Since the 1980s Universal Inverter enter the Chinese market, in just ten years time has been very widely used. At present, general-purpose inverters with its intelligent, digital, network, etc. more and more people of all ages. With the expansion of the scope of application of the general-purpose inverter, the problems exposed more and more, mainly in the following aspects:
① harmonic problems
② drive load matching problem
③ heating problem
These problems have caused the relevant authorities and the attention of factories, mines and development of the relevant technical standards. Problems such as harmonics, China in 1984 and in 1993 adopted the "Provisional Regulations on Administration of power system harmonics" and GB / T-14549-93 standard, harmonic pollution to limit the power supply system and electrical equipment. In response to these problems, this paper analyzes and proposed solutions and countermeasures.
2 Harmonic Problems and Solutions
General inverter main circuit is generally composed of three parts: rectifier, inverter section and the filter section. Three-phase rectifier bridge uncontrolled rectifier, inverter part IGBT three-phase bridge inverter, and the output of the PWM waveform. For bipolar modulation inverter, the output voltage waveform expansions:
Where: n- harmonic number n = 1,3,5 ......;
a1- switching angle, i = 1,2,3 ...... N / 2;
Ed- inverter DC voltage;
N- carrier ratio.
By the formula (1) can be seen, the amplitude of the harmonic