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DYNAMIC LOAD RESPONSE: As a result of the impressed inverter output wave form. Presenter: Dr Gawie van der Merwe 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 Copyright: Dr Gawie van der Merwe www.planmypower.co.za Experimental setup Sine 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: VARIABLE DCLINK – Fluorescent lights with electronic ballast – 700W Drill – Single phase induction motor – Microwave oven Copyright: Dr Gawie van der Merwe www.planmypower.co.za OUTPUT Test circuit and supply voltages 400 300 200 100 0 -100 -200 -300 -400 Sine 230V 250V 275V 310V THD CONTENT OF QS SIGNAL 230 PERCENTAGE OF MAIN HARMONIC 1 0.8 230 0.6 250 275 0.4 310 0.2 0 Copyright: Dr Gawie van der Merwe7 www.planmypower.co.za 1 3 5 9 11 HARMONIC 13 15 700W Drill Square Startup Current Running Current Peak (RMS) THD Sine 100ms 20 1.75A % Value QS 220V 80ms 11.2A 1.3 % Value QS 250V 60ms 18A 1.65 % Value QS 275V 60ms 19 1.7A % Value 20A 1.7A % Value QS 310V 140ms Result: Difference between QS with Peak in area of 275V approx the same as sinewaveCopyright: Dr Gawie van der Merwe www.planmypower.co.za – Higher peak at 310V slower response notable Electronic Ballast Sine wave Copyright: Dr Gawie van der Merwe Current Harmonic Content www.planmypower.co.za Current waveform with 220V Current Harmonic Content Electronic Ballast 250V Copyright: Dr Gawie van der Merwe 310V Current Harmonic content www.planmypower.co.za Current Harmonic Content Electronic Ballast Electronic 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 Copyright: Dr Gawie van der Merwe www.planmypower.co.za Electronic Ballast Lifetime reduction up to 60% Current peak of QS and Sine more or less the same Higher Harmonic content reduce capacitor lifetime Copyright: Dr Gawie van der Merwe www.planmypower.co.za Single Phase Induction motor Very applicable application for fridges, borehole pumps etc. Start up time Current Sinewave 240 ms 9A 220V DC link 580 ms peak 3,9A 250V DC link 630 ms peak 6,5A 275V DC link 440 ms peak 9A 310V DC link 2sec Copyright: Dr Gawie van der Merwe www.planmypower.co.za peak 10,5A 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 VOLTAGE AND CURRENT 220V DC LINK (MOTOR) 400 6 4 2 0 0 -2 CURRENT (A) VOLTAGE (V) 200 CURRENT VOLTAGE -200 -4 -400 -6 -40 7.2 54.4 101.6 148.8 TIME (10MS/DIV) VOLTAGE AND CURRENT 600 3 400 2 200 1 0 0 -200 -1 -400 -2 -600 -50 Copyright: 50 Dr 0Gawie van der Merwe 100 150 www.planmypower.co.za TIME (10MS/DIV) -3 200 CURRENT (A) VOLTAGE (V) 275V DC LINK (MOTOR) CURRENT VOLTAGE Comparative current harmonic content Sine Copyright: Dr Gawie van der Merwe 250V 220V www.planmypower.co.za 275 V Magnetic Ballast Fluorescent Lights 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 Copyright: Dr Gawie van der Merwe www.planmypower.co.za Microwave Oven Typical requirement for farmers and mobile industry. – Water boiling test – 1 Liter water 60 1500 40 1000 20 500 0 POWER (WATT) TEMP VARIATION (K) TEMPERATURE DIFFERANCE 0 SINE 230V 250V 275V 310 VARIATION IN SUPPLY VOLTAGE Copyright: Dr Gawie van der Merwe 1 LIT ER WAT ER www.planmypower.co.za 60 SECONDS 300 SECONDS POWER CONSUMED 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 Copyright: Dr Gawie van der Merwe www.planmypower.co.za 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 Copyright: Dr Gawie van der Merwe www.planmypower.co.za 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. Copyright: Dr Gawie van der Merwe www.planmypower.co.za