Motor drive

A motor drive, comprising:

• a rectifier bridge for connection with mains;
• a converter bridge configured to be connected with, and in-between, an elevator motor and an intermediate DC circuit, whereby between a positive and a negative branch of the intermediate DC circuit at least one capacitor and/or battery is connected;
• a controlled main relay with contacts at a mains side of the rectifier bridge, the controlled main relay with contacts configured to connect or disconnect the rectifier bridge with a corresponding mains phase;
• a charging circuit, the charging circuit including at least one charging switch connected in series with at least one current limiting component;
• and
• a voltage sensor connected between the positive and the negative branch of the intermediate DC circuit, the voltage sensor further connected to a fault evaluation circuit that includes a memory storing at least one reference value and a comparator, the fault evaluation circuit configured to detect an earth fault of the elevator motor, the fault evaluation circuit further configured to compare an actual sensor signal of the voltage sensor to the at least one reference value and to operate the controlled main relay based on a result of the comparing,
• wherein the charging circuit is connected between the mains and the intermediate DC circuit bypassing the rectifier bridge,
• wherein the charging circuit is connected in parallel to at least one of the contacts.

A motor drive, comprising:

• a rectifier bridge for connection with mains;
• a converter bridge configured to be connected with, and in-between, an elevator motor and an intermediate DC circuit, whereby between a positive and a negative branch of the intermediate DC circuit at least one capacitor and/or battery is connected;
• a controlled main relay with contacts at a mains side of the rectifier bridge, the controlled main relay with contacts configured to connect or disconnect the rectifier bridge with a corresponding mains phase;
• a charging circuit, the charging circuit including at least one charging switch connected in series with at least one current limiting component;
• and
• a voltage sensor connected between the positive and the negative branch of the intermediate DC circuit, the voltage sensor further connected to a fault evaluation circuit that includes a memory storing at least one reference value and a comparator, the fault evaluation circuit configured to detect an earth fault of the elevator motor, the fault evaluation circuit further configured to compare an actual sensor signal of the voltage sensor to the at least one reference value and to operate the controlled main relay based on a result of the comparing,
• wherein the charging circuit is connected between the mains and the intermediate DC circuit bypassing the rectifier bridge,
• wherein the charging circuit comprises a second current limiting component connected in parallel with at least one contact of a charging relay or main relay.

Method for detecting an earth fault of an elevator motor, using a motor drive that includes a rectifier bridge for connection with mains, the motor drive further including a converter bridge configured to be connected with, and in-between, the elevator motor and an intermediate DC circuit, whereby between a positive and a negative branch of the intermediate DC circuit at least one capacitor and/or battery is connected, the motor drive further including a controlled main relay with contacts at a mains side of the rectifier bridge, the controlled main relay with contacts configured to connect or disconnect the rectifier bridge with a corresponding mains phase, the motor drive further including a charging circuit, the charging circuit including at least one charging switch connected in series with at least one current limiting component, the motor drive further including a voltage sensor connected between the positive and the negative branch of the intermediate DC circuit, the voltage sensor further connected to a fault evaluation circuit that includes a memory storing at least one reference value and a comparator, the fault evaluation circuit configured to detect the earth fault of the elevator motor, the fault evaluation circuit further configured to compare an actual sensor signal of the voltage sensor to the at least one reference value and to operate the controlled main relay based on a result of the comparing, wherein the charging circuit is connected between the mains and the intermediate DC circuit bypassing the rectifier bridge, whereby the elevator motor is permanently connected to the converter bridge of the motor drive, wherein before closing the controlled main relay, a charging switch of the charging circuit is closed and a voltage of the intermediate DC circuit or a voltage over the current limiting component of the charging circuit is measured, and that the controlled main relay is closed only if a measured voltage over the current limiting component is below at least one reference value or if the voltage of the intermediate DC circuit exceeds at least one reference value.