Reactive Power Based Rotor Resistance Estimation Engineering Essay

Abstract

In this paper, a elaborate survey on the Model Reference Adaptive Controller ( MRAC ) using the reactive power is presented for the on-line appraisal of rotor opposition to keep proper flux orientation in an Indirect Vector Controlled Induction Motor Drive. Choice of reactive power as the functional campaigner in the MRAC automatically makes the system immune to the fluctuation of stator opposition. Furthermore, the alone formation of The MRAC with the instantaneous and steady-state reactive power wholly eliminates the demand of any flux appraisal in the procedure of calculation. Therefore, the method is less sensitive to integrator-related jobs like impetus and impregnation ( necessitating no integrating ) . Simulation consequences have been presented to corroborate the effectivity of the technique.

THE indirect field oriented ( IFO ) -controlled initiation motor ( IM ) thrust is widely used in high public presentation industry applications  due to its simpleness and fast dynamic response. However, feedforward accommodation of the faux pas frequence, which requires rotor opposition, makes this scheme dependant on machine parametric quantities. Of all the parametric quantities, the rotor opposition undergoes considerable fluctuation and if attention is non taken to counterbalance for the alteration, the flux orientation is lost, ensuing in matching between the d- and q-axes variables. As is good known, the yoke makes the public presentation of the thrust system sulky. Attention is focused to implement field orientation through on-line appraisal of the machine parametric quantities . Many on-line parametric quantity appraisal strategies are available in literature. They are loosely classified as follows

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1. Spectral analysis technique
2. Observer based techniques
3. Model mention adaptive system based techniques
4. Heuristic methods
5. Reactive power based technique

In one category of method, appraisal of rotor clip changeless is done utilizing the spectral analysis techniques. This group of methods is based on the measured response to a intentionally injected trial signal or an bing characteristic harmonic in the voltage/current spectrum. Stator currents and electromotive forces of the motor are sampled and the parametric quantities are derived from the spectral analysis of these samples. The 2nd categorization of rotor opposition designation strategy used observer based techniques. Most of the methods have used the Extended Kalman Filter, which is a computationally intensive technique.

Loron and Laliberte describe the motor theoretical account and the development and tuning of an drawn-out Kalman filter ( EKF ) for parametric quantity appraisal during normal runing conditions without presenting any trial signals. The proposed method requires terminal and rotor velocity measurings and is utile for car tuning an indirect field-oriented accountant or an adaptative direct field-oriented accountant. Zai, DeMarco, and Lipo propose a method for sensing of the reverse rotor clip changeless utilizing the EKF by handling the rotor clip changeless as the 5th province variable along with the stator and rotor currents. The drawbacks are that this method is computationally intensive.

The 3rd group of online rotor opposition version methods is based on rules of theoretical account mention adaptative control. This is the attack that has attracted most of the attending due to its comparatively simple execution demands.

In add-on to the above methods, there are besides a few techniques proposed which can non be classified in the above three class. These may be based on the measuring of steady province stator electromotive force, current and motor velocity, the rotor opposition can so be calculated algebraically from the equations derived. These methods are grouped to be Heuristic methods.

The chief drawback for the above techniques is that the Rotor Resistance depends on vitamin D and q axis axis rotor flux which in bend depends on Stator Resistance. Therefore if any mistake occurs in the Stator Resistance, the truth of rotor flux deteriorates which in bend affects the truth of estimated Rotor Resistance.

Reactive power based rotor opposition calculator overcomes the disadvantage of above job. Choice of reactive power as the functional campaigner in the Model Reference Adaptive Controller ( MRAC ) automatically makes the system immune to the fluctuation of Stator Resistance. The alone formation of the MRAC with the instantaneous and steady-state reactive power eliminates the demand of any flux appraisal in the procedure of calculation.

MRAS based rotor opposition appraisal for vector controlled initiation motor thrusts

The parametric quantity can be calculated by the theoretical account mention adaptative system ( MRAS ) , where the end product of a mention theoretical account is compared with the end product of an adjustable or adaptative theoretical account until the mistakes between the two theoretical accounts vanishes to zero. The mistake signal is used to drive an adaptative mechanism ( PI or I controller ) which provides rectification of the rotor opposition. In MRAS, the works 's response is forced to track the response of a mention theoretical account, irrespective of the works 's parametric quantity fluctuation and burden perturbation consequence. Such a system is defined as a robust system. The mention theoretical account may be fixed or adaptative.

Choice of reactive power as the functional campaigner in the Model Reference Adaptive Controller ( MRAC ) automatically makes the system immune to the fluctuation of Stator Resistance. The alone formation of the MRAC with the instantaneous and steady-state reactive power wholly eliminates the demand of any flux appraisal in the procedure of calculation. Therefore, the method is independent of Stator Resistance appraisal and integrating impetus jobs.

Theoretical Development of the Proposed Scheme

The vitamin D and q axis electromotive forces for IM mentioning to the synchronously revolving ( I‰e ) mention frame can be expressed as The instantaneous reactive power can be expressed as Substituting, the new look of Q is It is worthwhile to advert that the above looks of Q are free from stator opposition, which is a noteworthy characteristic of any reactive power-based strategy. In steady province the derivative footings are zero. Therefore, the look of estimated reactive power is obtained as reduces to Evaluations and Parameters of Induction Motor The parametric quantities of the initiation machine used for simulation are given in the Table shown below.

Simulation Consequences

The Performance of MRAS based rotor opposition calculator utilizing reactive power method for vector controlled initiation motor thrusts is analyzed with assorted alterations in rotor opposition for the operating status of 415V/50Hz with rated burden torsion of 7.5Nm

1. With 100 % measure alteration in Rotor Resistance.
2. With 100 % incline alteration in Rotor Resistance.
3. With 100 % trapezoidal alteration in Rotor Resistance

From the consequences, it is observed that estimated rotor opposition is tracking with existent rotor opposition. MRAS based Rotor opposition calculator utilizing reactive power method is studied and designed for vector controlled initiation motor thrusts. The public presentation of rotor opposition calculator utilizing reactive power is analyzed extensively for assorted alterations in rotor opposition. From the consequences obtained, it is observed the mistake between that existent and estimated rotor opposition is ever found to be less than 0.9 % and the subsiding clip is found to be about 1 sec.

Analysis of vector controlled drive public presentation with and without calculator

Vector control is besides known as the " field oriented control '' , " flux oriented control '' or " indirect torsion control '' . Using field orientation ( Clarke-Park transmutation ) , three-phase current vectors are converted to a planar rotating mention frame ( d-q ) from a 3-dimensional stationary mention frame. The " vitamin D '' constituent represents the flux bring forthing constituent of the stator current and the " Q '' constituent represents the torsion bring forthing constituent. These two decoupled constituents can be independently controlled by go throughing though separate PI accountants. The end products of the PI accountants are transformed back to the 3-dimensional stationary mention plane utilizing the opposite of the Clarke-Park transmutation. The corresponding shift form is pulse breadth modulated driving a Voltage beginning Inverter. This control simulates a individually exited DC motor theoretical account, which provides an first-class torque-speed curve. The transmutation from the stationary mention frame to the revolving mention frame is done and controlled with mention to a specific flux linkage infinite vector ( stator flux linkage, rotor flux linkage or magnetising flux linkage ) . In general, there exists three possibilities for such choice and hence, three different vector controls. They are: Stator flux oriented control, Rotor flux oriented control and magnetising flux oriented control.

As the torsion bring forthing constituent in this type of control is controlled merely after transmutation is done and is non the chief input mention, such control is known as " indirect torsion control '' . The most ambitious and finally, the confining characteristic of the field orientation, is the method whereby the flux angle is measured or estimated. Depending on the method of measuring, the vector control is divided into two subcategories: direct and indirect vector control.

In direct vector control, the flux measuring is done by utilizing the flux feeling spirals or the Hall devices. This adds to extra hardware cost and in add-on, measuring is non extremely accurate. Therefore, this method is non a really good control technique. The more common method is indirect vector control. In this method, the flux angle is non measured straight, but is estimated from the tantamount circuit theoretical account and from measurings of the rotor velocity, the stator current and the electromotive force.

One common technique for gauging the rotor flux is based on the faux pas relation. This requires the measuring of the rotor place and the stator current. With current and place detectors, this method performs moderately good over the full velocity scope. The most high-performance VFDs in operation today employ indirect field orientation based on the faux pas relation. The advantages of the vector control are to better the torsion response compared to the scalar control, full-load torsion near to zero velocity, accurate velocity control and public presentation nearing DC thrust, among others. This chapter gives complete inside informations about indirect vector control strategy.

The indirect field oriented control presented here is rotor flux oriented control. Figure 4 shows the complete schematic of rotor opposition appraisal for indirect field oriented control of initiation motor thrusts. The torsion bid is generated as a map of the velocity mistake signal, by and large processed through a PI accountant. The torsion and flux bid are processed in the computation block. The three stage mention current generated from the functional block is compared with the existent current in the hysteresis set current accountant and the accountant takes the necessary action to bring forth PWM pulsations. The PWM pulsations are used to trip the electromotive force beginning inverter to drive the Induction motor.

The IFOC thrust public presentation is analyzed without and with calculator for the operating status.

1. Reference speed = 100rad/sec
2. Reference rotor flux = 0.9wb
3. Load torsion = 7.5Nm ( invariable )
4. Rotor Resistance = 100 % measure alteration in rotor opposition is given at 1 2nd.

Significance of Estimation clip on the thrust public presentation

In the execution of the calculators, the clip taken for appraisal is an of import parametric quantity. Faster tracking will take to better dynamic public presentation. The cost of the calculator should be low to maintain the cost of the thrust system within the allowable degrees. Hence a survey on the thrust public presentation has been done for assorted appraisal times and the torsion and the flux responses are observed.

The appraisal clip decides the transeunt public presentation indices like settling clip and peak wave-off in both torsion and flux responses of the vector controlled thrust. The appraisal mistake has less impact on the transeunt public presentation. However the steady province mistake in both torsion and flux response chiefly decided by the appraisal mistake.

The thrust public presentation is analyzed with assorted calculators in which the appraisal mistake is kept changeless at 1 % and clip of appraisal is varied. The appraisal mistake and appraisal clip of the vector controlled initiation motor thrust is analyzed for the operating status for mention velocity 100rad/sec, mention rotor flux 0.9wb, the rated burden torsion ( 7.5Nm ) is reduced to 5.5Nm,40 % measure alteration in rotor opposition is given at 2 second.From this the transeunt response in torsion and flux are studied.

Similarly with same runing conditions the steady province analysis of the torsion and flux response of the thrust can be done by holding the appraisal clip as changeless with assorted appraisal mistakes. The public presentation is studied with a changeless appraisal clip of 20ms. The Torque and the flux responses for the above conditions are tabulated in Table 3.4 and 3.5. The bold Numbers shown in table 3.2, 3.3, 3.4 and 3.5 are the optimal allowable values of the appraisal clip and appraisal mistake.

It is obvious that as the appraisal clip and the appraisal mistake are increased the thrust public presentation is being deteriorated. However it is quiet appealing to settle down with the maximal allowable appraisal clip and appraisal mistake, so that the thrust public presentation is satisfactory. Therefore from the consequences it can be concluded that the public presentation of the thrust is satisfactory with the maximal appraisal clip of 20ms and an appraisal mistake of 1.5 % .

Decision

The MRAS based Rotor opposition calculator utilizing reactive power method is studied and designed for vector controlled initiation motor thrusts. The public presentation of rotor opposition calculator utilizing reactive power is analyzed extensively for assorted alterations in rotor opposition. From the consequences obtained, it is observed the mistake between that existent and estimated rotor opposition is ever found to be less than 0.9 % and the subsiding clip is found to be about 1 sec.

The public presentation of Vector Controlled Induction Motor Drive with and without Rotor Resistance calculator is studied. From the consequences, it is observed that the without rotor opposition calculator, the decouple control is lost which leads to important deteriorates in the public presentation of vector controlled initiation motor thrusts while with rotor opposition calculator, the decouple control is achieved and the public presentation of IFOC is truly enhanced. The maximal allowable appraisal mistake and appraisal clip for rotor opposition appraisal that does non deteriorate the public presentation of IFOC is found to be 1.5 % and 20ms severally.

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