Gwon-Jong Yu

Improved perturbation and observation method (IP&O) of MPPT control for photovoltaic power systems

Maximum power point tracking (MPPT) is used in photovoltaic (PV) system to maximize the PV array output power irrespective of temperature and irradiation conditions. In this paper, an improved perturbation and observation method (IP&O) based on adaptive algorithm is proposed, which is automatically adjusts the reference step size and hysteresis bandwidth for power comparison. The digital signal processor (DSP) was used to implement the proposed MPPT control system, which controls the dc/dc boost converter in the 3 kW grid-connected PV power systems. The experimental results show that the IP&O increases the total PV output power by 0.5% at an unsettled weather condition compare to traditional perturbation and observation method (P&O).

High-frequency DC link inverter for grid-connected photovoltaic system

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformerless inverter. This system consists of a high frequency inverter bridge, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter bridge, and an AD filter. The high frequency inverter bridge switching at 20 kHz is used to generate bipolar PWM pulse, which is subsequently rectified by diode bridge rectifiers to result in a full-wave rectified sine wave. Finally, it is unfolded by a low frequency inverter bridge to result in a 60 Hz sine wave power output. In this paper, the control algorithm for synchronous current feedback control method and a maximum power point tracking (MPPT) method using DSP are described. The simulation and experimental results are shown to verify the validity of the proposed system.

Maximum power point tracking with temperature compensation of photovoltaic for air conditioning system with fuzzy controller

Fuzzy control has received a great deal of attention due to its excellent behavior when applied to complex and nonlinear system. As fuzzy theory is close to human reasoning, fuzzy controllers are easy to design and cheap to produce. In this paper, we investigate the possibilities of P/sub max/ control using the fuzzy controller, and we also examine the optimal power converter using a step-up chopper circuit to operate the solar cell at an optimal voltage of compensated voltage (i.e. of determined transducer by temperature (-40/spl deg/C/spl sim/+100/spl deg/C)). The proposed step-up maximum power point tracking (MPPT) system is studied by simulation and is implemented by using a microcomputer which controls the duty ratio of an IGBT boost converter.

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

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.

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

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

Modelling and analysis of active islanding detection methods for photovoltaic power conditioning systems

Increasing numbers of photovoltaic arrays are being connected to power utilities through power conditioning systems (PCS). This has raised potential problems of network protection. If, due to the action of the PCS, the local network voltage and frequency remain within regulatory limits when the utility is disconnected, then islanding is said to occur. Representative methods to prevent islanding are described and a model based on PSiM (a simulation package for power electronics and motor control) and analysis of the reactive power variation (RPV) method are presented. A novel phase detector using an all-pass filter and digital phase locked loop (DPLL) is proposed, especially for the single-phase PCS. Finally, the paper provides the simulation and experimental results with a single-phase 3 kW prototype PCS. The islanding test method of IEEE Std 929-2000 was performed for verification.

Load sharing operation of a 14 kW photovoltaic/wind hybrid power system

In this paper, a design procedure for photovoltaic/wind hybrid power generation system is presented. The hybrid system is composed of a DC/DC converter for photovoltaic energy conversion, a DC/DC converter for wind energy conversion, a four switch IGBT inverter converting the combined DC power to the AC power and a backup power battery. Here, it is very important to select the desired battery size to meet the stable output and economic cost aspect since this system utilizes a fluctuating and finite energy resource. The purpose of this paper is to develop a sizing method for the PV/wind energy hybrid system with load sharing operation. The method demonstrates a simple tool to determine the desired battery size that satisfies the energy demand from the user with the photovoltaic and wind natural source. The proposed method is verified on a 14 kW hybrid power system including a 10 kW PV generator and a 4 kW wind generator established in Cheju island, Korea.

Design and experimental results of improved dynamic MPPT performance by EN50530

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.

Boundary conditions of reactive-power-variation method and active-frequency-drift method for islanding detection of grid-connected photovoltaic inverters

Photovoltaic (PV) power conditioning system (PCS) has been increased around the world since PV is becoming widespread as a clean and gentle energy source for earth. As a result, high-density grid-connected PV PCS will be interconnected with distribution network. In this situation, islanding phenomenon becomes most important issues for the safety and stability. Many methods to prevent islanding phenomenon have been proposed and analyzed. Especially, active frequency drift positive feedback (AFDPF) method is to process output current waveform of PV PCS by chopping fraction. However, AFDPF method is not fully identified the chopping fraction considering output power quality and islanding prevention performance in IEEE Std 929-2000 islanding prevention test. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF method considering output power quality and islanding prevention performance are performed by PSIM simulation and experiment in IEEE Std 929-2000 islanding prevention test.

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

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.