maximum power is called ‘maximum power point’ (or peak power voltage).and this is the major principle of MPPT. Maximum power varies with solar radiation, ambient temperature and solar cell temperature etc. Then MPPT checks output of PV module compares it to battery voltage then fixes what is the best power that PV module can produce to charge the battery and converts it to the best voltage to get maximum current into battery. It can also supply power to a DC load, which is connected directly to the battery. Now in this project MPPT with sensing only inductor current is done.
Let the PV power Ppv is the product of the PV and the PV voltage VPV..NOW if we are neglecting the power loss of the Super Lift Luo converter, then the PV power can also be expressed as the product of the dc-bus voltage Vdc and the average bus cur-rent ( Idc)TS within the switching period Ts
But in the Super lift Luo converter, the average bus current is equal to the product of the
The PV power PPV is directly proportional to the product of the average inductor current IL and the duty ratio Then the proposed MPPT with sensing only inductor current method is done by perturbation and observation method.
After changes in the duty ratio as per the signals , the sampling of inductor current and their new products are calculated (ie new product
Here from the above equation two comparisons are done. The former comparison is between the latest product and the previous product and then the comparisons in done be-tween the duty ratio and the previous duty ratio .
Consider one of the case as and also the duty ratio should keep increasing to move to maximum power point and the new control signal is obtained by adding a constant to the control signal simultaneously the duty ratio should also increase to move to the maximum power point and also same as for the case of and .
All the above equation is for MPPT for sensing only inductor current and additionally voltage bal-ancing control loop is required to detect voltage imbalance in the output side and also to maintain constant output voltage
Fig .4 Algorithm of Proposed MPPT with sens-ing only inductor current.
FIG.4
IV .SIMULATION RESULT
The main purpose of Simulation is that the discipline of designing a model of an actual or theoretical physical system executing the model on a digital computer, and analysing the execution output. There are many methods of modelling systems which do not involve simulation but which involve the solution of a closed-form system (such as a system of linear equations). Simulation is often essential in the following cases: 1) the model is very complex with many variables and interacting components , 2) the underlying variables relationships are non-linear; 3) the model contains random variants; 4) the model output is to be visual as in a 3D computer animation. The software used for simulation is MATLAB .There are many components like PV module, proposed MPPT with sensing only inductor current, voltage balancing control loop and Super Lift Luo converter.
Fig .5 Simulation model of proposed circuit
Fig.5
Fig .6 Simulation of proposed circuit of super lift luo converter with MPPT sensing only inductor current and voltage balancing control.
Fig. 6
After using the proposed MPPT with sensing only inductor current and also the voltage balancing control ,the output voltage can be seen, since by giving 12 volts of input and the output can be increased by three times than the input ,now the output voltage is 60 volts. In this proposed project the switching loss is reduced compare with the existing system and main advantages are high voltage transfer gain, reduced ripple voltage and high efficiency.
The simulation of output voltage is shown in fig 7
Fig.7voltage vs Time
The simulation of output current with sensing only inductor current is shown in fig .8
Fig .8 current vs Time
Finally the output voltage and output current can seen by the simulation diagrams.
V. CONCLUSION
This paper represents the performance of proposed MPPT with sensing only inductor current and voltage balancing control loop with the Super lift luo converter which mainly reduces the sensor count and reduces the switching losses ,high voltage transfer gain is obtained and voltage imbalance is detected by using voltage balancing control in output side. The converter can execute maximum power from the PV panel for a given temperature and insolation by increasing the duty ratio the output voltage can also be increased. In future development it can be extended by converting DC-DC output to AC by connecting an inverter which can used for high voltage industrial purpose.
REFERENCES
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3. K.RAMASH KUMAR, S. JEEVANANTHAN, “PI CONTROL FOR POSITIVE OUTPUT ELEMENTARY OF SUPER LIFT LUO CONVERTER.WORLD ACADEMY OF SCIENCE ENGINEERING AND TECNOLOGY VOL.4 2010-03-23
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