Simplorer for Ultra-capacitor Design
Design News, October 25, 2004

New scheme involving ultra-capacitor boost module requires no extra batteries

Average electrical burden in passenger vehicles, cars, and light trucks has escalated in recent years from 500 to 700W and higher. Year-over-year growth in electrical loads is now between 100 and 150W with no end in sight. OEMs maintain that a 14V electrical system can sustain such growth and, moreover, that 14V electrified ancillaries are containable as well. With alternator technology now exceeding 3,000W and currents above 200A, it is incumbent upon the industry to evaluate means to reset the vehicle power budget.

Ultra-Capacitor Boost Modules

The power budget of existing automotive products can be effectively reset with the addition of newly introduced D-Cell ultra-capacitor boost modules. Connected in a bootstrap, or totem pole configuration with the ultra-capacitor on top of the existing VRLA lead-acid battery, the combination electric energy storage system is capable of supporting future electrified power ancillaries while remaining backwards compatible with the existing 12V electrical component base. With this system, OEMs need not completely revise the automobile parts inventory, but simply add new 42V components as needed. The vehicle electrical charging system remains as is with the addition of a small boost converter needed to sustain charge on the D-Cell module.

In this system, a small boost converter maintains charge on the D-cell ultra-capacitor module (Rdlc and Cdlc). The power of the simulation tool Simplorer is exploited in this arrangement to develop the PWM control input to the boost switch from the ultra-capacitor voltage measurement, VMdlc, compared to a setpoint, and this error is used as feedback. Simplorer therefore completes closed-loop control of the boost regulator using only three basic equations. With the alternator and boost omitted from the simulation, the battery and ultra-capacitor respond to the connected loads. Note, the electrical distribution system (EDS) has the capacity to support the 42V bus for a significant time interval.

The Results

The major benefit of the ultra-capacitor bootstrap electric energy storage system as the charging system source for electrified ancillaries is that existing VRLA battery cycling is reduced by 60 percent. This means improved life of the VRLA battery, and better regulation of both the existing 14V EDS bus and the overlay 42V pseudo-PowerNet.

A D-Cell electric energy storage system can source power at much higher efficiency than if a second battery is installed. Under constant power discharge conditions the D-Cell exhibits better than 96 percent efficiency as opposed to the much lower efficiency of a lead acid battery. This in itself is reason for OEMs to give serious consideration to ultra-capacitor technology. Ultra-capacitor technology is expected to reach cost levels of $0.025/F, a point at which the system proposed here begins to fall within the cost targets of automotive systems.