• Journal of Power Electronics
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• v.17 no.1
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• pp.127-135
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• 2017

Recently the researches on modular multi-level converter (MMC) are being highlighted because high quality and efficient power transmission have become key issues in high voltage direct current (HVDC) systems. This paper proposes an improved pre-charging method for the sub-module (SM) capacitor of MMC-based HVDC systems, which operates in the nearest level control (NLC) modulation and does not need additional circuits or pulse width modulation (PWM) techniques. The feasibility of the proposed method was verified through computer simulations for a scaled 3-phase 10kVA MMC with 12 SMs per each arm. Hardware experiments with a scaled prototype have also been performed in the lab to confirm the simulation results.

• Journal of the Korea Society for Simulation
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• v.8 no.4
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• pp.33-51
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• 1999

In this study, the system level network simulation is considered with adaptive array antenna in CDMA mobile communication system. A network simulation framework is implemented based on IS-95A/B system to consider dynamic handoff, system level network behavior, and deploying strategy into the overall CDMA mobile communication network under adaptive array algorithm. Its simulation model, such as vector channel model, adaptive beam forming antenna model, handoff model, and power control model, are described in detail with simulation block. In order to maximize SINR of received signal at antenna, Maximin algorithm is particularly considered, and it is computed at each simulation snap shot with SINR based power control and handoff algorithm. Graphic user interface in this system level network simulator is also implemented to define the simulation environments and to represent simulation results on real mapping system. This paper also shows some features of simulation framework and simulation results.

• Nuclear Engineering and Technology
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• v.39 no.1
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• pp.63-74
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• 2007

In this paper, a reconfigurable controller consisting of a normal controller and a standby controller is designed to control the thermoelectric (TE) power in the SP-100 space reactor. The normal controller uses a model predictive control (MPC) method where the future TE power is predicted by using support vector regression. A genetic algorithm that can effectively accomplish multiple objectives is used to optimize the normal controller. The performance of the normal controller depends on the capability of predicting the future TE power. Therefore, if the prediction performance is degraded, the proportional-integral (PI) controller of the standby controller begins to work instead of the normal controller. Performance deterioration is detected by a sequential probability ratio test (SPRT). A lumped parameter simulation model of the SP-100 nuclear space reactor is used to verify the proposed reconfigurable controller. The results of numerical simulations to assess the performance of the proposed controller show that the TE generator power level controlled by the proposed reconfigurable controller could track the target power level effectively, satisfying all control constraints. Furthermore, the normal controller is automatically switched to the standby controller when the performance of the normal controller degrades.

• Nuclear Engineering and Technology
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• v.32 no.2
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• pp.157-168
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• 2000

The nuclear steam generator level control system is designed by robust control methods. The feedwater controller is designed by three methods of the H$\infty$, the mixed weight sensitivity and the structured singular value. Then the controller located on the feedback loop of the level control system is designed. For the system performance, the controller of simple PID whose coefficients vary with the power is selected. The simulations show that the system has a good performance with proper stability margins.

• Journal of Power Electronics
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• v.18 no.2
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• pp.588-603
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• 2018

This paper presents the idea of a smart load that can adjust the input power flow based on the intermittent power available from RESs (Renewable Energy Resources) to regulate the line voltage, and draw a constant power from the grid. To this effect, an innovative power flow controller is presented based on a Resistive ES (Electric Spring) in combination with a PEAT (Power Electronics based Adjustable Transformer), which can effectively shape the load power flow at the subnetwork level. With a PEAT incorporated in the step down transformer at the grid side, the proposed controller can supply non-critical loads through local RESs, and the critical loads can draw a relatively constant power from the grid. If there is an abundance of power produced by the RESs, the controller can supply both non-critical loads and critical loads through the RES, which significantly reduces the power demand from the grid. The principle, practicality, stability analysis, and controller design are presented. In addition, simulation results show that the power flow controller performs well in shaping the load power flow at the subnetwork level, which decreases the power demand on the grid. Experimental results are also provided to show that the controller can be realized.

• Journal of Power Electronics
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• v.17 no.2
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• pp.334-345
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• 2017

In order to meet the increasing needs of the hybrid energy source system for electric vehicles, which demand bidirectional power flow capability with a wide-voltage-conversion range, a bidirectional three-level DC-DC converter and some control strategies for hybrid energy source electric vehicles are proposed. The proposed topology is synthesized from Buck and Boost three-level DC-DC topologies with a high voltage-gain and non-extreme duty cycles, and the bidirectional operation principle is analyzed. In addition, the inductor current ripple can be effectively reduced within the permitted duty cycle range by the coordinated control between the current fluctuation reduction and the non-extreme duty cycles. Furthermore, benefitting from duty cycle disturbance control, series-connected capacitor voltages can also be well balanced, even with the discrepant rise and fall time of power switches and the somewhat unequal capacitances of series-connected capacitors. Finally, experiment results of the bidirectional operations are given to verify the validity and feasibility of the proposed converter and control strategies. It is shown to be suitable for hybrid energy source electric vehicles.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.349-360
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• 2006

Controller for doubly-fed induction-type wind generation system should be designed with mechanical power on blade. The controller in this paper consists of upper level controller and lower level controller. The upper level controller determines operating modes according to mechanical input power and calculates proper reference values. There are 4 operating modes - minimum speed control, variable torque control, torque limit control and idle mode. The lower level controller performs current regulated PWM control of rotor-side converter and grid-side inverter. A wind turbine simulator is implemented using doubly-fed induction-type generator and DSP based back-to-back converter to verify the performance of designed controller experimentally.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.4
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• pp.6-13
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• 1998

It is difficult to control for the level of the steam generator in the nuclear power plant because there is swell and shrink, and many disturbance such as, feed water rate, feedwater temperature, main steam flow rte, coolant temperature effect steam generator level. If the conventional PI controller use in this system, we cannot have a stability in the control of the lower power, the rejection function of disturbance, and the load following effectively. In this paper, e study the application of the of neural network based Kp, Ti for Pi controller to the level control of the steam generator of nuclear power plant through the simulation and experimental on the steam generator. We are satisfied with the resulting against the inturrupt of the disturbance, the change of setpoint through the simulation and the swell and shrink, the response of controller on the experimental steam generator.

• Journal of Power Electronics
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• v.17 no.3
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• pp.653-663
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• 2017

Multilevel active neutral-point-clamped (ANPC) converter combines the advantages of three-level ANPC converter and multilevel flying capacitor (FC) converter. However, multilevel ANPC converter often suffers from capacitor voltage balancing problems. In order to solve the capacitor voltage balancing problems for five-level ANPC converter, phase-shifted pulse width modulation (PS-PWM) is used, which generally provides natural voltage balancing ability. However, the natural voltage balancing ability depends on the load conditions and converter parameters. In order to eliminate voltage deviations under steady-state and dynamic conditions, the active voltage-balancing control (AVBC) methods of floating capacitors and dc-link capacitors based on PS-PWM are proposed. First, the neutral-point current is regulated to balance the neutral-point voltage by injecting zero-sequence voltage. After that, the duty cycles of the redundant switch combinations are adjusted to balance the floating-capacitor voltages by introducing moderating variables for each of the phases. Finally, the effectiveness of the proposed AVBC methods is verified by experimental results.

• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2080-2094
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• 2004

A model predictive controller is designed to control thermal power in a nuclear reactor. The basic concept of the model predictive control is to solve an optimization problem for finite future time steps at current time, to implement only the first optimal control input among the solved control inputs, and to repeat the procedure at each subsequent instant. A controller design model used for designing the model predictive controller is estimated every time step by applying a recursive parameter estimation algorithm. A 3-dimensional nuclear reactor analysis code, MASTER that was developed by Korea Atomic Energy Research Institute (KAERI), was used to verify the proposed controller for a nuclear reactor. It was known that the nuclear power controlled by the proposed controller well tracks the desired power level and the desired axial power distribution.