Developers of electrical power management and distribution systems for current and future force ground vehicles face several challenges. As new applications increase the number and size of electrical loads, vehicle power demand is exceeding generation and storage capability. These limitations impact vehicle operating range and mission effectiveness. Additionally, an overburdened power distribution system results in faults and reduced reliability. Electrical architectures also require flexibility to accommodate system components that are unique to the vehicle.

These challenges are being addressed using smart power management and distribution methods enabled by the latest generation of solid-state power controllers (SSPCs). In addition to providing protection for cable harnesses and loads, smart SSPCs are capable of accurately monitoring power quality and load conditions, permitting the system controller to react to power fluctuations and faults automatically and in real time. SSPCs also provide wide programmability, which allows power management systems to adapt to system reconfiguration and future equipment insertion.

Migration to Solid-State

Driven by a combination of factors, electrical power distribution and control in ground vehicles has evolved rapidly in recent years. Further, it is anticipated that the need for power technology advancements will continue. The present and projected future needs for the U.S. Army and U.S. Marines are driving technology developments and deployments in applications, hardware (such as C4ISR), networking, computing, power electronics and power distribution technologies. Systems that once relied on traditional electromechanical power distribution architectures and equipment are migrating from purely discrete electrical, mechanical and manual control to network-based, solid-state power distribution and control systems.

Solid-state power controller (SSPC) designs use microprocessors to manage the operation of high-efficiency switching MOSFETs. Their basic operation is to perform on/off control of the load and to protect wiring harnesses and loads from short circuit and overload conditions. SSPCs eliminate the EMI associated with the rapid changes in currents during on/off transitions of mechanical breakers, switches and relays. As shown in Figure 1, MOSFET gate drives can be designed to control the rise and fall time of channel currents. In comparison to electromechanical switching and protection, SSPC short circuit and overload protection is precise (typically ± 5 percent) and reliable. Additional protection is provided by series flyback diodes on the load side of each MOSFET to prevent inductive voltage transients from damaging the SSPC when the MOSFET deactivates or there's an abrupt open-circuit fault in the wiring or load.

Figure 2 shows the I²T curve implemented by the SSPC to mimic the time-current behavior of a thermal mechanical breaker, including the high instant trip value needed to accommodate capacitive loads. A well-designed I²T circuit will deliver ten or more times the channel's maximum steady state current rating before the instant trip mechanism opens the MOSFET switch to protect the load and itself. The value of the maximum steady state operating current for a given SSPC channel is programmed by the user as a percentage of the maximum current allowed for the given channel. Further, this type of "electronic thermal memory" enables SSPCs to mimic the desirable characteristics of thermal mechanical breakers. If an overload or short circuit fault is followed by a subsequent event, the second trip will occur more quickly than the first, protecting against heat accumulation in the wiring.

More Reliable Operation

SSPCs eliminate the deleterious effects of unpredictable contact closure time and contact chatter characteristic of thermal, high-performance thermal (temperature compensating, in other words), magnetic, thermal magnetic, hydraulic magnetic and remote controlled circuit breakers. Opening and closing circuits electronically, whether for on/off control or for load and wire protection purposes, eliminates the need for moving parts such as solenoid cores, springs, latches, hinges, bi-metallic strips and contacts. This eliminates components whose normal operation includes compression, friction, heat and arcing.

Electromagnetic arcing is a fundamental characteristic of the circuit breaker contact make/break cycle. The greater the current level, the larger the arcs, resulting in pit formations and carbon buildup. A common specification for mechanical breakers is the manufacturer's anticipated number of on/off cycles. Breaker "life" ("cycles" or "endurance") is adjusted according to percentages of the device's maximum rating or specified interrupt currents.