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Closed Loop Voltage Control of an Induction Motor using
SVM
Dr.S.Prakash, Dr.J.Hameed Hussain Professor & Head
Department of Electrical and Electronics Engineering
BIST, Bharath Institute of Higher Education and Research, Bharath University.
Abstract— This paper proposes a proficient implementation scheme for the voltage control of an
induction motor drive with ‘Space Vector Pulse Width Modulation (SVPWM)’. Voltage control is
required to meet the variation in the input voltage and to regulate the output of the inverter. Space
Vector Modulation (SVM) is an algorithm for the control of Pulse Width Modulation (PWM). For low
and medium power applications SVM is efficient and economical.The performance of Space Vector
Modulation technique and Sinusoidal Pulse Width Modulation are compared and SVM gives better
harmonic response with higher efficiency.
Keyword-Voltage control of Induction Motor; THD ; Space Vector Modulation; Three Phase Inverter
I. INTRODUCTION
Motor drives are popularly applied in air conditioning, fans, pumps, compressors, chillers, escalators,
elevators and industrial drives. One of the common and most popular drives with real applications is the
induction motor drive. Three phase induction machine is most widely used in industry because of its simple
construction, reliable operation, lightness and cheapness[1-6]. The AC induction motor drive is the fastest
growing segment of the motor control market.
Voltage controllers are increasingly applied as motor soft starters and sometimes as energy savers,
reducing the flux level in the connected induction motor in accordance with the load. When practical SCR
voltage controllers are used, they result in considerable harmonic distortion and substantial additional losses.
The use of Space Vector Modulation (SVM) inverter eliminates this drawback partially. SVM has the
advantage of lower harmonics in addition to the features of complete digital implementation by a single chip
microprocessor. Thus, SVM is advantageous over phase control and PWM. Due to the growing demand in
improving the performance of motor drives, there is an increasing need to improve the quality and reliability of
the drive circuit.
With the increasing availability and power capability of MOSFET and IGBT switches, SVM
converters can efficiently and economically be used.In an inverter, a variable voltage can be obtained by varying
the gain of the inverter. This could be done by PWM control within inverter. The gating signals are generated by
comparing a reference signal with a triangular carrier wave.The number of pulses per half-cycle depends on the
carrier frequency. But, this PWM involves relatively high harmonic distortion in the supply.
A generalized model of three phase induction motor using MATLAB\SIMULINK is described [1].
Three space vector pulse width modulation schemes called seven segments SVM, five segments SVM, three
segment SVM and basic principle of SVM is put forth. The various steps involved in the realization of SVM are
proposed [2] and [3].Voltage source inverter which is controlled with Space Vector Modulation (SVM) is
designed based on artificial neural network (ANN) [4].
An efficient implementation scheme for the closed loop speed control of an induction motor with
constant v/f control, slip regulation and SVM technique and a neural network based implementation of SVM of
a voltage source inverter is focused [5] and [6].The performance of Space Vector Modulation technique and
Sinusoidal Pulse Width Modulation are compared for harmonics, THD and output voltage. The various other
PWM techniques are discussed. It is observed SVM has better performance [7] and [8].The open and closed
loop speed control infers that performance is improved by SVM [9]. The need for energysaving and the control
scheme using variable voltage for the machine which operates at optimum efficiency have been focused [10].
In the above literature, the voltage control scheme for three phase induction motor drive is not
implemented using SVM. In this paper, the simulink model for the voltage control scheme of SVM fed
induction motor is developed and the results are presented.
II. SVM INVERTER FED INDUCTION MOTOR DRIVE
International Journal of Pure and Applied MathematicsVolume 119 No. 7 2018, 1599-1609ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu
1599
SVM is quite different from PWM methods. SVM treats the inverter as a single unit; the inverter can
be driven to eight unique states. The block diagram of voltage control of SVM inverter fed induction motor
drive is shown in Fig.1.
Fig 1. Block diagram of Voltage control of SVM Inverter fed Induction Motor Drive
The three phase inverter has six power switches S1 to S6 and are controlled by switching variables
aa', bb', cc'. When an upper transistor is switched on, i.e., when a, b or c is 1, the corresponding lower
transistor is switched off, i.e., the corresponding a′, b′ or c′ is 0.Therefore, the on and off states of the upper
transistors S1, S3 and S5 can be used to determine the output voltage. The output voltage is measured and is
given to the SVM controller[11-16]. The control circuit regulates the output voltage. The SVM treats the
sinusoidal voltage as a constant amplitude vector rotating at constant frequency. SVPWM technique
approximates the reference voltage Vref by a combination of the eight switching patterns (V0 to V7). Three-
phase voltage vector is transformed into a vector in the stationary d-q coordinate frame. The vectors (V1 to
V6) divide the plane into six sectors (each sector: 60 degrees). Vref is generated by two adjacent non-zero
vectors and two zero vectors.
III. SWITCHING TIME CALCULATOR
Realization of SVM involves
Step 1: Determination of Vd, Vq, Vref and angle (α)
Step 2: Determination of time duration T0, T1 and T2
Step 3: Determination of the switching time of each transistor.
Three phase (abc) system to two phase (dq) system is obtained using Park’s transformation.
Fig 2. Voltage space vectors and its components in (d, q)
From the Fig.2,
Vd =Van-Vbn.cos60-Vcn.cos60
Vq =0+Vbn.cos30-Vcn.cos30
The angle between Vd and Vref is calculated as
α =tan-1 (vq/vd)
International Journal of Pure and Applied Mathematics Special Issue
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Fig 3. Reference vector as a combination of adjacent vectors at sector 1
Switching time duration at any sector
= + + (1)
T1 = Tz.a. (2)
T2 = Tz.a. (3)
T0 = Tz - (T1+ T2) (4)
Switching time duration at any sector
T1 ==
=
= (5)
T2 =
= (6)
T0 = Tz - T1-T2, (7)
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Fig 4. Switching time calculator
The switching time calculator is used to calculate the timing of the voltage vector applied to the motor.
The block input is the sector in which the voltage vector lies, alpha and the magnitude of the reference
voltage[17-21]. The gate logic receives the timing sequence from the switching time calculator. This block
compares the triangle and the gate timing signals to activate the inverter switches at the proper time
IV. d-q MODEL OF AN INDUCTION MOTOR
The three phase induction motor is modelled using Krause’s theory. The equivalent d-q model of a three phase
induction motor is shown in Fig.5. From this figure, various equations required for the modelling are obtained.
The modelling equations are used in flux linkage form Fig 5.
Fig 5. d-q model of an induction motor
The induction motor block consists of three blocks; abc-syn conversion block (three phase voltages are
converted to two phase voltages in synchronously rotating frame), induction motor d-q block (flux linkage state
equations are used in this block) and syn-abc conversion block (it is opposite to that of abc-syn conversion
block).
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V. SIMULATION RESULTS OF OPEN LOOP OF VOLTAGE CONTROL OF THREE PHASE INDUCTION MOTOR
USING SVM
The open loop voltage control of an induction motor is shown in Fig.6. In open loop control, the
voltage fluctuations are introduced through the circuit breaker[22-28]. The output voltage varies with the
fluctuations in the input voltage and the result is shown in Figure 7.
Fig 6. Open Loop Voltage Control of an Induction Motor
The performance parameters of inverters are determined using PWM and SVM techniques. The
corresponding harmonic spectrums are given in Fig.8 and Fig.9. For each variation in the input voltage, the
respective output voltage is measured[29].
0 0.5 1 1.5 2 2.5 30
50
100
150
200
250
Time(sec)
Volta
ge(V
)
Fig7. RMS Output Voltage of the open loop control of an Induction Motor
Fig 8. Harmonic Spectrum of PWM Output Voltage using Fast Fourier Technique
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Fig 9. Harmonic Spectrum of SVM Output Voltage using Fast FourierTechnique
The comparison is made between PWM and SVM fed induction motor drive systems and is presented in Table I.
TABLE I COMPARISON BETWEEN PWM AND SVM FED INDUCTION
MOTOR DRIVE SYSTEMS
Parameters PWM SVM
V01 284 V 296 V
THD 16.63% 8.53%
From the Table I, it is observed that, SVM has improved fundamental voltage and lower THD. In open loop
voltage control, the voltage fluctuations are introduced through the circuit breaker as shown in Fig.6. In open
loop control, the output voltage varies with the fluctuations in the input voltage and the results are shown in
Fig.9.
5.1 Closed Loop Voltage Control
The closed loop voltage control of the induction motor drive system is shown in Figure 10. Here, the
RMS voltage is compared with the reference voltage. The subsystem of the closed loop scheme is shown in
Figure 11.The error signal is given to the PI controller[30]. From the error voltage signal, frequency is obtained
by suitable transformations. By using the voltage and frequency, the three phase voltages are produced. The
switching signals are generated for each switch. Based on the reference value, the voltage is obtained and thus
the voltage is controlled.
powergui
Continuous
v+-
V
err ers signal rms
M6
gm
DS
M5
gm
DS
M4
gm
DS
M3
gm
DS
M2
gm
DS
M1
gm
DS
Induction Machine
Tm m
A
B
C
a
b
c
gm
12
gm
12
gm
12
gm
12
100
<Rotor speed (wm)>
Figure 10. Closed Loop Voltage Control of an Induction Motor
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Figure 11. Subsystem of the Closed Loop Scheme
The three phase (abc) system to two phase (dq) system is obtained using Park’s transformation.
Equations 8, 9 are used for the conversion of three phases to two phase system. These equations are obtained
from obtained from Figure 12.
Vd =Van - Vbn cos 60 – Vcn cos 60 (8)
Vq =0 + Vbn cos 30 – Vcn cos 30 (9)
Figure 12 Three Phase to Two phase Transformation
The angle between Vd and Vref (alpha-α) is calculated using equation 10.
α=tan-1(Vq/Vd) (10)
The switching time is calculated to know the timing of the voltage vector applied to the motor. The block input
is the sector in which the voltage vector lies[31]. The timing sequence obtained is compared with the triangle
signal and the gate timing signals to activate the inverter switches at the proper time are generated. The RMS
output voltage of the closed loop control of an induction motor drive is shown in Figure 13.
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Figure 13. RMS Output Voltage of the Closed Loop Control of an Induction Motor
IV. CONCLUSION
Voltage control scheme for Induction motor drive using Space vector modulation is implemented and studies the
performance parameter by MATLAB/SIMULINK. It is observed that SVM has improved fundamental
component and reduced THD of 8.53%compared to the PWM technique. With the SVM inverter fed induction
motor, voltage can be effectively controlled with reduced harmonic content. Simulation results reveals that with
the open loop voltage control, the output voltage is not regulated and it varies with the fluctuations in the input
voltage[32-36]. This can be overwhelmed using closed loop voltage control, when the output voltage is
regulated irrespective of the fluctuations in the input voltage. In order to meet the constant voltage requirement,
the closed loop control is proposed. The performance characteristic of Space Vector Modulated Inverter fed
three phase induction motor is evaluated and it is found that, it gives better response and considerably less THD.
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