A bidirectional full-bridge CLLC resonant converter using a new symmetric LLC-type resonant network is proposed for a low-voltage direct current power distribution system. This converter can operate under high power conversion efficiency because the symmetric LLC resonant network has zero-voltage switching capability for primary power switches and soft commutation capability for output rectifiers. In addition, the proposed topology does not require any snubber circuits to reduce the voltage stress of the switching devices because the switch voltage of the primary and secondary power stage is confined by the input and output voltage, respectively. In addition, the power conversion efficiency of any directions is exactly same as each other. Using digital control schemes, a 5-kW prototype converter designed for a high-frequency galvanic isolation of 380-V dc buses was developed with a commercial digital signal processor. Intelligent digital control algorithms are also proposed to regulate output voltage and to control bidirectional power conversions. Using the prototype converter, experimental results were obtained to verify the performance of the proposed topology and control algorithms. The converter could softly change the power flow directions and its maximum power conversion efficiency was 97.8% during the bidirectional operation.

Design Methodology of Bidirectional CLLC Resonant Converter for High-Frequency Isolation of DC Distribution Systems

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.

A New LLC Series Resonant Converter with a Narrow Switching Frequency Variation and Reduced Conduction Losses

A new driving method for synchronous rectifier (SR) in LLC resonant converter is presented. By adding a zero-crossing noise filter (ZCNF) to the drain and source of the SR FET, the false-triggering of the SR can be effectively eliminated. Moreover, the resistor and the capacitor in the filter can be used as a compensator to solve the duty-cycle loss issue caused by the trace inductance of the MOSFET package. Only three passive components are needed in the proposed filter, which makes it reliable and easy to implement. Simulation and experimental results show that the ZCNF can significantly improve the reliability as well as the efficiency of the power circuit. A prototype of 400 V to 12 V 600-W half-bridge LLC resonant converter is built to verify the advantages of the ZCNF. An efficiency improvement of 0.8% is achieved by the ZCNF.

A Zero-Crossing Noise Filter for Driving Synchronous Rectifiers of LLC Resonant Converter

Power transformer is one of the most complex parts of power converters. The complicated behavior of the transformer is usually neglected in the power converter analysis and a simple model is mostly used to analyze the converter. This paper presents a precise analysis of a fifth-order resonant converter which has incorporated the resonant circuit into the transformer. The derived model, which is based on the accurate model of the power transformer, can fully predict the behavior of the fifth-order resonant converter. The proposed fifth-order resonant converter is able to effectively reduce the range of phase-shift angle from no load to full load for a fixed-frequency phase-shift control approach. Therefore, the converter is able to operate under zero voltage switching during entire load range with a fixed-frequency control method. Also, the proposed converter offers a high gain which leads to a lower transformer turns ratio. A 10-kVDC, 1.1-kW prototype has been prepared to evaluate the performance of the proposed converter. The experimental results exhibit the excellent accuracy of the proposed model and the superiority of the performance compared to the lower order resonant converters, especially for high-voltage applications.

Analysis of a Fifth-Order Resonant Converter for High-Voltage DC Power Supplies

According to the detailed essential concept of current balancing presented in this paper, an improved passive current balancing method based on capacitive scheme is proposed consequently. This method can also be extended to the application of isolated multioutput LED drivers. Compared with active method to achieve current balancing among the multioutput LED strings, the passive method exhibits its attractive advantages in cost efficiency and balancing accuracy. Both the macromodel simulation and the prototype experiment results demonstrate the feasibility of the proposed method. The proposed method can achieve precise balancing in steady state and dynamic state even with considerably different peripheral parameters.

Multioutput LED Drivers With Precise Passive Current Balancing

This paper proposes a current-driving scheme for a synchronous rectifier (SR) in an LLC resonant converter with a voltage-doubler rectifier. In the proposed scheme, only one current transformer (CT) with one secondary winding is used to drive two SRs in the voltage-doubler rectifier. Also, the sensed current from the CT can be fed to the output with an energy-recovery circuit. Compared to the conventional center-tapped rectifier, the CT count for the SR drive circuit is reduced, which saves both cost and space. Although the current rating of the SR in the voltage-doubler rectifier is doubled, the voltage rating is well reduced and a lower voltage rating device with lower ON-state resistance can be used to compensate the increased current rating. Furthermore, the SR voltage stress is well clamped to the output voltage under any condition which improves the reliability of the circuit. A prototype with 16 V/5.6 A output was built to verify the theoretical analysis.

A Current-Driving Synchronous Rectifier for an LLC Resonant Converter With Voltage-Doubler Rectifier Structure

This paper proposes a novel current driving scheme for synchronous rectifier (SR) in the LLC resonant converter with a voltage doubler rectifier structure. In the proposed current driving scheme, a simple current transformer (CT) with only one secondary winding is used to drive two SRs in the voltage doubler rectifier. Furthermore, the reflected current from the CT will feed to the output. Therefore, the proposed current driving scheme features simple structure, low power loss and good performance. A prototype with 300–400V input and 16V/5.6A output is built to verify the theoretical analysis.

A novel current driving scheme for LLC resonant converter with Synchronized voltage-doubler rectifier

This work presents a dynamic event-triggered sliding mode controller to solve the problem on cooperative formation flight for unmanned aerial vehicles (UAVs) under outside disturbances and communication delay. Initially, a second-order kinematic model for each UAV is established, and the leader-follower framework is adopted to realize the desired formation flight. Second, an effective design of disturbance observer is proposed based on that the disturbance in the UAV is generated by an external nonlinear system. Third, a new dynamic event-triggered mechanism (DETM) is presented and the triggering threshold is adjusted by an exogenous system, which can help reduce data transmissions and maintain control performance more efficiently. Then, a distributed dynamic event-triggered sliding mode control strategy is proposed for the UAV system, and two sufficient conditions on exponential stability of the overall closed-loop system are derived. Furthermore, the controller gain, observer gain, and triggering parameter can be obtained by solving the derived linear matrix inequalities (LMIs). Finally, a simulated example is exploited to illustrate the obtained results.

Jiawen Liao

Papers

A Current-Driving Synchronous Rectifier for an LLC Resonant Converter With Voltage-Doubler Rectifier Structure

A novel current driving scheme for LLC resonant converter with Synchronized voltage-doubler rectifier

Dynamic event-triggered formation control for UAVs under communication delay and outside disturbances