This is the third installment of a four-part article by: Kenneth Mendoza, Project Engineer, HiL Systems, Electronics in Applus IDIADA and Fabio Squadrani, Senior Manager, Braking Systems in Applus IDIADA on developing a control module for simulating hybrid regenerative braking on a brake dynamometer.
In the first part of the article the main objective of this study was presented and the main tools, introduced. The second part focused on the necessary mathematical models, while this third part will deal with the actual integration of regenerative braking on the dynamometer.
Regenerative Braking Integration on Dynamometer
There are mainly two approaches for determining the amount of regenerative torque to simulate in the brake dynamometers in order to reproduce vehicle behaviour:
- Regenerative braking logics: this would be equivalent to emulating the vehicles ECUs. The logics of the vehicle regarding braking would be executed in the brake dynamometer and dependencies such as the SOC, battery temperature, pedal effort, pedal stroke, among many others would need to be simulated as well, as they determine the outcome of regenerative logics.
- Vehicle testing profiles: this method would use data obtained from vehicle testing. A data logger would record the information of the motor torque, brake pressure and speed mainly and this would be used for commanding the brake dynamometer.
It is important to note that the current project is about providing the regenerative capabilities, not about completely emulating a hybrid braking system from the point of logics and other variables. That is why the chosen approach for this project relates with vehicle testing profiles. There are many reasons for using it: in one hand, with proper instrumentation it is possible to obtain directly the required variables for using the dynamometers regenerative capabilities; on the other hand it can be used for validating the developed functionalities. If the developed module works properly, profiles obtained from the vehicle will correspond to the ones obtained in the brake dynamometers. As well as that, using vehicle testing profiles will be useful to get an insight of how real electric vehicles braking systems work, which is vital for this project. As a summary, the regenerative braking concept to be implemented in dbDyno during this project is based in importing vehicle data and using it as a demand for the brake dynamometers. Additionally artificial manually generated profiles can be used.
Concept definition and model modification
Having previously developed the Inertia Simulation module eases a lot the task of implementing the regenerative capabilities concept presented in the previous section, as a means of controlling the torque of the motor during the brake applications already exists and the physical and logical interfaces between dbDyno and the drive unit of the electric motors have already been implemented.
In a very simplistic manner, starting from the main equation of the Inertia Simulation module,
The amount of torque required for the electric motor, T_mot in [Nm], taking into consideration regenerative braking results in:
T_regen is the torque of the regenerative braking system
Once the control algorithms have been defined, in this chapter the process of integration of the Inertia Simulation and Regenerative Braking modules into dbDyno is presented.
In order to implement these modules into dbDyno – Control System it has been necessary to perform the following steps:
Step 1: Create a LabVIEW API containing Inertia Simulation and Regenerative Braking functionalities.
Step 2: Integrate the developed functionalities into dbDyno’s control tasks, more specifically in the brake control phase. This function is in charge of generating a control demand in volts taking into consideration the configuration of the brake dynamometer, the actual torque feedback and the calibration of the drive unit of the motor.
Step 3: Modify dbDyno’s user interface to incorporate the set of parameters to configure the Inertia Simulation and Regenerative Braking behaviour. These parameters need to be distributed in different parts of the dbDyno software.
It is now possible to configure the electric motor in four different modes, allowing the user to activate or deactivate individually Inertia Simulation or Regenerative Braking on a per stop basis. This gives the system a certain degree of flexibility, as well as permits replicating the behaviour of real vehicles which, under certain conditions, disconnect the regenerative brake.
Another possibility during the configuration of the stop is to use a different value of inertia than the one configured in the vehicle.
Regarding the regenerative torque demand for the electric motor during the brake application, two options have been created: it is possible to manually enter a torque profile based on time and it also possible to import the profiles from vehicle data. In the latter case data to be imported is the torque of the electric motor on a specific wheel, the speed of the vehicle and the time base.
Step 4: Add the necessary modifications in the physical layer in order to allow communicating dbDyno and the drive units of the electric motors regarding torque control.
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