Speed Governor Research Articles

Time-delay compensation of a wide-area measurements-based hierarchical voltage and speed regulator

This paper presents a delay-insensitive version of a wide-area measurements-based two-level hierarchical controller. This hierarchical structure consists of a central controller, at the secondary level, dedicated to inter-generator interactions compensation, and conventional controllers (automatic voltage regulator, power system stabilizer, and speed governor), at the primary level, to dampen local oscillations. First, a Smith prediction approach is used to preserve performance in the presence of large remote-measurement time delays and communication time delays between central and local controllers. Second, an optimization algorithm is used to considerably reduce the complexity of the controller and thereby increase its reliability. Finally, sets of realistic tests are performed to assess the robustness of the proposed structure in the presence of uncertainties over time delays and power system parameters. Simulation results reveal that time-delay compensation is effectively required to enhance the hierarchical-structure performance in realistic situations. Furthermore, the performance of local controllers is considerably improved by the secondary-level controller action. The stability margin of the system is improved in the presence of severe contingencies.

Practical Power System Aggregation Considering Dynamic Loads

This paper presents a practical method for creating power system equivalents that can be used in power system stability analysis. The proposed method uses three branches to connect the boundary bus, generator, and load. The method is suitable to consider reactance from the boundary bus to the load for power system stability studies using a dynamic load model. Furthermore, this paper presents a practical procedure to determine the parameters of the aggregated generator, including control devices such as excitation systems, PSS (power system stabilizer), and speed governors. The quality of the various aggregation models is verified using power system stability simulations.

A Method for Optimal Spinning Reserve Allocation in Isolated Power Systems Incorporating an Improved Speed Governor Model

In isolated power systems, frequency stability is traditionally considered to be assured by maintaining sufficient spinning reserve that is usually equal to the largest generation output of all the units in operation. However, the system security depends on the spinning reserve allocation to the units in operation and the provision of adequate emergency or fast reserve that need be available in the first crucial seconds after a loss of generation event. The system emergency reserve is usually much lower than that expected if only the unit droops are taken into account. Also, the generating units can be overloaded for a short time period and this capability can contribute to a faster frequency restoration. This paper presents an improved speed governor model that utilizes the short time overloading capability of the generating units. The efficient computational method described in the paper for the optimal spinning reserve allocation in isolated power systems was developed by taking into account a composite security criterion in the most economic way. Furthermore, a statistical analysis is presented in order to investigate the contribution of spinning reserve to the short-term system security. In the paper the developed method is applied to a typical isolated power system and it demonstrates its advantages.

Structure-preserved power-frequency slow dynamics simulation of interconnected ac/dc power systems with AGC consideration

A structure-preserved power-frequency slow dynamics simulation model is suggested for interconnected ac/dc power systems with automatic generation control (AGC) consideration, which will be applied to study relevant emergency control in future so that the bulk system viability crisis caused by load-frequency slow dynamics can be released. In the model, the network structure of interconnected power systems is entirely preserved, and the multi-area dynamic load flow (DLF) is developed for simulation. The generator speed governor and rotor dynamics, load-frequency characteristics, simplified models for high voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) device thyristor controlled series capacitor (TCSC) suitable for long-term dynamics are considered with their AGC interfaces kept for future emergency-AGC study. However, at this stage, the sub-problem of reactive power and voltage is neglected for modelling simplicity and dc load flow is thus used for network solution. The concept of area centre of inertia (ACOI) is used based on the assumption of uniform frequency in each control area similar to that of the conventional single-area DLF calculation. The application of ACOI concept is attractive because the signal can be obtained from wide-area measurement systems (WAMSs) in real time and used to enhance long-term frequency stability through advanced control in future. The computer test results from 2-area 4-machine and IEEE 30-bus power systems demonstrated the validity and effectiveness of the suggested model and corresponding algorithm.

Research on H2 speed governor for diesel engine of marine power station

The frequency stability of a marine power system is determined by the dynamic characteristic of the diesel engine speed regulation system in a marine power station. In order to reduce the effect of load disturbances and improve the dynamic precision of a diesel engine speed governor, a controller was designed for a diesel engine speed regulation system using H2 control theory. This transforms the specifications of the system into a standard H2 control problem. Firstly, the mathematical model of a diesel engine speed regulation system using an H2 speed governor is presented. To counter external disturbances and model uncertainty, the design of an H2 speed governor rests on the problem of mixed sensitivity. Computer simulation verified that the H2 speed governor improves the dynamic precision of a system and the ability to adapt to load disturbances, thus enhancing the frequency stability of marine power systems.

APPLICATIONS OF POLE SHIFTING SELF TUNING SPEED GOVERNOR CONTROLLERS FOR MULTIMACHINE POWER SYSTEMS

Examination of the performance of fixed parameter controllers has resulted in the development of pole shifting strategies for speed governor control of multimachine power system. For a pole shifting controller design an input signal is incorporated in the self tuner. This input signal is of a composite output term of the terminal voltage and the rotor speed deviation of each generating unit. The control is based on a criterion which automatically generates a pole-shifting factor to shift the closed loop poles of the system towards the origin in the z domain without violating the control constraints. The pole-shifting factor is depicted on line at each sampling instant depending on the error measurements of the terminal voltage of each generating unit. The output of the pole shifting controller is fed in the summing point of the speed governor of each unit of the multimachine power system. Digital simulations of a 9 bus, 3 machine of a multimachine power system are performed and the comparisons of conventional governor control and self tuning control performances are presented. Nonlinear digital simulation results show the effectiveness of the proposed technique to damp out the oscillation and work effectively over a wide range of loading conditions.

Sampled-data Automatic Load Frequency Control of a Single Area Power System with Multi-source Power Generation

In this article, discrete-mode automatic load frequency control (ALFC) of a more realistic single area power system with multi-source power generation is studied. The system transfer function model comprises hydro, thermal and gas generations with speed governor models and system load for studying the dynamic performance for small load disturbances. A proportional plus integral (PI) load frequency control scheme is applied only to thermal and gas power generations, and hydro is allowed to operate at its scheduled generation level with only speed governor control. Genetic algorithm (GA) is used to obtain the optimal gains of the conventional discrete data proportional-integral controller. Integral squared error (ISE) and integral time absolute error (ITAE) performance indices are used to obtain optimal discrete ALFC parameters. The effects on transient performance of the system are investigated for common and individual ALFC controller gains of thermal and gas power generations. The effect of sampling period of the controller signal on the performance of the continuous system is also investigated. Finally, transient responses are shown for different scheduled loading conditions.

WATER GATE DYNAMICS AS INFLUENCED BY PARAMETERS OF HYDRAULIC TURBINE SPEED GOVERNORS AND CONTROLLERS

The paper investigates the effect of hydraulic turb ine speed governor parameters on water gates dynamics of the hydraulic turbines. These parameters are water starting time, temporary speed droop, transient time and permanent speed droop. This is done in order to improve the performance of the hydraulic turbine speed governor in power systems and to reduce water gate oscillations. This paper a lso investigates the application of the conventional and fuzzy logic con troller based on the hydraulic turbine speed governor on water gate dyna mics . Nonlinear simulations are performed in a 3 machine power syst em show that influences.

Frequency Deviation of Thermal Power Plants Due to Wind Farms

This paper presents the results of a study on the frequency deviation of the utility grid due to wind power fluctuations. The deviation is estimated by a deterministic method based on the transfer functions of system components. As the grid frequency is regulated, the deviation can limit high wind power penetration. The research identifies speed governors as one key component in enabling high wind penetration and there is need to factor their increased wear and tear into the ancillary services cost. It also raises the question as to whether the existing standards set for frequency deviation, which have to be complied at the points of connection of wind energy providers, are adequate to promote high wind penetration.

TRANSIENT STABILITY ENHANCEMENT USING ARTIFICAL INTELLIGENCE BASED GOVERNOR CONTROLLER

The paper investigates the application of a fuzzy logic – based governor controller as a technique of artificial intelligence techniques for stability enhancement of a multimachine power system. A fuzzy controller is designed to operate in real time to improve each generating unit transients in a multimachine system through the governor loop. The fuzzy controller requires two inputs signals, speed deviation and acceleration of the machine and generates one output as a supplementary signal into the governor loop when the excitation system is fixed. The developed fuzzy controller, whose control signals are adjusted using on line measurements, offers better damping effects for generator oscillations under large disturbances compared to turbine speed governor with conventional controller. Computer simulations of a 3 unit power system show that employing this type of control is effective in reducing excessive over and under frequency deviations.

Modeling and implementation of speed governor for the hybrid electric vehicle engine

A speed control analysis for an in-line gasoline fueled internal combustion (IC) engine is presented for the purpose of alleviation of high frequency oscillations in engine revolutions. A dynamic cylinder-by-cylinder model is proposed, base on slider-crank mechanism, which is extended to develop a digital governor providing a high fidelity estimation of rotary speed oscillation for hybrid vehicle engines. A modified PID controller that P and I gain is placed in feedback path is also described for hybrid electric vehicle (HEV) engine speed regulation. By comparison between measured and estimated signals, it is demonstrated that a good agreement has been achieved and the governor behaves an excellent damping speed ripple.

Study on a system frequency response model for a large industrial area load shedding

After reviewing the classical, simplified system frequency response (SFR) models for load shedding, the paper presents an up-to-date high order system frequency response model for load shedding of a large industrial area. The model possesses the dynamic performance of integrated turbine speed governors (reheat, non-reheat and gas turbine, etc.) and includes equivalent inertia constant of the motive loads during power system islanding. It also considers primary frequency regulation functions and the capability limits of turbines. For an industrial power system connected with the grid, an applicable under-frequency load shedding scheme considering minimum permissible non-shedding frequency is given in detail.

Bond graph dynamics of a rubber-belt continuously variable transmission

This paper analyses the system dynamics of a rubber-belt continuously variable transmission (CVT), which is widely adopted in the modern scooter powertrain systems. Dynamic mathematical models were derived from the physical configuration of the CVT directly via a bond graph approach. The CVT mainly consists of a varying-diameter driving pulley and another flange-moveable driven pulley, interconnected by a V-shaped rubber belt. Effective belt diameters of both driving and driven pulleys are controlled by a speed governor and a torque regulator, respectively. Each component was functionally analysed, employing the field theory in the bond graph technique. Mathematical equations were derived and then solved on a Matlab platform. Both static and dynamic performance simulations were examined for future electronic control implementation.

Nonlinear decentralized robust governor control for hydroturbine-generator sets in multi-machine power systems

A novel nonlinear decentralized robust governor control for hydroturbine-generator sets in multi-machine power systems is suggested in this paper. The nonelastic water hammer effect and disturbances are considered in the modeling. The advanced differential geometry theory, nonlinear robust control theory and the dynamic feedback method are combined to solve the problem. The nonlinear decentralized robust control law for the speed governor of hydroturbine-generators has been derived. The input signals to the proposed controller are all local measurements and independent to the system parameters. The derived control law guarantees the integrated system stability with disturbance attenuation, which is significant to the real power system application. Computer tests on an 8-machine, 36-bus power system show clearly the effectiveness of the new control strategy in transient stability enhancement and disturbance attenuation. The computer test results based on the suggested controller are compared favorably with those based on the conventional linear governor control.

Fuzzy Fuel Flow Selection Logic for a Real Time Embedded Full Authority Digital Engine Control

The control logic of the modern full authority digital engine control is comprised of many control loops, each of which has a specific purpose. Typical control loops include (but are not limited to) a high or low rotor speed governor, an acceleration and deceleration loop, and various limiting loops for temperature, speed, fuel flow, and rate of change of fuel flow. The logic that determines which of these loops is “in control” at any particular time has a history of being very simplistic. This selection logic is usually nothing more that a cascade of minimum and maximum selection logic gates. Since this logic is so simplistic, the control engineer often has to “fine-tune” the compensator design for each loop, in order to achieve proper performance.

Speed control in developing countries: issues, challenges and opportunities in reducing road traffic injuries

Speed has been determined to be one of the most common contributing factors in vehicle crashes. This study explores vehicle speed as a factor in the causation of road traffic crashes, using the example of Ghana. It examines the effectiveness of various speed control measures, based on policereported traffic crashes in Ghana and published works on speed control measures in both industrialized and developing countries. In Ghana, pedestrians were the main victims of road traffic injuries. The dominant driver error assigned by traffic police was loss of control, with the underlying factor being excessive vehicle speeds. The ‘speed factor’ alone accounted for more than 50% of all Ghanaian road traffic crashes between 1998 and 2000. While the enforcement of speed limits by traffic police may not be affordable for most developing countries, rumble strips and speed humps were found to be effective on Ghanaian roads. Rumble strips installed on the main Accra-Kumasi highway reduced crashes by about 35% and fatalities by about 55%. Reducing vehicle speeds may be one of the most effective interventions to stem traffic crashes in low-income countries. However, setting lower speed limits is not an effective intervention without the traffic law enforcement resources to ensure that limits are followed. Developing countries must also look to other speed reduction measures such as speed bumps and rumble strips, roads that segregate high- and low-speed users, and technological solutions such as speed governors, as well as greater public awareness of the problem.

Exploiting voltage support of voltage-source HVDC

The inherent voltage support in voltage-source converters (VSCs) which form a back-to-back VSC–HVDC asynchronous link can increase the power transmissibility by a factor of 1.68 if the installation is sited at the midpoint of the radial AC transmission line. The figure of 1.68 is the limit set by the ‘transient stability’ which is reached by simulations using HYPERSIM, a real-time digital simulator. The transmission line is modelled by the telegraph equations. The hydraulic turbine, speed governor, generator, field-excitation system, power-system stabiliser (PSS) and transformers are modelled in detail.

Deformation control of rotating shallow cap with unconstrained central hole

This work discusses a methodology for controlling deformation of a rotating shallow cap. The FEM is used to characterise the deformation in terms of shallow cap geometry and mechanical properties. A Computer Aided Engineering (CAE) method is developed for deformation control in terms of several dimensionless groups. Results showed diameter contraction of the central hole with speed build up for a range of geometrical parameters. This would exclude the shrink fit requirement for cases requested bearing seat mounting inside the central hole. Both upward and downward deformations are possible for the central hole edge. Therefore, a compensation for rotor length variations is possible in ultrahigh speed applications. Moreover, such a cap geometry can be adapted as a high speed governor. The rule of the holding wall mechanical properties on cap deformation are also discussed.

Restoration testing and training in Italian ISO

This paper describes the experiences encountered and the procedures adopted during a campaign of field tests that GRTN (the Italian independent system operator (ISO)) performed to check its restoration plan to restore power supply after a massive blackout. Some of the power system components and the restoration strategies involved were known to be critical, so careful planning, including the use of a dynamic power system simulator, preceded the field tests. The results of the analysis prompted the adoption of original solutions that, although unusual for classic restoration techniques, proved to be effective in testing Italian restoration procedures, voltage regulators, and speed governors, without significant disturbance to customers. This should enable the planning of frequent field tests to the advantage of both operators' training and the periodic check of the efficiency of this ancillary service.

Restoration Testing and Training in Italian Iso

This paper describes the experiences encountered and the procedures adopted during a campaign of field tests that GRTN (the Italian independent system operator (ISO)) performed to check its restoration plan to restore power supply after a massive blackout. Some of the power system components and the restoration strategies involved were known to be critical, so careful planning, including the use of a dynamic power system simulator, preceded the field tests. The results of the analysis prompted the adoption of original solutions that, although unusual for classic restoration techniques, proved to be effective in testing Italian restoration procedures, voltage regulators, and speed governors, without significant disturbance to customers. This should enable the planning of frequent field tests to the advantage of both operators' training and the periodic check of the efficiency of this ancillary service.