Variable Speed Pumped Storage Research Articles

Variations of flow patterns and pressure pulsations in variable speed pump-turbine during start-up process

Abstract In recent years, variable speed pumped-storage (VSPS) technology has become a hotspot of research and application due to its excellent power grid regulation capabilities. Since the speed of a VSPS unit is changeable, when switching operating conditions, more stable operating trajectories can be chosen to reduce vibration and damage. The simulations of transient processes of VSPS units normally use 1D method, which cannot judge the quality of operating conditions because of no flow pattern and pressure pulsation information. Using 3D CFD simulation based on OpenFOAM, we analyse the flow patterns and pressure pulsations when a VSPS unit with a full size frequency converter (FSFC) is in the turbine start-up process. The typical operating points in the variable speed transient trajectories obtained from 1D simulation are studied. It is found that in the initial stage of start-up, high-speed circulation flow arises in the vaneless space, leading to flow separation and large pressure pulsation. The results can provide a reference for the operation of VSPS power stations, so as to avoid operating conditions with adverse flow patterns and pressure pulsations.

Influence of asymmetric-paths winding on electromagnetic force of variable speed pump storage generator-motor

Stator asymmetric-paths winding of variable speed pump storage (VSPS) generator-motor can solve the problem of mismatch of unit speed, capacity and outlet voltage. However, different winding connection schemes will lead to the change of magnetomotive force (MMF) asymmetry of each branch, and then affect the electromagnetic force of generator-motor. In order to explore the effect of this winding type on the electromagnetic force, stator asymmetric-paths winding's MMF and electromagnetic force of 336 MW VSPS generator-motor is derived. Waveforms and harmonic contents of the stator asymmetric-paths winding MMF of the equal-pitch and unequal-pitch schemes are analyzed. Under the consideration constraints of factors such as minimizing MMF asymmetry and electromagnetic vibration, a reasonable asymmetric-paths winding scheme with unequal pitch is determined It is concluded that asymmetric-paths winding scheme with pitch of 14-15-16 can effectively weaken the low-order MMF harmonics and reduce the electromagnetic force under the limitation of asymmetric-paths winding form. The finite element model of VSPS generator-motor is further developed, and the electromagnetic force amplitude and spatial and temporal distribution characteristics under 6 winding schemes are calculated to verify the accuracy of the calculation model. The results of the study can provide technical support for the development of localized VSPS generator-motor.

Optimization of an Operation Strategy for Variable Speed Pumped Storage Power System Flexibility

With the increase in the grid-connected scale of new energy, the ability to flexibility regulate a power system is greatly challenged. Since a variable speed pumped storage (VSPS) unit has a wider power regulation range and higher operation efficiency than conventional pumped storage (CPS), this study focuses on improving system flexibility with the VSPS unit. First, the probabilistic characteristics of forced outages affecting the flexibility of power units are studied. Considering the uncertainty of the net load prediction error, a probabilistic density method is proposed to quantify the flexibility of the power system. Second, in order to improve the flexibility of the system and take into account the comprehensive benefits of the VSPS unit, an optimization model for the VSPS unit to improve the flexibility of the grid was established based on bacterial colony chemotaxis that takes into consideration the operational constraints of the VSPS unit. Finally, to verify the effectiveness of the proposed optimization strategy using simulation, the proposed optimization model is used to compare the advantages of the VSPS unit’s ability to regulate system flexibility with a conventional pumped storage unit.

Simulation of Different Control Strategies in Pumping Mode of Variable-speed Pumped Storage Unit

Because of the complex structure, the variable-speed pumped storage (VSPS) unit would face more stability problems in operation compared with conventional generators in the power grid. To overcome the shortcomings of the PI controller, the fractional order PI (FOPI) controller is applied for VSPS in pumping mode. To compare the quality of the two controllers, the WSCC 9-bus system with VSPS is studied under different disturbances. The dynamic performance is evaluated by calculating the integral of time multiplied absolute error criterion (ITAE) of rotor speed and active power of the stator. The result shows that the FOPI control strategy can effectively improve the dynamic performance of VSPS.

Modeling and Transient Response Analysis of Doubly-Fed Variable Speed Pumped Storage Unit in Pumping Mode

Doubly-fed variable speed pumped storage (VSPS) unit is an advanced hydropower system. In pumping mode, its input power can continuously be adjusted within a certain range via changing speed. Thus, it overcomes the major defect that the pumped storage unit cannot provide frequency regulation services to the power grid in pumping mode. However, for the pumping mode VSPS, how to establish its model is still a problem. In this article, an electromagnetic-electromechanical transient multi-time scale model of pumping mode VSPS is presented. This model depicts the intrinsic speed-power regulation characteristics and the extrinsic power-frequency coupling characteristics of pumping mode VSPS, which can be used for the power grid frequency regulation analysis. Firstly, the hydraulic subsystem model of VSPS is established within the electromechanical transient time scale. The model is built based on the variable speed characteristics of the reversible pump-turbine (RPT) in pumping mode and considers the hydrodynamics and additional friction effects of the wicket gate in the water conveyance system. Secondly, the electric subsystem model of VSPS is established within the electromagnetic transient time scale. The model mainly describes the operation characteristics of a doubly-fed induction machine (DFIM) and the control properties of the inner and outer loops of the back-to-back (BTB) converter system. Finally, comprehensive simulation and experimental results have fully verified the established model and theoretical analysis.

Optimal multi-energy portfolio towards zero carbon data center buildings in the presence of proactive demand response programs

Multiple geographically dispersed data center buildings have been increasingly positioned in renewable-rich areas due to their high energy consumption. This paper proposes an optimal multi-energy portfolio for zero carbon data center buildings in the presence of proactive demand response programs. In the data center buildings, the complementarities of hydro-solar-wind hybrid renewable energy sources (RESs) are fully exploited via multi-energy conversion and storage devices, which are modeled as 100% renewable energy hubs for zero carbon multi-energy supplies. In order to exploit the hub-internal operational dispatchability and flexibility, a comprehensive energy consumption model of data center buildings is proposed to facilitate the demand response in terms of available serves, while the variable speed pumped storage (VSPS) is modeled to capture its dynamic operational characteristics. The energy‑carbon production, conversion, storage, and consumption are formulated as an energy‑carbon matrix, which are solved via a two-stage method to obtain the optimal portfolio. Case studies on southwest China data center buildings are implemented to demonstrate the effectiveness and superiority of the proposed methodology on cost-effective accommodation of RESs. Simulations results show that the system portfolio cost can be reduced by at most 17.8% with a higher operational flexibility.

Cooperative control strategy for frequency regulation of wind-pumped storage system considering wind speed partition

In order to solve the problem of system inertia reduction and frequency response degradation caused by large-scale wind power interconnection, a strategy is proposed. This strategy incorporates a joint system model composed of doubly-fed wind turbine (DFWT) and variable speed pumped storage (VSPS), utilizing a fuzzy controller to dynamically determine the virtual inertia coefficient of the wind-pumped storage system based on the frequency state of the system, and adjusts the frequency-regulation participation factor of the DFWT in real time according to the operating conditions of it. The simulation results show that the proposed strategy can not only significantly improve the frequency nadir, speed up the system frequency and each generating unit in the system to restore to steady state, but also avoid the second frequency drop (SFD) caused by the wind farm out of primary frequency regulation (PFR), and improve the stability of the system frequency.

Small-Signal System Frequency Stability Analysis of the Power Grid Integrated With Type-II Doubly-Fed Variable Speed Pumped Storage

This article proposes a structurally distinctive doubly-fed variable speed pumped storage (VSPS), denoted as the Type-II VSPS. Where, the speed is controlled by a back-to-back (BTB) converter while the power is controlled by a speed governor, which is the exact opposite of the control method for conventional VSPS. The small-signal frequency stability analysis of a power grid integrated with the Type-II VSPS is carried out to investigate the influence of this type of VSPS on power grid stability. Firstly, the transfer function models of hydraulic and electric subsystems of the Type-II VSPS are established, and the system small-signal stability analysis is carried out based on the obtained models and Nyquist stability criterion. Secondly, an improved system frequency response (SFR) model for the power grid integrated with Type-II VSPS is presented. Such a model is applied to investigate the frequency response of the modern power grid integrated with a large-scale VSPS (the current single unit capacity has reached 450 MW). Furthermore, the small-signal stability of the modern power grid is analyzed based on the Nyquist stability criterion. Finally, time-domain simulations and experiments are conducted to validate the effectiveness of the small-signal stability analysis.

A hybrid energy storage system with a modified MMCC‐TSBC converter comprised of VSPS, BESS and supercapacitor storage

IET Power ElectronicsAccepted Articles ORIGINAL RESEARCHOpen Access A hybrid energy storage system with a modified MMCC-TSBC converter comprised of VSPS, BESS and supercapacitor storage First published: 05 December 2022 https://doi.org/10.1049/pel2.12296AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Due to a technical error, the following article was published in error on Wiley Online Library as an Accepted Article on 5 December 2022. The article has been temporarily removed. Wiley would like to apologize to the authors and the academic community for this error. Kasari, P.R. and Bhattacharjee, S. (2022), A hybrid energy storage system with a modified modular multilevel cascaded converter based on a triple star bridge cell converter comprised of variable speed pump storage, battery energy storage system, and supercapacitor storage. IET Power Electronics. Accepted Author Manuscript. https://doi.org/10.1049/pel2.12296 Accepted ArticlesAccepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future. RelatedInformation

Reduced-Order System Frequency Response Modeling for the Power Grid Integrated With the Type-II Doubly-Fed Variable Speed Pumped Storage Units

The traditional system frequency response (SFR) model is not applicable to the study of the frequency response of contemporary power grid due to the response of the large capacity (single unit up to 500 MW) type-II doubly-fed variable speed pumped storage (VSPS) unit is not considered. This article proposes an improved reduced-order SFR model for the power grid integrated with the large-scale type-II VSPS. proposed models Compared with the traditional SFR model, this model takes into account the active power coupling effect of this type of VSPS, and the computational burden increase of the model is small due to the model of VSPS has been reduced to the greatest extent. Therefore, the SFR model can be used by the system operators to rapidly calculate and evaluate the frequency response of contemporary power grid. Firstly, a reduced-order frequency response transfer function model of the Type-II VSPS is established by using the state-space model and small-signal incremental method. Compared with the higher-order nonlinear model of the Type-II VSPS, the state variables and computation burden of the established model is dramatically decreased. Secondly, an improved SFR model for the power grid integrated with the type-II VSPS is presented, and then the reduced-order analytical solution for the frequency response of the grid is put forward based on the parameter weighted aggregation method. The improved SFR model is more realistic and can better express the frequency response characteristics of the contemporary power grid. The proposed SFR model have demonstrated advantages in solving speed and efficiency when contrast it with the higher-order nonlinear model of the grid. Finally, the simulation and experimental results are respectively compared with the analytical solution of the reduced-order models, and the results have demonstrated the effectiveness of the.

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.

Power system joint energy and reserve scheduling model considering variable speed pumped hydro storage for mitigating wind curtailment

The large-scale integration of wind power brings great challenges to power system secure and economic operation. In order to address this challenge, the variable speed pump storage hydropower plant (VS-PSHP) technology and demand response technology have addressed a lot attention. In this paper, the coordination of the thermal power generator, the wind power plant, the VS-PSHP and multi-type flexible loads are considered, and a day-ahead and real-time coordinated scheduling model are proposed. The proposed model can formulate the generation, contingency reserve and power distribution factor schedules simultaneously. Numerical simulation results indicate that the coordination of VS-PSHP and multi-type flexible loads can increase the system operation economic and mitigating the wind power curtailment. The results also show that the VS-PSHP is good at providing contingency reserve, and the participation of VS-PSHP can lead to a relatively lower total system operation cost compared to the participation of fixed speed pump storage hydropower plant (FS-PSHP).

Wind power fluctuation compensation by variable speed pumped storage plant in a grid integrated system: Frequency spectrum analysis

An electrical power generation from the wind technology is the most rapidly growing technology due to its ample characteristics. Nevertheless, because of its stochastic feature, it has unnecessary impacts on the operation s and stability of the power grid system. The fluctuation of the grid frequency problem, for example, is more pronounced. The fluctuation of the frequency in turn impacts even the collapse of the power system. To minimize such problem, a droop-vector control strategy applied on a doubly-fed induction machine based (DFIM) variable speed pumped storage (VSPS) system is proposed in this paper. This method is supposed to be used as a wind power fluctuation compensation solution in the wind farm-grid integration system. The system model is made on the basis of the technique called a phasor model. The frequency spectrum analysis approach is used in the VSPS plant for determining the dynamic performances of the grid in case of contingencies including wind power fluctuation compensation. The software platform MATLAB/Simulink is used for verifying the performance of the proposed system. The results show that the method of frequency spectrum analysis technique is effective for determining the wind power fluctuation and stability requirement in the large power network. The control strategy proposed on this paper implementing the VSC-DFIM based VSPS plant integrated with the power gird and wind farm network achieves well-controlled power flow and stable grid frequency with the deviations in acceptable ranges.

Variable Speed Pump Storage for the Mitigation of SSR in Power System with Wind Generation

Subsynchronous resonance (SSR) can bring significant negative effects on the grid system like stability, security, and even generator shaft damage. This work presents a new method of using a doubly‐fed induction machine (DFIM) based system of variable speed pumped storage plant (VSPS) to mitigate SSR in the power system with high penetration of wind generation. The mitigation is reached based on the principle of balanced shaft mechanical input power and electromagnetic power. The fundamental concepts and phenomena of SSR with wind farm are discussed in brief in this work. For the sake of analysis and verification of performance of the proposed system, the network model including wind farm, VSPS, HVDC, and synchronous machine is built based on Ningxia grid for the SSR study using PSCAD platform. The result shows that VSPS brings significant effect to dampen the SSR in the power system with high penetration of wind generation.

A Variable Speed Pumped Storage System Based on Droop-Fed Vector Control Strategy for Grid Frequency and AC-Bus Voltage Stability

Harnessing wind energy is the most rapidly growing amongst renewable energy sources. However, because of its intermittency in nature, wind power results in unfavorable influences on power system control, operation and stability. The voltage sag and flicker and grid frequency fluctuation are significant in this regard. To minimize the effect of wind power fluctuations and other contingencies on the grid frequency and AC-bus voltage, this paper presents a droop-fed vector control strategy based variable speed pumped storage (VSPS) system comprising the doubly fed induction machine. Modelling of the system is undertaken based on a phasor model technique. The case study is made by considering the droop-controlled VSPS plant in a grid containing conventional synchronous machines for hydropower and thermal power plants and an induction machine wind farm. The performance is validated and analyzed using a MATLAB/Simulink platform. The proposed droop-fed control model is compared with the conventional control strategy (without being droop-fed) and tested to wind power fluctuations, start-up transients, load variations and three-phase fault. The results show that the droop-fed vector control strategy of the VSPS plant achieves better dynamic and steady state controlling responses for grid frequency and AC-bus voltage in the power system than the conventional vector control scheme during wind power fluctuations and contingencies.

Optimal bidding strategy for variable-speed pump storage in day-ahead and frequency restoration reserve markets

Variable-speed pump power storage is an innovative large-scale technology that is being deployed across the world. In addition to price arbitrage and provision of downward replacement reserve, its operational flexibility enables the provision of frequency restoration reserve (FRR) both in turbine and pump modes. This work proposes a bidding optimization strategy for the participation in the FRR market. The proposed framework encompasses a medium-term module to optimally allocate the yearly natural water inflows, representation of electrical and hydraulic losses in the water inflow/power curves, as well as forecasting techniques to predict market prices and natural water inflows. Moreover, it does not assume prior knowledge of the amount of activated FRR capacity band. An evaluation module is also proposed to replicate the “real” operation of the power plant and enables an accurate calculation of the revenue. A comparison between fixed and variable-speed Pump storage power (PSP) units participating in the Iberian electricity market presented an increase in revenue of almost 12%. Due to the low liquidity of the FRR market in Portugal, and the considerable capacity of the PSP unit, under some specific situations, it might be necessary to cap the size of the FRR bid to decrease the difference between the expected and realized revenue.

On the Profitability of Variable Speed Pump-Storage-Power in Frequency Restoration Reserve

The increase penetration of renewable energy sources (RES) into the European power system has introduced a significant amount of variability and uncertainty in the generation profiles raising the needs for ancillary services as well as other tools like demand response, improved generation forecasting techniques and changes to the market design. While RES is able to replace energy produced by the traditional centralized generation, it cannot displace its capacity in terms of ancillary services provided. Therefore, centralized generation capacity must be retained to perform this function leading to over-capacity issues and underutilisation of the assets. Large-scale reversible hydro power plants represent the majority of the storage solution installed in the power system. This technology comes with high investments costs, hence the constant search for methods to increase and diversify the sources of revenue. Traditional fixed speed pump storage units typically operate in the day-ahead market to perform price arbitrage and, in some specific cases, provide downward replacement reserve (RR). Variable speed pump storage can not only participate in RR but also contribute to FRR, given their ability to control its operating point in pumping mode. This work does an extended analysis of a complete bidding strategy for Pumped Storage Power, enhancing the economic advantages of variable speed pump units in comparison with fixed ones.

Contribution of variable-speed pump hydro storage for power system dynamic performance

This paper presents the study of variable-speed Pump Storage Powerplant (PSP) in the Portuguese power system. It evaluates the progressive integration in three major locations and compares the power system performance following a severe fault event with consequent disconnection of non-Fault Ride-through (FRT) compliant Wind Farms (WF). To achieve such objective, a frequency responsive model was developed in PSS/E and was further used to substitute existing fixed-speed PSP. The results allow identifying a clear enhancement on the power system performance by the presence of frequency responsive variable-speed PSP, especially for the scenario presented, with high level of renewables integration.

Phasor model simulation of a grid integrated variable speed pumped storage system

This study presents a phasor model simulation of a grid integrated variable speed pumped storage (VSPS) system focusing on generating mode. The VSPS is configured by the voltage sourced converter doubly-fed induction machine (DFIM) scheme. A wound rotor induction machine dynamic mathematical model and generalised averaging theory are adopted to derive the phasor model technique of the system. Based on the dq -axis synchronous reference frame concept, the direct power control strategy of the system is designed. The steady-state and transient stability responses of the proposed system are analysed in MATLAB/Simulink platform by considering a 300 MW/18 kV/50 Hz DFIM-based VSPS system and a grid consisting of two hydropower plants with synchronous generator, a diesel power plant with synchronous generator, a solar photovoltaic farm and fixed loads. A comparison of phasor model and detailed model simulations of the system is also conducted. The results show that the grid integrated VSPS system is stable without significant deviation in grid voltages, DC voltage and rotor speed of the DFIM unit under the designed control strategy. Moreover, the phasor model simulation achieves results with good accuracy as the detailed model, but with faster speed. Hence, the phasor model simulation is very effective for analysis and control design of large grid integrated VSPS systems.

Power Electronics Converters for Variable Speed Pump Storage

This paper proposed the power electronics solution to obtain variable speed of the variable-speed pump storage The study focused on the types of variable-speed pump storage consists of doubly fed asynchronous machine and power electronics converter. Power Electronics converters used in this model are cycloconverter, two levels, three levels voltage source- converter and H-bridge cascaded eleven levels converters. The total harmonic distortions of rotor currents of Doubly fed asychronous machine and speed change for each type of converters are analyzed. Study explained the H-bridge eleven level converter is the best solution than other types.All simulation models depended on the used of PSIM software program. DOI: http://dx.doi.org/10.11591/ijpeds.v3i1.1726