JP3237173B2 - Drive device for brushless DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a relative position between a magnet rotor and an armature winding based on an induced voltage induced in an armature winding of a brushless DC motor, and detects the detected relative position. The present invention relates to a brushless DC motor driving device that drives a brushless DC motor based on the following.

[0002]

2. Description of the Related Art A brushless DC motor is usually provided with a detector for detecting a magnetic pole position of a rotor.
Recently, the relative position between the magnet rotor and the armature winding is detected by the induced voltage induced in the armature winding in compressors used under high temperature and high pressure due to poor reliability. However, various detectors without the detector have been proposed. FIG. 4 shows a conventional brushless DC motor of this type. In FIG. 4, 1 is a DC power supply, 2 is an inverter, and 3 is a brushless DC motor. The inverter 2 includes six power transistors Q1 to Q6 and six diodes respectively connected in anti-parallel. The brushless DC motor 3 includes an armature winding 4 and a magnet rotor 5 connected in three phases. Reference numeral 6 denotes a position detection circuit, and reference numeral 7 denotes a microcomputer as drive signal generation means for controlling the inverter 2.

The position detecting circuit 6 is configured, for example, as shown in FIG. That is, for each phase, has a DC component removal circuit comprising a capacitor C ₁ and resistor R _1, a low-pass filter consisting of resistor R ₂ and capacitor C _2, the noise removing circuit comprising a resistor R ₃ and capacitor C ₃ And comparators 10a, 10b and 10c. Comparator 10a, 10b, respectively 10c, the low-pass filter triangular signal obtained by filtering by v _a, v _b, v and signal noise removal from _c, the v _a, v _b,
v neutral voltage of 3-phase star-shaped resistive coupling of _c v is compared with _n, the microcomputer, and outputs the rectangular wave signal Sa, Sb, and Sc representing the relative position.

At the time of startup, the microcomputer 7 cannot detect the position because no voltage is induced in the armature winding 4, so that the microcomputer 7 generates a synchronization signal whose frequency increases with time, and drives the inverter based on the synchronization signal. Signal U ',
V ', W' and U bar, V bar, W bar are output. The drive signals U ', V', W 'are OR signals provided for each phase.
The circuit 8 performs an OR operation with the chopping signal (Chop) to generate drive signals U, V, and W. That is, the upper-arm transistors Q _1, Q ₂ and Q ₃ are driven by chopped signals, and the lower-arm transistors Q ₄ , Q ₅ and Q ₆ are driven by non-chopped signals. When the brushless DC motor 3 rotates and a predetermined time has elapsed, the operation is switched to the position detection operation, and an inverter drive signal is output based on the output signals Sa, Sb, Sc of the position detection circuit 6.

FIG. 6 is a flowchart of the synchronous operation, and FIG. 7 is a timing chart thereof. Hereinafter, the operation of the synchronous operation will be described based on FIG. 6 with reference to FIG.
If there is a start command from step S1 to S2, step S
Proceeding to step 3, the frequency and the initial value of the voltage of the drive signal to be output are read from the table, the start is started in step S4, and the interrupt timer is started in step S5.
This interrupt timer counts the time T of the interrupt timing in FIG. This time T decreases as the frequency increases, and is calculated in step S7 based on the frequency read in start S6. Step S8 is a step waiting for an interrupt. That is, it waits for the interrupt timer to count the time T, and when the time T is counted, the process proceeds to step S12 to perform an interrupt, that is, to change the operation mode. Step S13
Then, the interrupt timer is set to the time T calculated in step S7, and the counting is started. Step S
In steps S13 to S16, after performing the mode calculation, the voltage value is read, and the duty ratio corresponding to the voltage value is calculated. Then, after outputting the drive signal of the duty ratio in step S17, the process returns to the main routine in step S18. In step S9 of the main routine, it is determined whether or not the conditions for switching from the synchronous operation to the position detection operation are satisfied. If the conditions for switching are not satisfied, step S6 is performed.
And the above operation is repeated. If the switching conditions are satisfied, the process proceeds to step S10, where the operation is switched to the position detection operation, speed control is performed in step S11, and then the normal operation is started.

[0006]

By the way, in the above-mentioned synchronous operation, the operation is started at a higher voltage (voltage with a larger duty ratio) than in the normal operation in order to stabilize the operation. Peak current when changing
(See FIG. 8), the power transistors Q _{1 to} Q ₆
However, there is a problem that a large capacity must be used. In addition, there is a problem that motor efficiency is poor due to large fluctuations in current. Therefore, an object of the present invention is to
Synchronization peak current during mode switching is reduced during operation, therefore, possible to reduce the capacity of the power transistor Q ₁ to Q _6, to provide a drive device for a brushless DC motor to be able to improve the motor efficiency during synchronous operation It is in.

[0007]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides an inverter 2 for energizing and interrupting a current to a three-phase armature winding 4 of a brushless DC motor 3; Position detecting means 6 for detecting the relative position between the magnet rotor 5 and the armature winding 4 based on the induced voltage induced in the inverter 2, and a drive signal for the inverter 2 based on a synchronization signal for a fixed time after the start-up. And a drive signal generation means 7 for generating a drive signal for the inverter 2 based on the output signal of the position detection means 6 after the lapse of the predetermined time. Generating means 7 for setting a time length of the mode of the drive signal at the time of synchronous activation;
One of the time lengths of the odd mode and the even mode is made shorter than the length set by the mode time length setting means, and the length set by the mode time length setting means is reduced by the shorter time length of the other. And a mode time length correcting means S7 'for making the length longer than the above.

[0008]

In the above configuration, at the time of synchronous startup, one of the time length of the odd mode and the time length of the even mode is shorter than the other, so that an increase in current in the mode having a shorter time length is suppressed, and Peak current becomes smaller. Therefore, the capacity of the switching element of the inverter 2 can be reduced, and the motor efficiency during synchronous startup can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. The driving device of this embodiment has the same configuration as the conventional device shown in FIG. 4, but the microcomputer 7 of this embodiment performs the operation shown in FIG. 1 instead of the conventional operation shown in FIG. It has a circuit configuration. Hereinafter, the operation of the present embodiment will be described based on the flowchart of FIG. 1 and the timing chart of FIG. The flowchart of FIG. 1 is the same as the flowchart of FIG. 6 except that an interruption time correction routine (steps S21 to S25) of step S7 'is inserted between steps S7 and S8. The same steps are denoted by the same reference numerals and description thereof will be omitted.

In the above interrupt time correction routine, if the interrupt time in the conventional example is T ', the interrupt time T is 0.75T' in the odd mode and T = 1.25T 'in the even mode. I have to. That is, the time in the odd mode is shorter than the time in the even mode. This is because it is chopping the transistor Q ₁ ~Q ₃ of the upper arm, the lower arm transistor Q4
This is because the peak current is reduced by reducing the current at the point when Q6 turns ON (when switching from the odd mode to the even mode).

For example, comparing the current waveform in the present embodiment shown in FIG. 3 with the current waveform in the conventional example shown in FIG. 8, when the mode is switched from mode 1 to mode 2, the time of mode 1 in the conventional example is Since the current value at the end of mode 1 is high because of the long time, the current value at the end of mode 2 is high. However, in this embodiment, the current at the end of mode 1 is small because the time of mode 1 is short. The current at the end of mode 2 is also small. As described above, when chopping the upper-arm transistor, the peak value of the current can be suppressed to a small value by making the time in the odd mode shorter than the time in the even mode. Conversely, when chopping the transistors in the lower arm, the time in the even mode may be shorter than the time in the odd mode. As described above, by changing the ratio between the odd mode time and the even mode time during the synchronous operation, the peak current can be suppressed to a small value.
The capacity of ₁ to Q ₆ can be reduced, thereby improving the motor efficiency during synchronous operation.

[0012]

As is apparent from the above description, in the drive device for a brushless DC motor according to the present invention, the drive signal generating means for generating the drive signal for the inverter sets the time length of the mode of the drive signal at the time of synchronous startup. Mode time length setting means, and one of the time lengths of the odd mode and the even mode is made shorter than the time length set by the mode time length setting means, and the other time length is shortened by the above-mentioned mode. Since a mode time length correction means is provided which is longer than the length set by the time length setting means, the peak current can be reduced, and therefore, the capacity of the inverter switching element can be reduced, and the motor efficiency during synchronous startup is improved. Can be done.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 2 is a timing chart of the embodiment.

FIG. 3 is a current waveform diagram of the embodiment.

FIG. 4 is a block diagram of a general brushless DC motor driving device.

FIG. 5 is a detailed diagram of the position detection circuit of FIG.

FIG. 6 is a flowchart showing the operation of the conventional example.

FIG. 7 is a timing chart of the conventional example.

FIG. 8 is a current waveform diagram of the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Inverter, 3 ... Brushless DC motor, 4 ... Armature winding, 5 ... Magnet rotor, 6 ... Position detection circuit, 7 ... Microcomputer, Q1-Q6 ... Power transistor.

Claims (1)

(57) [Claims] An inverter (2) for energizing and interrupting a current to a three-phase armature winding (4) of a brushless DC motor (3).
Position detecting means (6) for detecting a relative position between the magnet rotor (5) and the armature winding (4) based on an induced voltage induced in the armature winding (4); A drive signal for the inverter (2) is generated based on the synchronization signal for a predetermined time, and a drive signal for the inverter (2) is generated based on an output signal of the position detection means (6) after the predetermined time has elapsed. A drive device for a brushless DC motor comprising a drive signal generation means (7), wherein the drive signal generation means (7) is a mode time length setting means for setting a time length of a mode of the drive signal at the time of synchronous startup.
(S7) setting one of the time lengths of the odd mode and the even mode to be shorter than the length set by the mode time length setting means, and setting the mode time length by the shortened other time length. A brushless DC motor driving device, comprising: a mode time length correcting means (S7 ') for making the length longer than the length set by the means.