Things have gone quiet around the data-networked smart grid. The responsible federal ministry is now focusing on Industry 4.0 and trying to bring the next 'success story' into the public spotlight.

In order to operate virtual power plants based on recognized standards in the future despite suboptimal conditions, the VHPready industry forum adopted the specifications and implementation recommendations for VHPready 4.0 in September. As a result, the first standard for implementing efficient virtual power plants with different energy systems is now available, which enables cross-operator interoperability and implements the IT security requirements of the four German transmission system operators (TSOs) 50 Hertz, Amprion, TransnetBW and Tennet TSO.

M2M communication for energy systems

A virtual power plant according to VHPready 4.0: The connection is secured by closed user groups in mobile networks and an additional VPN based on Transport Layer Security (TLS).

© SSV Software Systems

The VHPready 4.0 specifications can make a technical contribution to the realization of the German energy transition with the help of virtual power plants. This allows large power plants with problematic primary energy to be replaced by decentralized energy systems with more environmentally friendly technologies.
The intelligent control of widely distributed energy systems using M2M communication and the storage of electrical energy in the form of heat or gas enable interconnected systems with a wide range of options for balancing fluctuating energy demand in public grids. In addition, the availability of renewable energies can be optimized. For example, modern heating systems (CHP plants, heat pumps), wind power, solar and biogas plants, controllable loads and storage systems can be integrated into the public power supply by adding a secure M2M communication interface - thus contributing to the conversion of the central energy grid into a decentralized grid.

Virtual power plants are mostly used for energy trading. The target markets can be reached via the Leipzig Energy Exchange. However, the TSO grid control network also offers great demand potential. Secondary balancing power, for example, is required here to ensure the balance between the physical supply of electricity and demand in the TSO control network and thus the stability of the German electricity grids. Secondary balancing power can be generated via decentralized generators (positive balancing power) or by means of orchestrated load separation or curtailment (negative balancing power) with a virtual power plant.

A data point list forms the functional core of VHPready 4.0. It supports the integration of different energy systems in virtual power plants using the telecontrol protocols IEC 60870-5-104 or IEC 61850-7-420 and TCP/IP as transport and network protocols.

Universal data points

In addition to a system park with a network of different energy systems, this data point list enables the integration of combined heat and power plants, wind power and solar systems, heat pumps, batteries, electric heating systems, boilers and buffer storage. There are also data points for meters and external signaling contacts. The data point list contains precise specifications for the data formats that are exchanged between the control center (LS) and decentralized energy systems (so-called technical units = TE) both in the monitoring direction (from the TE to the LS) and in the control direction (from the LS to the TE). When drafting the new specification, the VHP-ready experts assumed that the respective telecontrol protocol would not be terminated directly in the system controller, but in an upstream M2M communication gateway or adapter. In this respect, when defining the data points, care was taken to ensure that they can be converted to other system protocols, such as Modbus. In other words, the existing control system of an energy plant does not need to be changed for use within a virtual power plant with VHPready 4.0. The data points and protocols are implemented in the M2M gateway.

When designing the data point list, the fact that different energy markets and market segments are served by a virtual power plant was also taken into account. In addition to the spot market of the Leipzig Energy Exchange, the data points support the marketing of balancing power in the grid control network of the four German transmission system operators - but other forms of direct marketing are also technically possible.

Secure communication paths

IT security for a VHPready 4.0-compliant virtual power plant is based on a two-stage concept if the decentralized energy systems are to be used to provide secondary control power. First of all, the entire networking between the control center and the energy systems must be carried out by a closed user group in the wireless or wired network of a suitable provider. A VPN is then also used within this closed subnetwork. For security reasons, there must be no connection to the Internet from the closed user group.

The actual energy system is considered an insecure environment. For this reason, a 'verifiable media break' is required between the VHPready-compliant M2M communication gateway or adapter and the system control due to the IT security requirements of the TSOs. Both a different physical interface and a non-IP-based protocol must be used as the connection to the energy plant control system in order to prevent direct IP access from the control system to the control center of the virtual power plant. If the control system is equipped with an Ethernet LAN interface and supports Modbus TCP, for example, the media break must be implemented externally using appropriate modules (IP-Serial-IP coupler). In addition, the communication gateway or adapter of a system must be operated in an alarm-protected, locked switch cabinet with an appropriate access concept.

In order to maintain the IT security of an energy system in power plant operation over its entire service life, VHPready 4.0 requires 'patchable' communication gateways or adapters that allow the entire security-relevant software components to be replaced if necessary and support them with suitable functions. This is the only way to guarantee the security level if any vulnerabilities are discovered in the complex communication software over time.

4.0 as the first step

The VHPready 4.0 specifications represent an important step on the way to virtual power plants based on decentralized small power plants. Until now, there has been no comparable standard from an industry forum whose functionality and practical suitability for the energy markets has been proven by several independent companies.

However, due to the special role of the German TSOs and the associated security requirements for secondary control power, VHPready 4.0 is currently only suitable for plants with corresponding performance values. A virtual power plant with a combination of micro combined heat and power plants and the Tesla Powerwall batteries would be technically possible with VHPready 4.0, but not economically viable. The next step is therefore to examine the extent to which the standard can be integrated directly into energy systems using appropriate retrofit modules in order to enable virtual power plants with many decentralized smaller systems, which are then used for demand response instead of secondary control power. In the USA, for example, this process is used to automatically balance electricity demand and generation in regional distribution grids.

Author:Klaus-Dieter Walter is a member of the management team at SSV Software Systems.