High power frequency UPS (Uninterruptible Power Supply) is a power protection device designed for high-power loads (usually ranging from tens of kVA to thousands of kVA). Its core feature is the use of power frequency transformers as key components for rectification and inversion, with strong impact resistance, high reliability, and adaptability to harsh power grid environments. The following provides a detailed analysis from three aspects: working principle, core components, and operating mode:
1、 Core components
The structure of high-power power frequency UPS can be divided into five core modules, which work together to achieve the function of "uninterrupted power supply":
Input Rectifiers
Function: Rectify the alternating current (AC) of the power grid into direct current (DC) to charge the battery and power the inverter.
Features: Using controllable silicon (SCR) as the rectifier element (with higher efficiency than diodes in high-power scenarios), combined with a power frequency transformer to achieve input voltage transformation and isolation, enhancing the ability to resist grid interference.
battery pack
Function: As an energy storage unit, it provides DC power to the inverter in case of power grid interruption.
Characteristics: Valve regulated sealed lead-acid batteries (VRLA) or gel batteries are usually used to form battery packs in series/parallel according to backup time requirements (voltage mostly 192V, 240V, 384V, etc.).
inverter
Function: Invert direct current (from rectifier or battery) into stable alternating current to power the load.
Features: The output end is connected in series with a power frequency isolation transformer (which is the core symbol of "power frequency UPS"), which can filter out high-frequency interference, achieve electrical isolation, and enhance the driving ability of inductive/capacitive loads.
Static Switch (STS)
Function: To achieve fast switching between inverter output and grid bypass (switching time usually<10ms), ensuring uninterrupted power supply to the load.
Classification: including main static switch (between inverter and load) and bypass static switch (between grid bypass and load).
control system
Function: Real time monitoring of grid voltage, load status, battery level and other parameters through MCU or DSP chips, controlling module switching, and implementing protection functions (such as overvoltage, overcurrent, overload protection).
2、 Working principle and operating mode
The core logic of high-power power frequency UPS is to prioritize the stability of load power supply, which is achieved through seamless switching of three operating modes:
1. Normal mode (mains power supply)
technological process:
AC power grid → input rectifier → rectified into DC power → divided into two paths:
One route supplies power to the inverter, which converts DC into stable AC (isolated by a power frequency transformer) and then supplies the load through a static switch;
The other way is float charging of the battery pack (to maintain the battery level above 90% and avoid deep discharge).
Core: At this time, the load power supply relies on the power grid, but after the "purification" of the rectification inverter link, the output voltage and frequency accuracy are much higher than the power grid (usually voltage deviation<± 1%, frequency deviation<± 0.1Hz).
2. Battery mode (power grid interruption)
Trigger condition: The voltage/frequency of the power grid exceeds the allowable range of UPS (such as power outage, voltage dip/surge, harmonic exceedance, etc.).
technological process:
After the control system detects an abnormality, it immediately cuts off the connection between the rectifier and the inverter. The battery pack supplies power to the inverter through the discharge switch. The inverter continues to invert DC to AC and outputs it to the load through the power frequency transformer.
Key: Switching time<10ms (no load sensing), power supply duration depends on battery capacity and load power (can be extended by adding batteries).
3. Bypass mode (malfunction or maintenance)
Trigger condition: UPS internal failure (such as inverter damage, rectifier failure) or manual switching to maintenance mode.
technological process:
The static switch quickly switches to the "bypass channel", and the AC power of the power grid is directly supplied to the load through the bypass frequency transformer (of the same specifications as the inverter output transformer), avoiding power outage of the load.
Note: In bypass mode, the load is directly affected by the quality of the power grid (without voltage regulation or filtering functions) and is only used as an emergency or maintenance state.
3、 Core advantages of power frequency UPS (compared with high-frequency UPS)
Strong impact resistance: Power frequency transformers can withstand high current surges at the load end (such as motor start-up, short circuit moments), making them suitable for driving inductive high-power loads such as water pumps and elevators.
Thorough electrical isolation: Both input and output are isolated by power frequency transformers, which can effectively block interference such as surges and lightning strikes in the power grid and protect load equipment.
Adapting to harsh power grids: With a higher tolerance for voltage fluctuations (such as ± 20% or more) and harmonics (THD>15%), it is suitable for unstable power grid scenarios such as industrial plants and remote areas.
Flexible redundancy design: High power models can easily achieve "N+1" redundant parallel connection (multiple UPS share the load, and the rest work normally when one fails), further improving reliability.
4、 Summary
The core logic of high-power power frequency UPS is the closed-loop design of "rectification inverter power frequency transformer isolation", which provides stable and purified power during normal grid operation, seamlessly switches to battery power supply during grid interruption, and ensures basic power supply through bypass in case of failure. The presence of its power frequency transformer increases the volume and weight, but significantly improves the reliability and anti-interference ability in high-power scenarios. Therefore, it is widely used in data centers, industrial production lines, hospital ICUs, nuclear power and other fields that require extremely high power supply continuity.
