Jun-Gu Kim

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.

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.

Enteroendocrine cell counts correlate with visceral hypersensitivity in patients with diarrhoea‐predominant irritable bowel syndrome

Abstract  The objective of this study was to determine whether or not the number of enteroendocrine cells (ECs) in the gut is related to visceral hypersensitivity in patients with diarrhoea‐predominant irritable bowel syndrome (D‐IBS). Twenty‐five subjects with D‐IBS (mean, 43.1 years; 16 women, nine men) were recruited into our study, along with 13 healthy controls (mean, 40.7 years; nine women, four men). Maximally tolerable pressures were evaluated via barostat testing, and the levels of ECs were immunohistochemically identified and quantified via image analysis. The numbers of ECs between the D‐IBS subjects and the controls were not significantly different in the terminal ileum, ascending colon and rectum. However, the maximally tolerable pressures determined in the D‐IBS subjects were significantly lower than those of the control subjects (P < 0.01), and we detected a significant relationship between the maximally tolerable pressures and the numbers of ECs in the rectum (r = −0.37, P < 0.01). Rectal sensitivity was enhanced to a greater degree in D‐IBS patients exhibiting an elevated level of rectal ECs. This study provides some evidence to suggest that ECs play an important role in visceral hypersensitivity.

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.

Interleaved active clamp flyback inverter using a synchronous rectifier for a photovoltaic AC module system

An interleaved active clamp flyback inverter using a synchronous rectifier for a photovoltaic AC module system is proposed. In a conventional single flyback inverter for the photovoltaic AC module system, this inverter has drawbacks of a conduction losses of each switch, transformer copper and high ripple current of capacitor. To overcome these problems, two flyback converter modules with interleaved pulse-width modulation (PWM) are connected in parallel at the input and output sides reducing the ripple current on the input and output capacitors and decrease the current stress on the transformer windings. Thus, the transformer copper losses and the conduction losses on the switches are reduced. Also, reliability and life of capacitor are increased due to reducing the ripple current of input and output capacitors. In order to verify these, theoretical analysis and simulation are performed.

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.

Improved non-isolated high voltage gain boost converter using coupled inductors

In some cases of grid connected system using photovoltaic modules, high voltage gain is required to match the grid voltage. In this paper, non-isolated high gain boost converter with coupled inductors is proposed. The proposed converter consists of two-stage boost converter which has each inductor coupled and double/enhance circuit (DEC). This topology can reduce inductor current of each stage and diminish in inductor size so it is suitable for MIC(Module Integrated Converter). This coupled inductor method is verified through the theoretical method and designed from this equivalent circuit method that is finding the optimal coupling coefficient k. Also the operational characteristic of this proposed topology was verified through PSIM program and experimental waveform.

Effect of rescue surgery after non-curative endoscopic resection of early gastric cancer

Whether rescue surgery confers a survival benefit in patients undergoing non‐curative endoscopic resection of early gastric cancer remains controversial.

Flyback inverter using voltage sensorless MPPT for AC module systems

This paper presents a flyback inverter using voltage sensorless maximum power point tracking (MPPT) for AC module systems. In conventional MPPT technique, a PV voltage and PV current are required to calculate the PV output power for the MPPT operation. A proposed method only used for the PV current detection sensor to perform MPPT. When the PV current is sensed, proposed method calculates the electric charge quantity for MPPT control, which is essential to real systems. So, the perturbation and observation (P&O) MPPT is operated with PV current and the calculated electric charge quantity. Detailed analysis and the flowchart of the algorithm for the proposed scheme are included. The effectiveness of the proposed system is verified thorough PSIM simulation and experiments on a 200[W] prototype.