DYNAMIC LOAD RESPONSE: As a result of the impressed inverter output wave form. Presenter: Dr Gawie van der Merwe

DYNAMIC LOAD RESPONSE: As a result of the impressed inverter

output wave form.

Presenter: Dr Gawie van der Merwe

Copyright: Dr Gawie van der Merwe www.planmypower.co.za

Introduction

Single frequency inverters used for power conversion of 12 or 24V DC to 220V AC

Output waveform varies between– Sine wave, Square wave, Modified Sine wave

Various loads respond differently due to the voltage supply:– Examples: Single phase motors, fluorescent lights,

computers, Microwave ovens, etc


Experimental setupSine wave supply was generated using

an Escom supply line.

A H-Bridge inverter, with a varying DC link was used- to simulate square wave, and modified sinewave (refer sketch on next slide)

Loads tested:– Fluorescent lights with electronic ballast– 700W Drill– Single phase induction motor– Microwave oven

OUTPUTVARIABLEDCLINK


Test circuit and supply voltages

-400-300-200-1000

100200300400

230V 250V 275V 310VSine

0

0.2

0.4

0.6

0.8

1

HARMONIC

PER

CEN

TA

GE O

F M

AIN

HA

RM

ON

IC

1 3 5 7 9 11 13 15

230

250

275

310

THD CONTENT OF QS SIGNAL230


Result: Difference between QS with Peak in area of 275V approx the same as sinewave-– Higher peak at 310V slower response notable

QS

QS

QS

QS

Startup

100ms

80ms

60ms

60ms

140ms

CurrentPeak

20

11.2A

18A

19

20A

Running(RMS)

1.75A

1.3

1.65

1.7A

1.7A

CurrentTHD

% Value

% Value

% Value

% Value

% Value

Square

Sine

220V

250V

275V

310V

700W Drill


Electronic Ballast

Sine wave Current Harmonic Content

Current waveform with 220V Current Harmonic Content


Electronic Ballast

250V Current Harmonic content

310V Current Harmonic Content


Electronic BallastElectronic Ballast load represents, most

non linear loads, such as DC to DC converter, computers, etc

An increase in THD of the current is noticeable

QS inverter reduce lifetime of electronic ballast fluorescent lights


Lifetime reduction up to 60%

Current peak of QS and Sine more or less the same

Higher Harmonic content reduce capacitor lifetime

Electronic Ballast


Single Phase Induction motorVery applicable application for fridges,

borehole pumps etc.

310V DC link

250V DC link

Sinewave

2sec

630 ms

240 ms

peak 10,5A

275V DC link 440 ms peak 9A

peak 6,5A

220V DC link 580 ms peak 3,9A

9A

Start up time Current


Result

Single phase motor warm up when run by QS

With same load, power consumption varies

Higher current peak

Copyright: Dr Gawie van der Merwe www.planmypower.co.za-50 0 50 100 150 200

-600

-400

-200

0

200

400

600

-3

-2

-1

0

1

2

3

TIME (10MS/DIV)

VO

LTA

GE (

V)

CU

RR

EN

T (

A)

CURRENT

VOLTAGE

VOLTAGE AND CURRENT275V DC LINK (MOTOR)

-400

-200

0

200

400

-6

-4

-2

0

2

4

6

TIME (10MS/DIV)

VO

LTA

GE (

V)

CU

RR

EN

T (

A)

-40 7.2 54.4 101.6 148.8

CURRENT

VOLTAGE

VOLTAGE AND CURRENT220V DC LINK (MOTOR)


Sine 220V

250V 275 V

Comparative current harmonic content


Sinewave supply runs lights

When power factor correcting capacitor is installed, no QS inverter will run lights

To run fluorescent light, PF capacitor must be removed - non standard

Magnetic Ballast Fluorescent Lights


Microwave OvenTypical requirement for farmers and mobile industry.

– Water boiling test– 1 Liter water

0

20

40

60

0

500

1000

1500

VARIATION IN SUPPLY VOLTAGE

TEM

P V

AR

IATIO

N (

K)

PO

WER

(W

ATT)

SINE 230V 250V 275V 31060 SECONDS

300 SECONDS

POWER CONSUMED

TEMPERATURE DIFFERANCE

1 LITER WATER


Microwave Oven Results

Microwave Oven requires high voltage peak

Energy transfer of sinewave supply up to 15% more effective

Low QS wave form has no effect on working of microwave oven


Results & Conclusion

A wide variation in dynamic response is visible

Pure Sine wave is the best overall

Fluorescent lights & Microwave ovens prefer higher voltage peak

Motor warm up due to 3rd and 5th harmonic is visible

Delayed single phase motor startup due to higher harmonics


Summary and future work

The paper presented some load responses due to the impressed voltage wave form.

It is clear that the applied wave form has a influence on the load.

Lifetime reduction test are still being done.

Documents

DYNAMIC LOAD RESPONSE: As a result of the impressed inverter output wave form. Presenter: Dr Gawie van der Merwe