Hee-Jun Lee

Transient Response Improvement at Startup of a Three-Phase AC/DC Converter for a DC Distribution System in Commercial Facilities

In this paper, a soft-start method for improvement of the transient response during the initial startup of power converters in building applications is proposed. Most dc loads have sensitive electrical characteristics regarding the input voltage. In such systems, the power converter is operated after connecting with dc loads to minimize the overshoot of the control voltage that may occur during connection to the loads. But whenever the power converter is started, the parameters in the circuit can differ, since the power converter is connected with various load types at each startup. This is disadvantageous for PI controller design for power converters. In order to solve this problem, a novel voltage control method using sliding-mode control theory is proposed. The advantage of the proposed voltage controller is that it is able to minimize an overshoot of the control voltage at the startup of the converter in terms of the types of loads or the magnitude variation of loads because a sliding mode controller has the robust characteristic of a variation in the parameters and load. The characteristics of three types of voltage controllers were compared through simulations and experiments. Despite the variations of the system parameters, the proposed voltage controller has fast response in the steady-state and robustness characteristics in the transient state. In addition, the proposed controller fundamentally minimizes the overshoot of the control voltage. The proposed controller was applied to a three-phase ac/dc converter, and the controller performance was verified.

Control method for reduction circulating current in parallel operation of DC distribution system for building applications

In the large system such DC distribution for building, the method that a number of modules converters operation in parallel is commonly used. When parallel operation, circulating current is directly related to the loss of the entire system. Accordingly, each module to share the same current is the most important for the safety of the power system. In this paper, control method for reduction circulating current in parallel operation is proposed. Thus, Response and operation of steady-state with parallel system was verified by simulation and experiment.

A new soft switching ZVT boost converter using auxiliary resonant circuit

In this paper, soft switching boost converter with ZVT (Zero Voltage Transition) method was proposed. Each switch of the proposed ZVT converter is operated under soft switching condition through using auxiliary resonant circuit such as resonant inductor, two resonant capacitors and auxiliary switches. Using the resonant device, the proposed converter is operated by zero-current switching and zero voltage switching. It can reduce the switching losses. Moreover, proposed circuit added an additional auxiliary switch compared to conventional converter, so that it is able to increase efficiency. In this paper, the ZVT converter is verified through operational mode analysis and simulation.

Parallel system of bidirectional DC/DC converter for improvement of transient response in DC distribution system for building applications

In this paper, Parallel system of DC-DC Converter applied to DC distribution system for building Applications. Power supply device of DC distribution needs a large power system that is requires Efficiency and reliability of the power conversion systems. If A single converter supplies power to the all load connected to DC grid, Temperature rise, reduction in life of system and capacity expansion is limited. In power supply device which require high power system such as DC distribution for building applications, stability and response characteristic of DC gird voltage are critical in DC distribution system. For improving limited switching frequency in using the DC/DC converter, this paper present parallel operation method of bidirectional DC/DC converter. In this paper, ripple reduction and improved transient response was verified by simulation and experiment.

Convenient thermal modeling for loss distribution of 3-level Active NPC using newton's law

In this paper, a new thermal modeling method is proposed for loss control method of 3-level Active NPC inverter. In the drawback of conventional 3-level NPC, the generated thermal in each switch is unbalanced. And utilization of designed system has decreased. In order to compensate, 3-level Active NPC inverter can distribute switch loss in accordance with operation of active switch. Therefore thermal modeling is required for thermal calculation. This paper is simple proposed new thermal modeling method based on newtons law of cooling than conventional thermal modeling method. Thought loss of active NPC is controlled. Proposed thermal modeling is verified by simulation.

Minimization of input current ripple in 2-level full-bridge converter for fuel cell power system

In this paper, dual full-bridge dc-dc converter which is controlled by interleaved method is proposed. By using interleaved control two full-bridge converters with parallel input and series output connection, both input and output current voltage ripple can be reduced. Therefore, lower input current ripple mitigates heat in battery and it prolongs the lifetime of battery. In introduction, after choosing topology and designing hardware, discuss the proposed control method with waveform and mode analysis. The theoretical analysis is verified by implementing simulation and experimental result for a 1.5-kW interleaved full-bridge converter are provided in the paper.

The Voltage-doubler Rectifier type Full-bridge converter built in voltage-balancing circuit for bipolar LVDC distribution system

This paper proposes Voltage-doubler Rectifier type Full-bridge converter for bipolar LVDC distribution system. This converter is possible of bi-directional power flow and perform DC_link voltage balancing operation. System of bipolar structure has neutral-point unlike unipolar structure. But, this neutral point is incur DC_Link voltage unbalance between top and bottom capacitor. Thus, bipolar structure need voltage balancing-circuit for voltage unbalance compensation. In Voltage-doubler Rectifier type Full-bridge converter to proposes, secondary side diodes of transformer are replaced to power transistors. And perform voltage balancing control using secondary side circuit without additional balancing-circuit. Also, primary side circuit of Full-bridge type can perform ZVS by phase-shift. And last, step-up and step-down operation also can. Such validity of converter is verified by simulation and experimental results.

DC distribution system integrated BESS for commercial building applications

In this paper, DC distribution system for building including BESS is composed, and integrated operation is proposed by using the system. Control method of power conversion device is proposed by reference from upper level MCU(Micro Controller Unit). Especially, when parallel operation of BESS, control method is proposed, which is maintain same voltage, and put out different current. Simulation result is given for verification has proposed configuration of system and method of operation in this paper. Through simulation result, proposed configuration and operation methods are verified.

Power Control Method for Reducing Circulating Current in Parallel Operation of DC Distribution System

In general, for a large power system like DC distribution system for buildings, several power converters are modularized for parallel operation. However, in parallel operation, inconsistency of parameters in each module causes circulating current in the whole system. Circulating current is directly related to loss, and, therefore, it is most important for the safety of the power system to supply the suitable current to each module. This paper proposes a control method to reduce circulating current caused during parallel operation. Accordingly, the validity of parallel operation system including response characteristics and normal state was verified by simulation and experiment result.

Design and efficiency analysis of stand-alone power conditioning system for fuel-cell

In this paper, a fuel-cell power generating system using interleaved full-bridge converter has been designed and efficiency analysis was implemented. To generate power from fuel-cell stack, DC-DC converter and DC-AC inverter is needed. DC-DC converter boost from low voltage of fuel-cell stack to high voltage and supplies the power to inverter. To improve efficiency of converter, optimum design is needed. System stability, range of ZVS, system losses on full-bridge converter are analyzed. A fuel-cell power generating system using interleaved full-bridge converter has been designed and efficiency analysis was implemented. Simulation and experiment was implemented to verify theological analysis considering the characteristics of fuel-cell.