• Journal of Institute of Control, Robotics and Systems
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• v.8 no.10
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• pp.856-860
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• 2002

The guaranteed stability margin of LQ optimal regulators with cross-product terms in a performance index is derived for the discrete-time case. In order to obtain the guaranteed stability margin, the singular value of the return difference matrix is examined. A numerical simulation is provided to demonstrate the validity of the derived stability margin.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.125-129
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• 1987

The stability margin of the LQ regulator is investigated in the time domain. it is shown that the same guaranteed gain margin as that of the frequency domain analysis can be obtained with simple assumptions for the continuous time systems. It is also shown that the allowable modelling error bound can be expressed in terms of system matrices and Riccati equation solution. Guaranteed qain. margin and the allowable modelling error bound for the discrete time systems are also obtained by the similar procedures. In this case, through the some examples, the gain margin is shown to be less conservative than the frequency domain analysis result.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.460-465
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• 2004

In this paper, we present some properties on receding horizon $H_{\infty}$ control for nonlinear discrete-time systems. First, we propose the nonlinear inequality condition on the terminal cost for nonlinear discrete-time systems. Under this condition, noninceasing monotonicity of the saddle point value of the finite horizon dynamic game is shown to be guaranteed. We show that the derived condition on the terminal cost ensures the closed-loop internal stability. The proposed receding horizon $H_{\infty}$ control guarantees the infinite horizon $H_{\infty}$ norm bound of the closed-loop systems. Also, using this cost monotonicity condition, we can guarantee the asymptotic infinite horizon optimality of the receding horizon value function. With the additional condition, the global result and the input-to-state stable property of the receding horizon value function are also given. Finally, we derive the stability margin for the saddle point value based receding horizon controller. The proposed result has a larger stability region than the existing inverse optimality based results.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10a
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• pp.529-533
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• 1990

This paper treats the computational time delay issue in designing digital control systems. The computational time delay margin, within which the closed-loop stability is guaranteed, is analyzed using Rouche theorem. A PID control algorithm is proposed for compensating the computational time delay. Finally, the analyzed and the exact computational time delay margins are compared, and the performance of the proposed PID controller is shown through an illustrative example.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.487-495
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• 2015

This paper proposes a new robust decentralized power oscillation dampers (POD) design of doubly-fed induction generator (DFIG) wind turbine for damping of low frequency electromechanical oscillations in an interconnected power system. The POD structure is based on the practical $2^{nd}$-order lead/lag compensator with single input. Without exact mathematical model, the inverse output multiplicative perturbation is applied to represent system uncertainties such as system parameters variation, various loading conditions etc. The parameters optimization of decentralized PODs is carried out so that the stabilizing performance and robust stability margin against system uncertainties are guaranteed. The improved firefly algorithm is applied to tune the optimal POD parameters automatically. Simulation study in two-area four-machine interconnected system shows that the proposed robust POD is much superior to the conventional POD in terms of stabilizing effect and robustness.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1731-1737
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• 2007

The Korea electricity wholesale market is operated under the cost-based-pool system and the government regulation to the new generation capacities in order to insure the resource adequacy. The goal of government's regulation is the electricity market stability by attracting proper generation investment while keeping the reliability of system. Generation companies must mandatory observe that government plan by now. But if the restructuring is to be complete, generation companies should not bear any obligation to invest unless their profitability is guaranteed. Namely the investors' behavior will be affected by the market prices. In this paper, the system dynamics model for Korea wholesale electricity market to examine whether competitive market can help to stabilize is developed and analyzes the investors behavior. The simulation results show that market controlled by government will be operated stable without resulting in price spike but there is no lower price because of maintaining the reasonable reserve margin. However, if the competition is introduced and the new investment is determined by the investor's decision without government intervention, the benefits from lower wholesale price are expected. Nevertheless, the volatility in the wholesale market increases, which increases the investment risks.