Jong-Won Shin

Stable Configuration of a Li-Ion Series Battery Pack Based on a Screening Process for Improved Voltage/SOC Balancing

Differences in electrochemical characteristics among Li-ion cells inevitably result in state-of-charge (SOC) imbalance when the existing voltage balancing technique is used. This paper presents a new approach based on a screening process for improved voltage/SOC balancing of a Li-ion series battery pack. Two kinds of screening processes, capacity screening and resistance screening, are implemented in an orderly manner. The capacity screening process matches open-circuit voltage (OCV)-SOC relation for achievement of voltage/SOC balancing. In the resistance screening process, pulse-type discharging/charging currents are applied to various SOC points to select the cells with similar voltage variance. Through two screening processes, the cells that have similar electrochemical characteristics are finally selected, and can be used for stable configuration of a Li-ion series battery pack. The proposed screening process has been validated by extensive experimental results and SOC estimation results based on extended Kalman filter.

Selective flyback balancing circuit with improved balancing speed for series connected Lithium-ion batteries

In this paper, a cell balancing circuit for the Lithium-ion battery string based on the Flyback topology is proposed. The proposed circuit draws the charge out of the high voltage cell and recovers it to the overall battery pack. With the selectivity of the target cell, the proposed circuit uses the minimized power path to simplify the circuit and optimize the balancing efficiency. The circuit also employs the peak current mode control scheme to accelerate the balancing speed and reduce the balancing time. Experimental results with the laboratory prototype hardware for multi-cell battery string verify the feasibility of the proposed scheme.

Low-Common Mode Voltage H-Bridge Converter with Additional Switch Legs

H-bridge converter with additional switch legs (HA converter) and its offspring circuit are proposed in this paper with the intent to reduce the common mode noise. The proposed topology connects grounds of the input and output terminals, which gives zero common mode current in the ideal case. The operation of the proposed circuit is flexible and allows for the circuit to be capable of both ac–dc and dc–ac conversions. The proposed topology is especially advantageous when it is applied to the photovoltaic power conditioning system in dc distribution system or stand-alone power system because they include large stray capacitances and are prone to common mode EMI. In this paper, a 4-switch HA (HA4S) converter for both ac–dc rectification and dc–ac inversion is derived from the proposed HA converter as the implementation example. The experimental results based on the proposed and the conventional prototype circuits prove that the HA4S converter outperforms the conventional counterparts.

Digitally Implemented Average Current-Mode Control in Discontinuous Conduction Mode PFC Rectifier

This paper proposes a digital average current-mode control method in discontinuous conduction mode (DCM) power factor correction rectifier. The proposed control technique does not estimate, but directly senses the average value of the inductor current in each switching cycle. It is implemented by means of a conventional current sensing circuit and a microcontroller. The calculation burden of the microcontroller is the same with that of conventional two-loop-controlled converter because the additional calculation process is not required. The control method achieves lower total harmonic distortion and higher power factor than the conventional technique. Experimental results with a 200-W prototype verify the feasibility and performance of the proposed control method.

High-Efficiency Bridgeless Flyback Rectifier With Bidirectional Switch and Dual Output Windings

This paper proposes and analyzes a new bridgeless flyback power factor correction rectifier for ac-dc power conversion. By eliminating four bridge diodes and adding a few circuit elements, the proposed rectifier reduces the primary side conduction loss and improves efficiency. The addition of the new elements has minimal effect on the circuit simplicity because it does not need any additional gate driver and magnetic elements. The losses in the semiconductor devices of the proposed circuit are analyzed and compared with that of the conventional one, followed by transformer design guideline. Experimental results with the practically implemented prototype prove its higher efficiency than its conventional counterparts.

Digitally Controlled Current Sensorless Photovoltaic Micro-Converter for DC Distribution

In this paper, a digitally controlled photovoltaic (PV) micro-converter for dc distribution with sensing no current is presented. Current information for maximum power point tracking (MPPT) is estimated from system parameters, which leads to reducing power losses caused in sensing current and the number of components. Operation analysis of boundary conduction, quasiresonant, and discontinuous conduction modes is presented for its implementation. The high current estimation accuracy not only allows adaptive operation mode changes for efficiency optimization, but also guarantees achievement of high MPPT efficiency. Loss analysis of each operation mode is also presented to determine optimal transition points for mode change. A prototype PV micro-converter for a 120-W PV module is implemented by utilizing a digital signal processor. Experimental results verify that the proposed method is stable in both static and dynamic operations. European efficiency and MPPT efficiency are measured higher than 97.5% and 99.5%, respectively.

Cell balancing control using adjusted filters in flyback converter with single switch

Cell balancing method using multi-winding flyback converter is simple and easy to control, but it has unequal secondary voltages due to the non-uniform turn-ratios of secondary windings and the leakage inductance difference caused by multi-winding. Especially it is difficult to control multi-winding effect by using turn-ratio, because secondary-side has little number of turns. This paper proposes the control method eliminating the multi-winding effect without any additional switch in multi-winding cell balancing method. The individual cell control by making their frequency characteristic differently using single flyback converter and adjusted filter is proposed. Simulation and experimental results proved that each cell is equally balanced using adjusted filter and frequency selection.

Bridgeless isolated PFC rectifier using bidirectional switch and dual output windings

In this paper, a family of bridgeless power factor correction (PFC) rectifier which configures isolated single-stage is proposed. The proposed PFC rectifiers utilize bidirectional switch to handle both positive and negative input voltage without bridge diodes. Dual output windings of transformer enable the rectifiers dispense with any additional magnetic component. As a member of the proposed rectifier family, a bridgeless flyback PFC rectifier is analyzed and experimented to verify its higher efficiency than its conventional counterpart.

Screening process of Li-Ion series battery pack for improved voltage/SOC balancing

In order to minimize few problems of voltage balancing, a new approach of screening process for Li-Ion series battery pack is proposed in this paper. Pulse type discharging/charging currents are applied for various state-of-charge (SOC) points to select the cells with similar voltage variance. This process matches open circuit voltage (OCV)-SOC relations, therefore SOC balancing can be achieved using the voltage balancing. A total of 20 Li-Ion 18650 type fresh cells (1.3Ah) are used for implementation of the proposed screening process.

Digitally controlled open-loop master-slave interleaved boost PFC rectifier

In this paper, a digital control method for open-loop interleaving technique for two-phase critical conduction mode (CRM) boost power factor correction (PFC) rectifier is proposed. The proposed control method guarantees the exact phase shift between master and slave module, as well as proper soft switching of slave MOSFET. The phase shift between the modules is maintained in any time including the transient operation, but slight time deviation of turn-on instant of slave MOSFET may occur as a trade-off. The control circuit requires simple logic elements and digital control ICs, and does not require any two-loop control calculation and phase-locked-loop. The performance of the proposed control method is verified by 500-W laboratory prototype hardware.