Seung-Ho Song

Maximum Output Power Tracking Control in Variable-Speed Wind Turbine Systems Considering Rotor Inertial Power

This paper proposes a new maximum power point tracking (MPPT) algorithm for variable-speed wind turbine systems, which takes advantage of the rotor inertia power. In this method, a proportional controller is added to the power control to effectively reduce the moment of inertia of the wind turbines, which can improve the fast performance of the MPPT control. The PSIM simulation and experimental results for a doubly-fed induction generator wind turbine system have proved the validity of the proposed algorithm.

Improvement of power quality for PMSG wind turbine systems

This paper proposes an LVRT (low-voltage ride-through) of multi-pole permanent-magnet synchronous generator (PMSG) for wind turbine systems under the grid fault condition and varying wind speed using the energy storage system (ESS) and braking chopper (BC). The proposed topology can reduce the ESS power rating and improve the output performance. A detailed design procedure and control strategy for the ESS and BC are presented. The PSIM simulation results prove that the proposed system can give the ride-through capability and power smoothening for the PMSG wind turbine system. The validity of the proposed system is also verified by experiment results.

Ultra-sensitive magnetoelectric microcantilever at a low frequency

Here, we propose the device platform of energy domain transfer using a magnetoelectric microcantilever. By incorporating Tb0.3Dy0.7Fe1.9 (Terfenol-D) magnetostrictive materials onto a Pb(Zr0.52Ti0.48)O3 (PZT) piezoelectric microcantilever, we demonstrated energy conversion from the magnetic to the electric domain. By measuring the charge signal from a PZT layer under variable dc magnetic field at constant 60 Hz AC magnetic field, we acquired the magnetoelectric coefficient of 24.4 V/cm·Oe. The proposed magnetoelectric microcantilever enables the generation of a minimum detectable DC magnetic field up to 1 × 10−12 T at off-resonance.

Modeling and analysis of power system operation connected with wind turbine generation system and HVDC in Jeju island using PSCAD/EMTDC

This paper presents the modeling and analysis of Jeju power system operation connected with wind farm and HVDC system using PSCAD/EMTDC program. It is for indicating the influence of wind farm operation in Jeju power system. For the computer simulation, there are three main models, which are 100(MW) wind farm, 300(MW) HVDC system and Jeju power load. To verify the effectiveness of the proposed method, two kinds of simulation are carried out . One is the 50(MW) cut off and the other is 100(MW) cut off from the Jeju power grid instantaneously over the rated wind velocity . With the comparison of these results, this method shows the excellent performance. So it is very useful for understanding and applications of linking the wind farm to the power grid.

Analysis and Compensation of PCC Voltage Variations caused by Wind Turbine Power Fluctuations

The voltage variation problem at the point of common coupling (PCC) in a grid-connected wind turbine is investigated. The voltage variation problem is one of the most frequent power quality issues for the grid connection of large amounts of input power in a weak grid. Through the simplified modeling of the wind turbine and power network, the magnitude of PCC voltage variation is calculated by using the equivalent circuit parameters and output power of the wind turbine. The required amount of reactive power that can compensate the voltage variation is also presented analytically by using the vector diagram method. The proposed calculation and compensation method of the PCC voltage variation is verified by computer simulations and experiments.

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.

Current Control of 12-Pulse Regenerative Converter for High Current Magnetic Power Supply

High current magnetic power supply for superconductivity coil of tokamak requires fast dynamic performance of di/dt and smooth change over of current direction. To meet these specifications, high performance DSP-based controller is designed for 12-pulse thyristor dual converter with inter-phase transformer (IPT). Not only the total current of Y- and Delta-converter units, but also the difference for those, should be regulated fast and accurately. Proportional and integral controller is designed for difference current control and the controller output is compensated to Delta-converter. A new algorithm for the calculation of the initial firing angle is proposed for the minimization of non-ideal effect during the change over of dual converter currents.

Anomalous resonant frequency changes in piezoelectric microcantilevers by monolayer formation of Au films

Although the resonant frequency of a microcantilever has been reported to be changed by surface stress and/or flexural rigidity, the reasons still remained unclear. Here, we present an observation of anomalous resonant frequency change with positive values at 3.25 A thickness of Au, where it represents the monolayer formation of Au films. This result illustrates the surface stress-dependence of the resonant frequency. The thickness at where the resonant frequency shift would become zero through the compensation of the mass, and the surface stress is expected to be approximately three monolayers (9.7 A).

Calculation and compensation of PCC voltage variation using a grid connected inverter of a wind turbine in a weak grid

In a hybrid power system where wind power generators are installed in a weak grid, the prediction, investigation and compensation study about the power quality is necessary. Especially, the voltage variation is one of the most important issues for the application of high penetration of wind farm in a week grid. As part of an experimental program to evaluate wind turbine generator performance on the isolated diesel power system, a simplified model for voltage deviation calculation is developed and tested according to the installation capacity of wind power. A method of voltage compensation is proposed using the reactive power output which can be calculated analytically. Results of calculation and compensation algorithm are compared to mitigate the voltage variation problem. As a result the prediction error of the voltage variation at PCC (Point of Common Coupling) was tower than 10% of the actual value. The voltage variation is effectively compensated using the proposed method and the required increase of the inverter capacity for the compensation is calculated.

A prediction model of the voltage variation according to the wind power installation capacity in an isolated grid

In a hybrid power system where wind power generators are installed in an isolated system, the prediction and investigation study about the power quality is necessary. Especially, the voltage variation is one of the most important issues for the application of hig penetration of wind farm in an isolated grid. As part of an experimental program to evaluate wind turbine generator performance on the isolated diesel power system, a simplified model for voltage deviation calculation is developed and tested according to the installation capacity of wind power. Results of calculation from the proposed model, the simulation results using simplified PSCAD/EMTDC model of the grid system, and the measured voltage variation problem. As a result the prediction error of the voltage variation at PCC was lower than 10% of the actual value, which gives quick approximate calculation of the voltage variation limits with the planned size of the wind turbine installations.