How Real (Time) Are Virtual PLCs?

Production systems continuously need to become more cost-efficient and flexible. Hardware-based programmable logic controllers, while widely used in the industry, do not offer the level of flexibility and scalability required for future applications. Each hardware-based PLC entails costs for maintenance and they cannot keep up with resource-intensive loads, such as artificial intelligence. The virtualization of PLCs promises to solve these issues. A Virtual PLC at the local edge level between cloud and industrial assets provides the flexibility and resource capacity needed for modern control applications. In this paper, the concept of virtual PLCs in a COTS server is outlined as a SoftPLC that is running within a virtual machine managed by a hypervisor. In addition, the virtual PLC is implemented and evaluated to determine whether virtual PLCs can satisfy the requirements for specific domains of industrial automation. We compare multiple virtual PLC configurations to a SoftPLC without a hypervisor. Our results indicate that the virtual PLC implementation is on par in terms of switching and response time for applications requiring response times below 10 ms and deterministic behavior is achievable. While further work is necessary, virtual PLCs may offer tremendous advantages for future industrial systems.