WEI+Ping　WANG+Yan　WANG+Hui

【Abstract】This paper studics the problem of speed tracking for the three-phase induction motor with uncertain parametres and load torque disturbance.The PWM control is to control the width of pulse technique.The proposed controllerit is the most profound for induction motor with the the PWM control technology. It can control requirements of induction motor speed system under uncertain conditions. The overall control scheme is scientific and reasonable， the output performance of the system is greatly improved. The results of the MATLAB simulation illustrate the proposed approach effctively.

【Key words】Induction motor； Ihe MATLAB； Ihe PWM control

0 Introduce

With the development of computer science and control theories， the induction motor has become the mainly used electric drive[1]. There are a lot of mature control methods about induction motor speed control system. However， the traditional control method cannot solve the control requirements of induction motor speed system under different operating conditions due to the complex nonlinear construct. Therefore， designing a good control is significant to fit the complex characteristics of induction motor speed system. The PWM technology[2] is accompanied by the development of power electronic devices and developed， now already mature. The PWM technology has adapt to many areas of technology， such as DC chopper， harmonic absorption， reactive power compensation and frequency conversion devices[3]. The designed controller based on the PWM technique is simple， versatile， with a fixed switching frequency.The control performance of induction motor can effectively be improved by the proposed controller. Application of PWM control technology for motor control[4] is the most widely， in particular， speed control. This paper is based on the PWM voltage on the speed control of there-phase induction motor[5]. The results of the MATLAB simulation illustrate the effectiveness of the proposed approach. This study has lots of practical application value.

1 The PWM inverter

The PWM modulation technique is a variable-width multi-pulse modulation technique. Sinusoidal pulse width modulation and sinusoidal output waveform is equivalent to a series of amplitude of the rectangular pulse waveform with varying width. Put a half sine wave divided into n equal parts， and then the area of each aliquot sine curve and a horizontal axis are surrounded by a place of this area that is equal to the rectangular pulse， rectangular pulse of constant amplitude. Each pulses and the midpoint of the midpoint of the sine wave coincides with each aliquot. Similarly， the negative half-cycle sine wave can also be used in the same manner with a series of negative pulse wave equivale.

Fig.1 The circuit of the inverter

Fig.1： VTl ～ VT6 is six power inverter switching devices （in this painting is the transistor）， each one is headed by an anti-parallel freewheeling diode. Its control circuit is in a symmetrical three-phase sinusoidal reference voltage signal. It is provided by the reference signal generator. The inverter output frequency determines the fundamental frequency， so output frequency should be adjustable within the desired range. The amplitude of the reference signal may also be within a certain range， it determines the size of the output voltage. Triangular carrier signal is used in common.Respectively， it generates a “positive” or “zero” saturation output after each phase reference voltage.

2 The Circuit Design

Sources library selected in three sinusoidal signal and a triangular signal. To compare the size of the signal by the comparator. In this case， the amplitude of the sinusoidal signal is fixed to 0.9， the effect of adjusting the voltage does not reach.

Fig.2 The circuit MATLAB simulation model

3 MATLAB simulation circuit design

Build the system in Simulink main circuit as shown below. Simpower systems primarily used in the Toolbox and Simulink.

Fig.3 MATLAB simulation circuit block diagram

Fig.4 Phase bridge inverter module

In the design， select six IGBT and six diodes in SimoPwerSystems. In the Power Electronics library， according to the principle circuit diagram of the IGBT and diode connected in anti-parallel.

Fig.5 The measuring module

As shown in Fig.5： Choose a three-phase asynchronous motor module in SimoPwerSystems the Machines library while selecting an Machines Measurement Demux module to measure the change of the speed of the motor、 the stator current and electromagnetic torque. Wm is the angular velocity， so choose a Gain block to be translated into speed. Select a Timer Module to select different loads at different times.

4 The Simulation set

As is shown in the picture： Set the motor operating parameters.

Fig.6 The Motor of the parameters

5 The Simulation results and analysis

Add the desired speed signal to adjust ω■■ jump to 70r / min at 0.4s. As is shown from the observation system speed track performance. It is stator current curve as shown in the Fig.7， the speed curve is shown in the Fig.8.

Fig.7 Stator current curve

Fig.8 Speed curve

The simulation results are as follows： according to ωm=60f/np，if np is unchanging， the speed suddenly increases would inevitably lead to the current frequency increasing， the simulation results is shown in Fig.7. Seen from Fig.7， the speed can quickly track changes in expectations and stabilize the new setpoint.

6 Summary

The control performance of induction motor can effectively be improved by the proposed controller simulation in Matlab. The results show that the uncertainty in the motor parameters and the external load disturbance conditions. The results of the MATLAB simulation illustrate the proposed approach effctively.This study has been practical application value.

【References】

[1]BOSE B K.. Modern power electronic and AC drives[M]. Upper Saddle River， NJ， USA： Prentice Hall PTK. 2002：178-186.

[2]LI Yongdong， GA0 Yue， HOU Xuan. Development of PWM control technology in multi-level converter [J]. Power Electronics. 2005，39（5）：2-6.

[3]JIANG Weidong，WANG Qunjing，SHI Xiaofeng. Low frequency oscillation of neutral point voltage of neutral- point clamped three-level VSI under SVPWM control [J].Proceedings of the CSEE. 2009，29（3）：49-55.

[4]TALLAM R M， NAIK R， NONDAH T A. A carrier based PWM scheme for neutral—point voltage balancing in three-level inverters[J].IEEE Transactions on In- dustry Applications. 2005，41（6）：1734-1743.

[5]HU Cungang， WANG Qunjing， LI Guoli et a1. A neutral-point potential balancing algorithm three level inverter based on virtual-space. Vector[J].Trans-actions of China Electro technical Society. 2009，24（5）：100-107.

[責(zé)任編輯：湯靜]