closed loop voltage control of an induction motor using svm · 2018. 3. 15. · induction motor...

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

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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

1600

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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closed loop voltage control of an induction motor using svm · 2018. 3. 15. · induction motor...

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