Phase advance method in motors with permanent magnets presenting induced voltages with flat region
The present invention refers to the use of phase advance in motors with non-ideal induced voltages, especially in motors with induced voltages that present a flat region, to avoid instability in the control, wherein the first step is to detect the passage of the voltage induced by the flat region of instability, and then apply a fixed increment in the phase advance in order to avoid the flat region. Detection can be done in two ways: by direct measurement of induced voltage; and measuring the extinguishing time of the freewheel current.
1 . A phase advance method for allowing a use of phase advance, including monitoring of a rotor position, in at least one sensorless brushless direct current (BLDC) motor with non-trapezoidal or non-ideal induced voltages, the induced voltages being proximate a zero crossing point and characterized by a substantially flat region around the zero crossing point, the at least one sensorless BLDC motor being driven with a six-step drive mode and comprising a rotor, wherein the at least one sensorless BLDC motor is configured to permit detection of at least one passage of the induced voltages through the substantially flat region proximate the zero crossing point by direct measurement of the induced voltages, wherein the flat region proximate the zero crossing point that generates a nonlinear effect, the method comprising:
applying a gradual phase advance by advancing a commutation angle of a voltage applied to the at least one sensorless BLDC motor with a gradual phase advance level in relation to the rotor position;
monitoring, subsequent to applying the gradual phase advance, a bus voltage (Vbus) provided by a DC voltage source of an inverter connected to the motor; and
monitoring voltages of phases of the motor, wherein the phases comprise FA, FB, FC phases;
comparing an open phase corresponding to one of the phases that is open in one of a plurality of rotor positions including the rotor position with other phases different from the open phase of the phases using a parameter (H) that is calculated by H=H coef ×(rpm+k×torque), with rpm being rotational speed, H coef being a parameter proportional to a motor flux constant, associated with a characteristic of the motor, and k being a torque (or current) adjustment parameter; and
checking, at each of a plurality of phase advance levels, whether a value of the induced voltages at the plurality of rotor positions, including a first position, a second position, a third position, a fourth position, a fifth position, and a sixth position, is approximately equal to half of the bus voltage (Vbus/2) indicative of the motor reaching the substantially flat region proximate the zero crossing point, wherein when the value corresponds to approximately half of Vbus, a fixed Df increment is applied to the Hcoef parameter.
2 . A phase advance method for allowing a use of phase advance, including monitoring of a rotor position, in at least one sensorless brushless direct current (BLDC) motor with non-trapezoidal or non-ideal induced voltages, the induced voltages being proximate a zero crossing point and characterized by a substantially flat region around the zero crossing point, the at least one sensorless BLDC motor being driven with a six-step drive mode and comprising a rotor, wherein the at least one sensorless BLDC motor is configured to permit detection with the induced voltages of at least one passage of the induced voltages through the substantially flat region proximate the zero crossing point, by measuring an extinction time of a freewheel current, wherein the flat region proximate the zero crossing point that generates a nonlinear effect, the method comprising:
applying a gradual phase advance by advancing a commutation angle of a voltage applied to the motor with a gradual phase advance level in relation to the rotor position;
monitoring, subsequent to applying the gradual phase advance, a bus voltage (Vbus) provided by a DC voltage source of an inverter connected to the motor; and
monitoring voltages of phases of the motor, wherein the phases comprise FA, FB, and FC phases;
comparing an open phase corresponding to one of the phases that is open in one of a plurality of rotor positions including the rotor position with other phases different from the open phase of the phases using a parameter (H) that is calculated by H=H coef ×(rpm+k×torque), with rpm being rotational speed, H coef being a parameter proportional to a motor flux constant, associated with a characteristic of the motor, and k being a torque (or current) adjustment parameter;
measuring the extinction time of the freewheel current at each phase advance level by comparing the voltage of the open phase with the Vbus or a ground (GND) reference according to the rotor position, the extinction time of the freewheel current being composed of a switching freewheel current and a phase-advancing freewheel current; and
when the extinction time of the freewheel current is longer than a predetermined maximum value, applying a fixed Df increment to the parameter H.
3 . The phase advance method according to claim 1 , comprising:
recording a current rotational speed value (Sa) of the motor before applying the fixed Df increment;
recording a subsequent rotational speed value (Sd) after applying the fixed Df increment; and
obtaining a rotational speed increment value (DS) wherein: DS=Sd−Sa.