ELECTRIC DRIVES

CONVERTERS IN ELECTRIC DRIVE SYSTEMSMODULE 2

Dr. Nik Rumzi Nik IdrisDept. of Energy Conversion, UTM

2009

CONVERTERS - Module 2

AC-DC controlled rectifier approximate model SIMULINK examples open-loop closed-loop

Switch Mode DC-DC converter2-Q and 4-Q converters Small signal modeling unipolar bipolarSIMULINK example

Current-controlled for SM convertersBridge converter hysteresis fixed frequency3-phase VSI hysteresis PI controller

Current-Controlled Converters

Current need to be controlled (in drives):

To control the torque To limit the current – protect the switching devices

Motor

Example of current control in cascade control structure

converterspeed

controllerposition

controller

+*

1/s

+ +

current

controller

T**

kTKt

Current-Controlled Converters

ON-OFF Controllers Separated PWM block

Hysteresis

Non-linearcontrollers

PI controllers

Linearcontrollers

Current-Controlled Converters

iref

+

Vdc

−

ia

ia

va

+

Va

ierr

ierr

q

q

Hysteresis-based

Current-Controlled Converters

Hysteresis-based - extending to 3-phase system

Motor

+

+

+

i*a

i*b

i*c

Converter

Current-Controlled Converters

Hysteresis-based - extending to 3-phase system

• High bandwidth, simple implementation, insensitive to parameter variations

• Variable switching frequency – depending on operating conditions

• Instantaneous error for isolated neutral load can reach double the band

For isolated neutral load, ia + ib + ic = 0control is not totally independent

id

iq

is

hh

hh

Current-Controlled Converters

Hysteresis-based – simulink block

References

Hysteresiscomparators

VSILoad

Current-Controlled Converters

Hysteresis-based – simulation results

-10 -5 0 5 10

-10

-5

0

5

10

0.005 0.01 0.015 0.02 0.025 0.03

-10

-5

0

5

10

Actual and reference currents Current error

Actual current locus

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Current-Controlled Converters

Hysteresis-based – simulation results

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

x 10-3

-0.5

0

0.5

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

x 10-3

-0.5

0

0.5

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

x 10-3

-0.5

0

0.5

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

x 10-3

-2

0

2

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

x 10-3

-2

0

2

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

x 10-3

-2

0

2

Current-Controlled Converters

PI-based

vtri

Vdc

qvc

q

Vdc

Pulse widthmodulator

vc

Vdc

Pulse widthmodulator

vciref

PI+

q

Current-Controlled Converters

PI-based – extending to 3-phase

Motor

+

+

+

i*a

i*b

i*c

Converter

PWM

PWM

PWM

PWM

PWM

PWM

• Sinusoidal PWM

PI

PI

PI

• Interactions between phases only require 2 controllers• Tracking error

• Interactions between phases only require 2 controllers• Tracking error

Current-Controlled Converters

• Perform the control in synchronous frame - the current will appear as DC

• Perform the 3-phase to 2-phase transformation - only two controllers (instead of 3) are used

PI-based

Current-Controlled Converters

Motor

i*a

i*b

i*c

Converter

PWM

+

+

+

PWM

PWM

PI

PI

PI

PI-based

Current-Controlled Converters

Motor

i*a

i*b

i*c

Converter

3-2

3-2

SVM2-3

PI

PI

PI-based

Current-Controlled Converters

id*

iq*

PIcontroller

dqabc

abcdq

SVM or SPWM

VSIIM

va*

vb*

vc*

id

iq

+

+

PIcontroller

Synch speed estimator

s

s

PI-based

abc

sin_cosdq0

abc_to_dq0Transformation1

abc

sin_cosdq0

abc_to_dq0Transformation

v+-

Voltage Measurement

g

A

B

C

+

-

Universal Bridge

ia_s

To Workspace5

idref

To Workspace4

va

To Workspace1

Out1

Subsystem5

In1Out1

Subsystem3

Out1

Subsystem1

Step

Sine Wave2

Sine Wave1

Sine Wave

Series RLC Branch2

Series RLC Branch1

Series RLC Branch

Scope

Product2

Product1

Product

PID

PID Controller2

PID

PID Controller1

DC Voltage Sourcei+ -

Current Measurement2

i+ -

Current Measurement1

i+ -

Current Measurement

Current-Controlled Converters

Simulink and SimPowerSystems

References

32transformation

VSI 32transformation

PIcontrollers

Load

PI-based – simulation with control in stationary frame

Current-Controlled Converters

d and q current components viewed in rotating frame ia as viewed in stationary frame

PI-based – simulation with control in stationary frame

0.01 0.011 0.012 0.013 0.014 0.015 0.016 0.017 0.018 0.019 0.020

1

2

3

4

0.01 0.011 0.012 0.013 0.014 0.015 0.016 0.017 0.018 0.019 0.02-1

-0.5

0

0.5

0.03 0.035 0.04 0.045 0.05 0.055 0.06 0.065 0.07-3

-2

-1

0

1

2

3

Current-Controlled Converters

Simulink and SimPowerSystems

PI-based – simulation with control in synchronous frame

v+-

Voltage Measurement

g

A

B

C

+

-

Universal Bridge

ia_r

To Workspace4

va

To Workspace1

In1

Out1

Out3

Out4

Subsystem6

In1Out1

Subsystem3

a_b_cd_q

Subsystem1

Step

Sine Wave5

Sine Wave4

Sine Wave3

Series RLC Branch2

Series RLC Branch1

Series RLC Branch

Scope

Product2

Product1

Product

PID

PID Controller2

PID

PID Controller1

DC Voltage Source i+ -

Current Measurement2

i+ -

Current Measurement1

i+ -

Current Measurement

Current-Controlled Converters

PI-based - simulation with control in synchronous frame

d and q current components viewed in rotating frame ia as viewed in stationary frame

0.02 0.025 0.03 0.035 0.04 0.0450

1

2

3

4

0.02 0.025 0.03 0.035 0.04 0.045-1

-0.5

0

0.03 0.035 0.04 0.045 0.05 0.055 0.06 0.065 0.07-3

-2

-1

0

1

2

3