Optimizing Drive Systems for Energy Savings

Transcription

1 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 Siemens AG 2012 All rights reserved

2 Energy Savings from Drive Systems 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? Page 2/20

3 Five Areas of Evaluation Drives with common DC-Bus Active Line Infeed Technology Eliminate Mechanical Losses Replace DC-Drives with AC-Drives Motor Efficiency Page 3/20

4 AC/AC-Drive Overview The circuit arrangement of a modern PWM (Pulse Width Modulated) AC/AC-drive is made up of three sections 3-Phase Supply V AC Rectifier DC Link Inverter M 3-Phase Induction Motor V motor V DC I AC I DC I motor The input DC inverter link section is section the is middle the pulses rectifier section the DC-voltage which converts contains to single a three-phase capacitor bank phase power to smooth AC signal voltage and suitable buffer into for the an DC DC inverter-duty voltage AC-motor Page 4/20

5 AC/AC-Coordinated Drive Systems AC Line This is a typical example configuration of standard AC/AC applied as in a multiaxes coordinated drive system Fuses Reactor Contactor Notice how each individual drive is connected to the AC line via individual line components (fuses, reactors, contactors) and component wiring AC Converter Braking Resistor Each drive section must deal with its regenerative power individually AC Motors 45A 15A 30A 25A 75A UNWIND PULL ROLL COATER LAMINATOR REWIND In some cases a pseudo common DC-bus is made up of AC/AC drives with an external Notice how in this scenario the machine sections that add tension to the web (unwind and laminator) bus connection by connecting the buses This application is problematic as the current must return their power back to the drive, and in turn this energy is dissipated (wasted) by the regen capacity resistors connected of these bus to the connections individual drives does In not this always example match as much the as drive 75 A is power wasted rating as heat Precautions also must be taken to prevent the smaller drives from charging the larger drives Page 5/20

6 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 Fuses Line Reactor Contactor Infeed (Rectifier) AC Motor Inverters This common DC bus system will use almost 75 A less than the AC/AC drive system Common DC Bus 45A 15A 30A 25A 75A UNWIND PULL ROLL COATER LAMINATOR REWIND The Power line sharing components is now (ie possible contactor, between reactor, each fuses, different etc) and drive infeed sections can be linked sized on basing the DC on bus the maximum The drive current system drawn now draws from the less system power not from the the summation rectifier as of the individual generating motors drive This sections results return in a their more power size to optimized the DC bus and to energy be shared efficient by the design motoring as losses drive are sections realized in each individual line component and rectifier Page 6/20

7 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 Non- Regenerative Line Regenerative Line Line-current notching due to thyristor switching line commutation motoring DC-link motoring generating DC- link Line current Page 7/20

8 Active Line Infeed Technology Infeed Modules supply the energy for the DC-link Active Line Infeed Modules Regulated DC-link rectifier/regenerative unit Line Clean Power Filter Near unity Power Factor Reduced harmonics Highest performance Better motor utilization Line current DC- link Bus undervoltage control Page 8/20

9 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 095 When the customer s power factor drops below the minimum value, the utility collects low power factor revenue Page 9/20

10 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 % Gear box Motor 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 Torque Motor Page 10/20

11 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 E/P Controller 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 AC Motor AC Line Pull Roll Page 11/20

12 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 225 kw load requirement In this example 34 A of line current is wasted 75kW 22,5kW FLA Motor Current 125 A FLA Motor Current 40 A Magnetizing Current 50 A Magnetizing Current 16 A This means a current saving of 34 A Page 12/20

13 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 Page 13/20

14 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 1,20000 Euro of energy savings per year SYSTEM Drive Efficiency (%) MOTOR/DRIVE SYSTEM EFFICIENCY Motor Efficiency (%) System Efficiency (%) kwh/year Annual Power Cost (Euro) DC 990 % 880 % 871 % 377,152 30,172 AC 970 % 935 % 907 % 362,183 28,975 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 008 Euro/kWh Annual Savings 1,200 Euro Page 14/20

15 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 Page 15/20

16 Energy Efficient Motors Energy Savings 75 kw motor running at 90 % load (fixed speed, no drive) Efficiency Rating System Efficiency (%) kwh/year Annual Power Cost (Euro) Kilowatt Hours Annual hours of operation/system Efficiency Motor running 12 hours per day/7 days a week Assume 008 Euro/kWh Annual Saving (Euro) Standard, IEC IE ,337 28,107 - NEMA High, IEC IE ,789 27, NEMA Premium, IEC IE ,476 27, Page 16/20

17 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 Optimum Efficiency 0% 50% Flux Setpoint Flux Setpoint *075 Ф Setpoint 100% Flux Setpoint *05 As soon as load is connected to the drive, the setpoint (reference) flux linearly increases with the load Flux Setpoint * Motor Magnetizing Current / 2 Flux Setpoint * Motor Magnetizing Current Iq setpoint Page 17/20

18 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 Page 18/20

19 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 Page 19/20

20 Thank you for your attention! Questions? Richard Messer Siemens AG, Industry Sector, Drive Technologies, Motion Control Systems Erlangen, Germany Page 20/20 Siemens AG 2012 All rights reserved Siemens Industry, I DT CC P