外文翻译-现代变频器技术分析

Modern frequency changer technical analysis

Cheng Xi (Heilongjiang longmay mining group co., ltd.)

The general frequency changer by its merits and so on intellectualization, digitization, network receives people's favor more and more, but along with the general frequency changer application scope's expansion, exposes some questions. In view of these questions, this article carried on has analyzed and proposed the countermeasure.

First, overtone question and countermeasure.

The general frequency changer's main circuit form generally by the rectification part, the contra variant part and the filter part is composed. The rectification part for the three-phase bridge-type uncontrolled rectifier, the invertors part is the IGBT three-phase bridge-type invertors, and the output is the PWM profile. Because the general frequency changer's rectification part uses the diode uncontrolled bridge-type leveling circuit, the middle filter part uses the big electric capacity to take the filter, therefore rectifier's input current in fact is capacitor's charging current, assumes a higher more and precipitous pulse wave, its harmonic component is big. For the harmonic cancellation, may use:

1, Increases the frequency changer electric power supply internal resistance. Usually in the situation, power equipment's internal resistance may play the cushion frequency changer concurrent filter electric capacity's reactive power role. This kind of internal resistance is transformers short-circuit impedance. When power source capacity relative frequency changer capacity hour, then the internal resistance value relatively is bigger, the harmonic content is smaller; When the power source capacity relative frequency changer capacity is bigger, then the internal resistance value relatively is bigger, the harmonic content is bigger. Therefore best choice short-circuit impedance big transformer.

2, Installs the reactor. Installs the reactor is actually increases the frequency changer electric power supply's internal resistance from exterior. Installs the direct-current reactor in frequency changer's exchange side installment exchange reactor or in frequency changer's direct-current side, also or installs, suppresses the harmonic current.

3, Transformer heterogeneity movement. The general frequency changer's rectification part is six pulse wave rectifiers, therefore produces the overtone is big. If

using transformer's heterogeneity movement, causes phase angle mutual deviation 30°like Y-△, △-△the combination two transformer constitution to be equal to 12 pulse wave effects, then may reduce the low order harmonic current 28%, plays the harmonic suppression role.

4, Adjusts frequency changer's carrier ratio. So long as carrier compared to enough big, is inferior the overtone to be possible to suppress effectively, specially the reference wave peak-to-peak value and the carrier peak-to-peak value are smaller than 1:00, 13 following odd number overtones no longer appear.

5, Special-purpose filter. The special-purpose filter use in examining the frequency changer harmonic current the peak-to-peak value and the phase, and produces one with the harmonic current peak-to-peak value to be the same, but the phase just right opposite electric current, passes through in the frequency changer, absorption harmonic current.

Second, matching of load question and countermeasure.

Produces machinery's torque characteristics to divide into three types roughly: Permanent torque loading, air blower pump class load and permanent power termination. In view of the different load type, should choose the different type the frequency changer.

1, Permanent torque loading. The permanent torque loading is refers to the load moment to have nothing to do with the rotational speed, under any rotational speed, the torque maintains constant. But the permanent torque loading divides into the friction class load and the potential energy type capacity two kinds.

2, Air blower pump class load. The air blower pump class load is present industry field application most equipment, although the pump and air blower's characteristic are many and varied, but mainly by the centrifugal pump and the centrifugal fan application, the general frequency changers are primarily most in this kind of load application. This kind of load is not high to frequency changer's performance requirement, only requests the efficiency and the reliability, therefore the choice has the U/f=const control model frequency changer then, like Mitsubishi frequency changer FR-F540 (L) series. Air blower load in actual movement process, because the rotor inertia is quite big, therefore frequency changer's rise time and the deceleration time are a very important question.

The air blower load's system rotor inertia computation is very important. When frequency changer concrete design, according to the computed result, carries on the