Patent ID: 6992908

Claim:
A method for charging an intermediate circuit in a frequency converter, the intermediate circuit of the frequency converter comprising one or more capacitors and the frequency converter having means for charging the intermediate circuit, wherein the means for charging the intermediate circuit comprise a rectifier bridge that comprises an input and an output, the input being connected to supply voltage, a direct current choke, a direct-current transformer, a zero diode, and a semiconductor switch and a control circuit arranged to control the switch; the method comprising the steps of defining in advance a high current limit and a low current limit controlling the semiconductor switch to be conductive for connecting the output voltage of the rectifier bridge to the intermediate circuit of the frequency converter, monitoring continuously the magnitude of the charging current running from the rectifier bridge to the intermediate circuit with the direct-current transformer, controlling the semiconductor switch to be alternately conductive and non-conductive depending on the magnitude of the charging current in such a manner that when the charging current decreases to the level of the low current limit, the semiconductor switch is made conductive, whereby the voltage of the rectifier bridge is connected to the intermediate circuit of the frequency converter and the charging current runs through the semiconductor switch and direct current choke, and when the charging current increases to the level of the high current limit, the semiconductor switch is made non-conductive, whereby the voltage of the rectifier bridge is disconnected from the intermediate circuit of the frequency converter and the charging current runs through the zero diode and direct current choke, and stopping the controlling of the semiconductor switch when the charging current remains below the high current limit while the semiconductor switch is conductive.