Smart power distribution architecture benefits
Engineers are under pressure to implement greater power supply efficiency in electronic product designs. The competing demands for low loss, high power, and reliable safety have challenged the creation of a modern power distribution system that is efficient from the power source all the way to the supplies for interconnected devices.
These challenges have led to new approaches in power distribution technology, with smart power distribution being one of the newest innovations. Smart power distribution uses a decentralized power architecture based on multiple electronic and electrical modules rather than electromechanical devices such as fuses or relays. It is an ideal power management approach for applications such as transportation, aviation and robotics.
However, designing a different power distribution architecture is not easy because it often has to be customized to the application. It also requires engineers to minimize the costs of the architecture to deliver power safely under load variations. The best way to understand the benefits of smart power distribution is to examine how centralized and decentralized power distribution architectures work and differ.
Centralized versus decentralized architectures
Centralized power distribution architectures distribute electric power from the power source to individual systems in a network. Control panels, an associated main power source, power converters, input/output (I/O) modules, and protection circuits for each device are often located in a central location. A centralized architecture monitors the individual systems or end applications from one location.
A centralized approach has a significant advantage. The supply bus routing of circuits connecting the master and slave is complex, requiring a significant amount of cabling to interconnect them. Electrical efficiency is also low thanks to increased distribution losses. A good example of centralized power distribution is found in traditional automotive power electronics, which operate on 12V batteries. Sensors and actuators are supplied with power through copper cables wired from a central power controller.
Decentralized power distribution — also called distributed power architecture — is an architecture in which the system power requirements are divided into multiple intelligent power distribution centers (PDCs) spread throughout the product. PDCs communicate with each other via a local interconnect network (LIN) or controller area network (CAN). Smaller power units or PDCs are designed for and located near the operation of the devices in the system.
A decentralized architecture reduces weight, not only in the wire harness, but also by replacing the heavy relays with small, modern, and lightweight semiconductor devices. Using an automotive application as an example, a decentralized architecture not only reduces costs, but the resulting weight reduction improves the vehicle’s fuel efficiency and helps decrease CO2 emissions. Further efficiencies are made possible because power losses in semiconductors are often a factor of seven times lower than a fuse/relay combination.
Because PDCs communicate with each other as well as the rest of the vehicle, engineers can achieve greater control and higher levels of integration. This control makes possible enhanced functionality along with more intelligent and efficient use of energy. Combining this new type of architecture with advanced semiconductors yields huge benefits and solves the deficiencies of conventional electromechanical relay and fuses.
Another advantage of a decentralized architecture is it helps with the standardization and customization of PDCs for each subsystem. Designers can now pull together standard modules to design the power architecture. Any change in the system does not require a complete power supply system redesign; only a change in the section that needs modification is required.
Centralized power supplies are also bulky. Their higher power requirement leads to large transformers and thermal management components such as heat sinks and cooling fans. In a distributed architecture, heat is spread across all the modules, operating at reduced power levels. Transformers and heat sinks are smaller and cooling fans are eliminated in many cases.
A decentralized architecture enhances power distribution system’s reliability since the electronic devices operate in a safer environment. This efficiency increases because the conductors can carry power at high voltages and lower currents. These can be converted very close to the load points, which require low voltage and high currents. For instance, modern automotive electronics today are designed with a decentralized power architecture where the 12V battery power is distributed throughout the vehicle and converted to various voltages and currents required for each system, sub-system and device of the vehicle.
Smarter power information
Smart power distribution provides periodic and real-time information for each PDC module in the system to supply the correct power for a specific function. It also provides feedback from its protective or supervisory circuitry to send an alert about possible risk factors or system malfunctions.
Most smart power devices are dc-dc converters using buck/boost chopper or forward/flyback converter topologies. They have intelligent features such as over-temperature, overcurrent, and short circuit protection circuitry that act locally and report current status back to the master control.
The system components need to have fast communication capabilities to provide real-time information to an intelligent master controller, which acts as a central data processing unit. The communication methods often used are LIN, CAN, or FlexRay communication interfaces.
Smart power distribution architectures also enable engineers to replace relays with semiconductor switches. In conventional power distribution systems, relays connect or disconnect the power source to/from a load when an external voltage signal is applied to the relay from the controller. When a relay is energized, source current flows through the load; when it is disconnected, the circuit opens.
Though pervasive, relays are not the perfect switch since they require more voltage to turn on, are unregulated, and involve higher electromagnetic losses. Smart power switches open the door to the replacement of relays with semiconductor switches.
Smart switches turn on at low voltages, enabled by pulse width modulation (PWM) control signals. They have a very high current capacity (up to 40A), and extremely low on-resistance (down to 1.0m Ω). These devices deliver high-energy capacity of around 3000mJ, enabling them to replace relays in higher load applications. Semiconductor switches also reduce the losses and the overall power dissipation, thereby increasing the lifetime use and reliability of the system.
Fuses are another benefit of smart power distribution. In a relay switching system, using cut off fuses, which interrupt current flow at the instance of the overload fault condition, provides protection. A fuse box is critical to the system, as is a complex wiring harness.
Now, engineers can replace a traditional fuse with a smart power switch, which acts like a reprogrammable fuse and can be reset by software automatically when the fault condition is cleared.
Smart switch configurations
Smart switches connect or disconnect a power source to/from a load. Depending upon their location in the power circuit, they are defined as either high-side or low-side switches.
High-side switches connect or disconnect power to a load depending on the control voltage provided by the controller. They are connected between the positive power line and one end of the load. The other end of the load connects to ground. High-side switches can safely drive high currents into resistive, inductive and capacitive loads in applications with harsh environments.
Low-side switches connect between one end of the load and ground. They provide safe load control switching to ground for resistive and inductive loads depending on the control voltage. These switches are convenient for driving LEDs, relays, and motors.
Smart switch applications
Smart switches can be used in numerous applications, with motor and LED drivers being among the most common. But other interesting applications are emerging as well, including smart battery switches, decentralized power distribution centers, and power net management systems.
A smart battery switch is a high-current battery disconnect built with ultra-low ohmic TO-Leadless (TOLL) metal-oxide-semiconductor field-effect transistors (MOSFETs) in combination with an innovative inlay printed circuit board (PCB) technology. It has high current-carrying capability, low resistance, excellent thermal resistance and heat spreading, and high mechanical stability.
Smart battery switches can replace pyro-electric battery disconnect switches, or function as a safety switch for high current loads. They can also be used for quiescent current optimization, or resettable failure current shutdown.
Decentralized power distribution centers come next. Smart power distribution architectures have evolved to the point where multiple intelligent PDCs can be integrated throughout a product. While the basic architecture within PDCs retain the same control and communications interfaces, scalable semiconductors allow for a range of higher or lower power PDC modules with a common “core.” This commonality brings cost benefits in terms of economy of scale as well as reliability.
In automotive applications, for example, PDCs can be mounted almost anywhere in the vehicle. There is nothing for the driver to service so no access is required. This approach simplifies and reduces wire harnesses, saving weight and cost. As each PDC is microprocessor-controlled, functionality can be adapted in software and the PDC can be configured to suit different product needs.
Power net management systems also improve power distribution efficiency. In automotive applications, stop/start systems automatically shut down and restart the engine to decrease engine idling time, which improves fuel consumption and emissions. Despite the benefits of stop/start systems, they are a challenge for the power net, which needs to be stabilized during the stop/start transition. A board net stabilizer, using a smart power switch, can disconnect the starter and main battery from the auxiliary electrical systems during engine start.
The increased demands for power in electronic products, combined with the ever-evolving innovations in hardware and applications, require new approaches to power management. Smart power distribution architectures offer engineers safe, reliable and highly efficient power distribution alternatives that are much easier to configure and integrate.
Randall Scasny, senior community content specialist, element14. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, firstname.lastname@example.org.
Keywords: power distribution, smart power distribution
Smart power distribution uses decentralized power architecture.
Smart power distribution architectures are easier to configure and integrate.
Smart power distribution provides periodic and real-time information for each power distribution center (PDC) module.
What benefits could your company derive from a smart power distribution architecture?