| 摘要 |
An overvoltage protection system for the intermediate circuit of frequency converter, said frequency converter being a voltage-controlled PWM-frequency converter comprising an uncontrolled mains bridge ( 10 ) to be connected to an alternating-current source (U<SUB>L1</SUB>, U<SUB>L2</SUB>, U<SUB>L3</SUB>), a direct-voltage intermediate circuit and a controlled load bridge ( 12 ) for producing a multi-phase alternating voltage (U<SUB>U</SUB>, U<SUB>V</SUB>, U<SUB>W</SUB>) of variable frequency, wherein the direct-voltage circuit of the frequency converter contains a low-capacitance direct-voltage capacitor, the mains bridge ( 10 ) being connected to the load bridge ( 12 ) directly without a high-capacitance direct-voltage capacitor serving as an intermediate energy storage, and which overvoltage protection system contains a varistor (R 1 ). The overvoltage protection system consists of a series connection of the varistor (R 1 ) and a semiconductor switch (V 1 ), said series connection being connected in parallel with the direct-voltage capacitor, which semiconductor switch has a voltage rating lower than the normal operating level of the direct-voltage intermediate circuit.
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