JPH0236788A - Method and circuit for control of brushless electric motor - Google Patents

Abstract

PURPOSE: To improve the rotational moment property by electronically shifting the commutation switching point forward by a certain angle at the top of the specified limit of the quantity of operation property. CONSTITUTION: One piece of rotor position detector 3 is arranged at a rotor 2 of a brushless DC motor 1, and a winding 5 of a stator 4 is equipped with three lines of shunt windings 5a-5c which are made in star circuits. The output electronic circuit of this control circuit forms a bridge circuit 6 out of six pieces of transistors(Trs) 7, and these Trs 7 are controlled by a microprocessor controller 12 so as to apply currents to the two pieces out of the shunt windings 5a-5c of the winding 5. Then, for improvement of motor property, this is provided with a switch for switching of advanced rectification so as to advance the commutation switching point of the three lines of shunt windings 5a-5c of the stator winding 5 of the motor 1, and when it comes to the limit of the quantity of drive property, that switching signal is outputted immediately to an annexed logical circuit so as to change the allocation of the rotor signal. With this, the rotational moment goes up sharply, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The invention relates to a bridge circuit, in particular a transistor bridge circuit, in which a control signal introduced by a rotor position detector supplies current pulses to the windings of an electric motor. electronic circuit,
The present invention relates to a method for controlling a brushless electric motor, in particular a brushless direct current motor, which is used in particular to control a transistor, in which case the electronic circuit, in particular the commutation switching point for controlling the transistor, can be changed.

Furthermore, this invention... It is equipped with a rotor position detector, an associated logic circuit, and a plurality of transistors for supplying current pulses to the windings of the electric motor, the control input being connected to said associated logic circuit, possibly via a pulse width modulator. The present invention also relates to a control circuit for a brushless electric motor, in particular a direct current motor, which implements the method, comprising a transistor circuit coupled to a transistor circuit and a device for varying the commutation switching point controlling said transistor.

[Conventional technology]

BACKGROUND OF THE INVENTION In brushless electric motors, particularly DC motors, the rotor is equipped with permanent magnets, and the stator is typically equipped with three-phase foot-connected windings. The terminals of this winding are connected via a three-phase transistor bridge circuit to the positive or negative current path of the DC voltage of the intermediate circuit. The magnetization of the permanent magnets and the formation of the three-phase windings are selected such that the induced voltages of the three phases each exhibit an approximately trapezoidal waveform. The most desirable rotational moment waveform of the motor is given when the three-phase currents are block-shaped with a block length of 120 degrees and exactly coincide with the phase of the induced voltage.

Therefore, two of each of the six transistors are controlled, so that current flows through two of each of the three branch windings, and no current flows through the third branch winding. In this case, each angle of the rotor is detected by a rotor position detector in order to determine which of the three transistors current should be introduced into.

However, in reality, the ideal current waveform deviates significantly. If we limit ourselves to the induction of the three shunt windings, the current increases and decreases not intermittently, but in a first approximation according to the e-function. Therefore, a phase shift of the current block with respect to the induced voltage occurs, which prevents the formation of a rotational moment. The angle of this phase shift depends on the rotation speed. This is because, on the one hand, the value of the induced voltage increases with the increase in rotational speed,
On the other hand, this is because the time required to increase the current necessarily increases with respect to the period interval.

A known method for preventing the above-mentioned phase shift consists in advancing the commutation switching time, ie in controlling each transistor at an earlier time. Therefore, on the one hand it takes a long time for the current to rise and fall again, and on the other hand the induced voltage is still low at the moment when the current rises.

In known methods of the type mentioned at the beginning, the commutation switching point is preadvanced by mechanically shifting the sensor of the rotor position detector, which is a magnetic pole disk, in the opposite direction of the motor rotation.

Then, after performing this shift, the position of the sensor is fixed.

Furthermore, in the control section for each transistor of the control circuit of the brushless DC motor, a fixed resistor designed to shift the commutation switching point of each associated phase, that is, to select a closing period shorter or longer than 120 degrees, is provided. This is known (West German Patent No. 2629269). By this method, desired motor characteristics and rotational speed characteristics can be achieved. Therefore, switching of three phases can be realized at low cost without substantially overlapping each other.

What both known methods have in common is that the commutation switching point is moved mechanically or electrically by only a predetermined fixed value over the entire rotational speed range. The above values are determined with a constant rotation angle in the mechanical method and with a constant electrical phase angle in the electrical method.

However, the optimal value of the deviation at the time of commutation switching depends on the rotation speed, that is, it is close to 0° when the rotation speed is low;
When the rotation speed is high, the value is, for example, up to 60° or more. The above-mentioned method of providing a fixed deviation in commutation switching time only allows a compromise that provides an optimum state within a narrow range only for a constant rotational speed.

Furthermore, the advance of the commutation switching time is dependent on the direction of rotation. Therefore, a motor that moves the commutation switching point by a certain value and only in a predetermined direction will have extremely poor motor characteristics or will usually not function properly if the rotation direction is reversed. These known methods are unsuitable for motors whose direction of rotation is reversed.

[Problem of invention]

It is therefore an object of the invention to be able to effectively shift the commutation switching point with particularly simple means and in a purely electronic manner, so that significant improvements in the motor characteristics and in particular in the torque characteristics are achieved. The purpose of this article is to construct a method of the type mentioned at the beginning.

Furthermore, it is an object of the invention to provide a control device for carrying out the above method.

[Solving issues]

The problem with the method described above is that, according to the invention, the commutation switching point can be set at a constant angle above a predetermined limit of the operating characteristic, typically 60
This is solved by electronically advancing and moving the @.

Furthermore, the control circuit according to the invention is characterized in that the device for changing the commutation switching point has an input of a drive characteristic variable, a comparator and a switching device having an output for the advance commutation switching, and the said advance commutation switching signal is It is characterized in that it is introduced into the input terminal of the auxiliary logic circuit as a rectification switching signal for allocating the rotor position signal to a transistor control signal derived from this signal.

(Function/Effect) This method can be realized with extremely reduced circuit costs, and can nevertheless be achieved with a significant increase in the output of the electric motor, that is, a significant increase in the rotational moment in a high rotational speed range. A significant increase in maximum rotational speed is achieved.

Regarding the drive characteristic quantity derived from the command for performing advance commutation switching, the rotational speed is mainly a problem.

The reason for this is that the necessity or usefulness of advanced commutation switching depends first on the rotational speed, and the effect of advanced commutation switching is particularly small in the low rotational speed range, but it becomes very important in the high rotational speed range. Because it will be. Nevertheless, it is also possible, for example, to use rotational torques as drive variables.

According to an advantageous feature of the invention, in the case of a method of the type mentioned in the introduction, in which the control of the transistor supplying the current pulses to the windings of the electric motor is carried out according to steps of a fixed angle of rotation, the advanced commutation switching occurs in the rotor. This is done by changing the allocation of the position signal to the control signal of the transistor, and the next transistor is connected each time its turn comes as a set of transistors without advance rectification switching.

In this case, advancing the commutation switching time is done very simply in the following way. That is, compared to a procedure in which the rotation speed is slow and the rectification switching is not performed, the allocation between the rotor position signal and the transistor control signal derived from this signal is changed in the high rotation speed range. Without forward commutation switching, for example, the next set of transistors in sequence is controlled for the first time. Since no other circuit processing is required, there is no need to use the capacity of the computer for this purpose.

The advantages of the method according to the invention are particularly advantageous, especially if the turn-off of the transistor is undertaken solely by hardware control. This allows fabrication to be achieved with very low material outlay and is therefore cost-effective.

The method according to the present invention does not use any signal waveform that constantly corresponds to the rotation of the rotor in the control circuit, and the signal for the desired advance commutation switching is generated from the waveform to set the starting threshold value relative to the origin. Even a brushless electric motor that can be easily guided by moving it up or down can be used without any restrictions.

The circuit outlay of the switching circuit according to the invention is very low and consists, for example, of virtually only one simple comparator, which can be used for This is to check whether the

Other advantageous developments of the invention are described in the dependent claims.

〔Example〕

The invention will be explained in more detail below with reference to an embodiment shown in the drawing.

A brushless DC motor 1 schematically shown in FIG. 1 has a rotor 2. In this rotor. One rotor position detector 3, mainly a three-phase polar disk rotor position detector, is provided. The winding section 5 of the stator 4 of the motor 1 has three branch windings 5a, 5b and 5C in a foot-shaped circuit.

The output electronics of the control circuit of FIG. 1 includes a transistor bridge circuit 6 in which six transistors 7 form a complete bridge circuit. Normal rectifier bridge circuit 8
Inside, a direct current is formed from an alternating current power source 9, and a positive current path 10
and is introduced into the negative current path 11. These current paths include
A transistor 7 is installed. These transistors 7 are controlled by a microprocessor control unit 12,
The connection terminal of the winding part 5 is selectively connected to the positive current path so that two of the three branch windings 5a, 5b and 5c are energized, and no current flows to the third branch winding. connected to the negative current path.

FIG. 2 shows a microprocessor control section 20 control circuit without advance commutation switching.

The attached logic circuit 13 detects which two transistors 7 are being controlled from the three signals of the introduced rotor position detector 3. Furthermore, a control signal "sign (M)" is introduced into the auxiliary logic circuit 13 via an input terminal 14. This signal gives what sign the rotational moment is. This signal is supplied from the rotational speed control section 15. Using this signal, the associated logic circuit 13 can select between two different states of assigning the rotor to the controller of the transistor. The two signals formed from this are introduced into two pulse width modulators 16 and 17, where they are respectively coupled to the pulse width signal supplied from the rotational speed control 15. Both pulse width modulators 16 and 17 output pulsed control signals via an upper output 18 to the upper three transistors 7 and via a lower output 19 to the lower 3 transistors 7. do.

In order to improve the motor characteristics and in particular the shape of the rotational moment, an explanation is given in order to advance commutation, that is to say to advance the commutation switching times of the three branch windings 5a, 5b and 5C of the stator winding 5 of the motor 1. The microprocessor control section 12 of the circuit shown in FIG. 1 is replaced with the microprocessor control section 12' shown in FIG.

The switching device 20 for leading rectification switching has a limit of the driving characteristic quantity,
For example, when the rotational speed exceeds the limit or the output limit, an advance rectification switching signal is sent to the attached logic circuit 13 via the conductor 21.
' is output to the input terminal 22 of '.

The advanced commutation switching signal is generated by converting the rotor signal obtained from the rotor position detector 3 into the pulse width modulator 16 in the attached logic circuit 13'.
and 17 and also the control signal output to transistor 7 to initiate an allocation change. This allocation is changed so that when driving at a low rotational speed, there is no advance rectification switching, but the next set of transistors in turn is always connected. Therefore, the advance of the rectification switching point of the transistor 7 is about 90'.

If the driving characteristic quantity that leads to advanced commutation switching is rotational speed,
The input end of this drive amount switching device 20 is connected to the output end of a rotational speed control device 15 which outputs a signal dependent on the rotational speed. A comparator in the switching device 20 compares the obtained rotational speed-dependent signal with a predetermined limit value, and if the limit value is exceeded, a 60° advance rectification switching signal is sent via the conductor 21 to the attached logic. It is supplied to the circuit 13'.

In both pulse width modulators 16 and 17, the signal is converted into a pulse width signal supplied by the rotational speed control 15 before controlling the upper or lower transistor 7 in the same manner as described in FIG. Tie.

In FIG. 4, the rotational moment M of the electric motor 1 is plotted against the rotational speed n. Advance commutation switching is not performed below the rotational speed limit n1. If the advance commutation changeover is not carried out even at a rotational speed n1 or higher, the characteristic curve of the rotational moment will follow the flow shown by the dotted line. In other words, the rotational moment rapidly decreases at rotational speed n1 or higher.

The advanced commutation of up to 60°, which takes place above the rotational speed limit n1, results in a significant increase in the rotational torque in the high rotational speed range on the one hand and a significant increase in the maximum achievable rotational speed on the other hand.

Starting from the described method, it is also possible to carry out progressive switching at a number of predetermined limits of the drive characteristic, for example the rotational speed, in each case by a different fixed angle, for example an angle that increases as the rotational speed increases.

[Brief explanation of the drawing]

FIG. 1 is a simplified circuit diagram of a control circuit for a brushless DC motor. Figure 2: In the case of the normal method without advance rectification switching, the first
FIG. 3 is a block circuit diagram of the microprocessor control unit shown in FIG. FIG. 3 is a block circuit diagram of the microprocessor sensor control section of FIG. 1 for performing advance commutation switching; FIG. 4 is a characteristic curve of rotational moment and rotational speed of the brushless DC motor of FIG. 1 with and without advance commutation switching. Reference symbols in the figure: 1... Brushless DC motor, 2... Rotor, 3... Rotor position detector, 4... Stator, 5... Winding section, 5a, 5b, 5c -・- Minute winding, 6・・・7・・12゜13゜15・20・M・・n Dispute transistor bridge circuit, transistor, 2'...Microprocessor control section, 3'...
Attached logic circuit, ・Rotation speed control unit, 7...Pulse width modulator, ・Switching device, rotation moment, rotation speed.

Claims (8)

[Claims] 1. The control signal introduced by the rotor position detector is used to control an electronic circuit, in particular a transistor, in a bridge circuit, in particular a transistor bridge circuit, which supplies current pulses to the windings of an electric motor, in which case the electronic circuit, A method for controlling a brushless electric motor, in particular a brushless DC motor, in which the commutation switching point controlling the transistor can be varied, characterized in that the commutation switching point is electronically advanced by a certain angle above a predetermined limit of the operating characteristic quantity. how to. 2. 2. The method of claim 1, wherein the commutation switching points are each separated by 60 DEG. 3. 3. The method according to claim 1, wherein the drive characteristic quantity is a rotational speed. 4. 2. A method as claimed in claim 1, characterized in that the drive characteristic variable is a rotational moment. 5. The transistor that supplies current pulses to the windings of the electric motor is controlled in steps with a fixed rotation angle, and the switching to advanced commutation is performed by changing the assignment of the rotor position signal to the control signal of the transistor, without switching to advanced commutation. 3. A method as claimed in claim 1, characterized in that the transistors of the next successive set of transistors are connected in each case. 6. 6. The method as claimed in claim 1, wherein the commutation switching point is advanced by different fixed angle values at different predetermined limits of the drive characteristic. 7. It is equipped with a rotor position detector, an associated logic circuit, and a plurality of transistors for supplying current pulses to the windings of the electric motor, the control input being connected to said associated logic circuit, possibly via a pulse width modulator. A control for a brushless electric motor, in particular a direct current motor, comprising a transistor circuit coupled to a transistor circuit and a device for changing the commutation switching point for controlling said transistor, carrying out the method according to claims 1 to 6. In the circuit, the device for changing the commutation switching point has an input of a drive characteristic quantity, a comparator, and a switching device (20) with an output of an advanced commutation switching signal, and the switching device (20) has an input of a drive characteristic quantity, a comparator, and an output of an advanced commutation switching signal. A control circuit characterized in that the control circuit is introduced into the input terminal (22) of the attached logic circuit (13') as a rectification switching signal for allocating the position signal of the signal to the control signal of the transistor (7) derived from this signal. 8. The input end of the drive characteristic quantity switching device (20) is connected to a rotation speed control device (15) that outputs a signal depending on the rotation speed.
8. The control circuit according to claim 7, wherein the control circuit is connected to an output end of the control circuit.