JP2011217512A - Dc brushless motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rotate a DC brushless motor at a constant speed without using a position detecting signal even when ripples are generated in a DC voltage.SOLUTION: A DC brushless motor control device includes a zero-cross point detector 40 detecting the zero-cross point of an AC voltage, a switching time computing means (a microcomputer 50) computing a switching time of a conductive phase in future from a target rotational frequency and the switching time of the conductive phase and outputting the switching time of the conductive phase in future to a motor driver circuit 20, and a storage 52 storing a table recording the correction value of the switching time of the conductive phase in response to an elapsed time from the zero-cross point of the AC voltage. The correction value of the switching time corresponding to the elapsed time from the zero-cross point when the computed switching time of the conductive phase is output to the motor driver circuit 20 is read from the table, and the switching time of the conductive phase computed by the switching time computing means is corrected by using the correction value of the switching time and then output to the motor driver circuit 20.

Description

  The present invention relates to a DC brushless motor control device that switches and controls energization of each magnetic pole of a DC brushless motor.

  FIG. 6 shows an outline of a conventional DC brushless motor control device. This DC brushless motor control device receives a voltage Vac of a commercial AC power supply, and rectifies and smoothes it by a step-up chopper method by a step-up rectifying and smoothing circuit 10 to obtain a DC voltage Vdc. By switching with 20 transistors, the energized phases of the three-phase windings of the sensorless brushless DC brushless motor 30 are sequentially switched, and the DC brushless motor 30 is rotationally driven. Then, a position detection signal is obtained by detecting an induced voltage generated in the three-phase winding at the time of non-energization by the position detection circuit 60, and the position detection signal of the rotor is processed by the microcomputer 50A to obtain a DC. The switching of the transistors of the motor drive circuit 20 is feedback-controlled so that the brushless motor 30 rotates at the target rotational speed.

  As described above, in the conventional DC brushless motor control device that drives the sensorless brushless DC brushless motor, the rotor position is detected by using the induced voltage generated in the non-energized winding, and the rotation is performed to the target rotational speed. Control is in progress.

  By the way, when the DC brushless motor 30 is rotated at a high speed, it is necessary to reduce the induced voltage generated in the winding. Therefore, the phase angle of the energization phase to the winding of the DC brushless motor 30 is controlled to advance. (It is necessary to control so that the energization switching is advanced). As a result, the induced voltage appearing in the non-energized phase of the DC brushless motor 30 cannot be used for position detection, and the rotor position cannot be detected using the induced voltage.

  As a DC brushless motor control method in such a case, an estimated phase method is known in which the energized phase is switched by estimating the rotor phase. In this estimated phase method, the current flowing through the DC brushless motor 30 is detected, and the motor current corresponds to a predetermined rotational speed using the relationship obtained in advance between the current and the rotational speed of the DC brushless motor 30. This is based on open loop control in which the rotor phase is estimated to be a value to be controlled and control is performed based on the estimation result.

  However, a ripple may occur in the DC voltage Vdc obtained by the step-up rectifying / smoothing circuit 10. When ripple occurs, the phase difference between the rotor position of the DC brushless motor 30 and the energization phase cannot be made constant.

  When the rotor position can be detected using the induced voltage, feedback control is performed, so even if ripples occur, the phase difference between the rotor position and the energized phase can be kept constant. If a ripple occurs in the DC voltage Vdc, the phase difference between the rotor position and the energization phase cannot be kept constant, the peak of the input current of the DC brushless motor 30 varies, or the rotation of the DC brushless motor 30 varies. In the worst case, the DC brushless motor 30 is stepped out or stopped.

  As a related technique, Patent Document 1 discloses a rotation control device for a DC brushless motor in which a rectified and smoothed voltage is PWM-modulated by a switching unit and applied to a DC brushless motor, and the rotation of the DC brushless motor is controlled. DC brushless motor comprising: ripple detecting means for detecting ripple voltage fluctuation of rectified and smoothed voltage; and duty correcting means for correcting duty of PWM signal for switching control of the switching means based on a detection signal from the ripple detecting means The rotation control device is published. However, the technique disclosed in Patent Document 1 does not relate to a case where the rotor position cannot be detected using the induced voltage.

Japanese Patent Laid-Open No. 4-96683

  The present invention has been made in view of the above, and an object of the present invention is to stabilize an input current without using a position detection signal even when ripples occur, and to prevent fluctuations in the rotational speed of a DC brushless motor. It is to provide a DC brushless motor control device that can suppress the occurrence of adjustment, stop, and the like.

  In order to achieve the above object, the invention according to claim 1 switches and controls energization of each magnetic pole of the DC brushless motor by driving means for supplying a DC voltage converted from the AC voltage to the winding of the DC brushless motor. In the DC brushless motor control device, a zero-cross point detecting means for detecting a zero-cross point of the AC voltage, and a switching time for calculating a switching time of the energized phase in the future from the target rotational speed and the switching time of the energized phase and outputting the same to the driving means A calculation unit; and a storage unit that stores a table in which a correction value of a switching time of the energized phase is recorded in association with an elapsed time from the zero cross point of the AC voltage, and the switching time of the energized phase to be calculated is the driving unit. The correction value of the switching time corresponding to the elapsed time from the zero cross point when being output to the table is read from the table, and is used to switch the switching Switching time of the calculated conduction phases between calculation means corrects to the and outputting to the drive unit.

  According to the present invention, even if a ripple occurs in the DC voltage, the phase difference between the rotor position and the energization phase can be made constant by obtaining the detection signal of the zero cross point of the voltage. It can be stabilized, and the occurrence of rotational fluctuation, step-out, stop, etc. of the DC brushless motor can be suppressed. At this time, it is not necessary to detect the rotor position of the DC brushless motor, and it is not necessary to detect the DC voltage, thereby realizing low cost.

1 is a circuit diagram of a DC brushless motor control device according to one embodiment of the present invention. FIG. It is explanatory drawing in case DC voltage contains a ripple. It is explanatory drawing of the content of the correction table of the DC brushless motor control apparatus of a present Example. It is a flowchart of the rotation speed control process of the DC brushless motor control apparatus of a present Example. It is a wave form diagram of operation | movement of the DC brushless motor control apparatus of a present Example. It is a circuit diagram of the conventional DC brushless motor control device.

  FIG. 1 shows the configuration of a DC brushless motor control apparatus according to one embodiment of the present invention. The step-up rectifier circuit 10 includes a step-up coil L, bridge-connected rectifier diodes D1 to D4, step-up capacitors C1 and C2, and a smoothing capacitor C3. The motor drive circuit (inverter) 20 includes transistors QU, QV, QW, QX, QY, QZ and a free-wheeling diode connected between the collector and emitter of each transistor. The sensorless brushless DC brushless motor 30 has three-phase windings 30u, 30v, and 30w on a stator, and a magnet is attached to a rotor (not shown). The zero cross detection circuit 40 detects the zero cross point of the input AC voltage Vac every half cycle of the AC voltage Vac. The microcomputer 50 measures the time passage by the timer 51 using the zero cross point detected by the zero cross detection circuit 40 as a reference point, and refers to the correction value of the correction table stored in advance in the storage unit 52 every predetermined time. At the same time, referring to the target rotational speed as the command value, the transistors QU, QV, QW, QX, QY, QZ of the motor drive circuit 20 are switched to change the energized phases of the three-phase windings 30u, 30v, 30w. Switch in a predetermined order.

  Since the DC voltage Vdc is a full-wave rectified input AC voltage Vac, when the capacity of the smoothing capacitor C3 is small or when the load of the DC brushless motor 30 is large, as shown in FIG. The pulsation waveform includes ripples. When the ripple occurs, the phase difference between the rotor position and the energization phase is not constant. As a result, the input current cannot be stabilized, and the rotation speed of the motor fluctuates according to the ripple.

  Therefore, in this embodiment, when the DC voltage Vdc has a specific ripple, a correction time for correcting the forced switching time is obtained so that the influence of the ripple of the DC voltage Vdc does not affect the operation of the DC brushless motor 30. As shown in FIG. 2, the correction time is set such that the forced switching time is lengthened when the DC voltage Vdc is low due to ripple, and conversely the forced switching time is shortened when the DC voltage Vdc is high. So that the phase difference is constant. The correction time is determined in advance by a test or the like. As a method for obtaining the correction time, for example, the DC brushless motor 30 to be controlled is driven with a DC voltage Vdc having a specific ripple. Thus, the influence of the DC voltage Vdc having the specific ripple on the motor control is extracted, and the correction time is determined so as to be the forcible switching time for canceling the influence. The correction time is calculated at each time point between the zero cross point of the AC voltage Vac and the next zero cross point (each time point obtained by dividing a period from the predetermined zero cross point to the next zero cross at an arbitrary time interval). The value is obtained by a test or the like, and stored in the correction table of the storage unit 52 of the microcomputer 50 in association with the elapsed time from the zero cross point (timer time by the timer 51).

  This correction table is, for example, as shown in FIG. t1, t2,... are elapsed times from the zero cross point, and are obtained as timer values of the timer 51. T1 is a correction time to be referred to when the time for outputting the forced switching time to be corrected to the motor drive circuit 20 is t1, and T2 is the time to output the forced switching time to be corrected to the motor drive circuit 20. Is a correction time to be referred to when t2 is t2.

  The correction time set in this table is set so that the value becomes 0 when all the correction times T1 to Tn of t1 to tn are added. This is to prevent the average rotational speed from fluctuating by correcting the forced switching time using this correction table.

  Further, the setting of the table is not limited to the present embodiment. For example, for the correction time (T1, T2,...), The time for performing the process of adding T1 to the correction time described later is t1. The table may be set as a correction time to be referred to when the correction time to be referred to is sometimes referred to, or when T2 is a time for performing a process of adding a correction time to be described later at t2.

  Next, an outline of the determination of the forced switching time in the present embodiment will be described. First, the rotational speed (target rotational speed) of the target DC brushless motor 30 input from the outside is compared with the current rotational speed (actual rotational speed). Since the DC brushless motor 30 of this embodiment does not have a means for detecting the rotational speed, the actual rotational speed is increased or decreased according to the comparison result of the target rotational speed (described later) and the actual rotational speed, which was output last time. The number of revolutions calculated based on the forced switching time (forced switching reference time) is used. Thereafter, the switching time of the forced switching reference time output last time is increased or decreased according to the comparison result. Further, the correction time obtained from the correction table is added to the corrected forced switching time (forced switching reference time output this time) to generate a forced switching setting time that is not affected by the ripple. Then, the energization switching of the energizing phase of the DC brushless motor 30 is performed using the forced switching setting time.

  FIG. 4 shows a flowchart for performing the above-described control by the microcomputer 50. The program shown in this flowchart is stored in the storage unit 52 and executed by the CPU. When the forced switching set time TA is set at the time ta shown in FIG. 5 after the target rotation speed is input, the forced switching reference time (the setting of this time from TA) that is the basis of the forced switching set time TA is set. The actual rotational speed of the DC brushless motor 30 is obtained based on the forced switching time obtained by subtracting the correction time added at the time, and the actual rotational speed is compared with the target rotational speed (S1). Is lower (S1-YES), the forced switching reference time that is the basis of the forced switching set time TA is decreased by a predetermined value (S2), and the actual rotational speed is less than the target rotational speed. Is higher (S1-NO, S3-YES), the forcible switching reference time based on the forcible switching setting time TA is increased by a predetermined value (S4). However, when the actual rotational speed matches the target rotational speed (S3-NO), the forced switching reference time that is the basis of the forced switching set time TA is left as it is.

  Then, the correction time Tb at the end time (timer value tb) of the forced switching set time TA is read from the correction table and added to the forced switching reference time obtained in steps S1 to S4 (S5). As described above, a new forcible switching setting time TB from the time of the timer value tb is set, so that it is output at the time of the timer value tb (S8), and the transistors QU and QV of the motor drive circuit 20 are output. , QW, QX, QY, QZ are set to the next energized phase switching state only during the forced switching setting time TB.

  As described above, in this embodiment, even if the DC voltage Vdc includes ripples, the forced switching reference time is corrected according to the elapsed time from the zero cross point, and the corrected forced switching reference time is calculated from the correction table. By adding the read correction time, the DC brushless motor 30 can be rotated at a constant speed. At this time, it is not necessary to detect the rotor position of the DC brushless motor 30, and it is not necessary to detect the DC voltage Vdc.

DESCRIPTION OF SYMBOLS 10: Boosting rectification smoothing circuit 20: DC brushless motor control apparatus 30: Sensorless type DC brushless motor 40: Zero cross detection circuit 50: Microcomputer 60: Position detection circuit

Claims (1)

In a DC brushless motor control apparatus that switches and controls energization of each magnetic pole of the DC brushless motor by a driving unit that supplies a DC voltage converted from an AC voltage to a winding of the DC brushless motor.
Zero-cross point detecting means for detecting a zero-cross point of the AC voltage;
A switching time calculating means for calculating a switching time of the energized phase in the future from the target rotational speed and the switching time of the energized phase, and outputting to the driving means;
Storage means storing a table in which the correction value of the switching time of the energized phase is recorded in association with the elapsed time from the zero cross point of the AC voltage;
The correction value of the switching time corresponding to the elapsed time from the zero cross point when the switching time of the energized phase to be calculated is output to the driving means is read from the table, and is calculated by the switching time calculating means using this value. A DC brushless motor control device that corrects the switching time of the energized phase and outputs the corrected phase to the driving means.

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