Controlled Sine wave front end drives address electrical pollution from variable frequency AC drives by drawing current in a near sinusoidal waveform, producing near-zero harmonics. This technology enables unity power factor, reduces energy losses, and allows regenerative energy to be returned to the supply. The latest advancements provide additional benefits that reduce the total cost of ownership for large drive systems.

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 AC
Controlled Sine Wave Front Ends
drives addresses the issue of electrical pollution. This
for 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
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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 concerned
Effects 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 • ARCweb.com
USA • UK • Germany • Japan • India

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 • ARCweb.com
USA • UK • Germany • Japan • India

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
hshah@arcweb.com. Recommended circulation: All MAS clients.
© 2001 • ARC • 3 Allied Drive • Dedham, MA 02026 USA • 781-471-1000 • ARCweb.com
USA • UK • Germany • Japan • India