Efficiency analysis of a bidirectional DC/DC converter in a hybrid energy storage system for plug-in hybrid electric vehicles

doi:10.1016/j.apenergy.2016.08.178

Applied Energy

Volume 183, 1 December 2016, Pages 612-622

https://doi.org/10.1016/j.apenergy.2016.08.178 Get rights and content

Highlights

•
A detailed analysis method of the losses in the DC/DC converter has been proposed.
•
A theoretical model for calculate the efficiency of the converter has been proposed.
•
The influences on the converter’s efficiency are experimentally investigated.

Abstract

A bidirectional (Bi) DC/DC converter is one of the key components in a hybrid energy storage system for electric vehicles and plug-in electric vehicles. Based on the detailed analysis of the losses in the converter, this paper firstly develops a model to theoretically calculate the efficiency of the converter. Then, the influences of temperature, switching frequency, duty cycle and material of switching device on the converter’s efficiency are experimentally investigated. The analysis of the experimental results has shown that (1) The efficiency at the switching frequency of 15 kHz is about 2% higher than that of 25 kHz. (2) The efficiency at 25 °C is similar to that at 85 °C for the MOSFET SiC while the efficiency at 25 °C is 2% higher than that at 85 °C for the IGBT Si for both buck and boost modes. (3) In buck mode, when the duty cycles are decreasing from 66.7%, 50% to 33.33%, the peak efficiencies are also decreasing from 97.6%, 94.5% to 90.3%, respectively. In boost mode, when the duty cycle is increasing from 33.33%, 50% to 75%, the peak efficiency is decreasing from 96.9%, 96.5% to 92.4%, respectively. (4) The developed model can calculate the converter’s efficiency accurately

Introduction

Nowadays, the development of electric vehicles (EVs) and plug-in electric vehicles (PHEVs) has gained more attention as they can reduce greenhouse gas emissions and improve air quality. EVs, especially PHEVs, require energy storage systems (ESSs) with high energy and power density [1], [2], [3], [4], [5]. A single battery system cannot meet such requirement. A hybrid ESS which consists of a bidirectional (Bi) DC/DC converter, batteries and ultracapacitors is a solution, where the batteries mainly store energy and the ultracapacitors mainly release and absorb power. This can be realized by adjusting the voltage level of the ultracapacitors through Bi DC/DC converter in the ESS [6], [7], [8], [9]. Therefore, it is very important to understand the efficiency of Bi DC/DC converters under different working conditions, making efficient hybrid ESSs [10].

The influences of topology, frequency, switching method, temperature and duty cycle on the efficiency of Bi DC/DC converters have been investigated. In [11], [12], the influences of two topologies on the efficiency of the converter are studied. The simulation and experimental results show that the proposed topologies have the merit of high efficiency. The effect of the frequency on the efficiency of the converter is investigated by applying the adaptive frequency modulation [13]. The converter with low ripple achieves the maximum efficiency up to 87%. In [14], a new digital PWM technique is used to explore the relationship between frequency and efficiency. The results show that high switching frequency leads to low efficiency and vice versus. In order to increase efficiency of the converter, zero voltage switching based on resonant technique is proposed to reduce switching loss [15], [16], [17].

Some researchers study the influence of temperature on the efficiency of the converter [18], [19], [20]. They select SiC as the switching devices to evaluate the performance of the converter at high ambient temperatures. The high efficiency can be achieved at high temperature environment in the converter with the SiC switching devices. Different duty cycles are adopted in the converter to study their effects on the efficiency based on the proposed efficiency model [21]. The experimentally measured and theoretically calculated efficiencies are compared at two different duty cycles: D = 0.33 and D = 0.5 to show their effects.

There are two drawbacks in the above mentioned studies. First, they only explore the influence of one factor on the efficiency. Second, they do not consider the effect of the switching devices used in the converter: MOSFET SiC or IGBT Si, on the efficiency. One purpose of this study is to analyze the influences of multi-factors, such as temperature, switching frequency, duty cycle and material of switching device, on the efficiency of a Bi DC/DC converter. Another purpose is to develop the efficiency model of the converter. The experimental results verify the accuracy of the proposed efficiency model.

The rest of the paper is organized as follows. In Section 2, a Bi DC/DC buck-boost converter is analyzed. The efficiency model of the converter is established in Section 3. The experimental platform is introduced and the efficiencies from the experiments under different operating conditions are analyzed in Section 4. The efficiencies from the model and those from the experiments are compared in Section 5. Finally, the conclusions are presented in Section 6.

Section snippets

Selection of Bi DC/DC converter

Many topologies of Bi DC/DC converter are used in hybrid energy storage systems (HESSs) [2]. Fig. 1 shows the fundamental topology of the HESS which has been chosen in this study, where a battery pack is connected to a Bi DC/DC converter and the converter is then connected to an ultracapacitor pack.

Three reasons are considered in the selection of this Bi converter. First, the energy in HESSs should be allowed to transfer in two directions, where the current can either flow from the battery pack

Efficiency model of Bi buck-boost converter

To develop the efficiency model, the detailed analysis of the losses for each of components in a Bi buck-boost converter is conducted when the converter is operating in steady state. Generally, the losses include switching loss and conduction loss. In this paper, the efficiency model for the buck mode will be only developed and analyzed in detail since the procedure to develop the efficiency model for the boost mode is similar to that for the buck mode.

Experimental design scheme

Different temperatures, materials of the switching devices, duty cycles and switching frequencies as presented in Table 2 as well as two working modes for the Bi DC/DC converter will be considered in the experiments. In the buck mode, the input voltage is set to 300 V, the output voltage will be 100 V at K_D₁ = 33.33%, 150 V at K_D₁ = 50% and 200 V at K_D₁ = 66.67%, respectively. In the boost mode, the input voltage is set to 50 V, the output voltage is 75 V at K_D₂ = 33.33%, 100 V at K_D₂ = 50% and 200 V at K_D₂ = 75%,

Comparison of model and experimental efficiencies

The model and experimental efficiencies are compared under different working modes, duty cycles and the materials of the switching devices. Fig. 14, Fig. 15 show their comparison results and absolute errors (AEs), respectively.

It can be seen from Fig. 15(a)–(c) that the maximum AE is around 10% and the minimum AE is nearly 0.7% for the buck mode. It can also be seen from Fig. 15(d)–(f) that the maximum AE is 15% and the minimum AE is nearly 0.5% for the boost mode. The reasons to cause these

Conclusions

This paper develops the efficiency model for a Bi DC/DC converter. The model and experimental efficiencies are compared to show that the proposed efficiency model has high accuracy which can be applied to predict the efficiency of the Bi DC/DC converter under different working conditions. Furthermore, the influences of the multi-factors, such as temperatures, materials of the switching devices, duty cycles and switching frequencies, on the efficiency of the converter has been experimentally

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 51507012, 51675042) and the Joint Funds of the National Natural Science Foundation of China (Grant No. U1564206). Any opinions expressed in this paper are solely those of the authors and do not represent those of the sponsor.

References (30)

Baha M. Al-Alawi et al.
Review of hybrid, plug-in hybrid, and electric vehicle market modeling studies
Renew Sustain Energy Rev
(2013)
Y. Kim et al.
A scalable and flexible hybrid energy storage system design and implementation
J Power Sources
(2014)
S. Zhang et al.
Battery durability and longevity based power management for plug-in hybrid electric vehicle with hybrid energy storage system
Appl Energy
(2016)
F. Sun et al.
A systematic state-of-charge estimation framework for multi-cell battery pack in electric vehicles using bias correction technique
Appl Energy
(2016)
Z. Song et al.
Multi-objective optimization of a semi-active battery/supercapacitor energy storage system for electric vehicles
Appl Energy
(2014)
M. Venkatesh Naik et al.
Analysis of ripple current, power losses and high efficiency of DC-DC converters for fuel cell power generating systems
Renew Sustain Energy Rev
(2016)
M. Eccher et al.
Measurements of power transfer efficiency in CPV cell-array models using individual DC–DC converters
Appl Energy
(2015)
Ali Castaings et al.
Comparison of energy management strategies of a battery/supercapacitors system for electric vehicle under real-time constraints
Appl Energy
(2016)
E. Duran et al.
A high-flexibility DC load for fuel cell and solar arrays power sources based on DC-DC converters
Appl Energy
(2011)
J. Sun et al.
A study of efficiency characteristics and related issues of DC/DC converter
J Xi’an Univ Technol
(2013)

X. Ding et al.

Comprehensive comparison between silicon carbide MOSFETs and silicon IGBTs based traction systems for electric vehicles

Appl Energy

(2016)

J. Li et al.

SMES/battery hybrid energy storage system for electric buses

IEEE Trans Appl Supercond

(2016)

Hamed Mashinchi Mahery et al.

Mathematical modeling of buck-boost dc-dc converter and investigation of converter elements on transient and steady state responses

Int J Electr Power Energy Syst

(2013)

Hugues Renaudineau et al.

DC–DC converters dynamic modeling with state observer-based parameter estimation

IEEE Trans Power Electron

(2015)

H. Chiu et al.

Letter to the editor a DC/DC converter topology for renewable energy systems

Int J Circuit Theory Appl

(2009)

Cited by (62)

Nonsolitary two-way DC-to-DC converters for hybrid battery and supercapacitor energy storage systems: A comprehensive survey
2024, Energy Reports
Transport vehicles require an energy storage system (ESS) with a long lifespan to sustain their energy and power requirements during the start, acceleration, and recapturing of regenerative braking energy. However, a nonintegrated (i.e., single-use) ESS cannot satisfy the requirements of long lifespan, high energy, and power. Hence, a nonisolated direct current-to-direct current (DC-to-DC) bidirectional converter is widely used to integrate the battery and supercapacitor, thus meeting the requirements for vehicle starting, acceleration, and braking energy. Hybrid batteries and supercapacitor energy storage systems (HBSCESSs) are crucial because they preserve the battery lifespan. Supercapacitors handle the high transient currents and power requirements of these systems. However, the performance of HBSCESS depends on the converter configuration. There has been no comprehensive consolidated survey of nonisolated two-way DC-to-DC converters for possible HBSCESS development. It is imperative to compile this coherent analysis to help academia and industry select appropriate converter topologies for HBSCESS development, ideas, and guidance for new possible converters in transport vehicles, DC microgrids, and renewable energy source systems. This study provides an in-depth literature review and classification, assesses whether these converters provide a unified approach for HBSCESS development, and offers feasible solutions for future considerations. In addition, it provides recent research trends and recommendations for developing converters. This study analyzes the available literature on nonisolated converters for HBSCESS development. The analysis shows that multi-input, multi-port, three-port, coupled-inductor, switched-capacitor, and z-source/quasi-z-source converters are suitable for providing a unified hybrid energy storage system (HESS) comprising a battery and supercapacitor. They provide bidirectional power flow in both input ports for applications in transport vehicles, DC microgrids, and renewable energy source systems. The results also show that a single-inductor multi-input converter topology can be used for HBSCESS because it offers simple design, high efficiency, low component count, and moderate duty cycle operation.
A novel power control scheme for distributed DFIG based on cooperation of hybrid energy storage system and grid-side converter
2024, International Journal of Electrical Power and Energy Systems
Due to the uncertainty of wind energy, the wind power is difficult to be dispatched and may cause the voltage fluctuations for distributed network. Therefore, a novel power control scheme is proposed to manage the output power of the distributed doubly-fed induction generator (DFIG) by cooperating the hybrid energy storage system (HESS). In the proposed scheme, the grid-side converter of DFIG is controlled to manage overall output power of the DFIG/HESS hybrid system in accordance to the power dispatching command. The HESS is utilized to deal with the power difference between DFIG generation power and the power dispatching command. The HESS is embedded in the DC-link bus of DFIG and is composed of superconducting magnetic energy storage and batteries. Additionally, in order to avoid HESS from overcharging and over-discharging, the pitch angle control and power dispatching command are adjusted by considering the state of charge (SOC) of HESS. Finally, the simulation model of distributed DFIG and HESS is built on the real-time digital simulation (RTDS) platform, and the simulation results validate the effectiveness and reliability of the proposed power control scheme.
Enhancing hybrid energy storage systems with advanced low-pass filtration and frequency decoupling for optimal power allocation and reliability of cluster of DC-microgrids
2023, Energy
This study introduces an innovative power-split approach for hybrid energy storage systems (HESS) and diesel generators, utilizing frequency decoupling and a combination of classical and advanced low-pass-filtration techniques. The HESS dual-loop structure incorporates Super-Twisting-Sliding-Mode-Control, known for its remarkable robustness against uncertainties and external disturbances, effectively suppressing chattering. Among the low-pass-filtration techniques, Advanced Low-Pass-Filtering (ALPF) surpasses Classical Low-Pass-Filtering (CLPF), offering enhanced control statistics. The regulation of supercapacitor setpoint current based on the bank voltage ratio and control inaccuracy of battery current enables the ALPF to address dynamic battery issues. Under three waveforms, thorough simulations show superior load power allocation performance. Smoother waveforms boost supply voltage by 36% and power flow by 0.2%. Root-Mean-Squared-Error and Mean-Absolute-Error evaluations show exceptionally low average errors of 0.72% for Bus voltage, 0.16 A for battery current, and 3 A for supercapacitor current. The system also achieves 99.8% supply efficiency with a load setpoint deviation of less than 1%. ALPF improves supercapacitor performance by 8.4–11% while adjusting for uncompensated battery power. ALPF improves voltage regulation, power losses, load setpoint convergence, power peaks, and recovery. Ultimately, the proposed low-pass-filtration technique significantly enhances system dependability, relieving the burden on HESS while achieving superior loading efficiency.
Contribution to strengthening Bus voltage stability and power exchange balance of a decentralized DC-multi-microgrids: Performance assessment of classical, optimal, and nonlinear controllers for hybridized energy storage systems control
2023, Sustainable Cities and Society
Stability is the primary goal in standalone power systems due to the high penetration and uncertainties of renewable energy resources, so the system reliability is affected, and the hybrid energy storage system (HESS) and diesel generator (DG) compensate for renewables' failures. This study contributes to managing and controlling DC-coupled multi-Microgrids fed by Photovoltaic, HESS, and DG resources and subjected to pulsed loading and uncertain PV outputs, besides battery SOCs and DG fuel constraints. The Dual-loop control structure compares classical Proportional Integral (CPI), Super-Twisting-Sliding-Mode-Control (ST-SMC), and Linear Quadratic Regulator with Integral Action (LQR-I) to evaluate the robustness and control performance of the HESS. For the supercapacitor (SC), a hysteresis current control (HCC) tracks its setpoint currents using a frequency decoupling-based power-split control. Matlab simulations confirmed system reliability by combining controllers with different Key Performance Indicators, where adopting the LQR-I for bus voltage regulation and the ST-SMC for HESS current control outperformed the other combinations and revealed superior system performance, improving Bus voltage regulation, DG current tracking, overall system efficiency, and loading convergence by 67.63(%), 83.63(%), 77.92(%), and 2.72(%), respectively. Instead, the basic CPI enhanced battery and SC current control with 51.55 and 63.94 (%) compared to the winner scenario.
Proposed frequency decoupling-based fuzzy logic control for power allocation and state-of-charge recovery of hybrid energy storage systems adopting multi-level energy management for multi-DC-microgrids
2023, Energy
This paper proposes a decentralized multiple-Direct-Current-Microgrid (multi-DCMG) system to supply affordable load demands while addressing challenges posed by Hybridized-Energy-Storage-Systems (H-ESS) limitations, consumption/generation complexities, and renewables volatility. The paper's contributions include a system feasibility assessment for isolated users and a demonstration of the effectiveness of the control strategies adopted. To improve system resiliency and reliability, the proposed system adopts a high-control level for energy/power balances, using a Mamdani 50 rule-based Fuzzy Logic energy management system (FL-EMS) to supervise State-of-Charge (SoC) recovery. The low-control level manages/supervises DC-DC power converters' powers adopting Proportional-Integral (PI), Hysteresis-Current-Controller (HCC), and Linear-Quadratic-Regulator (LQR) in closed-Control-loops, besides an advanced low-pass-filtering (A-LPF) for load frequency decoupling. The results show that the proposed H-ESS outperformed single-ESS systems in dynamic load changes and renewables' uncertainty, and supercapacitors improved load supply, voltage regulation, and current tracking. However, expensive costs and slow restoration of H-ESS banks from critical SoCs are major drawbacks. The global system assessment demonstrated promising results through proper FL-EMS setpoint computation, stable Bus voltage with 0.55–6.9% deviations due to robust controllers, accurate SoC recovery of HESS batteries at critical SoCs (<10% and >90%), fast and accurate convergence with 3.35–3.37% mismatch, and 99.3% supply efficiency at minor power losses of 0.7–1.55%.
Active temperature control of electric drivetrains for efficiency increase
2023, Applied Energy
Electric vehicle sales have accelerated in recent years due to a wider customer acceptance. However, the still limited driving range continues to be a barrier to purchase for many customers. To improve the driving range, it is particularly important to further reduce all losses in the powertrain. This applies in particular to the temperature-dependent motor and inverter losses. In this context, this paper presents a high-fidelity motor model based on MotorCAD and ANSYS Maxwell, which is thermally controlled using an economic Model Predictive Control (MPC) approach to reduce the temperature dependent losses. A detailed explanation of the high-fidelity motor model is given, followed by a system-level validation including the thermal system model. The setup is used to simulate three different cycles, namely a highway drive, a rural road drive, and a long urban drive. A comparison between the MPC, which actively controls the rotor, winding and the inverter junction temperature, and a rule-based strategy is used to analyse the motor-level losses in detail. While the total MPC savings system level are up to 2.86% at 35 °C ambient temperature, 0.82% of this is saved due to increased temperatures of the motor caused by reduced cooling while driving first highway and then into the city. For a pure highway cycle the motor savings increase up to 1.12%. One major outcome, which is enabled by the detailed modelling approach, is that the majority of those motor savings are originating from reduced ac-copper losses at elevated temperatures. The reason was found to be a lower magnet flux density and a higher winding resistance which both lead to less eddy current losses in the winding. Moreover, the inverter losses were reduced by cooling the inverter prior to acceleration from standstill. By using the NTC behaviour of the IGBTs in low current region, temperature-dependent savings of up to 0.56% were achieved.

View all citing articles on Scopus

View full text

Efficiency analysis of a bidirectional DC/DC converter in a hybrid energy storage system for plug-in hybrid electric vehicles

Highlights

Abstract

Introduction

Section snippets

Selection of Bi DC/DC converter

Efficiency model of Bi buck-boost converter

Experimental design scheme

Comparison of model and experimental efficiencies

Conclusions

Acknowledgements

Renew Sustain Energy Rev

J Power Sources

Appl Energy

Appl Energy

Appl Energy

Renew Sustain Energy Rev

Appl Energy

Appl Energy

Appl Energy

J Xi’an Univ Technol

Comprehensive comparison between silicon carbide MOSFETs and silicon IGBTs based traction systems for electric vehicles

Appl Energy

SMES/battery hybrid energy storage system for electric buses

IEEE Trans Appl Supercond

Mathematical modeling of buck-boost dc-dc converter and investigation of converter elements on transient and steady state responses

Int J Electr Power Energy Syst

DC–DC converters dynamic modeling with state observer-based parameter estimation

IEEE Trans Power Electron

Letter to the editor a DC/DC converter topology for renewable energy systems

Int J Circuit Theory Appl