Engineering students from the Rochester Institute of Technology designed and implemented a test bench to evaluate a range of torques for high-power, electric vehicle motors. The test bench incorporates a dSPACE 1103 system for rapid control prototyping and dSPACE ControlDesk experiment and visualization software.
June 2016: In the world of design-build competition teams, efficiency of design and turnaround time are paramount. To speed the development of its electrical vehicle, the Rochester Institute of Technology (RIT) Electric Vehicle Team developed a dynamic load test bench.
The test bench uses the principles of dynamic braking to generate a variable load on a unit under test. This dynamic load can be used to simulate different road conditions and situations, and easily view the effects these conditions have on the controller, while in a controlled environment. The bench is modular by design, allowing it to be used with any motor within the operating limits of the device.
Prior to the development of the test bench, the Electric Vehicle Team had to complete all testing of major drivetrain systems at the full system level, with an actual driver and higher safety risks, and they were not able to catch problems earlier in the development process.
“We worked earlier this academic year to get a dSPACE DS1103 controller board (for rapid control prototyping) and dSPACE ControlDesk (experiment and visualization software) to be used in the development of our electric vehicle test bench,” said RIT Electric Vehicle Team member Shawn Falzone. “I’m happy to say that the test bench is working great!”
The Electric Vehicle Team is using the test bench to dynamically generate a load on the unit under test (UUT). This means that the load must be variable and must have the ability to predictably change through a range of torques.
The team’s final decision for load generation was to use a method similar to dynamic braking. This involved connecting the output of the UUT motor to the shaft of a DC generator. The current generated by the DC generator is modulated using Pulse Width Modulation (PWM) methods and then run through a high power, low resistance braking resistor, which limits the flow of current. This, in turn, limits the rotation of the motor and thus creates a torque on the UUT. By changing the duty cycle of the PWM signal, a range of torques can be applied to the UUT. This system, along with numerous safety measures, forms the backbone of the test bench.
Because the control of the PWM signal must be very precise to deal with constantly changing load and speed conditions, a software based control algorithm was chosen. This allows the controller to be tuned easily, and without the need for dealing with the tolerances and degradation of components. For this purpose, the team needed a processor with extremely fast analog to digital converters (ADCs), digital to analog converters (DACs), as well as a fast processing rate. The team chose DS1103 from dSPACE Inc.
A software interface was created using dSPACE’s ControlDesk to allow the user to apply loads and throttle commands to the system, and then read back the vital test information of the system in real time. Various fault detection and warning signals were integrated into this user interface so that they may be easily monitored as the test is run. The user interface developed for this project is shown in the figure below.
Software User Interface
This interface can be easily integrated with dSPACE’s AutomationDesk to create automated test plans, which can run tests for the user automatically. This software outputs full test report documentation automatically, which saves time and effort when trying to decide whether or not the controller is performing as expected.
“This software (AutomationDesk) is extremely modular, allowing users to easily make new test scripts with very little need for in depth programming knowledge,” said team member Benjamin Grimsley. “This makes the test software more accessible to all of the engineers on our electric vehicle team.”
Using the test bench, the team was able to thoroughly test and validate subsystem components for functionality. Each subsystem ran as expected, and the overall project successfully meets customer requirements.
The modularity of the bench and its components will allow future RIT teams to increase the capabilities of the bench to test larger motors, and increase the abilities of the bench to test and record more signals from the drivetrain components, as well as the components on the bench itself.
“We will pass the test bench off to the next Electric Vehicle Team so that they may continue to use the bench, along with the hardware and software, to vastly improve their turnaround times on controller design and development,” said Falzone.
Shawn Falzone earned BS/MS degrees in Electrical Engineering. He will be joining the Aircraft Systems Group at Moog, Inc.
Benjamin Grimsley graduated with a BS degree in Mechanical Engineering. He will be working at Vanderberg Air Force Base as part of the 1st Air and Space Test Squadron.
Ben Kraines earned a BS degree in Computer Engineering, and will be joining Air Force Research Labs.
Eric Reese received a BS degree in Mechanical Engineering. He will be working at Lawrence Livermore National Labs as part of the National Ignition Facility.