This document summarizes a research paper that proposes an improved indirect rotor flux oriented control method for PWM inverter-fed induction motor drives. The paper presents the modeling of an induction motor in the rotor flux reference frame and a method for estimating rotor flux using current models. Simulation results using MATLAB/Simulink are provided to demonstrate the effectiveness of the proposed current source inverter drive system under different operating conditions, showing improved performance over traditional voltage source inverter drives. The proposed control method aims to simplify design while reducing costs compared to other drive topologies.

1. ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010
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: gerald.gera@gmail.com, arulresearch2006@gmail.com
2
Thiagarajar College of Engineering /Department of EEE, Madurai, Tamilnadu, India
Email: preee@tce.edu
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 θ 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
alternatives for motor supply (cyclo-converters being confined feedback loop, but the flux is controlled by the feed
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
Vector Control) is also presented. To verify the design of Inverter (CSI) topology. This is partly due to the current
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
by an ac machine is controllable when vector control is - the possibility of internal short circuits resulting from
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 θ and sin θ) 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 ψr or stator flux ψs 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
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© 2010 ACEEE
DOI: 01.IJEPE.01.03.67

2. 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 ψr is compared with its reference ψr*
(4)
to generate d-axis stator current reference ids*. The q-axis
stator current reference iqs* is generated according to the
torque reference Te*. The feedback dq-axis stator currents The investigated induction motor’s parameters are given
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 Vabc* in Where
stationary reference frame. The rotor flux angle θ is used 34.7
in transformation blocks for field orientation.
Fig. 2 shows the block diagram of flux feed forward 0.1557
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 ‘θ’ can be calculated from the
the dc current of the rectifier. The q-axis (torque- following expressions.
producing) stator current reference iqs* and d-axis (flux-
producing) current reference ids* 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
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3. 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
the purpose of this control method is aimed to reduce the
3 3
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-
Simulink environment along with their respective control
cos (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)
Lrl=0.8e-3 Rotor leakage inductance (H)
(16)
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)
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4. 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)
Electromagnetic Torque with ripples
the speed reference suddenly changed at .2 sec. Fig. 5(b)
shows the electromagnetic torque response with refer to the
speed reference.
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5. 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
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© 2010 ACEEE
DOI: 01.IJEPE.01.03.67