skip to main content


Title: Design and implementation of a series resonant solid state transformer
The focus of this study is on the design of a full-bridge unidirectional resonant LLC Solid State Transformer. The proposed topology uses a high-frequency transformer to optimize the size and weight of the converter. This converter has the capability of operating at fluctuating load conditions while it keeps the voltage regulated in different operation point. The converter is designed to maintain soft switching by using a resonant circuit in this design to minimize the switching loss of the high frequency converter. ZVS in the leading leg for turn on mode and ZCS commutation in the lagging leg for all of the modes are achieved in the H-bridge through the suggested circuitry which is analyzed mathematically in detail in this study. A combination of Pulse frequency modulation (PFM) and Phase Shifting Modulation (PSM) are utilized to control this resonant converter. The experimental setup for the suggested configuration was implemented and the results of the simulation and calculations have been verified with test results. The hardware set up was tested with two different power levels and the output results confirm that the control method works properly to feed the load and keeps the converter working in the expected frequency range and maintaining the soft switching to decrease switching loss. The results shows conversion efficiency of 97.18% is achieved.  more » « less
Award ID(s):
1650470 1747757
NSF-PAR ID:
10082508
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
2017 IEEE Energy Conversion Congress and Exposition (ECCE)
Page Range / eLocation ID:
1282 to 1287
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    In this study, analysis and control of a highly efficient, high-power full-bridge unidirectional resonant LLC solid-state transformer (SST) are discussed. A combination of pulse frequency modulation and phase-shift modulation is utilized to control this resonant converter for a wide load range. The converter is designed to maintain soft switching by using a resonant circuit to minimize the switching loss of the high-frequency converter. Zero-voltage-switching (ZVS) is achieved for the H-bridge converter. The ZVS boundary for the proposed combined control method is also analyzed in detail. The experimental setup for the suggested configuration was implemented, and the performance of the proposed control scheme and resonant LLC SST have been verified with test results. The proposed combined control scheme improves control performance. The obtained results show that, the proposed system can regulate output voltage and maintain soft switching in a wide range of load. Thus, the efficiency of the system is improved and an efficiency of 97.18% is achieved. 
    more » « less
  2. This article proposes a matrix auto-transformer switched-capacitor dc–dc converter to achieve a high voltage conversion ratio, high efficiency, and high power density for 48-V data-center applications. On the high-voltage side, the proposed converter can fully leverage the benefits of high-performance low voltage stress devices similar to the multilevel modular switched-capacitor converter. Compared with the traditional isolated LLC converter with a matrix transformer, the proposed solution utilized a matrix autotransformer concept with merged primary and secondary side windings, thus leading to reduced transformer winding loss. The resonant inductor could be integrated into the transformer similar to the LLC converter. Because of the matrix autotransformer design, it can achieve a current doubler rectifier on the low voltage side. For less than 8-V low output voltage application, the current doubler rectifier design can fully utilize the best figure-of-merit 25-V device, which is more efficient than the full-bridge rectifier solution using two 25-V devices during the operation. All the devices can achieve zero voltage switching or zero current switching and can be naturally clamped without additional clamping circuits. A 500-W 48-V to 6-V dc–dc converter hardware prototype has been developed with optimized device selection and integrated matrix autotransformer design. Both simulation and experiment results have been provided to validate the features and benefits of the proposed converter. The maximum efficiency of the proposed converter can reach 98.33%. 
    more » « less
  3. In this paper, a new topology for grid-connected solar PV inverter is proposed. The proposed topology employs an LLC resonant converter with high frequency isolation transformer in the DC-DC stage. The DC-DC converter stage is controlled to generate a rectified sine wave voltage and current at the line frequency. An unfolder inverter interfaces between this DC stage and the grid. Both phase-shift and frequency control methods are used to control the LLC resonant converter. The switching frequency is determined depending on the phase-shift angle to extend the zero-voltage switching (ZVS) region. The transformer leakage and magnetization inductances are also properly designed to provide ZVS for wide operation area. The LLC converter operates in the ZVS region except the narrow band around the zero-crossings of the inverter output current. Since the LLC resonant converter has a high frequency transformer, the line frequency transformer requirement is eliminated, and thus more compact and efficient design is obtained. The proposed topology is validated by the simulation and experimental results. 
    more » « less
  4. In this paper, a high efficiency, decoupled on-board battery charger is proposed. The proposed topology is composed of two LLC resonant converters sharing the same full-bridge inverter with constant switching frequency. The outputs of two LLC resonant converters are connected in series. One of the LLC resonant converters is operated at the resonant frequency, which is the highest efficiency operation point. The magnetic control is adopted for the second LLC resonant converter to fulfill the closed-loop control of charge voltage and current for constant voltage (CV) and constant current (CC) charge modes. The proposed topology can achieve zero voltage switching (ZVS) for all primary switches and zero current switching (ZCS) for all secondary diodes during both CC and CV modes. Furthermore, thanks to constant frequency operation, the electromagnetic interference (EMI) filter design is simplified. Simulation and experimental studies are presented to verify the feasibility and validity of the proposed topology. 
    more » « less
  5. null (Ed.)
    With the growth in penetration number and power level of renewable energy resources, the need for a compact and high efficient solid state transformer becomes more important. The aim of this paper is to design a compact solid state transformer for microgrid application. The proposed transformer has four ports integrated on a single common core. Thus, it can integrate different renewable energy resources and energy storage systems. The transformer is operating at 50kHz switching frequency, and each port can handle 25kW rated power. In this paper, the ports are chosen to represent a realistic industrial microgrid model consisting of grid, energy storage system, photovoltaic system, and load. The grid port is designed to operate at 4160V AC, while the other three ports operate at 400V. Moreover, the grid, energy storage, and photovoltaic ports are active ports with dual active bridge topologies, while the load port is a passive port with full bridge rectifier one. In this paper, an extensive and complete design and modeling of the entire solid state transformer is presented. The proposed design is first validated with simulation results, and then the proposed transformer is implemented. Some preliminary experimental tests are also performed and the obtained results are reported. 
    more » « less