Optimizing Drive Systems for Energy Savings · Unwinds with mechanical brakes are an ideal place where lost energy can be recovered. Mechanical brakes create web tension by friction

© Siemens AG 2012. All rights reserved.

Optimizing Drive Systems for Energy Savings Richard Messer Siemens AG, Industry Sector, Drive Technologies, Motion Control Systems Erlangen, Germany AIMCAL Web Handling Conference 2012 Prague, Czech Republic

. AIMCAL Web Handling Conference 2012 Prague, Czech Republic Page 2/20

Energy saving is an extremely important topic in virtually every segment of industry today. There are several areas where energy saving can be realized from the major power consumers in converting lines and machinery.

In general, the largest consumer of power in a converting line or machine will be the drive system. As energy costs continue to increase and energy conservation becomes a greater priority, are there technologies or methods that can be implemented to reduce the energy consumption on converting machinery?

Energy Savings from Drive Systems


Drives with common DC-Bus

Active Line Infeed Technology

Eliminate Mechanical Losses

Replace DC-Drives with AC-Drives

Motor Efficiency

Five Areas of Evaluation


AC/AC-Drive Overview

The circuit arrangement of a modern PWM (Pulse Width Modulated) AC/AC-drive is made up of three sections

VDC

IDC

Vmotor

Imotor

IAC

VAC

3-PhaseInduction Motor

M

InverterRectifier

3-PhaseSupply

DC

Lin

k

The input section is the rectifier which converts single or three phase AC voltage into DC voltage The DC link is the middle section which contains a capacitor bank to smooth and buffer the DC voltage. The inverter section pulses the DC-voltage in to a three-phase power signal suitable for an inverter-duty AC-motor.


AC/AC-Coordinated Drive Systems

This is a typical example configuration of standard AC/AC applied as in a multi-axes coordinated drive system. Notice how each individual drive is connected to the AC line via individual line components (fuses, reactors, contactors) and component wiring. Each drive section must deal with its regenerative power individually.

~

~=

~

~=

~

~=

~

~=

AC Line

~

~=

UNWIND PULL ROLL COATER LAMINATOR REWIND

45A 15A 30A 25A 75A

Notice how in this scenario the machine sections that add tension to the web (unwind and laminator) must return their power back to the drive, and in turn this energy is dissipated (wasted) by the regen resistors connected to the individual drives. In this example as much as 75 A is wasted as heat.

Fuses

Reactor

Contactor

AC Converter

Braking Resistor

AC Motors

In some cases a pseudo common DC-bus is made up of AC/AC drives with an external bus connection by connecting the buses. This application is problematic as the current capacity of these bus connections does not always match the drive power rating. Precautions also must be taken to prevent the smaller drives from charging the larger drives.


Common DC-Bus Architecture

True common DC-bus drive systems are far more efficient than the system composed of stand alone AC/AC-drives in several ways. When drive systems utilize a common DC-bus design, a shared infeed section is used to convert the AC-power supply into a DC-bus which is common to the parallel connected inverters.

Power sharing is now possible between each different drive sections linked on the DC bus. The drive system now draws less power from the rectifier as the generating drive sections return their power to the DC bus to be shared by the motoring drive sections.

The line components (i.e. contactor, reactor, fuses, etc.) and infeed can be sized basing on the maximum current drawn from the system not the summation of the individual motors. This results in a more size optimized and energy efficient design as losses are realized in each individual line component and rectifier.

This common DC bus system will use almost 75 A less than the

AC/AC drive system

Fuses

Line Reactor

Contactor

Infeed(Rectifier)

AC Motor

UNWIND PULL ROLL COATER LAMINATOR REWIND

45A 15A 30A 25A 75A

~

=

~

=

~

=

~

=

~

=

~

=

Inverters

Common DC Bus


Standard Infeeds for Common DC-Bus

Infeed Modules supply the energy for the DC-link

Thyristor based line modules Regenerative or non-regenerative options Both are non-regulated rectifiers

Line current

motoring

DC-link

Line

DC-link

Line

motoring generating

DC-link

Line

motoring generating

DC-link

Line

Regenerative Non- Regenerative

Line-current notching due to thyristor switching line commutation


Active Line Infeed Modules Regulated DC-link rectifier/regenerative unit

Active Line Infeed Technology

Line current

Near unity Power Factor

Reduced harmonics

Highest performance

Better motor utilization

Bus undervoltage control

Infeed Modules supply the energy for the DC-link

DC- link

CleanPowerFilter

Line


Why Power Factor is Important

Power factor is a measure of how effectively electrical power is being used (True Power/ Apparent Power). A high power factor (close to unity) indicates efficient use of the electrical distribution system while a low power factor indicates poor utilization of the system.

When a utility serves an industrial plant that has poor power factor, the utility must deliver higher current levels to serve a given load. A utility is paid primarily on the basis of energy consumed and peak demand supplied.

As a means of compensation for the burden of supplying extra current, utilities typically establish a “power factor penalty” in their rate schedules.

A minimum power factor value is established, usually 0.95. When the customer’s power factor drops below the minimum value, the utility collects “low power factor” revenue.


Mechanical Losses – Direct Drive

High gear ratios are required when optimizing motor sizes for driving large diameter rolls or very low speed web applications. High-ratio multi-stage worm gear boxes can easily have efficiencies below 60 %.

Torque motors are low speed, high torque motors for direct drive. Direct drive motor solutions are now commonplace in many industry sectors. The torque motor solution can drastically eliminate lost motion and compliance, both energy wasters in high inertia applications.

Motor

Gear box

Torque Motor


Mechanical Losses – Driven Unwind

Unwinds with mechanical brakes are an ideal place where lost energy can be recovered. Mechanical brakes create web tension by friction and the heat generated in this process is in effect recoverable energy.

Pneumatic or electromechanical tension control brakes can be replaced by an AC-drive system equipped with line regenerative capability. Tension energy now is returned back to the line.

Pull Roll

AC Line

AC Motor

Controller

E/P


Drive Optimization – Sizing

Attention to drive and motor sizes in relation to their actual load requirements.

Oversized drive systems simply waste energy. The cost of energy waste is realized in the higher magnetizing current. An AC drive system’s magnetizing current can be nearly half of the full load current (FLA).

Consider a 75 kW AC drive system applied to an actual 22.5 kW load requirement. In this example 34 A of line current is wasted.

This means a current saving of 34 A

FLA Motor Current 125 A FLA Motor Current 40 AMagnetizing Current 50 A Magnetizing Current 16 A

75kW 22,5kW


Drive Optimization – Mechatronics

Improperly tuned drive speed loops can waste energy by an overactive current loop.

As industry trends push the drive systems performance, mechatronics can ensure higher performance without wasting energy. The main issues can arise from: Complex Loads Compliance Lost Motion Machine Resonances

Applied mechatronic support can help to maintain the required system performance without wasting energy and affecting machine life


Efficiency: AC vs. DC-Systems

Replacing outdated DC-drive and motor systems with AC-drive technology can offer energy savings from the improved efficiency of the AC-system. Improved power factor will also be realized. The AC-drive system can offer an efficiency improvement in the range of ~3 % when operating at nearly full load.

Consider the example of single stand alone drive systems both at 75 kW, running at 90 % load, 12 hours a day, and 7 days a week. Just a single AC/AC drive replacement can provide almost 1,200.00 Euro of energy savings per year.

Kilowatt Hours = Annual hours of operation/system efficiency Assume 75 kW motor is running at 90 % load Assume motor runs 12 hours per day/7 days a week Assume 0.08 Euro/kWh

MOTOR/DRIVE SYSTEM EFFICIENCY

SYSTEM Drive Efficiency (%)

Motor Efficiency (%)

System Efficiency (%)

kWh/Year Annual Power Cost (Euro)

DC 99.0 % 88.0 % 87.1 % 377,152 30,172 AC 97.0 % 93.5 % 90.7 % 362,183 28,975

Annual Savings = ~1,200 Euro


Efficiency: Across-the-Line Motors

EFFICIENCY LEVELS

Standard Efficiency & IEC IE1 - Pre-EPAct, Least Efficient

NEMA High Efficiency & IEC IE2 - EPAct Level, More Efficient

NEMA Premium & IEC IE3 - Best Efficiency


Energy Efficient Motors

Energy Savings

Kilowatt Hours = Annual hours of operation/System Efficiency Motor running 12 hours per day/7 days a week Assume 0.08 Euro/kWh

75 kW motor running at 90 % load (fixed speed, no drive) Efficiency Rating System

Efficiency (%)kWh/Year Annual Power

Cost (Euro)Annual Saving

(Euro)

Standard, IEC IE1 93.5 351,337 28,107 -NEMA High, IEC IE2 95.0 345,789 27,663 444.00NEMA Premium, IEC IE3 96.2 341,476 27,318 789.00


Energy Saving Drive Features

Functionality to enhance the efficiency (magnetizing current) of the drive/motor system during partial or no load operation (mainly for drives with low dynamic response requirements).

Efficiency optimization For 100 % efficiency, the flux in the motor under no-load operating conditions is reduced to half of the setpoint. As soon as load is connected to the drive, the setpoint (reference) flux linearly increases with the load.

Flux Setpoint

Ф Setpoint

Flux Setpoint*0.75

Flux Setpoint*0.5

Optimum Efficiency0%

100%

50%

Flux Setpoint * Motor Magnetizing

Current / 2

Flux Setpoint * Motor Magnetizing Current

Iq setpoint


Efficiency: Pump & Fan Motors

In the applications where across-the-line motors are utilized and the load varies, such as flow control, energy savings can be achieved by adding an AC-drive. The biggest potentials for saving are offered by pumps, fans and compressors that are still operated with mechanical throttles and valves. Converting to variable-speed drives can provide considerable economic benefits.

By adapting the flow rate precisely to actual requirements, energy savings of up to 60 % can be achieved. In this example, the input power requirement is only 56 % of the input power demand of the mechanical throttle example.


Conclusions

Drives and driven systems in converting lines are major energy consumers, but advances in technology continue to offer multiple avenues to reducing the total energy costs.

The major areas where energy savings or recovery can be found on converting lines and machinery have been addressed. As drive technology continues to make advancements, further energy saving options are expected to follow.

© Siemens AG 2012. All rights reserved. Siemens Industry, I DT CC P Page 20/20

Thank you for your attention!

© Siemens AG 2012. All rights reserved.

Questions?

Richard Messer Siemens AG, Industry Sector, Drive Technologies, Motion Control Systems Erlangen, Germany

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Optimizing Drive Systems for Energy Savings · Unwinds with mechanical brakes are an ideal place where lost energy can be recovered. Mechanical brakes create web tension by friction