Bidirectional DC-DC converter modeling and unified controller with digital implementation
ABSTRACT In this paper, a unified current controller is introduced for a bidirectional dc-dc converter which employs complementary switching between upper and lower switches. The unified current controller is to use one controller for both buck and boost modes. Such a controller may be designed with analog implementation that adopts current injection control method, which is difficult to be implemented in high power applications due to parasitic noises. The averaged current mode is thus proposed in this paper to avoid the current sensing related issues. Additional advantage with the unified digital controller is also found in smooth mode transition between battery charging and discharging modes where conventional analog controller tends to saturate and take a long delay to get out of saturation. The unified controller has been designed based on a proposed novel third- order bidirectional charging/discharging model and implemented with a TMS320F2808 based digital controller. The complete system has been simulated and verified with a high-power hardware prototype testing.
Conference Proceeding: Control of Ultracapacitor-Battery Hybrid Power Source for Vehicular Applications[show abstract] [hide abstract]
ABSTRACT: The energy storage system in electric vehicles (EV) must supply variable power levels and take regenerative power from braking. Ultracapacitors (UC) are more efficient than batteries for variable loads and recharging, but have a much lower energy density; the combination of these into a hybrid source can deliver better performance in an EV. We present several control systems, compare three active control schemes in-depth, and suggest a design. We describe a superior UC voltage control algorithm and a method of choosing optimal system parameters. Simulation validates the control approach of the complete system, and shows performance improvement of 48% by one metric. The test system includes a DC-to-DC converter with 97-98% typical efficiency.Energy 2030 Conference, 2008. ENERGY 2008. IEEE; 12/2008