Field Oriented Controlled PM Motor Drive System Analysis Engineering Essay

In this paper, a field oriented controlled PM motor thrust system is described and analyzed due to its importance in many applications particularly in Automotive applications. Permanent Magnet Synchronous Motors ( PMSM ) are widely applied in industrial and robotic applications due to their high efficiency, low inactiveness and high torsion – to – volume ratio. A closed cringle control system with a PI accountant in the velocity cringle has been designed to run in changeless torsion angle and flux weakening parts. A comparative survey of hysteresis and PWM control strategies associated with current accountants has been made. Then, the simulation of a field oriented controlled PM motor thrust system is developed utilizing Simulink. The simulation circuits for PM synchronal motor, inverter, velocity and current accountants include all realistic constituents of the thrust system. Simulation consequences for both hysteresis and PWM control strategies associated with current accountants are given for two velocities of operation, one below rated and another supra rated velocity.

Keywords: Permanent Magnet, Synchronous Motor, Field Oriented, Control, Simulink, Drive, PI Controller, Torque Angle, Flux Weakening, Hysteresis, PWM.

1. Introduction

Among the Ac thrusts, lasting magnet synchronal machine ( PMSM ) thrusts have been progressively applied in a broad assortment of industrial applications and automotive applications. The ground comes from the advantages of PMSM: high power denseness and efficiency, high torsion to inertia ratio, and high dependability. Recently, the uninterrupted cost decrease of magnetic stuffs with high energy denseness and coercitivity ( e.g. , samarium Co and neodymium-boron Fe ) makes the ac thrusts based on PMSM more attractive and competitory. In the high public presentation applications, the PMSM thrusts are ready to run into sophisticated demands such as fast dynamic response, high power factor and broad runing velocity scope. Consequently, a uninterrupted addition in the usage of PMSM thrusts will certainly be witnessed in the close future [ 1-3 ] . The vector control ( or called field-oriented control ) of Ac machines was introduced in the late sixtiess by Blaschke, Hasse, and Leonhard in Germany. Following their pioneering work, this technique, leting for the speedy torsion response of ac machines similar to that of District of Columbia machines, has achieved a high grade of adulthood and go popular in a wide assortment of applications. It is besides widely applied in many countries where servo-like high public presentation plays a secondary function to dependability and energy nest eggs. To accomplish the field-oriented control of PMSM, cognition of the rotor place is required. Normally the rotor place is measured by a shaft encoder, resolver, or Hall detectors. [ 4-8 ] . The advantages of PM machines late make them extremely attractive campaigners for “ direct thrust ” applications, such as intercrossed electrical vehicles ( HEV ) or electrical vehicles ( EV ) [ 11- 16 ] and rinsing machines, which are illustrated in Figure 1. By this engineering, the revolving working unit of a direct thrust system, such as the basket or membranophone of a lavation machine, is coupled to the motor shaft without transmittal assembly, which may include clasps, belts, blocks and/or gear boxs. The power is straight delivered to the working unit by the motor. The construct of direct thrust enables the high dynamic response, increased efficiency, low acoustic noise, and long life-time due to the riddance of the transmittal constituents. Such direct thrust systems usually require big shaft torsion at deadlock ( i.e. , zero velocity ) and low velocities every bit good as changeless end product power over broad velocity scope. In order to run into such demands, the PM machines are designed to run non merely in the changeless torsion manner when their velocity is below the base ( or rated ) velocity but besides in the changeless power manner when above the base velocity. In this manner, the cost and size of overall thrust system can be significantly reduced. The changeless torsion operation of PM motor can be easy achieved by conventional vector control. However, when the velocity is above the base velocity, the back-EMF of PM motor is larger than the line electromotive force and so the motor suffers from the trouble to continuously bring forth torsion due to voltage and current restraints. Thankss to the flux-weakening engineering, the operating velocity scope can be extended by using negative magnetizing current constituent to weaken the air-gap flux [ 9, 10 ] . transform are in widespread usage.

Figure 1. Applications of PMSM Drive System ; ( a ) HEV, ( B ) Washing Machine

2. Description OF DRIVE SYSTEM

This subdivision deals with the description of the thrust system which includes different constituents such as lasting magnet motors, place detectors, inverters and current accountants. The motor thrust consists of four chief constituents, the PM motor, inverter, control unit and the place detector. The constituents are connected as shown in figure 2.

Figure 2. Drive System Schematic

2.1. Current Controlled Inverter

The motor is fed organize a electromotive force beginning inverter with current control. The control is performed by modulating the flow of current through the stator of the motor. Current accountants are used to bring forth gate signals for the inverter. Proper choice of the inverter devices and choice of the control technique will vouch the efficaciousness of the thrust. Voltage Source Inverters are devices that convert a DC electromotive force to AC electromotive force of variable frequence and magnitude. They are really normally used in adjustable velocity thrusts and are characterized by a well defined switched electromotive force moving ridge signifier in the terminuss [ 17 ] . Both current beginning inverters ( CSI ) and electromotive force beginning inverters ( VSI ) can be operated in controlled current manners. The current beginning inverter is a “ natural ” current supply and can readily be adapted to command current operation. The electromotive force beginning inverter requires more complexness in the current regulator but offers much higher bandwidth and riddance of current harmonics as compared to the CSI and is about entirely used for gesture control applications. Current accountants can be classified into two groups, hysteresis and PWM current accountants. Both types are discussed below.

2.1.1. Hysteresis current accountant

Hysteresis current accountant can besides be implemented to command the inverter currents. The accountant will bring forth the mention currents with the inverter within a scope which is fixed by the breadth of the set spread. In this accountant the coveted current of a given stage is summed with the negative of the mensural current. The mistake is fed to a comparator holding a hysteresis set. When the mistake crosses the lower bound of the hysteresis set, the upper switch of the inverter leg is turned on. But when the current efforts to go less than the upper mention set, the bottom switch is turned on. Fig. 3 shows the hysteresis set with the existent current and the ensuing gate signals. This accountant does non hold a specific shift frequence and alterations continuously but it is related with the set width [ 17 ] [ 18 ] .

Figure 3. Hysteresis accountant

2.1.2. PWM Current Controller

PWM current accountants are widely used. The switching frequence is normally kept changeless. They are based in the rule of comparing a triangular bearer moving ridge of desire exchanging frequence with mistake of the controlled signal. The mistake signal comes from the amount of the mention signal generated in the accountant and the negative of the existent motor current. The comparing will ensue in a electromotive force control signal that goes to the Gatess of the electromotive force beginning inverter to bring forth the desire end product. Its control will react harmonizing to the mistake. If the mistake bid is greater than the trigon wave form, the inverter leg is held switched to the positive mutual opposition ( upper switch on ) . When the mistake bid is less than the trigon wave form, the inverter leg is switched to the negative mutual opposition ( lower switch on ) . This will bring forth a PWM signal like in fig. 4. The inverter leg is forced to exchange at the frequence of the trigon moving ridge and produces an end product electromotive force relative to the current mistake bid. The nature of the controlled end product current consists of a reproduction of the mention current with high-frequency PWM rippling superimposed [ 17 ] .

Figure 4. PWM current accountant

2.2. Field Oriented Control of PM Motors

The PMSM control is tantamount to that of the District of Columbia motor by a decoupling control known as field oriented control or vector control. The vector control separates the torque constituent of current and flux channels in the motor through its stator excitement. The vector control of the PM synchronal motor is derived from its dynamic theoretical account. Sing the currents as inputs, the three currents are:

where I± is the angle between the rotor field and stator current phasor, I‰r is the electrical rotor velocity. The old currents obtained are the stator currents that must be transformed to the rotor mention frame with the rotor velocity I‰r, utilizing Park ‘s transmutation. The Q and vitamin D axis currents are invariables in the rotor mention frames since I± is a changeless for a given burden torsion. As these invariables, they are similar to the armature and field currents in the individually aroused District of Columbia machine. The q axis current is clearly tantamount to the armature current of the District of Columbia machine ; the vitamin D axis current is field current, but non in its entireness. It is merely a partial field current ; the other portion is contributed by the tantamount current beginning stand foring the lasting magnet field. For this ground the Q axis current is called the torsion bring forthing constituent of the stator current and the vitamin D axis current is called the flux bring forthing constituent of the stator current. Idaho and intelligence quotient in footings of Is as follows:

The electromagnetic torsion equation is obtained as given below.

2.2.1. Changeless Torsion Operation

Changeless torsion control scheme is derived from field oriented control, where the maximal possible torsion is desired at all times like the District of Columbia motor. This is performed by doing the torsion bring forthing current iq equal to the supply current Is. That consequences in choosing the I± angle to be 90° . By doing the id current equal to zero the torque equation can be rewritten as:

Assuming that:

The torsion is give by

Like the District of Columbia motor, the torsion is dependent of the motor current.

2.2.2. Flux-weakening

Flux weakening is the procedure of cut downing the flux in the vitamin D axis way of the motor which consequences in an increased velocity scope. The motor thrust is operated with rated flux linkages up to a velocity where the ratio between the induced voltage and stator frequence ( V/f ) is maintained changeless. After the base frequence, the V/f ratio is reduced due to the bound of the inverter District of Columbia electromotive force beginning which is fixed. The weakening of the field flux is required for operation above the base frequence. This reduces the V/f ratio. This operation consequences in a decrease of the torque proportional to a alteration in the frequence and the motor operates in the changeless power part [ 19 ] . The rotor flux of PMSM is generated by lasting magnet which can non be straight reduced as initiation motor. The rule of flux-weakening control of PMSM is to increase negative direct axis current and use armature reaction to cut down air spread flux, which equivalently reduces flux and achieves the intent of flux-weakening control [ 20 ] . This method changes torque by changing the angle between the stator MMF and the rotor vitamin D axis. In the flux weakening part where I‰r & gt ; I‰rated angle I± is controlled by proper control of Idaho and intelligence quotient for the same value of stator current. Since intelligence quotient is reduced the end product torsion is besides reduced. The angle I± can be obtained as:

The current Is is related to id and iq by:

Using I± and rotor place the accountant will bring forth the mention currents ; so the current accountant makes utilizations of the mention signals to command the inverter for the coveted end product currents. The burden torsion is adjusted to the maximal available torsion for the mention velocity:

2.3. Execution of the Speed Control Loop of PM Motor

Many applications, such as robotics and mill mechanization, require precise control of velocity and place. Speed Control Systems let one to easy put and set the velocity of a motor. The control system consists of a velocity feedback system, a motor, an inverter, a accountant and a velocity puting device. A decently designed feedback accountant makes the system insensible to disturbance and alterations of the parametric quantities. The intent of a motor velocity accountant is to take a signal stand foring the demanded velocity, and to drive a motor at that velocity. Closed Loop velocity control systems have fast response, but become expensive due to the demand of provender back constituents such as velocity detectors. For a PM motor thrust system with a full velocity range the system will dwell of a motor, an inverter, a accountant ( changeless torsion and flux weakening operation, coevals of mention currents and PI accountant ) as shown in fig. 5.

Figure 5. Drive Block Diagram

The operation of the accountant must be done harmonizing to the velocity scope. For operation up to rated velocity it will run in changeless torsion part and for velocities above rated velocity it will run in flux-weakening part. In this part the d-axis flux and the developed torsion are reduced. The procedure can be easy understood with the flow diagram in fig. 6.

Figure 6. System Flow Diagram

Speed accountant calculates the difference between the mention velocity and the existent velocity bring forthing an mistake, which is fed to the PI accountant. PI accountants are used widely for gesture control systems. They consist of a relative addition that produces an end product proportional to the input mistake and an integrating to do the steady province mistake nothing for a measure alteration in the input. Block diagram of the PI accountant is shown in fig. 7.

Figure 7. PI Controller

Speed control of motors chiefly consist of two cringles the interior cringle for current and the outer cringle for velocity. The order of the cringle is due to their response, how fast they can be changed. This requires a current cringle at least 10 times faster than the velocity cringle. Since the PMSM is operated utilizing field oriented control, it can be modeled like a District of Columbia motor. The design begins with the innermost current cringle by pulling the block diagram. But in PMSM thrust system the motor has current accountants which make the current cringle. The current control is performed by the comparing of the mention currents with the existent motor currents. The design of the velocity cringle assumes that the current cringle is at least 10 times faster than velocity cringle, leting cut downing the system block diagram by sing the current cringle to be of unity addition as shown in fig. 8.

Figure 8. Block Diagram of Speed Loop

For our SPMSM ; kt = ( 3/2 ) ( P/2 ) i?¬af = 0.849 ; where: i?¬af = 0.283 ; P = 4 ; J = 0.0000144

The unfastened cringle transportation map of the motor is given by:

For stable system and to fulfill dynamic response without oscillations the stage border ( i?¦PM ) normally greater than 45° , here we prefer it to be 60° . Knowing the motor parametric quantities and the stage border, with the addition border definitions the qi and kitchen police additions can be obtained for the motor accountant utilizing the undermentioned equations.

For crossing over frequence ( selected ) fc = 100 Hz ; ( i?·c = 2 i?° fc = 628.3185 rad/sec )

The additions for the velocity accountant was obtained utilizing the motor parametric quantities and by choosing a crossing over frequence kp = 0.004615 ; ki = 1.674

A simple stableness cheque for these obtained values is done utilizing characteristic combining weight. ( 13 ) , in which GH ( s ) : Open cringle transportation map, G: Feed-forward transportation map, and H: Feed-back Transfer map.

The poles of the characteristic equation are: – 272. 0927 i‚± J 351.2237 ; it is clear they are in left manus side of the s-plane so the system will be stable with these values.

2.4. Inverter-Motor Equivalent Circuit

Sing the tantamount circuit of the system inverter-motor as in fig. 9 ; the line electromotive forces for the motor have the look [ 22 ] , [ 23 ] :

Figure 9. Inverter-motor tantamount circuit

The motor stage electromotive forces will hold the look:

Bing a star connexion, so at every clip instant the undermentioned relation is satisfied:

From Eq ( 15 ) and Eq ( 16 ) so the void electromotive force is derived as:

Having the pulsations for each inverter leg ( district attorney, dubnium, District of Columbia ) , the inverter ‘s leg electromotive forces can be found as:

Using the above Eq.s, the resulted line electromotive forces will hold the look Eq ( 19 ) :

Similarly, the stage electromotive forces can be found as:

The construction of the inverter Simulink theoretical account is presented subsequently.

2.5. Dc Source

The dc-link electromotive force Vdc, could be obtained utilizing Vsn ( maximal stage electromotive force ) as follow [ 21 ] :

Where Vsn: peak amplitude of stage electromotive force

2.6. Dynamic Modeling of PMSM

Figure 10 nowadayss tantamount circuit of PMSM in d-q axis to be used in both dynamic equations of PMSM, and inactive features.

Figure 10. PMSM Equivalent Circuit

It should be notified that, all lower instance symbols introduce instantaneous values, and upper instance for steady province. The two axes PMSM stator twists can be considered to hold equal bends per stage. The rotor flux can be assumed to be concentrated along the vitamin D axis while there is zero flux along the Q axis. Further, it is assumed that the machine nucleus losingss are negligible. Besides, rotor flux is assumed to be changeless ( fluctuation in the rotor flux with regard to clip is negligible ) . Variations in rotor temperature alter the magnet flux, but its fluctuation with clip is considered to be negligible. A dynamic theoretical account of PMSM can be dedicated as follow [ 24 ] :

where i?·r: Electrical speed of the rotor ; i?¬af: The flux linkage due to the rotor magnets associating the stator ; venereal disease, vq: vitamin D, q electromotive forces ; i?¬d, i?¬q: vitamin D, q flux ; I? ( i?¬af ) = 0, i?¬af = Lm ifr ; I? : Derivative Operator

The electromagnetic torsion is given by:

The electromechanical power

where Phosphorus: Poles No ; i?·rm: Rotor Mechanical speed

The general mechanical equation for the motor is:

Bacillus: Syrupy clashs coefficient ; J: Inactiveness of shaft and burden system ; Td: Dry clash ; Tl: Load torsion

3. PMSM DRIVE SIMULATION

In this subdivision, the simulation of a field oriented controlled PM motor thrust system is developed utilizing Simulink. The simulation circuit includes all realistic constituents of the thrust system. A closed cringle control system with a PI accountant in the velocity cringle has been designed to run in changeless torsion and flux weakening parts. Execution has been done in Simulink. A comparative survey of hysteresis and PWM control strategies associated with current accountants has been made. Simulation consequences are given for two velocities of operation, one below rated and another supra rated velocity.

3.1. Mold of PMSM

Mold of a lasting magnet synchronal motor is introduced in this subdivision utilizing the m/c equations ; with some premises like: Impregnation is neglected ; the induced EMF is sinusoidal ; Eddy currents and hysteresis losingss are negligible ; there are no field current kineticss ; all motor parametric quantities are assumed changeless ; Leakage inductions are zero. Detailed mold of PM motor thrust system is required for proper simulation of the system. The d-q theoretical account has been developed on rotor mention frame. This dynamic simulation of PMSM is done with the assistance of SIMULINK in MATLAB bundle. The electromotive force and burden torsion are considered as inputs, with the velocity and current as end products. This theoretical account is verified by the same writer as in mentions [ 25 ] , [ 26 ] , [ 27 ] .

Figure 11. Permanent Magnet Synchronous Motor Model

3.2. Simulink Simulation of PMSM Drive

The PM motor thrust simulation was built in several stairss like abc stage transmutation to dqo variables, computation torsion and velocity, and control circuit. The abc stage transmutation to dqo variables is built utilizing Parks transmutation and for the dqo to abc the contrary transmutation is used. For simulation purpose the electromotive forces are the inputs and the current are end product. Parks transmutation used for change overing Vabc to Vdqo is shown in mold and the contrary transmutation for change overing Idqo to Iabc is shown in figure 12.

Figure 12. Idqo to Iabc Block

The vector control requires a block for the computation of the mention current utilizing the I± angle, the place of the rotor and the magnitude of the Is. The block with the PI accountant is shown in fig. 13.

Figure 13. Vector Control Reference Current Block with PI Speed Controller

Inverter is implemented as shown in fig. 14, depending on the inverter dealingss introduced before.

Figure 14. Voltage Source Inverter

For proper control of the inverter utilizing the mention currents, current accountants are implemented to bring forth the gate pulsations for the IGBT ‘s. Current accountants used are shown in fig. 15 and 16.

Figure 15. Hysteresis accountant

Figure16. PWM current accountant

4. Simulation RESULTS

This portion deals with the simulation consequences of PMSM thrust system. Comparative survey of the current accountants used in the system is given. The system built in Simulink for a PMSM thrust system has been tested with the two current control methods, Hysteresis and PWM, at the changeless torsion and flux-weakening parts of operation. The motor is operated with changeless torsion up to its rated velocity and beyond that rated speed flux-weakening manner is adopted. Simulation consequences are given at electrical velocities of 2000 revolutions per minute ( 66.6667 Hz ) and 2400 ( 80 Hz ) . The above velocities represent rated and above rated velocity of the motor. The simulation was carried out utilizing two current control techniques to analyze the public presentation of the motor thrust. The techniques are Hysteresis current control and PWM current control. The secret plans of current, torsion and velocity are given for both instances.

4.1. Simulation for Operation at 2000 revolutions per minute

Figure 17. Electrical Speed with clip ( at 66.6667 Hz ) ; for Hysteresis accountant

Figure 18. Iabc with clip ( at 66.6667 Hz ) ; for Hysteresis accountant

Figure 19. Idq with clip ( at 66.6667 Hz ) ; for Hysteresis accountant

Figure 20. Torsion with clip ( at 66.6667 Hz ) ; for Hysteresis accountant

Fig. 17 shows a fluctuation of the velocity with clip. The steady province velocity is the same as that of the commanded mention velocity. Fig. 18 shows the three stage currents drawn by the motor as a consequence of the hysteresis current control. The currents are obtained utilizing Park ‘s contrary transmutation. It is clear that the current is non sinusoidal at the starting and becomes sinusoidal when the motor reaches the accountant bid velocity at steady province. The corresponding dq constituent of current is given in fig. 19 in which the value of Idaho is zero since field oriented control is used. Fig. 20 shows the developed torsion of the motor. The get downing torsion about is more than twice the steady province value. The old secret plans have been repeated with PWM control for comparing with hysteresis control.

Figure 21. Electrical Speed with clip ( at 66.6667 Hz ) ; for PWM accountant

Figure 22. Iabc with clip ( at 66.6667 Hz ) ; for PWM accountant

Figure 23. Idq with clip ( at 66.6667 Hz ) ; for PWM accountant

Figure 24. Torsion with clip ( at 66.6667 Hz ) ; for PWM accountant

Fig. 21 shows a fluctuation of the velocity with clip. The steady province velocity is the same as that of the commanded mention velocity. Fig. 22 shows the three stage currents as a consequence of the PWM current control obtained from Park ‘s contrary transmutation. It is clear that the current is non sinusoidal at the starting and becomes sinusoidal when the motor reaches the accountant bid velocity at steady province. The corresponding dq constituent of current is given in fig. 23 with id about equal to zero for changeless torsion operation. Fig. 24 shows the developed torsion of the motor.

4.2. Simulation for Operation at Higher Speed of 2400 revolutions per minute

Figure 25. Electrical Speed with clip ( at 80 Hz ) ; for Hysteresis accountant

Figure 26. Iabc with clip ( at 80 Hz ) ; for Hysteresis accountant

Figure 27. Idq with clip ( at 80 Hz ) ; for Hysteresis accountant

Figure 28. Torsion with clip ( at 80 Hz ) ; for Hysteresis accountant

Fig. 25 shows a fluctuation of the velocity with clip. The steady province velocity is the same as that of the commanded mention velocity. Fig. 26 shows the three stage currents as a consequence of the hysteresis current control obtained from Park ‘s contrary transmutation. It is clear that the current is non sinusoidal at the starting and becomes sinusoidal when the motor reaches the accountant bid velocity. The corresponding dq constituent of current is given in fig. 27. Both vitamin D and q axis current are present. However the Q axis current is little since the torsion gets reduced at higher velocity, runing at changeless power part. Fig. 28 shows the developed torsion of the motor with high get downing torsion.

The above secret plans have been repeated with PWM control for comparing with hysteresis control.

Figure 29. Electrical Speed with clip ( at 80 Hz ) ; for PWM accountant

Figure 30. Iabc with clip ( at 80 Hz ) ; for PWM accountant

Figure 31. Idq with clip ( at 80 Hz ) ; for PWM accountant

Figure 32. Torsion with clip ( at 80 Hz ) ; for PWM accountant

Fig. 29 shows a fluctuation of the velocity with clip. The steady province velocity is the same as that of the commanded mention velocity. Fig. 30 shows the three stage currents as a consequence of the PWM current control obtained from Park ‘s contrary transmutation. It is clear that the current is non sinusoidal at the starting and becomes sinusoidal when the motor reaches the accountant bid velocity at steady province. The corresponding dq constituent of current is given in fig. 31. Both vitamin D and q axis current are present. However the Q axis current is little since the torsion gets reduced at this higher velocity due to power being maintained changeless. Fig. 32 shows the developed torsion of the motor.

5. CONCLUSIONS

A elaborate Simulink theoretical account for a PMSM thrust system with field oriented control has being developed and operation at and above rated velocity has been studied utilizing two current control strategies. Simulink has been chosen from several simulation tools because its flexibleness in working with parallel and digital devices. In the present simulation measuring of currents and electromotive forces in each portion of the system is possible, therefore allowing the computation of instantaneous or mean losingss, and efficiency. Normally in such a thrust system the inverter is driven either by hysteresis or by PWM current accountants. A comparative survey has been made of the two current control strategies. A velocity accountant has been designed successfully for closed cringle operation of the PMSM thrust system so that the motor runs at the commanded or mention velocity.