Modal Control Theory Research Articles

Damping of common‐mode torsional oscillations using a modified NGH SSR damping scheme

AbstractThis paper presents the analyzed results on the application of a modified NGH SSR damping scheme for damping common‐mode torsional oscillations that occur in a power systems containing series‐capacitor compensation. The IEEE Second Benchmark Model, system‐2, which has two non‐identical turbine‐generator sets connected to an infinite bus through a series‐capacitor compensated transmission line, is employed to investigate the possible unstable subsynchronous resonance (SSR) which can be suppressed by the proposed damping scheme. A unified approach based on modal control theory is employed to design damping controllers for the modified NGH SSR damping module. Frequency‐domain approach based on eigenvalue analyses such as different operating conditions and stable regions on RE‐Xc plane is performed. Time‐domain approach based on non‐linear model simulations under a severe three‐phase short‐circuit fault at infinite bus is also carried out. It can be concluded from the simulation results that the proposed modified NGH SSR damping scheme incorporated with the designed damping controllers can effectively suppress the common‐mode torsional oscillations.

Application of static phase shifters on the damping of common‐mode torsional oscillations

AbstractA study on the application of thyristor‐controlled static phase shifters (SPS) to stabilize the common‐mode torsional oscillations occurring in a series‐capacitor compensated power system is presented in this paper. The IEEE Second Benchmark Model, system‐2, which has two non‐identical turbine‐generator sets connected to an infinite bus through a series‐capacitor compensated transmission line, is employed to investigate whether the possible unstable subsynchronous resonance (SSR) modal interactions can be suppressed by the proposed damping scheme. The torsional interactions due to one of the torsional oscillating frequencies in one machine is nearly the same as the one in another machine. In order to effectively suppress the unstable torsional modes in the studied system, a systematic approach based on modal control theory is proposed and a set of static phase‐shifter controllers (SPSC) is designed. The effectiveness of the proposed damping scheme is demonstrated by means of frequency‐domain approach based on eigenvalue analyses and time‐domain approach based on non‐linear model simulations. The simulations results show that the static phase shifters and the designed controllers can be applied to suppress common‐mode torsional interactions.

Suppression of torsional oscillations using thyristor‐controlled conductance in parallel to series‐capacitor segment

AbstractThis paper presents the analyzed results of a study on the application ofthyristor‐controlled conductance in parallel to one series‐capacitor segment for suppressing sub synchronous resonance (SSR) that occurs in a series‐compensated power system. The IEEE Second Benchmark Model, systems, which has one turbine‐generator set, is taken as a standard model for this study. In order to stabilize all SSR modes in the studied system, a unified approach based on modal control theory is proposed to design a damping controller which is a dynamic output feedback compensator using shaft speed deviation of the studied generator as a feedback signal. To demonstrate the effectiveness of the proposed control scheme, frequency‐domain approach based on eigenvalue analyses and time‐domain approach based on non‐linear model simulations are performed. The simulated results show that the proposed SSR damping scheme can effectively suppress torsional oscillations of the studied system.

97/02864 A direct approach to short-circuit current calculation without using symmetrical components

Power system stabilizers are used to improve the dynamic stability of large interconnected systems. They utilize signals derived from rotor speed deviation, accelerating power or a combination of these signals and provide a corrective input to the excitation system.The conventional design of the PSS (Power System Stabilizer) is based on classical control techniques. This paper presents a general approach of designing power system stabilizers based on modal control theory and applicable to multi-machine power systems. The objective of the design is to shift the closed loop poles to preassigned locations. Two specific methods are discussed. In the first method a least squares approach is used to select the feedback gains corresponding to the desired inputs to the PSS. In the second method, the dynamic compensator of a given order is designed using a nonlinear optimization technique.A comparison of the two methods is presented utilizing the example of a single machine system. The extensions to multimachine system are suggested.

The connection between modal analysis and electric torque analysis in studying the oscillation stability of multi-machine power systems

Modal analysis and electric torque analysis are two of the most widely used techniques for studying the oscillation stability of multi-machine power systems, such as for the design of Power System Stabilizers (PSS) or FACTS-based stabilizers. Modal analysis is based on modal control theory and electric torque analysis is established and developed from a physical understanding of the characteristics of the electromechanical oscillation loop of generators in power systems. These two techniques have been considered to be different, both in their principles of derivation and methods of calculation. However, in this paper, a connection between these two methods is revealed. It is found that they are basically equivalent. Through the revelation of the connection between these two methods, a deeper insight and understanding into the mechanisms of the methods is presented in the paper.

Damping effects of supplementary excitation control signals on stabilizing generator oscillations

The results of a comparison of three supplementary stabilizing signals, i.e., rotor speed deviation (Δω), accelerating power deviation ( ΔP a), and electrical power deviation ( ΔP e), on damping enhancement of power system steady-state stability is presented in this paper. A unified approach based on modal control theory is employed to design PID excitation controllers using each stabilizing signal as input. For clearly comparing the damping characteristics contributed by each stabilizing signal, the prespecified eigenvalues far mechanical mode and exciter mode of the studied system are respectively assigned to the same desirable locations on the complex plane for each signal. Both frequency-domain approach based on eigenvalue analysis under different operating conditions and dynamic response simulations based on a nonlinear model under torque disturbance are also carried out.

A Lateral Restraining Device for Large Telescope Mirrors

Abstract Telescope mirrors—like every rigid body—have six degrees of freedom (DOFs) to move: translation along three axes of space and rotation around these three axes. Hydraulic support systems, which are designed to hold the mirror in the required best optical shape, have to couple all six DOFs between the mirror and its supporting cell structure. While three DOFs are covered by the axial support system and two DOFs by the lateral support system, the last degree of freedom often remains uncovered. A good example is the lateral support system for the 8 m primary mirror of ESO's Very Large Telescope, which did not couple movements along the horizontal axis between the mirror and its cell and therefore required a lateral restraining device. Based on this example, a general method is shown how to control all degrees of freedom at a given supporting force distribution without any unwanted additional forces. According to the theory of modal control, a hydraulic network is used to decouple the oil flow to the hydraulic actuators and thereby to control the components of the supporting forces independently. The theory may be applied for other hydraulic support systems, too.

Damping subsynchronous resonance using superconducting magnetic energy storage unit

A novel damping scheme using superconducting magnetic energy storage (SMES) unit is proposed in this paper to damp subsynchronous resonance (SSR) of the IEEE Second Benchmark Model, system-1 which is a widely employed standard model for computer simulation of power system SSR. The studied system contains a turbine-generator set connected to an infinite bus through two parallel transmission lines, one of which is series-capacitor compensated. In order to stabilize all SSR modes, simultaneous active and reactive power modulation and a proportional-integral-derivative (PID) damping controller designed by modal control theory are proposed for the SMES unit. A frequency domain approach based on eigenvalue analysis and time-domain approach based on nonlinear model simulations are performed to validate the effectiveness of the damping method. It can be concluded from the simulation results that the proposed damping scheme can effectively suppress SSR of the studied system. >

A comparative study of damping schemes on damping generator oscillations

Results of a comparative study of the application of three different compensators, the power system stabilizer (PSS), the static VAR compensator (SVC), and the rectifier current regulator (RCR), for the damping enhancement of generator oscillations in a power system are presented. In order to enhance the dampings of both the mechanical mode and the exciter mode in the system, a unified approach based on modal control theory is proposed for the design of the PSS, the SVC, and the RCR. A proportional-integral-derivative (PID) type controller using generator speed deviation as a modulated signal to generate the desired damping is proposed, and it is shown that both affected system modes can be exactly located at the prespecified positions on the complex plane by the proposed damping schemes. To demonstrate the effectiveness of the proposed PID controllers and their relative merits, a frequency-domain study based on eigenvalue analysis under different operating conditions and a time-domain study based on nonlinear model simulations under disturbance conditions are performed. >

Application of simultaneous active and reactive power modulation of superconducting magnetic energy storage unit to damp turbine-generator subsynchronous oscillations

An active and reactive power (P-Q) simultaneous control scheme, which is based on a superconducting magnetic energy storage (SMES) unit, is designed to damp out the subsynchronous resonant (SSR) oscillations of a turbine-generator unit. In order to suppress unstable torsional mode oscillations, a proportional-integral-derivative (PID) controller is used to modulate the active and reactive power input/output of the SMES unit according to speed deviation of the generator shaft. The gains of the proposed PID controller are determined by pole assignment approach based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Dynamic simulations using the nonlinear system model are also performed to demonstrate the damping effect of the proposed control scheme under disturbance conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Suppression of common torsional mode interactions using shunt reactor controllers

The paper presents the results of a study on the utilization of shunt reactors for the damping of common torsional mode interactions of a power system containing series-capacitor compensation. The IEEE Second Benchmark Model, system-2, which has two sets of nonidentical turbine-generators connected to an infinite bus via a common series-capacitor compensated transmission line, is employed to investigate the possible unstable subsynchronous resonance (SSR) modal interactions which can be suppressed by using reactive power compensation. A set of shunt reactors are proposed and connected to the studied system and a unified approach based on modal control theory is employed to design shunt reactor controllers in order that all SSR modes in the system can be stabilized. For clearly demonstrating the effectiveness of the proposed scheme, SSR mode eigenvalues under different loading conditions and sensitivity analysis of shunt reactor controllers' parameters are performed. Dynamic responses of the nonlinear system simulation under a torque disturbance on a generator shaft and a severe three-phase short-circuit fault at an infinite bus are also carried out. >

Distributed Modal Identification and Vibration Control of Continua: Theory and Applications

Conventional transducers and actuators are “discrete” in nature, i.e., they usually measure and control spatially discrete locations. These discrete devices become useless when they are placed at modal nodes or lines. In this paper, a generic “distributed” modal identification and vibration control theory for sensing and control of continua, e.g., shells, plates, cylinders, beams, etc., is proposed. The generic theory is derived for a thin shell coupled with two electroded piezoelectric layers. One piezoelectric layer serves as a distributed sensor and the other a distributed actuator. The sensor output, or a reference signal, is processed, amplified, and fed back into the distributed actuator. Due to the converse effect, the injected high voltage induces in-plane strains which result in counteracting moments used to suppress the shell oscillation. System dynamic equations and state equations are also derived. The theory shows that the distributed sensor can identify all vibration modes and the distributed actuators also control all modes. Simplification of the generic theory to other geometries is also demonstrated.

Damping of torsional oscillations using excitation control of synchronous generator: the IEEE Second Benchmark Model investigation

A simple lead-lag excitation controller using generator shaft speed deviation ( Delta omega ) as a feedback signal to damp all of the IEEE Second Benchmark Model, system-1 torsional oscillations is presented. In order to stabilize all the torsional modes, modal control theory is used to determine the parameters of the dynamic output feedback controller. Various degrees of series compensation, different loading conditions, and torsional mode shapes for a torsional oscillations study are also investigated. In addition, time-domain simulation using a nonlinear system model are examined to demonstrate the effectiveness of the proposed countermeasure under torque disturbance conditions. >

Application of superconducting magnetic energy storage unit to improve the damping of synchronous generator

A systematic approach to the design of a controller for superconducting magnetic energy storage (SMES) units to improve the dynamic stability of a power system is presented. The scheme employs a proportional-integral (PI) controller to enhance the damping of the electromechanical mode oscillation of synchronous generators. The parameters of the PI controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis and nonlinear computer simulations show that SMES with the PI controller can greatly improve the damping of the system under various operating conditions. Although the PI controller is designed for a special load condition, it can also provide good damping under other load conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stabilizing torsional oscillations using a hunt reactor controller

Results of a study on the application of shunt reactors for the damping of torsional oscillations that occur in a power system containing series-capacitor compensation are presented. The IEEE Second Benchmark Model, system-1 is used to investigate the benefits of the utilization of modulated reactive power in suppressing unstable subsynchronous resonance (SSR) modal interactions. A set of shunt reactors is connected to the generator bus of the affected synchronous machine whose shaft is directly coupled to the turbine system of the benchmark model. In order to stabilize all the torsional modes, a unified approach based on modal control theory is proposed for the design of a shunt reactor controller, which is essentially a dynamic output compensator. To demonstrate the effectiveness of the damping enhanced by the proposed scheme, eigenvalue analysis for different loading conditions and sensitivity analysis for controller parameters are performed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of superconducting magnetic energy storage unit on damping of turbogenerator subsynchronous oscillation

A systematic approach is used to design a controller for a superconducting magnetic energy storage (SMES) unit to improve the torsional modes damping of a turbogenerator. To suppress the unstable torsional oscillation, a proportional-integral-derivative (PID) controller is employed to modulate the power input/output of the SMES unit according to generator speed deviation. The gains of the proposed PID controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Computer simulations using the nonlinear system model are also performed to demonstrate the damping effort of the proposed controller under disturbance conditions.

Design of controllers for the damping of torsional oscillations using time-scale decomposition

A new technique is presented for the design of an excitation controller and a static VAR compensator which are used to improved the damping characteristics of torsional oscillations in a capacitor-compensated power system. To facilitate the controller design, the system matrix is reduced by means of multi-time-scale decomposition while preserving the mechanical shift modes, which are the ones to be damped by the proposed controller. The parameters of the controller are then determined on the basis of the reduced system by using modal control theory. It is found that model reduction can save the effort in controller design without any significant drift in the eigenvalues of the closed-loop system. To demonstrate the effectiveness of the proposed damping scheme under disturbance conditions, computer-simulated dynamic response tests based on a non-linear system model are also performed. It is concluded that all subsynchronous oscillation modes can be effectively damped by the proposed controller.

Development of an ultrahigh-speed serial printer using the modal control theory.

Development of an ultrahigh-speed serial printer using the modal control theory.

Modal control of an HV DC system for the damping of subsynchronous oscillations

A novel control scheme is presented for the design of a supplementary subsynchronous damping controller (SSDC) equipped at the rectifier end of an HVDC link that is connected in parallel with an existing resonating AC line. To stabilise the unstable subsynchronous resonance (SSR) modes, an approach based on modal control theory is developed for the design of the SSDC. Since the subsynchronous oscillations resulting from high levels of compensation on the AC line can be effectively damped out, the power transfer capability of the AC line can be enhanced by the proposed SSDC.< >

Damping of a parallel AC-DC power system using PID power system stabilizers and rectifier current regulators

A scheme for improving the dynamic stability of a parallel AC-DC power system is presented. It uses a proportional-integral-derivative (PID) power-system stabilizer and a PID rectifier current regulator to enhance the damping for the electromechanical mode of the system. The parameters of the proposed PID controllers are determined using a unified approach based on modal control theory. Eigenvalue analyses are performed for the system under various operating conditions in order to compare the damping effects provided by the two different control schemes. The effectiveness of the proposed damping schemes under disturbance conditions is demonstrated by computer-simulated dynamic-response tests based on a nonlinear system model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>