Power analysis improves drive efficiency

| Information and Communication Technology

KEB uses the WT5000 Precision Power Analyser to help it develop frequency converters

Motor drive manufacturer KEB Automation uses Yokogawa power analyser to build higher efficiency motor drives

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.

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.

Accurate Power Measurement

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 believes that 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,” he says.

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.

Instrument Evaluation

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.

WT5000 Features

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 is an extremely easy task. Designed for flexibility, the WT5000 provides a full touch screen, supported by hardware hotkeys and powerful software for remote measurements.

Kater went on to say how much he likes the modular design of the channels on the WT5000, with KEB having 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.

“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,” he adds.

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.

Instrument Versatility

The WT5000 Precision Power Analyzer is a versatile instrument and is available in other versions, including the transformer version, with which engineers can measure either three or four different power phases at 10 MS/s (18 bits). The high resolution, 10.1-inch WXGA display allows split screen viewing of up to seven waveforms and can display up to 12 pages of measurement parameters, from products as diverse as inverter-driven motors, renewable energy technologies and traction applications such as pumps, fans, and electric vehicles and power transformers. Measurements can also be displayed in vector format or trending in time.

Yokogawa also offers supporting software packages that can be used to coordinate several instruments, including the WT5000, into a single measurement suite to view different data sources simultaneously. Some software features allow users to simultaneously view up to 22 waveforms and two harmonic bar graphs (six waveforms, sixteen trends, two vectors, and three harmonic bar graphs: WTViewerE) in split screen mode. Alternatively, they can zoom in using cursors to see more detail in a particular area of interest. Users can customise, save and load screen layouts as well as specify the data to be saved in CSV format. The software also allows users to create custom computations, combining values from multiple power analysers.

Jonathan Newell
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