• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.273-274
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• 2012

This paper investigates control algorithms for a doubly fed induction generator(DFIG) with a back-to-back three-level neutral-point clamped voltage source converter in medium voltage wind power system under unbalanced grid conditions. Two different control algorithms to compensate for unbalanced conditions are proposed. Evaluation factors of control algorithm are fault ride-through(FRT) capability, efficiency, harmonic distortions and torque pulsation. Zero regulated negative sequence stator current control algorithm has the most effective performance concerning FRT capability and efficiency. Ripple-free control algorithm nullifies oscillation component of active power and reactive power. Ripple-free control algorithm shows the least harmonic distortions and torque pulsation. Combination of zero regulated negative sequence stator current and ripple-free control algorithm control algorithm depending on the operating requirements and depth of grid unbalance presents the most optimized performance factors under the generalized unbalanced operating conditions leading to high performance DFIG wind turbine system.

• International journal of advanced smart convergence
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• v.10 no.2
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• pp.175-186
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• 2021

We have studied the speed regulation of the permanent magnet synchronous motor (PMSM) servo system in this paper. To optimize the PMSM servo system's speed-control performance with disturbances, a non-linear speed-control technique using a back-propagation neural network (BP-NN) algorithm forthe controller design of the PMSM speed loop is introduced. To solve the slow convergence speed and easy to fall into the local minimum problem of BP-NN, we develope an improved BP-NN control algorithm by limiting the range of neural network outputs of the proportional coefficient Kp, integral coefficient Ki of the controller, and add adaptive gain factor β, that is the internal gain correction ratio. Compared with the conventional PI control method, our improved BP-NN control algorithm makes the settling time faster without static error, overshoot or oscillation. Simulation comparisons have been made for our improved BP-NN control method and the conventional PI control method to verify the proposed method's effectiveness.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.232-242
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• 2015

For stealth performance consideration, many UAV designs are adopting tailless lambda-shaped configurations which are likely to have unsteady dynamic characteristics. In order to control such UAVs through automatic flight control system, more accurate estimation of dynamic stability derivatives becomes essential. In this paper, dynamic stability derivatives of a tailless lambda-shaped UAV are estimated through numerically simulated forced oscillation method incorporating dynamic mesh technique. First, the methodology is validated by benchmarking the CFD results against previously published experimental results of the Standard Dynamics Model(SDM). The dependency of initial angle of attack, oscillation frequency and oscillation magnitude on the dynamic stability derivatives of a tailless UAV configuration is then studied. The results show reasonable agreements with experimental reference data and prove the validity and efficiency of the concept of using CFD to estimate the dynamic derivatives.

• 제어로봇시스템학회:학술대회논문집
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• 1994.10a
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• pp.682-688
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• 1994

LSM(Least-Squares Method) has inherent limitation that precise system identification over wide frequency band is difficult especially at low frequency hand. In this paper we propose to use decimation, a spectrum analysis method widely used in signal processing. The merits of decimation are the flexibility of selection of the frequency hand concerned and the function of LPF(Low Pass Filter). In this paper, frequency-domain is divided into separate frequency bands which will be combined into full frequency-domain by using MDM(Multiple Decimation Method). In this way, free selection of sampling frequency for each hand is possible and the low frequency oscillation modes of LSM are avoided.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.7
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• pp.815-823
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• 1999

This study considers an implementation of artificial neural networks to the receding horizon optimal control and is applications to power systems. The Generalized Backpropagation-Through-Time (GBTT) algorithm is presented to deal with a quadratic cost function defined in a finite-time horizon. A decentralized approach is used to control the complex global system with simpler local controllers that need only local information. A Neural network based Receding horizon Optimal Control (NROC) 1aw is derived for the local nonlinear systems. The proposed NROC scheme is implemented with two artificial neural networks, Identification Neural Network (IDNN) and Optimal Control Neural Network (OCNN). The proposed NROC is applied to a power system to improve the damping of the low-frequency oscillation. The simulation results show that the NROC based power system stabilizer performs well with good damping for different loading conditions and fault types.

• Journal of Power Electronics
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• v.10 no.6
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• pp.749-761
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• 2010

The switching frequency of a power device is a very important parameter in the design of a parallel active power filter (PAPF), but so far, very little discussion has been conducted on it in a quantitative manner in previous publications. In this paper, an extensive analysis on the effects of the switching frequency on the performance of a PAPF is made, and a specification of the switching frequency values with different compensation results is presented. A first-order inertia element and a second-order oscillation element are considered as approximate models of a PAPF, respectively. The compensation characteristic for each order of harmonic current is obtained at different switching frequencies. Then, the THDs of each model for the system loads of a rectifier with resistance and inductance loads are proposed. The compensation results of a PAPF controlled as a first-order inertia element are better than those of a PAPF controlled as a second-order oscillation element. With two types of system loads which are rectifier with resistance and inductance loads and rectifier with resistance, inductance and capacitance loads, the THDs of the source current after compensation are presented with different switching frequencies. The compensation characteristics for the most widely used digital control system are investigated. The situation with an analog control is the theoretical characteristic and it is the best situation. The compensation characteristic of the digital control is worse than the compensation characteristic of the theoretical characteristic. Based on these analyses, the specifications of compensation characteristics with different switching frequencies are quite straightforward. Finally, a practical design example is studied to verify the application.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.4
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• pp.730-734
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• 2013

The dynamic simulation of machine tools and motion control systems has been widely used for optimization, design verification, control design, etc. There are three main streams in dynamic simulation: structural dynamic analysis based onthe finite element method, dynamic motion analysis based on equations of motion, and control system analysis based on transfer functions. Generally, one of these dynamic simulation methods is chosen and employed for specific purposes. In this study, an integrated dynamic simulation is introduced, in which the structure, motion, and control dynamics are combined together. Commercially well-known software is used in the integrated dynamic simulation: ANSYS, ADAMS, and Matlab/Simulink. Using the integrated dynamic simulation, the dynamics of a magnetic bearing stage is analyzed and the causes of oscillation and noise are identified. A controller design for suppressing a flexible dynamic mode is carried out and verified through the integrated dynamic simulation.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.5
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• pp.179-187
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• 2001

In this paper, a primary pressure regulating type ratio control system is developed for a metal belt CVT, and the CVT ratio changing characteristics are investigated by simulation and experiment. The hydraulic part of the ratio control system has a simple structure with one 3-way spool valve as a main ratio control valve and one bleed type variable force solenoid as a pilot valve. The mathematical modelling of the CVT hydraulic system is derived by considering the CVT shift dynamics. Simulation results of CVT speed ratio and the primary pressure agree with the experimental results demonstrating the validity of the dynamic models. It is found from the simulation and experimental results that the response time of speed ratio and primary pressure can be shortened by increasing the ratio control valve port area, and the size of feedback orifice of ratio control valve gives a damping effect on the primary pressure oscillation.

• 연구논문집
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• s.27
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• pp.141-151
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• 1997

Recently, the importance of electro-multifunction control valve which is digital control valve is increasing day after day. This is due to the demand of that the current industrial world wants the valve having simpler control circuit and higher operation reliability. It is the PWM controlled high speed electronic valve that satisfies the damands of current industrial world. But, the PWM controlled high speed electronic valve has some non-linearity characteristics like as the delay time of switching and the pressure oscillation phenomenon. These characteristics are an obstacle for the control of high speed & high efficiency in control system. Therefore, in this study, we set the studying purpose on analysis of parameter characteristics in solenoid, and on establishment of optimum design technique in high speed solenoid.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.33.2-33
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• 2001

The robust stability condition for sampled-data control systems with a sector nonlinearity was presented in our previous paper. Although it is applicable only to the sampled-data control system of a certain class, a usual discretetime control system can belongs to this type of class. This paper analyzes the amplitude dependent behavior of nonlinear sampled-data (i.e., discrete-time) control systems in a frequency domain. By considering restricted areas (sectors) in the nonlinear characterisitic, the existence of a sustained oscillation is estimated, and the relationship between the stable/unstable conditions and the result derived from describing function is compared. Based on these considerations, the stabilization of nonlinear discrete-time control systems is examined in the frequency domain.