• Journal of Power Electronics
• /
• v.10 no.3
• /
• pp.285-292
• /
• 2010

This paper presents a current mode integrated control technique (CM-ICT) using a modified voltage space vector modulation (MSVM) for Z-source inverter (ZSI) fed induction motor drives. MSVM provides a better DC voltage boost in the dc-link, a wide range of AC output voltage controllability and a better line harmonic profile. In a voltage mode ICT (VM-ICT), the outer voltage feedback loop alone is designed and it enforces the desired line voltage to the motor drive. An integrated control technique (ICT), with an inner current feedback loop is proposed in this paper for the purpose of line current limiting and soft operation of the drive. The current command generated by the PI controller and limiter in the outer voltage feedback loop, is compared with the actual line current, and the error is processed through the PI controller and a limiter. This limiter ensures that, the voltage control signal to the Z-source inverter is constrained to a safe level. The rise and fall of the control signal voltage are made to be gradual, so as to protect the induction motor drive and the Z-source inverter from transients. The single stage controller arrangement of the proposed CM-ICT offers easier compensation. Analysis, Matlab/Simulink simulations, and experimental results have been presented to validate the proposed technique.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.8
• /
• pp.580-588
• /
• 2009

This paper summarizes the experimentally-measured performance of small-scale, vertical-axis wind turbine for the purpose of improving the aerodynamic efficiency and its controllability. The turbine is designed to have a Savonius-Type rotor with an inlet guide-vane and an side guide-vane so that it achieves a higher efficiency than any lift- or drag-based turbines. The main design factors for this high-efficient, vertical wind turbine are the number of blades (Z), and the aspect ratio of Height/Diameter (H/D) among many. The basic model has the diameter of 580mm, the height of 464mm, and the blade number of 10. The maximum power coefficient of 0.50 was experimentally measured for the above-mentioned specifications. The inlet-guide vane ensures the maximum efficiency when the angle of attack to the rotor blade lies between $15^{\circ}$ and $20^{\circ}$. This experimental results for the vertical-axis wind turbine can be applied to the preliminary design of turbine output curve based on the wind characteristics at the proposed site by controlling its aerodynamic performance given as a priori.

• Journal of Power Electronics
• /
• v.13 no.3
• /
• pp.400-408
• /
• 2013

This paper presents a discrete state-space controller using state feedback control and feed-forward decoupling to provide a desirable control bandwidth and control stability for dynamic voltage restorers (DVR). The paper initially discusses three typical applications of a DVR. The load-side capacitor DVR topology is preferred because of its better filtering capability. The proposed DVR controller offers almost full controllability because of the multi-feedback of state variables, including one-beat delay feedback. Feed-forward decoupling is usually employed to prevent disturbances of the load current and source voltage. Directly obtaining the feed-forward paths of the load current and source voltage in the discrete domain is a complicated process. Fortunately, the full feed-forward decoupling strategy can be easily applied to the discrete state-space controller by means of continuous transformation. Simulation and experimental results from a digital signal processor-based system are included to support theoretical analysis.

• Journal of Electrical Engineering and Technology
• /
• v.11 no.4
• /
• pp.829-838
• /
• 2016

This paper focuses on the engineering trade-offs in designing capacitor voltage balancing schemes for modular multilevel converters (MMC) HVDC: regulation performance and switching loss. MMC is driven by the on/off switch operation of numerous submodules and the key design concern is balancing submodule capacitor voltages minimizing switching transition among submodules because it represents the voltage regulation performance and system loss. This paper first introduces the state-of-the-art MMC-HVDC submodule capacitor voltage balancing methods reported in the literatures and discusses the trade-offs in designing these methods for HVDC application. This paper further proposes a submodule capacitor balancing scheme exploiting a control signal to flexibly interchange between the on-state and the off-state submodules. The proposed scheme enables desired performance-based voltage regulation and avoids unnecessary switching transitions among submodules, consequently reducing the switching loss. The flexibility and controllability particularly fit in high-level MMC HVDC applications where the aforementioned design trade-offs become more crucial. Simulation studies for MMC HVDC are performed to demonstrate the validity and effectiveness of the proposed capacitor voltage balancing algorithm.

• Journal of Power Electronics
• /
• v.16 no.5
• /
• pp.1884-1893
• /
• 2016

The ride-through control of a doubly-fed induction generator (DFIG) for the voltage sags on wind farms utilizing crowbar circuits by which the rotor side converter (RSC) is disabled has being reported in many literatures. An analysis and calculation of the transient current when the RSC is switched off are of significance for carrying out the low voltage ride through (LVRT) of a DFIG. The mathematical derivation is highlighted in this paper. The zero-state and zero-input responses of the transient current in the frequency domain through a Laplace transformation are investigated, and the transient components in the time domain are achieved. With the characteristics worked out from the linear resolving without modeling simplification, the selection of the resistance in the linear crowbar circuit and the value conversion from a linear circuit to a nonlinear one is proposed to setup the attenuation rate. In terms of grid code requirements, the theoretical analysis for the time constant of the transient components attenuation insures the controllability when the excitation of the RSC is resumed and it guarantees the reserved time for the response of the reactive power compensation. Simulations are executed in MATLAB/SIMPOWER and experiments are carried out to validate the theoretical analysis. They indicate that the calculation method is effective for selection of the resistance in a crowbar circuit for LVRT operations.

• Fire Science and Engineering
• /
• v.32 no.6
• /
• pp.141-149
• /
• 2018

The perception of risk that firefighters have is closely related to their performance and emergency preparedness in nuclear power plant accidents. This study investigated the unique risk perception among firefighters working in nuclear power plants (NPPs) using a concept mapping method. Thirty three firefighters in NPPs participated in this study. Two core axes, "fear and control" and "coping resource", emerged in the firefighters' risk perception. In particular, the risk perception consisted of six clusters: fear of radiation exposure and low controllability; anxiety caused by the lack of control and authority; lack of trust and cooperation; lack of authority and professionals; lack of equipment, manual, and information; and lack of knowledge and training. Catastrophic expectation and a low sense of control caused by the lack of responsive resources were the main factors that increase the risk perception. The theoretical and practical contributions of this study were discussed.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38C no.8
• /
• pp.725-732
• /
• 2013

Recently, various applications for LED lightings are growing continuously due to their better performances such as low power consumption, longer life time, operation speed, controllability, high quality color rendering, and sustainability. However, in developing the high-powered LEDs illumination system, heat-sink problem is one of the important obstacle. In this paper, a heat-sink design with multi-layered structure for high-powered LEDs is proposed, which is composed of metal core PCB, heat-pipes, heat-sink plates, and fans. And also, in this paper, a design for LED controls using DMX512 protocols through RS-485 communications is proposed, which is considered as de facto international standard in LEDs illumination control and is widely used in landscape lighting and stage lighting. In this paper, LED control and its application techniques are introduced and the method of wireless remote control for main controller is proposed.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.49 no.6
• /
• pp.35-40
• /
• 2012

This paper has proposed a 3~5 GHz IR-UWB low power transmitter for range detection application. Proposed transmitter which has been implemented in a $0.13{\mu}m$ CMOS technology is all digital circuit that consist of simple digital logic. this feature insure low complexity and low power consumption. In addition, center frequency can be changed by adopting voltage controlled delay cell for avoiding existing another radio frequency in UWB low band. Proposed circuit consume only 10pJ/b from 1.2 V supply voltage. The simulation results show 3.3~4.3 GHz center frequency controllability, -51 dBm/MHz maximum output power and is satisfied with FCC regulation.

• Journal of the Korean Society of Industry Convergence
• /
• v.23 no.2_1
• /
• pp.115-124
• /
• 2020

In wireless power transfer (WPT) system, the conventional compensation topologies only can provide a constant current (CC) or constant voltage (CV) output under their resonant conditions. It is difficult to meet the CC and CV hybrid charging requirements without any other schemes. In this study, a switching hybrid topology (SHT) is proposed for CC and CV electric vehicle (EV) battery charging. By utilizing an additional capacitor and two AC switches (ACSs), a double-side LCC (DS-LCC) and an inductor and double capacitors-series (LCC-S) topologies are combined. According to the specified CC and CV charging profile, the CC and CV charging modes can be flexibly converted by the two additional ACSs. In addition, zero phase angle (ZPA) also can be achieved in both charging modes. In this method, because the operating frequency is fixed, without using PWM control, and only a small number of devices are added, it has the benefits of low-cost, easy-controllability and high efficiency. A 3.3-kW experimental prototype is configured to verify the proposed switching hybrid charger. The maximum DC efficiencies (at 3.3-kW) of the proposed SHT is 92.58%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.11a
• /
• pp.161-161
• /
• 2009

Ion bombarded inorganic materials for LC alignment has been researched as it provides controllability in a nonstop process for producing high-resolution displays. Many optically transparent insulators such as $SiOx$ and a-C:H have been investigated as potential candidates for inorganic alignment materials. Even so, LC orientation on a new material with superior capacity is required to produce high-performance displays. Many inorganic materials with high permittivities can reduce the voltage losses due to the LC alignment layer that are a trade-off for its capacitance. The minimum voltage for device operation can be applied to the LC under low external voltage using these materials. This means that low power consumption for LCD applications can be achieved using a high-k alignment structure in which the LC can be driven effectively with a low threshold voltage. Among the many other potential high-k oxides, HfO2 is considered to be one of the most promising due to its remarkable properties of high dielectric constant, relatively low leakage current, large band gap (5.68 eV), and high transparency. Due to these characteristics, HfO2 can be used in LC alignment to increase the capacitance of the inorganic alignment layer for low-voltage driving of LCs.