Yong-Su Noh

Battery-Integrated Power Optimizer for PV-Battery Hybrid Power Generation System

Recently, hybrid generation systems combine multiple energy sources or storage components to optimize the characteristics of the individual energy sources. PV-battery hybrid systems usually combine photovoltaic (PV) generation of electricity with energy storage components (i.e. batteries). These systems are often configured as mini-grids in which the generation sources supply loads through a relatively small local distribution grid. In these systems, to improve the utilization of solar energy, the output power mismatch between PV modules due to the non-identical solar irradiance has to be considered. In this paper, a battery integrated PV power optimizer for PV-battery hybrid power generation system is proposed. Proposed system can be applied to the conventional PV hybrid power generation systems, as well as, the normal centralized PV generation systems. By integrating the batteries to the PV power optimizer, PV system using proposed topology can easily increase battery capacity and stabilize input power for central power conditioning system (PCS). Proposed battery integrated power optimizer is verified by simulation results.

Analysis and Design of a Three-port Flyback Inverter using an Active Power Decoupling Method to Minimize Input Capacitance

In this paper, a new decoupling technique for a flyback inverter using an active power decoupling circuit with auxiliary winding and a novel switching pattern is proposed. The conventional passive power decoupling method is applied to control Maximum Power Point Tracking (MPPT) efficiently by attenuating double frequency power pulsation on the photovoltaic (PV) side. In this case, decoupling capacitor for a flyback inverter is essentially required large electrolytic capacitor of milli-farads. However using the electrolytic capacitor have problems of bulky size and short life-span. Because this electrolytic capacitor is strongly concerned with the life-span of an AC module system, an active power decoupling circuit to minimize input capacitance is needed. In the proposed topology, auxiliary winding defined as a Ripple port will partially cover difference between a PV power and an AC Power. Since input capacitor and auxiliary capacitor is reduced by Ripple port, it can be replaced by a film capacitor. To perform the operation of charging/discharging decoupling capacitor C x , a novel switching sequence is also proposed. The proposed topology is verified by design analysis, simulation and experimental results.

A study of grid-connected PV-AC module with active power decoupling and ESS

Because AC module system is directly connected to grid source, power pulsation is appeared at AC module input capacitor. So, it can adversely affect maximum power point tracking (MPPT) control. Furthermore, photovoltaic (PV) module power can be fluctuated with varying irradiation while constant load demand. To reduce power fluctuation for MPPT control and stabilize the PV system with varying conditions, conventional flyback converter has auxiliary circuits for active decoupling and energy storage system (ESS) is proposed for energy efficiency. Proposed AC module system can solve the above problem (i.e. power pulsation, varying irradiation and load demand) by auxiliary circuit operation. But when the proposed AC module system is operating, it has various modes according to power flowing. In this paper, analyzes proposed AC module of operating modes, which show perform the overall system operation. To confirming proposed AC module system, verified by PSIM simulation result.

A new active power decoupling using Bi-directional Resonant Converter for flyback-type AC-module system

In general, the photovoltaic (PV) power generation system has mismatch problem between oscillated AC power and constant input DC power. It has been solved by using large electrolytic capacitors. However, due to the low life span of electrolytic capacitors, the active power decoupling method is studied to substitute from the conventional type capacitor to film capacitor. This paper proposes new active power decoupling using bi-directional Resonant Converter (APD-BRC) for flyback-type AC-module system. Proposed APD-BRC circuit is composed of bi-directional buck-boost converter using soft-switching and it expected higher system efficiency than conventional decoupling system. Since voltage ripple of PV module output is reduced, electrolytic capacitor can be replaced to film capacitor. The proposed topology is verified by simulation results.

An Optimal Method to Design a Trap-CL Filter for a PV AC-Module Based on Flyback Inverter

The power factor and total harmonic distortion (THD) are important considerations when designing an output filter. In the case of the photovoltaic (PV) ac-module, the size and weight also have to be taken into consideration. This paper proposes an output filter to reduce size and weight, and provides the optimal design method for a PV ac-module. The proposed output filter consists mainly of a conventional CL filter with a trap filter. The trap filter is used to eliminate the harmonic at the switching frequency that contains most of the harmonics. Therefore, total inductance and the size of the filter can be reduced although the output filter components are increased. This paper presents analysis of the proposed filter characteristics in detail. Also, an optimal design method reducing the size of the output filter components including the damping resistor is proposed. The proposed methods are verified on the experimental prototype rated at 320 W with an ac-module based on the interleaved flyback inverter. The total filter inductance and volume are, respectively, reduced to 9.54% and 26.62% with the same performance.

Analysis and design of current-fed two inductor bi-directional DC-DC converter using resonance for high efficiency and high step-up application

This paper proposes current-fed two-inductor bi-directional DC-DC converter using resonance(CF_TIBCR) for high efficiency and high step-up applications. Conventional dual half bridge(DHB) converter have problems of high voltage spikes and unavailable charge/discharge resulting from uni-directional converter. Hence, operating frequency and the efficiency are also limited. To solve these problems and achieve high efficiency, in this paper, the diode of the high voltage side is replaced by metal oxide semiconductor FET(MOSFET). All active switches undergo zero voltage switching(ZVS) condition. Especially, switches of the low voltage side are satisfied with zero current switching(ZCS) condition and ZVS condition. The steady state analysis and operation principle of CF_TIBCR is introduced. The DC voltage conversion ratio is derived based on steady state analysis. Simulation using PSIM is implemented to verify CF_TIBCR.

Isolated Bi-directional DC/DC converter using quasi-resonant ZVS

In this paper, an isolated bi-directional DC/DC converter combined with dual half bridge converter and full-bridge is proposed. The conventional dual half bridge converter has problem of high voltage spike when switches are turned off. To solve this problem, the resonant capacitor and the resonant inductor are added to the proposed isolated bi-directional converter. And full-bridge converter is also operated under zero voltage switching (ZVS) condition using resonance components. Since all switches of proposed converter are achieved ZVS condition, efficiency of the proposed topology will be increased. The proposed bi-directional converter is verified by theoretical analysis, PSIM simulations and experiments.

Analysis and design of decoupling capacitor for single phase flyback-inverter with active power decoupling circuit

Recently, active power decoupling method is studied for reducing power oscillation on PV (Photovoltaic) module by grid side instantaneous power. However decoupling circuit input current delay and inverter system efficiency affect power oscillation when decoupling circuit is operating. This power oscillation disturbs MPPT (Maximum Power Point Tracking) control. To reduce power oscillation considering above conditions (i.e. input current delay and system efficiency), power oscillation is analyzed and optimal design method of decoupling capacitance is proposed. The validity of proposed methods is verified by simulation result.

Control method for increasing efficiency of current-fed isolated bi-directional dual half-bridge converter using resonant switch

This paper proposes a new control method for a current-fed isolated bi-directional dual half-bridge DC/DC converter using a resonant switch (CF-IDHCR) to improve efficiency. CF-IDHCR is based on a current-fed half bridge converter, and the diodes bridge are replaced with MOSFETs to provide bi-directional operation. The resonant components in CF-IDHCR are used to increase the efficiency by achieving soft switching for all active switches, thus the switching loss can be reduced. However, it is difficult to increase system efficiency because of large peak current and inherent reactive power. A proposed control method, which is named by dual phase-shift control, can decrease reactive power and switch peak current, thereby system efficiency can be improved. This paper presents theoretical analysis of the proposed control method, and it is verified by a PSIM 9.1.4 simulation results.

Current-fed two-inductor bi-directional DC/DC converter with wide output voltage range

The current-fed two-inductor boost converter (CF-TIBC) has previously been demonstrated to have advantages in operating low voltage and high current input applications. Such characteristics are suited for photovoltaic (PV) or battery application, likes energy storage system (ESS) or electric vehicle (EV). In this paper, the current-fed two-inductor bi-directional DC/DC converter (CF-TIBDC) is proposed. The proposed converter overcomes drawbacks of the conventional CF-TIBC, which are only one way power flow and voltage spike when the switches are turned off. By using the resonant components, the voltage spike problem is solved, and all switches in the CF-TIBDC meet the zero voltage switching (ZVS) condition. Likewise, the zero current switching (ZCS) condition is achieved through the switches on the low voltage stage. A wide range of output voltages with soft-switching is achieved by frequency-duty control. As a result, the proposed converter can maintain high efficiency across the entire range. The principles of the operation characteristics are presented with theoretical analysis, and the proposed converter is verified through PSIM simulation and experiment with a 300W laboratory prototype.