# Improved Indirect Rotor Flux Oriented Control of PWM inverter fed Induction Motor Drives

### Text-only Preview

Improved Indirect Rotor Flux Oriented Control of

PWM inverter fed Induction Motor Drives

I. Gerald Christopher Raj

*1, Dr. P. Renuga*

*2, and M. Arul Prasanna 1*

1 PSNA College of Engineering and Technology/Department of EEE, Dindigul, Tamilnadu, India

Email: [email protected], [email protected]

2 Thiagarajar College of Engineering /Department of EEE, Madurai, Tamilnadu, India

Email: [email protected]

**Abstract****-- In today's high-power electrical drives using vector**

transformer are

*d-q*axis current components

**and the rotor**

**controlled induction machines, voltage source inverters (VSI)**

position

*and the output is the current reference vector*

**based on PWM technology and current source inverters (CSI)**

based on the stator coordinate

**There is no interlinkage flux**

*.***based on based on PWM technology are the most important**

feedback loop, but the flux is controlled by the feed

**alternatives for motor supply (cyclo-converters being confined**

to very low speed applications). In this paper an Induction

to very low speed applications). In this paper an Induction

forward control utilizing the machine parameters [4]-[6],

**motor modeled in the rotor flux reference frame, the rotor**

[8], [9].

**flux orientation is obtained, a high performance current fed**

The vector controlled drives employ mostly a Voltage

**Indirect Rotor Flux Oriented Controller also proposed and a**

Source Inverter (VSI

**)**to control the motor armature,

**comparative performance analysis of the VSI & CSI drive**

despite the inherent advantages of the Current Source

**topologies in Flux-Feed forward Vector Control (Indirect**

Inverter (CSI) topology. This is partly due to the current

**Vector Control) is also presented. To verify the design of**

controllers and system performance, the drive system

controllers and system performance, the drive system

source nature of the topology and the complexity of the

**simulation is carried out using MATLAB/Simulink. The**

controls required, the voltage source being a more

**steady state and dynamic performance of the drive system for**

universal power supply and being easier to control [10]-

**different operating conditions are studied. The simulation**

[12]. The VSI has drawbacks that complicate control

**results are provided to demonstrate the effectiveness of the**

circuit implementation and may reduce the drive reliability,

**proposed drive system.**

including:

**Index Terms****-- CSI, Indirect, Rotor flux Orientation, Vector**

- the requirement for additional circuit to protect the

**control, VSI.**

converter against internal and external short circuit,

- the high

*dv/dt*of the pulse width modulated inverter

I. INTRODUCTION

output which is known to have resulted in motor

winding failures,

It is well known that the instantaneous torque produced

- the possibility of internal short circuits resulting from

by an ac machine is controllable when vector control is

applied. There are essentially two general methods of

improper gating, particularly under fast transients, this

vector control. One called the direct or feed-back method

reduces the converter reliability

was invented by Blaschke [1], and the other, known as the

To overcome these problems this paper proposes a

indirect or feed forward method, was invented by Hasse

voltage-regulated CSI fed Indirect Rotor-Flux-Oriented

[2]. The methods are different essentially by how the unit

Control (IRFOC) of induction motor drive which offers the

vector (cos

*and sin ) is generated for the control. It*

same features as its VSI counterpart, together with the

should be mention here that the orientation of

*ids*with rotor

added advantages inherent in the CSI topology, namely

flux

*r*or stator flux

*s*is possible in vector control [3].

suppression of high

*dv/dt*across motor windings, built-in

The rotor flux orientation gives natural decoupling control,

short-circuit protection, natural power reversibility and

whereas stator flux orientation gives a coupling effect

high reliability with minimum torque ripple. In section II

which has to be compensated by a decoupling the basic concept of flux feed forward control for VSI &

compensation current. Therefore the ac machine controlled

CSI drive topologies explained. The section III deals

by the vector control scheme is equivalent to a separately

induction motor model in rotor flux frame and the current

excited dc machine.

model of rotor flux estimation. The simulation circuit

Nowadays, the flux-feed forward vector control system

models and results are discussed in section IV.

is preferred to the flux-feedback type because it requires no

flux detector or flux calculator. The indirect vector control

II. FLUX-FEED FORWARD VECTOR CONTROL

circuit inputs the amplitude of the torque component

current reference vector and the amplitude of the

Fig. 1 shows the block diagram of flux feed forward

interlinkage flux reference vector and calculates the current

vector control of induction motor fed from voltage source

reference vector based on the rotor coordinate

**utilizing the**

*,*inverter. Here both inverter output voltage and frequency

machine parameters. The inputs of the coordinate

7

(c) 2010 ACEEE

DOI: 01.IJEPE.01.03.67

ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010

This converts the CSI into a voltage source, but preserves

the inherent features of the CSI topology listed above

closely as possible.

III. INDUCTION MOTOR MODEL AND ROTOR FLUX

ESTIMATION

Figure 1. Flux-feed forward vector control with VSI

The model of three-phase squirrel-cage induction motor

in the rotating rotor flux reference frame can be expressed

as

(1)

.

(2)

Figure 2. Flux-feed forward vector control with CSI

(3)

can be controlled by its PWM scheme. For the rotor flux

control the calculated

***

*r*is compared with its reference

*r*

(4)

to generate

*d*-axis stator current reference

*i **

*ds*. The

*q-*axis

stator current reference

*i **

*qs*is generated according to the

torque reference

*T **

The investigated induction motor's parameters are given

*e*. The feedback

*dq-*axis stator currents

are compared with their references, and errors are send to

in Table 1. The rotor flux can be calculated from the

current controllers to generate stator voltage reference in

following expressions.

*dq-*axis voltages in synchronous reference frame then they

.

are transformed to three-phase stator voltages

*V*

***

*abc*in

Where

stationary reference frame. The rotor flux angle is used

34.7

in transformation blocks for field orientation.

0.1557

Fig. 2 shows the block diagram of flux feed forward

vector control of induction motor fed from current source

0.8

34.7

35.5

inverter. Here the inverter output frequency is controlled by

PWM scheme but the inverter output current is adjusted by

The rotor flux angle `' can be calculated from the

the dc current of the rectifier. The

*q*-axis (torque-

following expressions.

producing) stator current reference

*i **

*qs*and

*d*-axis

*(flux-*

producing) current reference

*i **

*ds*are generated in the same

(5)

manner as in the case of VSI fed drives.

Where

The general control system block diagram of the

proposed CSI induction motor drive is shown in Fig. 3.

Here the gating patterns are generated in a manner such

The

*dq*-axis current components can be obtained from

that the inverter output voltage is regulated.

the following expressions.

(6)

(7)

The transformation of the three-phase (

*abc*-axis) current

components of an induction motor to the equivalent two-

phase (

*dq*-axis) current components can be performed by

2

4

2

3

3

.

3

2

4

3

3

The three-phase current components ias, ibs, and ics are in

stationary reference frame which does not rotate in space

whereas the two phase current components ids, iqs are in the

synchronous reference frame whose direct and quadrature

Figure 3. Proposed Rotor Flux-feed forward vector control with CSI

axes rotate in space at the synchronous speed

8

(c) 2010 ACEEE

DOI: 01.IJEPE.01.03.67

ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010

IV. ANALYSIS AND SIMULATION RESULTS

2

2

The proposed control algorithm is derived from the basic

3

3

.

principle of rotor field orientation control. Consequently,

4

4

so it is still vector control method. It should be noted that

3

3

the purpose of this control method is aimed to reduce the

money cost in hardware, and simplify the control design.

The rotor flux can also be calculated from the following

The drive architectures of Fig. 1, Fig. 2 and Fig. 3 have

equations

been completely implemented and assessed in the Mat lab-

cos

Simulink environment along with their respective control

(8)

systems. The simulation is based on the parameters shown

in Table I and Table II.

**Fig. 5 to 9 shows the dynamic**

sin

(9)

responds of VSI vector control and proposed CSI vector

control scheme in case of no load and 200 Nm load.

(10)

Rotor Flux vector estimation using current model

In the low-speed region, the rotor flux components can

be synthesized more easily with the help of speed and

current signals. The rotor circuit equations can be given as

0

(11)

0

(12)

Adding the terms

Figure 4. Simulink diagram of actual induction motor model in rotor flux

(13)

frame

Table I

Induction Motor Parameters

(14)

50HP, 460V, 4Pole, 60Hz, Squirrel-cage motor

Respectively, on both sides of the above equations (11),

Values in SI Units

Nominal Parameters

(12) the equations becomes

Rs=0.087

Stator resistance (Ohm)

(15)

Rr=0.228

Rotor resistance (Ohm)

Lsl=0.8e-3

Stator leakage inductance (H)

(16)

Lrl=0.8e-3

Rotor leakage inductance (H)

Lm=34.7e-3

Magnetizing inductance (H)

After simplification

P=4

Number of poles

(17)

J=1.662

Moment of inertia (kg.m2)

Bm=0.1 Torque

speed

coefficient

(18)

Table II

The above two equations give rotor fluxes as functions

Gains of Controller

of stator currents and speed. After knowing these signals,

the fluxes and corresponding unit vector signals can be

Kp = 100

Proportional Gain

estimated. Flux estimation by this requires a speed encoder,

but the advantage is that the drive operation can be

Ki = 2500

Integral Gain

extended down to zero speed.

TL= 350

Torque Limit (N.m)

9

(c) 2010 ACEEE

DOI: 01.IJEPE.01.03.67

ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010

**a)**

Fig. 6 shows the proposed flux feed forward vector

controlled drive's modeling results at no load TL = 0 N.m.

Fig. 6(a) shows the phase A stator current response when

the speed reference suddenly changed at .2 sec. Fig. 6(b)

shows the electromagnetic torque response with refer to the

speed reference.

Fig. 7 shows the proposed flux feed forward vector

controlled drive's modeling rotor speed response with refer

to the speed command. The speed command suddenly

increased at 0.2 sec. and suddenly decreased at 1.5 sec. the

motor speed follows the reference speed.

**b)**

Figure 7. Simulated waveforms of PWM current source inverter fed

induction motor drive's rotor speed response with refer to the rotor speed

Figure 5. Simulated waveforms of PWM voltage source inverter fed

reference-speed command change at 0.2sec. and 1.5sec.

induction motor drive with no load TL = 0 N.m a) phase A stator current.

**a)**

b) Electromagnetic Torque

**a)**

**b)**

**b)**

Figure 6. Simulated waveforms of PWM current source inverter fed

induction motor drive with no load TL = 0 N.m a) phase A stator current b)

Electromagnetic Torque

Fig. 5 shows the VSI fed flux feed forward vector

controlled drive's modeling results at no load TL = 0 N.m.

Figure 8. Simulated modeling waveforms of PWM VSI fed induction

Fig. 5(a) shows the phase A stator current response when

motor drive with load torque TL =200 N.m a) Phase A stator current b)

the speed reference suddenly changed at .2 sec. Fig. 5(b)

Electromagnetic Torque with ripples

shows the electromagnetic torque response with refer to the

speed reference.

10

(c) 2010 ACEEE

DOI: 01.IJEPE.01.03.67

ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010

**a)**

and transient state conditions. At very low speed, proposed

indirect rotor-flux-oriented control (IRFOC) of induction

motor drive is particularly sensitive to an accurate rotor

resistance value in the rotor flux. To overcome this

problem, the implementation of online tuning rotor

resistance variation of the induction motor is essential in

order to maintain the dynamic performance of the drive. So

the implementation of online rotor resistance tuning is the

main future scope of this paper.

REFERENCES

[1] F.Blaschke, "The principle of field orientation as applied to

**b)**

the new transvector closed-loop control

*system*for rotating

field Machines,"

*Siemens Review,*vol.34, pp.217-220, May

1972.

[2] Hasse, K., "Zum dynamischen Verhalten der

Asynchronmaschine bei Betrieb mit variabler

Standerfrequenz und Standerspannung" ETZ-A 89, 1968, pp.

387-391

[3] R. W. De Doncker and D. W. ovotny, "The universal field

oriented controller",

*IEEE IAS Annu. Meet. Conf. Rec.*,pp.

450-456, 1988.

[4] R. Krishnan and P. Pillay, "Sensitivity analysis and

comparison of parameter compensation scheme in vector

controlled induction motor drives," in

*IEEE-IAS Ann.*

*Meeting Conf. Rec.,*1986, pp. 155-161.

Figure 9. Simulated modeling waveforms of PWM CSI fed induction

[5] J. Holtz, "Sensorless Control of Induction Motor Drives,"

motor drive with load torque T

*Proceedings of the IEEE, Vol. 90, No. 8, Aug. 2002, pp. 1359*

L =200 N.m a) Phase A stator current b)

Electromagnetic Torque with reduced ripples

*- 1394.*

[6] G. Pellegrino, R. Bojoi and P. Guglielmi, Performance

Fig. 8.a) shows the phase A stator current with ripples,

Comparison of Sensorless Field Oriented Control

so these ripples developed high electromagnetic torque

Techniques for Low Cost Three-Phase Induction Motor

ripples shown in Fig. 8.b). The ripples are minimized in the

Drives", Industry Applications Conference, 42nd IAS

proposed system. Fig. 9.a) shows the ripple free phase A

Annual Meeting. 2007.

stator current, so the developed electromagnetic torque has

[7] P.Vas,

*Vector Control of AC Machines*, Clarendon Press,

Oxford, 1990.

low ripples shown in Fig. 9.b).

[8] B.K. Bose, Modern Power Electronics and AC Drives, 2001,

Pearson Education.

CONCLUSIONS

[9] P. C. Krause, O. Wasynczuk, and S. D. Sudhoff,

*Analysis of*

*Electric Machines and Drive Systems*, 2nd edition, Wiley-

In this paper, the control of a high performance PWM

IEEE Press, New York, 2002

current source inverter fed induction motor drive has been

[10] Miki, O. Nakao and S. Nishiyama, "A new simplified current

discussed. The control system has been realized in the

control method for fielddented induction drives",

*IEEE*

rotor-flux-oriented reference frame. The proposed CSI

*Trans. Ind. Appl.,*vol. 27, no. 6, pp. 1081-570, Nov./Dec.

drive topology exhibits the same high performance features

1991.

as the corresponding VSI topology, both in terms of

[11] B. Wu, S.Dewan and G. Slemon, "PWM-CSI inverter for

waveform quality and dynamic performance. It has

induction motor drives",

*IEEE Trans. Ind. Appl.,*vol. 28, no.

additional control flexibility (waveform and efficiency

1, pp. 317-325, Jan./Feb. 1992.

improvements) and the inherent advantages of the CSI

[12] H. Inaba, K. Hirasawa, T. Ando, M. Hombu and M.

Nakazato, "Development of a high-speed elevator controlled

topology (short-circuit protection, low output

*dv/dt.)*. The

by current source inverter system with sinusoidal input and

tests with the simulation model of Indirect Rotor Flux

output",

*IEEE Trans. Ind. Appl.,*vol. 28, no. 4, pp. 893-643,

Oriented Controller (Feed-Forward Vector Controller) for

July/August 1992

induction motor show excellent performance in both steady

11

(c) 2010 ACEEE

DOI: 01.IJEPE.01.03.67