Seung-Gi Jeong

The analysis and compensation of dead-time effects in PWM inverters

The quantitative prediction of the dead-time effect in pulse width modulated (PWM) inverters is addressed. Through analysis and simulation it is shown that the effect results in a decrease of the fundamental component and an increase in the low-order harmonics in the output voltage of the inverter. To compensate the effect, two simple methods, which are adequate for sinusoidal PWM and memory-based PWM, respectively, are presented. Experimental results show the validity of the analysis and the usefulness of the compensation methods. >

DSP-based active power filter with predictive current control

This paper presents an active power filter based on a digital signal processing (DSP) controller with enhanced current control performance. A novel predictive current control method is introduced to compensate the phase error of harmonic components caused by discrete sampling and finite nonnegligible execution time delay. The concept of average current control is also introduced that is adequate for digital current control. With a close coordination between the reference current prediction, PWM pattern generation, and control timing, a high performance control is achieved. Experimental results show that the developed system gives satisfactory performance in harmonic and reactive power compensation.

DSP based active power filter with predictive current control

This paper presents a static power convertor active power filter based on a DSP controller with enhanced performance of current control. A novel predictive current control method is introduced to compensate the phase error of harmonic components due to discrete sampling. With a close coordination between the reference current prediction, PWM pattern generation, and control timing, high performance control is achieved. Experimental results show that the developed system gives satisfactory performances in its harmonic/reactive power compensation.

Representing line voltage unbalance

Representing the degree of voltage unbalance with the voltage unbalance factor (VUF) derived from symmetrical transformation requires complex phasor manipulations. This paper investigates various ways of representing VUF to facilitate the calculation in field applications. A formula for VUF with readily available line-to-line voltage magnitudes is derived and a straightforward graphical way of determining VUF is proposed. Various approximate methods are examined and it is shown that some alternative measures can be more effective in approximating VUF than conventional ones.

Enhanced Dynamic Response of SRF-PLL System for High Dynamic Performance during Voltage Disturbance

Usually, a LPF (low pass filter) is used in the feedback loop of a SRF (synchronous reference frame) - PLL (phase locked loop) system because the measured grid voltage contains harmonic distortions and sensor noises. In this paper, it is shown that the cut-off frequency of the LPF should be designed to suppress the harmonic ripples contained in the measured voltage. Also, a new design method for the loop gain of the PI-type controller in the SRF-PLL is proposed with consideration of the dynamics of the LPF. As a result, a better transient response can be obtained with the proposed design method. The LPF frequency and the PI controller gain are designed in coordination according to the steady state and dynamic performance requirements. Furthermore, in the proposed method, the controller gain and the LPF cut-off frequency are changed from their normal value to a transient value when a voltage disturbance is detected. This paper shows the feasibility and usefulness of the proposed methods through the computer simulations and experimental results.

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.

Simulation Modeling and Experimental Validation of Generator Control Strategy in DFIG System

To investigate the dynamic response of WECS to the events in power system, an accurate simulation m odel for DFIG(doubly-fed induction generator) system is d eveloped using PSCAD/EMTDC and a hardware-in-loop si mulator is implemented using 3kW M-G set. The model c onsists of wind model, rotor dynamics, wound rotor induc tion generator, power electronics converter and control str ategies. Control strategies can be programmed at torque-s peed plane as needed and implemented in DSP controlled power converters. Simulation and experimental results sh ows smooth change of control modes and efficient power control performances.

Design of SRD-F-PLL system with consideration of low-pass filter for high dynamic performance during voltage disturbance

Usually, LPF(low pass filter) is used in the feedback loop of SRF(Synchronous Reference Frame) - PLL (Phase Locked Loop) system because the measured grid voltage contains harmonic distortions and sensor noises. In this paper, it is shown that the cut-off frequency of the LPF should be designed to suppress the harmonic ripples contained in the measured voltage. Also, a new design method of the loop gain of the PI-type controller in the SRF-PLL is proposed with the consideration of the dynamics of the LPF. As a result, a better transient response can be obtained with the proposed design method. The LPF frequency and PI controller gain are designed in coordination according to the steady state and dynamic performance requirement. This paper shows the feasibility and the usefulness of the proposed methods through the computer simulation and the lab-scale experiments

Improved current control dynamics at the point of inflection in tokamak coil power supply

Tokamak coil power supply for superconductivity coil of ITER(International Thermonuclear Experimental Reactor) requires fast dynamic performance of di/dt and smooth changeover of current direction. To meet the specification high performance this power supply is designed for 12-pulse thyristor dual converter with interphase reactor(IPR). The study about improving current control transient response had been progressed in the ac-dc thyristor converter when the sign of current reference changes from positive to negative or vice versa. When the gradient of the current reference changes, an additional feedforward compensator is proposed in this paper to supply the voltage change in the load inductance. For practical implementation of the derivative of current reference, a low pass filter is designed and tested in case of the reference signal contains noise.

Implementation of active and reactive power control strategy in a lab-scale DFIG simulator

To investigate the dynamic response of WECS to the events in power system, an accurate simulation model for DFIG(doubly-fed induction generator) system is developed using PSIM and a hardware-in-loop simulator is implemented using 3kW M-G set. The model consists of wind model, rotor dynamics, wound rotor induction generator, power electronics converter and control strategies. Control strategies can be programmed at torque-speed plane as needed and implemented in DSP controlled power converters. Simulation and experimental results shows control of Reactive Power and efficient power control performances.