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What is Hardware-in-the-Loop Simulation?

Embedded systems are designed to control complex plants such as land vehicles, satellites, spacecrafts, Unmanned Aerial Vehicles (UAVs), aircrafts, weapon systems, marine vehicles, jet engines, and many more. They generally require a high level of complexity within the embedded system to manage the complexity of the plant under control.

Hardware-in-the-Loop (HIL) simulation is a technique that is used increasingly in the development and test of complex real-time embedded systems. The purpose of HIL simulation is to provide an effective platform for developing and testing real-time embedded systems. HIL simulation adds the complexity of the plant under control to the test platform. The complexity of the plant under control is included in test and development by adding a mathematical representation of all related dynamic systems. These mathematical representations are referred to as the “plant simulation.”

For example, an HIL simulation platform for the development of automotive anti-lock braking systems may have mathematical representations for each of the following subsystems in the plant simulation:

  • Vehicle dynamics such as suspension, wheels, tires, roll, pitch and yaw
  • Road characteristics
  • Dynamics of the brake system’s hydraulic components

An HIL simulation must also include electrical emulation of sensors and actuators. These electrical emulations act as the interface between the plant simulation and the embedded system under test. The value of each electrically emulated sensor is controlled by the plant simulation and is read by the embedded system under test. Likewise, the embedded system under test implements its control algorithms by outputting actuator control signals. Changes in the control signals result in changes to variable values in the plant simulation.

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