Dynamic simulation of brushless doubly-fed machines

Dynamic and steady-state models for the simulation of the performance of experimental brushless doubly-fed machines (BDFM) are presented. The dynamic simulation results are obtained using a two-axis representation which has been developed from a detailed machine design model. In turn, it is shown that several forms of steady-state equivalent circuit can be developed from the two-axis model for different specific modes of operation. Test data in dynamic conditions are compared with the predictions given by the two-axis model. It is concluded that these simplified models will provide adequate representation of full performance for control, stability, and scoping studies     

无刷双馈风力发电机滑模功率解耦控制

首次采用现代控制理论中的滑模变结构方法研究了无刷双馈发电机(BDFM)运行时有功功率与无功功率的解耦控制,在状态方程的基础上,应用Lyapunov函数求得了有功功率与无功功率的滑模控制律,并在Matlab/Simu-link基础上建立了系统的仿真模型。仿真结果表明,滑模变结构控制能够有效的实现有功功率与无功功率的解耦控制,并实现了风能的最大功率捕获,证明了该控制策略的有效性。     

A novel finite-element transient computation of two-axis parametersof solid-rotor generators for use in power systems

An original finite element method for calculating the two-axis transient parameters of solid rotor turbine-generators is presented. Eddy current effects are lumped into equivalent damper circuits, representing layers of massive conductors within the rotor. The time variation of machine parameters of a two-axis model is determined and the equivalent circuits obtained are tested by comparing the two-axis and finite element simulations. The two-axis equivalent circuits can simulate a wide range of operating conditions, with appropriate modification of the magnetizing inductances     

基于反馈线性化的无刷双馈电机模型预测控制策略

提出一种无刷双馈电机(BDFM)基于反馈线性化的模型预测控制策略。基于BDFM状态空间方程,在控制电机磁场定向同步坐标系下,采用输入输出反馈线性化将BDFM转化为线性系统并证明系统稳定性,以此为基础计算系统预测值,根据BDFM离散预测模型,设计模型预测控制器,实现电磁转矩和控制侧电机磁链的独立控制。仿真试验结果证明该控制器具有优良的控制性能,能够实现平滑控制和系统解耦。     

Power balance considerations for brushless doubly-fed machines

This paper discusses the power balances in a brushless doubly-fed machine (BDFM). Equations of power in the two stator windings and the rotor circuit, showing the distribution of electrical and mechanical powers in the air-gap, are obtained in two different speed ranges of BDFM synchronous mode operation. Comparisons vis-a-vis power distribution are made between the wound-rotor induction machine (WRIM) and the BDFM. A brief analysis of the power balances, along with experimental data points obtained using a laboratory prototype machine, are given     

Characteristics and Performance Analysis of a Permanent-Magnet Motor with a Multistacked Imbricated Rotor

The paper studies the parameters and performance of a motor with a multistacked imbricated permanent magnet rotor. An experimental motor with ferrites for excitation is used in the investigation. Methods used in the determination of the parameters, Xd, Xq and the core-loss component, Rc, are described. Their variation with load and terminal voltage are also discussed. These parameters are applied in a model based on the classical two-axis machine theory for performance analysis. Detailed investigation shows that the reactance characteristics under steady-state conditions are similar to a wound rotor machine. Computed results using these values of Xd, Xq and Rc show agreement with experimental results. The significance of Rc is noted.     

无刷双馈风力发电机组的自抗扰功率解耦控制

对无刷双馈风力发电机组稳态运行时的功率分配关系进行了详细分析,在此基础上确定了最大风能捕获的控制策略.将自抗扰控制应用到无刷双馈电机有功功率与无功功率的解耦控制,将功率控制系统分解为有功功率子系统和无功功率子系统,从而建立了风力发电机组完整的功率控制模型.基于Matlab/Simulink的仿真结果表明无刷双馈风力发电机组自抗扰控制成功实现了有功功率与无功功率的解耦控制,不仅能够实现最大风能捕获,而且可以根据电网的实际需求调节机组无功功率的输出,验证了控制算法的有效性.     

Calculation of two-axis induction motor model parameters usingfinite elements

The paper presents the use of the finite element method for determining the parameters of a two-axis model of a three-phase cage induction machine. The model parameters are obtained from the finite element field solutions. The saturation of the motor is taken into account in calculation of the flux distribution by using a static nonlinear vector potential solution. The linear time harmonic vector potential field solution is used for the inductances determination. All the inductances are determined as functions of the magnetizing current. Rotor skew is also taken into account. The accuracy of the described identification procedure is verified through laboratory measurements of the parameters     

Coupled finite-element/state-space modeling of turbogenerators inthe abc frame of reference-the short-circuit and load cases includingsaturated parameters

In this paper, a coupled finite-element/state space modeling technique is applied in the determination of the steady-state parameters of a 733 MVA turbogenerator in the abc frame of reference. In this modeling environment, the forward rotor stepping-finite element procedure described in a companion paper is used to obtain the various machine self and mutual inductances under short-circuit and load conditions. A fourth-order state-space model of the armature and field winding flux linkages in the abc frame of reference is then used to obtain the next set of flux linkages and forcing function currents for the finite-element model. In this process, one iterates between the finite-element and state-space techniques until the terminal conditions converge to specified values. This method is applied to the determination of the short-circuit, and reduced- and rated-voltage load characteristics, and the corresponding machine inductances. The spatial harmonics of these inductances are analyzed via Fourier analysis to reveal the impact of machine geometry and stator-to-rotor relative motion, winding layout, magnetic saturation, and other effects. In the full-load infinite-bus case, it is found that, while the three-phase terminal voltages are pure sinusoidal waveforms, the steady-state armature phase currents are nonsinusoidal and contain a substantial amount of odd harmonics which cannot be obtained using the traditional two-axis analysis     

无刷双馈风力发电机的自抗扰解耦控制

针对无刷双馈电机(BDFM)结构的复杂性、随环境的可改变性及传统的PID控制在BDFM中应用不理想等,提出了一种新型基于扩张观测器的非线性PID控制——自抗扰控制方法来实现对风力发电系统有功功率和无功功率的解耦控制。仿真结果证明了该方法的正确性和有效性,具有更强的鲁棒性和可实现性。     

A machine winding model for switching transient studies using network synthesis

This paper describes a computer model for calculating the surge propagation in the winding of electrical machines. The model considers the winding as a combination of a multiconductor transmission line and a network of lumped parameters. The frequency dependence of the winding electrical parameters is calculated and incorporated into the analysis by means of Foster and Cauer circuits. The multiconductor transmission line provides the surge propagation characteristics for the winding model and its parameters are calculated from machine design characteristics. Finally, this hybrid model is validated by a comparison of calculated and measured results inside a high-voltage machine winding.     

Modeling and simulation of an integrated steam reforming and nuclear heat system

In this study, a dynamic and two-dimensional model for a steam methane reforming process integrated with nuclear heat production is developed. The model is based on first principles and considers the conservation of mass, momentum and energy within the system. The model is multi-scale, considering both bulk gas effects as well as spatial differences within the catalyst particles. Very few model parameters need to be fit based on the design specifications reported in the literature. The resulting model fits the reported design conditions of two separate pilot-scale studies (ranging from 0.4 to 10 MW heat transfer duty). A sensitivity analysis indicated that disturbances in the helium feed conditions significantly affect the system, but the overall system performance only changes slightly even for the large changes in the value of the most uncertain parameters.     

Effective identification of induction motor parameters based onfewer measurements

This paper applies genetic algorithms (GAs) to the problem of parameter identification for field orientation control (FOC) induction motors. Kron's two-axis dynamic model in per-unit system is given, and the model's parameters are estimated by a GA using the motor's dynamic response to a direct on line start. Results with different levels of measurement noise are presented for the model both in the per-unit system and in actual values. For comparison, the results of a simple random search (SRS) method under the same condition are also given. The results show that the parameter identification accuracy, the convergence speed and the practicality of the algorithm have been improved significantly by use of the model in the per-unit system. The results also show that fewer measurements are required to identify the induction motor parameters accurately     

Conventional hybrid photovoltaic/thermal (PV/T) air heating collectors: steady-state simulation

This investigation is concerned with the performance analysis of a conventional hybrid photovoltaic/thermal air heating collector. A simulation model is developed and various performance parameters are calculated for single-glass and double-glass configurations. Results are presented to show the effect of various design and operational parameters on the performance of a system. These results are useful for designing such systems more scientifically. However, final selection of design and operational variables must be based on the cost-effectiveness of the system.     

Speed-sensorless torque control of induction machine based on carrier signal injection and smooth-air-gap induction machine model

A speed-estimation technique for induction machines, based on carrier signal injection and the standard two-axis smooth-air-gap induction machine model, is presented. The proposed speed-estimation technique can work over a wide range of operating points, including fundamental dc excitation. The stability of the algorithm is analyzed using a two-time-scale approach. Based on the estimated rotor speed, a torque controller is designed. Experimental results are presented confirming the validity of this approach. A method to reduce torque ripple generated by the injected carrier signals is also introduced.     

Stability of doubly-fed induction generator under stator voltage orientated vector control

The stability of a doubly-fed induction generator (DFIG) under vector control in stator voltage orientation (SVO) is investigated. Prior art has tended to assume that the inner current loop dynamics can be neglected when an SVO is employed. As a result, the poorly damped poles of the DFIG system were considered unaffected by the inner current loop tuning. The state-space model of the machine including the inner current closed loop dynamics is developed for schemes where different feed-forward compensation terms are used. The interaction between inner current loop dynamics and damping of the critical poles of the system is illustrated through analysis and simulation. The main outcome of the analysis is that the stability of the machine system in an SVO depends solely on the parameters of the proportional-integral controllers. Erroneous tuning can lead to instability, irrespective of the particular feed-forward compensation scheme, which could cause the disconnection of the machine as a result of rotor current oscillations of unacceptable magnitude in an actual case. The main contribution is to provide the necessary methodology in order to ensure the stable operation of a DFIG under SVO vector control.     

Multiple reference frame analysis of a multistack:variable-reluctance stepper motor

A multistack variable-reluctance stepper motor is analyzed using the concept of multiple reference frames. The average-value model developed is shown to approximately predict steady-state and dynamic operation of this device. Moreover, the state variables of this model are constant in the steady state. Therefore, the differential equations which describe this model can be linearized whereupon an eigenvalue analysis can be used to investigate dynamic instabilities. It is shown that this approach can be used to approximately predict the occurrence of parametric instability which heretofore has not been achieved using an eigenvalue analysis. The average-value model established in this paper should serve as a unique tool to aid in the design of the machine as well as the controls associated with the electronic drive system     

Experimental investigations of a small-scale solar-assisted absorption cooling system

The present study deals with a small-scale solar-assisted absorption cooling system having a cooling capacity of 3.52 kW and was investigated experimentally under the climatic conditions of Taxila, Pakistan. Initially, a mathematical model was developed for LiBr/H₂O vapor absorption system alongside flat-plate solar thermal collectors to achieve the required operating temperature range of 75°C. Following this, a parametric analysis of the whole system was performed, including various design and climate parameters, such as the working temperatures of the generator, evaporator, condenser, absorber, mass flow rate, and coefficient of performance (COP) of the system. An experimental setup was coupled with solar collectors and instruments to get hot water using solar energy and measurements of main parameters for real-time performance assessment. From the results obtained, it was revealed that the maximum average COP of the system achieved was 0.70, and the maximum outlet temperature from solar thermal collectors was 75°C. A sensitivity analysis was performed to validate the potential of the absorption machine in the seasonal cooling demand. An economic valuation was accomplished based on the current cost of conventional cooling systems. It was established that the solar cooling system is economical only when shared with domestic water heating.     

Transient thermal analysis of induction motors

Induction machines transient thermal analysis has been a subject of interest for electric machine designers in their effort to improve machine reliability and in rotor design optimisation. The study of transient thermal behavior is useful to identify causes of failure in induction machines. This paper presents a 2-D transient analysis of induction machines using the available heat transfer coefficients in literature. A generalised finite element code developed with Galerkin's weighted residual technique is used for analysis. The model is applied to one squirrel-cage totally-enclosed fan cooled machine of 3.7 kW and another surface cooled machine of 5.7 kW. The predicted temperatures compare well with test results. The advantages and limitations of this model are discussed     

A generalized computer-aided formulation for the dynamic and steadystate analysis of induction machine inverter drive systems

A generalized formulation for the computer-aided analysis of induction machine drives including feedback controls is presented. A simple circuit model for the induction machine is developed to enhance the conventional drive formulation. This model eliminates a general difficulty encountered in the automatic formulation of machine dq -terminal constraints imposed by the drive operations. An efficient algorithm is proposed using a simple nodal approach for automatic formulation of power electronic circuits. This algorithm, combined with the proposed machine circuit model, can easily be used to simulate an arbitrarily configured drive system including the effects of control dynamics. A pulse-width-modulated current-source-inverter drive system is employed to demonstrate the efficiency of the proposed formulation. The dynamic and steady-state performance of this drive system including an effective harmonic control are simulated. The simulated results are experimentally verified