SEPIC CONVERTER

SEPIC CONVERTER

PREPARED BY :-

Soni Divyangkumar R.

(160410707008)

PAPERS

PAPER-1: Fast Dynamic Response of SEPIC Converter based Photovoltaic DC motor drive for Water Pumping System .

AUTHORS (1)Vijayakumar Gali (2)V Amrutha P.B• 2016 International Conference on Circuit, Power and Computing Technologies [ICCPCT]

PAPER-2: Solar PV Array Fed Water Pumping System Using SEPIC Converter Based BLDC Motor Drive .

AUTHORS (1)Rajan Kumar (2)Bhim Singh

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PAPER-2: Solar PV Array Fed Water Pumping System Using SEPIC Converter Based BLDC Motor Drive .

Outline :• Abstract.• Introduction.• P&O MPPT algorithm. • Design of proposed topology.a. Electric Motor model.b. SEPIC Converter design.c. DC motor drives.• Simulation and results.• Conclusions

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ABSTRACT A Single-ended primary-inductor converter (SEPIC) converter designed for Photovoltaic water

pumping system. This type of model avoids use of extra converter and use of battery which reduces the cost of

whole system. Photovoltaic (PV) cell having non linear P-V characteristics, it varies with changing solar

radiation. Maximum power point tracking (MPPT) algorithms are used to track the peak power point,

which helps to improve the efficiency of the system. The MPPT algorithms are incorporated with DC-DC converter which helps to track the MPP of

PV cell. The Advantage of SEPIC converter is reduce the ripple at the output stage and also gives the

same polarity as input polarity, which feeds the DC motor, so that the motor runs smoothly without any jerking moments, therefore life the DC motor will be increased.

The proposed system is tested with different in solutions conditions by changing the solar radiation and observed the DC motor characteristics.

The P&O algorithm is used to track the MPP point according to changes in solar insolation and tested using MATLAB simulink model and observed all the results.

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INTRODUCTION Photovoltaic (PV) based ground water pumping system implemented for agriculture,

drinking water system for rural areas. SEPIC converter based DC motor drive analyzed and tested with MATLAB simulink

model.

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Fig.1 basic model of photovoltaic cell Fig.2P-V characteristics of PV cell

The MPPT algorithms are working based on tracking the MPP, and change the duty cycle of power electronic converter (DC-DC converter) to match the load impedance is equal to source impedance.

P&O MPPT ALGORTHM

The implementation of P&O algorithm is very simple, need voltage and current sensor.

The tracking performance is also good. A Good DC-DC converter makes the output of solar panel with ripple free. The Proposed system tested with SEPIC converter which makes voltage stable

drives the DC motor with stable speed Moreover it reduces the current ripples from the input side therefore reduces the

ripple in speed of motor drive.

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DESIGN OF PROPOSED TOPOLOGY.

• The Proposed topology is implemented by P&O MPPT algorithm and SEPIC Converter.

• The P&O algorithm tracks the MPPT while with changing with the solar in solution.

• The implementation of P&O is very simple. • The Complete proposed system is shown in Fig.3. The DC motor is used to drive

the centrifugal pump.

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Fig 3.Schematic diagram of proposed DC motor drive system

A. ELECTRIC MOTOR MODEL

The DC shunt motor is used for this model. Instead of using AC motor, it has been investigated that DC motor are very useful by directly coupling with PV generators (reduce the intermediate DC-AC converter for AC motors).

In this motor, the torque is proportional to armature current and back emf proportional to speed, for optimum utilization of solar panel; the operation should take place at the maximum power point.

These DC motor drives the centrifugal pump. The driving torque for centrifugal pump is proportional to the square of the rotational speed as given in equation.

TP=TL=KPω^2

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B. SEPIC CONVERTER DESIGN Single-ended primary-inductor converter (SEPIC) is a type of DC-DC converter

which can be step up the voltage or step down the voltage by changing duty cycle of the switch. The switch may be transistor or MOSFET. SEPIC converter output has the same polarity as input voltage unlike buck-boost converter.

Selection of Duty cycle is calculated by as follows by :

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Figure. 4 Schematic of SEPIC

C. DC MOTOR DRIVES. For getting good efficiency and performance uses dc shunt motor drive. It is

common type of dc motor drive used in all types of systems. The advantages of this motor is that linear characteristics of voltage & torque and has more constant and controllable speed over various loads, this type of motor runs with constant speed regardless of load condition, speed can be controlled by inserting resistance in series with armature or field circuit.

The main purpose of using dc motor in pv drive application is to eliminate extra converter therefore the amount of total system cost will be reduce.

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SPECIFICATION OF PROPOSED SYSTEM

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SIMULATION AND RESULTS.

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Fig.5 MATLAB simulink model of SEPIC Converter based PV water pumping system

SIMULATION AND RESULTS.

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Fig .8 MATLAB Simulink model results

SIMULATION AND RESULTS.

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CONCLUSIONS

The Proposed system is verified in MATLAB Simulink software under different insolation conditions by changing the solar radiation at 7sec in MATLAB simulink model.

The P&O MPPT algorithms which tracks the MPP point if the insolation changes. The Advantage of SEPIC Converter is to reduce the ripple contain . The SEPIC converter drives the DC motor smoothly and life of the DC motor will

increase. The dynamic performance of SEPIC converter based dc motor drive shows in

simulation that it achieved good dynamic response under fast solar variation condition.

These DC motor drives the centrifugal pump to draw water from the bore wells in rural areas and agricultural fields with low cost

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PAPER.2SOLAR PV ARRAY FED WATER PUMPING SYSTEM USING SEPIC CONVERTER BASED BLDC MOTOR DRIVE .

Outline :• Abstract • Introduction • Configuration of the Proposed System• Design of the Proposed System (A). Design of Solar PV Array (B). Design of SEPIC (C). Design of Centrifugal Pump • Control of the Proposed System (A). Maximum Power Point Tracking (B). Electronic Commutation of BLDC Motor• Results and Discussion • Conclusions

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ABSTRACT This paper deals with the application of a single ended primary inductor converter

(SEPIC) in solar photovoltaic (SPV) array fed water pumping system. A permanent magnet brushless DC (BLDC) motor is employed to drive a

centrifugal pump coupled to its shaft. Soft starting of the BLDC motor is achieved by controlling the SEPIC through the

incremental conductance maximum power point tracking (INC-MPPT) algorithm. The SEPIC possesses the merits :I. non-inverting polarity output voltageII. simple gate-drive circuit III. low input current pulsation The SEPIC, operating as a DC-DC buck-boost converter can increase or decrease

the input voltage level at its output. This property provides the flexibility of optimizing the operating point of the SPV

array at any voltage level.

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INTRODUCTION

Due to its output gain flexibility, SEPIC acts as a buck boost DC-DC converter providing non-inverting polarity output voltage, where it changes its output voltage according to its duty cycle.

Unlike the DC-DC buck and boost converter, the SEPIC has an unbounded maximum power point tracking (MPPT) region.

The SEPIC has the desirable feature of the switch control terminal being connected to ground; this simplifies the gate-drive circuitry.

Because of its non-inverting polarity output voltage, unlike the buck-boost and a Cuk DC-DC converter, the use of either splitting power supply or optocoupler and associated circuit for negative voltage feedback sensing, which added complexity and slowed down the response of the system, is eliminated.

The inductor at the input of the SEPIC reduces the input current pulsation resulting in a high precision of MPPT.

Aforesaid merits of the SEPIC, makes its integral characteristics suitable for the solar photovoltaic (SPV) array fed water pumping system.

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Aforesaid merits of the SEPIC, makes its integral characteristics suitable for the solar photovoltaic (SPV) array fed water pumping system.

The SEPIC has been used for MPPT in various SPV based applications such as PV chargers and standalone PV systems.

In view of cost and efficiency, the SEPIC is not used for high power applications. In this paper, a BLDC motor driven water pump fed by the SPV array-SEPIC is proposed.

The SEPIC is always operated in continuous conduction mode (CCM) to limit the voltage and current stresses on its power device and components.

Switching pulse for the IGBT (Insulated Gate Bipolar Transistor) switch of the SEPIC is generated by an incremental conductance (INC) MPPT algorithm used to operate the SPV array at its optimum operating point.

Similarly, the switching sequence for the VSI (Voltage Source Inverter) is generated by an electronic commutation of the BLDC motor.

A permanent magnet BLDC motor is selected because of its high efficiency, high reliability, low radio frequency interference, no maintenance and low inertia and friction.

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The starting current of the BLDC motor is controlled within the permissible limit so that the motor has soft starting.

The soft starting is achieved by selecting the value of increment size properly in the INC-MPPT algorithm.

The SPV array is so designed and the rating of the BLDC motor is selected such that the water can be pumped under all the possible variations in solar insolation level.

The starting, dynamic and steady state behavior of the proposed system under the change in atmospheric conditions are demonstrated through simulated results using Sim-powersystem toolboxes of the MATLB/Simulink environment.

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CONFIGURATION OF THE PROPOSED SYSTEM

The proposed system under study is shown in Fig. 1. The system consists of the SPV array followed by the SEPIC which feeds the VSI, supplying the BLDC motor coupled to a centrifugal type of water pump.

MPPT algorithm generates switching pulse for the switch of SEPIC whereas the electronic commutation generates the switching sequence for the switches of the VSI.

The Hall Effect signals provided by the encoder, mounted on the BLDC motor is logically converted into the 6 pulses for the 6 switches of the VSI.

The design and control of each stage of the configuration shown in Fig. 1 are elaborated in the following sections.

Fig.1. Configuration of the proposed SPV array-SEPIC fed BLDC motor driven water pumping system21

DESIGN OF THE PROPOSED SYSTEM

The proposed system comprises a solar PV array, a SEPIC, a VSI, a BLDC motor and a centrifugal water pump.

The solar PV array, the SEPIC and the centrifugal pump are designed as per the requirement of the proposed system.

Power ratings of the BLDC motor and the centrifugal pump are selected as 2.2 kW and 2 kW respectively.

On the basis of these selected ratings, each stage of the configuration shown in Fig. 1 is designed as described in the following section.

(A). DESIGN OF SOLAR PV ARRAY: The SPV array is designed for Pmpp = 2.73 kW peak power capacity. A PV module of 36 cells connected in series is designed to produce an open circuit

voltage of 13.32 V and short circuit current of 4 A. It is reported that the peak power generally occurs between 71% and 78% of open

circuit voltage and between 78% and 92% of short circuit current. Hence, the voltage of a module at MPP, Vm = 0.78*13.32 = 10.39 V the current of a module at MPP, Im = 0.8*4 = 3.2 A.

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Voltage of the SPV array at MPP is considered as, Vmpp = 114.4 V in view of the DC link voltage of the VSI, Vdc which is the output voltage of the SEPIC and the DC voltage rating of the BLDC motor.

The current of the SPV array at MPP, Impp = Pmpp/ Vmpp = 2730/114.4 = 23.86 A.

Numbers of modules required to connect in series are as, Ns = Vmpp/ Vm = 114.4/10.39 = 11….. (1) Numbers of modules required to connect in parallel are as, Np = Impp / Im = 23.86/3.2 = 7.46 ≈ 8 …..(2) Based on these estimated values of parameters, the solar PV array of required size

is designed.

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(B). DESIGN OF SEPIC When the optimum operating point is reached, vpv = Vmpp = 114.4 V ……(1) ipv = Impp = 23.86 A ……

(2) Same current flows through the input inductor

of the SEPIC, therefore, the current flowing through the input inductor is as, iL1 = ipv = 23.86 A.

Duty cycle, D of the SEPIC is estimated as

……(3) where Vdc is the average value of DC link

voltage of VSI. An average current flowing through the DC link, Idc is estimated as,

Idc= Pmpp/Vdc=2730/130=20.98A ......(4)Table i. Design of SEPIC Converter

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(C). DESIGN OF CENTRIFUGAL PUMP The characteristic of a centrifugal pump is expressed in terms of speed and torque

as . …..(5) TL is the rated load torque ωm is the rated mechanical speed of the rotor in rad/sec. Then the constant kω in Nm/(rad/sec)2 is estimated as,

This designed value of centrifugal water pump is selected for the proposed water pumping system.

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CONTROL OF THE PROPOSED SYSTEM

The control at the various stages of the proposed system is classified into two parts as follows.

1. Maximum Power Point Tracking.2. Electronic Commutation of BLDC Motor

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RESULTS AND DISCUSSION

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Performance of SPV array-SEPIC fed BLDC motor-pump system at 1000 W/m2, (a) Solar PV array variables.

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(b) SEPIC variables.

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(c) BLDC motor variables

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