This paper proposes a high-efficiency wireless power transfer system with an asymmetric four-coil resonator. It presents a theoretical analysis, an optimal design method, and experimental results. ...Multicoil systems which have more than three coils between the primary and secondary side provide the benefits of a good coupling coefficient, a long transfer distance, and a wide operating frequency range. The conventional four-coil system has a symmetric coil configuration. In the primary side, there are source and transmitter coils, and the secondary side contains receiver and load coils. On the other hand, in the proposed asymmetric four-coil system, the primary side consists of a source coil and two transmitter coils which are called intermediate coils, and in the secondary side, a load coil serves as a receiver coil. In the primary side, two intermediate coils boost the apparent coupling coefficient at around the operating frequency. Because of this double boosting effect, the system with an asymmetric four-coil resonator has a higher efficiency than that of the conventional symmetric four-coil system. A prototype of the proposed system with the asymmetric four-coil resonator is implemented and experimented on to verify the validity of the proposed system. The prototype operates at 90 kHz of switching frequency and has 200 mm of the power transmission distance between the primary side and the secondary side. An ac-dc overall system efficiency of 96.56% has been achieved at 3.3 kW of output power.
In this paper, a phase-shifted full-bridge (PSFB) converter employing a new center-tapped clamp circuit is proposed to achieve high efficiency and high power density in electric-vehicle battery ...charger applications. By using a simple center-tapped clamp circuit, which consists of two diodes and one capacitor, many limitations in conventional PSFB converters are solved. The proposed center-tapped clamp circuit provides the clamping path and allows the secondary voltage stress to be clamped to the secondary-reflected input voltage. This results in a greatly reduced conduction loss in the secondary full-bridge rectifier (FBR) due to the low-forward-voltage drop of low-voltage-rated diodes, and the resistor-capacitor-diode snubber loss is eliminated. In addition, the circulating current in the primary side is removed without any duty-cycle loss. Furthermore, the turn- off switching loss in the FBR is substantially reduced due to the decreased reverse-recovery current and the reduced reverse voltage. With these advantages, high efficiency can be achieved. Besides, the size of the output inductor is considerably reduced with the aid of clamping voltage, resulting in a high power density with saving the cost. In order to confirm the effectiveness of the proposed converter, a 3.3-kW prototype was tested. Experimental results show that the proposed converter achieves high efficiency over the entire conditions with high power density.
Among various active cell balancing circuits, a switched capacitor circuit is promising because it can be implemented with low cost and small size. However, when the switched capacitor is applied in ...the lithium-ion battery, cell balancing speed is generally slow when the number of batteries is high. Therefore, this paper proposes the chain structure of the switched capacitor to increase balancing speed, particularly among outer cells. In this paper, the cell balancing principle of the conventional switched capacitor is explained, and the reason why slow cell balancing of the switched capacitor is shown in the lithium-ion battery is analyzed. To improve cell balancing speed, two circuits with chain structure are proposed. The balancing performance of the proposed circuits is confirmed by computer simulation, and a comparison between conventional and proposed circuits is presented. The theoretical analysis on the cell balancing speed of conventional structures and the proposed chain structure is also shown in this paper. Experimental tests were carried out to verify the validity of the proposed structures, and the experimental results show an improved balancing performance of the proposed circuit.
In fuel cell applications, numerous prior researches have concentrated on current-fed type pulsewidth modulation (PWM) resonant dc-dc converters to achieve a low input current ripple and high ...efficiency. However, conventional approaches still cause a non-negligible input current ripple in practice due to two factors. The first factor is roll-off and tolerance of inductance according to the instantaneous current. The second factor is desynchronized drain-source voltage transitions during the dead time. This article proposes a new primary-side zero-voltage switching (ZVS) PWM resonant dc-dc converter for fuel cell applications. The proposed converter with a novel synchronous rectifier modulation solves the aforementioned two factors that cause input current ripple. Besides, in the process of input current ripple improvement, the primary-side switches can also achieve the ZVS, so switching losses are also reduced. Therefore, the proposed converter can achieve near-zero-ripple input current and high efficiency. Its effectiveness is verified by 600 W prototypes with 35-45 V input and 380 V output conditions.
Generally, an LLC series resonant converter (LLC SRC) is an attractive topology for applications, which require wide input variation and high conversion efficiency because of its wide gain capability ...and soft-switching capability. However, there is a regulation problem in which the output voltage increases as the load current decreases. In this paper, Bode plot and impedance asymptote analysis were conducted to obtain an intuitive sense of the regulation characteristic of LLC SRC under the light-load condition. Moreover, to improve the regulation capability, a new resonant tank with an additional capacitor is proposed. Its design guidelines were determined by Bode plot and impedance asymptote analysis. Therefore, the proposed LLC SRC achieves very light load regulation, while it maintains the advantages of typical LLC SRCs.
In the lithium-ion battery systems for electric vehicles (EVs), a battery management system (BMS) is essential for enhancing the battery's life cycle and safety. As a result, a BMS is required to ...realize both the effective cell monitoring and balancing. Moreover, individual cell balancing and monitoring circuit with a smaller size are required in a large number of battery cells. To meet these requirements, a modularized charge equalizer using the monitoring integrated circuit (IC) is proposed for EV battery strings. The proposed scheme exhibits efficient charge equalization with simple control of the monitoring IC. In the proposed equalizer, the battery string is modularized into a master module and multiple slave modules. A central equalization converter in the master module is shared by all of the battery cells through the module and cell switches in the slave module, instead of a dedicated charge equalizer for each of the cells. Individual charge equalization can be controlled by the cell monitoring IC in the slave module. With this configuration, the battery monitoring and balancing can be effectively merged into one controller. Moreover, the individual charge equalizer can be effectively implemented without affecting the size or cost based on the numbers of cells. In this paper, a prototype for 88 lithium-ion battery cells is optimally designed and implemented. Experimental results verify that the proposed method exhibits outstanding balancing performance with simple operation methods.
An LLC series-resonant converter has many unique characteristics and improvements over pulsewidth-modulation topologies. However, many output capacitors are needed in parallel to satisfy an output ...voltage ripple and a rated ripple current of the capacitors. This paper deals with a novel two-phase interleaved LLC resonant converter using a phase of the resonant capacitor. The proposed converter satisfies low output-voltage ripple requirement and meets the rated ripple of output capacitor's current with few output capacitors. The operation and features are considered in detail, and a prototype with a 12-V-100-A output is investigated.
A new asymmetric half-bridge (HB) resonant converter for dc/dc power system with a wide range of low input voltage is proposed in this paper. The proposed converter is easily derived based on the ...switch integration technique, merging a buck-boost, which is the same with the active-clamp forward's primary circuit, and the HB LLC resonant converter. By adopting the buck-boost circuit in front of the HB LLC resonant converter, higher input voltage of LLC resonant converter stage can be achieved. As a result, the primary conduction loss can be significantly reduced. In addition, to cover wide input voltage range, an asymmetric pulse width modulation control is applied. It can mitigate the design limitation for a high efficiency. Moreover, the proposed converter can achieve not only the small conduction loss and the optimal design for high efficiency, but also high power density and low cost due to the switch integration technique. The validity of the proposed converter is confirmed by the experimental results of a prototype converter with 36-72 V DC input and 300 W (12 V/25 A) output.
A new LLC series resonant converter that has a narrow switching frequency variation and reduced conduction losses is proposed in this paper. In the proposed converter, one leg of the full-bridge ...diode rectifier is replaced with synchronous rectifier (SR) switches. In the nominal state, the proposed converter is controlled using frequency modulation, and the SR switches are controlled using in-phase switching signals with primary side switches in order that the proposed converter can obtain a reduced conduction loss in its secondary side rectifiers. During the hold-up time which is the condition where the input voltage of the converter decreases, the SR switches are controlled using phase-shifted switching signals in order that the proposed converter can obtain a higher gain without decreasing the switching frequency. Because the proposed converter operates with a narrow switching frequency variation, a small transformer core can be selected, which results in a decreased core size and loss. Furthermore, it is possible for the proposed converter to be designed optimally in the nominal state and this results in the proposed converter exhibiting a maximized efficiency over the entire load condition. The feasibility of the proposed converter is verified with a 400-250 V input and 200 V/1.5 A output prototype.
Duty-ratio-control-aided LLC converter for current balancing of two-channel light-emitting diode (LED) driver is proposed and analyzed. Conventional current-balancing methods have the limitation on ...the power density and losses from additional components. With the aid of duty ratio control of an LLC converter, the proposed driver does not require any additional component. The total output current is controlled with the frequency modulation, and the duty ratio control is added to obtain current balancing of each LED channel. The advantage of the proposed method is the high power density and high efficiency. Also, it does not affect design procedure of a conventional LLC converter. The prototype of two-channel LED driver with 400-V input and 150-100-V/0.3-A output for each channel verifies the effectiveness of the proposed driver.
