Influence of Selected Parameters of the Motor Controller on the Current Characteristics of the DC Brush Motor Used in the Silesian Greenpower’s Vehicle

The paper presents tests of the controller created by Silesian Greenpower team for a DC motor carried out on an motor test stand. The main scope of the work was to check how selected parameters of settings affect current characteristics and speed of the motor in order to optimize the efficiency of the chain transmission. Charts of current and revolutions of the Fracmo PM62 motor, a description of the applied testing methodology, photos of the testing process and results of measurements carried out on the test stand have been described in the article. The research has resulted in a comparison of obtained outcomes, summary and presentation of conclusions, which concern practical remarks related to the further development of the control system applied in the Silesian Greenpower’s car.


Introduction
The main scope of the research was to determine optimal current characteristics for Fracmo PM62 electric motor. This motor is powered by two 12 V batteries with a capacity of 36 Ah each and is used for driving the electric car created by Silesian Greenpower team. [1] Regarding the fact that the car takes part in racing series, the priority was to optimize energy consumption at the start and during the race. [2] Considering that motor controller used in research has never been tested on dyno station before, the original settings of its creator were tested at the very beginning. Next stages of the project were such adjustments that the energy consumption of the motor was optimized.
All tests have been carried out on the actual team's car -"Bullet II" in which chain transmission, Shimano derailleur, Shimano cassette and DT hub have been applied. Due to car's construction, only 3 out of 11 gears have been used in tests.
Interfaculty students' project Silesian Greenpower created at the Silesian University of Technology has been founded in 2010. Since then, the main goal of annual editions is designing and constructing an ecologic electric vehicle, which will take part in the Greenpower racing series. Besides competition, the project's aim is to promote ecological energy sources, especially in the automotive industry. [1] Throughout the race, the goal is to pass as many laps as possible in a given time.
In the last season, the team has won such awards as Siemens Award for telemetry application, IET Award for innovations applied in the car and 4th place in F24+ league (Fig. 1). One of the key tasks during designing an ecologic electric vehicle is minimizing the drag during a race and maximizing the efficiency of the drive system. Hence the need to ensure optimal motor operation through an efficient control system.

Test stand
The inertial part of the motor test stand of the Silesian Greenpower team was used for the tests, along with the "Bullet II" car ( Fig.2). In order to make current measurements, motor revolutions and further processing of obtained results, the "SG-Telemetry" measuring system by Adam Stalica was used.  3 Selected controller, SG MotorController" is created by one of the Silesian Greenpower team members -Adam Stalica. In comparison to other available controllers on the market, it is possible to configure many parameters to optimize power consumption and ensure the best possible motor performance. Specification of "SG MotorController" has been presented in Table 1. This controller enables integration with the aforementioned measuring system, which gives the possibility to control and change parameters in real time during the race. Parameters, which can be adjusted with its description have been presented in Table 2.

Test stages
The test consisted of three stages. The first stage was to inspect default values of the controller. The second stageinspecting the same values with the release of the throttle for five seconds. The third stage of the research was manipulating parameters set in stage 2. (Table 3.) and obtained results have been presented in Figure 4. In addition, during the tests, the difference in voltage was measured between this that was directly on the batteries and this that was delivered to the engine. The voltage summary, after the controller has reached the full PWM signal, is shown in Table 4.

Inspecting default values of the controller
The test objective was to release the throttle by the driver which was supposed to simulate the braking of the car before entering the corner, and then reengaging the gas, simulating the exit from the corner ( Figure 5). It is worth to mention that drivers of the car usually do not use a mechanical brake (it causes unnecessary energy loss), and it is only sufficient to release the throttle.

Manipulating parameters of the controller
The next step was modifying the parameters and observing the average current consumed by the engine. In the table below ( Table 5) the results of the tests were collected. As it can be seen above (Table 5), the ramp time has a significant influence on the average current consumed during the test. A short ramp results in a much higher current and a higher speed of the car. Obtained results should be used to set the controller for a specific track configuration.
3. Conclusions 1. Increasing "PWM UP_1" by 50 resulted in the sharpening of the starting ramp -the graph is linear with a greater inclination to the horizontal axis. As a result, the ramp has been shortened. Even though the current in the peak increased, the average current decreased significantly, which will have a positive impact on energy consumption during the race. 2. Fivefold reduction of "PWM Fast Time_2" caused in doubled time of the ramp. The speed of the car decreased and remained at a lower level for a longer time.