Abstract
A bidirectional DC–DC converter is required for an energy storage system. High efficiency and a high stepup and stepdown conversion ratio are the development trends. In this research, a series of bidirectional highgain Cuk circuits was derived by combining tapped inductors and bidirectional Cuk. After analyzing and comparing the characteristics of each circuit, a bidirectional highgain Cuk circuit with a tappedinductor (reverse coupling) was proposed. The proposed converter has a simple structure and a high voltage gain in both the stepdown (Buck) and stepup (Boost) operation modes. The voltage stress of S_{2} was low. The voltage stress of S_{1} was high, however, and this is a disadvantage of the proposed converter. The proposed circuit’s characteristics were thoroughly examined, including the voltage gain characteristics and the design of the main parameters. We established a power loss model of the new topology, and the tappedinductor turn ratio was optimized for high efficiency. Finally, a 400 W experimental implementation of the converter was shown to achieve efficiencies of 93.5% and 92.4% in the stepup and stepdown modes, respectively. These findings verified the validity of the proposed circuit’s theoretical analysis.
Introduction
Because of the scarcity of fossil fuels and serious environmental issues in recent years, significant effort has been focused on the development of environmentally friendly distributed generation (DG) technologies^{1}. Renewable energy, however, does not produce consistent energy because of weather conditions. Energy storage is required to provide stable power^{2}. Furthermore, the voltage of a storage battery is typically low, in the 12–48 V range, whereas the voltage of a DC bus is 400 V or higher to meet the requirements of an inverter or AC grid^{3}. As a result, for energy storage systems to connect a lowvoltage battery to a highvoltage DC bus, a bidirectional DC–DC converter with a high stepup/stepdown voltage conversion ratio is required^{4}. Furthermore, these converters have been researched extensively for a wide range of industrial applications, including uninterruptible power supply systems, electric vehicles, and aviation power supplies^{5}. The traditional buckboost converter can provide a high voltage gain with a large duty ratio, which will cause considerable conduction losses because of the large current ripples. Additionally, several bidirectional DC–DC converters based on isolated topologies have been presented in the literature. These topologies require a transformer and a high number of switching devices, which increases the cost and the switching losses, in addition to requiring more complicated control schemes.
Many bidirectional DC–DC converters with a high stepup/stepdown conversion ratio have been proposed to improve the voltage gain and efficiency of a converter. The cascade method was used in reference ^{6} to broaden the ratio range of a bidirectional converter whose gain was calculated by multiplying the gains of each level converter. The efficiency was low, however, because of the cascade, and there was an issue of instability. The proposed converter in reference ^{7} improved a bidirectional DCDC converter’s conversion ratio by connecting the lowvoltage side in parallel and the highvoltage side in a series, but the structure of the converter was complex. Some appealing solutions, such as switched capacitors^{8,9}, switched inductors^{10}, and coupled inductors^{11}, have been introduced for a basic bidirectional DC/DC converter to increase the voltage conversion ratio. The proposed bidirectional bridge modular switchedcapacitorbased resonant DC–DC converter achieved a high stepup/stepdown conversion ratio through a switched capacitor unit^{8}. However, it employed a large number of switches, and the voltage and current stresses on the switches were high due to resonance. As a result, although the circuit proposed in ^{9} reduced the number of switches, its conversion ratio range was limited. Reference ^{10} employed the coupledinductor technique to build a bidirectional DC–DC converter with a high stepup/stepdown voltage gain. The current ripple was large because the current waveform on the lowvoltage side of the topology was a square wave. In addition, reference ^{11} discussed nonisolated bidirectional DC–DC converters based on dualcoupled inductors, which could achieve a high voltage gain and reduced switch voltage stresses by connecting the secondary windings of two coupled inductors in series. However, it necessitated a complex control.
In summary, these isolated converter structures usually have too many switches, so the conduction losses of the switches were very high. Additionally, the practical implementation is complicated and expensive. The existing nonisolated highgain circuits are mainly switch capacitor converters and coupled inductor converters. The drawbacks of a switch capacitor converter include the switching loss and the current stress. The drawbacks of a coupled inductor converter include the complex circuit structure and the leakage inductance that results in spikes that need to be suppressed using snubber circuits.
Cuk converters are gaining popularity because the input and output inductors reduce electromagnetic interference problems and the output ripple is small^{12}. In this research, tapped inductance and bidirectional Cuk are combined to create a series of bidirectional highgain Cuk circuits. After analyzing and comparing the characteristics of each circuit, a bidirectional highgain Cuk circuit with a tappedinductor (reverse coupling) is proposed. The proposed converter has a simple structure and high voltage gain in both the stepdown (Buck) and stepup (Boost) operation modes. The proposed circuit’s characteristics, including the voltage gain characteristics and the design of the main parameters, are thoroughly examined. Based on this examination, we established a power loss model of the new topology, and the tappedinductor turn ratio was optimized for high efficiency. Finally, a 400 W 48 V/400 V prototype was created to verify the validity of the proposed circuit’s theoretical analysis.
A tappedinductor bidirectional Cuk
The bidirectional Cuk circuit features low input and output ripple and low EMI interference, and the circuit diagram is shown in Fig. 1. Because of the influence of the parasitic parameters, the voltage gain of this circuit is limited, and it is not suitable for occasions with a large voltage transformation ratio. Therefore, a series of bidirectional highgain Cuk circuits is created by combining tapped inductance and bidirectional Cuk to increase the voltage gain of bidirectional Cuk.
The proposed series of circuits use coupled inductors to replace the inductors L_{1} or L_{2} in Fig. 1. Because of the different connection methods of the coupled inductor, four different circuits can be derived. Additionally, because the coupled inductor has two coupling modes (i.e., samedirection coupling and reversedirection coupling), a total of eight circuits can be derived, as shown in Figs. 2 and 3. These converters with tapped inductors are formed by the samedirection coupling shown in Fig. 2. The reversedirection coupling is shown in Fig. 3. The tapped inductor is composed of L_{1} with the number of turns N_{1} and L_{2} with the number of turns N_{2}, where the tap ratio is n = N_{2}: N_{1}. Furthermore, D_{1} is the parasitic body diode of S_{1} and D_{2} is the parasitic body diode of S_{2}. The samedirection coupling means that the currents all flow from the samenamed end of the inductor and vice versa.
The voltage gain M of these converters versus the duty ratio D and the turn ratio n is obtained for the continuous current mode (CCM) mode by analyzing the working principles of the previously noted circuits, as shown in Table 1. S_{1}tap means that the inductor L_{1} of the bidirectional Cuk circuit is replaced by the tap inductor L_{t}, and the common terminal of the tapped inductor is connected to S_{1}, as shown in Fig. 2a and Fig. 3a. S_{2}tap means that the inductor L_{2} of the bidirectional Cuk circuit is replaced by the tap inductor L_{t}, and the common terminal of the tapped inductor is connected to S_{2}, as shown in Figs. 2b and 3b. C_{B}tap 1 means that the inductor L_{1} of the bidirectional Cuk circuit is replaced by the tap inductor L_{t}, and the common terminal of the tapped inductor is connected to C_{B}, as shown in Figs. 2c and 3c. C_{B}tap 2 means that the inductor L_{2} of the bidirectional Cuk circuit is replaced by the tap inductor L_{t}, and the common terminal of the tapped inductor is connected to C_{B}, as shown in Figs. 2d and 3d.
The corresponding curve can be drawn using the data from Table 1, as shown in Fig. 4. The voltagegain characteristic curve of the circuits formed by samedirection coupling is shown in Fig. 4a. The curves of the S_{1}tap circuit and capacitortap circuit 2 are overlapped, and the curves of the S_{2}tap circuit and capacitortap circuit 1 are overlapped. As shown in Fig. 4a, the bidirectional Cuk circuit with the tapped inductor derived from S_{2}tap and capacitortap circuit 1 can achieve a high voltage gain. The voltage conversion ratio characteristic curve of the circuits formed by the reversedirection coupling is shown in Fig. 4b. The curves of the S_{1}tap circuit and capacitortap circuit 2 are overlapped, and the curves of the S_{2}tap circuit and capacitortap circuit 1 are overlapped. As shown in Fig. 4b, the bidirectional Cuk circuit with the tapped inductor derived from S_{1}tap and capacitortap circuit 2 can achieve a high voltage gain.
The voltage conversion ratio characteristic curves of the circuits in Figs. 3d and 2b are plotted, as shown in Fig. 5, to obtain the circuit with a larger stepup ratio from the previously noted circuits. As a result, it is determined that the circuit in Fig. 3d is the best of the previously noted circuits.
Because the analysis of these converters in the stepdown mode is similar to the analysis in the stepup mode, it is not repeated here.
The feasibility analysis of the topologies’ large ratio is shown in Table 2 based on the preceding analysis. In the table, the term “inapplicable” means that the conversion ratio of this circuit is less than that of the bidirectional Cuk circuit, and the term “available” means that the conversion ratio of this circuit is greater than that of the bidirectional Cuk circuit.
A tappedinductor bidirectional high gain Cuk converter
The circuit topology
According to this analysis, we proposed a tappedinductor bidirectional Cuk converter with a high stepup/stepdown conversion ratio, as shown in Fig. 6. The proposed converter is made up of the following components: the lowside voltage V_{2}, the highside voltage V_{1}, the inductor L_{3}, the tapped inductor L_{t}, the capacitor C_{B}, and the two switches S_{1}–S_{2}. The tapped inductor L_{t} is composed of L_{1} and L_{2} coupled in the opposite direction, and the turns of the inductor are N_{1} and N_{2}(N_{1} > N_{2}). The equivalent circuits of these stages are shown in Fig. 7.
The effective turn ratio of the tapped inductor is expressed as follows.
The coupling coefficient of the tapped inductor is:
where L_{m} is the equivalent magnetizing inductance on the N_{2} side; and L_{k} is the leakage inductance on the N_{2} side.
Operational principles
When using the proposed circuit in energy storage systems, the battery voltage V_{2} is on the lowvoltage side and the DCbus voltage V_{1} is on the highvoltage side. The proposed converter can operate in both stepup mode and stepdown mode with bidirectional power flow. Reference ^{13} contains the operating principles and steadystate analysis. Hence, the simple results are discussed in the following, but the detailed analysis is not repeated.
As shown in Fig. 8, one switching period of the stepup mode has two switching stages. In Fig. 8, v_{gs2} is the driving signal of S_{2}, the currents flowing through the L_{1}, L_{2}, and L_{3} inductors are i_{Ls}, i_{Lp}, and i_{L3}, and i_{D1}, i_{S2}, and i_{CB} are the currents flowing through D_{1}, S_{2}, and C_{B}. The equivalent circuits of these stages are shown in Fig. 9.
The gain of the proposed circuit in the stepup mode can be derived as follows.
Ideally, the leakage inductor can be ignored, and the M_{up} can be derived as follows.
where M_{up} is the stepup conversion ratio of the proposed converter and D is the duty cycle of S_{2}.
As shown in Fig. 10, one switching period of the stepdown mode has two switching stages. In Fig. 10, v_{gs1} is the driving signal of S_{1}, the currents flowing through the L_{1}, L_{2}, and L_{3} inductors are i_{L1}, i_{L2}, and i_{L3}, and i_{D2}, i_{S1}, and i_{CB} are the currents flowing through D_{2}, S_{1}, and C_{B}. The equivalent circuits of these stages are shown in Fig. 11.
The gain of the proposed circuit in the stepdown mode can be derived as follows.
Ideally, the leakage inductor can be ignored, and M_{down} can be derived as follows.
where M_{down} is the stepdown conversion ratio of the proposed converter and D is the duty cycle of S_{1}.
Comparison analysis of the proposed converter
The characteristic comparison of the proposed converter with the counterparts is shown in Table 3 (NS is the number of power switches, NCI is the number of coupled inductors, NI is the number of inductors, and NC is the number of capacitors). The conventional buck/boost converter can achieve bidirectional power flows while employing the fewest number of power switches, but the converter’s conversion ratio range is limited. The converter in reference ^{14} has a high stepup/stepdown conversion ratio, but it is complex and inefficient. Compared with the converters in reference ^{14}, the converter’s efficiency in reference ^{15} has been improved by using soft switching technology, but the circuit structure is still complex. It can be seen that the proposed converter achieves a high and wide voltagegain range by employing two power switches. Additionally, it has a simple structure.
The feasibly control strategy for the proposed converter
To improve the dynamic performance and antidisturbance ability of the proposed converter, we proposed an improved fuzzy control strategy based on the Takagi–SugenoKang fuzzy control technique, as shown in Fig. 12. The operating principle and a detailed analysis of the control strategy can be obtained from reference ^{13}. Therefore, the detailed analysis is not repeated in this paper.
Analysis and design of the key parameters
Optimized design of turn ratio
Power loss model
A power loss model of the new topology is established in the stepup mode. The loss of the proposed converter is composed of the losses of S_{2}, L_{t}, L_{3}, and D_{1}. The specific analysis is given as follows.

(1)
The loss of S_{2}.
The conduction loss is expressed as follows
$$ P_{con\_S} = I_{rms\_S}^{2} \cdot R_{ds(on)\_S} $$(7)where I_{rms_S2} is the effective value of the current across S_{2}, and R_{ds(on)} is the forward conduction resistance of S_{2} at a certain temperature, which can be estimated from the datasheet and the ambient temperature.
The switching loss is found as follows
$$ P_{sw} = \frac{1}{2} \cdot f_{s} V_{ds} \cdot \left[ \begin{gathered} I_{d01} \cdot (t_{ri} + t_{fv} ) \hfill \\ { + }I_{d02} \cdot (t_{rv} + t_{fi} ) \hfill \\ \end{gathered} \right] $$(8)where t_{ri}, t_{fv}, t_{r}, and t_{fi} are the equivalent times of the four phases with the loss during the switching process, which can be calculated from the datasheet.
The loss of the equivalent output capacitance of S_{2} is found as follows:
$$ P_{{{\text{Co}} \_S}} = \frac{1}{2} \cdot C_{oss} \cdot V_{ds\_S2}^{2} \cdot f_{S} $$(9)Therefore, the overall loss of S_{2} is given by the following:
$$ P_{s} = P_{con\_S} + P_{sw} + P_{{{\text{Co}} \_S}} $$(10) 
(2)
The loss of D_{1}
$$ P_{D} = V_{F} \cdot I_{D} + V_{off\_D} \cdot Q_{rr} \cdot f_{S} $$(11)where V_{F} is the forward voltage drop of D_{1}, I_{D} is the average value of the current across D_{1}, V_{off_D} is the reverse voltage of D_{1}, and Q_{rr} is the reverse recovery charge of D_{1}.

(3)
The loss of the inductor
The core loss is found as follows:
$$ P_{core} = f_{s} \cdot Kf_{eq}^{{{{\alpha  1}}}} B^{\beta } \left( {C_{0} + C_{1} T + C_{2} T^{2} } \right) $$(12)$$ f_{eq} (D) = \frac{2}{{B^{2} \pi^{2} }}\int\limits_{0}^{T} {(\frac{dB}{{dt}})^{2} dt = } \frac{{2f_{s} }}{{\pi^{2} D(1  D)}} $$(13)
The winding loss is found as follows
Therefore, the overall loss of inductor is given by the following:
where the parameters K, α, β, C_{0}, C_{1}, and C_{2} can be obtained from the datasheet provided by the core manufacturer; T is the operating temperature of the magnetic core; V_{core} is the volume of the magnetic core; I_{L_rms} is the effective value of the current through the inductor; and R_{dc} is the equivalent resistance of the inductor.
The power loss models of L_{t} and L_{3} are similar to each other. Therefore, the description of the power loss model of L_{t} is not repeated here.
To summarize, the overall loss of the proposed converter in the stepup mode is given by the following:
Hence, the efficiency of the proposed converter in the stepup mode is given as follows
Similarly, the overall loss of the proposed converter in the stepdown mode is given by the following:
Hence, the efficiency of the proposed converter in the stepdown mode is given as follows
The optimization selection of turn ratio
The loss characteristics of the proposed circuit are analyzed using Mathcad and the power loss model from the previous section. The following are the converter’s main simulation parameters: V_{2} = 48 V, V_{1} = 400 V, P_{o} = 400 W, L_{3} = 1.5 mH, L_{1} = 0.9 mH, switching frequency: fs = 50 kHz.
According to Formula (16), the curves for the loss of the proposed circuit and the turn ratio under different loads can be drawn using Mathcad, as shown in Fig. 13.
From Fig. 13, when the output power is constant, the total loss of the circuit decreases at first and then increases as the turn ratio increases. As a result, a minimum loss point serves as the foundation for selecting the appropriate turn ratio in this research.
The calculation curve for the efficiency of the proposed circuit in the stepup mode can be drawn using Formula (17), as shown in Fig. 14a. Figure 14b depicts the calculation curve for the efficiency of the proposed circuit in the stepdown mode, according to Formula (19).
As shown in Fig. 14, the circuit’s efficiency increases at first and then decreases as the turn ratio increases. There is a maximum level of efficiency. As a result, to achieve the expected output and high efficiency, an appropriate turn ratio and steadystate duty ratio should be chosen. The turn ratio should be around 0.4, and the duty cycle should be around 0.75, according to Fig. 14.
Given the possibility of errors during the design and winding processes, the best turn ratio is \({\lambda }_{opt}\) = 0.375–0.412. The efficiency calculation curves are shown in Fig. 15. When the proposed converter operates under rated conditions, the best turn ratio is \({\lambda }_{opt}\) = 0.394. Figure 15a depicts the efficiency curve in the stepup mode, and Fig. 15b shows the efficiency curve in the stepdown mode.
Other parameters design
The selection of the inductor
To ensure that the circuit works in CCM mode, the values of L_{1}, L_{2}, and L_{3} must be greater than the inductance value with critical continuity. These values are given as follows:
The selection of capacitor
The selection of the capacitor mainly includes consideration of the voltage stress and the voltage ripple within a certain range. The value of C_{B} is found as follows:
Simulation and experimental verification
Simulation results
We performed detailed simulations in Matlab/Simulink to verify the correctness of the aforementioned theoretical analysis. The proposed converter operation is verified at V_{2} = 48 V, V_{1} = 400 V, P_{o} = 400 W, L_{3} = 1.5 mH, L_{1} = 0.9 mH, L_{2} = 0.33 mH, L_{k} = 0.92 uH, C_{B} = 2.2 uF, C_{o1} = 47 uF, C_{o2} = 47 uF, and the switching frequency fs = 50 kHz.
The simulation results in the stepup mode at full load are shown in Fig. 16. In Fig. 16, v_{gs2} is the driving signal for S_{2}, the currents flowing through the L_{1}, L_{2}, and L_{3} inductors are i_{Ls}, i_{Lp}, and i_{L3}, and i_{D1}, i_{S2}, and i_{CB} are the currents flowing through D_{1}, S_{2}, and C_{B}, respectively.
The simulation results in the stepdown mode at full load are shown in Fig. 17. v_{gs1} is the driving signal for S_{1}, the currents flowing through the L_{1}, L_{2}, and L_{3} inductors are i_{Ls}, i_{Lp}, and i_{L3}, and i_{D2}, i_{S1}, and i_{CB} are the currents flowing through D_{2}, S_{1}, and C_{B} separately.
In the stepup mode, the output voltage is stable at 400 V, as shown in Fig. 16. The duty cycle of S_{2} is 0.74. The voltage stresses of S_{2} and D_{1} are 457 V and 472 V. Similarly, Fig. 17 shows that the output voltage is stable at 48 V in the stepdown mode. The duty cycle of S_{1} is 0.26. The voltage stresses of S_{1} and D_{2} are 987 V and 180 V. The voltage and current spikes of S_{1}, S_{2}, and the inductor are caused by the leakage inductance of the coupled inductor. Thus, the results in Figs. 16 and 17 show that the simulation results closely match the theoretical analysis.
Experimental results
To validate the theoretical analysis, we built a laboratory prototype of the proposed converter. First, based on typical applications, we selected the operating conditions of the proposed converter as V_{2} = 48 V, V_{1} = 400 V, and P_{o} = 400 W. Second, according to Formulas (20)–(23), L_{3} = 1.5 mH, L_{1} = 0.9 mH, L_{2} = 0.33 mH, C_{B} = 2.2 uF, C_{o1} = 100 uF, and C_{o2} = 100 uF. Then the voltagecurrent stress of the semiconductor device can be obtained by analyzing the specific operating principle of the converter. The voltagecurrent stress of S_{1} is as follows:
The voltagecurrent stress of S_{2} is as follows:
where I_{1} is the average value of the highvoltage side current and I_{2} is the average value of the lowvoltage side current.
The maximum voltage and the current stress values of S_{1} and S_{2} are obtained by incorporating the corresponding parameters. Then, based on a certain margin, the specific type of switching tube that is required can be selected. The specific parameters of the proposed converter are listed in Table 4, and the prototype is shown in Fig. 18.
When v_{2} = 48 V, we obtain the experimental results in the stepup mode at a full load as shown in Fig. 19. Figure 19a shows the waveforms of v_{gs2}, v_{ds2}, and i_{ds2}, and the duty cycle of S_{2} is 0.75. The voltage stress of S_{2} is 325 V. Figure 19b shows the waveforms of v_{gs2}, v_{D1}, and i_{D1}, and the voltage stress of D_{1} is 675 V. Figure 19c shows the waveforms of v_{gs2}, v_{1}, i_{L1}, and i_{L3}, and the output voltage of the proposed converter in stepup mode is 400.8 V.
When v_{2} = 36 V, we obtain the experimental results in the stepup mode at full load as shown in Fig. 20. As illustrated in Fig. 20, the duty cycle of S_{2} is 0.81, and the output voltage of the proposed converter in the stepup mode is 400.4 V. The voltage stresses of S_{2} and D_{1} are 362 V and 669 V.
When v_{2} = 60 V, we obtain the experimental results in the stepup mode at full load as shown in Fig. 21. As illustrated in Fig. 21, the duty cycle of S_{2} is 0.69, and the output voltage of the proposed converter in the stepup mode is 400.1 V. The voltage stresses of S_{2} and D_{1} are 315 V and 725 V.
Compare with the simulation results in Fig. 16, the experimental results in the stepup mode are consistent with it. Both of them are then consistent with the theoretical analysis. The voltage and current spikes are caused by the leakage inductance.
When v_{1} = 400 V, we obtain the experimental results in the stepup mode at full load as shown in Fig. 22. Figure 22a shows the waveforms of v_{gs1}, v_{ds1}, and i_{ds1}, and the voltage stress of S_{1} is 731 V. Figure 22b shows the waveforms of v_{gs1}, v_{D2}, and i_{D2}, and the voltage stress of D_{2} is 225 V. Figure 22c shows the waveforms of v_{gs2}, v_{o}, i_{L1}, and i_{L3}, and the output voltage of the proposed converter is 47.9 V.
When v_{1} = 250 V, we obtain the experimental results in the stepdown mode at full load as shown in Fig. 23. As illustrated in Fig. 23, the duty cycle of S_{1} is 0.4, and the output voltage of the proposed converter in the stepup mode is 47.9 V. The voltage stresses of S_{1} and D_{2} are 640 V and 173 V.
When v_{1} = 250 V, we obtain the experimental results in the stepdown mode at full load as shown in Fig. 24. As illustrated in Fig. 24, the duty cycle of S_{1} is 0.253 and the output voltage of the proposed converter in the stepup mode is 47.9 V. The voltage stresses of S_{1} and D_{2} are 785.5 V and 245 V.
Similarly, compare with the simulation results in Fig. 17, the experimental results in the stepdown mode are consistent with it. Both of them are then consistent with the theoretical analysis.
We obtain the input and output current waveforms in the stepup/stepdown mode at full load as shown in Fig. 25. Figure 25a shows the current waveforms in the stepup mode, and Fig. 25b shows the current waveforms in the stepdown mode. As illustrated in Fig. 25, the input and output current ripple of the proposed converter is low.
The measured efficiency curve of the experimental circuit in the stepup mode is shown in Fig. 26a. Figure 26b shows the measured efficiency curve of the experimental circuit in the stepdown mode. Compare with Fig. 14, it can be seen that the proposed circuit’s measured efficiency curve agrees with the calculation curve. The trends of the curves are increased firstly and then decreased. Furthermore, because the actual total loss is not taken into account in the calculation, the maximum measured efficiency is less than the theoretical calculation value.
When the proposed converter operates under rated conditions and the best turn ratio is \({\lambda }_{opt}\) = 0.394, we obtain the experimental loss of the proposed converter as shown in Fig. 27. As illustrated in Fig. 27, the loss is mainly concentrated on the switching and the coupled inductor in the stepup/stepdown mode.
The conversion efficiency versus the output power in the stepup mode and stepdown mode is plotted in Fig. 28.In the stepup mode, the maximum efficiency of the proposed converter is 93.5%. In the stepdown mode, the proposed converter has a maximum efficiency of 92.2%.
Comparing Figs. 28 and 15, we found that the trends of the measured efficiency curve and the calculation curve ere consistent in the stepup/stepdown mode. The trends increased at first and then decreased as the output power increased. Similarly, because the actual total loss was not taken into account, the maximum measured efficiency was less than the theoretical calculation value.
Conclusion
The use of a tapped inductor in this research improved the bidirectional DCDC converter’s conversion ratio and overcame the shortcomings of the nonisolated bidirectional DC–DC converter’s low conversion ratio. Furthermore, a series of bidirectional highgain Cuk circuits was derived by summarizing and analyzing the various forms of the proposed coupled inductor. The best circuit was obtained by analyzing and comparing the characteristics of each circuit, and we proposed a bidirectional highgain Cuk circuit with a capacitortapped inductor (reverse coupling). In both the stepdown and stepup operation modes, this converter had a simple structure and a high voltage gain. Following this, the proposed circuit’s operational principles and characteristics were thoroughly examined. In addition, the efficiency of the proposed converter was improved further after the optimal selection of the coupled inductor’s turn ratio. Finally, we created a 400 W 48 V/400 V prototype to verify the validity of the proposed circuit’s theoretical analysis.
Data availability
The datasets of this study are available from the corresponding author on reasonable request.
References
Lai C.M., Lin, Y.C., & Lin, Y.J. Newlyconstructed bidirectional DC/DC converter topology with high voltage conversion ratio for vehicle to DCmicrogrid (V2DCG) system. in 2015 IEEE 2nd International Future Energy Electronics Conference (IFEEC). (IEEE, 2015).
Yamamoto, Y., Takiguchi, T., & Sato, T. et al. Twophase interleaved bidirectional converter inputparallel outputseries connection. in (Lee, W.C., Hyun, D.S., Lee, T.K. eds.) A novel control method for threephase PWM rectifiers using a single current sensor (ISPE 2015). IEEE Trans. Power Electron. 15(5), 861–870 (2000).
Hongfei, Wu. et al. High stepupstepdown nonisolated BDC with builtin DCtransformer for energy storage systems. IET Power Electron. 7(13), 2571–2579 (2016).
Wu, H. et al. High stepup/stepdown softswitching bidirectional DC–DC converter with coupledinductor and voltage matching control for energy storage systems. IEEE Trans. Indus. Electron. 63(5), 2892–2903 (2016).
Liu, H. et al. A novel reversal coupled inductor highconversionratio bidirectional DC–DC converter. IEEE Trans. Power Electron. 2017, 1–1 (2017).
Ardi, H., Reza Ahrabi, R. & Ravadanegh, S. N. Nonisolated bidirectional DC–DC converter analysis and implementation. IET Power Electron. 7(12), 3033–3044 (2014).
Zhang, Y. et al. Interleaved switchedcapacitor bidirectional DCDC converter with wide voltagegain range for energy storage systems. IEEE Trans. Power Electron. 33(5), 3852–3869 (2018).
Ding, Y., He, L., Liu, Z. Bidirectional bridge modular switchedcapacitorbased DCDC converter with phaseshift control. in 2016 IEEE Energy Conversion Congress and Exposition. Milwaukee, USA. (IEEE, 2016).
Cornea, O. et al. Bidirectional power flow control in a DC microgrid through a switchedcapacitor cell hybrid DCDC converter. IEEE Trans. Indus. Electron. 64(4), 3012–3022 (2017).
Hong, C.M. et al. Novel bidirectional DC–DC converter with high stepup/down voltage gain. 2009 Energy Conversion Congress and Exposition (IEEE, 2009).
Zhang, M., Xing, Y., Wu, H. et al. A dual coupled inductorsbased high stepup/stepdown bidirectional dc–dc converter for energy storage system. in 2017 IEEE Applied Power Electronics Conference and Exposition(APEC). Tampa, USA. (IEEE, 2017).
Hongxing, C. H. E. N., Weiming, L. I. N. & Tao, Z. E. N. G. A high gain stepup Cuk circuit with scalable cell. Proc. CSEE 39(23), 7013–7022 (2019).
Hongxing, C., Weiming, L. & Tao, Z. A novel high gain bidirectional DC–DC Cuk converter and its improved fuzzy control. Proc. Chin. Soc. Electr. Eng. 41(17), 6025–6039 (2021).
Akhormeh, A. et al. High gain bidirectional quadratic DC–DC converter based on coupled inductor with current ripple reduction capability. IEEE Trans. Indus. Electron. 68(9), 7826–7837 (2021).
Zhang, Y., Liu, H. & Li, J. A lowcurrent ripple and wide voltagegain range bidirectional DC–DC converter with coupled inductor. IEEE Trans. Power Electron. 35(2), 1525–1535 (2019).
Acknowledgements
This work was partially supported by the National Natural Science Foundation of China(No: 52172327) and the Fujian Province Natural Science Foundation(Nos.: 2021J011028, 2020J01860) and the Fuzhou Science and Technology Plan Project (No. 2021S236). And we thank LetPub (https://www.letpub.com) for its linguistic assistance during the preparation of this manuscript.
Author information
Authors and Affiliations
Contributions
H.X. contributed to the laboratory prototype experiments, study design, interpretation, analyses, and manuscript preparation. W.M. proposed the main idea and contributed to the study design and manuscript revision. W.R. contributed to the laboratory prototype experiments and manuscript preparation. W.H. contributed to the manuscript revision. All authors contributed to and have approved the final manuscript.
Corresponding authors
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Chen, H., Lin, Wm., Liu, Wr. et al. Tappedinductor bidirectional Cuk converter with high stepup/down conversion ratio and its optimum design. Sci Rep 12, 13745 (2022). https://doi.org/10.1038/s4159802217801z
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s4159802217801z
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.