Two kinds of commonly used Inverters/UPS; High Frequency and Low Frequency. In common man’s words, High-frequency Inverters/UPS are those without Transformers, and Low-Frequency Inverters/UPS are those with Transformers.
But there is more to it. Let us understand……..
The main difference between High-frequency and Transformer-based Low-Frequency Inverters/UPS is the frequency at which they operate. High-frequency inverters/UPS operate at 20,000 to 100,000 Hz frequencies, while transformer-based Low-frequency inverters/UPS operate at 50 or 60 Hz frequencies. Transformer-based Inverters are more expensive and bulkier compared to High-Frequency Inverters/UPS. They are also more tolerant of higher and lower voltage fluctuations. However, they are larger and heavier and less efficient than high-frequency inverters. Chinese players mainly dominate High-frequency Inverters. However, Low-frequency Inverters are majorly made in India.
High-frequency Inverters have several advantages over Transformer-based Inverters, including:
Smaller size and weight
Better noise performance
Wall hanging models
However, High-frequency inverters also have some disadvantages, including:
They don’t have isolation between the Neutral and Line
More complex circuitry
Less tolerant of voltage fluctuations and spikes, and surges
Difficult to repair
How to choose between High-frequency Inverter/UPS or Transformer based Inverter/UPS?
The best type of inverter for a particular application will depend on the specific requirement of that application. For example, a High-frequency inverter may be the best choice if size and weight are important considerations. But if there is high and Low-voltage fluctuation, spikes and surges in power supply at the site, you need Transformer based Inverters to protect your Inverter and appliances. For Heavy, Industrial, Mechanical, and Induction loads, Transformer based Inverters are always recommended due to their power to absorb voltage fluctuations and surges. Expensive and Sensitive Electronics devices are always at risk with High-frequency Inverters.
Why is a Transformer important in an Inverter/UPS?
Isolation plays a major role in the functioning of the Inverter/UPS during the charging period as there are voltage fluctuations, High and low voltage happening during that period which typically burn the MOSFETs in high frequency based Inverter/UPS.
Another challenge is weak Neutral in a few areas, which has become a major cause of MOSFET burn in high-frequency Inverter/UPS as there is no transformer to isolate neutral and line from the grid Power.
Since the High frequency based Inverter/UPS is working on a High frequency, they interfere some time with the TV or other running equipment, as the high frequency is transmitted around sensitive types of equipment like TVs, and one can see lines appearing in the TV when the Inverter/UPS is working.
The High-Frequency Inverters have no issues in Developed countries where the Grid power is very stable, like the USA, Britain, France, Russia, Denmark, Germany, Japan, Belgium, etc.
But suppose the same high-frequency inverters are installed in African countries like Nigeria, Sudan, Uganda, Kenya, Congo, Ethiopia, Botswana, South Africa, and Tanzania. In that case, Middle Eastern countries like Yemen, Syria, Iraq, and Lebanon or South East countries like Bangladesh, Pakistan, and Sri Lanka, wherein there is high and Low voltage fluctuation, then there are very high chances of MOSFET failure and other circuitry problems.
The transformer acts as an Isolator and balancer in the Mosfet-based circuitry, which creates the Isolation between the Line and neutral, so any disturbances on neutral or line can be grounded.
Also, the switching or transfer time can be lower for transformer-based Inverters/UPS. In this case, Computers and TVs can work uninterruptedly.
The sudden switching in high Frequency based Inverter/UPS can burn the MOSFETs compared to the Transformer based Inverter/UPS.
In case of multiple times Overload and short circuit, there is a high probability of Mosfet burns in high frequency based inverter/UPS.
Even in the installation of Online UPS based on High-Frequency technology, the same problem happens, and that’s why they are advised to install a separate external Isolation transformer alongside the High-frequency Online UPS.
The same concept is followed for the Solar grid feed Inverter installation, and the Isolation transformer is compulsorily installed in large buildings.
The Transformer based UPS with ATC feature has the advantage over the High Frequency based Inverter/UPS.
Here is a Table summarising the key differences between high-frequency inverters and transformer-based inverters:
20,000 to 100,000 Hz
50/ 60 Hz
Size and weight
Smaller and lighter
Larger and heavier
Multiple time Overload and Short circuit
Chances of MOSFET burn
Ability to handle high-voltage and low Voltage
More complex circuitry
Tolerance of high Surge current for running heavy motors etc.
Switching or transfer time
Ultimately, the best type of inverter for a particular application will depend on the specific country and the stability of the Power Grid.
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