Showing papers by "Jee-Hoon Jung published in 2021"

Series DC Arc Fault Detection Method for PV Systems Employing Differential Power Processing Structure

Abstract: Arc fault detection is an important process for ensuring the safety of PV and grid-connected inverters and is essential for producing PV systems in real applications. However, it is difficult to detect series dc arc faults using conventional fuses because these faults produce only small current variations. In addition, the arc fault detection devices have limited performance, because they focused on arc fault detection between PV arrays and inverter. Moreover, they require the additional current and voltage sensors to implement the arc fault detection algorithm. This article proposes an arc fault detection algorithm employing differential power processing (DPP) structure. The proposed algorithm only uses intrinsic voltage sensors of DPP and inverter, which can improve the cost-effectiveness of PV systems. In addition, the proposed algorithm can integrate the functionality of maximum power processing for each PV panel and arc fault detection. The voltage relationship between DPP and inverter is analyzed to detect the arc fault condition according to the DPP voltage sensing type. The performance of DPP units and its voltage relationship are verified with the control hardware-in-the-loop system. The arc fault detection performance is verified with the prototype PV system.

Segmented Differential Power Processing Converter Unit and Control Algorithm for Photovoltaic Systems

Abstract: Differential power processing (DPP) for photovoltaic (PV) systems can achieve high system efficiency and maintain maximum power production even under mismatched conditions. However, DPP converters applied to large-scale systems have challenges of complicated installation and high voltage ratings. The segmented DPP structure is introduced as a modular approach that utilizes groups of bidirectional DPP flyback converters to maximize PV power generation while minimizing converter power loss. Groups of four DPP converters are combined into a segmented DPP unit with maximum power point tracking (MPPT) control to maximize output power of the unit. The segmented DPP system and control algorithm are verified through simulation and hardware experimentation. Simulation results verify the effectiveness of the control algorithm with multiple segmented DPP units interacting with a typical inverter employing MPPT. Experimental results verify that system efficiency of the segmented DPP unit reaches 96.4% in even lighting conditions, reaches 92.7% in severe partial shading conditions, and shows an increase of up to 14.8% in uneven lighting conditions compared to an equivalent series-connected PV system.

Design Methodology of Quasi-Resonant Flyback Converter With a Divided Resonant Capacitor

Abstract: The leakage inductance in flyback converters can induce high-voltage spikes in power switches as well as power losses. Although conventional resistor–capacitor-diode (RCD) snubbers and active clamp circuits can be used to suppress these voltage spikes, the clamping operation of RCD snubbers increases power consumption, while the active clamps require additional power switches. To address these issues, a quasi-resonant flyback converter featuring a divided resonant capacitor is proposed in this article, in order to suppress voltage spikes in power switches and improve the power conversion efficiency. The operational principle of a divided resonant capacitor is analyzed to obtain the design methodology of the divided resonant capacitor. Furthermore, the validity of the proposed design method is verified via experiments, using 15-W prototype quasi-resonant flyback converter. The results indicate that the proposed design effectively reduces voltage spikes and improves power conversion efficiency.

Effective Magnetic Component Design of Three-Phase Dual-Active-Bridge Converter for LVDC Distribution System

Abstract: To improve the power conversion efficiency of a three-phase dual-active-bridge (3P-DAB) converter for low-voltage direct current distribution systems, a practical design methodology is proposed. Commonly, the 3P-DAB converter is designed by only specification, such as the rated power, input/output voltage, and frequency. However, using the conventional design method, the efficiency is low under heavy load conditions due to the high conduction loss. In this article, based on the practical power loss analysis, the effective design methodology of the coupling inductance in the 3P-DAB converter is proposed, focusing on power conversion efficiency. It can mitigate the drawbacks of the common design by reducing the peak and rms phase current and the insulated-gate bipolar transistors turn- off current. Experimental results verify the validity of the proposed design methodology and controller using a 25-kW prototype 3P-DAB converter.

Enhanced Computation Performance of Photovoltaic Models for Power Hardware-in-the-Loop Simulation

Abstract: For power hardware-in-the-loop (PHIL) simulation, a real-time simulator has to complete the target model calculations in a real-time manner without overrun errors However, a photovoltaic (PV) simulation model contains a nonlinear equation that demands a numerical method with long computation time Therefore, the complexity and operating condition of the target PV model are limited to reduce its computation burden Besides, it sacrifices the model accuracy and limits the simulation scenario of the PHIL simulation In this article, the PV simulation model employing an effective initial value selection method is proposed to enhance the real-time simulation performance for the PV PHIL simulation The proposed initial value selection method can reduce the number of iterations of the numerical method so that it can drastically reduce the computation time of the real-time simulation Therefore, the PHIL simulation model can increase it complexity with a fixed time step Moreover, the PV model can be scaled up with various operating conditions, which can increase the PHIL simulation accuracy The accuracy and the performance of the proposed PV model are evaluated by the PHIL simulation results The maximum number of the PV models for the target PHIL simulation is also discussed

Bidirectional CLLC Resonant Converter Employing PLC Capability and EM Noise Reduction Technique for Small-Sized ESS Application

Abstract: An energy storage system (ESS) requires high reliability with low electromagnetic (EM) interference, communication capability between ESS applications, and bidirectional power conversion for charging and discharging operations. However, a conventional ESS separately has power converters, communication devices, and large-sized EM interference filters for its stable operation. In this article, a current-fed capacitor-inductor-inductor-capacitor (CLLC) resonant converter employing asymmetric pulsewidth modulation and spread spectrum modulation is proposed to obtaining three functions, bidirectional power conversion with tight output voltage regulation, EM noise mitigation, and power line communication capability among ESSs, simultaneously. It can improve the cost-effectiveness, system's form factor, and communication flexibility. The proposed integration of three functionalities has design constraints on the implementation of each function. Design methodologies of power stage and control algorithm are also proposed for achieving the simultaneous operation of each function. The performance of the proposed converter and control algorithm are verified through a 20-W prototype converter.

Hybrid Power Balancing Method of Modular Power Converters to Achieve Enhanced Efficiency and Dynamic Performance

Abstract: In general, the master-slave output power balancing method has widely been used to stabilize parallel-connected modular power converters. However, it cannot consider the performance deviation among the modular power converters due to different stress and aging. Moreover, it degrades the dynamic performance of the modular power converters and induces the current oscillation due to different loop gains of the voltage control loop and the current sharing loop. In this paper, a hybrid power balancing method for the modular power converters is proposed to obtain enhanced efficiency and dynamic performance. It can increase the entire power conversion efficiency using an input power balancing strategy in the steady-state operation. In addition, it can enhance the dynamic performance of the entire converters by using an interleaving control strategy in the transient-state operation. The performance enhancement of the proposed method is verified by using a comparative study and experimental results.

Multi-port DC-DC Converter for Interconnecting Bipolar DC Buses of Bipolar DC Distribution System

Abstract: This paper proposes a multi-port dc-dc converter that can interconnect bipolar dc buses of the bipolar dc distribution system. The bipolar dc distribution system has enhanced features compared with the unipolar dc distribution system. However, the bipolar dc bus requires the voltage balancing capability to balance the bipolar voltage levels under unbalanced load conditions. The proposed multi-port dc-dc converter can interconnect two bipolar dc buses, which can transfer bidirectional power flows between two bipolar dc buses and can balance their bipolar voltage levels without additional voltage balancers. The proposed converter is based on the dualactive-bridge converter. Therefore, since two voltage balancers can be eliminated at each bipolar dc bus, the proposed converter can improve power conversion efficiency, power density, and cost-effectiveness, thereby enhancing the performance of the bipolar dc system. A 3-kW experimental result is provided to prove the effectiveness of the proposed converter.