Features and application analysis of the selected

2022-08-12
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Analysis and introduction of the characteristics and application of the selected parts of the frequency converter

1 AC reactor

is connected in series on the input side of the power supply and the frequency converter, which is used to suppress the high-order harmonic of the input current, reduce the impact of the power surge on the frequency converter, improve the imbalance of the three-phase power supply, and improve the power factor of the input power supply (up to 0..85). It is recommended to use the input AC reactor in the following cases: the ratio of the power capacity of the place where the frequency converter is used to the capacity of the frequency converter is more than 101; The same power supply is connected with thyristor equipment or power factor compensation device with switch control; The voltage imbalance of three-phase power supply is large (≥ 3%); Due to the large volume and high cost of AC reactor, the configuration of AC reactor is considered only when the power of frequency converter is more than 30kW

2 DC reactor

DC reactor is connected in series in the DC intermediate link bus (between terminals P1 and P +). It is mainly to reduce the high-order harmonic component of the input current and improve the power factor of the input power supply (to 0.95). This reactor can be used with AC reactor at the same time. The configuration is considered only when the power of frequency converter is greater than 30kW

3 filter

in the input and output circuits of the frequency converter, there are many high-frequency harmonic currents. The filter is used to suppress the conduction of electromagnetic interference noise generated by the frequency converter, as well as external radio interference and the interference of instantaneous impact and surge on the frequency converter. It can be divided into input filter and output filter according to the different use positions. There are two kinds of input filters, line filter and radiation filter:

(1) the line filter is connected in series at the input side of the frequency converter and is composed of inductive coils, which can reduce the harmonic current with higher frequency by increasing the impedance of the circuit; When the external control terminal is needed to control the frequency converter, if the control loop cable is long, the interference of the external environment may invade from the control loop cable, causing the frequency converter to malfunction. At this time, the line filter is connected in series with the control loop cable to eliminate the interference

(2) the radiation filter is connected in parallel with the input side of the power supply and the frequency converter and is composed of high-frequency capacitors, which can absorb harmonic components with high frequency and radiation energy for reducing radio noise. It is better to use line filter and radiation filter at the same time

the output filter is connected in series at the output side of the frequency converter and is composed of inductance coils, which can reduce the high-order harmonic components in the output current, suppress the surge voltage at the output side of the frequency converter, and reduce the additional torque caused by the high-frequency harmonic current of the motor. The specific operation test of the dynamic ring is allowed. In the static self loading system, the wiring from the output filter to the frequency converter and motor should be shortened as far as possible, and the filter should also be close to the frequency converter as far as possible

4 braking resistance and braking unit

when the frequency converter stops and slows down, due to the inertia of the motor, the motor will be in the regenerative braking state, and the regenerative energy will be fed back to the DC circuit and consumed on the built-in braking resistance. If the deceleration time is set short, the DC bus voltage will rise too fast, which can support the key enterprises of new materials to benchmark the international benchmark, and it is too late to consume it, It may exceed the withstand voltage of the capacitor or the allowable voltage of the switching element, which will cause damage to the frequency converter. Therefore, the manufacturer is equipped with braking resistors or braking units for frequency converters of different specifications. When using the frequency converter, the user connects the braking resistor (P, DB) or braking unit (P, n) to both ends of the DC bus, so that when the DC bus voltage rises to a certain level, the braking resistor or the braking unit of desolite overcoating, a new generation of optical fiber coating technology, will be announced at the international wire and cable Symposium (IWCS) to consume excess energy and protect the frequency converter

the braking resistance is closely related to the flywheel torque of the motor, and the flywheel torque of the motor changes during operation. Therefore, it is difficult and unnecessary to accurately calculate the braking resistance. Usually, an approximate value is taken by empirical formula

braking resistance R> = 2ud/ieud = 700V; Ie: rated current of frequency converter; Braking resistance P > = aud2/ie; A is a constant. When the motor capacity is small, it is taken as small, otherwise it is taken as large. In general, it is sufficient to select the appropriate braking resistor. If the motor power is large, in order to improve the braking capacity of the frequency converter during deceleration, it is better to use the appropriate braking resistor and braking unit at the same time

5 leakage protector

there are distributed capacitors in the input and output leads of the frequency converter and inside the motor, and Senlan frequency converter is a low-noise type, and the carrier frequency used is high. Therefore, the ground leakage current of the frequency converter is large (more obvious for high-capacity models), which sometimes leads to the misoperation of the protection circuit. In case of the above problems, in addition to appropriately reducing the carrier frequency and shortening the lead, leakage protectors should also be installed

when using the leakage protector, pay attention to the following points: the leakage protector should be set at the input side of the frequency converter, and it is more suitable to be placed behind the air switch (non fuse circuit breaker); The operating current of the leakage protector shall be 10 times greater than the leakage current (the sum of the leakage current of the line, radio noise filter, motor, etc.) when the line does not use the frequency converter under the power frequency power supply

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