Young-Hyok Ji

A Real Maximum Power Point Tracking Method for Mismatching Compensation in PV Array Under Partially Shaded Conditions

Conventional popular maximum power point tracking (MPPT) methods are effective under uniform solar irradiance. However, under solar irradiance mismatching conditions [partially shaded conditions (PSCs)], these MPPTs can fail for real MPPT (RMPPT), because multiple local maxima can be exhibited on the power-voltage characteristic curve. Although some researchers have worked on RMPPT under partial shading conditions, the methods have some drawbacks in terms of complexity and requirements for additional circuits, etc. In this paper, a novel MPPT method capable of RMPPT under PSCs is proposed. The performance of the proposed MPPT method is analyzed according to the RMPP position and is verified by simulation and experimental results.

Interleaved Soft-Switching Boost Converter for Photovoltaic Power-Generation System

In this paper, a interleaved soft switching boost converter (ISSBC) for a photovoltaic (PV) power-generation system is proposed. The topology used raises the efficiency for the dc/dc converter of the PV power conditioning system (PVPCS), and it minimizes switching losses by adopting a resonant soft-switching method. A detailed mode analysis of the proposed topology is presented. The feasibility of the proposed topology is experimentally verified for a 1.2-kW prototype. The experimental results imply that 97.28% efficiency is achieved under the full-load condition. Consequently, it is confirmed that the overall efficiency is increased by about 1.5% compared with the conventional hard switching interleaved boost converter.

An Islanding Detection Method for a Grid-Connected System Based on the Goertzel Algorithm

Islanding refers to a condition of a distributed generator (DG) in that it continues to power a location even though power from the grid is no longer present. This condition can be dangerous to grid workers who may not realize that the load is still powered even though there is no power from the grid. Adverse effects of islanding are low power quality, grid-protection interference, equipment damage, and personnel safety hazards. For these reasons, DG systems must detect an islanding condition and immediately stop producing power; this is referred to as anti-islanding. Islanding detection methods can be categorized into two major approaches: the passive and active methods. The passive methods are based on measurement of the natural effects of islanding. The active methods use intentional transients or harmonic effects. When the power generated by the DG matches the load power consumption, passive methods fail due to the small natural effects of islanding. Therefore, the passive methods have a nondetection zone (NDZ). The active methods can reduce the NDZ size. However, these methods reduce the grid power quality. In this paper, a novel anti-islanding method (AIM) is proposed. A single-phase DG using the proposed AIM injects the output current with a little harmonic current into the grid and monitors the harmonic components of the voltage at the point of common coupling using the Goertzel algorithm. The Goertzel algorithm is a kind of discrete Fourier transform. It extracts the magnitude and phase of the desired frequency from the input signal, with a minimum computation. The proposed islanding detection algorithm resolves the NDZ but also the bad effects on the grid power quality due to injecting harmonic components qualified by the interconnection standard. The proposed islanding detection method was verified using PSIM (see www.powersimtech.com) simulations and experimental results.

A New Control Strategy for Improving Weighted Efficiency in Photovoltaic AC Module-Type Interleaved Flyback Inverters

In this paper, a new control strategy for improving weighted efficiency in photovoltaic (PV) ac module-type interleaved flyback inverters (ILFIs) is proposed. The efficiency of the ILFI for PV ac modules has to be high, not only for the maximum power, but also for other power levels according to weather conditions. For PV power conversion efficiency improvement in all load ranges, a new control method for an ILFI according to the output of the PV module is proposed in this paper. The proposed method controls an active clamp circuit and each converter phase of an ILFI according to the output power of the PV module. Thus, the efficiency of an ILFI as a PV power conditioner can be improved in all power range of the PV module. Theoretical analysis, simulation, and experiment are performed in order to verify the proposed control method.

C-language based PV array simulation technique considering effects of partial shading

The performance of photovoltaic (PV) array is strongly dependent on the operating conditions especially the solar irradiation. The shading on PV array by the passing clouds or neighboring buildings causes not only power losses, but also non-linearity of V-I characteristics of PV array. Under partially shaded conditions, the characteristics have more non-linearity with multiple local maxima. In spite of several researchers have studied the PV characteristics under the partial shading condition, it is difficult to simulate the partial shading condition on the simulation tool for power electronics. The C-language based PV array simulation strategy proposed in here is to simulate the effects of partial shading condition for developing more advanced maximum power point tracking algorithms or power conversion systems. Proposed modeling strategy is easily connected to simulation tools. In this paper, the modeling of photovoltaic array is based on the numerical analysis, and the verification is performed using PSIM.

Maximum power point tracking method for PV array under partially shaded condition

Conventional popular MPPT methods are effective under uniform solar irradiance. However, under partially shaded conditions, these MPPTs can fail to track the real MPP because of the multiple local maxima which can be existed on PV characteristic curve under partially shaded condition. In spite of some researchers have worked on real MPP tracking under partial shading conditions, the methods have some drawbacks with complexity and requirement of additional circuit, etc. In this paper, a novel MPPT method that is capable of tracking the real MPP under partially shaded conditions is proposed. The performance of proposed MPPT is analyzed according to the position of real MPP and is verified by simulation and experimental results.

Dual mode switching strategy of flyback inverter for photovoltaic AC modules

In recent years, many topologies have been developed as PV module integrated converter for AC module system. Among these topologies, the flyback-type power converter have been occupied the attention due to its simplicities on configuration and control. In this paper, dual mode switching control method for flyback-type PV module integrated converter is proposed. Proposed switching control method changes the mode of operation in DCM and BCM alternatively. It is expected that the high performances in efficiency and transferred power quantity can be achieved through the conduction mode change. The efficacies of proposed switching technique are validated by simulation and experimental result.

Soft-Switching Bidirectional DC/DC Converter with a LC Series Resonant Circuit

In this paper, a soft-switching bidirectional dc/dc converter with a LC series resonant circuit is proposed. The proposed converter has been obtained by adding LC series resonant tank in the conventional bidirectional dc/dc converter. The proposed topology performs soft switching at both buck and boost operations. Through the theoretical boost and buck mode analysis, zero voltage switching operation is explained. Moreover, characteristics of the proposed topology are verified with simulation and experimental results.

Soft switching boost converter for photovoltaic power generation system

In this paper, a soft switching boost converter for solar power system is proposed. It is a topology, which raises efficiency for DC-DC converter of photovoltaic PCS (power conditioning system). And it minimizes switching losses by adopting soft switching method using resonance. It analyzes the operation characteristic of topology which was suggested through simulation, and proves the validity by analyzing loss and efficiency at real operation with experiment.

A current shaping method for PV-AC module DCM-flyback inverter under CCM operation

In the grid interconnected photovoltaic power generation system including PV-AC module system, the output current have to be sinusoidal synchronized with the grid voltage. Concerning the voltage-controlled current-source modification requirement and the characteristics of flyback topology, boundary or discontinuous conduction mode operations are suitable for the PV-AC module flyback inverter. However, the flyback inverter can be operated in continuous conduction mode (CCM) due to its operating conditions in spite of it is designed to operate under boundary or discontinuous conduction mode. Unfortunately, it causes unintended distortion to output current. In this paper, a current shaping method to reduce the output current distortion for the DCM-flyback inverter is proposed. Even though the flyback inverter operates under CCM, the output current distortion can be reduced by the unfolding H-bridge switching technique.