Turbine Time Constant Research Articles

A Two-Stage Data-Driven Method for Estimating the System Inertia Utilizing Event-Driven PMU Measurements

With the increasing penetration level of renewable energy resources with less system inertia, accurate estimation of the power system inertia has become a critical issue for maintaining the frequency stability of the entire power system. To tackle out this challenging task, a two-stage data-driven method is proposed in this paper for estimating the system inertia from disturbed PMU measurements. First, by integrating its low-order system frequency response model with the first-order turbine model, analytical expressions of the frequency response under the steady-state and these transient oscillatory components are derived. Then, based on this parametric model, a two-stage estimation algorithm will be developed. At the first stage, system parameters of oscillatory components can be extracted from PMU measurements by Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT). By utilizing frequency measurement data from PMUs and those estimated parameters from the ESPRIT algorithm, a weighted nonlinear least square approach is applied at the second stage to estimate physical parameters such as system inertia, damping coefficient, turbine time constant, and regulation coefficient. To validate the effectiveness of the proposed method, simulation studies of IEEE 39- bus system is investigated. Historical PMU measurements from various contingencies of Taiwan Power System will also be explored. All of these results demonstrated that the proposed method provides satisfactory performances with the mean relative error less than 10%. Comparisons with other existing methods are performed to demonstrate the advantage of the proposed method.

SMES-GCSC Coordination for Frequency and Voltage Regulation in a Multi-Area and Multi-Source Power System with Penetration of Electric Vehicles and Renewable Energy Sources

Frequency, tie-line power, and the terminal voltages of synchronized generators must all be kept within prescribed limits to ensure the stability of an interconnected power grid through combined automatic generation control (AGC) and automatic voltage regulator (AVR) loops. Thermal power plants, electric vehicles, and renewable energy sources—including solar and wind, geothermal, and solar thermal power plants—form the two-area integrated power system in present research. A new cascade controller named the cascaded proportional integral derivative (PID) and fractional-order PID (CPID-FOPID) controller is proposed for the first time, whose performance is compared with the PID and FOPID controller. The results show that the proposed cascade controller outperforms PID and FOPID in delivering superior dynamic characteristics, including short settling times and low oscillation amplitudes. A new metaheuristic algorithm named the coot algorithm was applied to optimize the parameters of these controllers. The suggested controller outperforms FOPID in the combined AGC and AVR problem under uncertain conditions (random load disturbance, variable input of solar irradiation, and wind power). Robustness of the controller is tested with significant variation in the turbine time constant of the thermal and geothermal power plant. In this study, authors also investigated the best possible coordination between the superconducting magnetic energy storage (SMES) and gate-controlled series capacitor (GCSC) devices to control both voltage and frequency simultaneously. The effect of communication time to the power system is analyzed in this study. Additionally, the obtained results are satisfactorily validated using OPAL-RT real-time digital simulator.

Cascade controller based modeling of a four area thermal: gas AGC system with dependency of wind turbine generator and PEVs under restructured environment

This paper investigates automatic generation control (AGC) of a realistic hybrid four-control area system with a distinct arrangement of thermal units, gas units and additional power generation. A proportional-integral-double derivative cascaded with proportional-integral (PIDD-PI) controller is employed as secondary controller in each control area for robust restructured AGC considering bilateral transactions and contract violations. The Harris Hawks algorithm is used to determine the optimal controller gains and system parameters under several scenarios. Electric vehicle (EV) aggregators are employed in each area to participate fully along with thermal and gas units to compensate for the unscheduled system demand in the local area. A comparison of non-cascaded controllers such as PI-PD, PD-PID and the proposed PIDD-PI proves the superiority of the last. The effect of the decline in inertia is closely examined because of the sudden outage of a generating unit while at the same time considering the change in area frequency response characteristics and area control error. EV fleets make significant contributions to improving the system dynamics during system inertia loss. The use of EVs in the presence of a wind energy-supported grid can provide a stable efficacy to the power grid. Numerous simulations with higher load demands, stochastic communication delays in presence of the WTG plant, and violations in system loadings and changes in gas turbine time constants in the absence of WTG demonstrate the robustness of the proposed control approach.

Combined Voltage and Frequency Control of Multiarea Multisource System Using CPDN-PIDN Controller

This paper discusses a multiarea multi-source system in combined automatic load frequency control (ALFC) and an automatic voltage regulator (AVR) model. The multiarea system comprises thermal and wind in Area-1, thermal-geothermal in Area-2, and hydrothermal plant in Area-3. Appropriate nonlinearity constraints are provided for both hydro and thermal plants. A maiden attempt has been made to employ a cascade proportional-derivative (PD) with filter coefficient (N) and PID with filter coefficient (N) (CPDN-PIDN) as a secondary controller in the combined ALFC-AVR system and optimized controller gains using artificial flora algorithm (AFA). It is examined that the CPDN-PIDN controller yields better dynamics responses than the PI and PIDN controllers. Analyze reflects that the system performance enhanced in the presence of AVR loop. This paper discusses the effect of renewable sources like wind and geothermal on the system dynamics. Analysis reveals that the geothermal power plant is more reliable than the wind plant. The parameter variations of the temporary and permanent droop and hydro turbine time constant (HTTC) of the hydro plant are examined through system responses. System response deteriorates significantly as permanent droop and HTTC are reduced. Peak overshoot and undershoot are reduced considerably as the temporary droop value is increased. Sensitivity analysis reveals that the AFA optimized CPDN-PIDN controller parameters obtained under the nominal condition are resilient enough and need not be reset with the system's substantial random variation. An experimental justification has been provided of the investigated system using a real-time simulation with the OPAL-RT OP4510 real-time setup.

Discrete Data AGC of Hydrothermal Systems Under Varying Turbine Time Constants Along With the Power System Loading Conditions

The paper deals with the discrete data automatic generation control (AGC) of two area hydrothermal power system operating at different loading conditions. The power system load varies considerably throughout the day and accordingly, thermal and hydropower systems are scheduled to operate at different loading conditions. It is found that steam as well as hydro turbine time constants vary as the power system loading varies. In earlier AGC studies, these parameters are considered to be constant, irrespective of power system loadings. This paper studies the dynamic performance of hydrothermal power system considering the variation of these turbine time constants along with the nominal loading of power system. The studies have been conducted for linear as well as nonlinear models of speed governor and hydroturbine models recommended by the IEEE committee. It is also discovered that conventional empirical formula-based hydraulic governor settings recommended by the IEEE working group are completely unacceptable for hydrothermal power system. A maiden attempt is made to optimize the hydraulic governor settings simultaneously along with the controller gains using metaheuristic algorithm. The comparison of system dynamic responses reveal that optimization-based hydrogovernor settings give the better dynamic performance in case of linear as well as nonlinear models of hydro system, and therefore are strongly recommended over the conventional settings. The paper also deals with the optimum selection of sampling periods for discrete data AGC operation of hydrothermal systems.

Automatic generation control using disrupted oppositional based gravitational search algorithm optimised sliding mode controller under deregulated environment

A disrupted oppositional based gravitational search algorithm (DOGSA) tuned sliding mode controller (SMC) is proposed in this study for the solution of automatic generation control of interconnected multi-area power system under deregulated environment. The novelty of the control scheme is established by performing the sensitivity analysis under different conditions such as variation of the system load, turbine time constant, governor time constant and tie-line power coefficient. The dynamic response of the system under consideration is also studied and analysed in the presence of non-linear constraints namely generation rate constraint with reheat steam turbine, governor deadband and time delay during signal processing. Further, in order to validate the effectiveness of the proposed DOGSA tuning over the genetic algorithm and differential evolution tuned schemes reported in the literature, it is also employed to tune the integral (I), proportional-integral (PI), integral-derivative (ID) and proportional integral derivative (PID) controllers. Moreover, the performance of the optimised SMC scheme is also compared with I, PI, ID and PID controllers. The comparative results reveal that SMC scheme tuned using DOGSA gives better results than the conventional controllers.

Automatic generation control of thermal power system under varying steam turbine dynamic model parameters based on generation schedules of the plants

This paper investigates the automatic generation control (AGC) of thermal power system operating under different power generation levels/schedules of the plants. The power system load varies considerably over the period of 24 hours and accordingly thermal power plants are planned to operate at different generation schedules. It has been discovered that the steam turbine dynamic model parameters also changes along with generation schedules of the plant. Typical steam turbine model parameters are the turbine time constants and power fractions. The literature survey reveals that steam turbine dynamic model parameters are assumed to be constant in all preceding studies pertaining to AGC systems, irrespective of generation schedules of the plant. In this paper, steam turbine dynamic model parameters have been computed for an actual 500 MW thermal unit at different generation schedules. These steam turbine dynamic model parameters have been used to study the dynamic performance of AGC system. The paper also presents the general mathematical procedure to calculate steam turbine dynamic model parameters from an actual generating unit using the heat balance data of a thermal power plant. Results for two area thermal power system demonstrate the potential of the proposed approach.

Discrete-Time Automatic Generation Control of Interconnected Reheat Thermal Systems Considering Generation Rate Constraints

This paper deals with some aspects of discrete-time automatic generation control (AGC) of a two-area reneat thermal system provided with classical controllers considering generation rate constraint (GRC). Investigations are carried out to examine the effects of variation of frequency bias setting, area capacity and several parameters of the system on optimum integral gain setting and dynamic performance. It is seen that the optimum integral gain setting decreases with increase in the frequency bias setting. Further, investigations reveal that steady state and dynamic performances in normal mode of Operation are not much affected with wide variation in the value of B. However, the steady-state performance in the abnormal mode improves with increase in B from B=β (area frequency response characteristic) and deteriorates with decrease in B from B - β . Investigations also reveal that if the relative capacity of one area is 7.5 times or more the caoacity of another area of a two-area system then the two area system can be replaced by an equivalent one-area and an infinite bus system. Detailed sensitivity analysis reveals that the optimal integral gain settings corresponding to a set of nominal oarameters is quite robust and practically insensitive to a substantial change of ± 25% in nominal values of inertia constant, steam turbine time constant, reheat time constant, reheat coefficient, speed regulation parameter, operating point and operating load.

Automatic generation control of an interconnected power system

This paper investigates the stability and optimum settings of conventional automatic generation controllers for an interconnected power system having reheat steam plants. Effective application of the parameter-plane technique for obtaining optimal controller setting and sensitivity analysis has been demonstrated. Rigorous sensitivity analysis reveals that reserve of stability and optimum controller setting are sensitive to inertia constant, governor time constant, turbine time constant and reheat coefficient and barely sensitive to base load condition, synchronising coefficient and reheat time lag. The optimum controller setting, however, is hardly sensitive to the speed regulation parameter whereas reserve of stability is quite sensitive to it. A significant part of this paper highlights the condition for which it is possible to optimise the controller setting of an individual area, treating the rest of the system as having infinite inertia. Analysis reveals that a reheat system has a slower response, providing smaller generation rate and higher frequency and tie deviations when compared with a nonreheat system. Investigation reveals that in a reheat system the optimum controller setting achieved without considering generation rate constraint becomes unacceptable in the presence of generation rate constraint. Also, while accounting for generation rate constraint, a relatively large value of governor speed regulation parameter can be well acceptable without significantly affecting the quality of the system response.