• The Transactions of the Korean Institute of Power Electronics
• /
• v.20 no.1
• /
• pp.19-30
• /
• 2015

A static synchronous compensator (STATCOM) applied to rapidly changing, highly unbalanced loads such as electric arc furnaces (EAFs), requires both positive-sequence and negative-sequence current control, which indicates fast response characteristics and can be controlled independently. Furthermore, a delta-connected STATCOM with cascaded H-bridge configuration accompanying multiple separate DC-sides, should have high performance zero-sequence current control to suppress a phase-to-phase imbalance in DC-side voltages when compensating for unbalanced load. In this paper, actual EAF data is analyzed to reflect on the design of current controllers and a pioneering zero-sequence current controller with a superb transient performance is devised, which generates an imaginary -axis component from the presumed response of forwarded reference. Via simulation and experiments, the performance of the positive, negative, and zero-sequence current control of a cascaded H-bridge STATCOM for EAF is verified.

• Journal of Power Electronics
• /
• v.13 no.5
• /
• pp.829-840
• /
• 2013

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC-DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification.

• Journal of Electrical Engineering and Technology
• /
• v.11 no.3
• /
• pp.618-628
• /
• 2016

Active power filter (APF) has been proved as a flexible solution for compensating the harmonic distortion caused by nonlinear loads in power distribution power systems. Digital repetitive control can achieve zero steady-state error tracking of any periodic signal while the sampling points within one repetitive cycle must be a known integer. However, the compensation performance of the APF would be degradation when the grid frequency varies. In this paper, an improved repetitive control scheme with frequency adaptive capability is presented to track any periodic signal with variable grid frequency, where the variable delay items caused by time-varying grid frequency are approximated with Pade approximants. Additionally, the stability criterion of proposed repetitive control scheme is given. A three-phase shunt APF experimental platform with proposed repetitive control scheme is built in our laboratory. Simulation and experimental results demonstrate the effectiveness of the proposed repetitive control scheme.

• Proceedings of the KIEE Conference
• /
• 2005.07b
• /
• pp.1339-1342
• /
• 2005

This paper presents a simple AC-DC power conditioner for a squirell-cage induction generator(IG) operating under variable shaft speeds. The necessary reactive power for the IG system is supplied by means of a capacitor bank and a voltage-source PWM converter. Using a capacitor bank to transfer the reactive power to the IG under the rated speed and no-load conditions starts the IG operation and reduces the PWM power converter size. A simple control compensating for changes in the electrical loads as well as the variation in speed was developed to regulate the voltages of the IG system by controlling the rotor flux through its reactive and active currents control implementation. This proposed power conditioning scheme can be used efficiently as a wind power generation system where the output voltage of the IG is maintained constant voltage despite the variable frequency and the DC bus voltage of the PWM converter can be used for either DC applications such as battery charging or AC power applications with 60/50 Hz by connecting a stand alone inverter. The experimental and simulated operating performance results of a 5 kW IG scheme at various speeds and leads are presented.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.21 no.4
• /
• pp.296-301
• /
• 2016

Using high magnetic flux from a 60 Hz high-current cable, a 2 W wireless-powered energy harvesting receiver for sensor operation, internet of things (IoT) devices, and LED lights inside electrical cable tunnels is proposed. The proposed receiver comprises a copper coil with a high number of turns, a ring-shaped ferromagnetic core, a capacitor for compensating for the impedance of the coil in series, and a rectifier with various types of loads, such as sensors, IoT devices, and LEDs. To achieve safe and easy installation around the power cable, the proposed ring-shaped receiver is designed to easily open or close using a clothespin-shaped handle, which is made of highly-insulated plastic. Laminated silicon steel plates are assembled and used as the core because of their mechanical robustness and high saturation flux density characteristic, in which the thickness of each isolated plate is 0.3 mm. The series-connected resonant capacitor, which is appropriate for low-voltage applications, is used together with the proposed receiver coil. The concept of the figure of merit, which is the product weight and cost of both the silicon steel plate and the copper wire, is used for an optimized design; therefore, the weight of the fabricated receiver and the price of raw material is 750 gf and USD $2 each, respectively. The 2.2 W powering capability of the fabricated receiver was experimentally verified with a power cable current of $100A_{rms}$ at 60Hz.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.16 no.5
• /
• pp.53-60
• /
• 2002

This paper presents exact autotransformer-fed AC electric railroad system modeling using constant current mode, and single-phase STATCOM(Static Synchronous Compensator) which has an effect on electric railroad system. An AC electric railroad is rapidly changing single-phase feeding electric power. To avoid voltage fluctuation under single phase loads, electric power should be received from a large source. The system modeling theory is based on the solution of algebraic. The AC electric railroad load model is nonlinear. Therefore this paper is considered nonlinear load using PSCAD/EMTDC. And the proposed modeling method is considered the line self-impedances and mutual-impedances that techniques for the AC electric railroad system modeling analysis, and that single-phase STATCOM can reliably compensate the voltage drop. In the case study, the allowance range of feeding voltage is 22.5∼27.5 kV, AT-fed AC electric railroad system circuit is analyzed by loop equation both normal and extension modes. The simulation objectives are to calculate the catenary and rail voltages with respect to ground, as the train moves along a section of line between two adjacent ATs. The results show that single-phase STATCOM can reduce the voltage drop in the feeding circuit and improve the power quality at AC electric railroad system by compensating the reactive power.

• Smart Structures and Systems
• /
• v.26 no.3
• /
• pp.373-390
• /
• 2020

Hybrid simulation (HS) is a versatile tool for structural performance evaluation under dynamic loads. Although real structural responses are often multiple-directional owing to an eccentric mass/stiffness of the structure and/or excitations not along structural major axes, few HS in this field takes into account structural responses in multiple directions. Multi-directional loading is more challenging than uni-directional loading as there is a nonlinear transformation between actuator and specimen coordinate systems, increasing the difficulty of suppressing loading error. Moreover, redundant actuators may exist in multi-directional hybrid simulations of large-scale structures, which requires the loading strategy to contain ineffective loading of multiple actuators. To address these issues, lately a new strategy was conceived for accurate reproduction of desired displacements in bi-directional hybrid simulations (BHS), which is characterized in two features, i.e., iterative displacement command updating based on the Jacobian matrix considering nonlinear geometric relationships, and force-based control for compensating ineffective forces of redundant actuators. This paper performs performance validation and application of this new mixed loading strategy. In particular, virtual BHS considering linear and nonlinear specimen models, and the diversity of actuator properties were carried out. A validation test was implemented with a steel frame specimen. A real application of this strategy to BHS on a full-scale 2-story frame specimen was performed. Studies showed that this strategy exhibited excellent tracking performance for the measured displacements of the control point and remarkable compensation for ineffective forces of the redundant actuator. This strategy was demonstrated to be capable of accurately and effectively reproducing the desired displacements in large-scale BHS.

• Journal of Power Electronics
• /
• v.17 no.6
• /
• pp.1587-1599
• /
• 2017

This paper proposes a real-time implementation of an optimal operation of a double stage grid connected wind power system incorporating an active power filter (APF). The system is used to supply the nonlinear loads with harmonics and reactive power compensation. On the generator side, a new adaptive neuro fuzzy inference system (ANFIS) based maximum power point tracking (MPPT) control is proposed to track the maximum wind power point regardless of wind speed fluctuations. Whereas on the grid side, a modified predictive current control (PCC) algorithm is used to control the APF, and allow to ensure both compensating harmonic currents and injecting the generated power into the grid. Also a type 2 fuzzy logic controller is used to control the DC-link capacitor in order to improve the dynamic response of the APF, and to ensure a well-smoothed DC-Link capacitor voltage. The gained benefits from these proposed control algorithms are the main contribution in this work. The proposed control scheme is implemented on a small-scale wind energy conversion system (WECS) controlled by a dSPACE 1104 card. Experimental results show that the proposed T2FLC maintains the DC-Link capacitor voltage within the limit for injecting the power into the grid. In addition, the PCC of the APF guarantees a flexible settlement of real power exchanges from the WECS to the grid with a high power factor operation.

• Structural Engineering and Mechanics
• /
• v.67 no.2
• /
• pp.207-217
• /
• 2018

In past years, numerous problems have vexed engineers with regard to buckling, corrosion, bending, and overloading in damaged steel structures. This article sets out to investigate the possible effects of carbon fiber reinforced polymer (CFRP) and steel plates for retrofitting deficient steel square hollow section (SHS) columns. The effects of axial loading, stiffness, axial displacement, the position and shape of deficient region on the length of steel SHS columns, and slenderness ratio are examined through a detailed parametric study. A total of 14 specimens was tested for failure under axial compression in a laboratory and simulated using finite element (FE) analysis based on a numerical approach. The results indicate that the application of CFRP sheets and steel plates also caused a reduction in stress in the damaged region and prevented or retarded local deformation around the deficiency. The findings showed that a deficiency leads to reduced load-carrying capacity of steel SHS columns and the retrofitting method is responsible for the increase in the load-bearing capacity of the steel columns. Finally, this research showed that the CFRP performed better than steel plates in compensating the axial force caused by the cross-section reduction due to the problems associated with the use of steel plates, such as in welding, increased weight, thermal stress around the welding location, and the possibility of creating another deficiency by welding.