Pumped Storage Unit Research Articles

A predictive governing control method of the pumped-storage unit based on lumped-parameter model equivalence

The speed governor is known as one of the most important control parts in the pumped-storage unit (PSU). When operating in transient processes, the stability of the PSU’s hydraulic and mechanical states maintains by the precise regulation of the speed governor. For the sake of improving the governing control performances, the lumped-parameter equivalent circuit model is first introduced for precise modelling of hydraulic-mechanical characteristics of PSU. Subsequently, a multi-variable generalized predictive control system based on receding horizon technique is applied at every sampling instant to optimize the control trajectory within certain finite time horizon. To validate the effectiveness of the proposed predictive control method, the simulation experiment of governing movements during turbine start-up process is conducted under a nonlinear lumped-parameter numerical simulation platform of PSU by comparative case studies, the overall control performance of the proposed control scheme is evaluated and compared with that of the traditional PID algorithm. Simulation results indicate that the proposed governing control method can achieve stronger frequency fluctuation alleviation and hydraulic oscillation damping performances than traditional PID.

Nonlinear simulation of speed variation of variable-speed unit under large disturbance by Simulink

The variable-speed pumped storage plant (VSPSP) has become an innovative technology and new orientation in recent years. Investigation of dynamic processes in operating and control of VSPSP is of great importance for safety, stability and efficiency. In this paper, a nonlinear integrated model for dynamic processes of VSPSP with doubly fed induction machines (DFIMs) is built based on Simulink. From the comparison between simulation results and on-site measurement data of a fixed-speed pumped storage plant (FSPSP), the model under load rejection is validated. Meanwhile, maximum rotational speed during transient processes is a key indicator for the safety of pumped storage units. Hence, the transient process and performance of VSPSP under load rejection are simulated and analyzed by using the model, and the speed variation of the variable-speed unit is specifically investigated. The speed rising value and relative speed rising value will decrease when the initial value increases because of the momentum conversion mechanism and the torque characteristic of pump-turbine. The result demonstrates that, if the initial speed increases in the operating range of variable-speed unit under load rejection, the maximum speed will not rise significantly, and there is a certain safety margin from the maximum allowable speed.

An experimental platform of variable speed pumped storage unit under wave disturbance: introduction and preliminary progress

The importance of pumped storage plants (PSPs) is continuously increasing in power systems with more and more variable renewable energies. For the research and development of PSPs, variable speed technology and sea-water PSP are two important new orientations. In this paper, an experimental platform of variable speed pumped storage unit under wave disturbance is introduced. The purpose of the platform is to study the design and operation mechanism of variable speed PSP based on various common technical problems, especially for the four aspects: transient processes, variable speed unit, coordination control, wave disturbance. The platform adopts a Chinese sea-water PSP in feasibility stage as the prototype, and a model scale of 1:4 is applied. It consists of nine sub-systems, including waterway system, variable speed reversible model unit, circulating water system, speed governor system, AC excitation and electric protection, coordination control, monitoring system, intelligent AC load and measurement system. The model unit contains a reversible pump turbine, a doubly fed induction machine, etc. The speed variation range is ±8%, and the rated power is 78.13 kW. The model runner meets the IEC standard with a reference diameter of 284.3 mm. The upstream water tank is a closed pressure tank that can adjust the pressure and discharge. The downstream water tank is an open water tank that can simulate wave level fluctuation. Regarding the control system, it has four core parts: local control unit, speed governor, converter and coordination controller. The experimental study content contains three key aspects: (1) performance validation for variable speed unit; (2) operating stability under complex disturbances; (3) capability of variable speed PSP during transient processes. The experimental study based on the platform aims for laying a theoretical and technical foundation for the follow-up construction and operation of real sea-water PSPs with variable speed units.

Cost advantage of adjustable-speed pumped storage unit for daily operation in distributed hybrid system

The combined operation of renewable energy and pumped storage unit (PSU) has become an important researching tendency in rural electrification, for handling the variable characteristics of power as well as load demand, particularly in standalone applications. Recently, adjustable-speed pumped storage unit (ASU) has been developed as an evolutionary version of fixed-speed pumped storage unit (FSU) due to its adjustable power in pumping mode, larger output range and higher efficiency in generating mode, but presents an increased capital outlay in terms of equipment. Therefore, it is a meaningful topic to appraise the economic benefit of using ASU as energy storage device for the hybrid system, which has rarely been studied quantitatively. In this paper, a scheduling model composed of a photovoltaic generator, a wind turbine, a diesel generator and a PSU, is presented and the technical features of two different PSUs are analysed. The main purpose of the proposed model is to highlight the potential of the ASU to reduce the operation cost for the developed hybrid system. The simulations have been carried out using Cplex called by Matlab. Two scenarios are investigated, including a summer and a winter case. The results show that using the ASU for the developed hybrid system, 46.7% fuel can be saved on a summer day and 11.24% fuel saving can be achieved on a winter day compared to the case where the FSU is used as the energy storage device.

Study of Hydraulic Disturbance of Pumped Storage Unit

The analysis of hydraulic disturbance is an important part of the analysis of the hydraulic transient process of a hydropower station. This paper introduces the relationship between the grid-connected operation mode of the power station and the hydraulic disturbance by the power station system, and performs simulation calculations under the same boundary conditions according to the hydraulic disturbance test cases, and predicts the extreme control conditions which provides the basis for the safe operation of the power station. It also provides reference for the design and calculation of similar projects.

Analysis of Electrical Parameters of Generator Motor No-load Operation Fault

In the context of my country’s full effort to build pumped storage power stations, my country has the ability to independently research and develop pumped storage power stations, and has set a development goal to manufacture pumped storage units with larger single-unit capacity and higher speed. Generator motors play an important role in the safe and stable operation of power systems, and have a significant impact on power grids and power stations. This paper establishes a physical model of the damping winding of the generator motor, simulates the change of electrical parameters when a short-circuit fault occurs in the no-load operation of the generator motor, and obtains and analyzes the change rule, which has great theoretical and practical significance.

Investigation on Dynamic Stresses of Pump-Turbine Runner during Start Up in Turbine Mode

The startup process occurs frequently for pumped storage units. During this process, the rotating rate that changes rapidly and unsteady flow in runner cause the complex dynamic response of runner, sometimes even resonance. The sharp rise of stress and the large-amplitude dynamic stresses of runner will greatly shorten the fatigue life. Thus, the study of start-up process in turbine mode is critical to the safety operation. This paper introduced a method of coupling one dimensional (1D) pipeline calculation and three-dimensional computational dynamics (3D CFD) simulation to analyze transient unsteady flow in units and to obtain more accurate and reliable dynamic stresses results during start up process. According to the results, stress of the ring near fixed support increased quickly as rotating rate rose and became larger than at fillets of leading edge and band in the later stages of start-up. In addition, it was found that dynamic response can be caused by rotor stator interaction (RSI), but also could even be generated by the severe pressure fluctuation in clearance, which can also be a leading factor of dynamic stresses. This study will facilitate further estimation of dynamic stresses in complex flow and changing rotating rate cases, as well as fatigue analysis of runner during transient operation.

Analysis of Inter-blade Vortex and Runner Blades Force of Pump Turbine during Load Rejection Period

Pumped storage unit as the most efficient energy storage equipment, it makes a great contribution to the development of renewable energy. The operating stability of pump turbine affects economical and safe operation of pumped storage plant directly, hence this study focuses on the transient process of pump turbine load rejection. Detached eddy simulation is adopted as turbulence model and dynamic mesh technique is used to achieve continuous guide vane closure. Internal fluid characteristics are presented based on the numerical analysis of inter-blade vortex and force of runner blades. The results show that:(1) Inter-blade vortex can be divided into two developing stages according to its location, which corresponds to the first and second half of guide vane closure respectively. (2) The incidence angle is the original reason that causes vortex in runner passage, which further development occupies the whole flow passage under the influence from centrifugal force and the interaction with the previous water. (3) The force distribution is aligned with the vortex zone, and the axial thrust keeps a downward tendency.

Coordination Control Between Excitation and Hydraulic System During Mode Conversion of Variable Speed Pumped Storage Unit

Variable speed pumped storage (VSPS) unit has various operation modes and it is often required by the dispatcher to convert rapidly and frequently between these modes. Unlike conventional units, however, VSPS is controlled by both excitation and hydraulic system, and control of them is independent of each other. The mismatch between the rapid electromagnetic response of the former and the relatively slow mechanical response of the latter could result in unfavorable transients or even conversion failure. Hence, coordination controls between excitation and hydraulic system during mode conversion is a meaningful topic but has seldom been investigated. To this end, the electromechanical transient model of VSPS considering the excitation dynamics of the converter is first established. Then, a multistage soft coordination control strategy is proposed in this article. By applying this strategy, the soft and smooth mode conversion of VSPS is achieved with favorable dynamic performances during the complete conversion process. And finally, simulation and experimental results verified the effectiveness of the strategy.

Developing an Optimal Scheduling of Taiwan Power System With Highly Penetrated Renewable Energy Resources and Pumped Hydro Storages

Recently, Taiwanese Government has announced an ambitious energy policy: up to 20% of total power will be generated from renewable energy resources by 2025. Under such high-level penetration level of renewable energy resources, the typical net load curve will be definitely reshaped as the so-called duck curve. Operation modes of pumped hydro storage units in Taiwan power system will be totally changed. To tackle out this difficulty, the optimal scheduling of Taiwan power system is developed in this article for examining the coordination of highly penetrated renewable energy resources and pumped hydro storage plants under the required spinning reserve. The associated cost function and various constraints used in this optimal scheduling problem are described first. Physical characteristics of pumped hydro storage units in Taiwan will also be studied. By following the data format in the open source MATPOWER optimal scheduling tool, platform developments of this optimal scheduling program are reported. To validate the effectiveness of the proposed scheme, intensive simulations of both current scenarios and future scenarios are conducted. Simulation results indicate that existing pumped hydro storage units in Taiwan can indeed mitigate the impact of the duck-shaped net load curve in the generator scheduling of future Taiwan power system even under the worst scenario.

Study on Optimization of Control Strategy for Pump Shutdown in Pumped-Storage Unit

In view of the formulation of power failure control strategy of pumped-storage unit at pump operation condition caused by hydraulic, mechanical and electrical factors, taking Heimifeng pumped-storage power station as an example, downtime control strategy at the pump working condition were analyzed under different heads. The transition characteristics at the pump condition of power outage for different guide vane opening were discussed. The stability parameter variation characteristics for the key points of vibration/sway and pressure pulsation at the process of shutdown were analyed. Combination the GCB characteristics of unit, the optimal load and the guide vane opening in the power outage process of shutdown at pump working condition were determined, and the electric life. The optimized shutdown strategy can ensure the safe operation of the unit, and the shutdown load can meet the requirements of the industry standard.

Modeling and Simulation of Mechanical and Electrical Transient of Variable-Speed Pumped Storage Units

In order to study the operation characteristics of large capacity variable-speed pumped storage units connected to the system, the electromechanical transient model is established. Firstly, based on the basic equations of the doubly-fed machine, the generator model represented by an equivalent voltage source is built. Secondly, on the premise of coupling term cancellation, the frequency conversion controller, frequency converter and generator connection module are normalized. Then, the generator model and variable frequency controller model are integrated to form the electromechanical transient model of the unit, which is not only the fitting of external characteristics but also retains the dynamic process of the motor flux linkage and the dynamic characteristics of the controller’s inner loop. Finally, the electromechanical transient model is simulated on the RTDS platform. The simulation results show that the model is correct and effective, which is of great significance to the study of transient problems of large-capacity doubly-fed units connected to the grid.

Research and Application on Numerical Simulation of Hydraulic Transients in Complex Water Conveyance System

Accurate simulation of hydraulic transients is crucial and complicated in the design of hydropower station and pumped storage power station. In this paper, key technologies for hydraulic transient simulation calculation in complex water conveyance system were studied. The structural matrix method with advantages of high accuracy and fast speed for numerical calculation was introduced. Complicated elements in the conveyance system were refined, such as high precision simulation of differential surge chamber, simulation of long and narrow upper chamber, new interpolation method for characteristic curve of pumped storage unit. Based on Jinping II hydropower station with special long headrace system and differential surge chamber, Baihetan hydropower station with complex tailrace system and large surge chamber and Xianyou pumped storage power station with complex unit characteristics and various working conditions, the application of the simulation software HYSIM in field test and inversion calculation was illustrated. The paper providing references for the design of similar projects.

A Fast High-Precision Model of the Doubly-Fed Pumped Storage Unit

With an increase of renewable energy permeability in power grids, doubly-fed pumped storage units with excellent regulation performance have become a popular research topic. Current models of the doubly-fed pumped storage unit are mostly used in the study of electromagnetic transients while the generator model is complex and the pump-turbine system model is simple, which is not conducive to the research on electromechanical transients and pump-turbine control systems. To overcome this problem, a novel fast high-precision model of the doubly-fed pumped storage unit is proposed in this paper. First, a novel efficiency optimization method is proposed, and a high-precision variable speed control model of the pump-turbine is established according to the pump-turbine’s complete characteristic curves of. A doubly-fed induction generator (DFIG) control model is then used to construct a detailed model of the doubly-fed pumped storage unit. The DFIG control model is analyzed and simplified, and a fast high-precision model of a doubly-fed pumped storage unit is obtained. Finally, this fast high-precision model is verified in the turbine and pump modes. The results indicate that compared with the detailed model, the proposed fast high-precision model can better describe the characteristics of a variable speed unit. The new model is simple, has high accuracy and its simulation step (10−2 s) is larger than that of the detailed model (5 × 10−6 s), which makes the simulation speed improved effectively.

Parameter identification and uncertainty quantification of a non‐linear pump‐turbine governing system based on the differential evolution adaptive Metropolis algorithm

Pumped storage units (PSUs) are now widely used for energy storage. However, the uncertainty of the identification results of the pump-turbine governing system (PTGS) caused by the random observation noises and the lack of prior knowledge remains an unaddressed issue. In recent years, the differential evolution adaptive Metropolis algorithm (DREAM) based on the Bayesian theory has been extensively used for parameter estimation and uncertainty analysis, but its application to the uncertainty analysis of PTGS has been rare. This study systematically evaluates the applicability of DREAM in the parameter identification and uncertainty quantification of PTGS. A real PSU in China has been employed as a case study for numerical experiments. Four groups of control experiments with different proportions of observation noises and different prior search spaces have been constructed in this study. It can be concluded from this study that: (a) accurate point identification results and effective uncertainty quantification can be obtained simultaneously using DREAM, (b) a lower proportion of observation noises can enhance the efficiency and effectiveness of the DREAM algorithm when applying to PTGS simulation. The DREAM method can narrow the prior search space of PTGS parameters effectively and thus help the hydropower engineers to make decisions.

Numerical simulation and stability analysis of pumping transients in the pumped-storage power plant

The pumped-storage unit (PSU) are of great significance in modern power system for its reversible operating mechanism in both power generation and water pumping directions. Aiming at the precise numerical simulation of pumping transient processes in PSU, this paper establishes a nonlinear and characteristic method-based mathematical model of the governing system of PSU in which the hydraulic behaviours of conduit pipes, surge tanks and the pump turbine as well as the mechanical-electrical characteristics of the generator-motor are taken into consideration. In this model, local hydraulic losses in model boundaries are specifically introduced to compensate for the unmodeled errors. To verify the modelling accuracy, simulation curves under both pump failure and pump shutdown conditions are compared with the practical data. Furthermore, the hydraulic oscillations in the two transient processes have been discussed specifically.

Research on Operation of Electrothermal Integrated Energy System Including Heat Pump and Thermal Storage Units Based on Capacity Planning

In view of the Three North areas existing wind power absorption and environment pollution problems, the previous scholars have improved the wind abandon problem by adding electrothermal coupling equipment or optimizing power grid operation. In this paper, an electrothermal integrated energy system including heat pump and thermal storage units was proposed. The scheduling model was based on the load data and the output characteristics of power units, each power unit capacity was programmed without constraints, and the proposed scheduling model was compared with the traditional combined heat and power scheduling model. Results showed that the investment and pollutant discharge of the system was reduced respectively. Wind power was fully absorbed. Compared with the traditional thermal power unit, the proportion of the output was significantly decreased by the proposed model. The proposed system could provide a new prospect for wind power absorption and environment protection.

Research on variable speed operation of static frequency converter for pumped storage units

Constant speed pumped storage unit is widely used, however it cannot adjust the input power when working in the electric mode, and cannot work in the best efficiency when the head of the reservoir changes greatly. Therefore, it is necessary to study and develop the variable speed pumped storage systems. This paper has studied on variable speed operation of static frequency converter for pumped storage units. Besides, development status of variable speed pumped storage system at home and abroad is investigated. Furthermore, classification and advantages and disadvantages of variable speed pumped storage system are also introduced, mainly including two typical variable speed pumped storage systems, i.e., doubly-fed variable speed system and full power variable speed system.

Analysis on the thrust bearing lubrication in pumped storage unit based on fluid-solid-thermal interactions

The bidirectional thrust bearings are used to balance the thrust load of the entire shaft system which play an important role in the pumped storage units. The lubrication is usually analyzed by simultaneously solving the Reynolds equation, energy equation, film thickness equation of the film and the heat conduction equation, elastic equilibrium equation of the pad. However, in this method the assumptions for the inlet temperature of the film and the wall heat coefficients on the pad greatly affect the numerical accuracy. This study used fluid-solid-thermal interaction method, built three dimensional (3D) FEM model for the pad and collar and the 3D CFD model for the oil film, and then analyzed the influence of the thrust loads and the Babbitt layer on the bearing performance. The results show that increasing the thrust load will rapidly decrease the minimum film thickness, increase the maximum pressure and maximum temperature on the pad. Increasing the thickness of the Babbitt layer on the pad sliding surface will increase the minimum thickness of the film, decrease the maximum temperature on the pad which improve the bearing lubrication.

Flow Characteristics of Pump Turbine in Four Operating Quadrants: Computational Fluid Dynamics Simulation and Particle Imaging Velocimetry Measurement

Owing to the need for power grid peak regulation and frequency regulation, the pumped storage unit has to undergo frequent working condition conversion, and the pump turbine runs across the four quadrants of the full characteristics during the transition. This study used the full flow numerical simulation and particle imaging velocimetry test to examine the internal flow characteristics of three guide vane openings (GVO). Consequently, the evolution law of the internal flow pattern of the pump turbine was obtained. According to our results, in the high-efficiency areas of the turbine and the pump, the runner and guide vane areas flowed steadily, whereas, under other unsteady conditions, there was a vortex structure between the runner area and the vane area. Except for the pump-braking mode, all the most unstable flow areas appeared in the vaneless space. The flow in the runner channel was most unstable in pump-braking mode. Finally, we obtained test images of different operating points in the four-quadrant operating area as well as vortex motion trends.