JP2533472B2 - Method of starting brushless DC motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting a brushless DC motor of the type in which rotor position detection is performed by using armature winding terminal voltage, and in particular, an inverter of a motor drive source. The present invention relates to a method for starting a brushless DC motor that ensures starting when a low-frequency synchronous starting method that starts as a synchronous motor as another system only when starting is adopted.

[Background of the Invention]

A technique of a brushless DC motor in which a rotor position detection signal is obtained from a terminal voltage of an armature winding through a filter circuit without providing a position detection sensor such as a hall element on the shaft end side of the rotor It is disclosed in Japanese Patent Publication No. Sho 52-80415. In this type of brushless DC motor, since an induced voltage is not generated in the armature winding at the time of starting, it is necessary to start it by some means up to the rotation speed at which the rotor position detection signal is generated. As this starting method, the inverter used as the drive source of the brushless DC motor, the other system only at the time of starting, to start as a synchronous motor, so-called low frequency synchronous starting method is shown in JP-A-58-29380. There is disclosed a technique of starting the synchronous motor after detecting that the synchronous motor is stopped.

However, when the synchronous motor in the stopped state is started, the stop position of the rotor is not taken into consideration, and the winding current applied to the armature winding of the synchronous motor and the magnitude of the load torque applied to the synchronous motor are No consideration was given to relevance. Furthermore, in order to reliably perform low-frequency synchronous startup, it is necessary to change the magnitude of the winding current according to the load torque, but in general the magnitude of the load torque is unknown, It has been difficult in the past to reliably start it.

[Object of the Invention]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the prior art and to provide a starting method for a brushless DC motor that can surely perform low frequency synchronous starting regardless of the magnitude of load torque.

[Outline of Invention]

In order to achieve the above-mentioned object, the outline of the present invention is to set a positioning mode prior to a period in which a three-phase inverter used as a motor drive source is operated in a separate control mode. When the flow direction is fixed to any one, the magnitude of the current flowing in this winding is gradually increased to the current value corresponding to the assumed maximum load, and when shifting to other control operation The starting method is performed after stopping the increase of the current and switching to the flow direction to the armature winding in which torque is generated in the direction in which the desired rotation direction is obtained.

That is, when the maximum output torque of the synchronous motor is T _MX during low frequency synchronous start, if a winding current commensurate with the torque constant (output torque / winding current) of the synchronous motor is applied to the armature winding, When the sum of the acceleration torque T _ac and the load torque T _L is less than or equal to the maximum output torque T _MX , the synchronous motor can be accelerated without step-out. However,
When a winding current is supplied to the synchronous motor such that the output torque becomes excessive with respect to the load torque applied to the synchronous motor, the following phenomenon occurs and the startup fails. Immediately after the start of low-frequency synchronous startup, in the 60-degree winding conduction mode that is first energized, if the current flowing in the armature winding is too large to correspond to the load torque,
The rotor stopped at an arbitrary position rotates in the direction of the position where the output torque becomes zero in the above-mentioned flow mode, overshoots that position by the inertia torque, and continues to rotate regardless of the flow mode. Depending on the arbitrary stop position, the rotation continues in the direction opposite to the desired rotation direction.

In order to solve the above-mentioned problems, the present invention adopts the above-mentioned method, whereby the rotor is moved and fixed to a position where the output torque becomes zero, and then the flow mode is set. Is to change and accelerate.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the overall structure of a brushless DC motor that is started by the starting method of the present invention. The DC voltage E _d is supplied from an AC power source 1 via a rectifier circuit 2 and a smoothing capacitor 3.
Is obtained and supplied to the inverter 4. The three-phase AC output of the inverter 4 is applied to the armature winding 5-1 of the synchronous motor 5 to drive the rotor 5-2 having a permanent magnet as a field. .

The inverter 4 includes six transistors A ⁺ , B ⁺ , C ⁺ ,
A ^-, B ^-, C ^- and consists of six reflux diodes D1 to D6. A 120-degree energizing inverter that energizes two of the three-phase armature windings. Further, among the above six transistors, only the transistors A ^{+ to} C ⁺ connected to the positive potential side of the DC voltage E _d are modulated by the checker signal CHP during the 120-degree conduction period, and the checker signal CHP is used. Controls the winding current by changing the conduction ratio of. In addition, DC voltage
Transistor A negative potential line side of the E _d ^- -C ^- common emitter and the terminal, a low resistance R1 is connected between the common anode terminal of the freewheeling diode D4 to D6, the armature current I _L flowing through the low resistance R1 The winding current flowing through the winding is detected from the voltage drop across the low resistance R1.

The control circuit uses a single-chip microcomputer 7, a position detection circuit 6 for detecting the magnetic pole position of the rotor 5-2 of the synchronous motor 5, and a winding current I _L of the synchronous motor 5 as a desired value ID.
R current control circuit 8 and transistor A ⁺ ~
It is composed of a base drive circuit 9 of C ⁺ , A ^{− to} C ⁻ . The position detection circuit 6 is the position detection circuit disclosed in Japanese Patent Laid-Open No. 52-80415, and the armature winding voltage of the synchronous motor 5 is used.
From V _{A to} V _C , a position detection signal 65 corresponding to the rotor magnetic pole position is generated and output via a filter circuit (not shown). The microcomputer 7 is a single chip such as HD6805V1 and used for CPU, ALU7-4, RAM7-5, ROM7.
-6, timer 7-7, input / output port registers 7-1 to 7-1
7-3 is built in. The ROM 7-6 includes various processes necessary for driving the brushless DC motor, for example, the drive signal 95 is output to the transistor for low frequency synchronous activation, and the position detection signal 65 is fetched for position detection operation. A program such as an output of the drive signal 95 corresponding to the position detection signal is stored.

FIG. 2 is a detailed circuit diagram of the current limiting circuit 8 in FIG. The current limiting circuit 8 includes an amplifier 10, a comparator 11 having a hysteresis characteristic, and a D / A converter 12. The amplifier 10 amplifies the voltage drop of the low resistance R1 described above and outputs it as a current detection value V _IL . The D / A converter 12 exchanges the 8-bit desired current value IDR output via the output port register 7-2 in the microcomputer 7 with the desired analog current value IDRA which is an analog quantity. comparator
At 11, the detected current value V _IL and the desired analog current value IDRA are compared, a checker signal CHP is created, and the winding current I _L is controlled according to the desired current value IDR. Note that R2 to R6 are resistors that are inserted and arranged at the positions shown in the figure.

In the above circuit configuration, the starting method of this embodiment operates as follows.

FIG. 3 (a) shows that during the period of low frequency synchronous activation,
The conduction modes of the six transistors forming the inverter 4 are shown, (b) shows the desired analog current value IDRA, and (c) shows the rotation speed of the synchronous motor 5, respectively. In the low-frequency synchronous start, the program processing of the micro computer 7 is used to use the timer 7-7 built in the micro computer for one cycle of the output frequency of the inverter 4.
The synchronous motor 5 is accelerated by shortening the time of 60 degrees for each flow mode as shown in FIG. 3 (a).

Period delta _t1 shown in FIG. 3 (a) it is a positioning period, in this period, from zero amperes current desired value IDR, up to the maximum current desired value corresponding to the maximum torque to be output as a synchronous motor, the third It is gradually increased as shown in FIG. As a result, the load torque T _L applied to the synchronous motor
When the output torque T _M overcomes, the rotor starts rotating.

FIG. 4 (a) shows the flow path of the winding current and the final movement position of the rotor during the positioning period. The position of 30 degrees counterclockwise from the winding axis of the phase a winding is θ = It is shown as 0. FIG. 4 (b) shows the rotation angle on the horizontal axis and the output torque T _M of the simultaneous motor on the vertical axis. The magnetic flux density distribution in the air gap of the synchronous motor is trapezoidal and the rotor is clockwise. The direction of the torque that rotates to is the forward torque.

If a current is passed from the a-phase winding to the b-phase winding during the positioning period, the magnetic flux direction of the armature winding is θ = 0, and the output torque T _{M with} respect to the rotation angle is shown in FIG. 4 (b). Thus, it increases with increasing winding current. However, when θ = 0, the output torque is zero, and the rotor that has started to rotate by overcoming the load torque T _M stops in the vicinity of θ = 0 regardless of the magnitude of the winding current.

FIG. 3 (c) shows the above-mentioned situation. When the load torque is small, the rotation starts at an early point in the positioning period, and vibration occurs in the vicinity of θ = 0 described above, but in one direction. It doesn't keep spinning. On the other hand, when the load torque is large, the rotation is started at a late point of the positioning period, but the rotation is stopped in the vicinity of θ = 0 without vibrating.

In the above-mentioned embodiment, when the rotor position is at the position of θ = −180 degrees shown in FIG. 4 at the time of t = 0, the output torque is zero even if the desired current value is increased. , Θ = 0 cannot be moved to the position. However, when the present invention is applied to those in which such a condition may exist,
The period of _Δt2 shown in FIG. 3A is set as the second positioning period, and this period can be solved by gradually increasing the desired current value from zero ampere.

Further, in the above-described embodiment, the desired current value IDR is output from the microcomputer 7 so that the desired current value increase pattern during the positioning period is shown in FIG. 3 (b).
In addition to the linearly increasing pattern as shown in FIG. 3, there is an advantage that it can be freely set according to the type of the synchronous motor or load torque to be used.

〔The invention's effect〕

As described above, according to the present invention, the positioning mode is set prior to the low frequency synchronous activation, and in this mode, the energizing direction to the winding current is fixed to any one,
The winding current is gradually increased from zero to the current value corresponding to the assumed maximum load torque, and the rotor is moved and fixed in the direction in which the torque becomes zero. In the subsequent low frequency synchronous start, the current increases. By stopping the motor and switching to the flow direction to the armature winding that generates torque in the direction in which the desired rotation direction is obtained, the starting method is performed, so that no matter where the rotor position is at the time of stop, Regardless of the magnitude of the load torque, the rotor starts to rotate when the output torque of the synchronous motor becomes higher than the load torque, and stops near the rotation angle at which the output torque becomes zero. Therefore, regardless of the rotor position at the time of stop, the positioning is reliably performed regardless of the magnitude of the load torque, and even after that, even if the inverter output frequency is gradually increased and the synchronous motor is accelerated, step out occurs. There is nothing.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram for explaining an embodiment of the present invention, FIG. 2 is a partial detailed circuit diagram in FIG. 1, and FIGS. 3 to 4 are operation explanatory diagrams of the embodiment of the present invention. 3 (a) is a transistor conduction mode, (b) is a desired current value, (c) is the number of revolutions of the synchronous motor, and FIG. 4 (a) is a winding current path and the final movement position of the rotor. (B) is a figure which respectively shows the relationship between a rotation angle and a synchronous motor output torque. 2 ... Rectifier circuit, 4 ... Inverter, 5 ... Synchronous motor, 5-1 ... Armature winding, 5-2 ... Rotor, 6 ...
Position detection circuit, 7 ... Microcomputer, 8 ... Current limiting circuit, 9 ... Base drive circuit, 10 ... Amplifier, 11 ... Comparator, 12 ... D / A converter.

Front Page Continuation (72) Inventor Nobuaki Kato 3-2-1, Saiwaicho, Hitachi City Within Hitachi Engineering Co., Ltd. (56) References JP-A-52-6919 (JP, A) JP-A-49-114026 ( JP, A)

Claims (1)

(57) [Claims] 1. A three-phase AC output of an inverter is connected to a three-phase armature winding of a synchronous motor having a permanent magnet as a field rotor.
A brushless DC motor that detects a position of the rotor from a terminal voltage of an armature winding of the synchronous motor and controls the synchronous motor at a variable speed based on a signal of the position detection. In the starting method of a brushless DC motor, in which the inverter is controlled by another method to start the synchronous motor by low-frequency synchronous start operation, prior to the low-frequency synchronous start operation, a current is passed through the three-phase armature winding. Fix the path to any one, gradually increase the current flowing in this armature winding from 0 to the current corresponding to the maximum load torque applied at startup, move the rotor to a position where no torque is generated, and fix it. After the positioning mode period is finished, the rise of the current is stopped once, and the flow direction to the armature winding is set to the desired rotation direction. Boot method of a brushless DC motor, characterized in that after switching the power mode as the direction of the torque is outputted has to perform the low frequency sync start being.