| 摘要 |
A method of protecting a frequency converter against overvoltage by controlling an AC motor during braking or during light load and a frequency converter, wherein the frequency converter is a voltage-controlled PWM frequency converter operating in single quadrant (1Q) and comprising at least one uncontrolled rectifier bridge (10) to be connected to a AC supply line (U L1 , U L2 , U L3 ), a direct-voltage intermediate circuit and at least one controlled inverter bridge (11) for feeding an AC motor (12) with an alternating voltage (U U , U V , U W ) of varying magnitude and frequency, in which method:
the angle (¸ ” ) between the output voltage vector (U s ) and current vector (I s ), i.e. the power factor, is measured,
the angle (¸ ” ) between the output voltage vector (U s ) and current vector (I s ), i.e. the power factor, is controlled on the basis of the measurement, and
the angle (¸ ” ) between the output voltage vector (U s ) and current vector (I s ), i.e. the power factor, is controlled so that the angle does not exceed a preset threshold value, preferably approximately À/2. |
