A Sensorless Boost-type Direct Vector Control for Induction Motor Drive

A Sensorless Boost-type Direct Vector Control for Induction Motor Drive

Jeng-Yue Chen, Tsung-Cheng Chen, Gwo-Jen Chiou and Jhang-Yu Wang

Department of Electrical Engineering National Formosa University No.64, Wunhua Rd., Huwei Township,

Yunlin 632, Taiwan, R. O. C.

E-mail of Corresponding Author: [email protected] Telephone: +886-5-6315607

Abstract -- In this paper, a novel sensorless boost-type DC/AC motor drive is proposed. Based on a generalized zero vector technique, the proposed drive has several advantages such as higher output voltage to increase motor efficiency, reduced weight and space of the battery etc. The magnitude, phase and frequency of air-gap flux can be obtained by adopting 120

control strategy for motor coil. Therefore, using the signals of air-gap flux some motor parameters can be modified easily in real time to achieve real vector control for driving motor.

Besides, the proposed drive can regenerate energy back to source to increase efficiency such that it can be applied to hybrid vehicle.

Finally, some experimental results are presented for verification.

Keywords -- Sensorless, Generalized zero vector, Vector control

I. I NTRODUCTION

Three-phase induction motor has been widely used in industrial applications. The field-oriented control is frequently adopted [1-2]. Due to variation of parameters, several control strategies such as flux estimation, adaptive control [3-7] are presented to improve the disadvantage. However the used control circuit is still complicated. In addition, the sensorless vector control of induction motor is presented [8-12]. Also, the control method without speed sensor can not achieve real vector control [13-17]. Hence, in this paper a sensorless boost- type direct vector control for driving induction motor is proposed to achieve real vector control, low cost and applications to mobile vehicle. Next, the proposed control method is described in detail as follows.

II. T HE PROPOSED INDUCTION MOTOR DRIVE

The proposed motor drive is shown in Fig. 1. In Fig. 1, the motor drive consists of one boost DC/DC converter and a three-phase inverter. The timing diagram of gating signals is shown in Fig. 2. When S

is closed, the current of inductor L increases and the capacitor C transfers its storing energy to three-phase inverter, which is operated in 120

conducting mode. Conversely, when S

is opened, six switches of the inverter are closed in order to restore energy into the capacitor C.

S1 S3 S₅

S2 S₄ S₆

S0

Vdc

L C

Fig. 1. The proposed induction motor drive

S

S

S

S

S

S

S

V

V

V

V

V

V

Fig. 2. The timing diagram of gating signals

Therefore, the terminal voltage which is applied to motor can be boosted.

) 1 ( D ₀ V

V _dc = _c − ⁽¹⁾

Where

D 0 : duty cycle of the switch S

In addition, any one of the three legs of the bridge is not conducted alternatively for anytime. Hence, from the open circuit coil, the phase angle and magnitude of back EMF can be obtained. To calculate the magnitude of back EMF, the induction motor rotor speed can be obtained without speed sensor. The motor control strategy is described as follows.

III. T HE STRATEGY OF DIRECT VECTOR CONTROL The control block of the proposed drive is shown in Fig.

3. In Fig. 3, the indirect vector control is adopted. Due to variation of motor parameters, the real vector control can not be achieved directly. However, those parameters can be adjusted by proposed control strategy to achieve real vector control. The output torque is expressed as follows.

δ ψ ^{|| | sin}

| ⋅

= t m qs

e K i

T 

(2)

gain L i

R L

qs r r r

sl m ⎠ ⋅⎟⎟ ⋅

⎜⎜ ⎞

⎝

= ⎛ | |

|

| ψ

ω  ⁽³⁾

With respect to maximum torque, the angle δ ^{is 90}

^.

Then, the back EMF e _CN of coil can be detected in one third cycle. In Fig. 4, to maintain maximum torque, the angle between back EMF e

with i _qs must be kept at 30 degree.

Therefore, from open circuit coil, the phase angle of back EMF can be controlled by adjusted the gain. Based on (3), the slip frequency ω

is modified to achieve real direct vector control without using any sensor.

ω

ω

*

i

*

i

*

ω

i

S

S

S

S

S

S

S

V

L C

ω

ω

*

i

V

Fig. 3. The control block of the proposed drive

axis b −

axis c −

axis a −

30

axis b −

qs

i

− axis axis a −

axis c −

ds

i

− axis

| ψ ^

|

a b c

- 1 2 V

1 2 V

- 1 2 V

1 2 V

- 1 2 V

1 2 V

1 2 V

- 1

2 V

1 2 V

- 1 2 V

1 2 V

- 1

2 V

- 1

2 V

1 2 V

I

II III

IV

V

VI

I II III IV

IV V VI

ψ ^

V

qs

i

Fig.4 The relationship phase diagram of back EMF and i _qs

IV. SOME E XPERIMENTAL RESULTS

The parameters of the proposed drive are listed as follows.

DC source: 48 V

L : 114mH C : 2000µF

Switching frequency: 100k Hz MOSFETs: IRF460

Induction motor: 750W, 110V, 2000r.p.m

Under duty cycle D

= 0 . 5 , the voltage across capacitor C is 82.5V, as shown in Fig. 5. Next, from the open circuit coil

C , the back EMF can be obtained. Based on the phase of i

, one can find the difference of 30

between e

with i

^as

shown in Fig. 6. The estimated rotor speed is shown in Fig. 7, one can find the trajectory of the estimated rotor speed ω

to follow the speed ω

, which is detected by encoder.

Therefore, the proposed drive can achieve real vector control without using speed sensor. Fig. 8 shows the dynamic speed responses of the drive system. It is observed clearly from Fig.

8 that the proposed IM drive system can follow the command

speed ω

without using speed sensor.

.

(50V/div, 2V/div, 1 μ ^s/div)

Fig. 5. The duty cycle D

and capacitor voltage V

(50V/div, 1A/div, 10ms/div) Fig. 6. The back EMF e

^and i

(500rpm/div, 2s/div) Fig. 7. The estimated rotor speed

ω

and the real speed ω

(250rpm/div, 500ms/div) (a)

(250rpm/div, 500ms/div) (b)

Fig. 8. The dynamic speed responses of the drive system

V. C ONCLUSIONS

This paper has proposed a novel sensorless boost-type DC/AC motor drive. Based on a generalized zero vector technique, the single-stage structure of the motor drive is configured with a boost converter and a full-bridge inverter.

The drive’s higher output voltage has some advantages of high efficiency for driving motor, reduced weight and space of the battery etc. The magnitude, phase and frequency of air- gap flux can be obtained by adopting 120

control strategy for motor coil. Therefore, using the signals of air-gap flux some motor parameters can be modified easily in real time to achieve real vector control for driving motor. A prototype of the designed motor drive for an induction motor (750W, 110V, 2000r.p.m) with 48 V

input has been successfully implemented and some experimental results are presented for verification.

V V _C = 82 . 5

5 .

0 = 0 D

e CN

i qs

r − EMF

ω

ω r

ω r

*

ω

ω r

*

ω

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