Showing papers by "Yan-Fei Liu published in 2022"

Integration of Three-Phase LLC Resonant Converter and Full-Bridge Converter for Hybrid Modulated Multioutput Topology

Abstract: A multioutput dc–dc topology based on hybrid modulation of pulse frequency modulation and the phase shift is proposed in this article. The proposed hybrid modulated multioutput converter is derived from the integration of a three-phase LLC resonant converter and the full-bridge converter. With the hybrid modulation, the multioutput is controlled independently free from cross-regulation and isolated from each other. With the three-phase interleaving operation, the resonant currents can be reduced, and thus, the efficiency will be improved. Furthermore, the output current ripple of the main output voltage is reduced; as a consequence, the lifetime of the output filter capacitor is extended, and the reliability is reinforced. What is more, the number of the power switches is reduced, and the zero-voltage switching of the power switches can be achieved within the entire load range by the proposed integrated topology. All the abovementioned features of the proposed converter will lead to a compact, efficient, and cost-effective design. Finally, a 1.4-kW triple-output laboratory prototype is built and tested to validate the feasibility and effectiveness of the proposed converter.

Accurate Analysis and Design of the Circuit Parameters of LLC DC–DC Converter With Synchronous Rectification

Abstract: In high-load-current LLC dc–dc converter, synchronous rectification (SR) is usually used to reduce the secondary loss. As a lossless, low-cost, and small-volume SR control strategy, the drain–source voltage of SR switches sensing method is used widely in industrial applications. However, when the load current increases, the voltage ringing across SR switches during O stage is more and more severe and reaches zero eventually. When the voltage ringing reaches around zero in LLC converter, the voltage-sensing-method SR controller will generate the false driving signal, which makes SR switches turn on early and causes the converter works abnormally. This article presents the accurate analysis and design of the circuit parameters of LLC dc–dc converter to prevent the voltage ringing across the SR switches reaches around zero. The voltage ringing model is established, and the parameters design principle is given. By using the proposed design guideline, the voltage ringing across SR switches will always be higher than zero over the full load range, which eliminates the turn-on early issue or turn-on several times in one cycle issue. Therefore, this article can provide a design reference and guideline for the high-load-current and high-output-power LLC converter with voltage sensing SR control strategy. A 2.16 kW SR LLC dc–dc converter prototype is built according to the proposed design guideline, and the experimental results verify the correctness and effectiveness of the analysis.

A Topology-Reconfigurable Fault-Tolerant Two-and-Single Stage AC-DC Converter for High Reliability Applications

Abstract: A novel topology-reconfigurable two-and- single stage AC-DC converter with fault-tolerant capability for high reliability applications is proposed in this paper. In the proposed converter, two bidirectional switches are used to connect the midpoints of the bridge branches between the rectifier stage and the DC-DC stage, and the proposed converter can be configured from the two-stage structure into the single-stage structure by turning on the bidirectional switches for the postfault conditions, therefore the reliability of the power supply is reinforced. The two-stage structure for the normal condition works with an interleaved bridgeless PFC rectifier and resonant DC-DC converter. The single-stage structure working under the postfault condition is made up of a PFC half-stage and resonant DC-DC half-stage, and the single-stage structure still has the same working performance as the two-stage structure. Operational principles, control scheme, and characteristics analysis of the topology-reconfigurable converter are analyzed. Finally, experimental results for both of normal condition and postfault condition based on an 1kW prototype are provided to verify the effectiveness of the proposed converter.

Investigation and Reduction of Common Mode Current in Center-Tapped Transformer of LLC Resonant Converters

Abstract: This paper investigates the effects of resonant tank arrangements on the common mode (CM) noise current. CM noise reduction methods with symmetrical transformer winding structure and split resonant tank are proposed for full bridge (FB) LLC converters. For half bridge (HB) LLC converters, CM noise cancellation capacitor $C_{can}$ is proposed to fully cancel the CM noise current flowing through the transformer. The corresponding extraction and calculation techniques of $C_{can}$ are provided. Both techniques are lossless and easy to implement. The capabilities and excellence of aforementioned methods are verified by experiments.

A Reconfigurable Single-Stage Three-Phase Electric Vehicle DC Fast Charger Compatible With Both 400V and 800V Automotive Battery Packs

Abstract: A novel three-phase Electric Vehicle (EV) DC fast charger with a wide output voltage range is proposed in this paper. One of the main features of the proposed EV charger is that it can provide a wide output voltage range (i.e., 250 V to 850 V) using low voltage rating mainstream switches/diodes (i.e., 650 V). The proposed EV charger takes advantage of Inductor-Inductor-Capacitor (LLC) resonant tanks for each phase allowing soft-switching performance for all switches so the major power loss will be only conduction loss. Consequently, by operating at a high switching frequency the size of passive components can be reduced leading to a high-power density. Moreover, as the AC to DC conversion is being realized in an isolated single-stage approach, the total conversion efficiency for the proposed EV charger is higher than conventional two-stage EV chargers. The analysis of the power circuit design and control of the proposed EV fast charger is provided in the paper for both 400 V and 800 V automotive battery systems. Moreover, the performance is verified by computer simulation results and experimental results of a 1.5 kW laboratory prototype.

Power Cycle Modulation Control of LLC Resonant Converters for Wide Voltage Gain Range Applications

Abstract: This paper proposes Power Cycle Modulation (PCM) control method of LLC converters for wide voltage gain range applications. Instead of switching frequency modulation, the proposed PCM method operates the LLC converter according to a control period comprising an on cycle operation mode for a duration $T_{on}$ and an off cycle operation mode for a duration $\boldsymbol{T}_{off}$. $\boldsymbol{T}_{on}, \boldsymbol{T}_{off}$ and the optimal switching frequency during $T_{on}$ are adjusted based on the sensed input and output voltages. Optimal switching pulse pattern can be maintained under the low output voltage and high input voltage conditions, which ensures the high efficiency. A 65W prototype is built to verify the feasibility and validity of the proposed control method.

An Instantaneous Power Balancing Control With Power Factor Correction for Single-Stage Three-Phase AC-DC Converters

Abstract: A novel inner control loop for phase-modular three-phase single-stage rectifiers is proposed in this paper to achieve both power factor correction and power balancing at the same time. The power balancing control is critical in single-stage three-phase AC-DC converters as any small voltage imbalance in the three-phase voltages reflects into the output in the form of double line frequency voltage ripple that will prohibit electrolytic capacitor less implementation. The proposed instantaneous power balancing control approach is implemented on a single-stage LLC-based three-phase AC-DC converter. Balanced and unbalanced three-phase systems are considered in computer simulations to verify the effectiveness of the proposed method in removing line frequency power decoupling from the output capacitor. Moreover, a harmonic polluted three-phase voltage is also considered in the simulation to further verify the performance under non-ideal grid conditions. Furthermore, experimental results of a digitally controlled laboratory prototype validated unity power factor correction and the effectiveness of the proposed power balancing control method in rejecting line frequency output ripple in the presence of three-phase voltage imbalances.

Efficiency Improvement of Single-Stage AC-DC LLC Converter Using a Line Cycle Synchronous Rectifier (SR) Driving Strategy

Abstract: Synchronous rectification that is being widely used in high-power Inductor-Inductor-Capacitor (LLC) DC-DC converters to improve efficiency can be challenging in single-stage AC-DC LLC converters with high output voltage levels (i.e., >100V) where synchronous driving ICs cannot be used. In this paper, a simple line cycle SR driving strategy with direct MCU control is proposed for single-stage AC-DC LLC converters. The principles of operation and methodology behind the proposed line cycle SR driving strategy are discussed. Simulation and experimental results validated the performance of the proposed SR driving strategy for a 250 V to 400 V output voltage range AC-DC LLC converter. A full-load efficiency of 98.1 % was achieved for the 250 V output voltage condition and a full-load efficiency of 97.3 % was achieved for the 400 V output voltage condition. Compared with a fixed ON time method, around 0.5 %, and 0.8 % efficiency improvements were observed in 250 V and 400 V output voltage conditions, respectively. In addition, it is observed that the proposed simple SR driving method obtains the same efficiency levels as more complex adaptive SR driving approaches.

Isolated Resonant Switched Capacitor Converter With Voltage Self-Balancing Ability

Abstract: This article proposes an isolated resonant switched capacitor converter (I-RSCC) for high-voltage applications. The dc capacitors’ voltages achieve self-balancing with the resonant switched capacitor units (RSCUs). The voltage stress of the switching devices is reduced. The isolated rectifier (IR) is used for galvanic isolation and energy transfer. The number of switching devices is reduced by multiplexing parts switching devices functions, which helps the compact design. In this article, the topology and operation principle of I-RSCC are introduced in detail. Then, the output characteristics of I-RSCC are analyzed, including the voltage balance operation, the energy transmission path, the voltage conversion ratio, and the output power. The design example of I-RSCC is also presented. Finally, a 10-kW prototype is built to verify the feasibility of the proposed I-RSCC topology. The results show that soft switching is realized, and the maximum operation efficiency is 96.5% and above 96% at the rated power.