Chang-Soon Lim

A Modularized Equalization Method Based on Magnetizing Energy for a Series-Connected Lithium-Ion Battery String

A single charge equalizer using the multi-winding transformer (SCEMT) is useful for the precise and fast equalization. Since this type of equalizer requires voltage sensing circuits for each battery cell, the size and cost of the overall equalizer system increase. In this paper, a novel switching method, which does not require voltage sensing circuits, is proposed for the SCEMT. However, due to the problems related to the implementation of multiwinding in a single transformer, the SCEMT is definitely difficult to apply to long series-connected lithium-ion battery string. In order to overcome these drawbacks, a novel module charge equalizer based on the configuration of the SCEMT is developed. Unlike the conventional module charge equalizer using additional components, the proposed novel module charge equalizer utilizes the magnetizing energy of the multiwinding transformer for the equalization among modules. Therefore, proposed module charge equalizer does not suffer from the size, cost, and loss related to the modularization. The validity of the proposed module charge equalizer is verified through experimental results.

Battery voltage sensorless charge equalizer using the multi-winding transformer

A simple and easy magnetic coupling equalizer for a series-connected lithium-ion battery string is presented. The equalizer applies identical duty cycle to all active power switches without using the voltage sensing circuits and the secondary side components of multi-winding transformer. During the turn-on switching interval, the equalizer automatically transfers energy from the high-voltage battery cells to the low-voltage battery cells. The proposed equalizer can effectively reduce size, cost, and design complexity of the equalizer system.

A modularized charge equalizer using the magnetizing energy of the multi-winding transformer

The modularized equalizers use additional components among the modules in the long series-connected lithium-ion battery string. In these approaches, the overall systems are heavy, bulky, and high-priced. Furthermore, the losses related to additional components decrease the system efficiency. To avoid these problems, a modularized equalizer, which has no additional components among the modules, is required. This paper proposes a novel control scheme using the magnetizing energy of the multi-winding transformer for the module equalization. In this scheme, the high duty cycle is applied to the module where the voltage is higher than the reference voltage and the low duty cycle is applied to the module where the voltage is lower than the reference voltage. Due to the different duty cycle, more electric charges are transferred from high voltage module to the low voltage module during the turn-off switching interval. Using the proposed control scheme, the equalizer system does not suffer from the size, cost, and loss related to the modularization. The experimental results are provided to verify the effectiveness of the proposed modularized equalizer.

Averaged modeling and control of a single-phase grid-connected two-stage inverter for battery application

This paper proposes a small-signal averaged model and control design of a single-phase grid-connected two-stage inverter to comprehend its dynamic characteristics for battery application. However, when the circuit analysis of two-stage inverter is attempted at the same time, mathematical procedure for deriving its dynamic equation is very complex and difficult. The main idea of modeling for two-stage inverter is that bi-directional DC-DC converter or single-phase full-bridge DC-AC inverter is replaced with an equivalent current source, and then the dynamic equations for the separated converter and inverter are derived by using state-space averaging technique. The procedures for building the small-signal model of two-stage inverter is described in detail. Based on the derived small-signal model, the individual controllers are designed in a frequency-domain analysis. The input current and DC-link voltage controllers are used for converter, while the grid current controller is used for inverter. The simulation results illustrate that the validity of the proposed modeling approach and the controller design is well verified.

A high efficiency non-isolated bidirectional DC-DC converter with zero-voltage-transition

A high efficiency bidirectional dc-dc converter is proposed for energy storage systems. In the proposed bidirectional converter, a simple auxiliary circuit has been applied to provide soft switching at both modes of operation. By added a resonant cell, the converter can realize zero-voltage-transition (ZVT) where both the switch and the rectifier diode achieve soft condition without increasing their voltage and current stresses. The proposed converter has the advantages of simple circuitry, reduced size, low cost and high efficiency because of a single resonant inductor. The operation principle of the converter is analyzed and described. Simulation results of the proposed bidirectional ZVT dc-dc converter are shown to verify its feasibility.

A Modularized Charge Equalizer Using the Magnetizing Energy of the Multi-Winding Transformer

The modularized equalizers use additional components among the modules in the long series-connected lithium-ion battery string. In these approaches, the overall systems are heavy, bulky, and high-priced. Furthermore, the losses related to additional components decrease the system efficiency. To avoid these problems, a modularized equalizer, which has no additional components among the modules, is required. This paper proposes a novel control scheme using the magnetizing energy of the multi-winding transformer for the module equalization. In this scheme, the high duty cycle is applied to the module where the voltage is higher than the reference voltage and the low duty cycle is applied to the module where the voltage is lower than the reference voltage. Due to the different duty cycle, more electric charges are transferred from high voltage module to the low voltage module during the turn-off switching interval. Using the proposed control scheme, the equalizer system does not suffer from the size, cost, and loss related to the modularization. The experimental results are provided to verify the effectiveness of the proposed modularized equalizer.

Analytical approach of circulating currents mitigation effect using coupled inductor in the parallel three-phase boost converters

This paper analyzes characteristic of the three-phase coupled inductor connected to ac source to effectively mitigate the high-frequency circulating current generated in the parallel three-phase boost converters. The three-phase coupled inductor analysis presented in this paper uses the three-phase coupled inductor structure and voltage equations. Based on this analysis, the three-phase coupled inductor is added to the conventional averaged model. As a result, the novel averaged model which can reduce the low and high-frequency circulating current simultaneously is developed. Using the zero-sequence component of the novel averaged model, each total inductance to the circulating current of the three-phase coupled inductor and line inductor can be obtained. Simulation and experiment results verify the usefulness of three-phase coupled inductor in the parallel three-phase boost converters.

Modeling and Control of Two-Stage Inverter for Battery Energy Storage System

This paper proposes a small-signal model and control design of two-stage inverter for battery energy storage system (BESS) to comprehend its dynamic characteristics. However, when the circuit analysis of two-stage inverter is attempted simultaneously, mathematical procedure for deriving its dynamic equation is very complex and difficult. The main idea of modeling for two-stage inverter is that bi- directional DC-DC converter or single-phase full- bridge DC-AC inverter is replaced with an equivalent current source, and then the dynamic equations for the separated converter and inverter are derived by using state-space averaging technique. The procedures for building the small-signal model of two-stage inverter is described in detail. Based on the derived small-signal model, the individual controllers are designed in a frequency-domain analysis. The input current controller is used for bi-directional DC-DC converter, while the dc-link voltage controller and grid current controller are used for single-phase full-bridge DC-AC inverter. The simulation results illustrate the validity of the small-signal model and the controller design.

Modularized battery cell voltage equalization circuit using extended multi-winding transformer

This paper proposes a new circuit for equalization of battery cell voltage. Proposed circuit is using extended multi-winding transformer. This circuit achieved the balancing operation between the modules by connecting the winding between the transformers. Cantilever transformer model is used to analyze the balancing performance. And the balancing deviation between the modules is drawn through this model. Contrary to the conventional circuit, the advantage of proposed circuit is easy to modularize and control and the number of batteries is not limited. This point can be important advantages to balanced many series connected battery cell voltages in applications such as HEV required the high voltages. This paper analyzed the proposed circuit theoretically. And to verify the proposed circuit, the prototype board is designed and implemented. Experimental results verify that this circuit achieved the good battery cell balancing performance.

Non-isolated bidirectional ZVT converter with a single resonant inductor for energy storage system

This paper proposes a non-isolated bidirectional dc-dc converter for use in renewable power generation, fuel cell, battery, electric vehicles (EV), and small scale DC-UPS systems. Compared to the traditional bidirectional dc-dc converters, the proposed converter integrates interleaved synchronous energy flow and soft switching technology. By using a resonant cell, the converter can realize zero-voltage-transition (ZVT) where both the switch and the rectifier diode achieve soft condition without increasing their voltage and current stresses. The proposed converter has the advantages of simple circuitry, reduced size, low cost and high efficiency because of a sing resonant inductor. The operation principle of the converter is analyzed and described. Simulation results of the proposed bidirectional ZVT dc-dc converter are shown to verify its feasibility.