An inverter is a device that converts direct current (DC) to alternating current (AC) to meet the needs of AC loads. Inverters can be further divided into high-frequency inverters and line-frequency inverters. So what are the characteristics of line-frequency inverters and high-frequency inverters?
I. High-frequency inverter
High-frequency inverters use high-frequency DC/AC conversion technology to convert low-voltage DC power into high-frequency low-voltage AC power. After being stepped up by a high-frequency transformer, the AC power is then rectified by a high-frequency rectifier and filter circuit into high-voltage DC power, which is usually above 300V. Finally, the AC power is converted into 220V AC power for the load through a power frequency inverter circuit.
Advantages and disadvantages of high-frequency inverters: High-frequency inverters use small, lightweight high-frequency magnetic core materials, which greatly improves the power density of the circuit, resulting in very low no-load losses and improved inverter efficiency. Typically, high-frequency inverters achieve a peak conversion efficiency of over 90%. However, they also have significant disadvantages: high-frequency inverters cannot operate at full load with inductive loads and have poor overload capacity.
II. Industrial Frequency Inverter
A power frequency inverter is a DC/AC converter designed using high-frequency pulse width modulation technology and microcomputer control technology to convert the DC power supply from the battery pack into AC power with stable output voltage and frequency.
Advantages and disadvantages of industrial frequency inverters: They are characterized by a relatively simple structure, and all protection functions can be implemented at lower voltages. Because of the industrial frequency transformer between the inverter and the load, industrial frequency inverters operate smoothly and reliably, with strong overload and impact resistance, and can suppress high-order harmonic components in the waveform. However, industrial frequency transformers are also relatively heavy and expensive, and their efficiency is relatively low. Currently, the load efficiency of small industrial frequency inverters on the market typically does not exceed 90%. Furthermore, because the iron loss of the industrial frequency transformer remains essentially unchanged under both full and light loads, its no-load loss is relatively large under light loads, resulting in lower efficiency.
III. Performance Comparison of Line Frequency Inverters and High Frequency Inverters
1. In terms of reliability, line-frequency inverters are superior to high-frequency inverters.
Industrial frequency inverters use thyristor (SCR) rectifiers. This technology has matured significantly after more than half a century of development and innovation, and its resistance to current surges is very strong. Because SCRs are semi-controlled devices, they do not suffer from shoot-through or false triggering faults. In contrast, high-frequency inverters use IGBT high-frequency rectifiers, which, although operating at higher frequencies, have strict voltage and current operating ranges, resulting in lower surge resistance. Therefore, in terms of overall reliability, IGBT rectifiers are less reliable than SCR rectifiers.
2. In terms of environmental adaptability, high-frequency inverters are superior to low-frequency inverters.
High-frequency inverters use a microprocessor as the processing and control center, burning complex hardware analog circuits into the microprocessor to control the UPS operation through software programs. Therefore, they are significantly smaller and lighter, produce less noise, and have less impact on space and the environment, making them suitable for office environments where reliability requirements are not too stringent.
3. In terms of load requirements for neutral-to-ground voltage, line-frequency inverters are superior to high-frequency inverters.
In high-power three-phase high-frequency inverters, the neutral wire is introduced into the rectifier and serves as the neutral point of the positive and negative buses. This structure inevitably causes high-frequency harmonics from the rectifier and inverter to couple onto the neutral wire, raising the neutral-to-ground voltage. This results in a higher neutral-to-ground voltage at the load end, making it difficult to meet the site requirements of server manufacturers such as IBM and HP, which require a neutral-to-ground voltage of less than 1V. Furthermore, during the switching between mains power and generator power, the high-frequency inverter often has to switch to bypass operation due to the absence of the neutral wire, which can cause significant load interruption failures under certain operating conditions.
