Applications of Power Semiconductors-Uninterruptible Power Supply

An Uninterruptible Power Supply (UPS) is a continuous power system designed to automatically provide backup electricity to connected loads in the event of a power outage or main power failure. The primary objective of a UPS is to deliver short-term power support—typically lasting only a few minutes—to prevent power interruptions or voltage fluctuations from affecting sensitive equipment and critical data. Unlike traditional backup power systems, such as diesel generators, UPS systems are characterized by their rapid response and uninterrupted power delivery, often achieving seamless power transfer within milliseconds. This instantaneous transition makes UPS systems particularly suitable for environments requiring high power reliability.

From a market demand perspective, the applications of UPS systems extend beyond ensuring uninterrupted operation of data centers, IT infrastructure, and other electrical equipment during power outages. They also provide reliable power to medical and life-support equipment, safeguarding critical healthcare operations. In industrial settings, UPS systems help prevent downtime caused by power fluctuations, which could otherwise lead to severe consequences such as injuries, data loss, and financial damages. The extensive applicability and flexible configuration of UPS systems make them an indispensable component for maintaining stability in mission-critical environments.

Uninterruptible Power Supply Components

Uninterruptible Power Supply (UPS) systems consist of four main components: rectifier, batteries, inverter, and static bypass switch.

Rectifier

The rectifier is the initial stage in a UPS system responsible for processing the input power. Its primary function is to convert alternating current (AC) into direct current (DC), providing energy support for the subsequent system components. Additionally, it charges the batteries while supplying DC power to the inverter. Modern UPS systems typically employ advanced rectification technologies, such as Pulse Width Modulation (PWM) rectifiers, to enhance energy efficiency and reduce harmonic distortion. These rectifiers utilize advanced power semiconductor devices, including Insulated Gate Bipolar Transistors (IGBTs) and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), enabling efficient and reliable power conversion.

Batteries

Batteries are the core energy storage component of a UPS system, providing emergency power when the primary power source fails. The rectifier or a dedicated charger ensures that the batteries remain in a charged state at all times. A UPS battery system typically consists of at least one string of batteries, with the number of batteries determined by the UPS's required DC voltage. Since the batteries are connected in series, a failure in a single battery can compromise the entire string.

In small-scale UPS systems, batteries are usually housed within the main unit. For larger solutions, UPS batteries are often installed in separate, dedicated cabinets to accommodate their size and capacity requirements.

Inverter

The inverter is a critical component of a UPS system, responsible for converting the DC power stored in the batteries into AC power for the connected load. The inverter must deliver a pure sine wave output to ensure high-quality power support for sensitive equipment. Like the rectifier, the inverter extensively utilizes power semiconductor devices to achieve efficient energy conversion and precise waveform control.

The performance of the inverter is pivotal to the UPS system's ability to adapt to varying load demands. In scenarios involving transient changes in electrical load, the inverter must respond swiftly to maintain uninterrupted power supply. Power semiconductor devices such as Insulated Gate Bipolar Transistors (IGBTs) and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) play a crucial role in the inverter's functionality, directly impacting its efficiency and reliability.

Static Bypass Switch

The static bypass switch is a protective mechanism within a UPS system. In the event of a system fault or overload, it automatically transfers the load to the main power supply, ensuring uninterrupted power delivery and preventing equipment from being damaged due to power outages.

Other Components

In addition to the core components mentioned above, UPS systems also include several auxiliary components:

• Fans or Capacitors: These are essential for heat dissipation and circuit stabilization, ensuring reliable operation of the UPS system even under high-load conditions.

• External Maintenance Bypass: This feature provides a temporary power transfer path during UPS maintenance, allowing the system to remain operational and preventing a complete shutdown.

Uninterruptible Power Supply Types

Modern UPS systems are commonly categorized into three types: On-line, Line-interactive, and Standby UPS systems.

• On-line UPS:
  This type uses a "double conversion" method to manage power. It first converts incoming AC power to DC through rectification, which charges the batteries and powers the inverter. The inverter then converts the DC back into AC (120V or 230V), delivering clean and stable power to the connected devices. On-line UPS systems are ideal for environments where power quality is critical.

• Line-interactive UPS:

  In this configuration, the inverter remains in standby mode during normal operation but stays connected to the output. When a power outage occurs, the system switches the battery's DC pathway from its charging state to power delivery mode, ensuring continuous power to the load. Line-interactive UPS systems are efficient and suitable for moderate power requirements.

• Standby (or Off-line) UPS:

  The load is powered directly by the input power under normal conditions. Only when a power outage occurs does the standby circuitry activate, drawing energy from the battery to supply power to the devices. This type is commonly used in small-scale or non-critical applications.

Most UPS systems rated under 1 kVA fall into the Line-interactive or Standby categories, as they are more cost-effective compared to On-line UPS systems.

Power Semiconductors In Uninterruptible Power Supply

With advancements in alternative battery technologies, UPS systems are evolving from simple power protection devices into smarter and more efficient systems. This trend is driving the integration of UPS systems with power grids, increasing the demand for bidirectional AC-DC converters, which operate similarly to energy storage systems. Additionally, the shift towards modular and prefabricated designs is gaining momentum, along with a focus on equipment standardization. These trends aim to lower equipment costs, shorten delivery and deployment times, and simplify maintenance and servicing.

The components of a UPS system, such as rectifiers and inverters, rely heavily on power semiconductors. Traditionally, devices like thyristors and IGBTs (Insulated Gate Bipolar Transistors) have been widely used. However, modern efficiency demands are reshaping these practices, with thyristors being phased out in favor of newer technologies. Many UPS manufacturers now prefer hybrid power semiconductors and silicon carbide (SiC)-based devices, which offer superior performance in terms of efficiency and reliability.

Nearly every major power semiconductor manufacturer includes solutions specifically designed for UPS systems in their product portfolios. Some manufacturers also provide customized components tailored to the unique design or performance requirements of UPS systems. The choice of power semiconductor devices depends on factors such as the UPS system's size, power rating, and operating environment.

UPS System Types and Power Semiconductor Device Requirements Table
 

With years of expertise in the power semiconductor field, Hitachi Energy offers a range of high-performance IGBT modules, diode modules, and thyristor modules. These modules are widely applicable across various types of UPS systems, from small home devices to large industrial data centers.

Specific Applications of Hitachi Energy Power Semiconductors in UPS Systems

Hitachi Energy Power Semiconductor Module Specifications Table

Global UPS Market Analysis

According to 2023 market data, the global UPS market reached a sales volume of $12.58 billion and is projected to grow to $16.59 billion by 2030, with a Compound Annual Growth Rate (CAGR) of 4.1%.

Major Manufacturers of Uninterruptible Power Supplies

Technological Trends and Future Outlook

• The Rise of Silicon Carbide (SiC) Devices
  With increasing demands for efficiency, the application of silicon carbide (SiC) devices is becoming more widespread. Their high voltage tolerance and low power consumption make them an ideal choice for high-end UPS systems.

• Modular and Prefabricated Design
  Modular UPS systems enable flexible scalability, allowing configurations ranging from 50 kVA to 1500 kVA through stackable designs. This approach reduces equipment costs, shortens deployment times, and simplifies maintenance.

• Smart Grid Integration
  Next-generation UPS systems are evolving toward energy storage solutions, supporting bidirectional interaction with the grid. This paves the way for advanced energy management capabilities in the future.

Uninterruptible Power Supply (UPS) systems play an indispensable role in modern society. Whether in data centers, medical equipment, or industrial production, they provide reliable protection for critical environments. With the widespread adoption of silicon carbide devices, modular designs, and smart grid integration, UPS systems are advancing toward greater intelligence and efficiency, offering enhanced possibilities for future energy management and equipment protection.