VOLTAGE SOURCE CONVERTER

WITH VARIOUS CURRENT

CONTROL METHODS

1Ms. B. Jyothi and 2Dr. P. Srinivasa Varma

1Vignan’s Institute of Information Technology,

Duvvada, Visakhapatnam, A.P., India.

2K L University, Vadeswaram, Guntur, Andhra

Pradesh, India. 1jyothi_chinni2002@yahoo.com,

2pinnivarma@kluniversity.in

April 14-15, 2017

Abstract

In modern practice, voltage source inverter with current

controllers is used in all applications to get faster response,

good accuracy and high level performance. In this paper

various methods of current controllers are discussed with three

phase voltage source PWM converter. The first method

includes PI current regulator, the second method comprises

predictive current regulator with constant switching frequency,

third method is hysteresis current controller and the fourth

method fuzzy-logic based controllers are discussed.

Index Terms- current control, inverters, pulse width modulation, switch mode

rectifiers.

1. INTRODUCTION

Performance of voltage source converters reckon on the endowment of

the control strategy of current applied to it. Therefore, in modern

International Journal of Pure and Applied MathematicsVolume 114 No. 8 2017, 101-111ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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Power Electronics, current control technique of Pulse Width

Modulation converters is extremely important concept. The advantages

of current controlled PWM converters[1-5] are

1. High accuracy

2. Rejection of over load

3. Good dynamics

4. Dc-link compensation.

The fundamental approaches and performance of different methods

are summarized.

CURRENT CONTROL METHODS Several VSI current control

methods have been evolved. They are differ from the type of

modulation and control used and these are

a. Linear control

b. Hysteresis control

c. Predictive control

d. Delta and sigma delta modulation

e. Fuzzy logic controls

f. Neural networks

Linear control The other name for linear control is ramp comparison

or sine triangle current regulator it hire with two three independent

PI error amplifiers and PR error amplifiers to produce reference

voltages for a three-phase triangular PMW modulator. Especially in

case of load emf, feed forward error correction has been used.

Modification is done in this method so that it well fitted to drives

and to all sinusoidal current and voltage waveforms are required is

that of the rotating frame current regulator shown in figure1. The

advantages of this control are satisfactory for drives of low and

medium performance, Cinch and robust, unresponsive to load

parameters and by increasing the switching frequency, performance

of Linear control can be improved [6-10].

INVERTER

DC

VOLTAGE

SOURCE

abc to

dq0

L-FILTER GRID

PLL

PWM

dq0 to

abc

PI

CONTROLLER

θ

PI

CONTROLLER

Vg

Ig

Si

id*

iq*

id

iqvd*

vq*

e

e

vabc*

Fig.1. Rotating Frame Linear Current Regulator

Hysteresis control It is a fast fuel back system. It detects the errors

in current and it directly gives the commands to the switches if and

only if an error exceeds and aligned band shown in figure 2. The

advantages of this control are simple, more Robust and it gives good

accuracy [11-15].

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INVERTER

DC

VOLTAGE

SOURCE

abc to

dq0

L-FILTER GRID

PLL

HYSTERESIS

CONTROLLER

dq0 to

abc

θ

Vg

Ig

Si

id*

iq*

id

iqe

e

eabc

Fig.2. Control Diagram of Hysteresis Current Controller

Predictive current control This method prognosticate the error in

current vector at the inception of each modulation and it also

determines the voltage vector which is developed by PWM during

the next modulation cycle to reduce the forecast error shown in

figure 3. Accurate response can be obtained by giving more

information to the regulator and it is also suitable for digital

implementation.

INVERTER

DC

VOLTAGE

SOURCE

L-FILTER GRID

PWM

Basic Vector

Timming

Predictive

Voltage Vector

Computation

Vg

Ig

Si

V(k)*

Load Parameter

Calculation

I(k)*

I(k)

Clock

Fig.3. Block Diagram of Basic Predictive Current Control

Delta modulation The fundamental diagram of a delta modulator

current control is shown in figure 4. It is same as that of hysteresis

control, but its operating principle is quite different. Error sign is

sensed by comparators and its output are sampled at fixed rate to

maintain constant inverter status during each sampling interval.

This control is simple and it is insensitive to load parameters.

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INVERTER

DC

VOLTAGE

SOURCE

abc to

dq0

L-FILTER GRID

PLL

HYSTERESIS

CONTROLLER

dq0 to

abc

θ

Vg

Ig

Si

id*

iq*

id

iqe

e

eabc

S/H

Fig.4. Delta Modulation Current Regulator

Neural and Fuzzy controllers These techniques are used to get over

the limitation of classical control methods. It improves the

performances of linear control and hysteresis control. In linear

control method, PI amplifiers are replaced with neural network and

it is shown in figure 5. And these are adjusts itself to compensate

study state errors at different loading conditions.

INVERTER

DC

VOLTAGE

SOURCE

abc to

dq0

L-FILTER GRID

PLL

abc to

dq0

LOAD

PWM

dq0 to

abc

FUZZY

CONTROLLER

θ

FUZZY

CONTROLLER

Vg

IL

Ig

Si

id*

iq*

id

iqvd*

vq*

e&δe

e&δe

vabc*

Fig.5. Fuzzy Current Controller Block Diagram

2. SIMULATION RESULTS

Fig.6. Simulation Diagram of Current Controlled Grid Connected

Inverter with Grid

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Fig.7. PWM Generator Simulation Diagram

Control of Grid current by using PI Current Regulator

Fig.8. Simulation Diagram of PI Current Control of Grid Connected

Inverter with Grid

Fig.9. Output waveforms of Voltage and Current with PI Controller

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Fig.10. Waveforms of Reference current and Grid Current with PI

Controller

Fig.11. Total Harmonic Distortion of the Grid Current

Control of Grid current by using PR Current Regulator

Fig.12. Simulation Diagram of PR Current Controller

Fig.13. Waveforms of Output Voltage and Current with PR Controller

Fig.14. Waveforms of Reference current and Grid Current with PR

Controller

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Fig.15. THD of the Grid Current Waveform

Control of Grid current by using Hysteresis Current Regulator

Fig.16. Simulation Diagram of Hysteresis Current Controller

Fig.17. Waveforms of Output Voltage and Current with Hysteresis

Controller

Fig.18. Waveforms of Reference current and Grid Current with

Hysteresis Controller

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Fig.19. THD of the Grid Current Waveform

Control of Grid current by using Fuzzy Current Regulator

Fig.20. Simulation Diagram of Fuzzy Current Controller

Fig.21. Waveforms of Output Voltage and Current with Fuzzy

Controller

Fig.23. THD of the Grid Current Waveform

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TABLE I: Comparison of THD for different Current Control

Techniques

Name of the Current Controller Total Harmonic Distortion(THD)

IN %

Linear PI Current Controller 1.18

Linear PR Current Controller 0.02

Hysteresis Current Controller 1.13

Fuzzy Current Controller 2.95

3. CONCLUSION

This paper gives an idea on various methods to control the voltage

source inverters. This paper describes the fundamental concepts to

control the current of VSI and the simulation results are shown. The

comparison of THD in same current control techniques is tabulated.

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