How to optimize Energy Efficiency in Factory Production Systems.
Electric motors are the main power units behind almost all automation devices in production plants. Over 40 percent of generated electricity is consumed by industry and two-thirds of energy is used by electric motors. Losses are an inevitable part of running a motor and they directly affect efficiency. Losses are minimized by using higher cutting edge motor designs, proper motor control selection, and considering the torque of the motor in high precision automated production systems.
Figure 1 describes the main elements in an automated machine or process found in a modern factory. The efficiency of the motors and the whole production process is determined by multiple control layers. The first control layer adjusts the power inverter switching sequence to manage the motor voltage and current and enhance torque production efficiency. Next is the position and speed controller that operates the machine efficiently. In process equipment, this could be a sequence of speed or position orders to perform an assembly function, whereas, in automation equipment, this could be a sequence of speed or position commands to execute an assembly function. In the latter scenario, the response time of the speed control will be more critical to the machine controller than torque production efficiency. As multiple motors are now synchronized across high-speed data networks that are also connected to the factory network, the communications and systems layer is becoming increasingly important.
Figure 1: Block diagram of automated machine control system
The torque produced per amp supplied at any given speed and terminal voltage influences motor efficiency. Torque is generated by electric motors by forces that tend to align their internal magnetic fields. When the stator currents are synchronized with the rotor motion to maintain continuous field misalignment, AC motors produce constant torque. The frequency of the motor currents is closely connected to the ac motor speed, therefore speed regulation necessitates the use of a variable frequency voltage source, such as VSDs or VFDs. When the rotor-stator field misalignment is at its maximum, the efficiency is maximum. Motor efficiency also depends upon motor construction and particularly the rotor field structure. Permanent magnet synchronous motors (PMSM) are more efficient, since no current is required to magnetize the rotor field. Because of their prominent magnetic core construction, ultrahigh efficiency interior permanent magnet (IPM) motors generate additional torque.
Using Soft Starters in AC Induction Motors:
When starting, the AC Induction motor develops more torque than is required at full speed. This stress is transferred to the mechanical transmission system, causing excessive wear and premature failure of chains, belts, gears, mechanical seals, and other components. Rapid acceleration also has a significant influence on electricity supply charges, with high inrush currents drawing +600% of the normal run current. The use of Star Delta only provides a partial solution to the problem. If the motor slows down during the transition time, the high peaks will be repeated and may potentially exceed direct on line current. Soft starters provide a reliable and economical solution to these issues by delivering a controlled release of power to the motor, resulting in smooth, step-less acceleration and deceleration, as illustrated in Figure 2. As damage to windings and bearings is reduced, motor life will be extended. Soft Start & Soft Stop is incorporated into three-phase systems, allowing for regulated starting and stopping with a selection of ramp times and current limit settings.
Figure 2: Performance curve as compared to direct-on line, Star-delta and Soft Start
By adopting Predictive and Condition Monitoring:
Condition Monitoring (CM) is the monitoring of several parameters such as equipment vibration and temperature to identify potential concerns such as misalignments or bearing failures. When a vibration analysis reveals a change in the harmonic frequency of rotating equipment components, condition monitoring tools can map equipment degradation. Frequency analysis can be performed using both vibrometer and microphone data. Continuous Predictive and Condition Monitoring techniques might be used on a range of equipment, including compressors, pumps, spindles, and motors, and they can also be used to detect partial discharge on machines or vacuum leaks. This analysis helps factories to maximize efficiency and equipment availability whilst lowering costs
Improving Efficient Motion Control with Precision Isolation and effective communications:
The combination of precision in motion control and communication timing enables shorter machine production cycles and reduces the amount of energy consumed to manufacture each part. PMSM service motors and drives designed for fast response and high precision in speed and position control are used by drive manufacturers to assist automation applications. The use of high-speed magnetic isolation technology allows for the safe isolation of analog and digital signal voltages without sacrificing speed or precision. Precision analog-to-digital converters integrated into the encoder position offer position feedback with up to a 24-bit resolution, enabling high dynamic velocity control at rates as low as 1 RPM.
This level of performance is appropriate for automation applications such as multiaxis milling of precision machine parts, assembly of fine geometry integrated circuits, and injection molding of cell phone parts. Furthermore, to ensure control precision, the motors' motion timing should be perfectly synchronized, because a timing error directly translates into a trajectory error in multiaxis position control. Industrial Ethernet protocols, such as PROFINET and EtherCat, use modified Ethernet network interfaces to support real-time data synchronization with clock jitter as low as 1μs. These network interfaces support both synchronized motion control and factory network connectivity for production system management.
