1. Field of the Invention
The present invention relates to an apparatus for controlling a motor, and more particularly, to a motor control apparatus for compensating a phase error of the output corresponding to a time delay generated by digital control to stably control a motor when controlling high-speed operation, and a method thereof.
2. Background of the Invention
Motors provided in a compressor do not include a sensor due to the difficulty of its installation. Accordingly, a control apparatus for driving the motor drives the motor using a sensorless algorithm. The sensorless algorithm calculates the position of a rotor to allow the user to drive the motor at his or her desired speed. A motor control apparatus corresponding to the related art may be operated up to a predetermined machine speed, for example, 120 Hz (hereinafter, normal operation), using this sensorless algorithm, but high-speed operation, for example, 150 Hz, is required to enhance the performance of a compressor. In order to operate a motor at a high speed, the stability of control should be secured and load responsiveness should be enhanced.
A motor control apparatus provided with a sensorless algorithm corresponding to the related art may be subjected to a comparator and a proportional integral controller to make the error to be “0” (zero) between a reference current and a detected current. Furthermore, the control apparatus controls the d-axis and q-axis of the synchronous coordinate system, respectively, to generate a reference voltage of the synchronous coordinate system, and converts it into a reference voltage of the stationary coordinate system. At this time, an angle of the stationary coordinate system may be represented θe as illustrated in FIG. 3.
As illustrated in FIG. 3, in a motor control apparatus corresponding to the related art, a phase error of the voltage output may be generated due to digital control using a microcomputer (hereinafter, referred to as a “microcontroller”). In other words, a phase error occurs in the coordinate transformation of the reference voltage because a predetermined time is required to output a signal having a pulse width modulation waveform from the microcontroller to the motor. In other words, as illustrated in FIG. 3, in a motor control apparatus corresponding to the related art, assuming that a current sample period is Ts and the current sample is carried out at time t, a pulse width modulation signal output (reference voltage) is updated at t+Ts. FIG. 4 is a graph illustrating a phase error in FIG. 3, and as illustrated in the drawing, a phase delay as much as Δθe may be generated at the output of the reference voltage. Accordingly, the motor control apparatus corresponding to the related art has a problem that actual output from the inverter to the motor may be implemented after time αTs, and a phase error of the voltage output may be further increased and its control stability may be reduced when operating the motor at a high speed.