Vsi Csi with various loads

VSI,CSI AND TO DETERMINE THD USING MATLAB

CHAPTER-1

INTRODUCTION

1.1DEFINITION

Higher-performance control such as V/f control, slip-frequency control and field-

oriented control require that the magnitude and frequency of the motor supply voltage

be varied simultaneously. Since AC mains voltage have fixed magnitude and

frequency, variable-voltage-variable-frequency supply can only be obtained by using

power-semiconductor-controlled inverters or cyclo-converters. The cyclo-converter

needs more number of power semiconductor devices and can only provide variable

frequency that is considerably lower than the frequency of AC mains. The most

favourable and commonly used one is the power semiconductor inverter. The basic

structure of a three-phase inverter is shown in Fig.1.4.

The three-phase inverter requires at least six power semiconductor power

devices that can be either BJTs, or MOSFETs, or IGBTs, etc. working in switching

mode. A DC source, which can be either voltage source or current source, is

connected to the inverter. For the voltage-source inverter (VSI), a capacitor is put

across the DC link to provide the inverter with constant DC voltage source. For the

current-source inverter (CSI), an inductor is connected in series with the DC link to

provide the inverter with constant current source.

Taking VSI as an example, the basic operation of the inverter can be

summarized as follows: (1) the upper and lower devices in the same phase are

switched complementarily, (2) each device works periodically, (3) devices of three

phases work sequentially with 120° phase difference. Under this mode of operation,

the inverter converts the DC voltage into three-phase AC square-wave voltages across

lines AB, BC and CA. It is obvious that the frequency of those AC square waves is

EN DEPARTMENT, SRMGPC, LUCKNOW Page 1


equal to the switching frequency of each device, hence it is variable since the

switching frequency can be varied at will using electronic circuits. In the VSI, the

anti-paralleled diode is necessary for freewheeling of the inductive load currents.

Operation of the CSI is the same as that of the VSI except that the output of the

inverter is three-phase AC square-wave currents. For inductive loads such as the

induction motor, the output currents of the CSI cannot change as square waves but

still can rise or fall at a high rate, inducing superimposed spikes on the terminal

voltage of the motor at commutation transients.

The CSI has several advantages when compared with VSI [23]:

The power circuit is more rugged and reliable because over current due to short circuits

or commutation failure is prevented by the series inductor;

The power circuit has fewer components, hence are more efficient and less expensive;

It offers fast and direct control of motor torque over a wide range.

However, CSI has several limitations [23] when used for drive applications:

It cannot operate at high frequency because of the inductive load;

It cannot operate under no-load condition;

Large voltage spikes occur on the output phases causing high voltage stresses on the

power devices;

Response at light load is sluggish.

It causes torque pulsations and speed oscillations due to interaction of the stepped

stator current and nearly sinusoidal flux.

Moreover, the CSI requires a large-size DC-link inductor that is heavy and

bulky in comparison with the DC-link capacitor required by the VSI. Due to those

limitations and disadvantages mentioned above, CSI is not as widely used as VSI.



1.2 PWM TECHNIQUES

The periodic AC square wave output from the inverter contains the fundamental

components and harmonics. The fundamental component dominates the running of

the motor and the harmonics contribute to torque/speed pulsations and copper/iron

losses. Frequency of the fundamental component is the same as that of the square

wave and hence can be varied by varying the switching frequency. Amplitude of the

fundamental component can be varied in two ways. A straightforward way is to vary

the amplitude of the DC-link source but a controlled bridge rectifier is then required.

Moreover, the square wave contains significant harmonics, causing significant

torque/speed pulsation and copper/iron losses. A better way is not to vary the

amplitude of the DC-link source but to shape the square wave into multiple pulses by

switching the power devices at higher frequency within the original ON/OFF cycle

and to vary the duty ratio of the pulses based on the amplitude of the desired input for

the motor. This method is called pulse-width modulation (PWM). By using PWM

techniques, simultaneous variations of the amplitude and frequency of the

fundamental component can be achieved by operating the inverter only, i.e., the

switching control of the power devices, and the DC-link source can be simply an

uncontrolled bridge rectifier. The sinusoidal PWM (SPWM) method varies the duty

ratio of the pulse as a sine function that represents the desired sinusoidal inputs for the

motor. It makes the low-frequency harmonics insignificant and pushes the harmonic

frequencies to higher values. This effect will be more significant if the switching

frequency is higher. High-frequency harmonics contribute very little to the torque

generation of the motor and can be filtered out using small filter components. In most

cases the leakage inductances of the stator windings of the motor are sufficient to

filter out high-frequency harmonics.



PWM signals can be generated by using sub-oscillation methods [21], which use the

sinusoidal modulation signals to compare with the triangular carrier signals. This

method is preferred to implement in hardware using analogue components. When

digital signal processing methods based on microprocessors (e.g., DSP) is used, PWM

signals can be generated by using natural sampling techniques, which use the digitised

modulation signals to compare with the actual timer counts at high repetition rates to

obtain the required time resolutions. With either of the two methods, frequency of the

modulation signal determines the synchronous frequency of the motor while the

carrier frequency determines the switching frequency of the power device of the

inverter.

1.3 PROJECT DEFINITION

The word ‘inverter’ in the context of power-electronics denotes a class of power

conversion (or power conditioning) circuits that operates from a dc voltage source or

a dc current source and converts it into ac voltage or current. The ‘inverter’ does

reverse of what ac-to-dc ‘converter’ does. Even though input to an inverter circuit is a

dc source, it is not uncommon to have this dc derived from an ac source such as utility

ac supply. Thus, for example, the primary source of input power may be utility ac

voltage supply that is ‘converted’ to dc by an ac to dc converter and then ‘inverted’

back to ac using an inverter. Here, the final ac output may be of a different frequency

and magnitude than the input ac of the utility supply.

Irrespective of power flow direction, ‘inverter’ is referred as a circuit that operates

from a stiff dc source and generates ac output. If the input dc is a voltage source, the

inverter is called a voltage source inverter (VSI) similarly a current source inverter

(CSI), where the input to the circuit is a current source. The VSI circuit has direct

control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac)

current’. Shape of voltage waveforms output by an ideal VSI should be independent

of load connected at the output

Some examples where voltage source inverters are used are: uninterruptible power

supply (UPS) units, adjustable speed drives (ASD) for ac motors, electronic frequency

changer circuits etc. commercially available inverter units used in homes and offices

to power some essential ac loads in case the utility ac supply gets interrupted. In such

inverter units, battery supply is used as the input dc voltage source and the inverter



circuit converts the dc into ac voltage of desired frequency. The achievable magnitude

of ac voltage is limited by the magnitude of input (dc bus) voltage. In ordinary

household inverters the battery voltage may be just 12 volts and the inverter circuit

may be capable of supplying ac voltage of around 10 volts (rms) only. In such cases

the inverter output voltage is stepped up using a transformer to meet the load

requirement of, say, 230 volts.



CHAPTER-2

PROJECT OVERVIEW

2.1 PROPOSED METHODOLOGY

Voltage source inverters can be classified according to different criterions. They can

be classified according to number of phases they output. Accordingly there are single-

phase or three-phase inverters depending on whether they output single or three-phase

voltages. It is also possible to have inverters with two or five or any other number of

output phases. Inverters can also be classified according to their ability in controlling

the magnitude of output parameters like, frequency, voltage, harmonic content etc.

Some inverters can output only fixed magnitude (though variable frequency) voltages

whereas some others are capable of both variable voltage, variable frequency (VVVF)

output. Output of some voltage source inverters is corrupted by significant amount of

many low order harmonics like 3rd, 5th, 7th, 11th, 13th the desired (fundamental)

frequency voltage. Some other inverters may be free from low order harmonics but

may still be corrupted by some high order harmonics. Inverters used for ac motor

drive applications are expected to have less of low order harmonics in the output

voltage waveform, even if it is at the cost of increased high order harmonics. Higher

order harmonic voltage distortions are, in most ac motor loads, filtered away by the

inductive nature of the load itself. Inverters may also be classified according to their

topologies. Some inverter topologies are suitable for low and medium voltage ratings

whereas some others are more suitable for higher voltage applications. Voltages may

acquire either positive dc bus or negative dc bus potential. For higher voltage

applications it may not be uncommon to have three level or five level inverters.



BLOCK DIAGRAM OF VSI

FIG2.1 BLOCK DIAGRAM OF INVERTER



EXPLANATION OF BLOCK DIAGRAM

The switches in bridge configurations of inverters need to be provided with isolated gate (or base) drive signals. The individual control signal for the switches needs to be provided across the gate (base) and source (or emitter) terminals of the particular switch. The gate control signals are low voltage signals referred to the source (emitter) terminal of the switch. For n-channel IGBT and MOSFET switches, when gate to source voltage is more than threshold voltage for turn-on, the switch turns on and when it is less than threshold voltage the switch turns off. The threshold voltage is generally of the order of +5 volts but for quicker switching the turn-on gate voltage magnitude is kept around +15 volts whereas turn-off gate voltage is zero or little negative (around –5 volts). It is to be remembered that the two switches of an inverter-leg are controlled in a complementary manner. When the upper switch of any leg is on the corresponding lower switch remains ‘off’ and vice-versa. When a switch is on its emitter and collector terminals are virtually shorted. Thus with upper switch on the emitter of the upper switch is at positive dc bus potential. Similarly with lower switch on the emitter of upper switch of that leg is virtually at the negative dc bus potential.

Emitters of all the lower switches are solidly connected to the negative line of the dc bus. Since gate control signals are applied with respect to the emitter terminals of the switches, the gate voltages of all the upper switches must be floating with respect to the dc bus line potentials. This calls for isolation between the gate control signals of upper switches and between upper and lower switches. Only the emitters of lower switches of all the legs are at the same potential (since all of them are solidly connected to the negative dc bus) and hence the gate control signals of lower switches need not be isolated among themselves. As should be clear from the above discussion, the isolation provided between upper and lower switches must withstand a peak voltage stress equal to dc bus voltage. Gate-signal isolation for inverter switches is generally achieved by means of optical-isolator (opto-isolator) circuits. The circuit makes use of a commercially available opto-coupler IC, shown within dotted lines in the figure. Input stage of the IC is a light emitting diode (LED) that emits light when forward biased. The light output of the LED falls on reverse biased junction of an optical diode. The LED and the photo-diode are suitably positioned inside the opto-coupler chip to ensure that the light emitted by the LED falls on the photo-diode junction. The gate control pulses for the switch are applied to the input LED through a current limiting resistor of appropriate magnitude. These gate pulses, generated by the gate logic circuit, are essentially in the digital form. A high level of the gate signal may be taken as on command and a low level (at ground level) may be taken as ‘off’ command. Under this assumption, the cathode of the LED is connected to the ground point of the gate-logic card and anode is fed with the logic card output. The circuit on the output (photo-diode) side is connected to a floating dc power supply.



The control (logic card) supply ground is isolated from the floating-supply ground of the output. In the figure the two grounds have been shown by two different symbols. The schematic connection shown in the figure indicates that the photo-diode is reverse biased. A resistor in series with the diode indicates the magnitude of the reverse leakage current of the diode. When input signal to LED is high, LED conducts and the emitted light falls on the reverse biased p-n junction. Irradiation of light causes generation of significant number of electron-hole pairs in the depletion region of the reverse biased diode. As a result magnitude of reverse leakage current of the diode increases appreciably. The resistor connected in series with the photo-diode now has higher voltage drop due to the increased leakage current. A signal comparator circuit senses this condition and outputs a high level signal, which is amplified before being output.

Thus an isolated and amplified gate signal is obtained and may directly be connected to the gate terminal of the switch (often a small series resistor, as suggested by the switch manufacturer, is put between the output signal and the gate terminal of the switch).



CHAPTER-3

VSI CIRCUIT DIAGRAMS ,MODELS,SUBSYSTSEM AND

WAVEFORMS

3.1 SINGLE PHASE HALF BRIDGE VSI WITH RESESTIVE

LOAD

FIG.-3.1 CIRCUIT DIAGRAM OF SINGLE PHASE HALF BRIDGE VSI



FIG.-3.2 VOLTAGE AND CURRENT WAVEFORM



In the power topology of a half-bridge VSI, where two large capacitors are required

to provide a neutral point N, such that each capacitor maintains a constant voltage

(Vi)/2. Because the current harmonics injected by the operation of the inverter are

low-order harmonics, a set of large capacitors (C+ and C-) is required. It is clear that

both switches S+ and S- cannot be ON simultaneously because a short circuit across

the dc link voltage source Vi would be produced. There are two defined (states 1 and

2) and one undefined (state 3) switch state as shown in Table 1. In order to avoid the

short circuit across the dc bus and the undefined ac output voltage condition, the

modulating technique should always ensure that at any instant either the top or the

bottom switch of the inverter leg is on.



3.2 SINGLE PHASE VOLTAGE SOURCE INVERTER WITH

(RL) LOAD

Without pwm:-

FIG.-3.3 MODEL OF SINGLE PHASE HALF BRIDGE VSI WITHOUT

PWM

With pwm:-



FIG.-3.4 MODEL OF SINGLE PHASE HALF BRIDGE VSI WITH

PWM



PARAMETER

TABLE-3.1



FIG.-3.5 THD VALUES



3.3 SINGLE PHASE FULL BRIDGE VSI WITH RESISTIVE

LOADS

This inverter is similar to the half-bridge inverter. however, a second leg provides the

neutral point to the load. As expected, both switches S1+ and S1- (or S2+ and S2-)

cannot be on simultaneously because a short circuit across the dc link voltage source

Vi would be produced. There are four defined (states 1, 2, 3, and 4) and one undefined

(state 5) switch states as shown in Table 2. The undefined condition should be

avoided so as to be always capable of defining the ac output voltage. It can be

observed that the ac output voltage can take values up to the dc link value Vi, which is

twice that obtained with half-bridge VSI topologies. Several modulating techniques

have been developed that are applicable to full-bridge VSIs. Among them are the

PWM (bipolar and unipolar) techniques.



FIG.-3.6 CIRCUIT DIAGRAM OF SINGLE FULL HALF BRIDGE VSI



FIG.-3.7 VOLTAGE WAVEFORM



FIG.-3.8 FFT ANALYSIS



3.3 THREE PHASE FULL BRIDGE VSI WITH RESISTIVE

LOADS

FIG.-3.9 CIRCUIT DIAGRAM OF THREE PHASEFULL BRIDGE VSI



Single-phase VSIs cover low-range power applications and three-phase VSIs cover

the medium- to high-power applications. The main purpose of these topologies is to

provide a three-phase voltage source where the amplitude phaseand frequency of the

voltages should alwaysbecontrollable.

Although most of the applications require sinusoidal voltage waveforms (e.g., ASDs,

UPSs, FACTS, VAR compensators), arbitrary voltages are also required in some

emerging applications (e.g., active filters, voltage compensators).The standard three-

phase VSI topology is shown in Fig eight valid switch states are given in Table . As in

single-phase VSIs, the switches of any leg of the inverter (S1 and S4, S3 and S6, or

S5 and S2) cannot be switched on simultaneously because this would result in short

circuit across the dc link voltage supply. Similarly, in order to avoid undefined states

in the VSI, and thus undefined ac output line voltages,the switches of any leg of the

inverter cannot be switched off simultaneously as this will result in voltages that will

depend upon the respective line current polarity. Of the eight valid states, two of them

produce zero ac line voltages. In this case, the ac line currents freewheel through

either the upper or lower components. The remaining states produce non-zero ac

output voltages. In order to generate a given voltage waveform, the inverter moves

from one state to another. Thus the resulting ac output line voltages consist of discrete

values of voltages that are Vi , 0, and -Vi for the topology shown in Fig. The selection

of the states in order to generate the given waveform is done by the modulating

technique that should ensure the use of only the technique to control the motor

armature, ac adjustable-speed induction motor drives employ mostly a voltage-source

inverter topology. Both scalar and vector control of induction motors are used in this

approach, the latter requiring current control of the. Although energy storage is more

practical and efficient in capacitors than in inductors, the use of VSIs may result in

reduced drive reliability due to the high of the pulse width modulated inverter output

voltage. However, the can be significantly lowered by filtering the VSI output

voltage. This can be achieved by adding filtering reactors, or better, LC filters.

The current-source inverter topology offers a number of inherent advantages,

including short-circuit protection, the output current being limited by the regulated

dc-bus current; 2) low output voltage .

AC drive CSI based on a phase-controlled front-end rectifier (50% nominal load and

60-Hz output). (a) Power topology. (b) Supply phase voltage and supply line current).



(c) DC rectifier voltage (vr) and dc-link current) CSI line current and load line

voltage(vab)Load phase voltage (vla) and load line current tages over conventional

CSI motor drive implementations:

1) the gating signals are directly generated by the spacevectordigital modulator (extra

circuitry is only necessary toensure overlaps

2) the potential resonances are eliminateddue to the feedback-based voltage

controller; 3) the stresseson power switches and the overall losses are always

minimumdue to the minimum dc-link current operation; and 4) due tothe constant

inverter modulation index operation, the motorvoltage harmonic distortion is constant,

which minimizes the induction motor losses and allows an accurate output

filterdesign. These features make the CSI drive an interesting alternative to VSI-based

drives operating at similar switching frequency, when the requested fundamental

reactive power could be disregarded with respect to output power.A complete

comparison with standard CSI-based ac drivesis also presented. Key performance

indices, such as harmonic distortion (THD), PF, and time response are evaluated

andtabulated for both the standard and the proposed schemes. Experimental results are

given for a 2-kVA induction motor drive.



3.4 THREE PHSE FULL BRIDGE VSI 180 DEGREE MODE WITH

RESISTIVE LOAD

FIG.-3.10 MODEL



FIG.-3.11 SUBSYSTEM



PARAMETER



FIG.-3.12 PHASE AND LINE VOLTAGE AND CURRENT WAVEFORM



FIG.-3.13 LINE VOLTAGE FFT ANALYSIS



FIG.-3.14 LINE CURRENT THD AND FFT ANALYSIS



3.5THREE PHASE FULL BRIDGE VSI 120 DEGREE MODE

WITH RL LOAD

FIG-3.15PHASE FULL BRIDGE VSI 120*MODE WITH RL LOAD



FIG-3.16 SUBSYSTEM




WITH R LOAD

FIG-3.17 MODEL



FIG-3.18 SUBSYSTEM




WITH RL LOAD

FIG-3.19 MODEL



FIG-3.20 SUBSYSTEM



3.7SINGLE PHASE FULL BRIDGE VOLTAGE SOURCE

INVERTER WITH (RL) LOAD

FIG-3.21 MODEL



FIG-3.22 SUBSYSTEM



FIG-3.23 FFT ANALYSIS CURRENT



FIG-3.24 FFT ANALYSIS VOLTAGE



FIG-3.25 VOLTAGE AND CURRENT WAVEFORM



3.8 THREE PHASE FULL BRIDGE VSI 180 DEGREE MODE

WITH INDUCTION MOTOR LOAD

Model:

FIG.-3.26 MODEL OF THREE FULL BRIDGE VSI 180 DEGREE MODE

WITH INDUCTION MOTOR LOAD



SUBSYSTEM OF VSI

FIG.-3.27 SUBSYSTEM OF VSI



PARAMETERS OF IM



FIG3.28 CHARACTERISTIC OF 120 MODE IM



IM THD FOR TORQE

FIG3.29 FFT ANALYSIS FOR TORQE



CHAPTER-4

CSI CIRCUIT DIAGRAMS ,MODELS,SUBSYSTSEM

AND WAVEFORMS

4.1 SINGLE PHASE FULL BRIDGE CSI WITH RESESTIVE

LOAD

FIG.-4.1 CIRCUIT DIAGRAM OF SINGLE PHASE FULL BRIDGE CSI



FIG.-4.2 MODEL DIAGRAM OF SINGLE PHASE FULL BRIDGE CSI



FIG.-4.3 VOLTAGE AND CURRENT WAVEFORM



FIG.-4.4 CURRENT FFT ANALYSIS



FIG.-4.5 VOLTAGE FFT ANALYSIS



CHAPTER-5

ADVANTAGE

5.1 FFT ANLYSIS

There are numerous industries where the surroundings are unsafe for the employment

of human labor due to the existence of hazardous environments. Robots can be used

effectively in such environments where handling of radioactive materials is involved,

such as hospitals or nuclear establishments, where direct exposure to human beings

can be dangerous for their health.

5.2 IMPROVE POWER FACTER

Robots perform operations with superior exactitude, ensure uniformity of production

due to which rejections are minimized, and reduce losses. Measurements and

movements of tools being utilized are more accurate. Thus, the quality of the product

manufactured is improved manifold compared to the performance by human beings.

5.3 TO IMPROVE IFFICIENCY

Robots have the ability to work continuously without pause, unlike human labor for

which breaks and vacation are essential. Thus, production is increased by the

utilization of robots in industrial applications, and consequently profits of the

production unit are increased.

5.4 EASY TO SELECT LOAD ACROSS VSI AND CSI

In many production establishments work required to be executed is awfully boring,

being cyclic and repetitive, due to which it is difficult for the operators to remain fully

dedicated to their tasks and generate interest in their work. When tasks are

monotonous, workers tend to be careless, thereby increasing the probability of

accidents and malfunctions of machines. Utilization of robots has eliminated

problems associated with boredom in production.



CHAPTER-6

APPLICATIONS AND LIMITATIONS

6.1APPLICATIONS

1. Monitoring and Security System

2. Tracking and navigation.

3. SURVIALLIANCE

4. NAVY AND ARMY

5. Rescuing purpose

6. Space mission

7. Find its path in difficult terrains and battle field

8. Use of renewable energy

9. Robotics and solarbotics

10. Obstacle detector

8.2 LIMITATIONS OF VSI AND CSI

An article about the advantages of sollarbotics wouldn't be complete without some

discussion of the limitations of sollarbotics. In spite of the very useful set of

advantages of sollarbotics discussed above, there are some tasks for which human

beings are better suited than robots. For example:

1. Robots are not suited for creativity or innovation

2. Robots are not capable of independent thinking



3. Robots are not good at learning from their mistakes

4. Robots are not as suitable for making complicated decisions

5. Robots can't as readily adapt quickly to changes in the surroundings

CHAPTER-7

FUTURE SCOPE

CHAPTER-8

CONCLUSION

Project spy amphibious solla roller acronym as SASR is completed by the use of

theory explained in the previous chapters. We faced some problems in the completion

of this project like balancing in the water, proper rpm to the motors & finally we

tackled all the problems with the help of our project guide the ratings & their

parameters are kept in mind in all applications project is tested successfully on land as

well as on water and it has completed our objective i.e. It is moving on land and of

course on water and takes videos sending them to ground stations where they can be

analyzed with the help of display devices particularly TV



Thus project SASR is completed successfully which covers basic electrical &

electronics concepts and basic microcontroller programming skills.


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Vsi Csi with various loads