B. Kawkabani

High-Order Modeling of Hydraulic Power Plant in Islanded Power Network

Numerical simulations of the transient operation of an islanded power network subject to load rejections are performed. The islanded power network case study consists of a 1-GW hydroelectric power plant featuring four generating units, a long penstock, and a surge tank connected to four 1.3-GW thermal power plants and passive consumers. The modeling of every network component is described and special care is paid to the modeling of the hydroelectric power plant. In particular, the high-order modeling used for these investigations enables the detailed simulation of water hammer, mass oscillations, and nonlinear hydraulic characteristics of the turbines interacting with the electrical components of the network. Moreover, the stability analysis of the systems is performed for different load conditions and the damping performances of a power system stabilizer IEEE PSS2B are investigated.

Investigation of Control Strategies for Variable-Speed Pump-Turbine Units by Using a Simplified Model of the Converters

This paper presents the modeling, simulation, and analysis of the dynamic behavior of a fictitious 2 × 320 MW variable-speed pump-turbine power plant, including a hydraulic system, electrical equipment, rotating inertias, and control systems. The modeling of the hydraulic and electrical components of the power plant is presented. The dynamic performances of a control strategy in generating mode and one in pumping mode are investigated by the simulation of the complete models in the case of change of active power set points. Then, a pseudocontinuous model of the converters feeding the rotor circuits is described. Due to this simplification, the simulation time can be reduced drastically (approximately factor 60). A first validation of the simplified model of the converters is obtained by comparison of the simulated results coming from the simplified and complete models for different modes of operation of the power plant. Experimental results performed on a 2.2-kW low-power test bench are also compared with the simulated results coming from both complete and simplified models related to this case and confirm the validity of the proposed simplified approach for the converters.

Trends in Electrical Machines Control: Samples for Classical, Sensorless, and Fault-Tolerant Techniques

This article has given a significant number of examples of contemporary control techniques for EDs. Of course, many more special machines or specific applications can be investigated as well. However, with IMs, PMSMs, SRMs, and hydrogenerators, the most current industrial applications have been addressed. Most of the presented techniques are not yet fully used in industry and are still under evaluation before diffusion at a large scale in the industry. Therefore, many control techniques, such as FTC schemes, are still under investigation for industrial applications with reliability requirements. Even if there are no standard schemes to implement these modern control techniques, it has been commonly admitted that sensorless and fault-tolerant structures will be used more and more in the future and that they are fully implementable on low-cost digital platforms with a high degree of integration.

A System for Wireless Power Transfer of Micro-Systems In-Vivo Implantable in Freely Moving Animals

A system for wireless power transfer of micro-systems in-vivo implantable in small animals is presented. The described solution uses a servo-controlled transmitter moved under the animal moving space. The solution minimizes the power irradiation while enabling animal speeds up to 30 cm/s. An x-y movable magnetic coil transmits the required power with a level able to keep constant the received energy. A permanent magnet on board of the implantable micro-system and an array of magnetic sensors form a coil tracking system capable of an alignment accuracy as good as 1 cm. The power is transferred over the optimized remote powering link at 13.56 MHz. The received ac signal is converted to dc voltage with a passive full-wave integrated rectifier and the voltage regulator supplies 1.8 V for the implantable sensor system. Experimental measurement on a complete prototype verifies the system performance.

Dynamical Behavior Comparison Between Variable Speed and Synchronous Machines With PSS

The dynamic performances of variable speed and fixed speed units are compared in the case of 2 × 320 MW pumped storage power plant. The case study of the pumped storage power plant with standard synchronous machine with PSS is presented and, then, the corresponding variable speed system is designed for this case. Unsteady numerical simulations of both architectures enable to demonstrate that the variable speed architecture improves the power system stability characteristics for both the local and the inter-area modes of oscillation. Moreover, the damping of active power oscillations originated by the part load operation of the pump-turbine in generating mode is investigated as well.

Unstable Operation of Francis Pump-Turbine at Runaway: Rigid and Elastic Water Column Oscillation Modes

This paper presents a numerical simulation study of the transient behavior of a 2x340MW pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

Start-up and synchronization of a variable speed pump-turbine unit in pumping mode

This paper presents the start-up and synchronization procedures of a variable-speed pump-turbine unit of 250 MW in pumping mode. These procedures applied to a doubly-fed induction motor-generator with three-level voltage source inverters VSI cascade in the rotor side, can be achieved without any supplementary equipment. The control strategy used in the start-up procedure and based on a stator flux oriented control, is described in details as well as different steps in order to reach the minimal speed required for synchronization. The controls of the amplitude, frequency and phase of the stator voltage related to the synchronization procedure are presented. Simulated results confirm the validity of the proposed approach.

Stability studies of a mixed islanded power network with varspeed units using simplified models of the converters

This paper presents the modeling, simulation and analysis of the dynamic behavior of a mixed islanded power network of 780 MVA comprising hydro, thermal and wind power plants. The modeling of each power plant is fully described. The model of the variable speed pump-turbine unit includes hydraulic system, electrical equipments, rotating inertias and control systems. The power plants are connected to five passive consumer loads via a 500 kV electrical line network. First, the capability of the pumped storage plant to stabilize the islanded power network is investigated through the time domain simulation of the dynamic behavior of the entire mixed power network by considering the complete models of the converters. Then a new approach related to simplified models of both converters feeding the rotor circuits is presented. Thanks to this approach, simulation time is significantly reduced. The scenarios considered consist of partial load rejection enabled by flywheel effect in generating mode and wind power fluctuations in pumping mode. The simulation results obtained by the complete and simplified models are presented and discussed.

A fully modular tool for small-signal stability analysis of hydroelectric systems

In electrical systems, the small-signal stability analysis method is usually applied to synchronous machines by using the Park representation (d, q-components). This paper presents the generalization of a different approach for this method, based on a, b, c phase variables. This approach is essential to software systems using phase variables as state variables and its generalization yields a small-signal stability analysis tool which is fully modular. Two test cases are presented to showcase the application of this approach to elements such as synchronous machines, automatic voltage regulator (AVR), power system stabilizer of type IEEE PSS2B, penstock, Francis turbine and speed regulator.

Influence of the Francis Turbine location under vortex rope excitation on the Hydraulic System Stability

Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow leaving the runner of a Francis turbine may act under given conditions as an excitation source for the whole hydraulic system. In high load operating conditions, vortex rope behaves as an internal energy source which leads to the self excitation of the system. The aim of this paper is to identify the influence of the full load excitation source location with respect to the eigenmodes shapes on the system stability. For this, a new eigenanalysis tool, based on eigenvalues and eigenvectors computation of the nonlinear set of differential equations in SIMSEN, has been developed. First the modal analysis method and linearization of the set of the nonlinear differential equations are fully described. Then, nonlinear hydro-acoustic models of hydraulic components based on electrical equivalent schemes are presented and linearized. Finally, a hydro-acoustic SIMSEN model of a simple hydraulic power plant, is used to apply the modal analysis and to show the influence of the turbine location on system stability. Through this case study, it brings out that modeling of the pipe viscoelastic damping is decisive to find out stability limits and unstable eigenfrequencies.