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Figure 1: Measuring power-train efficiency in an electric vehicle, showing four DC measurements (1 to 4) with the corresponding mechanical power measurements (M1 to M4)
In the rapidly evolving area of power electronics, the need for reliable testing to enhance safety, efficiency and performance has never been greater. In sectors as diverse as renewable energy, electric vehicles and energy-efficient technologies, changing application needs and evolving industry standards call for custom measurements and consistent accuracy. Engineers need a test and analysis platform that not only delivers reliable measurements today but is also ready for the challenges of tomorrow.
For example, in the automotive sector, meeting consumer demands for greater charging capacity, shorter charging times, and greater travelling range requires thorough positive and negative cycle evaluations of battery charge and discharge characteristics. Similarly, the evaluation of inverter signals needs to account for the harmonic superimpositions from switching circuits. Minimising the interference from this switching noise requires isolated inputs, high-speed sample rates, and long-term observations (Figure 1).
With the forthcoming advent of contactless charging, such evaluations will need to be conducted at lower power factors and frequencies with hundreds of kilohertz; areas that are outside the scope of traditional test instruments. In addition, motor-drive technology has become more complex in recent years, with pure sine-wave PWM signals becoming less common.
Similarly, in the area of power transmission and distribution, new developments such as renewable energy stations, energy-positive buildings and infrastructures mean that electricity no longer has a unidirectional flow from the power station to the consumer (Figure 2). With a multitude of renewable and non-renewable power stations feeding the grid, engineers in charge of ensuring a balanced grid need robust testing and accurate measurements to reduce the impact of noise, distortions and harmonics from multiple sources. Power generation stations and large consumers also need to evaluate the effects of their power outputs and usage levels on the grid and on other users.
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Figure 2: A precision power analyser helps engineers in renewable energy grids to improve conversion efficiency by offering precision insights in charging, discharging, storage and overall efficiency
These high-accuracy measuring instruments will need to include the ability to carry out high-frequency measurements. With mean voltages increasingly differing greatly from the fundamental voltage waveform, harmonic measurements are needed to establish the values of derived measurements such as active power. Similarly, addressing the challenges of measuring parameters such as energy efficiency, harmonic content and power factor will require both progressively greater accuracy and consistency in measurement over the specified ranges and conditions.
The simultaneous measurement of normal values with harmonics is also needed for overmodulation analysis of PWM waveforms and the high-speed measurement of power fluctuations.
Addressing the challenges
These challenges are now being addressed in a power analyser that sets new standards in terms of precision and accuracy, as well as being based on a flexible modular architecture that allows customisation to meet the needs of different applications (Figure 3).
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Figure 3: The Yokogawa WT5000 combines measurement accuracy of 0.03% with modular flexibility. Here, a WT5000 is configured for simultaneous synchronised measurements from four torque and rotation sensors to determine the overall efficiency of four motors
This instrument offers a high degree of isolation, noise immunity, current sensing and filtering in a modular architecture that provides an extensible measurement platform.
It combines an industry-leading basic power accuracy of ±0.03% with a frequency range of 5 MHz and a sampling rate 10 MS/s (18-bit). Current measurements are available via 5 mA to 5 A or 0.5 A to 30 A modules.
Seven built-in slots for user-swappable power input modules and diverse mainframe options enable users to expand or reconfigure the instrument as their applications and requirements change. In addition to measurements on power parameters, the torque and speed from four separate motors can be measured.
Other key features include the ability to use 5 A or 30 A input modules in conjunction with the split-screen touch display to compare multichannel measurements; carrying out measurements under highly fluctuating input and/or load conditions with an autoranging integration function and automatic data update rates and custom measurements for added flexibility, with user-defined triggers and computations, as well as functions such as dual-motor evaluation. The instrument performs harmonic measurements, including comparisons of two simultaneous measurements up to the 500th order.
A full touchscreen interface, supported by hardware hotkeys and powerful software for remote measurements, make connecting, configuring and measuring easier than ever before.
High-speed A/D convertor
This analyser achieves the world’s highest measuring accuracy: ±0.03% of total at 50/60 Hz - by using an 18-bit analogue/digital converter with a sampling frequency of 10 MS/s. This makes it possible to accurately capture waveforms from the latest high-speed inverter devices.
Noise immunity
Very high-speed power devices using semiconductor materials such as silicon carbide and gallium nitride are increasingly being used in power-conversion products such as invertors and drives. As a result, common-mode voltage effects can create noise problems that can affect the performance of measurement systems. The design of the new instrument minimises the effects of high-frequency common-mode voltage, resulting in an excellent CMRR (common-mode rejection ratio) characteristic.
Storage
The analyser incorporates optional internal memory of up to 32 Gbyte for storing large quantities of measurement data in field applications. This is achieved without the need for any external storage media, whilst at the same time enabling high-speed measurement.
Motor evaluation
In addition to the swappable 30 A and 5 A modules, the WT5000 offers multi-motor evaluations for applications in electric or fuel-cell vehicles, robotics, pumps etc. where developers are increasingly required to evaluate a number of different motors. Using the optional motor evaluation function, it is possible to evaluate up to four motors simultaneously with one unit (Figure 4).
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Figure 4: The WT5000 hasseven built-in slots for user-swappable power input modules and mainframe options that enable users to expand or reconfigure the WT5000 as their requirements change
The dual harmonic measurement function makes it possible to measure the carrier frequency component from the rotational speed of the motor in an inverter drive whilst checking the influence of the carrier frequency on the motor drive.
High-current measurements
An increasing number of applications require the evaluation of larger-current devices, typical examples being electric vehicles and large-scale solar installations. Since an external current sensor input function is fitted as standard in both the 30 A and 5 A input modules, the instrument can measure up to 30 A or 5 A with direct input. For much higher currents (up to 2000 A RMS) dedicated high-current sensors are available.
Automotive: Powertrain tests: From R&D to manufacturing and compliance testing, measurements on powertrains in electric vehicles not only require progressively greater accuracies but also consistency in measurement over the specified ranges and conditions.
Key requirements here are DC and multiphase AC measurements from the battery, inverter and motor; as well as mechanical motor characteristics such as torque, rotation speed and direction. In addition to harmonic evaluations of inverter signals, it is also important to account for superimpositions from switching circuits. In this context, the seven modular input elements of the WT5000, make it easy to evaluate total power and efficiency, whilst its ability to evaluate multiple motors on a single unit, allows the testing of two sets of torque and A/B/Z phases or four sets of torque and rotation speed.
Conclusion
The precision power analyser described in this article offers an unmatched 0.03% accuracy and modular architecture, helping engineers to innovate their power testing and analysis with precision, flexibility and confidence. Whether it is for the development of energy-efficient devices and appliances, plug-in hybrid/electric vehicles or renewable energy technologies, this instrument helps engineers to solve design challenges, improve productivity and ensure quality through reliable power measurements.
The accuracy and precision of the instrument are backed up by tests carried out at Yokogawa’s European standards laboratory at its European headquarters in The Netherlands. This facility is the only industrial (i.e. non-government or national) organisation in Europe to offer traceable power calibration, to national and international standards, at frequencies up to 100 kHz: A requirement for higher harmonic measurements specified in quality standards such as ISO 9000.
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