Resilient multi-master power management with DCS and PLC control
A critical power system is designed to ensure that power is available at all times, even when grid power fails. Backup power is typically supplied by generators or renewable sources like PV or battery storage; these power sources are controlled by one or more controllers that detect when grid power is unstable or unavailable. When the need arises, they bring one or more backup power sources online to compensate for lacking grid power. Needless to say, these controllers, like the rest of the critical power system, need to be extremely reliable. Reliability is the backbone of every PMS.
Avoiding single points of failure
Despite the need for reliability, critical power controllers have often been installed as a master-slave setup with one master controller monitoring all power sources, breakers, and other important system components. If that master controller fails, there is no control until the controller is repaired or replaced. This makes the installation vulnerable to shutdowns due to controller failure. The controller is a potential single point of failure (SPOF) – a component that can disrupt the entire system if it fails.
In many applications, this is an unacceptable risk, as power failures could result in loss of data, performance, productivity, money – or human life. In order to safeguard against SPOFs, critical power systems must be designed with full redundancy for all important components – including controllers. A critical power system designed with a number of interconnected controllers capable of assuming control if another controller fails is called a multi-master power management system (MM PMS).
MM PMS: a flexible, value-added solution
In an MM PMS, there is a controller on every single power source, and optionally on important breakers such as the bus tie breaker. All controllers are linked in a data network with full redundancy and have no-break power supplies. Because of controller and network redundancy, an MM PMS provides resilient and reliable operation, keeping the power system running close to 100% uptime.
It is possible to use distributed control systems (DCSes) or programmable logic controllers (PLCs) as controllers in an MM PMS; which controller type to use depends on the organisation’s capabilities, requirements, and setup. In fact, combining the two controller types will often be a good solution as it allows you to fully exploit their relative strengths for various tasks in the complete critical power system.
“For most complex applications, DCSes (MM PMS controllers) are the best choice for operating the gensets, in combination with PLCs taking control of mains incomers and being the gateway between the power system and the BMS”, says Critical Power System Specialist and Accredited Tier Designer René Kristensen of DEIF. “Their onboard MM PMS software is designed to handle all critical power applications, and they can easily be reconfigured if the need arises, even in a live running system. For specific control tasks that do not require advanced power management, PLCs are a good, tried and tested solution, for example for providing the gateway between the BMS and the emergency power system”.
Caption: Managing central power management tasks using DCSes and interfacing with auxiliary equipment or a BMS using PLCs is a good solution for most applications
Image tags: critical power, emergency power, backup power, back-up power, multi-master, multi master, grid, grid connection, CAN bus, distributed control system, DCS, programmable logic controller, PLC, redundancy, bus bar, busbar, bus tie breaker, generator, genset, controller, DEIF, reliability, uptime, availability
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A well-designed MM PMS is good news for your critical power system, and for your customers, colleagues, and end-users who rely on it, but there is no one right way of designing it. It all depends on your requirements, and there are many questions to consider:
- Do you prefer to carry out all programming tasks yourself, or would you rather configure well-proven, pre-existing software?
- How will you handle system changes, for example if you need to add or replace backup power sources or extend the system to cover more areas?
- Does your power system need to communicate with a BMS, a cooling system, or other auxiliary equipment?
- Will you require the system to deliver other benefits such as Close Before Excitation (CBE; also known as Dead bus sync or Black bus sync), Mains power export (Demand power), Load takeover (response power), peak shaving, and load distribution?
We have prepared a free whitepaper that gives you more information on these issues and includes an introduction to DCSes and PLCs as well as a useful comparison of their applications, strengths, and weaknesses. We hope that the whitepaper will increase your understanding of critical power control solutions, and help you define the solution you need.