Byunggyu Yu

Fuzzy-Logic-Based

Since natural distribution power generation systems such as wind energy contain electric power fluctuation, flywheel energy storage (FWES) equipment for power compensation is used. Fuzzy-logic-based V/f control of the induction motor is proposed for the speed sensorless power-leveling system in this paper. Only two sensors, including one DC voltage sensor and one DC current sensor, are utilized. The flywheel is composed of two modes, namely, the speed picking-up control mode and the power control mode. According to the DC-link average current of an inverter, the rotating speed of the flywheel in the speed picking-up control mode is detected by regulating the output frequency and the output voltage based on fuzzy logic control. The power control mode consists of the outer voltage loop and the inner current loop. Although the outer loop is also realized by fuzzy logic control, the inner loop is the key object in this paper, i.e., the proportional and integral gains of a proportional-integral regulator are optimized by means of fuzzy logic reasoning for the purpose of the reliability and rapid response of leveling power. The experiments are carried out with the FWES equipment of 40-kJ energy, and the results verify that the proposed method is reliable, and better dynamic and static performance is demonstrated.

V/f

Since islanding of photovoltaic (PV) generation can cause safety problems, it should be prevented. This paper proposes a correlation-based islanding-detection method (IDM) using current-magnitude disturbance for a PV system. As an islanding-detection index, this paper uses the correlation factor between current-magnitude disturbance and the corresponding inverter output voltage. The proposed IDM uses the characteristics in which the up/down current disturbance has a strong correlation with the PV output voltage when islanding occurs. The proposed method has fast islanding capability and high power quality. For verification of the proposed method, the simulated and experimental results of a 3-kW PV inverter by IEEE Std. 929-2000 and IEEE Std. 1547.1-2005 are provided. The proposed correlation technique can be used in other active antiislanding methods based on the correlation between the current and voltage after islanding occurs.

Control of an Induction Motor for a DC Grid Power-Leveling System Using Flywheel Energy Storage Equipment

In a modern power system, photovoltaic as distributed generated source is growing larger and it can cause a variety of problem. Most issued problem is an islanding phenomenon. In order to prevent islanding phenomenon, three kinds of active islanding detection methods have been studied. These are respectively to change magnitude, frequency, and the start phase of inverter output current. Among them, both frequency and start phase variation anti-methods make the islanding frequency drift away from the trip window of the frequency relay if an islanding is occurred. This paper presents a robust anti-islanding method, which are consisted of a frequency variation method as AFD (active frequency drift) method and a start phase variation method as SMS (slip mode frequency shift) method. Clearly, the proposed anti-islanding method shows the satisfied islanding detection ability to IEEE 1547 Standard. To validate the performance of the proposed method, simulation and experiment are performed. Possible islanding conditions are followed by the IEEE Standard 1547. The methodology presented in the paper can be extended to the other active anti-islanding methods

A Correlation-Based Islanding-Detection Method Using Current-Magnitude Disturbance for PV System

Photovoltaic (PV) system has been regarded as one of the most popular renewable energy sources due to its easy installation and safe operation. As one of the key control algorithms, maximum power point tracking (MPPT) function of PV inverter has been researched. Usually, its performance has been evaluated under a fixed environmental condition including irradiance and temperature. However, recently the dynamic MPPT performance under varying irradiance conditions has been paid attention to the PV society. As the European standard EN 50530, which defines the recommended varying irradiance profiles, was released lately, the corresponding researches have been required to improve the dynamic MPPT performance. This paper presents the design and experimental results of improved dynamic MPPT performance using dP P&O MPPT method, which is evaluated by EN 50530. By using 250kW PV inverter, the performance of dP P&O method is evaluated and compared with the conventional MPPT methods. The experimental results show that dP P&O method shows very high dynamic MPPT efficiency under EN 50530.

A Robust Anti-islanding Method for Grid-Connected Photovoltaic Inverter

The photovoltaic (PV) generators have a nonlinear V–I characteristics and maximum power points which vary with the illumination level and temperature. Using maximum power point tracker (MPPT) with the intermediate converter can increase the system efficiency by matching the PV systems to the loads. This paper presents an irradiation level estimator and a maximum power point tracker based on support vector regression (SVR) and a control scheme for and a control scheme for a single-phase inverter connected to the utility grid. SVR provides an adaptive nature for the system performance. Also the SVR provides excellent features such as fast response, good performance and the ability to change the regression function to improve control system. The single-phase dc/dc converter is designed to control the power flow to the maximum value. The simulation results have verified the validity of the proposed estimation algorithm.

Design and experimental results of improved dynamic MPPT performance by EN50530

Photovoltaic (PV) modules operate over a large range of meteorological conditions but manufacturers information is not sufficient to determine their overall performance. Designer and installer need a reliable tool to predict energy production from PV module under all conditions in order to improve and optimize PV system. The simulation model of PV module are useful to perform detailed analysis of PV system performance for changing meteorological conditions, verify actual rated power capacity of PV system and investigate the optimum design of PV system and components. This paper indicates performance results of various PV modules using simulation model. The accuracy and validity of this simulation results is identified by compared measured with simulated value by simulation model. These results will indicate that it is highly imperative to develop evaluation and diagnosis approach for PV system.

Support vector regression based maximum power point tracking for PV grid-connected system

A novel structure for power maximization of the PV (photovoltaic) system under partially condition is presented. By using CSI (Current Source Inverter) instead of VSI (Voltage Source Inverter), the structure of PV system becomes extremely both more simple and reliable than conventional one. It means that MICs (Module Integrated Converters) can be consisted of buck-only converters and electrolytic capacitors can be removed from the inverter. The experimental results confirmed that the total output power captured the sum of each maximum value of PV under shading conditions.

Comparison results of measured and simulated performance of PV module

This paper presents performance results of middle scale grid-connected Photovoltaic (PV) system for monitoring periods. The performance and losses of PV system is quantitatively evaluated and analyzed using calculation model with monitored data so that various PV system technologies are development. The objective of this paper is to develop reliable and valid evaluation method of Photovoltaic (PV) system performance so that maximum output is achieved over the system lifetime with performance improvement.

A novel current link distributed MPPT PV system - Overall system prototyping and evaluation

The objective of this paper is to develop a power converter module that charges a battery with solar power, and the design technique at the product level is introduced to realize a compact size and light weight. The main circuit is a buck-boost chopper so that it can cover wide range of charging voltage. The MPPT control is realized by a very simple algorithm of Limit-Cycle MPPT (LCMPPT) proposed by authors previously. All control functions are implemented in digital algorithm and a HITACHI H8 microprocessor is used for the control. In addition to the battery, a load can be directly connected also, which is automatically disconnected in the case of detecting a low voltage condition of the battery. RS-232C port is also available for observing the internal variables such as input/output voltages and currents through a PC. An example of obtained test results showing the relations of output power versus input/output voltages and efficiency are given. The efficiency is about 70-72% in a wide range of output power.

Performance monitoring and analysis of middle scale grid-connected PV system

Islanding phenomenon of Photovoltaic (PV) system should be prevented because it causes a safety problem to utility service personnel and power supply facilities. Until now, various antiislanding methods have been proposed. However, these are mostly focus on the islanding prevention method for single PV system. Recently, PV system using micro-inverters are widely disseminated in the field. Accordingly, an islanding issue for multiple PV microinverter systems has been paid attention due to their interaction not to detect islanding, even though the single micro-inverter unit can prevent islanding when the single unit is only tested. This paper presents an improved active frequency drift (AFD) anti-islanding method for multiple PV micro-inverter systems. The proposed method injects every half-line cycle asymmetrical signals and uses the correlation between the injected asymmetrical signal and the corresponding half line cycle. The proposed method is verified by using PSIM simulation, compared with the conventional AFD method. It shows that the proposed method is highly effective to detect islanding even under multiple micro-inverter system while the conventional one doesn’t detect islanding.