I. Performance Comparison of Linear Frequency Inverters and High Frequency Inverters
An inverter is a converter that transforms direct current (DC) energy (from batteries or storage batteries) into constant frequency and voltage alternating current (AC) or frequency and voltage regulated alternating current (typically 220V, 50Hz sine wave). It consists of an inverter bridge, control logic, and filter circuits. It is widely used in air conditioners, home theaters, electric grinders, power tools, sewing machines, DVDs, VCDs, computers, televisions, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting, etc. In foreign countries, due to the high rate of car ownership, inverters can be connected to batteries to power appliances and tools while working or traveling. Car inverters with output via the cigarette lighter socket are available in power ratings of 20W, 40W, 80W, 120W to 150W. Higher power inverters require connection to the battery via cables. Connecting household appliances to the output of the power converter allows for the use of various electrical appliances inside the car. Available electrical appliances include: mobile phones, laptops, digital video cameras, cameras, lighting, electric shavers, CD players, game consoles, handheld computers, power tools, car refrigerators, and various travel, camping, and medical emergency appliances.
Inverters come in two types: line-frequency inverters and high-frequency inverters. So, how do line-frequency inverters and high-frequency inverters compare in terms of performance?
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.
II. Inverter Classification
1. Based on the frequency of the AC power output, inverters can be divided into power frequency inverters, medium frequency inverters, and high frequency inverters. Power frequency inverters have a frequency of 50-60Hz, medium frequency inverters generally have a frequency of 400Hz to KHz, and high frequency inverters generally have a frequency of KHz to MHz.
2. Based on the number of phases output by the inverter, it can be divided into single-phase inverters, three-phase inverters, and multi-phase inverters.
3. Based on the destination of the output electrical energy, inverters can be divided into active inverters and passive inverters. An inverter that transmits the output electrical energy to the industrial power grid is called an active inverter; an inverter that transmits the output electrical energy to a certain electrical load is called a passive inverter.
4. According to the form of the main circuit of the inverter, it can be divided into single-ended inverter, push-pull inverter, half-bridge inverter and full-bridge inverter.
5. Based on the type of main switching device, inverters can be classified into thyristor inverters, transistor inverters, field-effect inverters, and insulated-gate bipolar transistor (IGBT) inverters. They can also be categorized into two main types: "semi-controlled" inverters and "fully controlled" inverters. The former lacks self-turn-off capability; the device loses its control function after being turned on, hence the name "semi-controlled." Ordinary thyristors belong to this category. The latter possesses self-turn-off capability, meaning that the on and off states of the device can be controlled by the control electrode, hence the name "fully controlled." Power field-effect transistors and insulated-gate bipolar transistors (IGBTs) belong to this category.
