Multi inputs and single output DC-DC Converter for Renewable Energy Resources

Multi inputs and single output DC-DC Converter for Renewable Energy Resources

Sathish Kumar S, Vinoth Kumar S, Marutha Muthu M, Soundar A, Kumaresan A.

Department of Electrical and Electronics Engineering, Gnanamani College of Technology, Namakkal-637018, India

Abstract A dual DC input power supply for high output efficiency DC-DC converter is developed. The proposed converter can boost the varied voltages of different power supply in the sense of hybrid power supply to obtain a stable output dc voltage for the load demand. Based on the varied situations the operational mode of the proposed converter can be divided into two modes including a single power supply mode and dual power supply mode .In dual power supply state the input circuits are connected in series get added together with the designed pulse width modulation can greatly reduce the conduction loss of the switches. Single mode power supply will operate whenever it is capable to meet the load demand, when it cannot meet the load demand then dual power supply mode will operate

.The proposed high efficiency DC-DC converter with dual input power supply greatly reduces the conduction and switching losses in the system. This topology is developed to cope with the demerits of large size

,complex topology, and expensive cost in conventional converter with single power supply mode. MATLAB has been used to make the model and simulate the system and PI controller is used.

Keywords DC-DC Converter, hybrid power supply

I.INTRODUCTION

One of the major concern of power generation sector is day to day increasing power demand

.Based on the current scenario all over the world especially India has lot of power shortage issues. The power developed from the fossil fuels are becoming so less as it degrade the environment and getting depleted day by day. So now days we are looking forward for the power generation from renewable energies like solar, wind, biomass, tidal etc which does not create any pollution to the environment. At present stand-alone solar PV system has been promoted around this global level on comparatively larger scale but this independent system cannot provide continuous energy as they are seasonal hence hybrid systems come into play. As the solar radiation varies throughout the day, the power generated also varies. Maximum power point trackers (MPPTs) play an important role because they maximize the power output for a set of conditions, and therefore maximize the efficiency generation from renewable energies like solar, wind, biomass, tidal etc which does not create any pollution to the environment. The use of renewable energy is helping the environment to reduce the global warming effect. In rural areas or remote areas where grid cant supply

the power there we can use this proposed dual input power source to meet the load demand.. The input impedance of the DC-DC converter is matched with the optimum impedance of PV panel. This method has good performance under MATLAB. R. J. Wai,.et.al [1] From this paper based on the environmental concern and the energy status, the developed electrical power may be insufficient to drive the load. To have the continuous power supply, we use hybrid power supply by using different kinds of sources. Those sources can be capacitor, fuel cell, rechargeable battery or best source renewable energies..

When the multi inputs are used in DC-DC converter simultaneous power will be delivered from all the sources which is not required at all the time, hence it increases complexity and cost of the system. As well the system design requires an enlarged storage equipment independently. Savita Nema,et.al[3] This paper helped in studying and modelling the PV panel using PV cell circuit model. Where the PV cell is been derived from the PN junction and it reflects the characteristics of the cell. In this paper we have come to know that how the conduction loss is been reduced across the switch, how the efficiency of the system is improved, Much more than the hard switching converter.

1. BLOCK DIAGRAM

   Figure: 1- block diagram.

   This block diagram shows the way in which the dual

   Mode 1 [t0

   ICONNECT – 2017 Conference Proceedings

   La

   input is fed to the boost converter. Solar and AC supply are the two input sources used here, these two sources are fed together to a boost converter to power the load based on load demand, so that the load demand is satisfied continuously.

   Hence to know the changes in load demand a feedback loop i.e PI controller is used.This feed back loop from the load is taken and given to the secondary input that is to the AC supply, so that whenever the load demand is not satisfied by solar then the AC supply will be added up to the solar supply to meet the load demand.

2. CIRCUIT DIAGRAM

Figre:2- Equivalent Circuit of High Efficiency DC-DC Converter with Dual Input Power Sources

Single Mode Power supply

In this mode only one switch will be turned ON/OFF at a time to meet the load demand. The duty cycle for one switch will be 50% so that in the given 25khz frequency 50% will be the on time & remaining off time.

t1 ]: At t0 , the auxiliary inductor current i

returned to zero. The switch S1 is continuously conducted and the auxiliary switch Sa is still turned OFF. The primary inductor L1 is linearly charged by the primary input voltage V1. The auxiliary switch voltage vSa is equal to the auxiliary capacitor

voltage Va .

Mode 2 [t1 t2 ]: At t1 , the switch S1 is turned OFF, the switch voltage vS1 is rising to the auxiliary capacitor voltage Va , and the auxiliary switch voltage vSa is decreasing to zero. The body diode of the auxiliary switch Sa is conducted for receiving the

primary inductor current iL1 to charge the auxiliary capacitor. Therefore, the switch current iSa is negative. Besides, the auxiliary inductor current linearly increases, and its slope is dependent on the auxiliary inductor voltage

vLa, which is equal to Va Vo . Continuously, the primary auxiliary diode Da1 is

conducted.

Mode 3 [t2 t3 ]: At t2 , the auxiliary switch Sa is turned ON with ZVS because the body diode has been already conducted for carrying the primary inductor current iL1 . After the auxiliary inductor current iLa increases to be larger than the primary inductor current iL1 , the auxiliary switch current iSa becomes positive. The discharging current from the auxiliary capacitor together with the primary inductor current iL1 releases the stored energy to the output voltage Vo .

Mode 4 [t3 t4 ]: At t3 , the auxiliary switch Sa is turned OFF. Because the auxiliary inductor current iLa is greater than the primary inductor current iL1 , the parasitic capacitor of the auxiliary switch Sa is charged by the auxiliary inductor current iLa so that the auxiliary switch voltage vSa rises. At the same time, the energy stored in the parasitic capacitor of the switch S1 will release to the output voltage Vo via the inductor current iLa so that the switch voltage vS1 decreases.

Fig-3; Topology modes in single mode power supply

The switch current iSa falls down to zero and the switch voltage vSa rises to the auxiliary capacitor voltage Va . The body diode of the switch S1 is conducted for carrying the differential current without strain. Besides, the auxiliary

inductor voltage vLa is equal to Vo, and the current iLa

linearly decreases.The energy stored in the auxiliary inductor La starts to discharge into the output voltage Vo as freewheeling.

Mode 5 [t4 t5 ]: At t4 , the switch S1 is turned ON wth ZVS upon the condition that the auxiliary inductor current iLa is still larger than the primary inductor current iL1 . The auxiliary inductor current iLa continuously decreases with

the slope Vo/La . After the current iLa is smaller than the

primary inductor current iL1 , the switch current iS1 is positive.

Mode 6 [t5 t6 ]: At t5 , the auxiliary inductor current iLa is equal to zero. In this mode, the parasitic capacitor of the primary auxiliary diode Da1 is charged by the output voltage Vo with a small reverse-recovery current.

Mode 7 [t6 t7 ]: At t6 , the diode voltage vDa1 is rising to the output voltage Vo , the secondary auxiliary diode Da2 is conducted for receiving the auxiliary inductor current iLa to charge the auxiliary capacitor voltage Va , and then the auxiliary inductor current iLa returns to zero. In the single power-supply state with the primary input power, the switch SP 2 is always turned OFF and the switch S2 is triggered all the while. It means that the switch S2 works as a synchronous rectifier for avoiding the current to flow through its body diode and reducing the power losses in modes 27.

Dual Mode Power Supply

When the proposed converter is operated in the dual power supply state with two input power sources, it can be taken as a superposition process of the primary and secondary input circuits. In this state, the summation of duty cycles d1 and d2 should be greater than 1, i.e., each of duty cycles d1 and d2 is securely greater than 0.5. Moreover, the symbols da1 and da2 denote the first and the second duty cycles of the switch Sa , respectively. ddcm1 and ddcm2 present the first and the second duty cycles of the freewheeling times of the auxiliary inductor. In this mode both the switch will be conducting that is switch S1 and S2 and at the same time the auxiliary switch Sa will be turned off, as the auxiliary inductor current will return to zero, where as the inductor current l1 and l2 increases or charged by the input voltages v1 and v2, the dual input voltage source will operate together and flows through the diode, as the auxiliary switch is switched off the current does not flow through the switch hence current across to it is zero.

The proposed converter is operated in this dual power supply state with dual input power sources, it is considered as superposition of both the input source that is been conducting, only because of this mode of operation the efficiency of the system is increased as the output voltage obtained is more stable .This mode is only highlighted in this project, and the entire concept used in this project is based on this dual power supply mode.

Fig-4. Equivalent Circuit of High Efficiency DC-DC Converter with Primary Input as Power Source

Mode 1 [t0 t1 ]: At t0 , the auxiliary inductor current iLa returned to zero. The switches S1 and S2 are continuously conducted. The auxiliary switch Sa is still turned OFF. The inductors L1 and L2 are linearly charged by the input voltages V1 and V2 , respectively.

Mode 2 [t1 t2 ]: At t1 , the switch S2 is turned OFF, the switch voltage vS2 is rising to the auxiliary capacitor voltage Va , and the auxiliary switch voltage vSa is decreasing to zero. The body diode of the auxiliary switch Sa is conducted for receiving the secondary inductor current iL2 to charge the auxiliary capacitor.

Therefore, the switch current iSa is negative. Besides, the auxiliary inductor current iLa linearly increases, and the slope is dependent on the auxiliary inductor voltage vLa,

which is equal to Va Vo . Continuously, the primary auxiliary diode Da1 is conducted.

Mode 3 [t2 t3 ]: At t2 , the auxiliary switch Sa is turned ON with ZVS. After the auxiliary inductor current iLa increases to be larger than the secondary inductor current iL2 , the auxiliary switch current iSa becomes positive. The discharging current from the auxiliary capacitor together with the secondary inductor current iL2 releases the stored energy to the output voltage Vo .

Mode 4 [t3 t4 ]: At t3 , the auxiliary switch Sa is turned OFF. Because the auxiliary inductor current iLa is greater than the secondary inductor current iL2 , the parasitic capacitor of the auxiliary switch Sa is charged by the auxiliary inductor current iLa, and the auxiliary switch voltage vSa rises. At the same time, the energy stored in the parasitic capacitor of the switch S2 will release to the output voltage Vo via the inductor current iLa, and the switch voltage vS2 decreases. The switch current iSa falls down to zero and the switch voltage vSa rises to the auxiliary capacitor voltage Va . The body diode of the switch S2 is conducted for carrying the differential current without strain. Besides, the auxiliary

inductor voltage vLa is equal to Vo , and the current iLa

linearly decreases. The energy stored in the auxiliary

inductor La starts to discharge into the output voltage Vo

as freewheeling.

Fig-5.Topological modes in dual power-supply state.

Mode 5 [t4 t5 ]: At t5 , the switch S2 is turned ON with ZVS upon the condition that the auxiliary inductor current iLa is still larger than the secondary inductor current iL2 . The auxiliary inductor current iLa

continuously decreases with the slope Vo/La . After the

current iLa is smaller than the secondary inductor current iL2 , the switch current iS2 is positive. By the same way, the switch current iS1 becomes positive as well as iS2 .

Mode 6 [t5 t6 ]: At t5 , the auxiliary inductor current iLa is equal to zero. In this mode, the parasitic capacitor of the primary diode Da1 is charged by the output voltage Vo with a small reverse-recovery current.

Mode 7 [t6 t7 ]: At t6 , the diode voltage vDa1 is rising to the output voltage Vo , the secondary auxiliary diode Da2 is conducted for receiving the auxiliary inductor current iLa to charge the auxiliary capacitor.

Mode 11 [t10t11]: At t10, the auxiliary switch Sa is turned OFF. Because the auxiliary inductor current iLa is greater than the primary inductor current iL1 , the parasitic capacitor of the auxiliary switch Sa is charged by the auxiliary inductor current iLa.At the same time, the energy stored in the parasitic capacitor of the switch S1 will release to the output voltage Vo via the inductor current iLa. The switch current iSa falls down to zero and the switch voltage vSa rises to the auxiliary

Mode 8 [t7 t8 ]: At t7 , the auxiliary inductor current iLa returns to zero. The switches S1 and S2 are continuously conducted. Mode 8 is similar to mode 1.

Mode 9 [t8 t9 ]: At t8 , the switch S1 is turned OFF, the switch voltage vS1 is rising to the auxiliary capacitor voltage Va , and the auxiliary switch voltage vSa is decreasing to zero. The body diode of the auxiliary switch Sa is conducted for carrying the primary inductor current iL1 to charge the auxiliary capacitor. The auxiliary inductor current iLa linearly increases with the

slope (Va Vo )/La . Continuously, the primary auxiliary diode Da1 is conducted.

Mode 10 [t9 t10]: At t9 , the auxiliary switch Sa is turned ON with ZVS. After the auxiliary inductor current iLa increases to be larger than the primary inductor current iL1 , the auxiliary switch current iSa becomes positive. The discharging current from the auxiliary capacitor together with the primary inductor current iL1 releases the stored energy to the output voltage Vo .

capacitor voltage Va . Similar to mode 4, both the switches currents iS1 and iS2 are negative. The energy stored in the auxiliary inductor La starts to discharge into the output voltage Vo as freewheeling.

Mode 12 [t11t12]: At t11, the switch S1 is turned ON with ZVS. The auxiliary inductor current iLa

continuously decreases with the slope Vo/La . After

the current iLa is smaller than the primary inductor current

iL1 , the switch current iS1 is positive. By the same way, the switch current iS2 becomes positive as well as iS1 .

III. EXPERIMENTAL RESULTS

The proposed topology canbe used to specific target applications for the high-voltage dc bus of an uninterruptible power supply or an inverter. The proposed converter can manipulate the high-efficiency power conversion with more than one input power source simultaneously to cope with the disadvantages of large size, complex topology, and expensive cost in conventional converter structure for individual power source.

For an example of a hybrid PCS composed of two input power sources with an FC and a battery module, it has the following several merits: 1) it can manage the input power sources and improve system efficiency; 2) during the start of the system, the battery module powers the load to ensure that the FC cold starts easily; 3) when the load steps up, the battery module can provide the insufficient energy if the FC cannot respond quickly so

that the dynamic characteristics of the entire system The minimum duty cycle dm in is designed to 0.55 slightly

higher than a half of 1, and the maximum duty cycle dm a x is

designed to 0.83 for avoiding the lack of freewheeling time of the auxiliary inductor operating in DCM. According to the relation between input voltages and duty cycles in (31), the two input voltages should be in the same level. Therefore, the voltage range of another power supply is chosen as 120170V for mimicking a battery module taken as the secondary power source with a maximum power of 2.5 kW. The proposed converter can boost the varied voltages of different power sources in the sense of hybrid power supply to a stable output dc voltage for the load demand.

By considering the later inverter applications with 220

Vac , the desired output dc voltage is set at 360 V and the maximum power of this converter proto-type is 5 kW in this study. Two magnetic contactors (S-P50T), manufactured by

can be improved; and 4) the battery module can provide the FC can be decreased and the total cost of the whole system can be reduced.

In order to verify the effectiveness of the proposed ZVS dual-input converter, the corresponding experimental results are pro-vided in this section. A power supply is used to emulate an FC taken as the primary power source with a maximum power of 2.5 kW, and the input voltage range is 120170 V. Note that the

summation of duty cycles d1 and d 2 should be greater than 1 for regular operation in the dual power-supply

state. Thus, each of duty cycles d1 and d2 should be bounded from a minimum value dm in to a maximum value dm a x .

Shihlin Company, are used to switch the power supply situation between the single power-supply state and the dual power- supply state in the proposed converter.

CONCLUSION

A solarAC hybrid generation system was proposed and implemented. This stand-alone hybrid generation system could effectively extract the maximum power from the solar energy sources .The proposed converter supplies continuous power to the load demand and greatly reduces the conduction and switching losses in the system. The simulation model of the proposed hybrid system is been developed using MATLAB/Simulink. Simulation results showed that the used PI controller could control the second switch properly so as to meet the load demand satisfactorily.

REFERENCES

1. T.Bhattacharya.T, V. S. Giri, K. Mathew, and L.Umanand, Multiphase bidirectional fly back converter topology for hybrid electric vehicles, IEEE Trans. Ind. Electron., vol. 56, no. 1, pp. 7884, Jan. 2009

2. Kwasinski.A, Identification of feasible topologies for multiple-input DCDC converters, IEEE Trans. Power Electron., vol. 24, no. 3,pp. 856861, Mar. 2009.

3. Savita Nema, R.K.Nema, Gayatri Matlab / simulink

based study of photovoltaic cells / modules / array and their experimental verification Volume 1, Issue 3, 2010 pp.487-500.