Chung-Yuen Won

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.

Fuel Cell Generation System With a New Active Clamping Current-Fed Half-Bridge Converter

In this paper, a new active clamping current-fed half-bridge converter is proposed, which is suitable for fuel cell power generation systems. The proposed converter is superior to conventional dc-dc converters in terms of efficiency and component utilization. The overall efficiency is estimated to be 94% at full load.

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.

Analysis and Design of a Soft-Switching Boost Converter With an HI-Bridge Auxiliary Resonant Circuit

A new soft-switching boost converter is proposed in this paper. The conventional boost converter generates switching losses at turn on and off, and this causes a reduction in the whole systems efficiency. The proposed boost converter utilizes a soft-switching method using an auxiliary circuit with a resonant inductor and capacitor, auxiliary switch, and diodes. Therefore, the proposed soft-switching boost converter reduces switching losses more than the conventional hard-switching converter. The efficiency, which is about 91% in hard switching, increases to about 96% in the proposed soft-switching converter. In this paper, the performance of the proposed soft-switching boost converter is verified through the theoretical analysis, simulation, and experimental results.

Design and Application for PV Generation System Using a Soft-Switching Boost Converter With SARC

In order to improve the efficiency of energy conversion for a photovoltaic (PV) system, a soft-switching boost converter using a simple auxiliary resonant circuit, which is composed of an auxiliary switch, a diode, a resonant inductor, and a resonant capacitor, is adopted in this paper. The conventional boost converter decreases the efficiency because of hard switching, which generates losses when the switches are turned on/off. During this interval, all switches in the adopted circuit perform zero-current switching by the resonant inductor at turn-on, and zero-voltage switching by the resonant capacitor at turn-off. This switching pattern can reduce the switching losses, voltage and current stress of the switching device. Moreover, it is very easy to control. In this paper, we have analyzed the operational principles of the adopted soft-switching boost converter, and it is designed for PV generation system. Simulation and experimental results are presented to confirm the theoretical analysis.

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.

Bi-directional dc-dc converter for fuel cell generation system

Fuel cell (FC) has slow response characteristic for load variation. In this paper, bi-directional dc-dc converter for FC generation system is proposed to improve load response characteristic. The bi-directional converter interfaces the low voltage battery to the inverter dc link of FC generation system. When power flows from the low voltage side (battery: 48 V) to the high voltage side (dc link: 380 V), the circuit works in discharge operation (boost mode) to power the high voltage side load; otherwise, it works in charge operation (buck mode) to charge the low voltage side battery. A simple voltage clamp branch is used to limit transient voltage across the current-fed full bridge and realize zero-voltage-switching (ZVS) during discharge operation. A soft switched, isolated bi-directional dc-dc converter has been developed for FC generation system, in which the 48 V battery for the system accessory loads is also used to start up the FCs and to charge the energy consumed on operating of FC generation system.

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.