JPH05219785A - Driving device for brushless motor - Google Patents

Abstract

PURPOSE:To prevent torque increase and the step-out of a motor from being generated at the time of switching by lowering the applied voltage of the motor before synchronous operation is switched to position detecting operation. CONSTITUTION:To a DC power source 1, an inverter circuit (IV) 2 is jointed, and to the AC output end of the IV 2, the armature winding 4 of a brushless motor 3 is jointed. With a position detecting circuit 6, the magnetic pole positions of a magnet rotor 5 are detected by detecting voltage with a counter- electromotive force to be induced to the armature winding 4. By a micro-computer (MP) 7, the 6 transistors of the IV 2 are controlled in specified order, based on start signal. To a pulse width modulation circuit 8, chop signal from the MP 7 is applied, and the duty of voltage for electrifying the transistors of U, V, W phases is varied. Besides, immediately before switching conditions are regulated, the voltage is slightly lowered. When the switching conditions are regulated, then synchronous operation is switched to position detecting operation with the counter-electromotive voltage, and a speed is controlled due to position detecting operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor using an inverter circuit, and more particularly, to a voltage signal induced in an armature winding of a brushless motor having a magnet rotor to detect the voltage signal. The present invention relates to a brushless motor drive device that detects a relative position with respect to a child winding and drives and controls the motor based on the detected position.

[0002]

2. Description of the Related Art In a brushless motor drive device,
Detects the counter electromotive force induced in the armature winding without using a position detection element such as a Hall element to detect the relative position between the stator armature winding and the permanent magnet rotor. The scheme is known. In this method, since the back electromotive force is induced in the armature winding only when the rotor is rotating, magnetic pole position information cannot be obtained when the rotor is stopped. Therefore, at the time of startup, a synchronous startup method is used in which the motor is started as a synchronous machine. That is, at the time of start-up, regardless of the magnetic pole position of the rotor, a drive signal that causes a rotating magnetic field is applied to the armature winding, the frequency is gradually increased, and then the counter electromotive force is applied to the armature winding. Switch to position detection operation when is sufficiently generated.

However, if a voltage is applied while ignoring the magnetic pole position of the rotor at the time of starting, a large starting current will flow at the time of starting. As a method of solving this problem, so-called pulse width modulation, which controls the voltage by controlling the duty ratio of the voltage pulse applied to the motor at the time of start-up, as disclosed in, for example, Japanese Patent Laid-Open No. 2-197291, is adopted. It has been proposed that the duty ratio and the frequency of the output signal for the synchronous operation are increased with time along a straight line having a constant slope.

[0004]

However, in the above method, in order to increase the stability at the time of starting, it is necessary to start with a higher voltage. At that moment, the torque rapidly increases. Therefore, when such a start-up method is used, for example, in the operation of a compressor of an air conditioner, there is a risk that stress may be applied to the refrigerant pipes and the motor may lose step due to a transient phenomenon. The present invention is to solve the above-mentioned problems, and in a starting method for switching from synchronous operation to position detection operation, while stabilizing the operation at the time of start,
An object of the present invention is to provide a brushless motor drive device that can smoothly switch without causing a sudden increase in torque at the time of switching and without causing a step out of the motor.

[0005]

To achieve the above object, the present invention provides a position for detecting the voltage induced in the armature winding of a brushless motor having a magnet rotor to detect the position of the rotor. A detection circuit, an inverter circuit having a switching element for converting a DC voltage into an AC voltage to supply a voltage to the brushless motor, and a switching element of the inverter circuit are drive-controlled according to a signal from the position detection circuit. In a brushless motor drive device including a control circuit, the control circuit increases a frequency of a rotating magnetic field generated in an armature winding of the motor and a duty ratio of a motor applied voltage in a predetermined pattern for a certain period of time after the motor is started. The inverter circuit is controlled so that the voltage applied to the motor is decreased by a predetermined value immediately before the elapse of a certain time, and the position is adjusted after the elapse of the predetermined time. Based on a signal from the detection circuit is obtained so as to control the inverter circuit.

[0006]

According to the above construction, the control circuit increases the frequency of the rotating magnetic field generated in the armature winding and the duty ratio of the motor applied voltage in a predetermined pattern for a fixed time after the motor is started, and immediately before the fixed time elapses. In addition, the inverter circuit is controlled so that the duty ratio of the motor applied voltage is reduced by a predetermined value. After a certain period of time, the inverter circuit is controlled based on the signal from the position detection circuit that detects the rotor position from the voltage induced in the armature winding. By switching from the synchronous operation to the position detection operation in this way, the torque does not suddenly increase at the moment of switching.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a main configuration of a brushless motor driving device. In FIG. 3, an inverter circuit 2 for converting a DC voltage into an AC voltage is connected to a DC power supply 1, and an armature winding of a brushless motor 3 is connected to an AC output terminal of this inverter circuit 2. The inverter circuit 2 connects the transistors, which are six switching elements, in a three-phase bridge connection,
A diode is connected in parallel with each transistor. The brushless motor 3 comprises a three-phase armature winding 4 star-connected to the stator and a permanent magnet rotor 5. The position detection circuit 6 detects the magnetic pole position of the magnet rotor 5 by detecting the voltage due to the back electromotive force induced in the armature winding 4 of the brushless motor 3. This position detection signal Sa, S
b and Sc are input to the microcomputer 7 as a control circuit for driving and controlling the brushless motor 3.

The microcomputer 7 conducts the conduction of U, V, W and the six transistors of each phase of U-bar, V-bar, W-bar of the inverter circuit 2 in a predetermined procedure based on a predetermined start signal. Control. Microcomputer 7
A pulse width modulation circuit 8 is interposed on the output lines from the U ', V'and W'terminals. This pulse width modulation circuit 8
Is supplied with a chop signal output from the microcomputer 7, and the chop signal causes U, V, W
The duty of the voltage for conducting the phase transistors is changed. The outputs from the U-bar, V-bar and W-bar terminals of the microcomputer 7 control the conduction of the U-bar, V-bar and W-bar phase transistors.

Next, the starting operation of the apparatus of this embodiment will be described. FIG. 1 shows a temporal change pattern of the voltage and frequency applied to the motor from the synchronous operation to the position detection operation at the time of starting the motor, and FIG. 2 shows the same conventional pattern. Figure 1
As shown in FIG. 5, in the present invention, the voltage and the frequency are gradually increased from the start in a predetermined pattern, and then the voltage is slightly decreased immediately before the switching to the position detection operation. 4 and 5 are flowcharts of the motor starting operation processing and the interrupt processing by the microcomputer 7 in the apparatus of this embodiment. FIG. 6 is a time chart of signals before and after switching from the synchronous operation to the position detection operation.

The procedure of the starting operation will be described below with reference to FIGS. If the start signal is turned on (YE in # 1
S), start a timer for measuring the startup time (t) (# 2). Next, a predetermined start-up mode M0 and start-up voltage V0 for the synchronous operation are set (# 3) and started (# 4). The motor operation mode is set from 0 to 5 in this embodiment, and a predetermined phase of the armature winding is energized for each mode. After the start, the interrupt timer for updating the mode is started (# 5), and the frequency f at that point is determined from the change pattern with respect to time as shown in FIG. 1 which is preset and stored in the table or the like. Then, (t) is read (# 6), the next interrupt time is calculated (# 7), and then the interrupt is waited (# 8).

The interrupt time T in the mode 1 section has a relation of the reciprocal of the frequency. For example, T = {1 / 2πf
(T)} × (1/6) Therefore,
At the time of the low frequency immediately after the start, the interruption time T, that is, the section of 1 mode is long, and the section becomes shorter as the frequency gradually increases. After # 8, it is checked whether or not the switching conditions are satisfied (# 9), and the processes from # 6 to # 8 are repeated until the switching conditions are satisfied. As this switching condition, it is possible to adopt whether or not the time from the start, for example, 5 seconds has elapsed.

When the timer is up, that is, the interrupt time is reached, the interrupt process of FIG. 5 starts. In this process, the timer for the next interrupt is restarted (# 21),
And the mode to be set is calculated (# 22). Here, the modes 0 to 5 are sequentially incremented by 1,
Mode 0 is followed by mode 0. Then, the voltage value V
(T) is read (# 23), and the duty of the voltage is further calculated (# 24). This calculation is obtained by the ratio of the voltage value Vdc of the DC power supply 1 to the previously read voltage value V (t), and the voltage value V (t) is chopped so that the duty becomes this duty. It can be applied to the motor. After that, the signal for driving the motor is output in the mode obtained above (# 2
5), the process returns.

Frequency f (t) read in # 6 above
Then, the voltage value V (t) read in # 23 gradually rises with the passage of time in the pattern shown in FIG.
Just before reaching the almost constant value and the switching conditions met in # 9,
For example, after 4.9 seconds from the start, the voltage is slightly decreased. This reduction amount may be, for example, about 20%.
When the switching conditions are satisfied in # 9, the synchronous operation is switched to the position detection operation by the back electromotive force (# 1
0) and thereafter, speed control by the same position detection operation is performed (#
11).

Further, in FIG. 6, time tx shows the timing for lowering the voltage, and time ty shows the switching timing. At this point in time when the switching time is reached, the position detection signals Sa, Sb, S from the position detection circuit 6 are sufficiently large.
c is obtained. By performing such start-up control, it is possible to prevent the torque from rapidly increasing at the time of switching to the position detection operation, and it becomes possible to perform the switching smoothly. Therefore, even when the present brushless motor is used for driving a compressor, for example, stress is not applied to the pipes or the motor is out of step due to a transient phenomenon.

[0015]

As described above, according to the present invention, in the starting method for switching the brushless motor from the synchronous operation to the position detection operation, the voltage applied to the motor is slightly lowered immediately before the switching. Even if a high voltage is applied to stabilize the start-up during synchronous operation, a sudden torque increase does not occur at the time of operation switching, the motor does not get out of step, and a smooth position is achieved. It is possible to switch to the detection operation.

[Brief description of drawings]

FIG. 1 is a diagram showing changes over time in a voltage applied to a motor and a frequency by a brushless motor driving device of the present invention.

FIG. 2 is a diagram showing a time variation of a motor applied voltage and a frequency in a conventional brushless motor.

FIG. 3 is a configuration diagram of main parts of a brushless motor driving device according to an embodiment of the present invention.

FIG. 4 is a flowchart of a startup operation of the device.

FIG. 5 is a flowchart of an interrupt operation in a start operation of the device.

FIG. 6 is a time chart showing the operation before and after the operation switching in the same device.

[Explanation of symbols]

 2 Inverter circuit 3 Brushless motor 4 Armature winding 5 Permanent magnet type rotor 6 Position detection circuit 7 Microcomputer (control circuit) 8 Pulse width modulation circuit

Claims (1)

[Claims] 1. A position detection circuit for detecting a voltage induced in an armature winding of a brushless motor having a magnet rotor to detect the position of the rotor, and a switching element for converting a DC voltage into an AC voltage. A brushless motor drive device comprising an inverter circuit for converting and supplying a voltage to the brushless motor, and a control circuit for driving and controlling a switching element of the inverter circuit according to a signal from the position detection circuit, Is to increase the frequency of the rotating magnetic field generated in the armature winding of the motor and the duty ratio of the motor applied voltage in a predetermined pattern for a certain time after starting the motor, and decrease the motor applied voltage by a predetermined value immediately before the elapse of the certain time. The inverter circuit is controlled as described above, and after a certain period of time, the inverter circuit is controlled based on the signal from the position detection circuit. A drive device for a brushless motor characterized by being controlled.