What is the main harmonic produced by a transducer? How about the degree?
Indirect frequency conversion has three different structure forms: (1) using controllable rectifier to change voltage, frequency conversion with inverter, voltage regulation and frequency modulation are carried out in two aspects respectively, and the two should coordinate with each other in control circuit. (2) with uncontrolled rectifier rectifier chopper inverter transformer, inverter, filter the inverter rectifier, voltage with pulse width (3) with uncontrolled rectifier rectifier, PWM inverter and inverter, this inverter device fully controlled only by controlled shutdown (such as IGBT) can output waveform is very realistic sine wave.
From the structure point of view, the inverter can be divided into indirect frequency conversion and direct frequency conversion of two major categories. The indirect frequency conversion turns the power frequency current into DC through the rectifier, and then converts the DC to the controllable frequency AC through the converter. The direct frequency converter transforms the power frequency exchange into the controllable frequency exchange, without the intermediate direct current link. Each phase is a reversible circuit in which two thyristor rectifier devices are antiparallel. The two groups of positive and negative switches are switched by a certain period, and the alternating voltage is gained on the load. The amplitude of the U0 is decided by the control angle of each rectifier device, and the frequency is determined by the switching frequency of the two sets of rectifier devices, and the frequency of the U0 is determined by the switching frequency of each rectifier unit. At present, more or more inter frequency converter.
The frequency converter is a nonlinear load, which absorbs nonsinusoidal current from the grid and causes the voltage distortion of the network. It is not only a harmonic source, but also a harmonic receiver. As harmonic source, it has different influence on all kinds of electric equipment, automatic device, computer, measuring instrument and communication system. As for the power supply line, due to the harmonic effect, the quality index of the power grid is deteriorated, the reliability of the power grid is reduced, the loss of the power grid is increased, and the service life of the electric equipment is shortened.
The main hazards are:(1) the possibility of resonance in the power grid is increased, thereby causing high overvoltages or overvoltages to cause the risk of accidents.(2) increasing additional losses, efficiency of transmission and electrical equipment, and utilization of equipment.(3) make the electrical equipment (rotating motor, capacitor, transformer, etc.) run abnormally, accelerate the insulation aging, and shorten their service life.
To reduce the influence of harmonics, various measures can be taken, but for the inverter, the main circuit is to install an AC reactor.The input side of the inverter generates the harmonic mechanism: for the inverter, as long as there is a rectifier circuit on the power supply side, it will produce harmonics caused by nonlinearity. Based on the three-phase bridge rectifier circuit for example, AC grid voltage for a sine wave, square wave AC input current waveform, the waveform, according to Fourier series can be decomposed into fundamental and harmonics, usually containing 6m + 1 (m=1,2) harmonics, the harmonics in power grid. A single fundamental wave, combined with several harmonic waves, is called an abnormal wave
