Why and how to use component-based distributed power architecture in robotics
To maximize the runtime between charges, designers of battery-powered systems must always take into account the efficiency of energy conversion as well as the size and weight of the structure.
Battery-powered robots are increasingly used in industrial automation, agriculture, campus, and consumer delivery, as well as warehouse inventory management. To maximize the runtime between charges, designers of battery-powered systems must always consider energy conversion efficiency as well as size and weight.
These issues become critical as workloads increase, as well as design complexity and weight, resulting from safety and measurement functions such as vision, proximity sensors, and location determination. And at the same time, the required additional processing electronics also consume more energy.
To maximize battery life in the face of these added challenges, designers can leverage a component-based distributed power architecture to power motors, processors, and other subsystems. In this approach, individual components of DC converters can be placed at the point of consumption (PoL) and optimized for high efficiency, small size (high power density), and overall performance. This approach allows for lighter power systems in general, and hence further advantages in terms of the performance of battery-powered robotic systems. Flexibility is also increased as the energy conversion components can be connected in parallel to meet the increasing power demand of the robot. It is also possible to use the same power architecture for an entire robot systems platform of different sizes.
The article briefly describes the power requirements for several robotic applications such as agricultural harvesting, campus and consumer delivery, and inventory handling. It then examines the benefits of using a component-based distributed power architecture and provides sample Vicor DC converter solutions, evaluation boards, and related software to help designers get started.
Robot power requirements
The power requirements of specific types of robots depend on the application:
- Agricultural harvesting robots: planting, care, and harvesting of crops (fruit, vegetables, grains) using automatic driving, image recognition and multiple sensors to analyze environmental and soil conditions. Large robotic vehicles are typically powered by high voltage direct current sources of 400V and above.
- Delivery robots: the final stage of campus and consumer delivery of a wide variety of items. The loads can vary in size and weight, however, these robots typically run on batteries ranging from 48 to 100V and require longer run times compared to the robots used to move inventory.
- Inventory Moving Robots: Perform inventory management and order fulfillment tasks in large warehouse environments. Robots of this class are usually powered by battery sources with a voltage of 24 to 72V, which can be charged when needed.
Component-based distributed power architectures for use in robotics
This section presents four examples of distributed power architectures based on robot components: from 15.9kW systems for agricultural harvesting robots with a 760V battery pack, to 1.2kW systems for inventory handling robots using 48V battery packs. A common feature of three of the above applications is the main bus splitting the power supply of relatively high voltage to the robot, followed by one or more step-down sections that provide power to the subsystems. The high-voltage power splitter improves efficiency and lowers the supply currents, allowing the use of smaller, lighter and less expensive power cables. The fourth application is a simplification that allows you to create smaller robots using 48V battery power systems.
The Power Grid (PDN) for Agricultural Harvesters includes a 760V Main Power Bus (Figure 1). It is supported by a series of isolated constant-ratio (unregulated) DC converters (left-hand BCMs) with an output voltage of 1/16 of the input voltage. These converters are used in parallel, which allows the size of the system to be adapted to the needs of a specific design.
Downstream there are a series of constant ratio converters (NBM, top center) and adjustable step-down converters (PRM, center) and step-down converters (bottom) powering the lower voltage buses as needed. In this design, the servos are powered directly from an intermediate 48V bus without additional DC converters.
The power grid (PDN) for campus and consumer delivery robots has a simplification that can be used in medium power systems by using a lower voltage of the main power bus (in this case 100V) and adding regulation in Isolated DCMs on the main bus power distribution in order to obtain the 48V intermediate bus voltage (fig. 2).
This approach allows the use of non-insulated step-up and step-down DC converters to power a variety of subsystems. In addition, the use of a lower voltage on the main power bus allows direct connection of motor drives to the main bus, while the servos can connect directly to the 48V intermediate bus. Smaller campus and consumer delivery robots may include a 24V intermediate bus and either 24 or 48V servos, but the overall architecture is similar.
The power supply network (PDN) for warehouse robots using a 67V battery pack contains uninsulated DC step-up converters (PRM) on the main power bus (Figure 3). These converters offer an efficiency of 96% to 98% and can be connected in parallel for higher power. This architecture also includes a non-isolated constant gear DC converter (NBM) to power the graphics processing unit (GPU) and non-isolated regulated step-down converters powering the logic sections.
In smaller robot designs using 48V batteries, there is no need to generate an intermediate voltage bus, which simplifies the design (Figure 4). The receivers are powered directly by the battery voltage in direct conversion using non-insulated DC converters. The elimination of the intermediate bus in the power system increases the efficiency of the system and reduces the weight and cost of the power system.
Figure 1: Power Grid (PDN) for 15.4kW Agricultural Harvesting Robots includes a 760V distribution bus to support a low voltage converter network (DCM, PRM, NBM and step-down). (Image credit: Vicor)
Figure 2: The campus and consumer delivery robot network (PDN) uses direct power to motors and indirect rails to power other subsystems. (Image credit: Vicor)
Figure 3: The Power Distribution Network (PDN) for warehouse robots uses a 67V main power bus and a 48V intermediate power distribution bus. (Image credit: Vicor)
Figure 4: Power Supply Network (PDN) for warehouse robots using 48V battery packs eliminates the need for an intermediate power rail, which greatly simplifies the design. (Image credit: Vicor)
Design considerations for distributed power architectures
As shown above, designers have to make numerous power system decisions to optimize a component-based power network (PDN) for robotic applications. There are no one size fits all solutions. Generally, in larger robots, it is preferable to use higher battery voltages, which allows for higher power distribution efficiency and the use of lighter and smaller distribution buses.
The choice between insulated and uninsulated DC converters is an important consideration when optimizing overall system efficiency and minimizing costs. The closer the DC converter is to the low voltage receiver, the greater the chance that the selected uninsulated power component will be cheaper and increase the overall efficiency of the power network (PDN). Where possible, the use of cheaper constant-ratio DC converters (unregulated) can also increase the efficiency of the supply network (PDN).
Vicor offers DC power converters to meet the needs of designers in a wide range of component-based distributed power architectures, including the four described above. The following discussion focuses on the specific devices that may be used in power systems similar to those used in the campus and consumer delivery robots shown in Figure 2.
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