DIGITAL SIGNAL PROCESSING BASED ON MOTOR CONTROL

PREPARED BYB MANISHA

ECE1

Contents• Introduction• What is DSP ?• Why and how the digital platform ?• Motor control trend• DSP Controllers• TMS320 Family overview• TMS320C24X DSP Controller• AC Induction motor• The scalar control• The vector control• Application• Conclusion

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Introduction• Motor Control industry is a strong aggressive sector.• We have major problems in this industry are Power

consumption reduction and EMI Radiation reduction imposed by Government and power plant lobbies.

• This results lead to need of enhanced algorithms.• DSP technology allows to achieve the high level

performance as well as system cost reduction.• Texas instruments launches a new DSP , referenced

TMS320C240, specifically designed for the digital motor control segment.

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What is DSP ?• DSP stands for Digital Signal Processing, deals with

processing on signals to get desired output/response on digital processors.

• some of basic processes/operations on signals involves1. Filtering,2. Scaling(Amplification/Attenuation),3. Addition or Substraction of two or more signals,4. Integration/differentiation,5. Modulation(Amplitude/Angle), etc.

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Why and how the digital platform ?• Why Digital ?• Advantage1. Flexibility2. Accuracy3. Storage4. Low cost5. Compact size6. Reliability

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Cont...

• Disadvantages1. Limitation of A/D2. Expensive3. Quantisation error

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Motor control trend• Market analysis shows that most of all industrial motor

applications use induction motor.• Traditionally motor control was designed with analog

components. However there are several drawbacks with analog systems.

• Digital systems offer improvements over analog design. They are:

1. Drift is eleminated.2. Upgrades can easily be made in software.

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Cont.....

• Digital signal processors go on further to provide high speed and high resolution in order to reduce system costs.

• Generally fixed point DSPs are preferred for motor control for two reasons

1. Less cost.2. Dynamic ranfe is 16 bit.

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DSP Controllers

• DSP controllers are known as Digital signal controllers(DSC).

• Digital signal controllers are hybrid of microcontrollers and DSPs.

• In DSCs, DSP is used as control element.

• The top three DSC vendors are Texas Instruments,Freescale, and Microchip Technology.

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cont....

A Large Range of ApplicationsØ AppliancesØ AppliancesØ Industrial servo drivesØ Automotive control

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Cont...

Benfits of DSCs• favours system cost reduction by an efficient control in

all speed range implying right dimensioning of power device circuits.

• enables a reduction of harmonics using enhanced algorithms, to meet easier requirements and to reduce filters cost.

• removes speed or position sensors by the implementation of sensorless algorithms.

• provides single chip control system.• enables a reduction of harmonics using enhanced

algorithms, to meet easier requirements and to reduce filters cost.

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cont....

DSPs controllers may also performs the following:• enables control of multi-variable and complex systems.• performs adaptive control.• provides diagnostic monitoring with FFT of spectrum

analysis.• produces sharp-cut-off notch filters that eliminate narrow-

band mechanical resonance.

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TMS320 Family overview• This family consists of fixed point,multiprocessor digital

s ignal processors (DSPs) , and f ixed-point DSP controllers.

• TMS320 DSPs have an architecture designed specifically for real-time signal processing.

• The TMS320 supports the power switching device commutation, control algorithm processing,data communications and system monitoring functions.

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History of the TMS320 family

• The TMS320 family currently includes five generations of DSP.

• TMS320C25, a CMOS 40-MHz digital signal capable of twice the performance of the TMS320C1x devices.

TMS320C1x, TMS320C2x, TMS320C3x, TMS320C4x,

and TMS320C5x

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TMS320C24X DSP Controller• The TMS320C24x is a member of the TMS320 family

of digital signal processors(DSPs). • The ’C24x is designed to meet a wide range of digital

motor control(DMC) and embedded control applications.

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cont.....

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Cont....

TMS320C240 • Texas Instruments launches a new DSP, referenced

TMS320C240, specifically designed for the Digital Motor Control segment.

• The TMS320C240 device combining a 16 bit fixed-point DSP core with microcontroller peripherals in a single chip solution is part of a new generation of DSPs called the DSP controllers.

• These systems lack the ability to execute advanced algorithms fast enough for real-time control.

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cont...TMS320C240 Architecture

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AC Induction motor

• The motor studied in this note is part of the Alternative Current supplied motors. It is the squirrel c a ge a s ync h r onous m o t o r, named AC induction motor.

• The least expensive and most widely spread induction motor is the squirrel cage motor.

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cont.....

• There are several ways to control an induction motor in torque, speed or position, they can be categorized into two groups they are :

1) Scalar control2) Vector control

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The scalar control• Scalar control means that variables are controlled only in

magnitude and the feedback and command signals are proportional to dc quantities.

• A scalar control method can only drive the stator frequency using a voltage or a current as a command.

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cont...

AdvantagesØ Its simplicity,Ø It is easy and fast to program,Ø Requires only few calculation capabilities.DrawbacksØ Very poor reaction time,Ø In this both flux and torque are the function of

voltage/current and frequency. This tends the system into instability due to higher order harmonics.

Ø This method needs some characteristic plots to describe part of the control.

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The vector control• The vector control is referring not only to the magnitude

but also to the phase of these variables.• This method takes into consideration not only successive

steady-states but real mathematical equations that describe the motor itself.

• Though the induction motor have a very simple structure, its mathematical model is complex due to the coupling factor between a large number of variables and then on-linearities.

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cont...

• The Field Oriented Control (FOC) offers a solution to circum vent the need to solve high order equations and achieve an efficient control with high dynamic.

• There are two approaches to vector control:1. Direct field oriented current control2. Indirect field iriented current control

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cont....

Principles of Vector Control• The basic conceptual implementation of vector control is

illustrated in the below block diagram:

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Field oriented control

• The FOC consists of controlling the stator currents represented by a vector.

• The goal of the FOC (also called vector control) on the asynchronous machine is to control the torque producing a n d m a g n e t i z i n g t h e f l u x components seperately.

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cont...

cont...

• Advantages of vector control1. Transient response will be fast,2. Vector control allows for speed control in all four

quadrants (without additional control elements),3. Reduction in size of motor, cost and power consumption.

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Applications• Refrigerators,• Washing machine,• Dryers,• Pumps,• Fans,• Blowers, etc.

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Conclusion• The DSPController TMS320C240 combines the

performance of a DSP architecture with the optimized peripherals of a Microcontroller in a single chip solutions for the control of an induction motor.

• With the DSP controller an intelligent control approach is possible to reduce the overall system costs and to improve the reliability of the drive system.

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