Background
SwRI has identified electrified vehicles (xEVs) as a strategic priority. This project addresses the need to operate an OEM inverter using an open controller to control a permanent magnet synchronous motor (PMSM) for traction applications of xEVs
Approach
This approach allows full flexibility in operating the xEV’s motor at both standard and custom operating points. This flexibility enables test-cell characterization of the electrified axles (e-axle) while eliminating the need for bespoke tethered-vehicle solutions. While it is possible to use a SwRI silicon carbide open inverter, as is being investigated in IR&D project 03-R6030, doing so likewise eliminates the stock gate drivers and bridge modules. Retaining the stock gate driver and bridge modules is critical for certain projects, particularly those involving inverter calibration and thermal management. Hence, it is essential to implement this new capability to satisfy the rapidly growing market for comprehensive system testing, performance and durability evaluations, and component development for various xEV applications. The ability to fully control the OEM inverter will be beneficial to sell projects involving regenerative braking of electrified vehicles and speed up projects involving efficiency; friction; durability; and noise, vibration, and harshness (NVH).
Accomplishments
The team benchmarked high voltage and current signals of a Chevrolet Bolt battery EV at different speeds and torque on a hub dynamometer. A data processing algorithm- based observer was also developed to obtain the stock control strategy. In addition, motor control software was designed that duplicates the stock control strategy to take full control of the electric machine for EV application. It was evaluated on a Tesla Model 3 battery EV drive unit for more than 60 steady state points covering a wide array of operating conditions, as well as a transient driving cycle. As indicated by the testing results, the control software achieved excellent control stability and transient performance.
For the OEM inverter modification, the power electronics of the stock Bolt inverter were analyzed, and a novel method was developed to integrate it with a palm-sized open controller. The modified Bolt inverter and the motor control software were evaluated together on a permanent magnet synchronous motor (PMSM), which is of the same type as EV traction motors. Motor field-oriented control (FOC) and a 10 kHz inverter switching frequency were implemented to match the benchmarked control strategy. Finally, the modified OEM inverter controlled the motor successfully over the predetermined five speeds and load points. The speed transition was rapid and smooth with minimal ringing or overshoot. Each speed point can be held stable continuously as commanded by the motor control software.