Current limit strategy for hoist application

A method of operating a hoist application system, the method comprising:

• driving a motor in accordance with a final duty command;
• generating, in a closed-loop control unit, a closed-loop duty command;
• generating, in an open-loop control unit, an open-loop duty command;
• and
• generating the final duty command from one of the closed-loop duty command and the open-loop duty command based on direct current (DC) system information,
• wherein the generating of the final duty command comprises:
• transitioning from the closed-loop duty command to the open-loop duty command when a DC-link current exceeds a threshold value from the DC system information for a predetermined time;
• and
• transitioning from the open-loop duty command to the closed-loop duty command when the DC-link current is lower than the threshold value for the predetermined time and, for a commanded motor speed and a load applied on the system, the closed-loop operation is possible without crossing the threshold value.

A method of operating a hoist application system, the method comprising:

• driving a motor in accordance with a final duty command;
• generating, in a closed-loop control unit, a closed-loop duty command;
• generating, in an open-loop control unit, an open-loop duty command;
• and
• generating the final duty command from one of the closed-loop duty command and the open-loop duty command based on direct current (DC) system information,
• wherein the generating of the final duty command comprises one of switching from the closed-loop duty command to the open-loop duty command and switching from the open-loop duty command to the closed-loop duty command,
• wherein:
• the switching from the closed-loop duty command to the open-loop duty command comprises comparing a DC-link current to a threshold value from the DC system information and transitioning from the closed-loop duty command to the open-loop duty command in an event the DC-link current exceeds the threshold value for a predetermine time, and
• the switching from the open-loop duty command to the closed-loop duty command comprises determining whether the DC system information indicates that a DC-link current is lower than a threshold value for a predetermined time and a closed-loop operation is possible without crossing the threshold value and switching from the open-loop duty command to the closed-loop duty command in an event the DC system information indicates that the DC-link current is lower than the threshold value for the predetermined time and, for a commanded motor speed and a load applied on the system, the closed-loop operation is possible without crossing the threshold value.