Chai Jianyun

A novel position sensor-less control scheme of Doubly Fed Induction Wind Generator based on MRAS method

This paper presents a novel position sensor-less method based on model reference adaptive system (MRAS) for the control of variable speed constant frequency (VSCF) doubly fed induction generator (DFIG). In this method the components of the stator flux in stationary reference coordinates are used for both reference and adjustable models. The reference model is given by stator equations with flux as the outputs while the rotor equations are used for adjustable model to calculate the stator flux by using rotor quantities such as rotor currents, position and flux. In order to get the accurate rotor flux of the adjustable model, a modified integrator has been used. No stator current sensors are used in the proposed position and speed estimation method, therefore it can reduce the costs and improve the control system reliability compared with other position sensor-less methods. The proposed control method has been experimentally verified on a 7.5 kW DFIG system using back-to-back converter. The experimental results show that good performance has been obtained with proposed position sensor-less control method.

A nonlinear analytical model for switched reluctance motor

This paper presents a simplified nonlinear model for the switched reluctance motors (SRM), which uses the fundamental mathematical functions to describe the saturation of the flux linkage depending on the winding current and rotor position. The model requires a minimum of pre-calculated or measured input data. Therefore, it is convenient for use in earlier stage of SRM design in order to minimize the design and analysis time. Moreover, the simulation results show that the analytical model can obtain the accurate flux linkage-current relationships.

A Variable Pole Pitch Linear Induction Motor for Electromagnetic Aircraft Launch System

A variable pole pitch linear induction motor (VPPLIM) is proposed as a new member of the family of electromagnetic aircraft launch system (EMALS). With proper designing of the variation of the pole pitch, the VPPLIM could accelerate the aircraft almost uniformly at the condition of the usual ac supply, avoiding the use of large-scale power electronic converters. Special considerations in the design of VPPLIM, such as the structure topology, the variation of the pole pitch, and the winding arrangement are discussed in detail in this paper. The acceleration performance of the VPPLIM fed by a constant-voltage constant-frequency supply is analyzed by means of the quasi-steady-state 2-D magnetic field model and the difference model of movers dynamics. A two-stage method is proposed to simulate the acceleration performance of the VPPLIM based on a 2-D thrust table of the motor achieved by the finite-element method. The calculated features of the prototype VPPLIM consist well with those expected for EMALS.

Speed sensor-less control of an induction machine with rotor flux tracking at very low speed

This paper presents a novel method to estimate the rotor flux position of an induction machine by injecting a high frequency signal at very low speed, including zero speed. When the high frequency fluctuating signal is injected in the terminal of an induction machine, the difference of impedance between the d-axis and q-axis of the synchronous rotating reference frame can be measured. This phenomenon is explained by a high frequency model of the induction machine, which is oriented with a high frequency signal space vector. The rotor flux angle can thus be tracked by tuning the space vector of the high frequency signal. Experimental results are provided to verify that this algorithm is robust against parameters variations and load changes.

A new ripple-free torque brushless DC motor without requirement for square-shape magnet flux distribution

A new structure of the brushless DC motor with ripple-free torque performance is first proposed. The steady torque of the motor is guaranteed even if the shape of rotor magnet flux distribution is arbitrary. It adopts 180/spl deg/ square-wave current and 120/spl deg/ or less flux distribution. The reason of torque ripple in conventional square-shape brushless DC motor is presented. The theoretic proof of ripple-free performance of torque in novel brushless DC motor is given under commutating and noncommutating stage. The principle of novel motor design including one tooth pitch skewed slot in stator and method for decrease the 60/spl deg/ residual magnet flux is given, the influence to effective width of uniform current density by skewed slot is analyzed. Serial connected and parallel connected power circuit topology is discussed. The experiment comparison between novel and conventional brushless DC motor is investigated. Experimental results verify that the output torque is constant in noncommutating stage. The method to decrease current fluctuating caused by commutation is given.

A novel linear induction motor for electromagnetic aircraft launch system

A variable pole pitch linear induction motor (VPPLIM) is proposed as a new member of the family of electromagnetic aircraft launch system (EMALS). With proper designing of the variation of the pole pitch, the VPPLIM could accelerate the aircraft almost uniformly at the condition of usual AC supply, avoiding use of large scale power electronics converters. The special considerations in the design of VPPLIM, such as the structure topology and the variation of the pole pitch are discussed detailedly in the paper. The acceleration performance of the VPPLIM fed by a constant voltage constant frequency supply is analyzed by means of the quasi-steady-state 2D magnetic field model and the difference model of movers dynamics. A two stage method is proposed to simulate the acceleration performance of the VPPLIM based on a 2D thrust table of the motor achieved by finite element method (FEM). The calculated features of the prototype VPPLIM consist well with those expected for EMALS.

A method of speed observation based on least-squares linear-fitting with weight factor

In industry application, the speed usually has to be observed with the position signal. But the position signal noises have been analyzed and modeled rarely. In this paper, by analyzing the characteristics of the position noises, white noise of uniform distribution model and the triangle wave noise model are proposed. The two models can be used to evaluate the influence of position measurement noises on the observed speed. Among the speed observation methods, the methods based on model predicted error can be used to observe the speed faster, due to the use of some priori knowledge. But these methods cannot be suitable for the case when the accurate model parameters cannot be obtained. Though the IIR filter has better low-pass filtering characteristic, it does not have linear phase and the stability is also a potential problem. There are not such drawbacks mentioned above for the FIR filter. The least-squares linear-fitting with weight factor speed observer based on position signal, which is a FIR filter essentially, is proposed in this paper. Compared with the direct differentiator, the wider bandwidth and smaller the maximum amplitude of speed fluctuation are validated by simulation results and experimental results.