Reactive Power Output Of Generators Research Articles

Real‐time spatio‐temporal trend and level (T&L) filtering scheme for early detection of voltage instability

Discovering early signatures of voltage instability can enhance situational awareness and facilitate emergency control. Such signatures usually appear as decaying trends in load voltages and increase in reactive power output of generators. Discrete control actions such as frequent switching of load tap changer (LTC) and capacitor banks, that are otherwise unmonitored, can also be crucial indicators of a voltage problem. Hence, the authors propose a unified early warning scheme (EWS) for detecting voltage instability. To quantify and correlate spatial, temporal (spatio-temporal) trends and level changes, the authors use a multivariate, adaptive trend and level (T&L) filter. A unique feature of the proposed scheme is the signature authentication, by verifying simultaneity in T&L changes across multivariate time series. The authors show that, by extrapolating trends, limit violations in bus voltages and generator reactive power output can be estimated well in advance. Further, the level-change detection logic is shown to have the ability to detect frequent LTC-actions directly from the bus voltage time series. While the T&L filtering scheme is validated on field phasor measurement unit (PMU) datasets, EWS and emergency control is demonstrated on the classical 10-bus voltage stability test system.

Coordinated Voltage Control With Online Energy Margin Constraints

Based on data available from phase measurement units (PMUs), this paper proposes an energy margin constrained online coordinated voltage control (CVC) algorithm. First, the energy function model is established, which is based on detailed device models that include the effects of shunt capacitor banks, reactive power output of generators and under-load-tap-changers (ULTCs). In order to improve the computational efficiency, a Lie derivative-based method is used to map the energy change into the system trajectory along the energy manifold. Then, the change of energy margin based on the Lie derivative is used as the objective function and the reactive power margin is used as a constraint to formulate a linear programming problem. A coordinated strategy is proposed to help achieve the optimal solution when the linear programming problem is solved. In comparison with the other control modes, the proposed method improves the stability margin and the control effectiveness of voltage profile. Numerical results are provided for a three-machine system, the IEEE-30 bus system and the New England-39 bus benchmark system.

Voltage Stability by Reactive Power Rescheduling Using PSO Algorithm

Voltage stability is a major issue in a power system and in this paper, generator reactive power rescheduling is used for voltage stability enhancement without additional installation cost. Due to system disturbances the active power as well as reactive power flows changes. Generators being always connected to the system reactive power rescheduling of generators can be effectively done. The optimum values of rescheduling is found using Particle Swarm Optimization (PSO) algorithm. The procedure is simulated with an objective of minimizing total reactive power lost in the system with constraints of load balance, bus voltages with suitable limits, and real and reactive power outputs of generators within the maximum and minimum load. The simulations are done using MATLAB.

Determination of Whitening Filter Order for Estimation of Electromechanical Mode by Regression Model Representing Power System Damping Characteristics

SUMMARYThis paper proposes a new method of estimating accurately the modal damping of a weakly damped electromechanical oscillation in power systems. The proposed method is based on a whitening filter (finite impulse response filter) to estimate the modal damping from the system response and a regression model to express the relation between the modal damping and system state variables, such as the active and reactive power outputs of generators. The feature of the method is that an optimal order of the whitening filter is determined so as to minimize the error of the linear regression model. A simulation study using the IEEJ EAST 10 machine model shows that the proposed method is effective for accurate estimation of weakly damped oscillation modes.

Wide-area nonlinear robust voltage control strategy for multi-machine power systems

This paper presented a novel wide-area nonlinear excitation control strategy for multi-machine power systems. A simple and effective model transformation method was proposed for the system’s mathematical model in the COI (center of inertia) coordinate system. The system was transformed to an uncertain linear one where deviation of generator terminal voltage became one of the new state variables. Then a wide-area nonlinear robust voltage controller was designed utilizing a LMI (linear matrix inequality) based robust control theory. The proposed controller does not rely on any preselected system operating point, adapts to variations of network parameters and system operation conditions, and assures regulation accuracy of generator terminal voltages. Neither rotor angle nor any variable’s differentiation needs to be measured for the proposed controller, and only terminal voltages, rotor speeds, active and reactive power outputs of generators are required. In addition, the proposed controller not only takes into account time delays of remote signals, but also eliminates the effect of wide-area information’s incompleteness when not all generators are equipped with PMU (phase measurement unit). Detailed tests were conducted by PSCAD/EMTDC for a three-machine and four-machine power systems respectively, and simulation results illustrate high performance of the proposed controller.

Determination of Whitening Filter Order for Estimation of Electromechanical Mode by Regression Model Representing Power System Damping Characteristics

SUMMARY This paper proposes a new method of estimating accurately the modal damping of a weakly damped electromechanical oscillation in power systems. The proposed method is based on a whitening filter (finite impulse response filter) to estimate the modal damping from the system response and a regression model to express the relation between the modal damping and system state variables, such as the active and reactive power outputs of generators. The feature of the method is that an optimal order of the whitening filter is determined so as to minimize the error of the linear regression model. A simulation study using the IEEJ EAST 10 machine model shows that the proposed method is effective for accurate estimation of weakly damped oscillation modes.

전력계통 구조를 고려한 발전기 무효예비력 산정

This paper defines a generator reactive reserve considering power system network. Conventional generator reserve is calculated by the difference between the maximum reactive power output of generator and the current reactive power of generator. However, all generators could not affect on the whole power system. Thus, the effective generators should be selected by sensitivity analysis. The sensitivity depends on network configuration is the relation between generator reactive power outputs and reactive power loads. Using the sensitivity, the effective generator reactive reserve can be calculated.

DGA-BASED VAR RESCHEDULING FOR TRANSMISSION LOSS REDUCTION

This paper presents a method to reduce the transmission losses by using a Differential Genetic Algorithm (DGA) for VAR rescheduling. Considering all the standard equality and inequality constraints, solutions are obtained that minimize losses by changing the tap settings of various transformers and by varying the injected reactive power. It has been demonstrated that there are certain buses in the system where reactive power injections from capacitor banks can improve the voltage profile and reduce the transmission losses. In this paper minimum reactive power output of generators are kept at zero to care that generators do not draw reactive power. A comparison has been made to show that the DGA produces better results than the Conventional Genetic Algorithm with regard to loss minimization. This paper considers the New England 39-bus power system as a test case.

Application of Hybrid Multiagent-based Particle Swarm Optimization to Optimal Reactive Power Dispatch

Reactive power dispatch (RPD) is an optimization problem that determines variables, such as reactive power outputs of generators, output of shunt capacitors/reactors, etc., and minimizes the transmission losses, satisfying a given set of constraints. To solve the optimal reactive power dispatch (ORPD), this article proposes a new method, called hybrid multiagent-based particle swarm optimization, which does not allow the search to struck at local optima and search in different zones of the search space. Simulation results show that the proposed approach converges to better solutions faster than the earlier approaches when evaluated on IEEE 30-bus and IEEE 118-bus systems.

A decoupled quadratic programming approach for optimal power dispatch

This paper presents a decoupled approach for optimal active and reactive power dispatch for the economic operation of an electric utility. The proposed iterative scheme reported in this paper decomposes the optimal load flow problem into a P-subproblem and a Q-subproblem, where the control variables are the active and reactive power outputs of generators. At each iteration the subproblems are solved by quadratic programming using the flexible tolerance optimization method (FTOM). In this approach, constraints are linearized by using sensitivity analysis and the perturbation technique, in order to obtain a wider near-feasible region for this quadratic programming method. This approach has a good computation speed. The results of two test systems and three cases are presented and compared with the results of other methods.

Security Based Economic Operation of Electric Power System

The increased loading of transmission lines, the insufficient local reactive power supply, and the transmission of power through long distances have been major reason behind voltage problems. Optimal powerflow, on the other hand, allocates real and reactive power generation among available generators and/or var sourses. Given that the general trend is towards higher loading of the system and closer to the security limits, this paper develops a mathematical model for economic operation which integrates the voltage security assessment.The paper provides the location, causes, and cures for voltage collapse as an integral part of economic operation problem, which is decomposed into security assessment and optimal powerflow subproblems. The security assessment subproblem provides a set of security constraints in the form of security margins or proximity to voltage collapse and voltage security. The optimal power flow subproblem provides real and reactive power outputs of generators and/or var sources, and transformer tap settings under the set of security constraints.