Frekvenční měniče Katalogy, manuály (EN+CZ)

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Vydal: ABB s.r.o, ELSYNN Autor: ABB ELSYnn

Strana 802 z 825







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This technique eliminates harmonics of the series 5th, 7th, 17th and 19th etc. 12-pulse circuit To minimise both the harmonic influence the drive the supply system and the ripple the motor torque, rectifier and inverter normally operate 12-pulse mode. Control system The main purpose the control system to generate the firing impulses for the thyristors in the rectifier and inverter the right instants to maintain the desired voltage and frequency across the motor. very low speeds (0.5 rated speed), the motor voltage too low guarantee reliable commutation and pulse mode commutation has employed. It provides the field current over the entire speed range and standstill. Excitation The excitation the synchronous machine can the brushless slipring type.MEGADRIVE-LCI system The main components adjustable speed drive are shown the diagram the right. The following explanation is therefore confined the components the frequency converter and its operation. Since the drive system is self-controlled, cannot fall out-of-step. inverter this type referred to as load-commutated inverter (LCI). The principal applied that four- quadrant drive which permits driving and braking both directions. The rectifier supply converter conjunction with the reactor the link circuit form a fully controllable current source. The diagram the right shows a simplified 6-pulse circuit and alternative 12-pulse circuits b), c) and d). Inverter Thyristors the inverter electronically switch the current such produce three- phase system variable frequency and voltage for supplying the motor. The best one use for a particular application largely determined the power and voltage ratings the drive. The design of the inverter basically the same that of the rectifier with the exception that the inverter phase currents are commutated the motor voltage. DC link reactor The reactor the link circuit smoothes the DC current and limits the rate current rise in the link circuit the event fault. 3 . Although the transformer and the motor are designed for operation conjunction with a converter, they not differ essentially from normal versions.. A synchronous motor for this kind of operation equipped with two sets of windings electrically displaced 30°.. Similarly, the supply transformer also has two secondary windings shifted by 30°. Voltage, current and speed are regulated closed-loop control. Rectifier The rectifier the controlled line-commutated type similar those used for drives