A novel voltage lifting technique of switched-inductor cell based modified LUO converter topology for water pumping system

ABSTRACT


INTRODUCTION
Water has become more important than ever before as population growth has increased the demand for it.In rural areas, the significant energy source for lifting water from canals, rivers, ponds has become increasingly important in recent days [1].The stand-alone solar-PV operated water-pumping system has been widely installed in rural areas for irrigation, household and drinking purposes.It excludes the usage of traditional diesel-operated pumping systems because of increased oil prices in global markets, environmental implications, high maintenance cost, low efficiency, short life-time and forced to adopt new alternative [2].
The renewable energy sources (RES) have extensive potentiality to limit the severe causes coming from diesel-operated pumping system.Also, many researchers or engineers are highly focused towards the renewable energy driven pumping system [3].Globally, sincere efforts are being made to adopt renewable energy for social and economic growth.Among several renewable sources, solar-PV is the most promising and practical source for water-pumping applications that can be easily installed on a building's roof [4]- [6].The solar-PV powered water pumping system is established to be eco-friendly, more economical, more reliable with low maintenance factor, high life span it can produce 20% to 38% of more energy compared to traditional pumping system [7]- [9].The generalized block diagram of solar-PV powered water pumping system is shown in Figure 1.Generally, the solar-PV driven pumping system comprises of several components such as, solar-PV panel, front-end DC-DC converter, DC-AC inverter, AC electric motor, control unit, sensors, mechanical pump, storage unit and water outlet, so on.The available solar-PV energy is integrated to AC electric motor through power-electronic conversion interface, such interface comprises of DC-AC inverter followed by front-end DC-DC boost converter.The front-end DC-DC converter with high voltage boost capability is widely used in an energy conversion operation at voltage ranges from millivolts to kilovolts levels [10]- [13].
Generally, it converts low DC to high DC voltage by temporarily stored some energy in inductors or capacitors and delivers to load at higher levels.Some of prominent basic DC-DC converters are boost converter [14], CUK, SEPIC, LUO type converters [15] and so on.These basic DC-DC converters are inappropriate because, which are mostly functioned in high duty ratio's for producing higher voltage levels.In recent time, various DC-DC boost topologies have been explored to achieve higher voltage gain by modernization of basic DC-DC converter topology by including voltage multiplier or sub-module circuits.In this approach, features, technical analysis, merits and demerits of basic and modern DC-DC converter topologies for solar-PV powered water pumping system are presented in [16].
The main background of this work is from various literatures, Babaei and Mahmoodieh [17] proposed the design considerations of SEPIC converter for calculation of ripple factor in output-voltage under certain range of load resistance and input DC voltage.Varma and Ramkumar [18] proposes the novel modified nonisolated SEPIC converter for solar pumping system, it produces the high boost voltage without using any coupled inductors and coupled transformers.Tuvar and Ayalani [19] presents the technical analysis of interleaved non-isolated modified-CUK converter for high voltage gain application.Along with voltage gain, this converter reduces the ripple content and low settling time under load variations.Anbarasan et al. [20] proposes the solar-PV integrated grid connected system by using basic LUO converter topology.Most of researchers and practitioners are more interested on LUO converter due to simple operation, high voltage gain, compact structure, greater power density, high efficiency, reduced ripple content and inrush current.Pansare et al. [21] proposed the positive output modified LUO converter for solar-PV system.This modified LUO converter topology produces the high voltage gain, greater power capacity by utilizing the inductors and capacitors which are combined as sub-modules [21]- [23].
The above-studied converter topologies are not suited for this application due to several demerits such as requires more switching elements; it increases the dv/dt stress, complex design, high switching loss and reduced efficiency [24], [25].The major problem in conventional topologies are, coupled inductors, multi-winding transformers can be adopted but [26], it has high leakage inductance, owing to high current ripples, more complicated design and requires large number of windings for attaining high-voltage gain.The proposed solution, an inventive idea of modified LUO converter topology has been developed to overcome above demerits by employing switched-inductors for lifting the voltage gain at load terminals.In this regard, a novel switched-inductor type modified LUO converter (SI-MLUO) has been proposed for solar-PV powered water pumping system.The proposed SI-MLUO converter delivers the high voltage gain, simple structure, low leakage currents, low current ripples, reduced voltage spikes, low dv/dt stress and high efficiency over the several conventional DC-DC converters.The operation and performance of proposed SI-MLUO converter topology is verified by using MATLAB/Simulink tool, simulation results are validated with conventional topologies.
during mode-1 (Sa1 ON, ton=DT), the voltage induced and current flow in the switched inductors are formulated as: during mode-II, (Sa1 OFF, ton=(1-D)T), the voltage induced and current flow at load terminals are formulated as (5).
Based on switch-OFF period, the induced voltages are expressed as (6).
According to principle of volt-sec balance principle across the switched inductors La1 and La2 as expressed as (7).
Therefore, the relation for voltage gain ratio can be expressed as in (8).
The ( 8) can be simplified and the final voltage gain (VGCCM) is expressed in (9).

RESULTS AND DISCUSSION
The performance of proposed SI-MLUO converter topology is verified by using MATLAB/Simulink tool, simulation results are validated with conventional topologies.The MATLAB/Simulink design specifications of proposed SI-MLUO converter topology are illustrated in Table 1

Performance of proposed SI-MLUO converter topology
The simulation results of proposed SI-MLUO converter topology have been presented as shown in Figure 5 (see Appendix).The proposed SI-MLUO converter topology is energized with input DC voltage Vin1-65 V for charging the switched inductors to attain required voltage at load terminals as depicted in Figure 5(a).It delivers the required load voltage of 500 V with a load current of 2 A to drive the resistive load as shown in Figures 5(b) and 5(c).The switching pulses of switch Sa1 is given by switching frequency of 50 KHz as shown in Figure 5(d).The switched-inductors La1, La2 of SI cell are charged by switching the switch Sa1 through gatepulses, then the inductors are charged linearly in a positive-slope region with an average current iLa1, iLa2 of 0.59 A and voltage across inductor VLa1, VLa2 of 60 A as shown in Figures 5(e The voltage across diodes and diode currents of proposed SI-MLUO converter topology is shown in Figure 6 (see Appendix).In mode-I, the switch Sa1 is to be conducted, the voltage appeared across the switch is zero and maximum current flow during switch-ON of Sa1 of 21 A. Likewise, in mode-II, the switch Sa1 is to be non-conducted and then the zero current flow and some voltages are appeared across switch Sa1 during OFF-state i.e., 220 V as shown in Figures 6(a) and 6(b).In mode-I, the diodes Da1, Da2 are in forward bias and Da12 are in reverse-bias, thus the average current flow of diodes during these modes is 0.55 A, 0.55 A, 0.6 A, and some voltage is appeared across the diodes is -75 A, -75 A, and -60 A, respectively as shown in Figures 6(c) and 6(d).The diodes Da3 is in forward bias in mode-I and Da3 is in reverse-bias in mode-II, thus the average current flow through diode during these modes is 14 A, and voltage appeared across the diode is -220 A, respectively as shown in Figures 6(e) and 6(f).
The current and voltage across load-side capacitor/diodes of proposed SI-MLUO converter topology is shown in Figure 7 (see Appendix).The boost capacitor Ca1 is in forward bias during mode-I and reverse bias in mode-II, thus the average current flow through capacitor these modes are 14 A and voltage appeared across the diode is 64 A as shown in Figures 7(a) and 7(b).The diode DO is in reverse-bias during mode-I and DO is in forward-bias during mode-II, thus the average current flow through output diode during these modes is 2.7 A and the voltage appeared across diode during these modes is -220 V as shown in Figures 7(c) and 7(d).And also, the maximum current flow through output capacitor during these operating modes is 1.8A is shown in Figure 7(e).
The comparison of voltage gain (MCCM) vs duty ratio (D) in conventional and proposed SI-MLUO DC-DC boost converter topology is illustrated in Table 2.The proposed SI-MLUO converter topology produces high voltage gain over the various conventional basic and modified DC-DC converters.The comparison of semi-conductor devices and energy storage devices in conventional and proposed SI-MLUO converter topologies is illustrated in Table 3.The proposed SI-MLUO converter topology requires low semiconductor and energy storage devices over the various conventional basic and modified DC-DC converters.

Figure 1 .
Figure 1.Generalized block diagram of solar-PV powered water pumping system

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ISSN: 2252-8792Int J Appl Power Eng, Vol. 12, No. 4, December 2023: 416-428 4182.PROPOSED METHODThe proposed SI-MLUO converter is comes in non-isolated converter category; it transforms low voltage to high voltage and maintains constant DC voltage at load terminals.The proposed SI-MLUO converter is designed based on basic LUO converter, the main inductor in LUO converter is replaced with reduced rating of one switched-inductor cell.In fact, the switched-inductor cells reduce the leakage currents, low spikes at switches and have major advantages such as simple structure, high voltage gain in low duty ratio's, continuous input current, low dv/dt switch stress and high efficiency.The high voltage boosting capability of proposed SI-MLUO converter is attained by using low switching elements and SI cell, it may operate either in continuous or discontinuous conduction modes (CCM/DCM) with aero current function in DCM mode.In reality, the operation of SI-MLUO converter is more significant in CCM because of load reliance on voltage boost capability, high current ripples, more voltage spikes and low efficiency are the key issues faced in DCM operation.The schematic diagram of proposed SI-MLUO converter is shown in Figure 2. It consists of one MOSFET switch Sa1, one switched inductor cell named as SI cell-1, one boosting capacitor Ca1, one clamping diode Da3, one output capacitor Co and one output diode Do, respectively which energizes the resistive load Ro.The SI cell-1 comprises of two inductors named as La1, La2, three diodes named as Da1, Da2, and Da12, respectively.The proposed converter topology is generally powered by input DC voltage of Vin1 and produces high voltage gain and constant output voltage Vo at load terminals.The high voltage at load terminal is produced by energizing the respective inductors in SI cell and boost capacitor symmetrically through sequential switching of switch Sa1 by means of output diode Do and output capacitor Co in a certain manner.

Table 2 .
Comparison of voltage gain (MCCM) vs duty ratio (D) in conventional and proposed SI-MLUO DC-DC boost converters

Table 3 .
Comparison of semi-conductor devices and energy storage devices in conventional and proposed SI-MLUO DC-DC boost converters Int J Appl Power Eng, Vol. 12, No. 4, December 2023: 416-428