Power electronics-based energy storage devices like energy storage systems (ESS for short) and power protection systems (PPS for short) are among the fastest growing technologies for solving power quality problems, providing ancillary services and supporting the development and access to affordable clean energy for a wide range of segments and applications.

As trends such as decarbonisation, sustainability of operations, digitalisation and the adoption of the industrial internet of things (IIoT for short) have a major impact on the flow of global business, the role of power protection systems such as single conversion static UPS systems (SC SUPS for short) becomes more important as many critical applications rely on an uninterrupted supply of good quality power to remain operational.

Single conversion static UPS systems are a high performance, flexible, compact, modular and cost-effective type of power electronics solutions with the ability to store energy that provide an instantaneous response in low or high voltage electric power systems. They protect critical equipment and facilities, enable longer equipment lifetime, and can help reducing energy losses, energy costs and environmental impact of operations, complying with most demanding power quality standards, grid codes, and energy efficiency and sustainable energy requirements.

Power electronics-based energy storage devices

Since the market introduction of energy storage devices built with power electronic switches, they have been gaining considerable attention as replacement technology for conventional solutions like mechanically switched energy storage media and standby generators The drawbacks of these conventional solutions like their slow response time, bulky size and limited power quality and energy efficiency improvement capabilities together with the price reduction of power electronic switches resulted in the increased use and widespread adoption of these devices in recent years.

Latest power electronics-based energy storage devices are typically built with energy storage inverters that can be controlled to act as current or voltage generators having an energy storage media able to provide active power for a certain amount of time when needed. They can be installed to any point of the electric power system (low or high voltage) in parallel or in series with the equipment that causes problems, needs to be protected, or needs to comply with certain requirements. Devices connected in parallel are usually energy storage systems (ESS) and devices connected in series are usually power protection systems (PPS).

Over the years, the design of power electronics-based energy storage devices has been tailored to deliver specific functionalities. They are able to provide protection against power supply interruptions, compensate current-based distortions such as current harmonics and current unbalances, and compensate voltage-based distortions such as voltage harmonics, voltage fluctuations and voltage unbalances. They are able to provide ancillary services like frequency containment reserve, ramp rate control, voltage control, reactive power control, fault ride through capability and black start capability. They can also support the development and access to affordable clean energy by power factor correction, capacity firming, peak shaving, load levelling and load shifting.

Power protection

Importance of power protection

Poor power quality or energy efficiency can cause innumerable problems for any facility in the electric power system like electricity generating plants (renewable or non-renewable), consumers (loads) or prosumers. Typical sources of problems include:

• End user equipment.
• End user electric power system and earthing.
• Weather phenomena (lightning, wind, rain, ice, etc.).
• Electric transmission and distribution system.
• Electric power generation system.

The damage caused by a momentary power quality or energy efficiency problem to an otherwise clean and efficient supply of electricity can be devastating. With the frequency and severity of power quality and energy efficiency problems on the rise, many facilities are opting to install power protection systems to safeguard equipment and protect continuous or critical processes. Even a noticeably short loss of power supply or voltage going outside the required operation limits can cause severe damage to sensitive equipment, machinery, production materials, final products and stored data. The restart of affected equipment or processes can also be very time-consuming and expensive.

The sensitivity of modern equipment and facilities to power quality and energy efficiency problems and the increased levels of automation in modern industrial processes make that the negative impact of these problems is greater than ever before. Power protection has become a very critical issue nowadays because of several reasons:

• Even short power quality problems can trigger events that can keep critical equipment or facilities unavailable for long time.
• Downtime is costly, especially for critical processes and manufacturing plants.
• Electric utility power supply is not always within the required power quality limits and can cause significant problems for equipment and facilities.
• Conventional power protection devices are not enough to take care of latest problems and requirements.
• Availability is especially important nowadays. When equipment or facilities are down, core business processes quickly come to a standstill.
• Facilities need to achieve high availability while reducing power consumption costs. Highly-efficient power protection systems can help with this goal.

Power protection systems

Modern electric power systems demand continuous and highly efficient power supply free from any power quality problems. Momentary voltage variations or interruptions could damage electrical equipment, cause stoppages of manufacturing processes or even of the generation and supply of energy. These problems could be created either from the electrical supply side or from the load side of installations. Power protection systems are cost-effective solutions offering protection against power supply interruptions and other power quality problems that can also help facilities to comply with latest energy efficiency and grid code requirements.

Power protection systems are connected in series with the equipment or facility that needs to be protected, directly or through a matching transformer or choke. The main energy storage technologies that they use are electrical (supercapacitors and capacitors), electrochemical (batteries and fuel cells) and mechanical (flywheels). 

Depending on their design and the functions provided, these devices can be divided into four groups:

• Power and voltage conditioners (PVC).
• Static UPS systems (SUPS).
• Rotary UPS systems (RUPS).
• Continuous power supply systems (CPS).

Static uninterruptible power supply systems

Static uninterruptible power supply systems (SUPS for short) have been around since the 1960s. Description of their topology and operating principle can be found as far back as 1965. They are the most commonly used UPS systems. They have a wide variety of applications ranging from low power personal computers to medium power industrial machinery to high power critical facilities.

Depending on their design, static UPS systems used in applications over 10 kVA can be divided into:

• Single conversion static UPS systems (SC SUPS).
• Double conversion static UPS systems (DC SUPS).
• Delta conversion static UPS systems.

Static UPS systems protect against full range of power disturbances affecting equipment and facilities thanks to the seamless transition between the electrical supply and the energy storage. During a power supply event like an interruption the transfer or switching time delay of this transition is typically around two milliseconds.

The next article of this series will discuss the functions and applications of single conversion static UPS systems.