Uninterruptible Power Supply (UPS) in energy management

A UPS, or uninterruptible power supply, consists of a rectifier, an energy storage unit - most commonly lithium-ion or VRLA (Valve Regulated Lead-Acid) batteries, which are maintenance-free sealed lead-acid batteries equipped with pressure-regulating valves - an inverter, and a control system. In industrial applications, online UPS systems dominate, continuously processing power to ensure the highest power quality.

Under normal operating conditions, grid power is converted by the rectifier into direct current, which powers the inverter and charges the batteries simultaneously. In the event of a power failure, the UPS system immediately switches to battery mode with minimal or zero transfer time, which is critical for sensitive industrial processes.

Depending on topology, there are three primary types of UPS systems: offline, line-interactive, and online (double conversion). The differences between these three UPS types mainly stem from how the load is powered during normal, fault-free operation - directly from the grid, through a voltage regulation circuit, or via a continuously operating double-conversion power path.

The simplest offline UPS does not interfere with the power supply under normal conditions - electricity flows directly from the grid to the connected device. The UPS remains in standby mode and activates only when it detects a power outage or significant deviations in power parameters. In such cases, it switches to battery operation, although this transfer takes a few milliseconds. For many simple devices this is sufficient, but more sensitive systems may be affected by such an interruption. In addition, this type provides virtually no improvement in power quality - voltage fluctuations and disturbances pass directly through the system.

A line-interactive UPS is an intermediate solution. Under normal conditions, it still relies on grid power but includes an integrated voltage regulation system. This means it can correct minor voltage drops or increases without switching to battery mode. As a result, it offers better equipment protection and reduces battery wear. However, in the event of a complete power failure, it must still switch to battery operation, causing a brief interruption - shorter than in an offline UPS, but still present.

The most advanced type is the online UPS, also known as double conversion. In this case, the load is never powered directly from the grid. Electricity is continuously processed within the UPS - first converted into direct current and then back into alternating current with stable parameters. As a result, the device provides a very high degree of isolation from disturbances occurring on the utility side of the power supply. When a failure or blackout occurs, there is no transfer visible from the load perspective - the UPS is already operating on its internal power path, so the supply remains uninterrupted. This solution provides the highest power quality and is therefore widely used in industry and wherever even a fraction of a second of downtime is unacceptable.

In summary, the distinction can be simplified as follows: an offline UPS primarily reacts to failures, a line-interactive UPS additionally stabilizes voltage, while an online UPS continuously controls and “recreates” the power supply, ensuring the highest level of protection.

Traditionally, a UPS has been treated solely as a backup protection system. Today, with the ongoing digitalization of industry and the growing importance of energy flexibility, uninterruptible power supplies are increasingly becoming active components of Energy Management Systems (EMS).

It is important to distinguish conventional UPS systems, designed primarily for short-term backup power, from hybrid solutions in which the UPS operates together with a larger energy storage system and EMS platform. Only such a configuration enables broader energy management capabilities extending beyond the protection of critical loads alone. Modern UPS systems can:

• participate in peak shaving,
• stabilize voltage and frequency within the facility,
• support local energy balancing,
• cooperate with renewable energy sources (RES).

Thanks to their fast response time and high efficiency - exceeding 96% even in online mode - UPS systems can serve as short-term energy buffers, relieving stress on the grid during critical periods. In practice, however, this potential depends on battery capacity, system configuration, and the method of integration with EMS platforms or larger energy storage systems.

One of the key development directions for UPS technology is integration with Battery Energy Storage Systems (BESS) and smart grid infrastructure. In practice, this means that UPS systems can cooperate with photovoltaic installations or cogeneration systems, industrial energy storage facilities, Demand Side Response (DSR) systems, and local microgrids.

In such configurations, the UPS may act as:

• a stabilizer for RES installations (compensating for generation instability),
• an energy flow management component,
• protection for critical loads in island mode operation.

The greatest benefits are achieved in hybrid configurations where the UPS cooperates with a larger-capacity energy storage system. The UPS is responsible for immediate response (milliseconds), while the energy storage system takes over power supply over a longer time horizon (minutes to hours). Such a solution not only increases energy security but also optimizes energy costs through price arbitrage and reduction of contracted capacity charges.

In the event of disturbances in the electrical grid, the UPS acts as the first line of defense. During short-term voltage sags (so-called dips), an online UPS completely isolates the load from grid-related problems. In the case of a total power outage, the UPS instantly switches to battery mode.

Backup runtime depends on battery capacity and load level - in industrial applications it typically ranges from several to several dozen minutes. This is usually sufficient time to:

• safely shut down industrial processes,
• start backup generators,
• switch to alternative power sources.

In more advanced systems, the UPS can cooperate with Automatic Transfer Switch (ATS) automation, ensuring seamless transitions between power sources without interruptions to connected loads.

Another important feature of modern UPS systems is cold start capability, more broadly recognized as part of black start functionality. This refers to the ability to start the UPS and power connected loads solely from batteries, without the presence of grid voltage. This enables the restart of critical systems following a total blackout before external power is restored or backup generation sources are activated.

UPS applications in industry are extensive, but they are particularly important in sectors highly sensitive to power disturbances:

• chemical and petrochemical industries - where process interruptions may lead to raw material losses or safety hazards,
• food industry - especially in continuous production lines (e.g., refrigeration and processing), where power loss results in product quality losses,
• data centers and IT infrastructure - requiring uptime levels of 99.999%,
• pharmaceutical industry - where stable production conditions are critical to product quality,
• automotive and discrete manufacturing - where production line shutdowns generate substantial downtime costs,
• energy and critical infrastructure sectors - where UPS systems protect control and automation systems.

An important application area also includes healthcare systems and strategically important public infrastructure. In hospitals, UPS systems ensure uninterrupted power supply for medical equipment such as life-support systems, operating theatres, diagnostic imaging devices, and IT infrastructure handling patient data. In these cases, even a brief power interruption may directly threaten human life, which is why highly reliable, often redundant systems integrated with backup generators are used. Redundancy refers to duplication of system elements (hardware, data, connections) to ensure operational continuity in the event of failure.

Similar requirements apply to government systems, security infrastructure, and mission-critical server facilities - including public administration data centers, crisis management systems, telecommunications infrastructure, and national security-related systems. In such applications, UPS systems are a fundamental element ensuring service continuity and data integrity, while their configuration is designed with high redundancy, scalability, and island-mode operation capability in mind.

UPS selection should be based not only on the power demand of connected loads, but also on the nature of the protected process. Key considerations include required backup time, acceptable transfer time, power quality requirements of the loads, compatibility with generators or energy storage systems, environmental conditions, and the required level of redundancy. In industrial applications, downtime impact analysis is equally important - a production line where shutdown results in product quality losses will have different requirements than a process automation system responsible for operational safety.

UPS systems are no longer merely backup power protection devices - increasingly, they serve as active components of a company’s energy infrastructure. Integration with energy management systems, energy storage solutions, and renewable energy sources aligns with the broader trend toward building flexible and resilient power systems. This enables not only minimization of downtime risks, but also a tangible impact on energy costs and energy utilization within industrial facilities.

In the context of increasingly unstable power systems, the growing share of renewable energy sources, and mounting pressure to improve energy efficiency, the role of UPS systems will continue to expand. Hybrid solutions, combining the functions of traditional guaranteed power supply systems with energy storage and energy optimization capabilities, are becoming particularly important. This approach enables companies not only to secure their processes, but also to actively participate in the energy transition.

From an industrial perspective, this means a necessary shift in the design philosophy of power systems - from a reactive to a proactive model. In this context, the UPS becomes one of the most critical elements of infrastructure, combining operational reliability with a modern approach to energy management, supporting both production continuity and the long-term competitiveness of the enterprise.