Abstract
DC–DC converters are playing a vital in the electric vehicles (EVs) application. In current EVs, a separate DC–DC converter is used to charge both in the low voltage and the high-voltage batteries. These factors have resulted in higher output voltage ripples, higher switching and device conduction losses, all of which can have an impact on EV performance. In addition, the previous mulitport converters have more number of energy storage elements and switching devices for EV application. To address these issues, this article proposes a multiport DC–DC converter charging circuit for EVs. The proposed circuit has a single-input dual-output (SIDO) structure that consists of a positive output boost converter (POBC) with integration of buck converter (POBCIBC). Here, the POBC is used to stepping-up the voltage, while the buck converter is used to step-down the voltage. The POBC is a fundamental topology composed of Cascaded Boost Super Lift Luo Converters. The designed POBCIBC has several advantages such as reduced output voltage ripples, high-voltage transfer gain, proficient efficiency, lower switching and conduction losses, less number of storage components, and a compact structure over the existing multiport converters. The performance of the POBCIBC is tested at different operating conditions by constructing the MATLAB/Simulink and prototype models. The proposed converter has produced different output voltage levels based on their duty cycles variations. The results are presented to show the proficient POBCIBC for the EV application.
1. Introduction
Electric vehicles (EVs) can play a critical role in combating climate change around the world by lowering emissions and decreasing reliance on the fossil fuels. The main components of EVs are the battery, DC–DC converters, inverter, electrical machinery, battery management system (BMS), and control unit. The DC–DC converter is used to charge the battery in EVs while also increasing the high voltage from low-voltage renewable energy sources [1, 2]. However, in existing EVs, an individual DC–DC converter was used to charge both in the low voltage and the high-voltage batteries, which can result in increased switching losses, increased output voltage ripples, massive conduction losses, and a decrease in system efficiency. These issues affect the performance of the EVs. To solve these issues, this article introduces a single-input and multioutput (SIMO) DC–DC converter for EV. Positive output boost converter (POBC) with integration of buck converter (POBCIBC) in continuous conduction mode (CCM) with various duty cycles is considered as a SIMO converter for study in this article. In this article, the POBC is used for high voltage and the stepping down converter is used for low voltage. The POBCIBC outperforms existing EV battery charging multiport DC–DC converters in terms of voltage transfer gain (VTG), tenacity, and ripple voltage [3, 4]. The Luo converter with integration buck converter for EV application is well-executed [5]. However, the efficiency of this converter has produced 94.2%. The DC–DC converter fed small power rating of brushless DC motor drive for EV is well-presented [6]. However, the efficiency of the converter is low for this work. An enhanced deep learning method for driver detection and assistance EV with proficient performance has been presented [7].
Multi-input and multi-output (MIMO) DC–DC converters are currently hot topics in EVs. SIMO transformer based DC–DC converter with varying output voltage is well-executed [8]. However, this converter had a number of issues such as big transformer size, higher cost, and more quantity of power switches, higher on–off losses, and a complex control as well as driver circuit, which can reduce their efficiency. The SIMO with coupled inductor is well-presented [9]. A soft switching based SIMO converter has been reported in [10]. However, from these woks, the coupled inductors have resulted in more leakage current, more on–off losses and complex design steps. The modified buck–boost DC–DC converter has been systematically addressed [11]. According to this article, the converter is designed for small power applications by using three switches with hard switching concepts to compute the lower and maximum surge inductor currents.
Design of sliding mode controller (SMC) for multiphase charger and discharger bidirectional DC–DC converters have been well-reported [12]. From this work, the inductor current of this converter with this control has produced a ripple current of 1.58 A and peak overshoots of 1 V during the load variations. Furthermore, the structure of the designed converter has more complex, and charged only a single battery. The zero voltage switching (ZVS) DC–DC converter using IC UCC389 control for low-voltage battery charging in EV is well-presented [13]. However, the designed converter has charged single battery with a complex structure and produced conduction losses of 20 W. Furthermore, the cost of phase shifter IC is excessive due to increased power losses. A real-time analysis of a five-stage DC–DC boost converter with a series LC for EVs is well-presented [14]. However, this converter has more storage elements (like 10 capacitors, and one inductor) and 8 diodes. Similarly, the output voltage of this converter has generated peak overshoots of 34.9% and a settling time of 100 ms. The performance of various DC–DC converters with their control methodologies for EVs has been reviewed, and their parameters have been recorded in [15]. Based on these analyses, the converter efficiency ranges starts from 61.8% to 92.1% with a single battery. An improved current-operated bidirectional power converter for EV battery charging has been discussed [16]. But, this converter has charged a single battery with moderate efficiency. The Super Lift Luo Converter with buck converter integration for EV has been discussed [17]. However, this converter has produced an efficiency of 98% with two switches, two inductors, three capacitors, and three diodes. Table 1 indicates the comprehensive analysis of the proposed POBCIBC with previous converters research gaps for EV applications. From these works, it is evident that the proposed POBCIBC has produced efficiency of 99.39% with minimum number of elements over the existing converters.
According to the literature review, no design of POBCIBC with duty cycle control for EV battery charging application has been reported.
Therefore, in this article, it is to design the POBCIBC for EV application. The complete model is validated at various working conditions by making the MATLAB/Simulink and the prototype models.
The following is the main objectives of this article:(i)First, the VTG and design equations for components of the POBCIBC are derived, and then the duty cycles for the converter are varied to achieve a wide range of regulated output voltages.(ii)Next, the POBCIBC is tested at different duty cycles and load resistance variations by constructing the Simulink and the experimental models.(iii)Finally, the results of proposed converter has analyzed via. time domain specification, output voltage ripples, and efficiency analysis at different converter parameter variations.
This article is organized as follows: Section 1 discusses the introduction, literature review, and main objectives of this article. Sections 2 and 3 discuss the operation and mathematical VTG of POBCIBC. Section 4 presents the proposed converter components designs formulas. Section 5 performs the efficiency calculation. Section 6 contains the results and discussions of POBCIBC at different operating conditions. Conclusions and future works are listed in Section 7.
2. Proposed POBCIBC Working
The POBCIBC for EV application is illustrated in Figure 1. It includes input voltage Vin, two MOSFET switches S1, S2, storage components such as inductors (L1, L2)/capacitor (Co1, Co2), power transfer diodes D1, D2 and load resitances Ro1, Ro2. The main aids of the POBCIBC has single input and two output voltage at different levels. This POBCIBC is more suitable for power source in various components of EV. The output voltage (Vo1) of POBCIBC has been improved by using boost converter whereas the low-output voltage voltage (Vo2) of it can be generated with the help of buck converter. The POBCIBC has good VTG, reduced circuit components, minimized current and voltage ripples, simple strucure, good power density and efficiency in comaprion with tradtional multiport converters, and KY converters and SEPIC. The working of the POBCIBC is divided into four modes of operation and its equivalent circuits are represented in Figure 2(a)–2(c).
(a)
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Mode 1 (0 < t < t1) (Refer Figure 2(a)): During the Mode 1 operation, S1 is closed and S2 is open. The stored energy in the previous mode of inductor L1 is de-energized to energize the inductor L2 in this mode and to supply the buck load Ro2. This mode is completes after the (d1-d2/2)Ts time interval. The S1 voltage is zero due to the resonance path between the L1, L2, and Co2 in the earlier switching state time interval. Besides, the D1 and D2 are in reverse polarized mode.
Mode 2 (t1 < t < t2) (Refer Figure 2(b)): In Mode 2 operation, S1 is open and S2 is closed. The stored energy in the inductor L2 is released energy to load Ro2. In addition, L1 is energized with Vin. The D2 is inverse polarized in this mode. The time interval for this mode is d2Ts time interval.
Mode 3 (t2 < t < t3) (Refer Figure 2(a)): The operation in this mode is same as that of Mode 1.
Mode 4 (t3 < t < t4) (Refer Figure 2(c)): In this mode, S1 and S2 are in open states. The L1 and L2 is released energy to supply the loads Ro1 and Ro2.
Gate pulses, voltage, and current key waveforms for the different components of POBCIBC are illustrated in Figure 3. The parameters of POBCIBC are cataloged in Table 2.
3. Mathematical Computation of VTG of POBCIBC
For computing the VTG of POBCIBC, assuming that the proposed converter has ideal components and minimal ripples for the inductors potential. The VTG of the POBCIBC is derived from the modes of operation of it and also depends on the voltage-second balancing of inductors. The VTG for step-up output of boost converter is arrived as Equation (4).
Likewise, VTG of the step-down output of buck converter is engraved as Equation (5)
The VTG (G1) of POBC output voltage depends on duty cycle d2, whereas the VTG (G2) of buck output is a function of d1 and d2. The graphical representation of theoretical analysis of the proposed converter is depicting in Figure 4. It is more suitable for EV due to utilizing the different ranges of output voltages. From the Figure 4, 0 < d1 <0.9, 0 < d2 < 0.9, the VTGs are redefined as Equations (6) and (7)
4. Design of Circuit Components of POBCIBC
This part deals about the circuit components of the POBCIBC. The inductors, L1 and L2 decide the switch current stress and output current ripples [17]. Therefore, designing the optimal ranges of inductors plays a significant role. Figure 4 show the inductor peak-to-peak current ripple is evaluated by Equation (8).
The linear decreasing of inductor peak-to-peak current ripple L2 (see Figure 4) is obtained by Equation (9).
The preferred ranges of L1 and L2 are evaluated using the Equations (8) and (9).
Next, the proper ranges of filter capacitors of POBCIBC are obtained by using Equation (10).where ΔVco is peak-to-peak capacitor ripple voltage and Δq is charge.
Hence, the output capacitors are computed [17] with help of the Equation (11).
Using Equation (11) at fixed switching frequency, the minimal ranges of Co1 and Co2 are mainly affected by d1, d2, and Vin. In addition, the voltages stresses of S1, S2, D1, D2, and D3 computed with help of the Equation (12).
Also, the current stresses of the devices are evaluated by Equation (13) with assuming free ripple of the inductors of this converter.
5. Efficiency Computation
The element losses are considered when calculating the converter efficiency. It is written as Equation (14).
The overall power losses of the converter are then expressed as Equation (15).
The switching power losses are calculated during on and off conditions
Using the Equations (17)–(20), the switching power losses in on/off operating conditions are evaluated.
Diode conduction and nonconduction state losses are calculated with help of Equations (21) and (22).where rf is diode forward resistance and Vf is threshold or forward voltage of the diode.
Storage elements power losses are computed by using Equations (24) and (25).where r1 is internal resistance of inductors and r2 is internal resistance of capacitors.
6. Results and Discussions
This section describes the simulation and experimental responses of the POBCIBC for EV applications at various load operating conditions, with the specifications of the same converter cataloged in Table 2. The following are the specifications of the converter circuit: MOSFTE IRFN 540 switches S1–S2, diodes, D1, D2-UF5803, inductors, L1, L2-Ferrite core (10 A), capacitors, Co1, Co2 -electrolytic type, pulse width modulation (PWM) generation using microcontroller PIC 18f6310 (32 MHz, PC1, and PC2) and driver IC-Fan 6832 with amplification circuit. Figure 5(a) depicts the Simulink model of the POBCIBC, while Figure 5(b) depicts the prototype model of the same converter. The PWM pulses for switches of the converter are generated by using the PIC18f6310. Then, it is applied to the Fan 6832 driver circuit to provide isolation between the power and control units. The driver IC outputs are then connected to the gate and source of the switches S1 and S2 to regulate the output voltages with different duty cycles.
(a)
(b)
Figures 6(a) and 6(b) depict the simulated and experimental responses of the output voltages, Vin, and PWM pulses of the proposed POBCIBC with Vin = 12 V and duty cycles of switches d1 = 60% and d2 = 30%. From these figures, it is clearly found that the POBCIBC output voltages have Vo1 = 17.14 V and Vo2 = 5.14 V matched theoretical values (refer Table 2) with small overshoots and a quick setting time of 0.001 s. In addition, output voltages of the proposed converter has produced little ripples in both the experimental and the simulation responsess. Figures 7(a) and 7(b) show the experimental and simulation responses of the output voltages, input voltage, and PWM pulses of the proposed POBCIBC with Vin = 12 V and d1 = 90% and d2 = 80%. From these figures, it is clearly observed that both the experimental and the simulation responses of output voltages of the POBCIBC have Vo1 = 60 V and Vo2 = 6 V, negligible overshoots and a setting time of 0.02 s. Furthermore, the Vo1 and Vo2 of the proposed converter have produced little ripples in both experimental and simulation analysis. Theoretical values (Table 2) are closely matched to both in the experimental and the simulation results.
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(b)
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Figures 8(a) and 8(b) depict the POBCIBC simulated gate pulses, voltage across the switches, and current through the switches/inductors/diodes responses with Vin = 12 V and d1 = 60% and d2 = 30% at different load resistance. It is found that the voltage across the switches, current through the switches, inductor, and diodes of the designed POBCIBC has no voltage and current stresses during the converter operation.
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The POBCIBC was also operating in CCM/discontinuous conduction mode (DCM) because the inductor currents were continuous. All of the parameters correspond to the theoretical key waveform (see Figures 3 and 8). The performance of POBCIBC at rated load conditions is recorded in both the simulated and the experimental numerical results in Table 3. From theses result, it is evident that the proposed POBCIBC has produced efficiency of 99.39% (simulation) and 98.49% (experimental) at load of Ro1 = 25 Ω and Ro2 = 12.5 Ω and minimum ripples of the output voltages (1.2 V (simulation), 1.6 V (experimental) and 0.005 V (simulation), 0.0007 V (experimental)) with duty cycles of switches d1 = 0.6 and d2 = 0.3.
Tables 1 and 3 indicate the comprehensive analysis of the proposed POBCIBC with previous converters for the EV applications. From these works, it is evident that the proposed POBCIBC has produced efficiency of 99.39% (see Table 3 highlighted in bold) with minimum number of elements over the existing converters.
The percentages of loss breakdown at nearly full load for various POBCIBC components are shown in Figure 9 using Equations (14)–(25). As a result, power losses are dominated by semiconductor device losses. It should be noted that the conduction loss of the switches and diodes becomes dominant due to the high current flow through them in the high-voltage gains and output powers. As a result, high-power semiconductors with low on-resistance should be used to improve the efficiency of the same converter. Figure 10(a)–10(d) depicts the experimental voltage across the S1 and S2, and current through the inductor (iL2), and ID1 responses for POBCIBC with Vin = 12 V and d1 = 60% and d2 = 30% at rated load. From these results, it is found that the voltage across the switches, current through the inductor and the diode of the same converter has no voltage and current stresses during the POBCIBC operation. Therefore, the designed converter has more efficiency for EV application.
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7. Conclusions
In this article, the theoretical analysis, design and output voltage regulation of multiport POBCIBC operated in CCM using different duty cycle has been successfully demonstrated. The PWM pulses were generated using PIC18f6310 for POBCIBC. The main merits of the designed POBCIBC over the previous multiport converter as follows:(i)Obtain the good VTG and flexibility to change the different output voltages;(ii)Excellent efficiency like 99.39%;(iii)Minimal output ripple voltages as well as inductor ripple currents;(iv)Simple structure and less number of components; and(v)Low conduction and switching losses.
The experimental and simulation results are presented in order to prove the competence of the designed multiport POBCIBC at different load and duty cycle operating conditions. It is, therefore, mainly designed for EV battery charging application.
In future, multiport converter based LUO and KY topologies to be built for EV and renewable energy applications.
Data Availability
The data are used to support the findings of this study are included within the article.
Disclosure
It was performed as a part of the Employment of Ramash Kumar K, Department of Electrical and Electronics Engineering, Dr. N.G.P. Institute of Technology, Coimbatore-48, Tamilnadu, India.
Conflicts of Interest
The authors declare that they have no conflicts of interest.