Synchronous Machine Infinite Bus Research Articles

Modulated Oscillations of Synchronous Machine Nonlinear Dynamics With Saturation

This paper discusses a potential mechanism from bifurcation analysis to explain the occurrence of modulated oscillations (which are observed from real PMU measurements) in synchronous machine nonlinear dynamics. We show that in special system configurations synchronous machine dynamics can be very sensitive to sustained low frequency oscillations which are amplified to a great extent by nonlinear effects. A comprehensive bifurcation analysis illustrates that a small sustained oscillation evolves into a torus through the Neimark-Sacker bifurcation, creating a modulated oscillation with a higher amplitude and a much slower but new oscillatory frequency. The analysis further predicts a new bifurcation type, the Chenciner bifurcation, that has never been reported in power engineering. The Chenciner bifurcation introduces much more complex dynamical behaviors including co-existence of two stable attractors and chaos. It can be a potential reason for the sudden appearance of a benign modulated oscillation without any system configuration change. We use a detailed synchronous machine infinite bus system with an automatic voltage regulator and a steam turbine to demonstrate the phenomenon and to study the bifurcation. Then, we perform a model order reduction to establish the main states responsible for nonlinear effects and show a potential critical role of the exciter saturation for the investigated bifurcation.

Design of an automatic voltage regulator based on symmetric root locus technique

An automatic voltage regulator (AVR) design based on symmetric root locus (SRL) technique for a synchronous machine infinite bus (SMIB) power system is presented. The SRL technique is used to minimise the amplifier saturation by placing the closed-loop poles (CLPs) of the system at desired locations. The desired CLPs are decided by considering the dominant pole locations that provide maximum damping on the SRL plot. The design incorporates an extended estimator to deal with uncertainties introduced due to variations of parameters or operating conditions. They reconstruct the state information including the state of disturbance dynamics simultaneous to implement full state feedback and using the reconstructed disturbance estimate to compensate the effect of external disturbance or parameter uncertainties. The performance of the system is analysed through simulating at different operating conditions. The control method improves the tracking response and provides zero estimation error in the steady-state. Illustrative examples have been provided to demonstrate the effectiveness of the developed methodology.

Design of an automatic voltage regulator based on symmetric root locus technique

An automatic voltage regulator (AVR) design based on symmetric root locus (SRL) technique for a synchronous machine infinite bus (SMIB) power system is presented. The SRL technique is used to minimise the amplifier saturation by placing the closed-loop poles (CLPs) of the system at desired locations. The desired CLPs are decided by considering the dominant pole locations that provide maximum damping on the SRL plot. The design incorporates an extended estimator to deal with uncertainties introduced due to variations of parameters or operating conditions. They reconstruct the state information including the state of disturbance dynamics simultaneous to implement full state feedback and using the reconstructed disturbance estimate to compensate the effect of external disturbance or parameter uncertainties. The performance of the system is analysed through simulating at different operating conditions. The control method improves the tracking response and provides zero estimation error in the steady-state. Illustrative examples have been provided to demonstrate the effectiveness of the developed methodology.

Optimization of Active Current for Large-Scale Wind Turbines Integrated into Weak Grids for Power System Transient Stability Improvement

Power system transient stability is a challenge when integrating large-scale wind turbines into weak grids. This paper addresses the issue of transient stability in such situations by optimizing a wind turbine’s active current behavior. A wind turbine’s active current reference controller and its setting optimization method are proposed based on analyses of two associated problems: the mechanism for improving transient stability of a single (synchronous) machine infinite bus (SMIB) system, as well as the various physical factor dependencies dictating how active and reactive wind turbine currents affect the swing dynamics of synchronous machines. Analysis of the first problem guided the design of the controller’s main structure. Analysis of the second problem guided selection of the control object within a wind turbine’s active and reactive currents, as well as helped recognition of the influential physical factors that must be considered in the parameter setting process. The efficiency of the controller and the validity of the analyses were verified by case studies using Kundur’s two-area system.

A rule-based fuzzy power system stabilizer tuned by a neural network

A fuzzy logic power system stabilizer (FPSS) has been developed using speed and active power deviations as the controller input variables. The inference mechanism of the fuzzy logic controller is represented by a (7/spl times/7) decision table, i.e. 49 if-then rules. There is no need for a plant model to design the FPSS. Two scaling parameters have been introduced to tune the FPSS. These scaling parameters are the outputs of a neural network which gets the operating conditions of the power system as inputs. This mechanism of tuning the FPSS by the neural network, makes the FPSS adaptive to changes in the operating conditions. Therefore, the degradation of the system response, under a wide range of operating conditions, is less compared to the system response with a fixed-parameter FPSS. The tuned stabilizer has been tested by performing nonlinear simulations using a synchronous machine-infinite bus model. The responses are compared with the fixed-parameter FPSS and a conventional (linear) power system stabilizer. It is shown that the neuro-fuzzy stabilizer is superior to both of them.

A novel fuzzy state feedback controller for power system stabilization

A novel fuzzy logic controller (FLC) is developed for damping electromechanical modes of oscillations and enhancing power system synchronous stability. The proposed controller is based on state feedback control system. The input signals to the controller are the weighted sum of the mechanical states and the electrical states weighted sum, while its output signal is added to the conventional fixed-gain PI controller output signal to give the excitation control signal. The simulation results using the proposed controller are carried out on an synchronous machine infinite bus system. Moreover, a comparison between the conventional fixed-gain PI controller and the proposed FLC is presented. The results validate the effectiveness of the proposed FLC in terms of less overshoot/undershoot and enhancing the power system stability over a wide range variation of operating conditions.

A decoupler design method for synchronous-machine-infinite-bus system

The transfer matrix for the linearized model of a synchronous machine infinite bus (SMIB) system is derived. A decoupler is designed using this form of plant model. Simulation results show the effects on decoupling as the generator operating points move from MVAr export to import.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Decoupler Design Method for Synchronous-Machine-Infinite-Bus System

The transfer matrix for the linearized model of a Synchronous Machine Infinite Bus (SMIB) system is derived in this paper and a decoupler is designed using this form of plant model. Simulation results show the effects on decoupling as the generator operating points move from Mvar export to import.

A dynamic observer for a synchronous machine†

The closed-loop optimal control law obtained for a linear time-invariant system always requires the entire state vector to be available for direct measurement. It is seldom that all the state variables of a physical system are available for measurement. A compatible dynamic observer of the Luenberger type is designed to reconstruct the entire state vector for a synchronous machine-infinite bus system. The performance of the system with the observer cascaded to the optimal controller is compared with the performance of the system when all the state variables are available for feedback. The transfer matrix relating the output and input is derived.