The so-called inverter refers to the reverse converter of a rectifier (also known as a smooth converter). The so-called IGBT three-phase SPWM inverter refers to a power electronic converter that uses the semiconductor power switching device IGBT as a switch and adopts the SPWM control method to convert DC power into a three-phase AC power close to a sine wave.
Inverter technology is the most important conversion technology in power electronics. The principle of inverter was mentioned in related literature as early as 1931.
In 1947, the first transistor was born, and solid-state power electronics was born. In 1948, Westinghouse in the United States used a mercury arc rectifier to make a 300Hz inverter for induction heating. In 1956, the first thyristor came out and began to enter a period of traditional development. Inverters began to develop after rectifiers. First, SCR voltage-type inverters. In 1961, an improved forced-commutation SCR inverter appeared, which laid the foundation for the development of inverters and began to notice improvements in inverters. The importance of the output voltage waveform of the converter. In 1962, the “harmonic neutralization and elimination method” was proposed, that is, the later “multiple superposition method”.
In the late 1970s, turn-off thyristor GTO, power transistor GTR and their modules were put into practical use one after another. Since the 1980s, the combination of power electronics technology and microelectronics technology has produced a variety of high-frequency fully-controlled switching devices, which have been rapidly developed, such as power MOSFETs, insulated gate transistors, IGBTs, etc. This makes the power electronic technology enter the high frequency period from the traditional development period. During this period, a new type of inverter technology with miniaturization and high performance characteristics gradually appeared, especially pulse width modulation technology has been developed rapidly.
In 1964, A. Schonung and H. Stemmler proposed the application of modulation technology of communication system to sinusoidal pulse width modulation technology (Sinusoida PWM, SPWM) in the inverter system. Due to the slow speed of switching devices at that time, it was not promoted in time until It was only in 1975 that the SPWM control technology was officially applied to the inverter technology, and the performance of the inverter was greatly improved. Since then, various PWM technologies have appeared one after another, such as third harmonic injection PWM, spatial phase remodulation (SVM), random PWM, current hysteresis PWM, etc., which have become the dominant control method for high-speed switching device inverters.
It is generally believed that the development of inverter technology can be divided into the following three stages.
① 1956~1980 was the traditional development stage. The characteristics of this stage are that the switching devices are mainly low-speed devices, the switching frequency of the inverter is low, the sine of the output voltage waveform is mainly multi-superposition method, the volume and quality are large, the inverter efficiency is low, and the sine wave inverter Start to appear.
②1981~2000 is the stage of high-frequency new technology. The characteristics of this stage are that the switching devices are mainly high-speed devices, the switching frequency of the inverter is higher, the sine of the output voltage waveform is mainly SPWM, the volume and quality are small, the inverter efficiency is high, and the sine wave inverter technology is The development is becoming more and more perfect.
③2000 has been a high-frequency and low-pollution stage. The characteristics of this stage are mainly the comprehensive performance of the inverter. Low-speed and high-speed switching devices are used together, and the multiple superposition method and SPWM method are used together. It is no longer biased to pursue high-speed switching devices and high switching Frequency, efficient and environmentally friendly inverter technology began to appear.
The current development status of inverter technology is focusing on reducing the size and quality of inverters. In the SPWM inverter, the volume and quality of the output transformer and AC filter account for the main part. In order to reduce the volume and quality of output transformers and AC filters, and increase the power density of inverters, high frequency is still one of the main development directions, such as increasing the switching frequency of SPWM inverters and adopting internal high frequency loops. Increasing the switching frequency can reduce the volume and quality of the AC filter, and the use of an inner high-frequency loop can reduce the volume and quality of the transformer. However, the high frequency of the inverter also has some problems, such as increased switching loss and increased electromagnetic interference. In addition, the skin effect and proximity effect of the conductor, the ESR of the capacitor, and the parasitic parameters of the magnetic components all need to be resolved. The most important of these are the switching loss and electromagnetic interference. There are two most effective ways to solve these problems: one is to increase the speed of the switching device; the other is to use resonance or quasi-resonance to make the inverter switch work in a soft switching state. This has prompted people to be interested in the study of resonance. The current resonance technology was proposed in 1970, and the voltage resonance technology was proposed in 1975. Both of these technologies use L, C and switching devices to form a series or parallel resonance circuit, and use the full resonance of the circuit in a switching cycle to make the switch work In the soft switching state of zero current conversion (parallel vibration control) or zero voltage conversion (series resonance), the switching loss is reduced to zero. This is the earliest soft switching method. Although this method is effective, it cannot work in accordance with the SPWM method. In the early 1980s, someone improved the resonance technology and proposed a quasi-resonant conversion technology, that is, the full resonance of the L and C loops in a switching cycle is changed to semi-resonant or partial resonance, which makes soft switching and SPWM The combination of technology becomes a reality. This set off a quasi-resonant converter heat. In 1986, someone proposed the DC resonant loop soft-switching inverter technology; in 1987, someone also proposed the pseudo-resonant branch (polar) soft-switching technology, which received widespread attention from the power supply industry. Since then, there has been a global upsurge of research on soft-switching inverter technology.
SPWM soft-switching inverter technology is one of the most active research contents in the field of power electronics today. It is the best way to achieve high-frequency power electronics technology, and it is also a highly theoretical research work. Its research is of great significance to the improvement of inverter performance and further promotion and application, as well as the development of power electronic technology, and it is one of the current development directions of inverters. But it must be pointed out here that soft switching is not completely loss-free, it just reduces some losses, or transfers most of the switching loss of the switch itself to the resonant components in the additional resonant circuit for soft switching.
The background of the above-mentioned SPWM high-frequency soft switching technology is to overcome the poor output waveforms of traditional inverters, which have higher du/dt, di/dt, and the resulting shortcomings of greater switching stress and EMI. Under the same background, some people proposed the multi-level inverter technology in 1981 in response to the shortcomings of low switching devices of high-power inverters, which has become a development direction of current high-voltage high-power inverters. Contrary to the idea of SPWM high-frequency soft-switching inverter technology, the starting point of multi-level inverter technology is to transform the main inverter circuit so that all inverter switches work at the fundamental frequency or low frequency to reduce switching. The purpose of stress, improving the output voltage or current waveform.
Large and medium power inverters adopt the cascade superposition method of SPWM inverters (ie, the combined application of SPWM control technology and cascade superposition technology) to obtain the advantages of SPWM multi-level output inverter technology. It can not only improve the waveform of the output voltage, make it tend to be sine wave, but also realize linear voltage regulation and stabilization. Compared with the traditional two-level inverter, it also requires the least number of components.
There are the following types of inverters that can be applied in three-phase green UPS circuits.
IGBT three-phase SPWM inverter:
①Three-phase half-bridge SPWM inverter
②Three-phase four-leg SPWM inverter
③Three-phase full-bridge SPWM inverter
④Independent SPWM DC power supply cascade superimposed multi-level inverter
⑤2N-1 Binary Multilevel Inverter
⑥The 2H bridge 3N-1 ternary cascade superimposed multilevel inverter with transformer superposition
⑦Three-phase Y-△cascade superposition Udc– PWM inverter
③Boost SPWM inverter