Bidirectional Cuk Converter Research Articles

Analysis and Design of a Battery and Supercapacitor‐Based Propulsion System for Electric Vehicles

ABSTRACTThis work deals with the design and development of a dual source based propulsion architecture for electric vehicles. The converter utilized for the propulsion system is derived from a conventional CuK converter, which operates in a bidirectional power flow mode. The proposed propulsion system has two energy sources: a battery and a supercapacitor (SC). The proposed system has continuous input and output currents at low and high voltage sides, which improves the cycle life of hybrid energy storage (SC and battery) and the DC‐link capacitor. Further, the proposed converter has magnetic reduction compared to a conventional two‐input bidirectional CuK converter. Moreover, an effective and simpler control strategy (only one switch is pulse width modulated (PWM) operated at a time) has been developed for energy management between sources during charging (regenerative braking) and discharging (propulsion), which is effectively verified by simulation and experimental results. Further, a frequency domain (bode plot)‐based technique is used for controller design and stability analysis of the proposed system.

Active Equalization for Lithium-Iron Battery Pack Based on Reduced-Order Solving Strategy for the Hanoi Tower Problem

In order to address the energy imbalance issue of a series-connected lithium-iron battery pack, this paper proposes an active equalization method based on a reduced-order solving strategy for the Hanoi Tower problem. The proposed scheme utilizes a combined structure of a switching-network circuit and a bidirectional Cuk converter and leverages an ultracapacitor cell as the energy-transfer carrier. Simulation and comparison demonstrate that the exchange of unbalanced energy within the battery pack can be achieved. The proposed approach can effectively achieve various balancing modes such as cell-to-cell, cell-to-string, string-to-cell, and string-to-string with a relatively fast balancing speed.

An improved equalization circuit with bidirectional CUK converter for series-connected battery strings

This paper proposed an improved equalization circuit based on a bidirectional CUK converter. Compared with traditional bus equalization circuits based on CUK converter, it owns a simpler structure with fewer inductors, resulting in a smaller volume and higher energy density of the proposed equalization circuit. The operation principle and steady-state characteristic of the equalizer are analysed. The equalizer is applied to the energy balance of the series-connected battery strings, and the balance principle is designed. The proposed equalization system achieves a fast energy balance of the battery pack. Simulation results verify the effectiveness of the designed equalization circuit and balance strategy.

An Active Equalization Method of Battery Pack Based on Event-Triggered Consensus Algorithm

In this paper, a control strategy of a cell-based multi-agent system is proposed to solve the problem of inconsistency of series lithium-ion battery packs. The bidirectional Cuk converter is utilized as an equalizing circuit serving for balancing adjacent cells in a pack. A SOC-based consensus control with a time-triggered mechanism (TTM) is proposed. In order to reduce the actuator updates, the control method is ameliorated by altering TTM to an event-triggered mechanism (ETM). Adjustable balancing currents are designed in both TTM and ETM methods for the acceleration of the equalization process. The cases in dynamic environments under externally imposed charging/discharging currents by adopting TTM and ETM methods are investigated in detail. By comparison, the simulations and hardware-in-the-loop (HIL) experiments with a Typhoon real-time simulator are illustrated to show that, both in standby or external charging/discharging conditions, the proposed ETM algorithms are superior to TTM’s in terms of equalization time and adaptability to the external environment.

Tapped-inductor bi-directional Cuk converter with high step-up/down conversion ratio and its optimum design

A bidirectional DC–DC converter is required for an energy storage system. High efficiency and a high step-up and step-down conversion ratio are the development trends. In this research, a series of bidirectional high-gain Cuk circuits was derived by combining tapped inductors and bidirectional Cuk. After analyzing and comparing the characteristics of each circuit, a bidirectional high-gain Cuk circuit with a tapped-inductor (reverse coupling) was proposed. The proposed converter has a simple structure and a high voltage gain in both the step-down (Buck) and step-up (Boost) operation modes. The voltage stress of S2 was low. The voltage stress of S1 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 tapped-inductor 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 step-up and step-down modes, respectively. These findings verified the validity of the proposed circuit’s theoretical analysis.

Design of energy balancing circuit for battery cells connected in series based on modifying the bidirectional CuK converter

<abstract> <p>This paper proposes a design of energy balance circuit for two adjacent Lithium-ion battery cells in the cell string based on the modifying of the bidirectional CuK converter principle. This design only uses one MOSFET to transfer energy between two cells in a direction controlled by the first relay, second relay controls the cutting energy balance circuit off the cells when they have the same energy level. The control command sent by the management battery system (BMS) to the energy balance circuit via an RS485 communication protocol controls the direction of transferring energy, the amplitude of the balance current, the frequency and duty of PWM, the PWM signal applied to MOSFET is programmed by a microprocessor PIC18F2685. This design overcomes some disadvantages caused by applying the principle of bidirectional CuK converter to design the energy balancing circuit, these are the need for a multiple level DC source to open MOSFETs and issue of the energy loss on the elements of energy balance circuit. This design is also easy to expand for the battery string with a large number of cells. The energy balance control strategy can be implemented directly by each the energy balance circuit or remotely by BMS using RS485 communication. The experimental results of online optimal energy balance control based on state of charge (SoC) feedback for 07 SAMSUNG 22P battery cells connected in series are presented to prove the efficiency of the energy balance circuit design for two adjacent cells proposed in this paper.</p> </abstract>

Optimal SoC Balancing Control for Lithium-Ion Battery Cells Connected in Series

The optimal state of charge (SoC) balancing control for series-connected lithium-ion battery cells is presented in this paper. A modified SoC balancing circuit for two adjacent cells, based on the principle of a bidirectional Cuk converter, is proposed. The optimal SoC balancing problem is established to minimize the SoC differences of cells and the energy loss subject to constraints of the normal SoC operating range, the balancing current, and current of cells. This optimization problem is solved using the sequential quadratic programming algorithm to determine the optimal duties of PWM signals applied to the SoC balancing circuits. An algorithm for the selection of the initial points for the optimal problem-solving process is proposed. It is applied in cases where the cost function has no decreasing part. Experimental tests are conducted for seven series-connected Samsung cells. The optimal SoC balancing control and SoC estimation algorithms are coded in MATLAB and embedded in LabVIEW to control the SoC balancing in real time. The test results show that the differences between the SoCs of cells converges to the desired range using the proposed optimal SoC balancing control strategy.

Contribution management of lead‐acid battery, Li‐ion battery, and supercapacitor to handle different functions in EVs

One of the most concerning issues regarding electrical vehicles (EVs) is limited driving cycle and protracted charging process. In order to improve the efficiency of current batteries, appropriate energy management systems (EMSs) could be deployed to compensate these defects. To overcome these obstacles, an EMS including a bidirectional Cuk converter and a battery storage with two types of batteries is proposed. Lithium-ion (Li-ion) and lead-acid battery types are considered as the main battery and auxiliary battery packs, respectively. Moreover, a supercapacitor is utilized to help the auxiliary battery for handling fast dynamics of the power delivery in braking and acceleration conditions. While the function of the main battery is to be charged and discharged in normal conditions, handling harsh conditions lies upon the auxiliary battery. So, the auxiliary battery can be rapidly discharged during acceleration and quickly recharged in charge stations. Furthermore, it can be used for an exchangeable battery strategy aimed at reducing congestion at charge stations. In order to plan for different scenarios, a Cuk converter is employed as a convenient interface between the batteries to manage power sharing. Operation of the system in different modes are discussed comprehensively. The performance of the proposed topology is assessed using some simulations and experiments in different conditions.

Bidirectional Quasi-Cuk DC/DC Converter with Reduced Voltage Stress on Capacitor and Capability of Changing the Output Polarity

In this paper, a bidirectional topology for quasi-Cuk dc/dc converter with capability of zero-voltage and zero-current-switching (ZVZCS) is proposed. The bidirectional quasi-Cuk (BQ-Cuk) converter has different voltage and current transfer ratio, reduced voltage stress on capacitor and capability of changing the output polarity in comparison with conventional bidirectional Cuk converter. In this paper, steady-state analysis of the quasi-Cuk converter with capability of ZVZCS in turn-on is presented. Then, critical inductances for transient from this operation to two new operations are calculated. Next, besides values designing of used elements, maximum and minimum value of their current and voltage are calculated. Finally, experimental results to verify the accuracy of the proposed converter in different operating modes are presented.

Photovoltaic Maximum Power Point Tracking System Based on Bidirectional Cuk Converter

外界环境温度和光照强度等因素直接影响着光伏阵列的输出特性，如果能够使光伏电池一直工作于最大功率输出状态，就可以大大提高太阳能的利用率。本文介绍了当前常用的几种光伏电池最大功率点追踪(maximum power point tracking, MPPT)方法，论述了一种基于双向Cuk变换器电路对光伏电池进行MPPT的方法，利用Matlab/Simulink仿真平台对光伏发电系统的整体结构进行了仿真，仿真结果表明了该方法的可行性。 The output of photovoltaic (PV) array is influenced by the environmental factors such as irradia-tion and temperature, if we can make sure that the photovoltaic array operates at the maximum power point, solar energy can get a high utilization rate. This paper introduces a variety of com-mon photovoltaic maximum power point tracking (MPPT) methods, discusses one using of a bidirectional Cuk converter method for MPPT of photovoltaic cells, through the simulation of photovoltaic system based on the Matlab/Simulink platform, the results verify the feasibility of this method.

Fuzzy Controlled Individual Cell Equalizers for Lithium-Ion Batteries

A fuzzy logic control battery equalizing controller (FLCBEC) is adopted to control the cell voltage balancing process for a series connected Li-ion battery string. The proposed individual cell equalizer (ICE) is based on the bidirectional Cuk converter operated in the discontinuous capacitor voltage mode (DCVM) to reduce the switching loss and improve equalization efficiency. The ICE with the proposed FLCBEC can reduce the equalizing time, maintain safe operations during the charge/discharge state and increase the battery string capacity.

Individual Cell Equalization for Series Connected Lithium-Ion Batteries

A systematic approach to the analysis and design of a bi-directional Cuk converter for the cell voltage balancing control of a series-connected lithium-ion battery string is presented in this paper. The proposed individual cell equalizers (ICE) are designed to operate at discontinuous-capacitor-voltage mode (DCVM) to achieve the zero-voltage switching (ZVS) for reducing the switching loss of the bi-directional DC/DC converters. Simulation and experimental results show that the proposed battery equalization scheme can not only enhance the bi-directional battery equalization performance, but also can reduce the switching loss during the equalization period. Two designed examples are demonstrated, the switch power losses are significantly reduced by 52.8% from the MOSFETs and the equalization efficiency can be improved by 68-86.9% using the proposed DCVM ZVS battery equalizer under the specified cell equalization process. The charged/discharged capacity of the lithium-ion battery string is increased by using the proposed ICEs equipped in the battery string.