Controlled sine wave front end ac drives


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Controlled sine wave front end ac drives

  1. 1. Controlled Sine Wave Front End AC Drives – The Future for Harmonic Control and Energy Savings BY HIMANSHU SHAH DECEMBER 12, 2001 ARC INSIGHTS 2001-055M Keywords AC Drives, Harmonics, Power Factor, Energy Savings Summary Variable frequency AC Drives offer many benefits, but users must be aware of the potential for additional costs. Power factor variation and harmonic distortion can result in electrical pollution on the power lines adversely af- fecting power line efficiency and other equipment or services connected to the lines. Controlled Sine Wave Front Ends for large ACControlled Sine Wave Front Ends drives addresses the issue of electrical pollution. Thisfor large AC drives addresses the technology ensures near zero harmonic introduction on issue of electrical pollution. the power lines during both the motoring and regenera- tive modes, enables a drive to return regenerative energy to the supply, and improves the line power factor. Latest advancements in this technology provide more benefits that reduce the Total Cost of Ownership (TCO) for users when seeking a solution. Analysis It is not surprising that the use of AC Variable Frequency (VF) drives is be- coming widespread. AC drives are now being used worldwide in a myriad of applications as the demand for energy savings and higher productivity continues to push their use. Understanding all of the potential costs associ- ated with these products and the means to cost-effectively address these issues is therefore vital. Utility companies have valid concerns regarding the problems caused by widespread use of variable frequency AC Drives, particularly in large drive applications. Excessive harmonics and highly reactive loads can pose a number of problems in managing a reliable power system. That is why utility companies around the world scrutinize large loads connected to ENTERPRISE & AUTOMATION STRATEGIES FOR INDUSTRY EXECUTIVES
  2. 2. ARC Insights, Page 2 their power lines and require users to follow directives and recommenda- tions for connecting loads, such as AC drive systems. Scrutiny from the utilities can be a serious concern for a company wishing to install large AC drive systems. AC drives generally have pulse diode or thyristor front end rectifiers. Line current is drawn in a ‘choppy manner’ creating harmonics on the line. AC drives are a reactive load on the line thereby lowering the power factor. Inductive or capacitive input filters are typically installed on large AC drive systems to minimize these effects; however this is complex and costly. Utility Companies Establish Recommendations and Directives Directives or recommendations from utility companies vary from country to country. In the US, IEEE 519 standards outline recommended practices to limit the harmonic injection; in the countries of the European Economic Area (EEA) standards are specified under IEC 1000-3 and IEC 1800-3 tech- nical reports; in the UK, national recommendations Cause malfunction on other equipment such as the Engineering Council Recommendation G5/4 exist. Corrupt data on nearby telecom lines Change peak and RMS values of supply Studies to evaluate the potential impact can be ex- Cause more power losses pensive. If the utility company is overly concernedEffects of Harmonics and Power Factor that a drive system installation may cause excessive harmonic generation or negative effects on power factor a project can be delayed or even cancelled. Even if the project is eventually approved, it can still become significantly more expensive when additional compensating equipment must be installed. Controlled Sine Wave Front End AC Drives Provide Answers Controlled Sine Wave Front End drives take line current in a near sinusoi- dal manner, significantly reducing harmonics and present a resistive load to the power system. Advanced IGBT technology and high processing power in drive electronics is now making this approach practical for a broad range of applications. High voltage IGBTs are becoming more reli- able, less costly, available from many vendors, and easier to design into power-bridges for high power drives. So what is the catch? The Controlled Sine Wave Front End adds cost to the drive, but the upfront cost can be off- set with savings in other areas: © 2001 • ARC • 3 Allied Drive • Dedham, MA 02026 USA • 781-471-1000 • USA • UK • Germany • Japan • India
  3. 3. ARC Insights, Page 3 • Eliminates site surveys or complex harmonic analysis before or after drive system installations. • Energy loss in cables and transformers is reduced as the harmonics are near zero level. • A unity power factor reduces the utility bill as no cost is added for the reactive energy component. Most drives today do not use Controlled Sine Wave Front Ends, but a few suppliers offer this technology as an option for high power products. High speed computing at lower cost has made implementation of complex real- time control algorithms for the Controlled Sine Wave Front End more prac- tical. ABB incorporates these features in their Regenerative IGBT drives or in Inverter Supply Units (ISU) with their ACS600 drives. ALSTOM offers Active Energy Management (AEM) with their MV3000 drive product line. Siemens offers an Active Front End (AFE) option on their Simovert Master drives. Vacon has the low voltage CXR regenerative drive. At Medium Voltage, and if regeneration is not a requirement, ASI Robicon offer their Perfect Harmony Series and ALSTOM offer Symphony drives; both with 18 pulse diode rectifiers. These drives meet IEEE 519 at the point of common coupling to the supply. Latest Advancements in Technology Establish the Future While most Controlled Sine Wave Front End AC drives create minimal elec- trical pollutions, all sine wave front end drives do not offer the same level of harmonic controls. With clever control algorithms, drives not only draw current from the line in pure sine wave form, but also improve the supply line. ALSTOM’s Active Energy Management (AEM) drives use special con- trol algorithms that provide benefits in three ways. First, they draw current in almost pure sine wave form and reduce harmonic levels across the broader frequency spectrum. Secondly, the special control algorithms draw power from the supply at phase angles that support unity power factor and thereby improve the line condition. Utility companies welcome such ‘help- ful’ loads. And thirdly, energy is put back on the lines during the regenerative cycle in a sine wave form and at phase angles that again sup- port unity power factor. Material Handling Applications Save Energy Gracefully Controlled Sine Wave Front End drives are ideal for downhill conveyor lines and for large cranes that are commonly found in metal & mining, ce-© 2001 • ARC • 3 Allied Drive • Dedham, MA 02026 USA • 781-471-1000 • USA • UK • Germany • Japan • India
  4. 4. ARC Insights, Page 4 ment, or at sea-ports. During the downhill regenerative phase clean energy is returned to the lines. A significant energy saving is also derived where long power cables, which are common in these applications, would other- wise incur significant energy loss from excessive harmonics and poor power factor. In certain circumstances, the poor power factor can be of more significance than higher harmonics. For example, the current in the cable increases by 25% at 0.8 power factor. While techniques of feeding en- ergy back into the power system have been used for many years, this always worries utility companies as it usually injects harmonics in the process. With the advent of Controlled Sine Wave Front End AC drives the utility company’s concerns can be eliminated as energy can be returned gracefully. Recommendations • Users should always consider TCO during the selection of drives. The cost of site surveys from utilities companies and compliant efforts for their directives should be included in a drive installation cost to deter- mine true TCO. • Users must recognize that even though AC drives are considered com- modity products today, all drives are not designed equal. Options offered by some suppliers can make a significant contribution towards lowering your overall TCO for this equipment. • To help lower TCO, more suppliers should offer the Controlled Sine Wave Front End option across a broader product portfolio. The devel- opment efforts put forth will also help achieve a ‘supplier of choice’ status among users in the highly competitive market. For further information, contact your account manager or the author at Recommended circulation: All MAS clients. © 2001 • ARC • 3 Allied Drive • Dedham, MA 02026 USA • 781-471-1000 • USA • UK • Germany • Japan • India