How is HIL testing used for onboard EV chargers?

Hardware-in-the-loop (HIL) testing is a real-time simulation that enables designers to test embedded code for EV chargers without needing the actual system hardware. It speeds development efforts and reduces development costs.

This article begins with an overview of HIL testing and onboard chargers (OBCs), looks at specific types of HIL testing applied to OBCs, and concludes by considering how HIL testing of OBCs can improve vehicle-to-grid (V2G) operations.

HIL testing of OBCs includes testing interactions with the power grid or electric vehicle supply equipment (EVSE) on the input and high-voltage power supply and electronic load to test bidirectional operation, a low-voltage electronic load, a cooling system (chiller), various actuators and sensors and the HIL simulator (Figure 1).

SASE security — Figure 1. HIL simulations of EV OBCs enable designers to test interactions between embedded code and hardware. (Image: *Meta System*)

Some features of HIL testing platforms for OBCs include:

Realistic software models of the OBC, EVSE, battery pack, battery modules, battery management system, cooling/heating system, sensors, actuators, and other components.
Library of preprogrammed automated tests.
Specific tests to confirm compliance with industry standards like the combined charging standard (CCS), CHAdeMO, ISO 15118-2, IEC 61851-1, J1772, and so on.
Ability to test the controller functionality during fault conditions and simulated grid disturbances.
Simulation using actual OBC and EVSE communication messages.

Using HIL testing enables EV developers to test a wide range of hardware, such as different battery pack sizes and configurations, different types of EVSE, and interactions with various grid specifications, to ensure global compatibility without using many complex and expensive physical hardware configurations.

HIL testing for power electronic systems like OBCs can focus on signal simulations or power simulations. Signal simulations validate the controller’s performance under actual operating conditions. The simulated controller must accurately imitate the actual hardware, including communications protocols and battery charging algorithms, under nominal and abnormal operating conditions.

Power simulations can be performed at reduced power levels or at full power. Both tests use the same software but may require different hardware. Reduced power testing is often used initially to test the integration of the controller and power conversion components. It’s performed using a lower-power AC source and lower-power electronic loads. That can speed initial validation of the system with minimal cost.

Full-power HIL simulation is used as a final validation step before actual hardware testing begins. In addition to testing the overall system performance and integration, full power HIL simulations are often used for testing new subsystems and related control software before final system integration.

HIL and V2G integration

Numerous challenges are associated with V2G system integration. A V2G system must accommodate the needs of the electric grid to dynamically minimize voltage and frequency excursions in real time to support stable grid operation. Due to the complex nature of the grid structure and the different types of vehicles that will be used for V2G, HIL testing is needed to integrate V2G systems cost-effectively.

HIL testing can simulate power electronic systems like OBCs while simultaneously simulating the complexities of distribution grid operation. In one case, a V2G simulation was implemented that included a 2.5 mega-volt-amp (MVA), 230 kilovolt (kV), and 4.8 kV, 37-bus, three-phase balanced network for the distribution grid. The loads included a combination of houses and V2G systems. The simulation included 10 neighborhoods of 16 homes each. There was a total of 320 end-nodes (160 homes and 160 V2G systems).

This HIL system was designed to enable simulation of a decentralized V2G control algorithm under various operating assumptions and study the impact on the voltage stability of the grid. A key element in the simulation was a bidirectional OBC using real-time control. The grid simulator sends a grid voltage signal to the bidirectional power converter and receives instantaneous current feedback from the power converter enabling the simulation to determine power consumption from each individual node. The results of the simulation on voltage stability are viewed on an oscilloscope (Figure 2).

Summary

HIL testing gives OBC designers a powerful tool for quickly and inexpensively testing system operation and integration. It can also test compliance with industry standards and is being used to develop distributed control algorithms for V2G systems that support grid voltage stability.