Test & Measurement: Power point

Lee Thomas (left) and Anoop Gangadharan with the Yokogawa WT5000 precision power analyser

Steve Rogerson takes a look at Yokogawa’s latest precision power analyser that is claiming a world record in accuracy

The electric vehicle industry still has work to do if battery-powered vehicles are going to be the dominant means of transport in years to come. Among the areas that need to be addressed are range anxiety – drivers want to be confident the vehicle will get to where it is going without running out of power – and charging time; nobody wants to sit around for hours at a service station waiting for the car to charge.

To achieve this, strides still have to be made in terms of powertrain efficiency. And for engineers to succeed in this, improvements will also be needed in the test and measurement equipment they use.

“The engineers are the architects of all the challenges around us,” said Anoop Gangadharan, product marketing manager for Yokogawa in Europe. “They always have to be on the money.”

He was speaking at the launch of the WT5000, a precision power analyser that has a measurement accuracy of ±0.03%, a figure that the Japanese company claims is a world record, and one it hopes will go a long way to helping automotive engineers achieve the efficiency they desire.

“When they are making their products, they want to make data-driven development decisions,” he said. “And they want to avoid product recalls. And their testing conditions are changing constantly. What we have created is not just a power analyser but an extensible power management platform. It is an evolving product; users will be able to add more capabilities over the years.”

As well as electric vehicles, the company is targeting markets in renewable energy, home and office appliances, and industrial equipment.

A key part of this is its modular design. The rear contains seven swappable input modules. Different modules can be put in depending on the application, and Yokogawa has promised to introduce new modules as market demands change. In an automotive application, for example, it can be configured to measure up to four motors simultaneously. It will be looking at electromechanical parameters for multi-phase motors, torque sensors and rotation sensors for measuring the likes of rotation speed, rotation direction, torque, mechanical power, synchronous speed, slip, electrical angle and motor efficiency.

“Automotive is a very important market, with electric vehicles booming like there is no tomorrow,” said Gangadharan. “It is a very exciting market. The biggest names in automotive have all started work on electric vehicles. It will be one of the fastest growing markets for us.”

However, he said consumer adoption of electric vehicles had not taken as much as the car makers wanted for reasons such as range anxiety and charging time.

“It will be some time before it takes off like we hope,” he said. “We need to reduce charging time to under 30 minutes. The one area of testing that will be increasingly important is improving the efficiency of the powertrain. The ±0.03% accuracy stands automakers in good stead, but we may need to improve that as automotive standards evolve.”

Powertrain development involves taking measurements form multiple phases for battery, inverter and motor to evaluate the likes of torque, rotation speed and direction, and slip. Multiple six-phase motor systems need to be evaluated and there also needs to be harmonic evaluation of inverter signals due to superimposition from switching circuits.

The WT5000’s accuracy and the ability to evaluate four motors simultaneously could be important here along with its wide input range, sensor compatibility and the seven swappable input modules slots, which fit into a chassis that has the same dimensions as existing models in the WT series.

With a seven elements input capability, multi-system measurement is increased in harmonic measurements on three-phase systems, for example. The unit can carry out two harmonic measurement functions simultaneously, each at up the 500th order and up to 300kHz fundamental waveform. This makes it possible to measure the carrier frequency component from the rotational speed of the motor in the inverter drive and to check the influence of the carrier frequency on the motor drive.

At the moment, only two modules are available – one for 30A and one for 5A – and two more are in the pipeline.

“As the industry progresses, there will be more depending on what the market is asking for,” said Gangadharan. “You will be able to have a library of modules and just plug in the ones you want. It is power to the people.”

Lee Thomas, a Yokogawa sales manager, added: “What excites me most about this is the modularity. This stops engineers having to invest in new instruments. This is future proof for power measurement applications.”

The instrument itself, without modules, comes in at just under £10,000; the modules will be priced according to their functionality.

The ±0.03% accuracy at 44 to 66Hz is made up of ±0.01% of reading and 0.02% of range. This drops for DC measurements to ±0.02% of reading and ±0.05% of range.

“The ±0.03% figure is the world’s best accuracy,” said Gangadharan.

One of the essential elements for determining the performance of a power measuring instrument is the analogue-to-digital converter. To obtain the measurement accuracy, the unit uses an 18bit converter with a sampling frequency of up to 10MS/s. As a result, it becomes possible to capture waveforms accurately from the latest high-speed inverter devices. It is said to be very effective for stable measurement results.

The unit will also be able to be controlled remotely, with a laptop in charge of multiple units. As of now though, the free software will only control a single unit but paid-for software is due out by the end of this financial year to allow control of multiple units.

Another plus is its noise resistance.

“It doesn’t suffer when the instrument is, say, close to a hybrid powertrain that is electrically noisy,” said Thomas. “It works fine.”

The instrument has gone out to car makers for evaluation, but many of them fed information during the design of the machine.

“There have been more primitive versions out with them to look at, but not the finished version until now,” said Gangadharan.


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