Soo-Cheol Shin

Soft-Switching Current-Fed Push–Pull Converter for 250-W AC Module Applications

In this paper, a soft-switching single-inductor push-pull converter is proposed. A push-pull converter is suitable for low-voltage photovoltaic ac module systems, because the step-up ratio of the high-frequency transformer is high, and the number of primary-side switches is relatively small. However, the conventional push-pull converter does not have high efficiency because of high-switching losses due to hard switching and transformer losses (copper and iron losses) as a result of the high turn ratio of the transformer. In the proposed converter, primary-side switches are turned ON at the zero-voltage switching condition and turned OFF at the zero-current switching condition through parallel resonance between the secondary leakage inductance of the transformer and a resonant capacitor. The proposed push-pull converter decreases the switching loss using soft switching of the primary switches. In addition, the turn ratio of the transformer can be reduced by half using a voltage-doubler of secondary side. The theoretical analysis of the proposed converter is verified by simulation and experimental results.

Auxiliary Switch Control of a Bidirectional Soft-Switching DC/DC Converter

In this paper, the auxiliary switch control using a lookup table is proposed to enhance the efficiency of the bidirectional dc/dc converter used in electric vehicle, which performs soft switching. Continuous current data are difficult to obtain during a resonant operation due to the limit of DSP ADC capacity. The proposed auxiliary switch control has a lookup table reference of the auxiliary switch turn-on time. The control method properly controls the auxiliary switch turn-on time according to the required load current; this auxiliary switch control brings the more efficient control in generative and regenerative mode operation. The proposed approach has been validated by the results of experiments on a bidirectional dc/dc converter, inverter, and interior permanent magnet synchronous motor.

Weighted-Efficiency Enhancement Control for a Photovoltaic AC Module Interleaved Flyback Inverter Using a Synchronous Rectifier

In this paper, a weighted-efficiency enhancement control method for an interleaved flyback inverter using a synchronous rectifier is proposed based on photovoltaic ac modules. In this control method, the operation of the synchronous rectifier is classified according to the voltage spike across the main switch. When the voltage spike across main switch is lower than the rating voltage of main switch, the operation of the active clamp circuit is interrupted to reduce the switching loss of the auxiliary switch. At this time, the synchronous rectifier is operated for the zero-voltage switching of main switch. When the voltage spike across main switch is higher than the rating voltage of main switch, the active circuit is activated to reduce the voltage spike. The synchronous rectifier is operated to reduce the conduction loss of the secondary output diode. Thus, the switching loss of the main switch can be reduced in the low power region, and the weighted efficiency can be improved. A theoretical analysis and the design principles of the proposed method are provided. The method is validated through simulation and experimental results.

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.

Position control of PMSM using jerk-limited trajectory for torque ripple reduction in robot applications

In the modern industry, the motor control is required for the accurate position control. Particularly, the frequent acceleration and deceleration are operated in the robot control. Also, the short time of acceleration and deceleration is demanded for the reduction of process cycle. However, in case the inertia of motor is large, the vibration of motor is occurred in the section of short acceleration and deceleration. Therefore, the algorithm of position pattern is considered for the condition of the optimal drive. In the section of short acceleration and deceleration, the vibration of motor is reduced by the S-curve output of speed pattern. In this paper, the position reference in consideration of jerk is generated in the control system of permanent magnet synchronous motor (PMSM). The reduction of vibration occurred in acceleration and deceleration of motor is verified through the simulation and experimental results.

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.

Performance Improvement of Isolated High Voltage Full Bridge Converter Using Voltage Doubler

The performance of an isolated high voltage full bridge converter is improved using a voltage doubler. In a conventional high voltage full bridge converter, the diode of the transformer secondary voltage undergoes a voltage spike due to the leakage inductance of the transformer and the resonance occurring with the parasitic capacitance of the diode. In addition, in the phase shift control, conduction loss largely increases from the freewheeling mode because of the circulating current. The efficiency of the converter is thus reduced. However, in the proposed converter, the high voltage dual converter consists of a voltage doubler because the circulating current of the converter is reduced to increase efficiency. On the other hand, in the proposed converter, an input current is distributed when using parallel input / serial output and the output voltage can be doubled. However, the voltages in the 2 serial DC links might be unbalanced due to line impedance, passive and active components impedance, and sensor error. Considering these problems, DC injection is performed due to the complementary operations of half bridge inverters as well as the disadvantage of the unbalance in the DC link. Therefore, the serial output of the converter needs to control the balance of the algorithm. In this paper, the performance of the conventional converter is improved and a balance control algorithm is proposed for the proposed converter. Also, the system of the 1.5[kW] PCS is verified through an experiment examining the operation and stability.