Compact permanent magnet synchronous motor extends control range and reduces total cost of ownership.
In many applications – metering ingredients in the pharmaceutical or food industry, for example – pumps are required that can not only be precisely controlled in terms of flow rate and dosing time, but also convey the ingredients particularly gently. To enable the proven pump units of the ecodos series from Lewa to fulfil this demanding task with even more flexibility and energy efficiency in the future, the manufacturer is expanding the portfolio to include a new form of wide-range speed control. Alongside asynchronous motors and servomotors, permanent magnet synchronous motors, or PMSMs for short, are also used now. They are characterised by high energy efficiency and a control range greater than 1:200. This significantly expands the range of applications. With PMSMs, it is no longer necessary to use several pumps for different flow rates or oversize asynchronous motors for low speeds. Since PMSMs can be designed without a fan, they remain compact and easy to clean. The latter feature predestines them for hygienic applications. High efficiency rating over the complete control range in accordance with energy efficiency class IE5+ also reduces energy costs, thus ensuring a lower total cost of ownership (TCO).
The diaphragm metering pumps in the ecodos series are particularly well suited for applications in the food or pharmaceutical industries. All materials in contact with the fluids used in the pump units meet the FDA and USP Class VI requirements, and the EU directives for the food industry. In the hygienic version, for example, the pump head is made of PP or electropolished stainless steel with a surface roughness <0.5 µm. This facilitates cleaning of the surfaces in contact with the product.
The motor technologies used to date have had to make sacrifices: “For classic asynchronous motors whose rotor is a squirrel-cage rotor, the control range remains limited to 1:10 (1:50 is possible in individual cases). With encoder feedback, significant expansion is possible,” said Maurice Wirkner, an application manager at Lewa. “In addition, the drive is relatively inefficient outside the rated speed range – especially at low speeds. This requires the drive to be oversized, which increases operating costs.” Servomotors are optimised for highly dynamic requirements and also cover the complete control range (1-210 pump strokes), however, they are more expensive to purchase and in addition, require a servo inverter for control.
Wide-range speed control
Lewa has now expanded its own portfolio with a drive technology that does not have these weaknesses. “Unlike the asynchronous motor, the rotor of this drive consists of permanent magnets and rotates synchronously, i.e. without load-dependent slip,” Wirkner explained. “Among other things, it features an extreme control range, which often makes the use of multiple pumps for different flow rates unnecessary.” Particularly in the case of multiple pumps, an additional manual stroke adjustment or electric stroke adjustment can be dispensed with and the required flow rate can be realised by speed control only. The PMSM also has a constant torque. The complete torque can be applied from engine speed 0rpm (standstill) up to the rated speed of the motor. This ensures particularly smooth and gentle system start-up, since each process can be started with a pump capacity of 1% instead of the usual 10%.
It also features a high short-term overload capacity, which enables a drive design without oversizing for the starting torque. As a result, smaller, more cost-efficient sizes can be realised than with classic drives. “Like the asynchronous motor, the PMSM can be controlled via a standard frequency converter, so users can rely on common parts,” Wirkner explained. “With the servomotor on the contrary, it would be necessary to purchase expensive servo controllers.” The compact drive can be easily cleaned due to its fanless design and offers high IP protection. If required an additional conversion process – called nsd tupH – can be applied to the aluminium body for FDA requirements. This makes the surface extremely resistant and even easier to clean – ideal for applications with stringent hygienic requirements, such as aroma metering in the food industry or additive dosing in the pharmaceutical industry.
Enabling cost reduction
The sole limitation of the currently used PMSM is that it is only available for safe areas. “Thanks to wide-range speed control with IE5+ PMSM, we can meet the increasing customer demands for a wider adjustment range and lower energy consumption, as well as overall costs,” said Wirkner to sum up the situation. “The topic of energy efficiency in particular is becoming increasingly important for our customers. A decentralised solution in which the frequency converter is installed directly on the PMSM, can now be implemented with Getriebebau Nord, our motor partner for PMSM, too.”