A design framework for reconfigurable controllers with emphasis on electric drive wheels
Conventional controllers for traction motors used in electric and hybrid electric vehicles are presently designed to operate under fixed operating conditions, with a little or no flexibility in control over the hardware. The operator does not have the ability to control the performance in real time due to lack of available controller choices. However, electric and hybrid electric vehicles need to operate over a wider set of operating conditions, therefore controllers for their traction motors need to be designed to maximize choice to best manage performance. This report proposes a step by step method for the design of a reconfigurable controller, the goal of which is to provide the motor with the ability to operate efficiently over its entire torque speed range. This would enable the operator to have more choices, therefore give him the ability to maximize the performance (against multiple criteria) of the motor drive system in multi-speed drive wheel. The principle theme of the study is reconfiguration. The controller designed and simulated is for a Switched Reluctance Machine (SRM), based on the Asymmetric H Bridge (AHB) topology with a matrix of independently controllable switches. A systematic process of selection of switches for the AHB topology for the SRM application has been laid out based on the minimization of total losses for the switch when mapped onto the torque speed curve of the motor. For each of the selected switches, the report structures a step by step process for the selection of different gate drive circuit components. Controllers, based on the developed design methodology have been designed and simulated for 1KW and 20hp SRMs. The research has been able to show improvements of 15 percent in efficiency in the low torque and low speed regions of the motor’s range of operation. This is a significant result and it suggests that further improvements may be possible. The report provides different methods of real time reconfiguration and control based on performance maps and look up tables and recommends ten “component” parameters that can be reconfigured in real time to control the performance of the motor. To achieve the desired output, various motor input parameters are controlled based on the look up table and performance maps available to the operator. To improve the responsiveness of the system, the report recommends the use of boost capacitors and proposes further research in the area of ultracapacitors. It is also recommended to look into upcoming technologies like SiC and GaN switches. However, work still needs to be done to make the controllers cost effective, which can be done by making a standard set of reconfigurable motor controllers, doing in-depth testing to document the performance and making sure that the controller meets the set performance requirement in the market.