Salient-pole Synchronous Motor Research Articles

Experience with standstill frequency response (SSFR) testing and analysis of salient pole synchronous machines

Standstill frequency response (SSFR) testing and analysis of salient pole synchronous generators and motors performed by the members of the Working Group are summarized. The papers presented in a panel session at the 1997 Winter Power Meeting are condensed into this paper for the benefit of future researchers. The pertinent features of SSFR testing and analysis of salient pole machines are described to point out the differences from those of round rotor turbogenerators extensively published in the literature.

Model Description Method of AC Motors Using 3×3 Balanced Circular Matrices

This paper presents a new model description method for AC motors such as salient-pole synchronous motor, synchronous reluctance motor and induction motor. The method uses specific 3×3 balanced circular matrices together with 3×l balanced vector signals. It does not require concept of rotational orthogonal coordinates but has the same vector description form as the orthogonal coordinates. The method is useful for easy comprehension of motor dynamics especially by students and engineering-beginners.

Sensorless torque control of salient-pole synchronous motor at zero-speed operation

A position and speed sensorless control using the counter electromotive force of a permanent-magnet motor (PM) debases the control performance at a low speed. We propose a controllable system at full speed, including a zero speed using saliency. At low speed, the sensorless control is made by observing a current ripple at a time when alternating voltage has been applied to a salient-pole motor. Also, for discriminating the S and N poles of the magnet, magnetic saturation is used. A device has been applied to the motor rotor to allow the magnetic saturation to come about easily. Furthermore, at a time of high speed, drive at a full-speed range has been accomplished by switching smoothly over to a sensorless driving system making use of counter electromotive force. All algorithms are implemented by software, and this system can operate successively from starting to high-speed operation. The paper discusses the operational principles at a low speed, analysis and experimental results, the control scheme, how to changeover the control mode at high speed, and the experimental results.

Prediction of starting performance of synchronous motor by DC decay testing method with the rotor in any arbitrary position

This paper presents a novel method to predict the starting performance of synchronous motors. This proposed strategy is based on a simple standstill response testing method using a small-capacity DC power supply unit, tentatively named the DC decay testing method in this paper, and can be applied to standstill synchronous motors with the rotor in any arbitrary position. The proposed testing method is carried out on a 10 kW, 200 V, 31.9 A, 50 Hz four-pole laminated salient-pole synchronous motor with damper windings. The results measured by on-load test and those predicted by the proposed method on starting performance clearly show the validity of the proposed method.

Variation of Saturated Reactances of a Salient-Pole Synchronous Motor in the Field-Weakening Region

In this paper we present a method for calculating saturated reactances of salient-pole synchronous machines and calculate variations of reactances of a vector-controlled salient-pole synchronous motor using the method. We also consider the causes of the variations of reactances.The proposed method uses two-dimensional numerical magnetic field analysis and revised dq-axis equations in which the effect of the cross-magnetizing phenomenon is included. The values of the field currents calculated with the method show good agreement with the measured values.The method is used to calculate and analyze the reactances of the vector-controlled motor at various load points. The findings are as follows.(1) Numerical values of the mutual reactances between d- and q-axis xdq, xfq are not negligible.(2) Variations of the armature leakage reactance xl and the field leakage reactance xlf in the field-weakening region are considerable despite the small main magnetic flux.(3) The main cause of the variation of xl, xlf is saturation at the pole tips. This saturation occurs because of the difference between the armature m. m. f. distribution and the field m. m. f. distribution.

Experimental nonlinear torque control of a permanent-magnet synchronous motor using saliency

In this paper, a new nonlinear control strategy is proposed for a permanent-magnet salient-pole synchronous motor. This control strategy simultaneously achieves accurate torque control and copper losses minimization without recurring to an internal current loop nor to any feedforward compensation. It takes advantage of the rotor saliency by allowing the current (i/sub d/) to have nonzero values. This, in turn, allows us to increase the power factor of the machine and to raise the maximum admissible torque. We apply input-output linearization techniques where the inputs are the stator voltages and the outputs are the torque and a judiciously chosen new output. This new output insures a well-defined relative degree and is linked to the copper losses in such a way that, when forced to zero, it leads to maximum machine efficiency. The performance of our nonlinear controller is demonstrated by a real-time implementation using a digital signal processor (DSP) chip on a permanent-magnet salient-pole synchronous motor with sinusoidal flux distribution. The results are compared to the ones obtained with a scheme which forces the i/sub d/ current to zero.

Effect of torsional dynamics on salient pole synchronous motor-driven compressors

This paper presents a rigorous treatment of the starting problem of a salient pole synchronous motor driving a complex multicompressor load. This is aimed at analysing the resulting torsional oscillations and calculating the different transmitted torques and twist angles of the multi-shaft assembly. For this purpose, the necessary mathematical models and corresponding digital simulation are developed. The results obtained show that there is a pressing need for taking care of the torsional effects on the different shafts during the design stage, otherwise serious problems could arise.

TRANSIENT PERFORMANCE OF A SYNCHRONOUS DRIVE FOLLOWING A SHORT STATOR CURRENT INTERRUPTION

ABSTRACT The object of the study is torque and current stress after automatic reswitching of a salient-pole synchronous motor. The three parts of the simulated transient process are: phase-by-phase switching off, operation of the loaded motor isolated from the net and finally the performance after reswitching. The actual load torque as dependent on velocity is taken into account and the pulling into step is checked.

Field Oriented Control of Synchronous Machines using a Novel Feedback System

Field orientation method of speed control has emerged as a powerful tool for ac machines. The dynamic performance of such a drive is comparable to that of a converter fed four quadrant dc drive. An over view of various control strategies to implement the principle of field orientation in synchronous motors is presented. In addition, a novel scheme of hysteresis current control with field orientation for a salient pole synchronous motor is illustrated. In view of the significant reduction in cost and simplification of the circuit complexity of the scheme, it can very well replace the commonly favoured separately excited dc motor drive.

Measurement and computation of starting torque pulsations of salient pole synchronous motors

Five basic methods of synchronous motor torque measurement are described. The first method is the traditional mechanical measurement using an accelerator; the second method involves an electrical technique using search coils as flux sensors; the remaining techniques employ either terminal voltage and current or input power and speed. Measurements of instantaneous electromagnetic torques of a medium-size 25 HP salient pole synchronous motor using these methods are compared with simulation results obtained from a full-order model as well as with a quasi-linear algebraic approximation. It is shown that torque measurement using search coils in the stator windings gives the best correlation with the simulation results, followed by a modified terminal measurement based on terminal voltage and current. The accelerometer method give the poorest results in that it is unable to capture the low-frequency components of the electromagnetic torques. It is also demonstrated by simulation that the approximate method for calculation of pulsating torques based on a quasi-linear model of the motor gives an estimate comparable to that of the full-order model, particularly for large machines. >

An improved model for saturated salient pole synchronous motors

An improved model for the transient analysis of saturated salient pole synchronous motors is presented. With the aid of saturation factors obtained by test or with finite elements, Park's equations for a synchronous machine are modified to independently account for the saturation of the magnetizing flux linkages in the region of the stator teeth and rotor pole face as well as saturation of the total flux linking the stator core. The model is used to calculate the starting performance for a direct online start as well as the transient performance during a load change. The model shows improvement over more traditional models, indicating that representation of both main flux and core saturation are important for synchronous machine analysis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An Improved Model for Saturated Salient Pole Synchronous Motors

An improved model for the transient analysis of saturated salient pole synchronous motors is presented. With the aid of saturation factors obtained by means of test or finite elements, Park's equations for a synchronous machine are modified to independently account for the saturation of the d and q-axis magnetizing flux linkages in the region of the stator teeth and rotor pole fact as well as saturation of the total flux linking the stator core. The model is used to calculate the starting performance for a direct on line start as well as the transient performance during a load change. Both transients are correlated with both test results and the results predicted by a traditional model employing only d-axis main flux saturation. The new model demonstrates an improvement over more traditional models indicating that an appropriate representation of the main flux and core saturation effects are important for synchronous machine analysis. Figure 1 shows the complete equivalent d-q circuit model developed in the full paper. The inductance Lsa represents the reluctance of flux lines which are primarily in air. Lsc represents the magnetic reluctance of the stator core, Lsb accounts for the leakage inductances which are primarily iron related, i.e., slot leakage, tooth top and harmonic leakage. Lmd, Lmq account for the magnetizing flux linkages representing the MMF drop in the stator tooth top and field pole. In general, all of these inductances except Lsa can saturate.

Analysis of pulling-into-step phenomena of salient pole synchronous motor by Lyapunov's direct method.

Analysis of pulling-into-step phenomena of salient pole synchronous motor by Lyapunov's direct method.

Maximum Permissible Slip for Synchronizing Salient-Pole Synchronous Motors

The paper presents a method for determining the maximum permissible slip for synchronization of a salient-pole synchronous motor using machine, load and system parameters. An exact differential equation of motion of the salient-pole rotor during the synchronizing period is derived and then solved by means of a digital computer program using a fourth-order Runge-Kutta method. The synchronizing criterion involves two factors: the displacement angle must decrease, and this angle must not exceed 540 electrical degrees. Curves showing the relationship between load torque and maximum permissible slip with load inertia as a parameter are shown for a given motor. These results are compared with test data on the actual machine.

Torque Oscillations of Synchronous Motors Under Starting Conditions

Salient-pole synchronous motors develop an average torque and a twice-slip frequency oscillating torque during starting. If coupled to a complex mechanical system, with resonance in the oscillatory frequency range, severe stresses may result in shafts, gears, and couplings. The objective of the paper is to develop motor and mechanical system models, which can lead to the analysis of the torsional response of the motor load, and to avoid the use of specific motors that yield excessive values of stress or take steps to mitigate the oscillation magnitudes. The effect of the field discharge resistance was investigated.

Method for evaluating the starting characteristics of solid salient-pole synchronous motors

A brief description is given of existing methods of calculation of the asynchronous starting performance of solid salient-pole synchronous motors. These methods evaluate an equivalent impedance to represent the eddy-current loss in the solid-iron pole. This impedance is a variable, dependant on the rotor slip frequency and flux. The power factor of this equivalent impedance is a fixed quantity. The lumped-circuit parameter is then used in an equivalent circuit to calculate the asynchronous values. The harmonic torque and current associated with the Gorges effect need to be examined as these can affect the shape of the characteristics close to half speed and can cause a synchronous motor to run in the region of half speed with a heavy current pulsation. A new computational direct-search method is then described and used to evaluatethe average asynchronous values of torque and current for a solid salient-pole synchronous motor. The method allows for the provision of the distributed entry of flux into the saturable solid pole, pole-tip saturation and the evaluation of space-harmonic flux values. The need to make assumptions about eddy current distribution is eliminated by taking a path of integration on the pole surface. The method is completely general and any relative stator and rotor position can be analysed. Comparisons between the results from this new method, existing methods and test results show that the new method gives consistently accurate answers.

Method for evaluating the starting characteristics of solid salient-pole synchronous motors

A brief description is given of existing methods of calculation of the asynchronous starting performance of solid salient-pole synchronous motors. These methods evaluate an equivalent impedance to represent the eddy-current loss in the solid-iron pole. This impedance is a variable, dependant on the rotor slip frequency and flux. The power factor of this equivalent impedance is a fixed quantity. The lumped-circuit parameter is then used in an equivalent circuit to calculate the asynchronous values. The harmonic torque and current associated with the Görges effect need to be examined as these can affect the shape of the characteristics close to half speed and can cause a synchronous motor to run in the region of half speed with a heavy current pulsation. A new computational direct-search method is then described and used to evaluatethe average asynchronous values of torque and current for a solid salient-pole synchronous motor. The method allows for the provision of the distributed entry of flux into the saturable solid pole, pole-tip saturation and the evaluation of space-harmonic flux values. The need to make assumptions about eddy current distribution is eliminated by taking a path of integration on the pole surface. The method is completely general and any relative stator and rotor position can be analysed. Comparisons between the results from this new method, existing methods and test results show that the new method gives consistently accurate answers.

極間の導体棒の有無による突極同期電動機の同期引込み特性および定態安定度の実験による比較

極間の導体棒の有無による突極同期電動機の同期引込み特性および定態安定度の実験による比較

サイリスタインバータで駆動時の三相突極同期電動機の特性

サイリスタインバータで駆動時の三相突極同期電動機の特性

Oscillatory Torques During Synchronous Motor Starting

A fundamental characteristic of the salient-pole synchronous motor is a twice-slip frequency torque pulsation during acceleration. Although frequently neglected, sound application engineering requires an understanding of this subject. The way twice-slip frequency torques are produced in synchronous machines is discussed, as are the effects of these torques on mechanical system considerations such as critical speeds and stress buildup in shafts. Finally, specific areas of design coordination between designers of electrical power systems, synchronous motors, and the mechanical components of the system are suggested.