Major Improvements In Modern Industrial Processes

Published Date: 02 Nov 2017

1.0 Introduction

Major improvements in modern industrial processes over the past 50 years can be largely attributed to advances in variable speed motor drives. Prior to the 1950’s most factories used DC motors because three phase induction motors could only be operated at one frequency [1]. Now thanks to advances in power electronic devices and the advent of DSP technology fast, reliable and cost effective control of induction motors is now common place.

In 1997 it was estimated that 67% of electrical energy in the UK was converted to mechanical energy for utilization [2]. At the same time the motor drive market in Europe was in excess of one billion pounds. The increase in the use of induction motors was largely attributed to major oil and mining companies converting existing diesel and gas powered machinery to run off electricity [2]. Over the past five years however, the area of AC motor control has continued to expand because induction motors are excellent candidates for use in Electric or Hybrid Electric Vehicles.

In this application high performance control schemes are essential. Over the past two decades a great deal of work has been done into techniques such as Field Oriented Control, Direct Torque Control and Space Vector Pulse Width Modulation. Another emerging area of research involves the application of sensorless control. This differs from conventional methods because it doesn’t require mechanical speed or position sensors. Removing these sensors provides a number of advantages such as lower production costs, reduced size and elimination of excess cabling. Sensorless drives are also more suitable for harsh inaccessible environments as they require less maintenance. This undergraduate thesis thoroughly investigated the aforementioned techniques and used them to develop a Field Oriented Control Scheme for use in an Electric Vehicle.

[1] T. Wildi, Electrical machines, drives and power systems – 5th ed., Prentice Hall, New Jersey 2002

[2] N Moham, T.M. Undeland, W.P. Robbins, Power Electronics: Circuits, Devices and Applications 2nd ed., John Wiley & Sons, 1995

1.4 Why do we use an Induction motor?

For this application, the only external input for the electric motor applied by the user is

the accelerator; which is essentially a variable torque input. There are two existing

options for an electric motor: the .Direct current (DC). type or the .Induction. type.

Induction motors are universally used in industry because of their high robustness,

reliability, low price and high efficiency (up to 80% [15]). However, the brush-less DC

motor has been, traditionally, the more attractive option for variable torque control. This

is because the torque can be controlled by varying the .armature current (ia)., while the

flux can be controlled by varying the .field/exciting current (ix).. These two quantities

operate in a decoupled manner, which is highly advantageous from a design perspective.

Also, an induction machine has been difficult to control due to its complex mathematical

model, its non-linear behavior during the saturation effects and the electrical parameter

oscillation that depends on the physical influence of temperature [15].

However, the recent fruition of .digital signal processors (DSPs). has swung the

pendulum toward the induction motor for torque control. These high computational

power silicon devices have made it possible to realize far more precise digital control

algorithms. Field Orientated Control (FOC), for instance, is a vector control method that

demonstrates the capability of performing direct torque control. FOC provides an

induction motor every advantage that DC machine control can have, while freeing itself

from mechanical commutation drawbacks [9]. It is anticipated that the application of the

2001 Thesis Project A4 Gareth S Roberts

correct control algorithm combined with the inherent efficiency and power potential will

make this design very compatible for use in a hybrid car. Additionally, the induction

machine makes execution of .regenerative braking. relatively simple. Regenerative

braking is a means of using the induction machine as a brake. It is anticipated that the

outcomes from this thesis project support the claim that an induction motor is a better

means of motivating a hybrid or an electric car.

1. INTRODUCTION

Because of advances in solid state power devices and microprocessors ,switching power converters

are used in more and more modern motor drives to convert and deliver the required energy to the motor.

Variable frequency ac drives are increasingly used for various applications in industry and traction. Pulse

width modulated (PWM) dc-ac converters have a wide range of applications in ac motor drives and ac power

conditioning systems [1]. The PWM strategy plays an important role in the minimization of harmonics and

switching losses in these converters, especially in the three-phase applications.Various modulation strategies,

control schemes, and realization techniques [2].

In the design of a PWM control IC, there are many factors need to be considered, such as simplicity,

flexibility, and complexity in the circuit design. The width of the pulses changes from pulse to pulse

according to a modulating signal. When a PWM signal is applied to the gate of a power transistor, it causes

the tum on and turn off intervals of the transistor to change from one PWM period to another PWM period

according to the same modulating signal.

As to modulation is concerned the space vector modulation (SVM) has attracted great interest in

recent years. Because the harmonic better than those of the other modulation method. The advantage of

lower THD is without increasing the switching losses. The emergence of multilevel inverters has been in

increase since the last decade. These new types of converters are suitable for high voltage and high power

application due to their ability to synthesize waveforms with better harmonic spectrum.

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IJRES Vol. 1, No. 1, March 2012 : 11 – 18

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Thus this paper demonstrates that a more efficient and faster solution is the use of Field

Programmable Gate Array (FPGA’s), it investigates how to generate a variable PWM waveform based on

Xilinx FPGA and the proposed design is tested by functional/timing simulation and experiments.The rest of

the paper is organized as follows. Section II pictorial representation of a three phase inverter circuit.Section

III briefly introduces the principle of symmetrical space vector PWM method. Section IV details on

FPGA.Section V the hardware circuit represented as an block diagram. Section VI explains the experimental

results and Section VII is the conclusion.

[1] H.W. Van der Broek, H.C. Skudelny, and G.V. Stanke, "Analysis and realization of a pulse width modulator based on

voltage space vectors", IEEE Trans. Ind. Applicat., Vol.24, p.p.142 – 150, Jan / Feb.1988.

[2] Z. Yu, A. Mohammed, and I. Panahi, "A review of three pwm techniques", in Proc. Amer. Control Conf., 1997, pp.

257 – 261.

PWM inverters are becoming more and more popular in

today’s motor drives. Sinusoidal Pulse Width Modulation

(SPWM), is used to control the inverter output voltage and

maintains a good performance of the drive in the entire range

of operation between zero and 78 percentage of the value that

would be reached by square operation [1][2]. The Pulse

Width Modulation (PWM) Technique called "Vector

Modulation", which is based on space vector theory, is the

most important development in the last few years[3][4][5].

Although, several of PWM methods have been created in the

past, the vector modulation technique appears to be the best

alternative for a three phase switching power converter

[6][7][8]. FPGA’s development reached a level of maturity

that made them the choice of implementation in many

fields[9].Recent applications of FPGA’s in industrial

electronics include mobile- robot path planning and

intelligent transporation [10][11],current control applied to

power converters [12][13],real-time hardware in the loop

testing for control design[14], controller implementation

[15][16], separating and recovering independent source

signals[17], and neural computation[18]. Since the concept of

multilevel PWM converter was introduced, various

modulation strategies have been developed and studied in

detail, such as multilevel sinusoidal PWM, multilevel

selective harmonic elimination and space vector modulation.

Among these strategies, the space vector PWM (SVPWM)

[19][20] stands out because it offers significant flexibility to

optimize switching waveforms and is well suited for digital

implementation. Complexity and computational cost of

traditional SVPWM techniques increases with the number of

levels of the converter, and most of all use trigonometric

functions or precomputed tables [21][22].The

implementation of FPGA of in SVPWM control for a

voltage source inverter has been described in detail in

[23][24]

A symmetrical space vector modulation PWM pattern is

proposed in this paper, it shows the advantage of lower THD

without increasing the switching losses. Thus this paper

demonstrates that a more efficient and faster solution is the

use of Field Programmable Gate Array (FPGA’s),it

investigates how to generate a variable PWM waveform

based on Xilinx FPGA [25 ]and the proposed design is tested

by functional/timing simulation and experiments.

The rest of the paper is organized as follows. Section II

briefly introduces the principle of symmetrical space vector

PWM method. Section III details on FPGA. Section IV the

hardware circuit which acts as the interface between the

FPGA and the VSI circuit. Section V explains the

experimental results and Section VI is the conclusion

[1] H.W. Van der Broek, H.C. Skudelny, and G.V. Stanke, "Analysis and

realization of a pulse width modulator based on voltage space vectors",

IEEE Trans. Ind. Applicat., Vol.24, p.p.142 – 150, Jan / Feb.1988.

[2] Z. Yu, A. Mohammed, and I. Panahi, "A review of three pwm

techniques", in Proc. Amer. Control Conf., 1997, pp. 257 – 261.

[3] Jin-Woo Jung, Ph.d Student, Ohio State University. "Space Vector

PWM Inverter".

[4] Ying-yu Tzou; Hau-Jean Hsu; Tien-Sung Kuo. Industrial Electronics,

Control, and Instrumentation, 1996, Proceedings of the 1996 IEEE

IECON 22nd International Conference. "FPGA based SVPWMcontrol

IC for 3-phase PWM inverters". Volume 1, Issue, 5-10 Aug 1996

Pages(s):138-143.

[5] Wenxi Yao, Haibung Hu, Zhengyu Lu, "Comparison of space vector

modulation and carrer based modulation of multilevel inverter", IEEE

Trans., Power Electronics, Vol.23, pp. 45 – 51, Jan 2008.

[6] J. Klima, "Analytical model for the time and frequency domain

analysis of space-vector PWM inverter fed induction motor based on

the Laplace transform of space-vectors", in Proc. Power Conversion

Conf., Osaka, Japan, 2002, pp. 1334 – 1339.

[7] G. Narayanan and V.T. Ranganathan, "Extension of operation of space

vector PWM strategies with low switching frequencies using different

overmodulation algorithms", IEEE Trans. Power Electron., Vol.17,

pp.788 -789, Sept. 2002.

[8] Bosquets Monge. S, Bordonau. J., Rocabert. J, "A virtual vector pulse

width modulation for a four level diode clamped DC-AC converter",

Power Electronics, IEEE Transaction, Vol.23, pp.1964 -1972, July

2008.

[9] J.J. Rodriguez-Andina, M.J. Moure, and M.D. Valdes, "Features,

design tools, and application domains of FPGAs", IEEE Trans. Ind.

Electron., vol.54, no.4, pp.1810 – 1823, Aug. 2007.

[10] K. Sridharan and T. Priya, "The design of a hardware accelerator for

realtime complete visibility graph construction and efficient FPGA

implementation," IEEE Trans. Ind. Electron., vol.52, no.4, pp. 1185 –

1187, Aug. 2005.

[11] S. Sanchez-Solano, A.J. Cabrera, I. Baturone, F.J. Moreno-Velo, and

M. Brox, "FPGA implementation of embedded fuzzy controllers forrobotic applications" IEEE Trans. Ind. Electron., vol.54, no.4,

pp.1937-1945, Aug. 2007.

[12] M.W. naouar, E. Monmasson, A.A. Naassani, I. Slama-Belkhodja, and

N. Patin, "FPGA-based current controllers for AC machine drives – A

review", IEEE Trans. Ind. Electron., vol.54, no.4, pp. 1907 – 1925,

Aug. 2007.

[13] M. Aime, G. Gateau, and T.A.Meynard, "Implementation of a peak

current-control algorithm within a field-programmable gate array",

IEEE Trans. Ind. Electron., vol.54, no.1, pp. 406-418, Feb.2007.

[14] B. Lu, X. Wu, H.Figueroa, and A. Monti, "A lo-cost real-time

hardware-in-the-loop testing approach of power electronics controls",

IEEE Trans. Ind. Electron., vol.54, no.2, pp.919-931, Apr. 2007.

[15] Y.F. Chan, M. Moallem, andW.Wang, "Design and implementation of

modular FPGA-based PID controllers", IEEE Trans. Ind. Electron.,

vol.54, no.4, pp. 1898 – 1906, Aug. 2007.

[16] J.Qin, C. Stroud, and F.F. Dai, "FPGA-based analog functional

measurements for adaptive control in mixed-signal systems", IEEE

Trans. Ind. Electron., vol.54, no.4, pp. 1885 -1897, Aug. 2007.

[17] H. Du, H. Qi, and X. Wang, "Comparative study of VLSI solutions to

independent component analysis", IEEE Trans. Ind. Electron., vol.54,

no.1, pp.548-558, Feb.2007.

[18] H. Zhuang, K.S. Low, and W.Y.Yan, " A pulsed neural network with

on-chip learning and its practical applications", IEEE Trans. Ind.

Electron., vol.54, no.1, pp. 34-42, Feb. 2007.

[19] H. Van der Broeck, H. Skudelny, and G. Stanke, "Analysis and

realization of a pulsewidth modulator based on voltage space vectors",

in Proc. IEEE Ind. Appl. Conf., 1986, pp.244-251.

[20] L. Franquelo, M. Prats, R. Portillo, J. Galvan, M. Perales, J. Carrasco, E.

Diez, and j. Jimenez, "Three-dimensional space-vector modulation

algorithm for four-leg multilevel converters using abc coordinates",

IEEE Trans. Ind. Electron., vol.53, no.2, pp. 459-466, Apr. 2006.

[21] D. W. Chung, J.S. Kim, and S.K. Sul, "Unified voltage modulation

technique for real-time three-phase power conversion", IEEE Trans.

Ind. Appl., vol.34, no.2, pp.374-380, Mar./Apr.1998.

[22] O. Alonso. L. Marroyo, and P. Sanchis, "A generalized methodology to

calculate switching times and regions in SVPWM modulation of

multilevel converters", in Proc. 10th Eur. Conf. Multilevel Converters

EPE.2001, pp. 920-925.

[23] Y.Y. Tzou and H.J. Hsu, "FPGA realization of space-vector PWM

control IC for three-phase PWM inverters" IEEE Trans. Power

Electron., vol.12, no.6, pp. 953-963, Nov. 1997.

[24] S.T.Jung,M-Y.Chang,J-Y.Jyang,L-C.Yeh and Y-Y.Tzou,"design and

implementation of an FPGA based control IC for AC-voltage

regulation," IEEE Trans. Power Electron., vol.14, no.3, pp. 522-532,

May. 1999.

[25] Xilinx Inc.,"Foundation Series ISE 3.11 User Guide’"2000.

Introduction

AC Induction motors are the most widely used motors in industrial motion control systems,

as well as in home appliances thanks to their reliability, robustness and simplicity of control.

Until a few years ago the AC motor could either be plugged directly into the mains supply or

controlled by means of the well-known scalar V/f method. When power is supplied to an

induction motor at the recommended specifications, it runs at its rated speed. With this

method, even simple speed variation is impossible and its system integration is highly

dependent on the motor design (starting torque vs maximum torque, torque vs inertia,

number of pole pairs). However many applications need variable speed operation. The

scalar V/f method is able to provide speed variation but does not handle transient condition

control and is valid only during a steady state. This method is most suitable for applications

without position control requirements or the need for high accuracy of speed control and

leads to over-currents and over-heating, which necessitate a drive which is then oversized

and no longer cost effective. Examples of these applications include heating, air

conditioning, fans and blowers.

During the last few years the field of electrical drives has increased rapidly due mainly to the

advantages of semiconductors in both power and signal electronics and culminating in

powerful microcontrollers and DSPs. These technological improvements have allowed the

development of very effective AC drive control with lower power dissipation hardware and

increasingly accurate control structures. The electrical drive controls become more accurate

with the use of three-phase currents and voltage sensing.

This application note describes the most efficient scheme of vector control: the Indirect Field

Oriented Control (IFOC). Thanks to this control structure, the AC machine, with a

speed/position sensor coupled to the shaft, acquires every advantage of a DC machine

control structure, by achieving a very accurate steady state and transient control, but with

higher dynamic performance.

In this document we will look at the complete software integration and also the theoretical

and practical aspects of the application.

Induction motors are the most widely used motors for

appliances, industrial control, and automation; hence,

they are often called the workhorse of the motion industry.

They are robust, reliable, and durable. When power

is supplied to an induction motor at the recommended

specifications, it runs at its rated speed. However,

many applications need variable speed operations. For

example, a washing machine may use different speeds

for each wash cycle. Historically, mechanical gear systems

were used to obtain variable speed. Recently,

electronic power and control systems have matured to

allow these components to be used for motor control in

place of mechanical gears. These electronics not only

control the motor’s speed, but can improve the motor’s

dynamic and steady state characteristics. In addition,

electronics can reduce the system’s average power

consumption and noise generation of the motor.

Induction motor control is complex due to its nonlinear

characteristics. While there are different methods for

control, Variable Voltage Variable Frequency (VVVF) or

V/f is the most common method of speed control in

open loop. This method is most suitable for applications

without position control requirements or the need

for high accuracy of speed control. Examples of these

applications include heating, air conditioning, fans and

blowers. V/f control can be implemented by using low

cost PICmicromicrocontrollers, rather than using

costly digital signal processors (DSPs).

Many PICmicro microcontrollers have two hardware

PWMs, one less than the three required to control a

3-phase induction motor. In this application note, we

will generate a third PWM in software, using a general

purpose timer and an I/O pin resource that are readily

available on the PICmicro microcontroller. This application

note also covers the basics of induction motors and

different types of induction motors

PWM inverters are becoming more and more popular in today’s motor drives. As a result, PWM inverter

powered motor drives offer better efficiency and higher performances compared to fixed frequency motor

drives. Sinusoidal Pulse Width Modulation (SPWM), is used to control the inverter output voltage and

maintains a good performance of the drive in the entire range of operation between zero and 78 percentage of

the value that would be reached by square operation. In the other hand, Space Vector Modulation Techniques

have been increased by using in last decade, because they allow reducing commutation losses and the

harmonic content of output voltage, and to obtain higher Amplitude modulation indexes if compared with

convectional SPWM techniques. The Pulse Width Modulation (PWM) Technique called "Vector

Modulation", which is based on space vector theory, is the most important development in the last few years.

Space Vector Modulation (SVM) was originally developed as a vector approach to pulse width

modulation (PWM) for three phase inverter. Field programmable gate arrays (FPGA's) are standard

integrated circuits that can be programmed by a user to perform a variety of complex logic functions. The

high level of integration available with these devices (currently up to 500,000 gates) means that they can be

used to implement complex electronic systems.

This paper presents a space vector pulse width modulation for an inverter circuit which drives the three

phase induction motor. The SVPWM pulses are thus generated by developing VHDL coding burnt in the

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FPGA kit and the triggering pulses are viewed by using the Xilinx software. Therefore this paper is a real

time implementation.

Thus the work is divided into 3 main sections.(I)the FPGA kit along with the coding(II)the driver circuit

which acts as the interfacing circuit board between the FPGA and the power electronics circuit board

(III)which consists of the hardware circuit of an three phase voltage source PWM inverter and the three

phase motor.