Variable-speed Generator Research Articles

Dual-Electrical-Port Control of Cascaded Doubly-Fed Induction Machine for EV/HEV Applications

This paper presents a dual-electrical-port control scheme for four-quadrant operation of cascaded doubly-fed induction machine (CDFIM), which has conventionally been used as a variable-speed drive or variable-speed constant-frequency generator for limited-speed-range applications. The proposed control method enables the synchronous control of both power winding (PW) and control winding (CW) currents, and as a consequence, not only the control complexity but also the rotor slip frequency and related core losses are significantly reduced in comparison with the previously proposed single-electrical-port control scheme. It is for the first time revealed that the CDFIM drive that indirectly couples PW and CW through induction behavior can be readily controlled like a conventional induction motor to achieve the highest torque density. The torque density–speed region of the CDFIM falls within that of the power machine in singly-fed operation mode, and only a half of that of the power machine in doubly-fed operation mode, which shows the urgent need for torque density enhancement of brushless doubly-fed machines for electric vehicle/hybrid electric vehicle applications. Computer simulations and experiments are implemented to verify the dynamic performance of the proposed control method.

Role of pump hydro in electric power systems

This paper provides an overview of the expected role that variable speed hydro power plants can have in future electric power systems characterized by a massive integration of highly variable sources. Therefore, it is discussed the development of a methodology for optimising the operation of hydropower plants under increasing contribution from new renewable energy sources, addressing the participation of a hydropower plant with variable speed pumping in reserve markets. Complementarily, it is also discussed the active role variable speed generators can have in the provision of advanced frequency regulation services.

Dynamic Safety Constraints by Scenario-Based Economic Model Predictive Control of Marine Electric Power Plants

This paper studies scenario-based model predictive control (MPC) for dynamic safety constraints. For marine electric power plant with direct current distribution and variable speed generator set, the speed of the generator sets should be as low as possible to increase the efficiency of the diesel engines. However, a safety margin toward underspeed is necessary. In this paper, a dynamical safety constraint is achieved by including a fault scenario in the MPC formulation. This is done using a nominal trajectory of the predicted states for the fault-free operation, and adding fault trajectories starting from the samples of the nominal trajectory. The fault trajectories simulate the fault scenario and dynamically constrain the nominal trajectory. The controller is shown to be effective using closed-loop simulations of a marine electric power plant.

Nonlinear adaptive backstepping control for variable-speed wind energy conversion system-based permanent magnet synchronous generator

In this paper, a robust nonlinear adaptive controller based on backstepping control strategy is adopted for a variable-speed wind energy conversion system with permanent magnet synchronous generator (PMSG). Firstly, field-oriented control law based on PI controllers has been introduced. Nevertheless, it presents a noticeable tracking error; thus, the system control is improved by using a backstepping controller. This method provides a simple and fast tracking. However, it is sensitive to parameter uncertainties and load torque disturbances. Therefore, an adaptive backstepping control system is then designed to compensate the parameter uncertainties of the system. Simulation results validate the effectiveness of the proposed control law.

Power-Flow Control and Short-Circuit Current Limitation of Wind Farms Using Unified Interphase Power Controller

This paper presents analytical and simulation studies of wind farms (WFs) connected to power system through a unified interphase power controller (UIPC), which should control power flow and the short-circuit contribution of WF. The UIPC is based on an interphase power controller (IPC) in which the phase-shifting transforms are replaced by two series converters (SECs). In this paper, the UIPC model is developed based on phase angles of injected SEC voltage and a control scheme is proposed to control power flow and limit the short-circuit contribution of WF. The WF model is based on an equivalent aggregated variable-speed double-fed induction generator. The PSCAD/EMTDC simulation results show that the UIPC is an effective and novel solution for power-flow control and limitation of short-circuit contribution of WF in power systems.

Reducing Fuel Consumption Using Flywheel Battery Technology for Rubber Tyred Gantry Cranes in Container Terminals

Flywheel Energy Storage System (FESS) is used as an energy regeneration system to help with reducing peak power requirements on RTG cranes that are used to load or unload container ships. Nevertheless, with the use of FESS, Port Operator can deploy undersized generator for new RTG as this will further reduce fuel consumption. This paper presents the investigation of the amount of energy and fuel consumption that can be reduced in Rubber Tyred Gantry (RTG) cranes in container terminals by the use of simulation. In addition, Variable Speed Generator is integrated to the simulation-hybridized RTG. Simulation results reveal that the total energy saving exceeded 30% relatively to conventional RTG. A hardware-in-loop system is introduced for the purpose of validating the simulation results. The hardware components procured include a FESS, a Variable Frequency Drive (VFD) and brake resistors.

Intelligent Control for Doubly Fed Induction Generator Connected to the Electrical Network

<p><span lang="EN-US">In this paper we are interested in optimizing the wind power capture, using the Doubly Fed Induction Generator (DFIG). This machine is preferred to other types of variable speed generator because of their advantages in economic terms and control. The Artificial Neural Network (ANN) based on Direct Torque Control (DTC) which is used to control the electromagnetic torque in order to extract the maximum power, The main objective of this intelligent technique is to replace the conventional switching table by a voltage selector based on (ANN) to reduce torque and flux ripples. Moreover, the fuzzy logic controller is used to grid side converter to keep DC link voltage constant, and also to achieve unity power factor operation. The main advantage of the two control strategies proposed in this paper is that they are not influenced by the variation of the machine parameter. The pitch control is also presented to limit the generator power at its rated value. Simulation results of 1,5 MW, for (DFIG) based Wind Energy Conversion System (WECS) confirm the effectiveness and the performance of the global proposed approaches.</span></p>

A proportional integral synthesis for a variable speed wind energy conversion system using a permanent magnet synchronous generator

A wind energy conversion system applied to battery charge is proposed in this paper. A permanent magnet synchronous generator (PMSG) is used as a variable speed generator in the proposed system. In order to extract the maximum power, the generator torque control is carried out by the pulse width modulation (PWM) converter, which requires controllers (PI controllers are used). A new approach is developed to settle easily and effectively the PI controller for the first order system. This approach is based on the compensation pole method. The system is simulated in the Matlab/Simpower environment and the results show that the new approach is better than the conventional method.

Operation and Control of Stand-alone Brushless Doubly Fed Induction Generator Using Control Winding Side Converters

The brushless doubly fed induction generator has wide applications as a stand-alone variable-speed constant-frequency generator in some embedded generation systems. In this article, a controller for a stand-alone brushless doubly fed induction generator using control winding side converters is introduced, which was implemented as a ship shaft generation system located in a container ship. The primary goal of the control system is to obtain constant output voltage and frequency of the brushless doubly fed induction generator, regardless of the load and speed condition variation. The main obstruction of working with the brushless doubly fed induction generator is its inherent complexity. To overcome this problem, the mathematical description, power flow, and performance evaluation of the stand-alone brushless doubly fed induction generator is comprehensively developed and analyzed. The experiments presented in this article were implemented on a 2/6-pole 250-frame-size wound-rotor brushless doubly fed induction generator.

Short-Circuit Calculation in Distribution Networks with Distributed Induction Generators

This paper presents an improved current source equivalent model method to determine the short-circuit current of a distribution system with multiple fixed-speed and variable-speed induction generators (IGs). The correlation coefficients of flux components between stator and rotor under the unsymmetrical fault are analyzed using the positive and negative sequence steady-state equivalent circuits of an IG. The terminal voltage and current responses of fixed-speed and variable-speed IGs with and without the rotor slip changes under different penetration levels are compared to investigate the coupling relation between the short-circuit currents of IGs and the nodal voltages in the distribution network. Then the transient equivalent potential of an IG at the grid fault instant is derived. Sequence components of the short-circuit current in the network can be determined using the proposed technique. The correctness of the proposed method is verified using dynamic simulation.

Comparison of Wireless Power Controllers for Induction Aerogenerators Connected to a Smart Grid Based on GPRS and EGPRS Standards

In recent years, wind plants have undergone major changes due to new technologies developed for smart grids (SG). For its success, it becomes necessary the use of modern information and telecommunication infrastructure with bidirectional data flow. In Brazil, due to the high penetration of data networks based on GSM technology (Global System Mobile), such as GPRS (General Packet Radio Service) and EGPRS (Enhanced GPRS), it has attracted the interest of energy companies to carry out the tasks of measurement, monitoring, and control in SG. The use of cellular technology enables at first a significant reduction in the SG deployment costs while providing reliability and security of the information. In this context, the use of a cellular network for monitoring and control data sharing in intelligent wind farms has recently aroused great interest. This work proposes the analysis of a wireless control system based on GPRS and EGPRS data services for variable-speed squirrel-cage induction generators (SCIG) connected to the power grid. The wireless communication system is employed to send the reference power signals to the SCIG controller with the necessary reliability to ensure the power quality provided by the wind turbine. The performance of the proposed system is evaluated by several simulations and tests.

Fundamental study on aerodynamic force of floating offshore wind turbine with cyclic pitch mechanism

Wind turbines mounted on floating platforms are subjected to completely different and soft foundation properties, rather than onshore wind turbines. Due to the flexibility of their mooring systems, floating offshore wind turbines are susceptible to large oscillations such as aerodynamic force of the wind and hydrodynamic force of the wave, which may compromise their performance and structural stability. This paper focuses on the evaluation of aerodynamic forces depending on suppressing undesired turbine's motion by a rotor thrust control which is controlled by pitch changes with wind tunnel experiments. In this research, the aerodynamic forces of wind turbine are tested at two kinds of pitch control system: steady pitch control and cyclic pitch control. The rotational speed of rotor is controlled by a variable speed generator, which can be measured by the power coefficient. Moment and force acts on model wind turbine are examined by a six-component balance. From cyclic pitch testing, the direction and magnitude of moment can be arbitrarily controlled by cyclic pitch control. Moreover, the fluctuations of thrust coefficient can be controlled by collective pitch control. The results of this analysis will help resolve the fundamental design of suppressing undesired turbine's motion by cyclic pitch control.

Modelling, control and frequency domain analysis of a tidal current conversion system with onshore converters

To optimise a tidal energy conversion system, the operation, maintenance and power generation aspects have to be taken into account. As a result the key focus of this study is to propose and investigate an alternative method of implementing a tidal energy conversion system using a pitch-regulated turbine and a variable-speed squirrel cage induction generator with long distance converters. The generator power output can be optimised by utilising variable-speed control strategies allowing the system to operate at maximum power coefficient while availability can be increased by reducing the components installed offshore by using long three-phase cables between the generator and onshore voltage source converters. The tidal current energy conversion system is investigated by developing a full resource-to-grid model in MATLAB/SIMULINK and by performing system analysis regarding the effects of harmonics in the long subsea cables. Simulation results show that optimised filter design and the choice of suitable operating frequency for the generator controller can minimise the overvoltages associated with the harmonics and the reflecting voltage waves in the cables.

Maximum Power Point Tracking of Hybrid Tidal Current—Supercapacitor Energy Conversion System

This paper proposes control of maximum power tracking system of tidal current energy system. A permanent magnet synchronous generator (PMSG) works as a variable speed generator in the proposed energy system. A controller was applied to achieve the maximum power control of tidal current turbine on a wide range of water current speed change. A dynamic model and simulation of the energy system coupled with current change are presented. The measured DC voltage and DC current are used to determine the position of maximum power point that controls the DC/DC boost converter duty cycle depending on the Hill Climb Search (HCS) algorithm. This algorithm doesn’t require any information or measurements about current’s speed change or generator’s characteristics. A supercapacitor added to fix the load voltage despite of tidal current speed or load variations. Simulation results show the effectiveness of the controller proposed system.

Control design and experimental verification of the brushless doubly‐fed machine for stand‐alone power generation applications

In this study, a control scheme for the stand-alone generation system based on brushless doubly-fed machine (BDFM) is presented. The output voltage amplitude and frequency are kept constant under variable rotor speed and load by regulating the amplitude and frequency of the control winding (CW) current of BDFM appropriately. The control scheme utilises a CW current vector controller as the inner loop, and a power winding voltage amplitude controller and a frequency controller as the outer loop. The proposed control scheme has been implemented on a prototype BDFM designed for the variable-speed stand-alone ship shaft generation application. Moreover, the satisfactory dynamic performance and low total harmonic distortion of the output voltage in the proposed stand-alone generation system is verified by experiments with two kinds of typical loads: three-phase induction motor load and three-phase RL inductive load.

Improved Direct Torque and Reactive Power Control of a Matrix-Converter-Fed Grid-Connected Doubly Fed Induction Generator

Doubly fed induction generator (DFIG) is the most popular variable-speed generator for wind energy application due to its superior performance, lower cost, and control flexibility. Instead of back-to-back converters, matrix converter (MC) can be a good alternative for connecting the DFIG rotor to the grid. This paper presents a novel lookup-table-based hysteresis controller for a variable-speed constant-frequency DFIG supplied from a direct MC. For the machine control, a modified direct torque controller (DTC) with reactive power and speed control in the outer loops has been used. The reactive component of the MC input current has been also controlled using a hysteresis controller considering all active switch states based on estimated input current and load power factor. This upgradation of the input current control switching table reduces the distortion in the grid-supplied current waveform. Overall, the performance of the DFIG with MC is experimentally shown to be superior while using the proposed controller compared with a standard DTC-based control or space-vector-pulsewidth-modulation-based vector control of MC-fed DFIG reported in the literature.

Fault-Tolerant Inverter for Power Flow Control in Variable-Speed Four-Wire Permanent-Magnet Generators

A strategy for fault detection and tolerance on the inverter that controls power flow in variable-speed permanent-magnet generators is proposed in this paper. The performance of the proposed strategy is analyzed in two different four-wire topologies. In the first topology, the neutral point of the generator is connected to the middle point of the dc-link capacitor bank, whereas in the second topology, it is connected to a fourth leg of the inverter. The main contribution of this paper resides in the control scheme, which allows a steady operation through a fault occurrence without the need of reconfiguring neither the inverter topology nor the control algorithm. In this way, transients and the use of extra hardware components are avoided. In addition, a control loop that allows limiting the generator losses at any operation point is presented in order to protect the machine. Finally, experimental results, obtained from a laboratory prototype, validate the practical feasibility of the proposed strategy.

Analysis of Converter Circuits for Switched Reluctance Generator in Wind Energy Conversion Systems

Wind generation is one of the renewable energy power sources that constitute a remedy for greenhouse gas emission treatments. Conventionally various types of wind energy generators such as Induction Generators or Synchronous Generators have been used as wind Generators. The shortcomings of these conventionally used Generators like complex in structure and limited rotor converter rating have turned research attention to more simple and robust variable speed Generator topologies such as Switched Reluctance Generator (SRG). Investigations have proved that this technology is promising due to the new recent advances in the field of variable speed drives. In this research paper, the operation of split DC Power converter required for SRG with even number of phases is discussed along with the operation modes. Then the converter circuit is simulated and the results are presented to gain knowledge about the characteristics of this converter.

Hybrid AC-DC Offshore Wind Power Plant Topology: Optimal Design

The aim of this paper is to present a hybrid AC-DC offshore wind power plant (OWPP) topology and to optimize its design in order to minimize the OWPP's total cost. This hybrid concept is based on clustering wind turbines and connecting each group to an AC/DC power converter installed on a collector platform which is located between the AC wind turbine array and the HVDC offshore platform. Thereby, individual power converters of each wind turbine are not required, since such AC/DC converters can provide variable speed generator control for each cluster. The optimal design for an OWPP based on the hybrid AC-DC topology is formulated as a MINLP problem. The capital costs of each component within the OWPP as well as the costs associated to the inherent losses of this topology are minimized. The optimal number of AC/DC converters and offshore collector platforms needed, as well as their locations, are determined. The cable route connecting the wind turbines between each other is also optimized. The results suggests a good potential for the hybrid AC-DC OWPP topology achieving a total cost saving of 3.76% for the case study compared to the conventional OWPP topology.

Self-Tuning Resonant Control of a Seven-Leg Back-to-Back Converter for Interfacing Variable-Speed Generators to Four-Wire Loads

This paper considers the control of a seven-leg back-to-back voltage source inverter arrangement, feeding a four-wire load from a three-phase permanent-magnet synchronous generator (PMSG) operating at variable speed. The PMSG is controlled using a sensorless model reference adaptive system to obtain the rotor position angle. The seven-leg converter is regulated using resonant controllers at the load side and self-tuning resonant controllers at the generator side. The control system is augmented by a feedforward compensation algorithm that improves the dynamic performance during transients. Experimental results, which are obtained from a prototype, are presented and discussed.