Variable-speed Pumped Storage Power Plants Research Articles

Calculation method of external fault short-circuit current for variable-speed pumped storage units based on time-domain dynamic circuit

The calculation method of the external fault short-circuit current of large units with clear mechanisms and practicality is of great value in engineering practice. Due to the special AC excitation structure and control mode, the external fault short-circuit characteristics of variable-speed pumped storage units (VSPSUs) are very different from those of conventional units. Therefore, this paper proposes a calculation method for external fault short-circuit current based on a time-domain dynamic circuit. According to the excitation and control characteristics of VSPSUs under external fault, the VSPSU under external fault is divided into two cases: continuous excitation and jumper action. Based on space vector analysis, the time-domain dynamic circuit models are established, respectively. On this basis, the analytical formula of the external fault short-circuit current of VSPSUs is derived by combining the transition boundary conditions of the two cases and the dynamic characteristics of the stator flux linkage. Finally, the comparison with PSCAD/EMTDC simulation results shows that the proposed VSPSUs’ external fault short-circuit current calculation method has high accuracy and practical value, which can meet the needs of primary equipment selection and relay protection of variable-speed pumped storage power plants.

A novel topology of drive & thermal model for variable speed pump-storage power plant

Improving drive techniques in variable-speed pumped storage power plants (VSPSPs) for optimal performance, higher efficiency and lower loss is an ongoing challenge in light of these plants' considerable high power output and consumption. Introducing a new direct torque & flux controller (DTFC)-based driver with 3 level voltage source convertor-active neutral point clamped (3LVSC-ANPC) for this power plant, this paper proposes a novel communication and operation topology for the voltage converter with a 5 + 1 layout, in which a driver central control unit (DCCU) controls each converter as an independent power module. This layout consists of five parallel and one redundant power module. Hydraulic and electric VSPSP models are presented to allow for a better grasp of the topic. In the following, models and thermal equivalent circuits of the drivers are presented before investigating the results of MATLAB and PLEXIM simulations in the end. The project is also verified and validated by statistical analysis, proving improved efficiency, reduced THD and lower driver losses by employing the new driver in the power plant.

Modeling and simulation to optimize direct power control of DFIG in variable-speed pumped-storage power plant using teaching–learning-based optimization technique

The issues related to the optimal control of large-scale storage systems in electric power systems such as pumped storage (PS) plant have turned into vital challenges in the way of integrating renewable energy sources into power systems to provide reliable and economical electric energy. In this regard, this paper uses the direct power control strategy to model and simulate a variable-speed PS plant, which includes a doubly fed induction generator (DFIG). The active and the reactive power of the stator would be able to be controlled, separately. This approach has a better dynamic performance compared to other methods, while it would be quite simple to implement. But there are some shortfalls with this method, such as high ripple relating to the active power as well as reactive power together with the current harmonics. In this respect, the space vector modulation (SVM) is applied to eliminate these shortfalls. In the proposed control technique, including SVM, the dynamic performance of the studied DFIG unit is controlled using the proportional–integral (PI) controller. It should be noted that the teaching–learning-based optimization (TLBO) method is employed to tune the PI controller for controlling the DFIG system in the PS plant. Finally, in order to validate the performance of the suggested framework, a comparison is made between the results obtained by the TLBO and the ones reported by other optimization methods. The obtained results using the TLBO algorithm indicate better performance of the PI controller to reduce the ripples of the active and reactive power of the stator as well as the harmonic power.

Fault Diagnosis and Fault-Tolerant Control of Megawatt Power Electronic Converter-Fed Large-Rated Asynchronous Hydrogenerator

In recent years, it has been difficult to achieve power converter redundancy in the multichannel voltage-source inverter (VSI)-fed large-rated doubly fed induction machines (DFIMs), and it has not yet been adopted in any commissioned variable-speed pumped storage power plants. Multichannel VSIs are a fundamental part of DFIMs, and they control the real and reactive powers of the machines. This paper presents the fault-tolerant operation of a large-rated DFIM hydrogenerating unit at open-switch faults in back-to-back VSIs. A technique for diagnosing the open-switch faults in grid-side and machineside converters is proposed. An open-switch fault is detected based on the variation in rotor currents and dc link voltage, which reduces the computational efforts during fault diagnosis. A 250-MW DFIM with five-channel three-level VSIs (each rated at 9 MVA) is simulated in the MATLAB/Simulink environment to observe the drive behavior. Finally, a 2.2-kW DFIM is tested in a laboratory environment to verify the experimental results.

Full-size converter operation of hydro power generators: a state-of-the-art review of motivations, solutions, and design implications

This paper reviews motivations and solutions for variable-speed operation in large hydro power plants with a special emphasis on full-size converter operated synchronous generators. First, the established concepts of conventional pumped storage power plants are briefly described. Then, the implemented applications with use of power converters and synchronous machines in hydro power plants, their power ratings, power converter topologies used, and the experiences obtained during operation are reviewed. Concerning its state-of-the-art position in variable-speed pumped storage power plants, the variable-speed capability offered by doubly-fed induction machines is also briefly described, including the power range that can be achieved in pumping mode as well as the power converter ratings of existing power plants. Following this comprehensive analysis, this paper identifies the requirements of today’s power converters and synchronous machines for utilization in large pumped storage power plants as full-size converter operated synchronous generators. It analyzes the design implications on the electric machines driven by such converters, and investigates the advantages of the additional possibilities given by the full-size converter operation that may outweigh the added cost, system complexity, and power loss.

Reliability of Variable Speed Pumped-Storage Plant

The multi-channel (MC) back-to-back voltage source inverter (VSI)-fed doubly fed induction machine (DFIM) is emerging as a highly interesting topic in large-rated variable speed pumped-storage power plants (PSPP) in view of cost, optimal efficiency, and space requirements. Although the VSI is the fundamental part of the drive controlling the active/reactive power of the plant, redundancy is presently not adopted in practice causing the unit as a whole to shut down upon a failure in the converter and control circuit. This paper evaluates a large-rated (250 MW) DFIM-fed variable-speed unit of a PSPP in terms of its reliability and availability. A Markov model is developed to assess the reliability of the drive based on a number of factors including survivability and annual failure rate (FIT). Further, the Markov model is applied to different PSPPs for comparison of reliability among them.

Voith undertakes Discover Hydropower Tour

Voith embarked on its first influencer tour in the hydropower sector between 10–16 June 2018 visiting Europe's largest variable-speed pumped storage power plant in Portugal, two highly efficient small hydropower plants in Scotland and a run-of-river power plant in Iceland.

A novel technology for control of variable speed pumped storage power plant

Variable speed pumped storage machines are used extensively in wind power plant and pumped storage power plant. This paper presents direct torque and flux control (DTFC) of a variable speed pumped storage power plant (VSPSP). By this method both torque and flux have been applied to control the VSPSP. The comparison between VSPSP’s control strategies is studied. At the first, a wind turbine with the capacity 2.2 kW and DTFC control strategies simulated then a 250 MW VSPSP is simulated with all of its parts (including electrical, mechanical, hydraulic and its control system) by MATLAB software. In all of simulations, both converters including two-level voltage source converter (2LVSC) and three-level voltage source converter (3LVSC) are applied. The results of applying 2LVSC and 3LVSC are the rapid dynamic responses with better efficiency, reducing the total harmonic distortion (THD) and ripple of rotor torque and flux.