JPH0681545B2 - Brushless DC motor drive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a drive device for a brushless DC motor, and more particularly to a drive for a brushless DC motor for a compressor mounted in an air conditioner, a refrigerator or the like. It relates to the device.

[Prior Art] FIG. 5 is a circuit configuration diagram showing a conventional brushless DC motor drive device disclosed in, for example, Japanese Patent Laid-Open No. 61-1290. Further, each of (a) of FIGS. 6 to 8 is a characteristic diagram showing the relationship between the time and the output frequency at the time of starting the motor by the conventional brushless DC motor driving device, and FIGS. Similarly, each (b) is a characteristic diagram showing the relationship between time and phase current corresponding to (a) in each figure.

In the figure, (1) is an inverter circuit that converts direct current to alternating current, and is a switching element such as a power transistor.
It is composed of T _{U to} T _Z and diodes D _{U to} D _Z.
(2) is a brushless DC motor whose drive is controlled by the inverter circuit (1), and (3) is position detection for detecting the position of the rotor based on the voltage across the armature windings of the brushless DC motor (2). circuit, (4) is a control circuit for appropriately controlling the operation of the inverter circuit (1) by supplying an operation signal to the respective switching elements T _U through T _Z of the inverter circuit (1). (5) is a current detector that detects the current supplied to the inverter circuit (1), and (6) outputs a current limiting signal to the control circuit (4) based on the detection value of the current detector (5). It is a current limiting circuit.

The conventional brushless DC motor drive device is configured as described above, and operates as follows.

First, a switching signal corresponding to preset frequency data and output voltage data is output from the control circuit (4) to each of the switching elements T _{U to} T _Z of the inverter circuit (1). Upon receiving this signal, the inverter circuit (1) is activated, the DC power applied to the inverter circuit (1) is converted into AC of a predetermined frequency and voltage, and supplied to the brushless DC motor (2). It Upon receiving the signal from the inverter circuit (1), the brushless DC motor (2) starts low frequency activation.

When the brushless DC motor (2) is started, an induced electromotive force is generated in the armature winding as the number of rotations of the rotor increases. Then, the position detection circuit (3) detects the position of the rotor based on the voltage between the terminals of the armature winding due to the induced electromotive force, and this detection signal is transmitted to the control circuit (4).

Next, the control circuit (4) compares the switching signal transmitted up to that time with the detection signal from the position detection circuit (3), and when both signals are synchronized at a predetermined switching maximum frequency or less after a certain time has elapsed. ((C in FIG. 6 (a)
Point), the control circuit (4) controls the inverter circuit (1) by controlling the inverter circuit (1) by another control, that is, from asynchronous operation to synchronous operation, and continues driving the inverter circuit (1) (see FIG. 6).

If an overcurrent occurs during this switching (point D in (a) of FIG. 7), the current limit circuit (6) changes the control circuit (4) based on the detection value of the current detector (5). ) Is output to the stop signal. As a result, the inverter circuit (1)
The output of the switching signal to is stopped (see FIG. 7).

Even if the switching maximum frequency is reached, if the synchronization is not achieved ((a) in FIG. 8), the switching signal output from the control circuit (4) up to then is stopped as a start failure (see FIG. 8). ).

[Problems to be Solved by the Invention] In the conventional brushless DC motor driving device as described above, since the switching operation from another system to the synchronous system is performed under a relatively high frequency state, an overcurrent is likely to occur. It was Further, when the switching signal from the control circuit (4) to the inverter circuit (1) is stopped due to the occurrence of this overcurrent or the failure of synchronization, it is necessary to perform the starting operation again by the other system from the beginning. was there. Therefore, these stop requests are likely to overlap with each other, and the stop requests may be continuously made. Therefore, the brushless DC motor (2) may be stopped for a long time.

Therefore, smooth operation of a system such as an air conditioner or a refrigerator may be hindered.

Therefore, an object of the present invention is to provide a drive device for a brushless DC motor, which can ensure synchronous start-up in a safe state by a low frequency and can ensure smooth operation on the load side.

[Means for Solving the Problems] A brushless DC motor drive device according to the present invention is
An inverter circuit (1) for driving the brushless DC motor (2) by switching from another system to a synchronous system after starting by another system control, and the brushless DC motor (2)
Of a position detection circuit (3) for detecting the position of the rotor based on the voltage between the terminals of the armature winding at the time of starting, and the inverter circuit (1) at the time of other control of the inverter circuit (1). The output frequency is raised and lowered within a predetermined range, and when the output frequency is in the lowered state, the control of the inverter circuit (1) is changed from other control to synchronous control based on the position detection signal from the position detection circuit (3). And a control circuit (7) for switching.

[Operation] In the present invention, when the brushless DC motor (2) is started, the inverter circuit (1) is controlled by another control, and the output frequency of the inverter circuit (1) at this time is increased or decreased within a predetermined range. When the output frequency is in a decreasing state, the control of the inverter circuit (1) is switched from the other control system to the synchronous system to drive the brushless DC motor (2). It is possible to suppress, and it is possible to reliably perform synchronous startup at a low frequency under safe conditions.

[Embodiment] FIG. 1 is a circuit configuration diagram showing a drive device of a brushless DC motor according to an embodiment of the present invention. In the figure,
Since (1) to (3), (5), and (6) are the same as or equivalent to the above-described conventional example, duplicate description will be omitted here.

In the figure, (7) is a control circuit including a microcomputer for controlling the operation of the inverter circuit (1) by supplying a switching signal to the switching elements T _{U to} T _Z of the inverter circuit (1), and a memory (7a ) And a counter (7b). Also in this embodiment, the position detection circuit (3) for detecting the position of the rotor based on the voltage across the armature winding of the brushless DC motor (2),
Further, it is provided with a current limiting circuit (6) for outputting a current limiting signal to the control circuit (7) based on the detection value of the current detector (5).

The drive device for the brushless DC motor of this embodiment is configured as described above and operates as follows. The operation of this embodiment will be described along the flow of the flowchart of FIG.

FIG. 2 is a flow chart showing the operation of the brushless DC motor drive device of this embodiment, and each (a) of FIGS. 3 and 4 shows the time when the motor is started by the brushless DC motor drive device of this embodiment. It is a characteristic view showing a relationship with an output frequency, and each (b) of FIGS. 3 and 4 is a characteristic view showing a relationship between a time and a phase current corresponding to each (a) of each drawing.

First, in step S1, the preset other control data is read. This control data is stored as a table in the memory (7a) of the control circuit (7). In step S2, and outputs a switching signal based on the output frequency rising data in the control data of the other formality from the control circuit (7) to each of the switching elements T _U through T _Z of the inverter circuit (1). Therefore, receiving the signal, the output frequency of the inverter circuit (1) increases. In step S3, it is determined whether or not the current rising output frequency has reached the maximum frequency in the other system control stored in the memory (7a). If the current output frequency is lower than this maximum frequency, the process returns to step S2 again, and the operations of steps S2 to S3 are repeated. That is, the switching signal based on the output frequency increase data is output until the output frequency of the inverter circuit (1) reaches the maximum frequency. on the other hand,
When it is determined in step S3 that the current output frequency has reached the maximum frequency stored in the memory (7a), the process proceeds to step S4, and this time the switching is performed based on the output frequency decrease data in the control data of the other system. Signal from control circuit (7) to each switching element of inverter circuit (1)
Output to T _{U to} T _Z. Therefore, receiving the signal, the output frequency of the inverter circuit (1) decreases. While the output frequency is in the decreasing state, the switching signal from the control circuit (7) and the position detection signal from the position detection circuit (3) are compared in step S5 to check whether the two signals are in synchronization with each other. Determine whether or not. If it is determined that both signals are synchronized (point A in FIG. 3 (a)), step S6
Then, the control of the brushless DC motor (2) is continued by switching from the other control to the synchronous control.

The series of operations described in steps S1 to S6 above are shown in the characteristic diagrams of FIGS. 3A and 3B. It should be noted that FIG. 3 shows a case where the output frequency is synchronized with the first rising and falling operations.

On the other hand, if it is determined in step S5 that the switching signal from the control circuit (7) and the position detection signal from the position detection circuit (3) are not synchronized, the current output frequency that is descending is determined in step S8. It is determined whether or not the minimum frequency has been reached during the other system control. This minimum frequency is also stored in the memory (7a) of the control circuit (7). And if the current output frequency, which is still falling, is higher than the minimum frequency,
Again, return to step S4, step S4 from the above
Repeat the operation of S8. That is, the switching signal based on the output frequency decrease data is output until the output frequency of the inverter circuit (1) reaches the minimum frequency. If synchronization is confirmed while the output frequency is decreasing (step S5), synchronous control is started (step S6). When it is determined in step S8 that the current output frequency that is decreasing has reached the minimum frequency, the process proceeds to step S9, and the counter (7b) of the control circuit (7) adds the number of times the output frequency is decreased. Then, in step S10, it is determined whether or not the number of lowering times has reached the set number of times stored in the memory (7a). If the number of times of lowering is still less than the set number of times, in order to increase the output frequency, the step S2 is performed again.
Return to and repeat the above series of operations. But step S1
When the number of lowering reaches the set number at 0, it is determined that the starting is impossible, and in step S11, the output of the switching signal from the control circuit (7) to the inverter circuit (1) is quickly stopped.

FIGS. 4A and 4B show the case where the output frequency is synchronized with the second lowering operation. That is, it indicates that the synchronization is made at point B in FIG.

The synchronous control of the inverter circuit (1) in step S4 is continued according to a predetermined routine until the stop signal is input. This stop command is transmitted in step S7 by sequence control or manual control. Then, the drive of the brushless DC motor (2) is stopped by this stop command.

Although not shown in FIG. 2, in this embodiment also, when an overcurrent occurs during the switching operation from the other control system to the synchronous system, the current limiting circuit ( 6)
Outputs a stop signal to the control circuit (4), which stops the output of the switching signal to the inverter circuit (1).

As described above, the brushless DC motor drive device of this embodiment is provided with the other control system of the inverter circuit (1) that continuously drives the brushless DC motor (2) after it is activated by the other control system and then switched to the synchronous system. The output frequency at the time of control is increased and decreased within a predetermined range (within the range of the preset maximum frequency to the minimum frequency). A position detection circuit (3) for detecting the position of the rotor from the voltage between the terminals of the armature winding when the brushless DC motor (2) is started when the output frequency is in a decreasing state. Based on the signal, the control of the inverter circuit (1) is switched from the other system to the synchronous system by the control circuit (7). In particular, in this embodiment, the increase and decrease operations of the output frequency in the case of the control of the inverter circuit (1) in the other control system are repeated a predetermined number of times until the control is switched from the other control system to the synchronous system. Then, the stop signal is transmitted to the inverter circuit (1) only when it cannot be started without synchronizing.
Moreover, in the unlikely event that an overcurrent occurs during the switching operation from the other control system to the synchronous system, the stop signal is output from the current limiting circuit (6) to the control circuit (4).

Therefore, when the control of the inverter circuit (1) is switched from the other control system to the synchronous system, it is possible to suppress the occurrence of overcurrent, which has been apt to occur in the past, so that the synchronous start at a low frequency is surely performed under an extremely safe condition. it can. As a result, safe and reliable starting is possible, and the brushless DC motor (2) may be in a stopped state for a long time due to continuous stop requests that have been pointed out in the past. It can be avoided, and the smooth operation of the system such as the air conditioner or the refrigerator can be ensured.

By the way, in the above-described embodiment, when the output frequency of the inverter circuit (1) is once increased during the other-type control and the output frequency is not synchronized in the subsequent falling state, the output frequency is increased and decreased again. However, the second and subsequent raising and lowering operations do not necessarily have to be based on the initially set output frequency raising and lowering data, and may be appropriately changed according to the number of times the output frequency raising and lowering operations are repeated. You may set it to and make the start-up more reliable.

[Effects of the Invention] As described above, the brushless DC motor drive device of the present invention controls the inverter circuit by other control when the brushless DC motor is started, and the output frequency of the inverter circuit at this time is within a predetermined range. Ascend and descend,
When the output frequency is in a falling state, the control of the inverter circuit is switched from the other system to the synchronous system to drive the brushless DC motor, so that the generation of overcurrent is suppressed during this switching, and the low frequency Since the synchronous start can be surely performed, safe and reliable start can be performed, and smooth operation of the load of the air conditioner or the refrigerator can be ensured.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a brushless DC motor drive device according to an embodiment of the present invention, and FIG. 2 is a flowchart showing an operation example of the brushless DC motor drive device according to an embodiment of the present invention. Each of FIGS. 4A and 4A is a characteristic diagram showing a relationship between a motor starting time and an output frequency by the brushless DC motor driving device according to the embodiment of the present invention, and FIG. FIG. 5 is a characteristic diagram showing a relationship between time and phase current corresponding to (a), FIG. 5 is a circuit configuration diagram showing a conventional brushless DC motor drive device, and (a) of FIGS. 6 to 8 are conventional diagrams. FIG. 4B is a characteristic diagram showing the relationship between the time and the output frequency at the time of starting the motor by the brushless DC motor driving device of FIG. 4B, and FIG. 6B is a characteristic diagram showing the relationship between time and phase current corresponding to FIG. It is a figure. In the figure, 1: inverter circuit 2: brushless DC motor 3: position detection circuit 7: control circuit 7a: memory 7b: counter. In the drawings, the same reference numerals and symbols indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An inverter circuit for starting a brushless DC motor by another control and then switching the driving from the other control to a synchronous system, and an inverter circuit based on a voltage between terminals of an armature winding when the brushless DC motor is started. A position detection circuit for detecting the position of the rotor; and an output frequency of the inverter circuit that rises and falls within a predetermined range when the control of the inverter circuit is controlled, and when the output frequency is in a falling state, And a control circuit for switching the control of the inverter circuit from other control to synchronous control based on a position detection signal from the position detection circuit.