PWM pulse width modulation technology (Pulse Width Modulation, PWM) refers to the use of a reference wave (usually a sine wave, sometimes a trapezoidal wave or a sine wave or square wave injected with zero sequence harmonics) as a modulating wave (Modulating Wave) ), and F (F is the carrier ratio) times the frequency of the modulation wave triangle wave (sometimes also used sawtooth wave) as the carrier wave (Carrier Wave) for waveform comparison, the modulation wave is greater than the carrier wave to produce a group of equal amplitude, and A rectangular pulse sequence whose width is proportional to the modulation wave is used to equivalently modulate the wave, and the analog quantity is replaced by a switch quantity, and the DC power is turned into an alternating current technology through the on/off control of the switch tube of the inverter. Since the upper and lower widths of the carrier triangle wave (or sawtooth wave) vary linearly, this modulation method is also linear. When the modulating wave is a sine wave, the pulse width of the output rectangular pulse sequence changes according to the sine law, so this modulation technique is usually also called sine pulse width modulation (Sinusoidal PWM) technique.
With the wide application of inverters in AC drives, UPS power supply and active filters, as well as the appearance of a large number of high-speed fully-controlled switching devices, PWM pulse width modulation technology has become the core of inverter technology, and it has been highly regarded by people. Pay attention to. Especially in recent years, the application of microprocessors and the realization of digital control have promoted the development of PWM pulse width modulation technology.
The development process of PWM pulse width modulation technology is a process of gradual improvement. In 1963, FGTurnbull proposed a method to eliminate specific harmonics; in 1964, A.Schnoung and H.Stemmler applied the modulation technology in the communication system to the AC drive inverter, resulting in sinusoidal PWM technology (Sinusoidal PWM) , Referred to as SPWM technology. S.R. Bowes of the University of Bristol in the United Kingdom promoted and applied it in 1975, making SPWM technology a hot spot of widespread concern. Later, Bowes successively proposed a fully digital SPWM technology solution, a regular sampling digital PWM solution, and a quasi-optimized PWM technology to improve the utilization rate of the DC voltage. In 1983, J. Holtz and others proposed the space phasor PWM technology. From the perspective of asynchronous motors, the technology directly uses the control method for the circular trajectory of the motor flux, so it is more intuitive and more intuitive to use. convenient.
Based on Tumbull’s method of eliminating specific harmonics, an optimized PWM concept to find the maximum or minimum appears. From 1977 to 1986, G.S.Buja, F.C.Zack and K.Taniguchi et al. proposed the optimal PWM method with the smallest current harmonic distortion (THDi), the best efficiency, and the smallest torque ripple. These methods have the advantages of high voltage utilization, fewer switching times, and can achieve control with specific optimization purposes. Therefore, people have been conducting research in this area. With the continuous improvement of microprocessor computing speed, J. Sun et al. proposed a real-time optimized PWM scheme in 1994.
In addition, it should be mentioned that the current hysteresis comparison PWM technology proposed by ABPlunkett in 1980, and the fully digital Dead-beat Control PWM technology developed on this basis, both of which have simple implementation specialty. In order to eliminate noise, AM Tragnadlowsky, VGAgelidis and others proposed random PWM method from 1993 to 1994. It starts from changing the frequency spectrum of harmonics, so that the harmonics are evenly distributed in a wide frequency band to achieve noise suppression and The purpose of mechanical resonance.
The emergence of these new PWM technologies mentioned above is based on SPWM technology. In 1983, the author published an article “Mathematical Analysis of SPWM Inverter Theory” in the Proceedings of the Second Research Institute of the Ministry of Aerospace Industry, which rigorously proved the SPWM technology.
The PWM technology of the inverter can be divided into three major categories: waveform modulation PWM technology, optimized PWM technology and random PWM technology. PWM technology can be used for voltage-type inverters and current-type inverters, and it has greatly promoted the development of inverter technology.