pmsm_2012.ppt

PERMANENT MAGNET SYNCHRONOUS MOTOR

INTRODUCTION

DC field winding of the rotor replaced by permanent magnet.

AdvantagesElimination of field Cu lossHigh power densityLower rotor inertiaRobust construction of the rotor

DisadvantagePossible demagnetization effect

COMPARISON WITH INDUCTION MOTOR

Higher efficiency. But cost is high.

COMPARISON WITH BLDC

WORKING PRINCIPLE

Difference from BLDCM is the way in which the stator windings are excited.

Phase windings connected to a 3 phase AC supply of line frequency producing a smooth rotating stator mmf .

Permanent magnet rotor will follow the stator rotating field ,the north and south pole of the rotor continuously attracted by the north and south pole of the stator mmf respectively.

CLASSIFICATION

Sinusoidal Surface Magnet Machine (SPM)

Sinusoidal Interior Magnet Machine(IPM)

SINUSOIDAL SURFACE MAGNET MACHINE

stator- three phase sinusoidal windings creating synchronously rotating air gap flux.

The PMs glued on the rotor surface using epoxy adhesive.

Rotor has iron core-solid or punched laminations.

Low armature reaction effect.

SINUSOIDAL SURFACE MAGNET MACHINE

SINUSOIDAL INTERIOR MAGNET MACHINE(IPM)

Stator-three phase winding. Magnets mounted inside the rotor. More robust and higher speed of operation

possible.

SINUSOIDAL INTERIOR MAGNET MACHINE

SINUSOIDAL SPM MACHINE DRIVES

Speed of the machine uniquely related to the frequency of the inverter.

Machine will run at synchronous speed or will not run at all.

Two methods of control Open loop mode Self- control mode

OPEN LOOP VOLT/HERTZ CONTROL


Synchronous speed is directly proportional to frequency.

But the induced voltage is proportional to frequency and speed ,it will be necessary to adjust the voltage also.

Simplest Inferior performance compared with the

vector control.


Closed speed tracking essential among no. of machines for certain applications like fiber spinning mills.

All the machines connected in parallel to the same inverter.

They connected in parallel to the same inverter so that they move in synchronism corresponding to the command frequency ωe* at the input.


The phase voltage command Vs* generated through a function generator (FG) where voltage proportional to frequency so that stator flux ψs

remains constant. Ψs maintained constant at

rated value- permits maximum available torque/ampere of stator current and fast transient response.


Front end of voltage fed PWM inverter supplied from utility line through a diode rectifier and LC filter.

Machine normally built with a damper or cage winding to prevent oscillatory or underdamping behaviour during the transient response.


During deceleration, the electrical energy is recovered and this is dissipated in dynamic brake [DB ] installed in the DC link.

Speed reversal is possible by reversing the phase sequence.

TORQUE-SPEED CHARACTERISTICS


Assume initially load torque is zero.

The machine initially started from stand-still condition at point O to point A by increasing frequency.

At this point, the load torque TL gradually increased.

At steady-state condition, Te =TL , the operating point will move vertically along AB. *Is - stator current

δ =torque angle

Torque angle, stator current will increase gradually until the rated torque is reached at point B .

Operating point can be changed from B to C by gradually increasing frequency.It can be brought back to D by reducing TL.

Any sudden change in ωe* will make the system unstable because of loss of synchronism.

For variable-speed operation, the motor speed should be able to track the command frequency without losing synchronism.

The rate of ωe* change or maximum acceleration/deceleration dictated by the following equation

For acceleration

For deceleration


At base speed, voltage Vs

will saturate. Beyond this point-field

weakening mode –available torque will be reduced due to reduced ψs

SELF CONTROL MODEL

SELF CONTROL MODEL

A self controlled synchronous machine has a close analogy with a DC machine except

Unlike a DC machine, field-rotating and armature stationary.

Unlike a mechanical position –sensitive inverter, we have an electronic converter controlled by absolute position encoder.

fluxes and phasor diagram are rotating at synchronous speed .

SELF CONTROLLED PMSM

• Stator winding of the machine fed by an inverter that generates a variable-frequency variable voltage sinusoidal supply.

• Here, variable frequency converter control pulses are derived from an absolute rotor position .

• Instead of controlling the inverter frequency independently, the frequency and phase of the output wave controlled by an absolute position sensor mounted on machine shaft.

• Stator supply frequency varied so that the synchronous speed same as rotor speed.

• Rotor runs at synchronous speed for all operating points. Consequently rotor cannot pull out of step and hunting oscillations eliminated.

SELF CONTROLLED SYNCHRONOUS MOTOR DRIVE EMPLOYING LOAD COMMUTATED

THYRISTOR INVERTER

Employs 2 converters termed as source side converter and load side converter.

When firing angles changed such that 0 ≤ αs ≤90˚, 90 ˚ ≤ αl ≤180˚ the source side converter works as a rectifier load side converter works as a inverter power flow from ac source to the motor giving motoring

operation. When firing pulses changed such that 90 ˚ ≤

αs≤180˚ and 0 ≤ αl ≤90˚ Load side converter operates as rectifier source side converter works as a inverter power flow reverses and machine operates in

regenerative braking

For self control mode operation ,rotating field speed should be same as that of rotor speed. Realized by making the frequency of the load side

converter output voltage equal to the frequency of the voltage induced in the armature.

CLOSED LOOP SPEED CONTROL

wm*

ac supply

Outer speed loop control-inner current control loop with a limiter

Voltage sensor generates reference pulses same frequency as the machine induced voltages

Phase delay circuit-phase delay-to obtain suitable constant commutation lead angle.

Depending on sign of speed error- βlc set for motoring or braking operation.

Positive speed error- βlc set for motoring Speed controller and current limiter-set the dc link

current reference-set at max. permissible value-machine accelerates fast-desired speed obtained

Negative speed error- βlc set for regenerative braking-decelerates.

VECTOR CONTROL OF PMSM

VECTOR CONTROL Separately excited DC drives simple in

control because they independently control flux and torque.

Independent control of flux and torque is possible in a.c drives by the use of vector control.

PRINCIPLE OF VECTOR CONTROL

To explain the principle of vector control, an assumption is made that the position of rotor flux linkage (λr ) is known and concentrated along d-axis and zero flux along q-axis.

The stator current is resolved into idsr (if ) and iqs

r (iT ) .

The current phasor is produces the rotor flux λr

and torque Te .

Component of current producing rotor flux is in phase with λr -if .

Perpendicular component iT –torque producing component.

Vector control of PMSM

STEPS OF VECTOR CONTROL

STEPS OF VECTOR CONTROL

Synthesize these currents by using an inverter.

When they are fed to the PMSM ,the required flux and torque can be produced.

VECTOR CONTROLLED PMSM SYNCHRONOUS MOTOR DRIVE

CURRENT VECTOR CONTROL WITH MAXIMUM TORQUE/AMPERE

Control the PMSM machine with maximum torque/ampere principle to minimize losses Minimum converter rating Maximum efficiency

TORQUE EXPRESSION

Defining the base torque as

……..(2) Base current IB defined as

Dividing (1) by (2)

where

TeB = (3/2)(P/2) Lm Ifr IB

IB = Lm Ifr /(Lq –Ld )

MAXIMUM TORQUE/AMPERE TRAJECTORY ON CONSTANT TORQUE LOCI

Consider for example, Te(pu) =1.0 locus in the second quadrant.

Any radial distance on the locus from the origin represents the stator current magnitude

Point A on the locus represents minimum stator current

For higher Te(pu) ,the corresponding optimum points are B,C,D etc.

For positive torque , the polarity of iqs positive. wheras the polarity of ids is negative.

Polarity of torque reversed by reversing iqs current.

STATOR CURRENT COMPONENTS AS FUNCTION OF TORQUE FOR MAXIMUM TORQUE/AMPERE

SPEED CONTROL SYSTEM WITH OPEN LOOP MAXIMUM TORQUE/AMPERE

Speed control loop generates the torque command Te

*. From Te

* signals, command currents ids

* and iqs*

generated with the help of function generators FG1 and FG2 respectively.

Polarity of ids* negative

irrespective of torque polarity.

Polarity of iqs* dictated by Te * .

The absolute position signal θe converts the rotating frame signals ids

* and iqs*

into stationary frame phase current commands ia* , ib* and ic* .

SENSORLESS CONTROL

SENSORLESS CONTROL

Unlike trapezoidal SPM machine ,the sensorless control of sinusoidal SPM machine difficult because Three devices in the inverter conduct at any

instant Continuous position signal of the rotor required

for the control. Three methods of sensorless control

Terminal voltage and current sensing Inductance variation or saliency effect State elimination based on the extended Kalman

Filter (EKF method)

TERMINAL VOLTAGE AND CURRENT SENSING

Simplest method . unit vectors derived from machine terminal

voltages and currents.


The estimation equations are

…….(1)

…….(2)

Cos(θr + δ) and sin (θr + δ) are unit vector signals

…….(3)


Cos(θr + δ) and sin (θr + δ) are unit vector signals

The estimated speed can be calculated using (3) .

SENSORLESS CONTROL OF SINUSOIDAL SPM DRIVE

SENSORLESS CONTROL OF SINUSOIDAL SPM DRIVE

The error between reference speed (ωr*) and the estimated speed (ωr) fed to a function generator to generate the corresponding command signals Is and Im .

These fed to a vector rotator(VR) and transformed into a three phase stator current command.

PMSM MOTOR CONTROL USING DSPIC 30F2010

SALIENT FEATURES

Potentiometer R14 selects the desired speed (Reference Speed).

Rotor position is detected using Hall effectsensors connected to pins RB3, RB4 and RB5.

The current is sensed using a 0.1 ohm resistor(R26).

SOFTWARE BLOCK DIAGRAM

OVERVIEW When the motor is running, Measured Speed is subtracted from

Reference Speed (desired speed) and the resulting error is processed by the PID controller to generate the amplitude of the sine wave. The Reference Speed is set by an external potentiometer,

Measured speed is derived from a Hall effect sensor. Once Amplitude is known, two additional parameters are needed

for sine generation. One parameter is the period of the sine wave, which is taken from one of the Hall effect sensors. The other parameter is the Phase, which is calculated using Phase Advance, depending on speed range requirements and the rotor position from the Hall effect sensors.

The Amplitude variable sets the amount of motor current and the resulting torque. An increase in torque corresponds to an increase in speed. The speed ontrol loop only controls Amplitude. The value of Phase from the Phase Advance block is derived .

Main State machine, interacts with all the other software blocks using global variables

TORQUE-SPEED CHARACTERISTICS (OF IPM PMSM)

FLUX-SPEED RELATION

where

REGIONS OF OPERATION

constant torque region constant power or field weakening region.Boundary between two regions of operation

depends upon the dc input (or battery) voltage Vd .

With higher Vd, the limit of phase voltage Vs increases proprtionally.

pmsm_2012.ppt

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