lecture 6 induction motor inverter control

Palestine Polytechnic University

Workshop Matlab/Simulink in Drives and Power electronics – Lecture 618-21 May 2009 / 18

WorkshopMatlab/Simulink in Drives

and Power electronics

Lecture 6 : Induction Motor Inverter Control

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Ghislain REMY Jean DEPREZ



Workshop Programe• 8 lectures will be presented based on Matlab/Simulink :

– 1 Introduction to Matlab

– 2 Introduction to Simulink

– 3 DC-Motor Control design

– 4 DC-Motor Chopper design SimPowerSystems

– 5 Introduction to Stateflow/Statechart

– 6 Induction Motor Inverter Control

– 7 Synchronous Motor Modeling

– 8 Synchronous Motor Control

• Two system applications (four quadrants electric drives of mechanical systems) will be used as "conducted lines" during the workshop.

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Summary• Short presentation of induction motor

• Model of Induction Motor using SimPowerSystems

• Scalar Control principle

• Vector Control principle

• Some examples of control architectures in Simulink

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Introduction• Variable speed control of AC electrical machines makes use of

forced-commutated electronic switches such as IGBTs, MOSFETs, and GTOs.

• Asynchronous machines fed by pulse width modulation (PWM) voltage sourced converters (VSC) are nowadays gradually replacing the DC motors and thyristor bridges. With PWM, combined with modern control techniques such as field-oriented control or direct torque control, you can obtain the same flexibility in speed and torque control as with DC machines.

• This lecture shows how to build an AC drive controlling an asynchronous machine

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• SimPowerSystems a specialized library containing 13 models of DC and AC drives. These “ready to use” models will enable you to simulate electric drive systems without the need to build those complex systems yourself.

• The Machines library contains four of the most commonly used three-phase machines and especially the asynchronous machine.

• Combined with linear and nonlinear elements such as transformers, lines, loads, breakers, etc., they can combined with power electronic devices to simulate drives.

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Power Electronics• In Lecture 4, we have seen that the Power Electronics library

contains blocks allowing you to simulate diodes, thyristors, GTO, MOSFETs, and IGBT devices. three-phase bridge.

• For example, an IGBT inverter bridge needs six IGBTs and six anti-parallel diodes.

• To facilitate implementation of bridges,the Universal Bridge block automatically performs these interconnections for you.

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Model of Induction Machine• In the Library Machines:

– The Asynchronous Machine block operates in either generator or motor mode.The mode of operation is dictated by the sign of the mechanical torque:

• If Tm is positive, the machine acts as a motor.

• If Tm is negative, the machine acts as a generator.

– The electrical part of the machine is represented bya fourth-order state-space model and the mechanical part by a second-order system.

– All electrical variables and parameters are referred to the stator.All stator and rotor quantities are in the arbitrary two-axis reference frame (dq frame).

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Model of Induction Motor (SimPowerSystems)

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The subscripts usedare defined as follows:



Effect of Saturation in the Induction Machine• The power_asm_sat demo illustrates the effect of saturation

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PWM Control of an Induction Motor

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Type 2 levelMode of operation Un-synchronizedCarrier frequency 18*60Hz (1080 Hz)Internal generation of selectedmodulating signalsModulation index m 0.9Output voltage frequency 60 HzOutput voltage phase 0 degreesSample time 10e-6 s

Power electronic device IGBT/DiodesSnubber Rs 1e5 Ω

Cs infRon 1e-3 Ω

Forward voltagesVf 0 VVfd 0 V

TailTf 1e-6 sTt 1e-6 s



Example 1: Induction Machine in Motor Mode• The power_pwm demo illustrates the use of the

Asynchronous Machine block in motor mode. It consists of an asynchronous machine in an open-loop speed control system.– The machine's rotor is short-circuited, and the stator is fed by a PWM

inverter, built with Simulink blocks and interfaced to the Asynchronous Machine block through the Controlled Voltage Source block. The inverter uses sinusoidal pulse-width modulation. The base frequency of the sinusoidal reference wave is set at 60 Hz and the triangular carrier wave's frequency is set at 1980 Hz.

– The 3 HP machine is connected to a constant load of nominal value (11.9 N.m). It is started and reaches the set point speed of 1.0 puat t = 0.9 second.

– The parameters of the machine are those found in the SI Units dialog box above. Tsimulate a smoothing an inductor is placed between the inverter and the machine.

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power_pwm: 3-Phase Asynchronous Machine

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What Control type for Induction Motor?• Classical technique :

– Six-Step Induction 3HP Motor Drive

– Space Vector PWM Induction 3HP Motor

– Field-Oriented Control Induction 200 HP Motor Drive

– Direct Torque Control (DTC) Induction 200 HP Motor Drive

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Six-Step

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• ac1_example: Six-Step Induction 3HP Motor Drive



Space Vector PWM

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• ac2_example: Space Vector PWM Induction 3HP Motor

Blue : Detailed Converter,Red : Average-Value Converter



Field Oriented Controller

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• ac3_example: Field-Oriented Control Induction 200 HP Motor Drive

Blue : Detailed Converter,Red : Average-Value Converter



Direct torque and flux control (DTC)

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• ac4_example: DTC Induction 200 HP Motor Drive



Solving Algebraic Loops• Example of a Self-Resetting Integrators

Because the two values are mutually dependent, Simulink software cannot determine either. It therefore signals an error if you try to simulate or update this model.

• Solution : State output– Or, adding a delay

In the feedback loop18

• It is a self-resetting integrator by feeding the integrator's output, subtracted from 1, back into the integrator's reset port.

• In so doing, the model creates an algebraic loop: To compute the integrator block's output, Simulink software needs to know the value of the block's reset signal, and vice versa.

lecture 6 induction motor inverter control

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