How vector and servo drives deliver savings for manufacturers

Motor and drive insights

• Switching to electric drives from hydraulic systems not only boosts energy efficiency but also reduces scrap rates, rework time and material waste, enhancing overall production efficiency.
• Advances in motor and drive technology, such as high-efficiency motors and vector drives, are key to optimizing energy use in industrial applications, offering significant long-term cost savings.
• Investing in vector and servo drives, despite higher initial costs, provides long-term benefits including reduced energy consumption, improved production efficiency and lower operational costs to align with Industry 4.0 goals.

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For decades, manufacturers and their equipment suppliers have relied on tried-and-proven hydraulic and pneumatic actuators in their automated equipment. But due to fluid leaks, inaccuracy, and related inefficiencies, many machine builders and manufacturers replace fluid power systems with electric drives in applications where it makes sense.

For example, injection molding machines (IMMs) with all-electric drives consume less energy than IMMs that rely on hydraulically operated presses. In such machines, electric wires, motors and drives replace hydraulic components such as fittings, lines and oil coolers. The design is cleaner and more environmentally friendly. However, there’s more to this story than energy efficiency.

In addition to increased energy efficiency, the improved speed, accuracy and repeatability of electric drives can result in faster changeovers, higher-quality manufactured parts, and a higher volume of output. This increased production efficiency is achieved through reduced scrap rates, with less lost material, rework time, and waste.

Arguably, vehicle and other machine designs, including their fluid power systems, must be reassessed with the growing implementation of electrification, especially in mobile applications. Many companies have already developed or are working on solutions specifically for electrified applications in the fluid power industry’s key markets, such as construction equipment and automotive. It is up to manufacturers to decide whether these benefits outweigh the higher costs of electric drive technology in their operations.

Improve energy efficiency, reduce consumption

Replacing fluid power systems is just one approach to reducing global energy consumption with electric drive technology. A push for efficiency has stimulated a new influx of clean electric drive technology development. Use of this technology continues to increase as advances in permanent magnet motors and silicon carbide (SiC) semiconductors increase insulated gate bipolar transistor (IGBT) performance and make drive technology more efficient.

The next generation of IGBTs makes modern inverters, where all the fast switching takes place, more energy efficient. Drives are also enabling the digital transformation of machines and equipment, leading to advances in simulation and data analysis, resulting in improved efficiency, according to Craig Nelson, senior product manager at Siemens Industry, Inc.

Other improvements, such as battery-less encoder technology, reduce component counts while improving axis performance, according to Ben Strong, servo product marketing manager at Mitsubishi Electric Automation.

Strong said, “Improved simulation techniques allowed us to improve motor torque density, decreasing motor sizes in our new MR-J5 series products by 10 to 20% over previous servo drive and motor series.”

Xudong Tao, deputy director of the R&D center at VEICHI Electric Co., Ltd., agrees that vector frequency converters and servo drives will become important parts of the digital transformation of industrial equipment. He notes that digital transformation will have a profound impact on the industrial economy by integrating data, improving production efficiency, and optimizing operations.

“Most manufacturers are just starting to really understand where they’re using energy,” Nelson explains. “The latest drive technology can help them better understand where and when they’re using most of their energy by gathering all the information from running all their machines. Then they can use simulation and data analytics to model various energy-saving scenarios.”

Specify the motor first

Choosing the right motor depends on factors such as the application load and inertia, as well as dynamic positioning requirements and motor inductance. A high inductance winding can kill performance in an attempt to go from 0 to 1,000 rpm in 25 msec, for example. Servo motors and drives are generally used in applications with low inertia and high dynamics. Anything else needs to be considered on a case-by-case basis.

A large part of motor selection for any given application comes down to power and speed requirements, according to Nelson.

“Stepper motors are economical, but they are typically used in applications less than 1,000 rpm and under 1 kW. Permanent magnet servo motors are more expensive but very dynamic and typically applied up to 6000 rpm and 25 kW.”

For less dynamic and large power requirements induction motors with encoders are an economical alternative.

Vector drive versus servo drive

After a motor has been chosen, the next step in the design of an electrically driven system is to select a vector or servo drive. In industrial settings, vector and servo drives are used in different applications with different requirements for accuracy, dynamic performance, and load variations.

Chloe Wei, an overseas technical support engineer at VEICHI, said vector drives are more suitable for speed control applications, whereas servo drives are more suitable for positioning applications, such as those in computer numerical control (CNC) machines, printing machines and robotics.

Vector drives are used to control the speed of an AC motor to improve system efficiency, reduce energy consumption and achieve accurate motor control in equipment. In manufacturing and industrial facilities, vector drives are commonly used to power fans, pumps, compressors, winders, and other equipment that requires speed control. The output frequency and voltage to the motor can be adjusted using internal components, such as rectifiers, filters, inverters and control circuits.

Achieve peak performance

Voltage and current measurements (sensor-less vector control) or encoder feedback (vector control) can be used to determine rotor position. These values are used to calculate the optimum output for peak motor performance. Vector drives control a motor’s position, speed, or torque output. Variable frequency drives (VFDs) with vector control functionality are used to operate induction motors and permanent magnet motors (PMMs). Vector drives offer better speed and torque control, especially at lower speeds.

In pump control systems, which are common in industrial production, vector drives use a PID algorithm to adjust the running speed of the pumps according to demand.

VEICHI overseas technical support engineer Liam Wang said, “Vector controls can achieve pump sleep and external wake-up functions to avoid excessive operation.”

HVAC fan control systems also use vector drives to adjust the speed of the fan according to demand and to ensure that the system runs at the best working state to avoid excessive air flow and wasted energy. Vector drives are also commonly used in compressor control systems. Vector drives can help with accurate compressor control, adjust compressor speed based on air demand, and prevent unnecessary energy consumption, especially when loads are light.

Feedback provides greater accuracy

Servo drives are more expensive and rely on encoder or resolver feedback to determine motor position with a high degree of accuracy. Most servo motors are PMMs. However, some servo drives support asynchronous servo motors. Compared with a VFD utilizing vector control, a servo drive will have significantly higher intermittent torque capacity, a faster response to changes in motor speed, and more accurate torque control. “In most circumstances, a servo drive is combined with a motor from the same manufacturer,” Strong explains. “Usually, a servo drive and motor will cost more than a vector cable VFD and induction motor.”

Servo drives not only provide energy savings during motor operation but also offer all-around cost saving during production, according to Wang. In addition to energy-efficient motor operation, servo drives’ high dynamic speed, accuracy, and repeatability save processing time, materials, and other costs during production.

“For example, waste reduction results from precision control capability,” Wang said. “Servo drives can help products meet the exact size and quality requirements, reduce the scrap rate, reducing material loss and waste, and achieve higher production efficiency.”

Wang explains that servo drives are also more flexible and can quickly adapt to changing production needs. This flexibility reduces downtime and speeds changeovers, resulting in improved production efficiency. Servo drive technology also reduces labor needs by enabling industrial and collaborative robots and automated material handling.

Energy-efficient technologies

The new generation of electronics and heat dissipation technology allows modern vector drives to provide higher power density in a smaller physical package, suitable for applications in limited space. Some vector drives now have energy feedback technology, feeding energy generated during braking back into the grid, thus reducing energy waste and improving the energy efficiency of the system.

New high-efficiency motors, such as synchronous reluctance motors and auxiliary magneto motors, require better drive algorithms to support higher efficiency.

By controlling current and speed, vector drives can help prevent unnecessary energy consumption in AC motors while simultaneously maintaining their best working state. For example, if the load is lighter, the vector drive will detect the change and adjust the output current for less electric consumption by the motor.

“On the other side, with the energy feedback function, vector drives can feed the braking energy back to the power grid or other devices to reduce the energy waste,” explains Wei. “The energy-saving modes in servo drives are nearly the same as vector drives. The difference is that because of the quicker and more accurate response on the load changes on the motor, servo drives can achieve the expected motion control tasks in shorter time, avoiding unnecessary energy consumption.”

Vector control is critical to controlling permanent magnet motors with VFDs in either closed-loop or open-loop modes, according to Strong. According to a Toshiba white paper, “In laboratory testing at Toshiba for variable torque loads, a 7–12% increase in motor efficiency was achieved. A 7 to 9.5% increase in motor efficiency was measured for constant torque loads.”

“A motor accelerated from stopped condition by a vector or servo drive to 60 Hz consumes less energy than the same power induction motor will consume when started with contactors,” Strong said. “In large-horsepower applications, vector drives can reduce utility costs incurred by starting large loads.”

Soft starters’ role in motors

Soft starters are mostly used to start motors smoothly as well as to reduce current and mechanical shock. Compared to vector and servo drives, the most significant difference is that soft starters rarely provide dynamic reaction to changes in the operating motor.

“Soft starters offer only a small part of what a vector drive can achieve,” Wang said. “They are simple devices that are mainly used to minimize mechanical shock during the start and stop process for some large-power motors. In contrast, vector drives and servos typically have high dynamic responsiveness and can quickly adapt to load changes for a more flexible system response.”

While the initial cost of soft starters is usually lower, during the operation phase, soft starters may not be as energy efficient as vector inverters and servo drives in many applications. Vector inverters and servo drives decrease operating costs more by improving energy efficiency during operation, resulting in better cost-effectiveness in the long term, according to Wang.

If the application requires precision control, high performance, and flexibility, and users can afford a high initial investment cost, vector inverters and servos may be a better choice. If the primary concern is to reduce mechanical impact at start-up and initial investment costs, and the need for dynamic control is not high, soft starters may be an economical and practical option.

Energy feedback

Vector and servo drives can capture and reuse regenerative energy caused by deceleration or external torques acting on the motor. This can be accomplished using a common DC bus solution, active front-end technology, or a combination of both. Energy generated by the motor can be utilized by another axis in a shared common DC bus arrangement or be returned to the AC power line to be used by other AC loads.

“When regenerating energy from the motor, it’s less expensive to share it across the DC bus than it is to design a system that takes the motor energy all the way back to the incoming power supply,” Nelson said. “We do both all the time, but the upfront costs for regenerating the energy back to the line are much higher.”

In recent years, the single-axis servo drives in machine tools and in all-electric IMMs are gradually being replaced by multi-axis drive technology, according to Tao. “Multi-axis drive technology uses multiple inverter units to share a rectifier unit, compared with the previous single inverter with a rectifier,” he said. “On the one hand, the common bus program effectively improves the energy efficiency in the multi-axis drive, but it also reduces the cost of the product produced. For example, VEICHI’s multi-axis drive products SD810 and SD860 series consume 5 to 30% less energy on the same multi-driving task compared to using single-axis drives.”

Investing in energy efficiency

Vector inverters and servo drives will increasingly be adopted as core components of automation systems. As the requirements for energy efficiency, environmental protection, and sustainability increase, the high-performance characteristics of vector inverters and servo drives will become more important. Carbon footprints around the world may be reduced significantly with greater adoption of technologies designed to exceed recent energy regulations and standards.

As the level of automation in factories and production lines increases, the demand for servo drives will also increase. Vector and servo drive technology is critical to the realization of Industry 4.0 and intelligent manufacturing. By marrying the Internet of Things (IoT) and cloud computing technologies, vector and servo drives can help manufacturers achieve remote monitoring, diagnosis and optimization, providing greater intelligence and flexibility for industrial production.

When determining the economic benefits of using vector and servo drives, it’s important to think long term. While the initial investment may be higher, there are significant energy savings over the operating life of these systems, especially in systems that require high precision or frequent load changes. With the adjustment of output frequency and voltage in real time based on changes in demand, motors and other system components are also likely to last longer.

Other advantages that come from greater efficiency and improved performance include less labor, reduced downtime, faster changeovers, lower material costs, and enhanced product yields. As a result, the deployment of vector and servo drives in industrial applications can be viewed as a strategic investment for ensuring profitable and sustainable operations.

– The Association for Advancing Automation (A3) is a content partner.

Original content can be found at Association for Advancing Automation (A3).

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