Motor drive device having function of estimating dead time in output stage
A motor drive device includes an inverter for generating an AC voltage from a DC voltage by switching power elements, a current detection unit for detecting a current to be inputted to a motor, a current controller for generating a voltage command from a current command and a current detection value, a gate drive command generator for generating drive commands for the power elements such that a dead time in an output stage, that is a period of time in which both of the power elements for upper and lower arms that compose the output stage of the inverter are turned off, becomes a predetermined value, a gate drive circuit unit for outputting gate drive signals for the power elements, and a dead time estimator for estimating the dead time in the output stage that is produced by the gate drive signals for the power elements.
1. A motor drive device of a motor for driving a feed shaft and a main shaft of a machine tool, or arms of an industrial machine or an industrial robot, comprising:
an inverter having a plurality of power elements, configured to generate an alternating current voltage for driving the motor from a direct current voltage by switching of the plurality of power elements;
a current detection unit configured to detect a current to be inputted from said inverter to the motor;
a current controller configured to generate a voltage command from a current command and a current detection value detected by said current detection unit;
a gate drive command generator configured to generate drive commands for the plurality of power elements upon receiving the voltage command from said current controller, such that a dead time in an output stage, that is a period of time in which both of the power elements for an upper arm and a lower arm that compose the output stage of said inverter are turned off, becomes a predetermined value;
a gate drive circuit unit configured to output signals to drive gates of the plurality of power elements upon receiving the drive commands from said gate drive command generator; and
a dead time estimator configured to estimate the dead time in the output stage that is produced by the signals to drive the gates of the plurality of power elements, from a difference between the current command and the current detection value.
2. The motor drive device according to claim 1 , wherein said dead time estimator estimates the dead time (T) produced by the signals for driving the gates of the plurality of power elements, from the difference (E) between the current command and the current detection value and a dead time (Tset) set by said gate drive command generator, based on an expression T=Tset+A×(E−B) by using constants A and B.
3. The motor drive device according to claim 1 , wherein said dead time estimator estimates the dead time in the output stage of each of three phases, by measuring a current flow detected by said current detector for a plurality of times with changing a phase of a three-phase current.
4. The motor drive device according to claim 1 , wherein said current controller adds a voltage to the voltage command by a deficiency due to the dead time or subtracts a voltage from the voltage command by an excess due to the dead time in accordance with the dead time (T) in the output stage estimated by said dead time estimator, in order to correct an effect of the dead time.
5. The motor drive device according to claim 1 , wherein in estimating the dead time (T) in the output stage, said current controller operates in a specific operation mode to estimate the dead time (T) in the output stage.
6. The motor drive device according to claim 1 , wherein said dead time estimator has dead time memory for storing the estimated dead time (T) in the output stage.