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  1. In this study, a sliding mode control (SMC) scheme is proposed for the single-phase cascaded H-bridge (CHB) multilevel active front end (AFE) rectifier with LCL filter. A PI controller is employed to control the DC voltage of the rectifier modules and to obtain the amplitude for the reference grid current. The SMC based current control scheme uses the grid current and filter capacitor voltage feedbacks. The resonance of the LCL filter is damped using the voltage feedback of the capacitor. Therefore, the requirement for additional damping circuitry is removed. Simulation and experimental results are presented to verify the performance of the SMC for the CHB multilevel AFE rectifier. The overall proposed control scheme provides almost unity power factor and fast transient response. It is seen from the results that the current drawn from the grid is in sinusoidal waveform with low THD.
  2. In this study, a power converter topology and control schemes for the power converter stages are proposed for a DC extreme fast charger. The proposed system is composed of a cascaded H-bridge (CHB) converter as the active front end (AFE), and an input series output parallel (ISOP), which includes three parallel connected dual active bridge (DAB) cells. A modified Lyapunov Function (LF) based control strategy is applied to obtain high current control response for the AFE. An additional controller to remove the voltage unbalances among the H-bridges is also presented. Additionally, the triple phase-shift (TPS) control method is applied for the ISOP DAB converter. A Lagrange Multiplier (LM) based optimization study is performed to minimize the RMS current of the transformer. The performance of the proposed converter topology and control strategies is validated with MATLAB/Simulink simulations.
  3. The increasing demand for electric vehicles, due to advantages such as higher energy efficiency, lower fuel costs, and less vehicle maintenance, is expected to drive the need for electric vehicle charging infrastructure. Due to their reduced size and weight, high power and scalable compact solid state transformers (SST) are growing in popularity. This study presents the total loss analysis and control design for a direct grid connected single-phase SST for a fast charging station. A control strategy to achieve robust current control, DC voltage and power balancing, and power loss minimization (PLM) is implemented for this system. Detailed analyses and simulation results obtained from MATLAB/Simulink are given to prove the effectiveness of the proposed control techniques.
  4. In this paper, a 10 kV SiC MOSFET-based solid-state transformer (SST) operating at 13 kV to 7.2 kV, 667 kW, and 20 kHz is modeled and optimized to reach maximum power density and efficiency. In order to reach optimum configuration, different core material/type/size, primary/secondary turns, insulation type/thickness, and cooling systems are considered; then based on a systematic approach the best solution is obtained. To reach this goal, the magnetic part of SST forced air-cooling, and the water-cooling system is modeled in ANSYS MAXWELL/Simplorer, ANSYS-ICEPAK, and ANSYS-FLUENT, respectively. The simulation results show a high efficient SST with an effectiveness of the cooling system.
  5. The increasing viability of wide band gap power semiconductors, widespread use of distributed power generations, and rise in power levels of these applications have increased interest and need for medium voltage converters. Understanding the definitions of insulation coordination and their relationship to applications and methodologies used in the test environment allows system engineers to select the correct insulation materials for the design and to calculate the required distances between the conductive surfaces, accessible parts and ground accurately. Although, design guidelines are well established for low voltage systems, there are some deficiencies in understanding and meeting the insulation coordination requirements in medium voltage, medium frequency applications. In this study, an overview on standards for insulation coordination and safety requirements is presented to guide researchers in the development of medium voltage power electronic converters and systems. In addition, an insulation coordination study is performed as a case study for a medium frequency isolated DC/DC converter that provides conversion from a 13.8kV AC system to a 4.16kV AC system.
  6. The primary purpose of this paper is to obtain accurate analytical expressions of the dual active bridge (DAB) converter under the three-degree of freedom control technique. This technique, known as triple phase-shift (TPS) modulation, is utilized for the efficiency optimization of different operating zones and modes of the DAB. Three operating zones and modes have been retained to analyze the converter. Depending on the operating regions and due to the high nonlinearity of the obtained expressions, two optimization techniques have been used. The offline particle swarm optimization (PSO) method is utilized in local optimization (LO) and results in a numerical value. The Lagrange Multiplier (LM) is utilized in global optimization (GO) and results in a closed form expression. In the case of LO, the optimal duty cycles that minimize the power loss are not the optimal values for the minimum root-mean-square (RMS) current or peak current stress. Conversely, in the case of GO, the optimal duty cycles minimize the RMS, peak current and power loss at the same time for the entire power range. Detailed analyses and simulation results from MATLAB/Simulink are given to prove the effectiveness of the proposed method.
  7. High frequency modular power converters are increasingly becoming popular due to their small size and weight. Targeting the input-series and output-parallel (ISOP) dual active bridge (DAB) DC-DC converters, this paper proposes a control scheme based on optimal triple phase-shift (TPS) control for both power sharing control and RMS current minimization. This achieves balanced power transmission, even under mismatched leakage inductance of a DAB module of the ISOP. In order to obtain the optimal zones of operation for the converter, the RMS current was minimized using the Lagrange multiplier method to obtain the optimal duty cycles. The power balancing was added to compensate unbalanced power sharing for variations in model parameters or module shutdown. Analyses and simulation results through MATLAB/Simulink are presented to validate the proposed controller.
  8. The cascaded H-bridge multilevel active rectifier is a prominent converter configuration. It presents compelling advantages, including high adjustability for a number of applications, such as in solid-state transformers, traction applications, medium and high power motor drives and battery chargers. However, when the H-bridge is operating under an unbalanced load and asymmetrical voltage conditions, it becomes important to design advanced control strategies to maintain the stability of the system. In this study, a Lyapunov-function based control method is proposed for controlling the single-phase cascaded H-bridge active rectifier to achieve global asymptotic stability. A capacitor voltage feedback is added to the conventional Lyapunov-function based stabilizing control method to minimize the resonance of the LCL filter. Additionally, a Proportional-Resonant (PR) control approach is adopted to obtain the reference current signal. This increases the robustness of the current control scheme. A DC voltage balancing control procedure is also employed to prevent the unbalanced DC voltage conditions among the H-bridges. The DC voltage is controlled via a PI controller. The capability of the control approach is verified with simulation and experimental studies.
  9. 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 aremore »reported.« less
  10. 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.