Ever since the so-called "Battle of Currents" – a fierce competition between Thomas Edison and Nikola Tesla in the late 1880s to prove which current (DC or AC) was better for power transmission – There isn't a lot of innovation around electricity.
Although electricity plays a vital role in powering our world, the inherent dangers of AC or DC transmission systems make these systems expensive to deploy and maintain. To make power transmission safer and more efficient, East Greenwich, Rhode Island-based company VoltServer has developed a patented technology called Digital Electricity (DE). It enables AC or DC power to be distributed remotely with the safety and economy of low voltage power systems.
Figure 1 shows a simplified block diagram that explains how digital power technology works. It first takes an analog power input (AC from mains or a wall outlet, or DC from a battery factory) and converts it into a digital electrical current in a power transmitter. After that, the digital power is sent over the copper cable to the DE power receiver, which converts the digital power back to AC or DC, depending on which load the user wishes to power on the remote end.
Figure 1: Digital Power Block Diagram
A typical use case for this technology can be represented by radio. When mobile service providers deploy 4G or 5G networks, they want to deploy those radios where they are best for RF coverage and capacity, which often don't happen to be where the sockets are. VoltServer technology allows vendors to power network radios using the same type of practice as a Power over Ethernet (PoE) connection.
“We have developed what we call a packet energy transfer，” said Luke Getto， director of product management at VoltServer. “To make it very simple to understand， think about a square wave with a 75% duty cycle. For three-quarters of the packet， we are sending power， while for one-quarter of the same packet， we are doing what we call our safety check. The safety check allows us to know if the packet has been properly sent and received.”
During a safety check, the system can determine if there is a short circuit, resistance failure, open circuit, etc. The system continues to send energy packets as long as no faults are detected, and stops transmission as soon as an error is detected. Packets are sent at a very high rate – around 500 packets per second. However, each individual packet requires a small amount of energy. If a fault is detected, the sending of packets is stopped so that only about 1 joule of energy is dissipated into the fault. This allows the VoltServer to use higher voltages to reduce current and allow the use of small conductors (18–16 AWG).
"A receiver is a device that converts digital power back to AC or DC," Getto said. “We are using Vicor converters because their DE to DC conversion is very efficient. This allows our receivers to be smaller because there is much less heat dissipation. Our receivers are close to 96% to 98% efficient and rated at 1 , 200 W.”
Figure 2 shows the RX548 receiver, which has four digital electrical input channels, a 48-VDC output, and is IP65 rated.
DE is different from PoE, which is limited to 90 W, has a maximum range of 100 meters, and operates over very thin CAT6 cables. This produces a voltage of about 50 V and a current of 2 A. However, since the cable is very small (only 23 AWG), we have to account for the voltage drop. Therefore, the further away from the PoE switch, the less power is available at the point of load. With Cat6 cable, PoE can only provide 70 W at a maximum range of 100 meters.
According to VoltServer, DE is also different from a Class 2 low-voltage power system, which provides 54 V at 2 A and goes through a 12/14/16 gauge cable. If we need to move the power supply further away from the power supply, we have to use thicker, less flexible and more expensive cables. Category 2 can only deliver 80 W at 300 meters using 14-AWG cable.
"Using the same wiring practices as low voltage, we are able to deliver higher power, and we can go further than PoE and Class 2: we can deliver up to 400 W at 2 km, 2 at 300 m, 000 W of power, 2,400 W at 100 meters," Getto said.
Higher power is sent from the transmitter to the receiver via a lightweight cable. There, it can be converted to a load using Vicor's high efficiency BCM6123 fixed ratio converter. The power efficiency provided by the BCM6123 allows receivers to be placed in tight enclosures that are too small to use active cooling. This allows VoltServer's platform to run more efficiently with a smaller receiver footprint.
In terms of applications, VoltServer Digital Electricity can be used to provide remote power for devices such as security cameras, access points or radios, IoT devices, etc. DE technology enables these devices to be placed almost anywhere. The transmitter can be placed in a central location along with a UPS, battery system or generator to support all power sources there.
"One application we're doing a lot now is indoor farming," Getto said. "In an indoor farm, you have to provide light to the plants. You have to basically replicate the sun."
What VoltServer offers here is more like an IT network, where DEs can be plugged directly into lamps. This is an example of controlled environment agriculture, where LEDs can be controlled remotely through a dedicated software application, simulating the behavior of the sun from sunrise to sunset. This allows each LED to be turned on or off, slowly raising them to full power or lowering them. The good news is that deploying these lights in an indoor farming facility can cost up to 20% to 30% less, and powering the lights can cost up to 50% of the money to build an indoor farm.
Figure 3 shows an example of VoltServer's digital electric farming platform. The AC grid or microgrid input is connected to a bank of ETX8 transmitters capable of delivering 3 kW of output power on eight output channels. Each transmitter is connected to the DRX8 receiver via an 18-AWG communication cable. The receiver then drives the driverless LED light fixtures to provide the plants with the light they need. A dedicated software application running on a PC controls the transmitter rack to implement custom lighting profiles.
Figure 3: VoltServer’s Digital Electric Agriculture Platform
Digital power provides the advantages of low voltage with the power and distance capabilities of AC high voltage. Longer runs are easier to install with lightweight cabling and are NEC and CEC compliant.