Technology

What is the Digital Grid?

To address the issues of the grid, a new Digital Grid system is proposed where a wide-area synchronized grid is subdivided into small or medium sized cells, and connected through asynchronous and coordinated control power exchanges

Asynchronous coordination is the exchange of power through connecting separate unsynchronized AC sub-grids using multi-leg AC/DC/AC conversion via power semiconductors (IGBT) with accompanying communication. These devices we call “Digital Grid Routers” (DGR).

Features of the Digital Grid

  • Independent cells with mutually unsynchronized phases and frequencies are connected using DGRs composed of power converters and coordinated transmission lines, which exchange electric energy between selected cells by supplying specified energy directly through power converters to the designated end point defined by an address
  • In each synchronized system within a cell, power equipment control devices called digital grid controllers (DGCs) are used to transfer information and thereby to control power equipment such as generators and energy storage devices
  • Each DGR and DGC has a CPU, memory and network communications, and are assigned unique IP addresses and communicate using an IP protocol like on the Internet
  • For communications, the power transmission line can be used so as to integrate power and information on a single line, or an external data network may also be used
  • A DGR may have two types of leg: either with power conversion or without power conversion.   Each point-to-point connection is composed of a set of legs, one with power conversion and the other without. This avoids the undesirable and unnecessary double conversion of power.

The Digital Grid as described so far enables a robust wide-area grid through segmentation and planned energy flows.  This subset of the Digital Grid concept is a logical extension of the Tres-Amigas* project under construction in Texas, which seeks to connect the three North American primary interconnections through a similar AC/DC/AC link.

However, the Digital Grid supports smaller segments, and has addressable exchange of energy between cells which are not directly connected. The digital grid is a new architecture for the grid, not a single point solution like Tres-Amigas.  In order to enable very high penetration of renewables, each cell must be made substantially self sustaining, with pre-planned injections of energy to meet forecast shortfalls.  This next stage of diffusion of the Digital Grid will require energy storage.

If each cell has suitable energy storage, it is freed from the conventional restriction of exactly matching generated power with demand each second.  With the existing grid, the value of energy is inherently tied to the time it is produced as well as the time it is required, which is the time-related value of electric power.

Our Digital Grid removes this time-related value of energy, and enables true commodity pricing of energy

Digital Grid Routers

Computer Controlled Multi-Leg AC/DC/AC converters with Internet communications

The Digital Grid Routers are:

  • Computer controlled, like network routers

  • Addressable from anywhere on the grid, like network routers

  • Connect multiple sub-grid cells through existing AC lines, where each sub-grid cell is synchronized internally but not synchronized with other cells

  • Exchange energy with other cells on a pre-planned self-coordinating basis

  • Can support frequency regulation from cell to cell

  • Uses IGBT devices for AC/DC and DC/AC conversion

  • Have multiple “legs” for connection to multiple external cells



Digital Grid Controllers

Digital Grid Controllers (DGC) are distributed, intelligent and network addressable devices which are associated with each active grid element, such as generators or storage devices.  DGCs make energy transfer requests, initiate and terminate energy transfers, implement the energy transfer protocol, and provide autonomous operation for each active element within a cell.

The diagram below shows a group of autonomous cells, each with multiple Digital Grid Controllers, and linked to the other cells via Digital Grid Routers.

Power Routing Example

The digital grid transmits discrete energy flows from the source cell to the target cell, possibly being routed through intermediate “digital grid routers”.   One important aspect of the digital grid is that power and information are transmitted together, thereby making a more robust architecture.   The information encoded with the power identifies unambiguously the source and destination among other key data.


The illustration shows four cells, each connected with digital grid routers and transmission lines.  Each transmission lines is point-to-point.  This illustration shows two possible routes for the power exchange.  The green line shows the direct path from Cell #1 to #3, and the red line shows an alternate route from cell #1 to #2 and finally to #3.

Power Exchange Protocol

Here is an example of one cell requesting a power exchange, to be supplied by the successful bidder.

First, a power request is broadcast.  The power request includes bid information such as the amount of power (kWh), when it is requested, the desired price, and any other qualification such as green certification.  Any other cells who wish to supply power under the broadcast conditions responds to the requesting cell.  The original requesting cell selects the best offer, using its own criteria, and sends an acceptance response to the selected bidder.  At the appointed time, the power is transfered to the requesting cell.  A unique attribute of the digital grid is that the transmitted power is tagged with the information about the transaction, including source, destination, and any green credits or other meta data.

Energy Transaction Tracking

Energy transactions between DGRs and/or DGCs are initiated through requests from others.  Each DGR and DGC operates autonomously based on their local policy, algorithms and rules, initiating the power transfers as needed.

Energy flows are monitored by built-in metering devices and recorded together with reservation information, including time, seller, buyer, price, energy source, energy amount, etc.   These records are retained in a database like a bankbook for ordinary financial transactions.  This enables the unambiguous confirmation of green energy use, carbon credits and third party supply of energy.