Variable speed drives already offer users substantial power savings, as they reduce the power input when driving motors at less than the maximum rated load. Motor drive manufacturers are improving the performance of their devices still further by introducing faster switching capabilities. These allow motor drives to use smaller capacitors and magnetic components, saving both space and weight.
One such company is German automation and motion control specialist KEB Automation, which is using Yokogawa’s WT5000 Precision Power analyzer to develop the latest generation of frequency converters for variable speed drives, ensuring they meet the latest EU energy efficiency regulations. Founded in 1972, family-owned KEB has grown to become a global operation employing some 1,500 people, of which 150 are development engineers.
EU's Ecodesign Directive requirements
The company’s latest challenge is to meet the requirements of the EU’s Ecodesign Directive, which introduces tough new regulations governing the energy efficiency of drives and automation equipment. However, faster switching makes it harder to get accurate measurements of key power parameters such as voltage and current because of the higher level of common mode noise present.
Yet, very accurate power measurements are required if motor drive manufacturers are to fine-tune their systems and maximise the efficiency of their designs.
David Kater, development engineer at KEB, says: “Fast-switching semiconductors generate common-mode voltages at high frequencies, inducing parasitic common-mode currents even in small capacitances. We only want to see the differential mode in the measurement, which is why common-mode rejection is extremely important.”
KEB uses power analyzers at several stages of a product’s lifecycle, including in the development of the design, for final validation of the design’s performance and also to prove the characteristics of production units. Developing frequency converters for drives requires analyzers that can maintain accurate measurements of power parameters.
The measurement equipment must offer high common-mode noise rejection, as the output voltages of the inverters display high dV/dt, producing spectral components at very high frequencies.
Versatility through the Yokogawa WT5000
Following a rigorous comparison with other products, KEB found that the analyzer that most suited its needs was the Yokogawa WT5000. Analysis of its performance showed KEB engineers that the currents due to common mode noise were at an extremely low level, outperforming KEB’s previous analyzer, which was also a Yokogawa product.
In its tests of the WT5000, KEB found no significant crosstalk from channels affected by common-mode noise to other channels, even when operating at the system’s full measurement bandwidth of 5 MHz for current and 10 MHz for voltage. The WT5000’s power measurements are accurate to 0.01% (reading) and 0.02% (range) at AC mains frequency (50/60 Hz).
The device also offers several other major benefits to the user. Not least is its reliability – the WT5000 has a guaranteed accuracy of ±0.03%, can conduct harmonic comparisons up to the 500th order, and offers custom computation facilities. This ensures the WT5000 produces multi-channel measurements which the user can trust.
The WT5000 also offers extreme versatility, with features that include seven slots for user-swappable input elements, as well as a number of mainframe options. It can evaluate up to four motors simultaneously while allowing the user to expand or reconfigure the instrument as applications and needs change. The WT5000 can stream its raw captured data to a PC for detailed analysis.
Connecting, configuring and measuring power has never been easier. Designed for flexibility, the WT5000 provides a full touchscreen, supported by hardware hotkeys and powerful software for remote measurements.
“I really like the modular design of the channels on the WT5000. KEB has used the seventh channel, for example, to measure auxiliary power supplies or the DC link, while the first six are measuring the input and output of the drive controller,” says Kater.
“The WT5000 also helps make engineers more productive with features such as immediate recognition of the module configuration after switching on, followed by automatic initialization of the channels. Intuitive navigation also reduces the time it takes to configure and run a test – it is easy to bring up and select menus via the touchscreen,”
With the capabilities of the WT5000, KEB can design the next generation of highly efficient motor drives, with their engineers able to rely on their test equipment to get the results they need.
“The WT5000’s extremely high immunity to common-mode noise and the high channel-to-channel isolation indicate to me that I can safely rely on the instrument when analyzing the voltages and currents which are switched by semiconductor power components,” concludes Kater.
The full case study is available at this link.
