Hardware-in-the-loop simulation

Hardware in the Loop (HiL, also hitl, HITL ) refers to a process in which an embedded system (eg real electronic control unit or real mechatronic component) via its inputs and outputs to a matched counterpart, which generally HiL simulator is called and is used as a replica of the real environment of the system is connected.

Hardware in the loop is a method for testing and validating embedded systems, to support during the development and the premature operation of machinery and equipment.

HIL for embedded systems

Here, the system to be controlled (e.g., car) on simulated models for testing the correct functioning of the control device to be developed (for example, engine control unit). The HIL simulation is usually necessary to run in real time and is used in the development, in order to shorten development times and reduce costs. In particular, recurring processes can be simulated. This has the advantage that a new development version under the same criteria can be tested as the previous version. Thus it can be demonstrated in detail whether an error has been corrected or not ( see also Fehlernachtest (English re -testing) ).

The inputs of the control unit are stimulated with the sensor data from the model. To close the control loop (loop ), the reaction of the outputs of the control device, such as driving an electric motor, read back into the model.

The HIL simulator thus consists of a computer, which can meet the real-time constraints of the particular application ( increasingly PC-based), digital and analog input and output interfaces to the control unit and equivalent loads, simulating the internal ECU output stage diagnosis that all actuators correctly are connected.

The tests on real systems can thereby be greatly reduced, and in addition can determine system limits, without endangering the target system (eg car and driver).

The HIL simulation is always a simplification of reality and can stand the test in the real system not therefore replace them. If too large discrepancies between the HIL simulation and reality occur, the underlying models are too simplistic in the simulation. Then the simulation models need to be developed further.

HIL in the automotive sector

With the rapid growth of electronic control units and increasing functionality, especially in the drive electronics, with a wealth of new rule-based functions, the early 1990s, hardware in the loop was introduced as a measure to improve the testing capabilities in the automotive sector. HiL this is applied in two important characteristics for the test.

First adaptation of an electronic system (eg engine, transmission or brake electronics) to a HIL simulator as a so-called component or module test.

2 Adapted from several electronic systems to one or more coupled HiL simulators as so-called integration test. This includes the electronic systems in general to the same segment of the automobile ( drive electronics, comfort and body electronics, infotainment electronics). The use of the name HiL in connection with convenience and infotainment electronics is colloquially indeed common, due to the lack of real control loops in these systems, however, only in some cases incorrect.

When performing tests with the HIL in the initial phase manually performed tests be replaced by automated test sequences. This process is called test automation. This test can be almost arbitrarily parameterize and repeat accurately. A check of the fault shutdown is therefore much more possible. Test automation has helped the HiL test method to a breakthrough and made ​​of the development-related test procedures become an integral part of the testing process.

In the meantime, high quality of the models used in the vehicle dynamics or engine range is the HIL process since the early 2000s, more and more application in the development of new control algorithms. This leads to significant reductions in the meantime the development times.

Besides the pure connection of the electronic control unit to a HIL simulator there is also a variant of the mechatronic process. Here, a part of the mechanism will be integrated in the control loop. This method is often used in the electronic steering systems, wherein a part of the steering linkage being coupled as a real mechanism of the HIL simulator.

HiL in machine and plant engineering

In the machinery and plant a programmable logic controller via a fieldbus to a physics model of a machine or system is connected for hardware in the loop normally. Used for this purpose also the designation system simulation. The system simulation usually contains a picture of the behavior and the material flow. Can monitor the machine function via an optional 3D visualization as well as issues of the physics simulation then an observer.

Purpose is the creation and testing of control programs before the components of a machine are manufactured and assembled. This can shorten the start-up phase. Another advantage lies in the ability to test without danger to the operator interface situations such as driving on hardware limit switches.

Future areas of application can include with the remote diagnosis and remote maintenance of machines and equipment. About a telecommunication line (eg via the Internet), the current state of a control by the machine operator in a service center is transferred from the machine manufacturer. There first diagnoses can be made then on the basis of the physical model and recommendations are derived.

HIL in the aerospace

In the aerospace industry conditions are tested in HIL systems, which are not always replicate on the ground. For the approval of the flight control is already replaced for the Superjet 100, the iron bird through the virtual or Electronic Bird.

HIL and the real world

Due to the technological progress and the development of high-performance microprocessors it is now state of the art that HiL systems are increasingly replacing the real environment. Just for the development of electronic control units is made possible with the help of the HIL simulator as the creation of an ideal test environment in the laboratory. Depending on the system requirements to move the computation time of a complete simulation cycle in the range of 1 ms, for special applications, it extends into the microsecond range.

Regardless of the technical possibilities, however, the HIL simulator, only a limited and largely reduced section of the real world environment whereas, in particular functions where the customer is in interaction with the technique, you will quickly reach the limits of simulation capability.

An environment simulation is always based only on the present findings, collected measurement and empirical values ​​, which are converted into simplified mathematical formulas and then find themselves the models in the HIL simulator. Because of this and despite the advances in environmental simulation HiL simulator can only to a limited extent replace the test in the real world.

Software in the Loop

In the method of Software in the Loop ( SiL ) as opposed to HiL no special hardware is used. The created model of the software is only converted into the code understandable for the target hardware. This code runs on the development machine along with the simulated model, instead of running as hardware in the loop on the target hardware. It involves a method that is applied before the HiL.

Benefits of SiL are among other things that the target hardware has not yet been determined, and that the costs be far lower due to the lack of simulation environment. As used herein, the model of the plant can also be used in HIL on, and thus the individual test runs are compared.