Optimal efficiency analysis of induction motors fed byvariable-voltage and variable-frequency source

The authors discuss the efficiency analysis and experimental data for an induction motor fed by a variable-voltage and variable-frequency (VVVF) source. Nonideal factors (core saturation, source harmonics, and skin effect) affecting the efficiency are included in the analysis to yield practical results from computer simulation. Based on the simulated results, an experimental system, composed of a DC link power converter with a VVVF feature, a dynamometer and a PC/AT, was developed to evaluate the efficiencies of the induction motor from low to rated speed and torque. Both analysis and experimental results indicate that the efficiency with VVVF is superior to that of constant flux operation. Experimental results showed that 10-15% improvement in the efficiency of a 2 hp induction motor at 0.4 per unit load using VVVF can be achieved as compared to the constant flux operation     

Optimization of a photovoltaic pumping system based on the optimal control theory

This paper suggests how an optimal operation of a photovoltaic pumping system based on an induction motor driving a centrifugal pump can be realized. The optimization problem consists in maximizing the daily pumped water quantity via the optimization of the motor efficiency for every operation point. The proposed structure allows at the same time the minimization the machine losses, the field oriented control and the maximum power tracking of the photovoltaic array. This will be attained based on multi-input and multi-output optimal regulator theory. The effectiveness of the proposed algorithm is described by simulation and the obtained results are compared to those of a system working with a constant air gap flux.     

Optimization of single-phase induction motors-part II: magnetic and torque performance under optimal control

The magnetic and torque performance of a capacitor-run single-phase induction motor operated at constant torque under the optimal efficiency control, as presented in Part I, is analyzed. The magnetic field analysis demonstrates that magnetic saturation is considerably decreased with optimal efficiency control. Although triac-based optimal voltage controller introduces voltage and current harmonics, torque pulsations and acoustic noise are reduced due to magnetic flux weakening. The reduction of torque pulsations and acoustic noise is considerable in the low torque region where significant energy savings are also achieved. Selected calculated and experimental results are presented to validate the theoretical considerations and the resulting improvements.     

Design of an integrated propulsion, guidance, and levitation system by magnetically excited transverse flux linear motor (TFM-LM)

A magnetically levitated vehicle dedicated for transportation systems requires propulsion, guidance, and levitation forces. The components used to generate these forces, such as linear motors and magnets, must have less mass especially because the magnetically levitated vehicle has to carry its own linear motor and magnet. In this paper, an integrated propulsion, guidance, and levitation system by magnetically excited transverse flux linear motor (TFM-LM) with high force and high efficiency is introduced. Analytical equations with one-dimensional magnetic equivalent circuit are developed to predict the propulsion force and to guide the design of TFM-LM. A three-dimensional (3-D) finite-element (FE) program calculates the propulsion force, the guidance force, and the levitation force of TFM-LM also, in order to verify the given specification. To verify the results of 3-D FE calculation, the computed propulsion force, guidance force, and levitation force are compared with the experimentally measured forces detected on the experimental setup. The calculated and measured performances of TFM-LM reveal a high potential of mass reduction for magnetic-levitated vehicles.     

Solar powered induction motor-driven water pump operating on a desert well, simulation and field tests

A photovoltaic-powered water pumping system, employing an induction motor pump, capable of supplying a daily average of 50 m³ at 37-m head has been developed. The system was installed on a desert well in Jordan, where: the average solar radiation amount to 5.5 kW h/m³/day, to provide the Bedouins living in the well area with drinking water.A mathematical model to enable testing the system performance by computer simulation was developed. This model allows the representation of motor torque in function of speed (and slip) at different supply frequencies, as well as the flow rate and efficiency of the system in function of supply frequency and pumping head.Prior to its installation on the desert well, the system performance, in accordance with frequency and head, was thoroughly tested in the laboratory. As illustrated in this paper, simulation and laboratory testing results are well matched. At constant pumping head, the flow rate is proportional to the supply frequency of the motor. At constant flow rate, the pumping head is proportional to the supply frequency squared only in the range below the peak efficiency of the pump. For higher flow rate values, a special algorithm based on the experimental results could be developed.Higher system efficiency is achievable at higher frequency. It is advisable to operate the motor pump at the nominal frequency, flow rate and head corresponding to maximum efficiency.Long-term field testing of the system shows that it is reliable and has an overall efficiency exceeding 3%, which is comparable to the highest efficiencies reported elsewhere for solar powered pumps.     

Optimization of Three-Phase Induction Motor Design Part I: Formulation of the Optimization Technique

This two-part paper deals with the optimization of the induction motor designs with respect to cost and efficiency. Most studies on the design of an induction motor using optimization techniques are concerned with the minimization of the motor cost and describe the optimization technique that was employed, giving the results of a single (or several) optimal design(s). In the present paper, a more comprehensive study on the optimization of a three-phase induction motor design was performed. This includes the relationship between motor cost, efficiency, and power factor; the effect of the properties of the electrical steel; and other effects as they occur in an optimal design. In addition, the optimization procedure that was used in this paper includes a design program, where some of the secondary parameters (which are called here variable constants), are modified according to the optimal results, in contrast to other studies where these parameters remain constant for the entire optimization. In this part, a new mathematical formulation of the optimization problem of the induction motor is presented.     

Sensorless scalar-controlled induction motor drives with modified flux observer

This paper presents a simple sensorless scalar control algorithm to control the speed of an induction motor. First, a modified flux observer was employed to estimate the stator flux with the voltage command and the feedback current. Then, based on the mathematical model of the induction motor, the slip frequency was calculated, and the frequency of the voltage command was compensated. An auto-boost controller was designed to overcome the decrease in voltages of the stator resistance and to maintain constant stator flux amplitude. To improve the pure integration problem, a highpass filter was installed in the stator flux observer. In this filter, the cut-off frequency is proportional to the voltage frequency; therefore, the phase shift and amplitude degradation of the estimated flux can be corrected easily. Finally, to demonstrate the proposed control algorithm, a PC-based experimental system was constructed in a 1-hp induction motor. Experimental results are presented to validate the effectiveness of our design.     

An improved efficiency of fuzzy sliding mode control of permanent magnet synchronous motor for wind turbine generator pumping system

This paper presents an analysis by which the dynamic performances of a permanent magnet synchronous motor (PMSM) motor is controlled through a hysteresis current loop and an outer speed loop with different controllers. The dynamics of the wind turbine pumping drive system with (PI) and a fuzzy sliding mode (FSM) speed controllers are presented. In order to optimize the overall system efficiency, a maximum power point tracker is also used. Simulation is carried out by formatting the mathematical model for wind turbine generator, motor and pump load. The results for such complicated and nonlinear system, with fuzzy sliding mode speed controller show improvement in transient response of the PMSM drive over conventional PI. The effectiveness of the FSM controller is also demonstrated.     

Performance of interior permanent magnet motor drive over widespeed range

This paper investigates the performance of an interior permanent magnet synchronous motor (IPMSM) drive over wide speed range for high precision industrial applications. The scheme incorporates the maximum torque per ampere (MTPA) operation in constant torque region and the flux-weakening operation in constant power region in order to expand the operating limits for an IPMSM. Improved mathematical expressions are derived to analyze the performances of the IPMSM. The power ratings of the motor and the inverter are considered. The effects of motor parameters particularly, the saliency ratio (X_q/X_d) on the voltage limit constraint and the power capability of the inverter are also investigated. The efficacy of the above mentioned drive system and the improved steady-state analysis are evaluated by both experimental and computer simulation results. The complete drive is implemented in real-time using digital signal processor (DSP) controller board DS 1102 on a laboratory 1 hp interior permanent magnet synchronous motor     

Induction motor dynamic and static inductance identification usinga broadband excitation technique

The performance of indirect vector control depends upon accurate prediction of the motor slip angular frequency (ω_s) for the demand torque. The required slip gain depends upon the rotor time constant of the motor (T_r). This value varies significantly over the operating temperature range and saturation level of a typical motor. This variation, if not compensated for, results in a significant degradation in torque production from a vector control system. The saturation effect can be compensated by an adaptive flux model if precise knowledge of the induction motor magnetizing curve is available. The aim of this paper is to present the application of an advanced system identification methodology enabling the off-line estimation of the magnetizing curve (dynamic and static inductance) of induction motors     

Research on melting and solidification processes for enhanced double tubes with constant wall temperature/wall heat flux

Latent heat thermal energy storage (LHTES) improves the energy utilization efficiency between energy supply and energy demand of heating storage in buildings and liquid desiccant air conditioning systems. The present work is focused on validated numerical investigation of the thermal performances of LHTES inside enhanced double tubes. The effects of the number of fins ranging from 2 to 10 and boundary conditions of the inner tube wall on the melting and solidification processes are examined. The results indicate that number of fins and wall boundary conditions play an important role in the thermal performances of LHTES. It is noted that recirculation flow in the liquid phase change material region is formed remarkably. The enhancement ratio for constant wall temperature is more significant than that of constant wall heat flux during the melting process. However, the discrepancy of the enhancement ratio for different inner wall temperatures is limited during the solidification process.     

Robust SVM-direct torque control of induction motor based on sliding mode controller and sliding mode observer

This paper proposes a design of control and estimation strategy for induction motor based on the variable structure approach. It describes a coupling of sliding mode direct torque control (DTC) with sliding mode flux and speed observer. This algorithm uses direct torque control basics and the sliding mode approach. A robust electromagnetic torque and flux controllers are designed to overcome the conventional SVM-DTC drawbacks and to ensure fast response and full reference tracking with desired dynamic behavior and low ripple level. The sliding mode controller is used to generate reference voltages in stationary frame and give them to the controlled motor after modulation by a space vector modulation (SVM) inverter. The second aim of this paper is to design a sliding mode speed/flux observer which can improve the control performances by using a sensorless algorithm to get an accurate estimation, and consequently, increase the reliability of the system and decrease the cost of using sensors. The effectiveness of the whole composed control algorithm is investigated in different robustness tests with simulation using Matlab/Simulink and verified by real time experimental implementation based on dS pace 1104 board.     

Core loss in buried magnet permanent magnet synchronous motors

The steady-state core-loss characteristics of buried-magnet synchronous motors operating from a sinusoidal constant frequency voltage supply are investigated. Measured and calculated core loss, with constant shaft load, is shown to increase with decreasing terminal voltage due to an increase in armature reaction-induced stator flux-density time harmonics. Finite-element modeling is used to show that the additional loss due to the time-harmonic fields can increase core loss by a factor of six over the loss associated with only the fundamental component field at low motor flux levels. A simple air-gap model of motor flux components shows that this increased loss is due to localized rotor saturation. Thus, stator-core harmonic fields should be expected for all buried-magnet rotor synchronous motors (with or without a cage) operating at low flux levels. This factor becomes increasingly important when the motors are operated in the high-speed low-flux mode in conjunction with a variable-speed drive     

Speed and efficiency control of an induction motor withinput-output linearization

A combination of a composite adaptive speed controller and an explicit efficiency control algorithm is proposed to control the speed and power efficiency of the induction motor in this paper. First, the input-output linearization method is used to dynamically decouple the motor speed and rotor flux. Then, a composite adaptive control algorithm is designed to control the speed of the induction motor. At steady-state light-load condition, the magnetizing current command is adjusted on the basis of the product of magnetizing current command and torque current command such that the steady-state power loss is minimum. A PC-based experimental drive system has been implemented, and some experimental results are provided to demonstrate the effectiveness of the presented approach     

Analysis and evaluation of hybrid scooter transmission systems

This paper presents a new design concept of transmissions for the hybrid scooters. These transmissions consist of a one-degree-of-freedom planetary gear train and a two-degree-of-freedom planetary gear train to from a split power system and to combine the power of two power sources, a gasoline engine and an electric motor. In order to maximize the performance and reduce emissions, the transmissions can provide a hybrid scooter to run five operating modes: electric motor mode; engine mode; engine/charging mode; power mode, and regenerative braking mode. The main advantages of the transmissions proposed in this paper include the use of only one electric motor/generator, need not use clutch/brake for the shift of the operating modes, and high efficiency. The kinematics, power flow, and mechanical efficiency analyzes are performed; and according to these results, the evaluation of transmission power performances are accomplished.     

Analysis of flux distribution and core losses in interior permanentmagnet motor

The interior permanent magnet (IPM) motor with its robust rotor construction, hybrid torque production nature and flux-weakening capability is suitable for electric vehicle applications when wide speed and torque range is required. At high-speed operations, core losses become an important issue because they affect efficiency and raise operating temperatures. This paper discusses the results of two-dimensional finite element analysis into the relationship between flux distribution and core losses in the IPM motor. The analysis is further supported by flux measurements using search coils installed in an experimental motor. Three methods of predicting the core losses in IPM motor are also investigated. These methods are the empirical formula method, finite element computed waveform method and the search coil induced voltage method     

An efficient high performance voltage decoupled induction motordrive with excitation control

The state of the art in indirect slip frequency-controlled induction motor drive systems is fast response, high performance, voltage decoupling control. However, decoupling control needs to operate at a constant rotor flux, which makes energy conversion inefficient. A variable-flux decoupling model of a voltage-fed induction motor which provides optimal efficiency and quick response is proposed. An optimization scheme determines the flux level for maximum efficiency at any operating condition, and a coordination controller assures quick torque response without torque pulsations. Application to a 100 hp and a 7.5 hp motor shows that a substantial saving in controllable losses during low-load operation is possible while maintaining high performance     

Speed control of a three-phase induction motor based on robust optimal preview control theory

A synthesized method for speed control of a three-phase induction motor (IM) based on optimal preview control system theory is implemented in this article. An IM model comprises three-input variables and three-output variables that coincide with the synchronous reference frame that is implemented using the vector method. The input variables of this model are the stator angular frequency and the two components of the stator space voltage vector, whereas the output variables are the rotor angular speed and the two components of the stator space flux linkage. The objective of the synthesized control system is to achieve motor speed control, field orientation control, and constant flux control. A novel error system is derived and introduced into the control law to increase the robustness of the system. The preview feed-forward controller, which includes the desired and disturbance signals, is used to improve the transient response of the system. A space vector pulse-width modulation (PWM) control technique for voltage source-fed IM is prepared for microprocessor-based control. Spectral analysis of the output voltage is evaluated to predict the effect of the proposed space vector modulation technique on the dynamic performance of the IM. The optimal preview controlled system is implemented, and its applicability and robustness are demonstrated by computer simulation and experimental results.     

基于动态透平效率的有机朗肯循环性能分析及优化

常规有机朗肯循环(ORC)中透平效率多假设为定值,而实际上透平效率因工质种类和运行参数的不同而有较大差异。因此,采用向心透平效率计算模型,将动态透平效率与ORC系统耦合,分析透平效率随蒸发温度与冷凝温度的变化规律,比较固定透平效率与动态透平效率ORC系统热效率的差异。综合考虑热力性与经济性,采用多目标优化算法,对固定透平效率与动态透平效率ORC系统进行工质筛选及参数优化,并对优化结果进行分析比较。结果表明:透平效率随蒸发温度的下降或者冷凝温度升高而增大;不同工质及不同蒸发冷凝温度条件下,透平效率差异较大,最大达0.148。固定透平效率ORC系统与动态透平效率ORC系统的热效率随蒸发温度的变化规律有较大差异,尤其在高蒸发温度区间更为明显。对于固定透平效率ORC系统,R245ca和R236ea为最佳工质;而对于动态透平效率ORC系统,R114为最佳工质。在引入动态透平效率前后,各工质的最佳蒸发温度与最佳冷凝温度也有较大变化。     

A rotor-flux-observer-based composite adaptive speed controller foran induction motor

A composite adaptive speed controller for an induction motor based on a rotor-flux-observer is proposed in this paper. The rotor flux is estimated with the simplified rotor-flux-observer on the rotor reference frame and the input-output linearization theory is used to decouple the motor speed and the rotor flux. Then, the composite adaptive algorithm is used as the speed controller of the induction motor drive. The resulting system is verified to be stable. Some experimental results are provided to demonstrate the effectiveness of the proposed adaptive controller. Good speed tracking and load regulating responses can be obtained by the proposed composite adaptive controller. Moreover, the system can be operated in a wide range of speed and is robust to parameter variations