Analysis of Dual Phase Dual Stage Boost Converter for Photovoltaic Applications

In the previous two decades, the depletion of fossil fuels has led to applications with renewable energy sources. The approach for renewable energy application is to achieve eminent static boost ratio from with miniaturized ripple content in both current and voltage. The novel converter discussed in this paper is derived by combining the concept of interleaving and cascading of boost converters. The presented design has a dual phase boost converter followed by a stage of boost converter which as a whole acts like dual phase dual stage boost converter. The interleaving concept is utilized in dual phase boost converter to reduce the voltage current stress created in boosting process and its output is boosted by the dual stage boost converter which improves overall efficiency with respect to the existing systems. The converter is designed for a power rating of 200W with output voltage of 192V for an input voltage of 12V obtained from photovoltaic source at a switching frequency of 50KHz this illustrate the advantages over other existing converters . The different parameters of the proposed boost converter are contrasted with that of a conventional boost converter. Furthermore, the simulations results of the proposed converter are presented to validate the system design. The results exhibit that this converter achieves a predominant performance over other dc-dc boost converters by offering improved efficiency and voltage gain, while having lower input current ripple.


I. INTRODUCTION
The demand for electricity is getting expanded day by day. Electricity generation by non-renewable energy sources is facing the issue of its limited availability and its heavy expenditure [1]. The way to deal with the demand is by extracting more energy within the available ones and by shifting to renewable sources of energy [2]. The spontaneously restored renewable energy sources such as sunlight, wind, tides can be utilized forever .Solar energy is considered as the ultimate resource as it is a costless neverending energy source which is enormously accessible across the globe [3].For the sake of attaining large voltage level at output the series arrangement of solar photovoltaic cell or arrays is not viable. DC-DC converters with high boost ratio are crucial to generate large level of output from solar photovoltaic [4], [5].
The conventional DC voltage boost converter is a critical power converter in the electronics domain, and has been utilized broadly in many industrial, automotive, commercial and numerous modern battery powered applications. Now a day there is a huge interest for outstanding efficiency, high stationary gain, minute size and low-cost DC chopper. However, the conventional DC chopper converter is a solution towards a DC voltage step up but needs to manage with issues of high ripple currents, high power dissipation and non-isolation. Another option is to use flyback converter. Though flyback converter gives isolations but uses transformer for achieving high gain which makes the converter bulky [6].
The flaws in isolated converters can be handled by implementing multilevel DC-DC converters [7]. Conjoining non-isolated with voltage multiplier gives high voltage boost ratio in the multilevel DC-DC converters. The step-up ratio of voltage in dc choppers with many levels relies on the count of levels at the output. In this way with a specific end goal to accomplish high voltage pick up, levels in the output must be expanded and it will build its unpredictability [8].
In the last couple of years, research attention has been diverted towards the development of high voltage converters with less percentage of duty cycle ratio by cascading more than one conventional boost converters. The Cascading causes in higher ripple content at the output voltage and current. To overcome the problem of ripple content in voltages and current due to switching a method is to interleave more than one converter [9]. The ripple frequency has surged up by cause of interleaving in multi-phasing following cut down of the filter dimensions. Specifically, the dc-dc converters utilizing interleaved concept [10] has the upper hand because of cutback in ripple content of inductor current and output voltage. Interleaved boost converter using Silicon Carbide (SiC) power switches offers higher switching frequency with reduced losses and restricts the maximum dv/dt ratio [11]. Control over the current sharing between the phases can be achieved by utilizing digital pulse width modulation Techniques [12].
Cascading the input voltages of buck converter in series and paralleling their output was the method proposed by Leong et al. [13]. The analysis and design of a dc step up converter with low current stress by integrating the concepts of multi-phase and multi-stage scheme was presented by Retana et al. [14].
The proposed dual phase dual stage converter will provide rise of step up gain with the help of dual stage boost converter with reduced current and voltage stress benefitted by the interleaving of dual phase boost converter.

1)
Circuit Description and Operational Analysis of Dual Phase Boost Converter: The dual-phase boost converter can be built by paralleling one more leg to conventional boost converter as shown in Fig. 1.  Fig. 2 exhibits a 180-degree phase shift between the triggering of switches to provide interleaving in dual phase boost converter. Reduced ripple content and doubling in frequency occurs due to elimination in ripple among the different phases [15]. The output to input ratio of dual-phase boost converter and conventional boost converter are identical.
2) Design Consideration of Dual Phase Boost Converter: The conventional boost converter is designed first. With the same obtained values of inductor and capacitor one more leg is connected parallel to the conventional boost converter to construct the dual phase boost converter. For the following specifications the conventional boost converter equations are presented. Output Power( ) =200W The static gain of the conventional boost converter is expressed as: where is the switching duty cycle. Therefore, for above given parameters switching duty cycle [16] is calculated as = The Equivalent load is calculated as: The inductor current is given by, Considering 40% peak to peak ripple, ripple current * _"ℎ#$% = 6.67( The inductor value is given by where T is the switching period. Considering 4% ripple in output voltage, the capacitance value is given by

B. Dual Stage Boost Converter
With a specific end goal to accomplish a larger step up in ordinary chopper circuit the enforced duty ratio required is more. The duration for which the semiconductor control switch is kept closed is more as the inductor keeps accumulating the charge. In such case, the OFF time will be of short parts, contrasted with ON interval of the switch. The discharge of the inductor needs to be within the OFF interval. Duty ratio near to 1 will continuously be a danger to the framework, making the semiconductor devices get harmed as the dissipated power surpasses the rated.
The Dual Stage boost converter is a series of two boost converters with an outcome of voltage at the output expanding in a geometric progression. The Fig. 3 demonstrates the architecture of boost converter with two stages to accomplish a huge boost ratio. The outcome of each stage will move as the input of the accompanying stage and in this manner the step up occurs.

1) Circuit Description and Operational Analysis of Dual Stage Boost Converter:
The architecture of boost converter with double stages is achieved by connecting two individual boost converters in series manner. Higher static gain can be obtained by appending a greater number of stages. Since same duty cycle is given for the switches of all the stages in the converter, circuit operations in a switching cycle can be concluded for two states, ON and OFF cycles. The Table 1 interprets the status of the two step-up converters in series connection for different states of the two switches. The equivalent circuit diagram of the two state operations are shown in Fig. 4 and Fig. 5.  The dual stage boost converter is designed for the following specifications The rated load for given output power The static gain of dual stage boost converter is given by where is the switching duty cycle. Therefore, for above given parameters switching duty cycle is 0.75.
First stage output capacitance voltage is given by Second stage output capacitance voltage or the output voltage is given by First stage inductor current or the input current, for the load current of = 1.04(for above specifications is given by Second stage inductor current is given by Considering 40% peak to peak ripple, for switching time period T the inductance values are given by Where I , R JKL is the equivalent load of first stage and second stage.

C. Dual Phase Dual Stage Boost Converter
Generally, as per the power equality law the dc-dc chopper with high boost ratio must deal with its very high current at the input compared to that of its output. Thus, the semiconductor control switches at the input undergoes stress. In boost converters with more than one stages, compared to other control switches the switches in first stage must deal with higher stress.
To accomplish the benefits of the two modalities, dual phase booster is incorporated in dual stage step-up. To interleave the stress due to larger input current dual phase is employed at the primary level of the double stage boost converter. A Dual phase Dual-stage boost converter which provides a high boost ration and has significantly less stress is demonstrated in Fig. 6. Though, the dual phase dual stage boost converter has more components it is remunerated by better efficiency.

A. Simulation Results of Dual Phase Boost Converter
The Dual Phase Boost Converter was simulated with the parameters mentioned in Table 2 and the MATLAB Simulink model of the same is shown in Fig. 7. The waveforms of voltages at input, output and output current of Dual Phase Boost Converter are shown in Fig. 8. For the input voltage of 12V DC the output reaches steady state value of 47.92V after 2ms. The input voltage, output voltage and current waveforms of Fig. 8 has been enlarged for a time interval of 7.1ms to 7.6ms which demonstrates the ripples in the output voltage is shown in Fig. 9. The equation for ripple percentage is given by  The Fig. 11 depicts the magnified individual phase and resultant inductor currents of Fig. 10 for a time interval of 6.65ms to 7.0ms which demonstrates the ripples in the inductor current. Theoretical ripple reduction and doubling of ripple frequency in inductor current of dual phase boost converter due to parallel modality which is depicted in Fig. 2 and is strongly validated by the simulation result shown in Fig. 11. The switching pulses for the two switches S11, S12 respectively of Dual Phase Boost Converter are shown in Fig. 12 Each switching pulse has a 180-degree phase shift among them for the same duty ratio of 0.75. The ripple percentage in the output voltage and resultant inductor current can be calculated using equation (18) with the statistics of peak to peak and mean shown in Fig. 9 and Fig. 11 respectively. The Output voltage, Output current, inductor current ripple and output voltage ripple percentage of Dual Phase Boost Converter obtained in simulation for a input of 12V DC are shown in Table 3. The conventional boost converter was designed for inductor current ripple of 40% and output voltage ripple of 4%. With the help of dual phasing in the boost converter the ripple in inductor and output currents has dropped to 24.58% and 1.38% respectively.

B. Simulation Results of Dual Stage Boost Converter
The Dual Stage Boost Converter with the parameters as shown in Table 4 was simulated using MATLAB Simulink and is shown in Fig.13 Fig. 17 inductor current IL1 is the current flowing through the inductor at first stage and inductor current IL2 is the inductor current of second stage. IL2 is the output current of first stage boost converter. The Magnitude of IL2 will be less than that of IL1 as the converter is of boost type.  The Fig.19 gives the statistics of inductor currents IL1, IL2 flowing through the two stages from the Fig.18. Fig. 19 Signal statistics of inductor current IL1, IL2 The switching pulses for the two switches S1, S2 of dual Stage Boost Converter with duty cycle of 75 percentage is shown in Fig. 19. Both switching pulses are identical with no phase shift between them. The ripple percentage in the output voltages at first stage and second stage and inductor currents of first stage and second stage can be calculated by equation (18) with the statistics depicted in Fig. 16 and Fig.20 respectively. The first stage output voltage, second stage output voltage, output current of Dual Stage Boost Converter obtained in simulation for an input of 12V DC are shown in Table 6.

C. Simulation of Dual Phase Dual Stage Boost Converters
The MATLAB Simulink model of Dual Phase Dual Stage Boost Converter simulated with the parameters depicted in Table 5 is shown in Fig.23. The Fig. 20 demonstrates the waveforms of voltages at input, output and output current of Dual phase dual Stage Boost Converter. Since the input voltage of 12V is applied, time interim of 4ms is taken for the output at first stage and second stage to settle at steady state values of 47.9V and 191.8V respectively. The Fig. 21 is stretched from 7.3ms to 8.9 ms to demonstrate the ripples in output voltages of first sage and second stage boost converter and is shown in Fig. 22. First Stage output is nothing other than output of dual phase stage.   Fig. 24 inductor current IL11 is the inductor current through the first phase of first stage, IL12 is the inductor current of second phase in first stage. Magnitude of IL11 and IL12 are same but with a phase shift of 180̊ in charging and discharging cycle. Resultant is the resultant inductor current at first stage. IL2 is the current flowing through second stage inductor.   The control pulses for the two switches S11, S12 shown in Fig. 28 are of dual Boost Converter which overall makes i the first stage of the proposed converter.S11 and S12 are 180̊ phase shifted .The switching pulse the switch S2 in second stage of the converter is identical to that of switch S11 in dual phase boost converter. Fig. 28 Switching pulses of three switches S11, S12, S2 The equation (18) can be used with the statistics portrayed in Fig. 23 and Fig. 26 can be utilized to calculate the ripple percentage in the output voltages at first stage and second stage and inductor currents of first stage and second stage. The Table 6 depicts the comparison of dual stage boost converter and dual phase dual stage boost converter. From the table it has been observed that the proposed converter provides drop in inductor current and output voltage ripple at first and second stages which makes the dual phase dual stage boost converter more efficient. Resultant inductor is considered as the first stage inductor current.

IV. CONCLUSIONS
The dual phase dual stage Boost Converter effortlessly overwhelms the flaws in conventional single stage boost converter. By indistinguishable parallel methodology, current at input gets partitioned. In dual phase boost converter reduced ripple content and doubling in frequency occurs due to elimination in ripple of inductor current among the different phases. This gives the best approach to cut down the size of the filter, prompting to a compressed converter. The dual phase dual stage booster topology will be best appropriate proficient framework for the applications which desire reduced ripple. The simulation results confirm the theoretical assumes.