Evaluation Of Electric Vehicles For Performance, Safety And EMC

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Electric vehicles (EVs) are often seen as the green transport option. As the automotive industry advances in power conversion and battery technologies, it also improves EV testing performance and cost by developing flexible automated power conversion test platforms and regenerative battery test systems.

The electric vehicle (EV) industry is constantly improving its technologies to reduce carbon footprint and meet customers’ expectations for a good driving experience and a reasonable recharge time. These factors are driving EV manufacturers to develop efficient power converters, inverters, alternators, faster charging techniques/batteries and improved battery performances. EV supply equipment (EVSE) is evolving to encompass quick-charging batteries, public charging stations and sophisticated onboard components that enhance battery performance and ensure future EV compatibility with EVSE infrastructures.

If EVSE components are not evaluated properly, these can cause battery failures and danger to vehicle operators in hazardous conditions. To deliver safe and high-performing EVs, several regulation standards are established. Safety test applications include motors, power systems, batteries, charging systems, wiring and connectors, as well as charging stations. Many laboratories are replicating a variety of environmental conditions, such as temperature extremes, vibrations, shocks and impact, and simulating hazards that may arise during vehicle transportation or operation to evaluate performance.

Electric vehicle supply equipment (Credit: https://afdc.energy.gov)
Electric vehicle supply equipment (Credit: https://afdc.energy.gov)

EV battery test system

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Battery testers should be regenerative, high-precision systems specifically designed for cell-, module- and pack-level battery testing. From charge/discharge to drive cycle simulation, accuracy in measurements ensures exact and reliable testing for battery capacity, performance, production and qualification. The rapidly-emerging EV, hybrid EV (HEV) and plug-in HEV (PHEV) markets are poised for continued growth and change.

Hybrid and electric batteries test conditions include cell-, module- and pack-level testing, cycle life hybrid pulse power characterisation (HPCC), safety certification testing, overcharge, short-circuit, mechanical shock, thermal shock, vibration, temperature, humidity, failure analysis, battery management solution (BMS) simulation and monitoring, connector/service disconnect cycling and durability, battery safety, battery performance, battery fire and abuse, engage/disengage force, maximum current and mechanical overstress.

A battery test system (Credit: www.odacore.com)
A battery test system (Credit: www.odacore.com)

There are three main types of EV charging points, each defined by power output and, hence, how quickly these can charge an EV. Slow charge (up to 3kW) can fully charge an EV in around six to eight hours. Fast charging (7kW – 22kW) time is two to four hours. Rapid charge (up to 50kW) typically takes under 30 minutes. Most EVs come with multiple cables to allow connections with a wide range of EV charging points.

High-speed transition testing

This includes testing for charge and discharge with freely programmable set values for current, voltage, power or resistance in test programs. Due to the specific requirements of fast load changes and simulation of driving cycles, this type of testing uses IGBT technology. High-speed transition from charge to discharge, and vice versa, make this technology ideal for EV and HEV battery testing. A portable data logger used to record drive cycles during a real test drive provides reproducible test results.

BMS testing

Introduction of new storage technologies and interconnection of multiple energy storage cells to form modules require an intelligent BMS. It predicts safety, control and regulation functions by measuring various parameters such as voltage, current, temperature or state of charge. It is also responsible for thermal management, energy management, cell balancing and performance, which is a great challenge in BMS development and validation.

For reproducible testing and BMS optimisation, modern energy storage devices have to meet high-quality and market demands for power and energy density, safety and durability. This requires comprehensive tests to be carried out to ensure successful battery production.

EV motor testing

To ensure good quality of the motor, dynamic power of an EV needs to be tested with impulse/surge testers and hipot testers. EV motor test functions include inductance and resistance testing of windings, short-circuit testing between adjacent layers in the winding, and safety rating testing of the windings and armature. Voltage withstand test is required to meet the specifications of international electrical safety codes so that motor products can readily comply with their certification requirements.

For motor inductance tests, additional measurements of frequency, voltage and inductance are required. Inductance is measured with an AC signal, which is why an LCR meter is necessary. Layered short-circuit testing provides consistency during the motor manufacturing process by comparing waveforms. Wave comparison of a motor testing system include total area comparison, differential area comparison, flutter and corona.

Electromagnetic compatibility (EMC) testing

Electromagnetic shielding of cables constitutes an important concern in EV applications with considerations for developing particular standards for human exposure levels in radiated electromagnetic fields. It has been determined that the switching-frequency-related magnetic field radiation generated by power electronic converters using pulse width modulation (PWM) techniques can be of particular importance, overwhelming the fundamental frequency effects.

Simulation analysis of exposure levels due to variable frequency magnetic fields is done on anatomically-detailed human models in EV cabin environments. Testing performed using real-world simulations reduces cost and risk, and improves test coverage and overall design.

Increasing voltage of the traction battery or decreasing switching time of the power transistor to increase efficiency of an electric traction system results in an increase in the system’s electromagnetic interference (EMI). To meet the challenges of new components, new measurement methods and new requirements considering EMI and immunity of HV components are continuously added to automotive standards.

An electric drive system consists of a high-voltage power source, an electric motor, a power converter, and shielded or unshielded high-power cables. These components set a path for electromagnetic emission. To avoid problems with EMI, extensive EMC components of vehicles are being developed. As electric cars need recharging after driving, it may cause problems when electromagnetic waves are over-generated while a battery is being recharged. So, electric cars need to be evaluated using two methods: driving mode with no charging on the power grid and rest in charging mode coupled to the power grid.

Some EV testing service and solution providers

Given below are some service and solution providers for EV testing.

  • MET LAB provides EVSE testing, evaluation and certification to regional and international EV standards for safety and EMC. It determines what standards apply to a vehicle and develops a custom testing plan to help reach the intended markets efficiently and cost-effectively.
  • Chroma provides automated test systems for EVs and HEVs, consisting of standard test platforms to test most power components in an EV’s power system. Its automatic data recording and statistical report creation provide opportunities for product improvement. This combination of configurable hardware and software enables manufacturers to reduce cost and ensure consistency through all phases of the product lifecycle.
  • Intertek offers lab capacity for EVs, HEVs and PHEVs, and automotive battery testing services on a global scale to certify charging stations and electrical components for worldwide distribution. From cells to large battery packs, the company offers performance, durability, safety and abuse testing to meet the latest industry, national and international standards and regulations.
  • Scienlab supplies a hardware-in-the-loop test environment to emulate various cell types of a range of cell models. It accompanies the entire development and production process of an energy storage device.
  • EVSELLC provides EV charger testers to ensure proper operation of equipment. It allows installers to check new EV chargers after installation, and verify a number of vital power and safety requirements, as these simulate the connection of an EV charger with an EV.
  • Microtest provides motor tester series for performing static tests that measure electrical properties of a motor when it is not energised. It measures layered short-circuits, insulation voltage, inductance and DC resistance.
  • NH Research’s test equipment and software tools are used to validate designs and confirm manufacturing processes by using real-world simulations. Its battery emulation mode provides testing of chargers, DC/DC converters, inverters and vehicle-to-grid features.
  • Seaward provides testers to ensure that all types of AC EVSEs are operating both safely and in accordance with IEC61851 at the point of installation and throughout their lifecycle. Testers can store diagnostic data supplied by the charge points, and data can be transferred wirelessly to an Android device running EVSE mobile app. Data can be sent to any remote location for in-depth fault diagnosis for traceability purposes. It can be used to measure output voltage of charge stations, maximum available charging current, earth loop impedance, RCD test, insulation resistance test, presence of correct mains supply and earth connection (single and three phases). It can also be used to simulate a number of fault conditions, disconnection time measurement, amplitude measurement, frequency measurement, duty cycle of PWM signal and so on.

To sum up

As the automotive industry advances in power conversion and battery technologies, it also improves EV testing performance and cost by developing flexible automated power conversion test platforms and regenerative battery test systems. Automated test solutions provide safe and real-time monitoring of test processes and reduces inspection time, significantly reducing production costs.


 

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