PLCs with in-built functional safety and fail-safe condition monitoring are the unsung heroes of many renewable installations like wind turbines, electric battery-operated AGVs and hydrogen tank stations. 

Their off-the-shelf availability, high reliability, fast processing speeds and proven safety functions are tackling many challenges faced by the renewable sector. 

Using programmable logic controllers (PLCs) to control wind turbines or direct solar arrays has been a common solution for many years. What is not yet fully appreciated is the fail-safe condition monitoring and advanced functional safety capabilities built within today’s PLCs and how they can be applied to renewable applications. Not everyone has grasped the importance that functional safety plays in renewable energy applications and the influential role that a safety PLC can play.

In traditional machinery applications, such as those in packaging or food & beverage, the safety PLC requirements are usually quite simple:

• read the status of digital safety inputs with connected safety sensors, like position switches, laser scanners, light curtains
• carry out safety logic processing
• activate safety functions like safe torque off, safe stop 1, safe brake control using built-in drive safety functions or using contactors to de-energize and trip the machines.

Renewable applications, however, often require complex safety calculations driven by the need to process vast amounts of information to safely supervise the permissible range for temperature, pressure, charge rate, vibration level or position and speed tracking in real-time. Simultaneously, there is a need to safely monitor these complex renewable processes and/or machine characteristics. Ideally placed for this are safety PLCs, with support for trigonometric functions, floating-point calculations, PROFINET/PROFIsafe communication, CODESYS and structured text (ST) for safety programming.

Wind turbine safety is becoming increasingly important. In many countries, regulations stipulate that safety during wind turbine operation is critical to prevent accidents due to potential wind turbine collapse.

The ABB AC500-S safety PLC supports function block diagrams (FBD) and ladder usage (LD). It also supports structured text (ST) for the complex safety function implementations required in renewable applications like wind turbines. For instance, ABB AC500-S safety PLC performs different tasks including fail-safe control of pitch, torque and state for the entire wind turbine. Should there be a safety-related incident, the fail-safe control re-orientates the blades so the air-flow bypasses them without causing blade rotation.

In addition to a state-of-the-art wind turbine safe control, the ABB AC500-S safety PLC with condition monitoring provides fail-safe condition monitoring of vibrations within the turbine’s tower. This enables advanced safety functions to be implemented within wind turbines to avoid structural damage which could lead to accidents.

Typically, around 100 sensors and actuators are connected to the PLC, mixing digital and analog signals. As part of the turbine’s speed supervision, the strength of the wind is actively measured and its impact on vibrations is monitored. If problems, like vibrations, are detected in the mechanical structure of the wind turbine, then fail-safe condition monitoring through the PLC can stop the turbine and prevent collapse of the blades which could lead to accidents.

Distributed safety and non-safety modules, combined with modern fieldbuses such as PROFINET, ensure optimal performance, reliability and availability. Safety is seamlessly integrated into the ABB AC500 series, complying with SIL 3 (IEC 61508, IEC 61511 and IEC 62061) and PL e (ISO 13849-1). Meanwhile, AC500-XC and AC500-S-XC devices feature increased operating temperatures, resistance to vibration and resistance to hazardous gases and salt mist. To increase quality and monitor the wind turbines, it is mandatory to track a large amount of data. 

Airports and harbors are becoming the epitome of green design, with shore-based wind turbines powering, for instance, the charging stations used to replenish electric battery-operated automated guided vehicles (AGVs) transporting goods. When the power in the electric battery-operated AGVs falls to a certain level, they automatically return to the charging station, whereby a manipulator replaces the drained battery with a fully charged one.

But as these workplaces become increasingly automated, the need for workers and electric battery-operated AGVs to interact safely is of paramount importance. The safety PLC allows increasing productivity using optimized transport routes, safely limited speed control in dedicated areas and supervision of restricted safety areas.

The safety PLCs can restrict battery-operated AGVs to designated areas creating safe zones where workers can move about freely. Unable to enter these restricted areas, safety barriers no longer need to be able to withstand the full-force of an AGV, leading to a more open collaborative environment. In areas where the two must mix, the PLC can take input from the AGV’s laser-scanner to safely stop the vehicle if it detects a worker or other object in its path.

The safety PLC provides floating-point calculations and trigonometric functions to implement even the most complex mathematical calculations in real-time. These include safely monitoring restricted safety areas for battery-operated AGVs and collision detection.

To go further afield, people are increasingly turning to hydrogen fuelled vehicles to provide easy long-distance travel with much lower emissions than with conventional fuel like gasoline, gas, etc. Hydrogen is seen as an alternative to electric vehicles, featuring smaller batteries and generators, yet able to be used for longer distances. The key to this ease is the speed at which a vehicle can refill its tanks with this zero-emission fuel.

Critical to the safe operation of a hydrogen fuel tank is the need to precisely control the pressure and temperature. The tanks are packed with sensors monitoring these parameters and the PLCs provide fast processing speed to handle the large range of pressure and temperature calculations including safety functions like hydrogen leak detection, smoke detection, high pressure protection of inlet and outlet, etc. The fuelling stations use safety PLCs to precisely monitor the pressure, temperature and tank integrity, whilst providing controlled shut off of the safety valves in the event of a problem.

Many renewable installations are remotely located and sending service engineers to a site can be costly and time-consuming. PROFINET and PROFIsafe allow implementing remote machine control with the use of HMIs and implement fail-over safety control scenarios to avoid unnecessary downtimes.

The scalable PLC AC500 is based on a modular design that incorporates a CPU, AC500-S functional safety, condition monitoring, communication modules and I/O modules. The system can be easily expanded when required and includes advanced functional safety functionality like fail-safe condition monitoring, trigonometric functions and floating-point calculations. As such, the AC500 and AC500-S are used in wind turbines, hydrogen tank stations, harbour AGVs, solar-tracking photovoltaic systems and in thermosolar plants of all sizes worldwide.