Inverter harmonic interference prevention instance

This paper, the mechanism of the inverter harmonics, harmonic interference channel, harmonic interference hazards and harmonic interference suppression methods commonly used in the analysis, harmonic interference suppression also given a few typical examples.

1, Introduction Recent years, the need for speed and energy efficiency, more and more occasions used the Frequency Converter. One of the core part of the inverter is the electrical and electronic components, electronic components, computer chips, susceptible to external electrical interference of some, therefore, put into power inverter run-time, need to consider whether the grid voltage symmetry, size and distribution transformer capacity whether the bus connected with nonlinear devices; the other hand, the input side converter itself is a nonlinear circuit, the waveform of the power supply will be affected, inverter output side voltage, current, or complete non-sine sine waves rich in harmonics. As for high power inverter to rectifier diode, high power transistor inverter, the result is the input and output circuit current generated high harmonics, interference-powered systems, load and other nearby electrical equipment. In actual use, the inverter harmonic interference problems often encountered, the following brief inverter harmonic generation mechanism, interference channels, hazards and effective countermeasures to prevent or suppress interference.

2, inverter harmonic generation mechanism Generally the main circuit inverter AC - DC - AC component, the frequency of external input 380V/50Hz power by the three-phase bridge uncontrolled rectifier into DC voltage signal by the filter capacitor filter and high-power transistors inverter switching devices for the exchange of variable frequency signals.

Input side of Harmonic Mechanism: not limited to general purpose inverter, thyristor power supply DC motor, commutator motors, etc. all in the power supply side of rectifier circuit, will produce its non-linear of harmonics caused. In the three-phase bridge rectifier circuit, the input current waveform is rectangular wave, wave by Fourier series decomposition of the fundamental and harmonics, usually contain 6n +1 (n = l, 2,3 ....) Subharmonic wave. One of the high harmonic disturbance input supply system.

Harmonic output side of the mechanism of production: in the inverter output circuit, the output voltage and current are harmonic. For PWM control inverter, as long as voltage converters, no matter what kind of PWM control, the output voltage waveform is square wave. Which is the level of harmonic frequency converter frequency modulation, low frequency modulation (such as 1 ~ 2KHz), the human ear can hear frequencies generated by high harmonic electromagnetic noise (scream). If the high frequency modulation (such as IGBT inverter up to 20KHz), human ears gone, but the high-frequency signal is an objective. Spread from the current sine sawtooth voltage side, with the Fourier series is not difficult to analyze the harmonic content. Therefore, the output loop current signals are decomposed into only the fundamental sine wave and the other containing all the harmonics and high harmonic currents on the load direct interference. Another high harmonic currents through cables to the space radiation, interference with nearby electrical equipment.

3, harmonic interference channels Inverter harmonic interference channel or radio interference with the normal conduction and radiation as points in the conduction process, and the inverter output line parallel to the laying of the wire will produce electromagnetic interference coupling of induction; inverter output side of the harmonic radiation will, in the vicinity of the radio interference, the interference channel shown in Figure 1.

4, harmonic interference hazards (1) Transformers: current harmonics will increase the copper loss, voltage harmonics will increase the iron loss and the overall effect is to make transformer temperature rise, affecting the insulation capability, and result in reduced capacity margin. Harmonics may also cause transformer winding and the line between the resonance between the capacitor and the magnetic flux caused by core saturation or skew, caused by noise.

(2) Motor: output harmonic impact on the main motor, causing additional motor heating, resulting in the additional temperature rise of motors, motor derating often used, because the output waveform distortion, increased motor repetitive peak voltage, affecting the motor insulation, harmonics also cause motor torque ripple and noise increase.

(3) Power Capacitor Group: General capacitors standards, regulations allow a maximum current of only 35% of the overload, but the actual operation, because harmonic, it is therefore a serious overload. As the capacitor impedance decreases as frequency increases, so harmonic generation, the capacitor becomes a trap flow point, a lot of current flows, resulting in overheating, increased dielectric stress, or even damage the power capacitor. When the capacitor and the line impedance conditions to achieve resonance, vibration will occur short-circuit, over current and generated noise.

(4) switching equipment: Due to the presence of harmonic currents, switching equipment at the start instantly generate high di / dt of the current rate of change, resulting in increased peak transient recovery voltage, resulting in destruction of insulation.

(5) protection of electrical: current contains harmonics, will generate additional torque, change the electrical characteristics of the action, so that the wrong operation.

(6) Measuring Instruments: Measuring instruments such as electric energy meter, which will cause a result of harmonics generate additional electromagnetic induction rotary torque, cause errors, reducing accuracy.

(7) power electronic equipment: In many occasions, electronic equipment often generate harmonic current source, and is easy to feel the harmonic distortion and malfunction.

(8) Other well as lighting equipment, communications equipment, television and audio equipment, computer equipment, carrier frequency remote control equipment are susceptible to harmonic interference affecting its normal work or reduce its service life.

5, harmonic interference suppression measures Harmonic means of transmission is conduction and radiation, conduction disturbances resolve the main conduction in the circuit to filter out or isolate the high frequency current; solve radiated interference is interference on the line sources or shielding. Specific common methods are:

5,1 in the converter input side of the responses: (1) variable frequency power supply system, power supply and other equipment independently of each other, or in the inverter and other electrical equipment installed on the input side of the isolation transformer, cutting off harmonic current.

(2) Set the AC reactor. (3) set the AC filter.

(4) multiple rectifier technology for large capacity thyristor converter can take this approach, the power supply side of the rectifier in two, in the input side of the installation of Y, yd, or D, yd transformer winding connection, using the inhibition of multiple power supply side of the flow of high harmonics. Rectifier because of the need to separate

I am a professional writer from China Products, which contains a great deal of information about electric paint scraper , bathroom basin sinks, welcome to visit!

Comment on "Inverter harmonic interference prevention instance"