Harmonic Mitigation Harmonic Data Comparisons

Transcription

1 Harmonic Data Comparisons 1336 PLUS, 1336 PLUS II, 1336 IMPACT and 1336 FORCE AC Drives with 6-Pulse, 12-Pulse, and 18-Pulse Front-Ends

2 Topologies 6-Pulse drive 12-Pulse drive 18-Pulse drive Harmonic Spectrum Comparison This document provides a comparison of the harmonic spectrum for 1336 PLUS, 1336 PLUS II, 1336 IMPACT and 1336 FORCE AC drives utilizing various AC/DC converters (front-end) topologies. The comparison is based on the following topologies: 6-Pulse drive using a 6-Pulse SCR bridge, 12-Pulse drive using a 12-Pulse phase shifting auto-transformer with a 12- Pulse diode bridge, and 18-Pulse drive using an 18-Pulse phase-shifting auto-transformer with an 18- Pulse diode bridge. All three topologies utilize the same Pulse Width Modulated (PWM) inverter and 1336 PLUS II control board. A customer s specific electrical power distribution system should be considered in the selection of a harmonic mitigation solution. Table 1 is a summary of the typical harmonic current spectrum for the various front-ends of the PWM AC drives. Keep in mind that harmonic distortion levels for PWM AC drives are significantly impacted by varying the customer s power system impedence. When looking up limits in IEEE , the ratio of short circuit current, which can be estimated from supply transformer impedence, to load current must be considered. Category 6-Pulse Drive 12-Pulse Drive 18-Pulse Drive 1. Current THD 30 35% % 4.5 5% 2. Power Factor DPF K-Factor th Harmonic % % % 6. 7 th Harmonic % % % th Harmonic % % % th Harmonic % % % th Harmonic % % % th Harmonic % % % Table 1 Typical normalized harmonic current spectrum of PWM AC drives. The data obtained from factory floor measurements is presented in the graphs (Figures 1-4). The Point of Common Coupling (PCC) was picked at the input terminals of the 1336 PLUS II AC drive (460 volt AC, 3-phase, 350 horsepower) which supplied a 3-phase, 460 volt AC, 400 horsepower, 4-pole induction motor with base speed of 1785 RPM. The load to the AC motor was a DC motor connected to the shaft. The DC motor was rated at 400 horsepower, 500-volt armature, and was operated by a 460V AC, 400 horsepower 1395 DC drive. The test measurements were taken at intervals of 15 minutes.

3 Figures 1 and 2 indicate that the voltage Total Harmonic Distortion (THD) increases with speed and load. Also note that load and speed affect the 6-Pulse drives more than the 18-Pulse drives. Voltage THD of 6 pulse vs 18 pulse Drives THD, % Speed, RPM 6 pulse Voltage THD Rms, % 18 pulse Voltage THD Rms, % Figure 1 Voltage harmonics of the Allen-Bradley AC drives at different speeds. Voltage THD of 6 pulse vs 18 pulse Drives THD, % Load, % of rated current 6 pulse Voltage THD Rms, % 18 pulse Voltage THD Rms, % Figure 2 Voltage harmonics of the Allen-Bradley AC drives at different loads.

4 Figures 3 and 4 show that current THD decreases with increasing load and increasing speed. As expected, the 18-Pulse front-end has much lower current distortion than the 6-Pulse front-end Current THD of 6 pulse vs 18 pulse Drives TH D, % Speed, RPM 6 pulse Current THD Rms, % 18 pulse Current THD Rms, % Figure 3 Current harmonics of the Allen-Bradley AC drives at different speeds. Current THD of 6 pulse vs 18 pulse Drives THD, % Load, % of rated current 6 pulse Current THD Rms, % 18 pulse Current THD Rms, % Figure 4 Current harmonics of the Allen-Bradley AC drives at different loads.

5 Figures 5 and 6 are typical scope plots of input current waveforms for the various PWM AC drive front-ends. Notice that the waveforms more closely resemble a sine wave as the level of distortion decreases. Input Current Input Current Amps Amps Time (msec) Time (msec) Current THD = 31.4% Current THD = 24.2% 6-Pulse Front-end 6-Pulse Front-end plus 3% Line Reactor Figure 5 Input Current Waveforms for PWM AC drive front-ends Input Current Input Current Amps Amps Time (msec) Time (msec) Current THD = 9.1% Current THD = 4.8% 12-Pulse Front-end 18-Pulse Front-end Figure 6 Input Current Waveforms for PWM AC drive front-ends

6 Harm. Number Freq. Hertz Table 2 contains data collected for the different front-ends during these tests. The harmonic components that are typically significant in PWM AC drives are highlighted in bold italics. 6-Pulse w/ Bus Choke %I RMS Pulse Width Modulated Variable Frequency Drives 12-Pulse w/ 12-Pulse w/ Bus Choke Bus Choke %I RMS I, θ (phase 6-Pulse w/ Bus Choke I, θ (phase angle) 18-Pulse w/ Bus Choke %I RMS 18-Pulse w/ Bus Choke I, θ (phase angle) angle) Table 2 Typical normalized harmonic current spectrum for input current waveforms of Allen-Bradley AC drives. This document allows the designer of an electrical power system including Allen- Bradley 1336 PLUS, 1336 PLUS II, 1336 IMPACT, and 1336 FORCE AC drives, using this data, a computer model and one of the previous mitigation techniques, to help evaluate and reduce the harmonic distortion within the customer s power system.

7 NOTES Harmonic Mitigation

8 1336 IMPACT and 1336 FORCE are trademarks of Rockwell Automation. Corporate Headquarters Rockwell Automation, 777 East Wisconsin Avenue, Suite 1400, Milwaukee, WI, USA, Tel: (1) , Fax: (1) Headquarters for Allen-Bradley Products, Rockwell Software Products and Global Manufacturing Solutions Americas: Rockwell Automation, 1201 South Second Street, Milwaukee, WI USA, Tel: (1) , Fax: (1) Europe: Rockwell Automation SA/NV, Vorstlaan /Boulevard du Souverain 36-BP 3A/B, 1170 Brussels, Belgium, Tel: (32) , Fax: (32) Asia Pacific: Rockwell Automation, 27/F Citicorp Centre, 18 Whitfield Road, Causeway Bay, Hong Kong, Tel: (852) , Fax: (852) Headquarters for Dodge and Reliance Electric Products Americas: Rockwell Automation, 6040 Ponders Court, Greenville, SC USA, Tel: (1) , Fax: (1) Europe: Rockwell Automation, Brühlstraße 22, D Elztal-Dallau, Germany, Tel: (49) , Fax: (49) Asia Pacific: Rockwell Automation, 55 Newton Road, #11-01/02 Revenue House, Singapore , Tel: (65) , Fax: (65) Publication DRIVES-WP012A-EN-P September, 2001 Copyright 2001 Rockwell Automation. All rights reserved. Printed in USA.