Testing Times for Electric Vehicles

­With the growing awareness of the damage that can be caused by fossil fuels, electric vehicles are certainly having their moment in the sun. But are potential drivers and buyers of EVs convinced that these vehicles can give them what they need? To really allow the EV market to take off, consumers need to know that electric vehicles have the range, performance, reliability and handling characteristics they demand.

Proving this requires manufacturers to develop extensive testing regimes to ensure their new car meets expectations. The numerous components and systems, including battery and motor, drivetrains and transmission, electronic and communication systems, demand a wide range of tests, as well as data logging and analysis.  Many of these components affect the operation or performance of subsequent systems, so the instruments employed will need the ability to log and compare many types of data simultaneously from several sources, both electrical and mechanical.

These types of highly capable test equipment will allow manufacturers to capture large amounts of data over hundreds of hours, giving them the insights, they need to improve their designs. If we take a subsystem approach to testing, we can identify three major power related subsystems in electric vehicles.

 These are:

·      Charging – of the battery, charging monitoring systems, regenerative braking

·      Powertrain – the power inverter sub-system for power delivery, and associated control signals

·      Motors – three-phase brushless DC motors used in various applications

Charging

Above all, EV drivers must know that their vehicle has the range and efficiency required, so the charging system is critical to consumer confidence.

A vital task is to characterise the charging and discharging of the battery. A measurement solution here would need to measure positive and negative cycles of power captured at high sampling rates.

A major reason for moving to EVs is to save energy and regenerative braking, harvesting the energy from braking and using it later to provide acceleration, is a major plus point. Analyzing this function will involve using multichannel power analyzers that can measure electrical output, efficiency and losses in the regenerative systems, as well capturing data from the braking and motor generator systems. One of the major blocks to widespread adoption of EVs is range anxiety. A possible solution to this is wireless charging (Figure 1). Built on two electromagnetic coils to support particular frequency profiles, wireless charging systems must show they can transfer power efficiently and prevent power loss. This often involves evaluating performance at frequencies up to several hundred kHz and at low power factors.

This test regime will require precision power scopes, which combine the time-based measurement used by oscilloscopes with the features of power analyzers. This allows them to perform standard multi-phase power measurements while also being able to analyse waveforms that can have transient components.

As well as electrical signals, solutions are needed that can evaluate electromechanical relationships between components and systems – they also need to record over long periods of up to 200 days. Yokogawa has met this demand with its ScopeCorder, a data acquisition recorder that combines a mixed signal oscilloscope with a multi-channel, multiple speed data acquisition system that offers long-term recording. To capture electromechanical events, the device can be connected to 21 types of input modules, including voltage/temperature modules, acceleration/voltage modules and strain modules. Activated sensors and communications systems will also affect the load and efficiency of the battery and a data acquisition recorder allows developer to assess the effects of these events. 

Power train

EV manufacturers need an accurate evaluation of motor and inverter control to achieve higher precision and greater efficiency. They also need to analyse inverter waveforms without interference from switching noise. An ideal test solution for these applications is a single power analyzer that connects to all the major components - the battery, booster, converter and the three-phase motor. It would also gather mechanical measurements from torque and speed sensors. This gives a complete picture of torque, rotation speed and direction, combined with electrical parameters such as voltage, current and power. (Figure 2).

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Figure 2: A precision power scope and a ScopeCorder are ideal for testing the power train

Again, a data acquisition recorder is best to assess electromechanical events, particularly over prolonged periods. With flexible inputs, it can combine electrical and physical measurements in a single overview, while also offering measurement of frequency, temperature, distortion, acceleration, and other signals. Measuring efficiency and comparing higher order harmonics between input and output will be the role of a power analyzer, which can also be used to measure parameters like electrical angle, rotation speed and direction.

Motors

Modern vehicles also use motors in many other applications, with power steering, automatic doors, windows and mirrors being just some of them. Many of these applications use Brushless Direct Current Motors (BLDCs). To evaluate these, manufacturers will need to capture real-time, multichannel measurements of parameters that include DC input power, three-phase inverter output, and motor & sensor feedback of parameters such as vibration, RPM, angle and temperature.

Using flexible modular inputs that can combine electrical and physical measurements, ScopeCorders can provide data on frequency, temperature, distortion, acceleration, and other signals. (Figure 3). BLDCs also need to be evaluated for transient behaviours. These can be assessed by power scopes in great detail, at high accuracies that compare well with power analyzers.

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Figure 3: ScopeCorders can provide data on a wide range of parameters for different EV motor applications

Getting a complete overview

It is often necessary to bring these measurements together to give an overall view of system performance. However, it can be challenging to bring signals from different instruments into a single view, making it difficult to find relationships between measurements. Yokogawa’s IS8000 software platform offers tight integration of the timing, control, and data collection from several instruments. This allows rapid set up and easy control of all the instruments needed, ensuring development engineers can start measuring data more quickly and efficiently. (Figure 4).

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Figure 4: Yokogawa’s IS8000 software platform brings together data from several instruments

Beyond the development lab

In addition to research and development, electric vehicles need to be tested during production. New, more portable test equipment will be needed, with instruments that allow in-car testing of different parameters in different climatic and road conditions.  A handheld version of Yokogawa’s ScopeCorder can be used along with different modules to test actual conditions in a driven car.

With wider use of EVs, there will also be more need for after sales battery testing to ensure the battery is producing the power demanded and is not degrading. Re-generative power systems will also need assessing. Test instruments in general will be faced by the challenge of capturing and assessing vastly increased amounts of data from systems such as high-speed inverters. In consequence, these instruments will need to get faster, be more adaptable and have larger memories. 

Yokogawa has been producing high precision, high-quality instrumentation for the automotive industry for years. Its latest measurement instruments are being optimised for the types of testing and development tasks that electric vehicles need. With its instrumentation and calibration services, Yokogawa is trying to support the next generation of sustainable technologies and electric vehicles are a major part of that. 

Yokogawa Europe B.V.