Young-Seok Jung

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.

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.

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.

Time-Delay Effects on DC Characteristics of Peak Current Controlled Power LED Drivers

New discrete time domain models for the peak current controlled (PCC) power LED drivers in continuous conduction mode include for the first time the effects of the time delay in the pulse-width-modulator. Realistic amounts of time delay are found to have significant effects on the average output LED current and on the critical inductor value at the boundary between the two conduction modes. Especially, the time delay can provide an accurate LED current for the PCC buck converter with a wide input voltage. The models can also predict the critical inductor value at the mode boundary as functions of the input voltage and the time delay. The overshoot of the peak inductor current due to the time delay results in the increase of the average output current and the reduction of the critical inductor value at the mode boundary in all converters. Experimental results are presented for the PCC buck LED driver with constant-frequency controller.

Performance results of 15 kW BIPV sunshade system

15 kW grid-connected building integrated photovoltaic (BIPV) sunshade system has been installed at Korea Institute of Energy Research (KIER) and monitoring system has also been constructed for measuring and analyzing performance of BIPV sunshade system to observe the overall effect of environmental conditions on their operation characteristics by long-term field test. Before installation of BIPV system, the performance of BIPV components such as power conditioning unit (PCU) and PV module under standard test conditions, which was measured and evaluated through short-term performance test. The performance of BIPV system has been evaluated and analyzed for component perspective (PV array and PCU) and global perspective (system efficiency, capacity factor, and electrical power energy, power quality etc.) for one year monitoring periods and loss factors are reviewed.

Novel AFD method with pulsation of chopping fraction for islanding prevention of grid-connected photovoltaic inverter

This paper proposes a novel active frequency drift (AFD) method for the islanding prevention of grid-connected photovoltaic inverter. To detect the islanding phenomenon of grid-connected photovoltaic (PV) inverters concerning about the safety hazards and the damage to other electric equipments, many kinds of anti-islanding methods have been presented. Among them, AFD method using chopping fraction (cf) enables the islanding detection to drift up (or down) the frequency of the voltage during the islanding situation. However, the performance of the conventional AFD methods, which have a certain value of cf only, is inefficient and difficult to design the appropriate cf value analytically to meet the limit of harmonics. In this paper, the periodic chopping fraction based on an AFD method is proposed. This proposed method shows the analytical design value of cf to meet the test procedure of IEEE Std. 929-2000 with the power quality and islanding detection time. To verify the validation of the proposed method, the islanding test results are presented. It is confirmed that the proposed method has not only less harmonic distortion but also good performance of islanding detection compare with the conventional AFD method

Performance Improvement of Sensorless Control of IPMSM using Active Flux Concept by Improved Current Estimators

In this paper, the performance improvement of the sensorless control of IPMSM employing the active flux concept by the improved current estimator is presented. The accuracy of the current estimator used in a previous report is degraded when the motor parameters are not known exactly. A simple current estimator derived from estimated flux is proposed to improve the position estimation performance. In order to show the usefulness of the proposed estimation method, the simulation results using Matlab/Simulink and the experiment results are presented.