JPH0510039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a control system for an electric motor having a rotor that rotates magnetically.

(B) Prior Art Motors with rotors that rotate with magnetism include, for example, motors with coils for forming magnetic poles in the rotor, motors with magnets embedded in the rotor, etc. Recently, they have been widely used under the names of commutatorless DC motors, AC servo motors, AC synchronous motors, etc. in which ferrite magnets are attached to the rotor.

Figure 1 shows a typical example of a drive circuit for such a non-commutator DC motor. In the figure, 1 is a single-phase AC power supply and 2 is a rectifier circuit. Although not shown, it has a well-known thyristor bridge configuration. Reference numeral 3 denotes an inverter for obtaining a rotating magnetic field in the stator 4 by using the DC output rectified by the rectifier circuit 2.

The elements constituting this inverter 3 may be thyristors or other elements as long as they can perform switching control in response to signals from a control circuit 5, which will be described later, but in the following explanation, six elements connected as shown in the figure will be used. The description will be given using transistors Tr ₁ to Tr ₆ as representative examples. 5 is a control circuit that outputs a signal for controlling the firing of the transistors that constitute the inverter 3 in a predetermined order, and mainly detects the rotor position using Hall elements H ₁ , H ₂ , and H ₃ The firing order of the transistors Tr ₁ to Tr ₆ of the inverter 3 is determined by using the rotational position of the rotor 7 detected by the inverter 6 as an input signal. Note that N and S written on the rotor 7 indicate magnetic poles magnetized on the surface of the rotor 7.

An outline of the operation of the commutatorless DC motor having such a configuration will be explained. The control circuit 5 is supplied with DC power from the single-phase AC power supply 1 via the rectifier circuit 2.
The transistor of the inverter 3 receives the signal of the rotational position of the rotor 7 obtained from the position detector 6 as an input.
For example, signals as shown in FIG. 2 are applied to Tr ₁ to Tr ₆ . That is, in the first mode, transistors Tr ₁ and Tr ₅ are turned on, and the other transistor Tr _{2 is} turned on.
When a control potential is applied to each transistor so that Tr ₄ and Tr ₆ are turned off, a current flows between the stator windings U and V as shown by the arrow I in the figure, and then (in the second mode ) When each transistor is controlled so that transistors Tr ₁ and Tr ₆ are turned ON and other transistors Tr ₂ to Tr ₅ are turned OFF, a current flows between windings U and W as shown by the arrow in the figure, and a third When the transistors Tr ₂ and Tr ₆ are controlled to be turned on and the others are turned off in the mode, a current flows between the stator windings V and W as shown by the arrow in the figure. Similarly, from the third mode to the sixth mode, the transistors Tr ₁ to Tr 1 to
Tr ₆ is controlled to fire as shown in FIG. 2b, and the cycle of the first to sixth modes is repeated.

Due to the output of such ignition control from the control circuit 5, current flows in the stator 4 in the direction described above.
A timing chart like that shown in Figure C is obtained. For each phase U, V, and W in the diagram, the continuity indication above the center line indicates that current is flowing from the inlet of each phase toward the neutral point N in the stator 4 in Figure 1.
Similarly, the continuity display on the lower side indicates that current is flowing from the neutral point N toward the inlets U, V, and W of the windings of each phase.

When current flows through the stator windings U, V, and W in this way, a rotating magnetic field is formed in the stator 4, so that, for example, one point M on the rotor 7 moves from point P in FIG. The rotor 7 rotates once in response to each ignition mode of X, Y, and Z, and thereafter rotates in response to the sequentially repeated modes, allowing continued operation as an electric motor.

(c) Problems to be Solved by the Invention However, this type of conventional electric motor uses the Hall element H ₁ , as a sensor for detecting the rotational position of the rotor 7.
H ₂ and H ₃ are embedded in three parts of the stator 4, and the position of each rotating state of the rotor 7 is detected by the Hall elements H ₁ to H ₃ , and the stator windings U, V, Since a controller 5 is used to control the power supply to W, there are disadvantages in that it is difficult to operate the motor in accordance with the various load conditions under which the motor is used, or precision machining of the parts and structure used in the motor is required. Moreover, there are disadvantages in that the usage conditions of the motor are limited and the motor is prone to failure.

In addition, three Hall elements embedded in the stator 4
In order to extract the signals from H ₁ to H ₃ to the outside of the motor, 12 lead wires (4 in total for each Hall element) are required, and in addition, 3 feed wires are required to energize stator 4. In the end, in order to control this type of three-phase motor, the motor could not be operated satisfactorily unless the power supply to the motor was controlled using 15 conductive wires.

For this reason, the terminals that connect the motor and the lead wires have become more complicated, the positioning of the Hall element installed in the stator, the accuracy control when fixing the Hall element to the stator, or the need for continuity between each element and device. It is difficult to avoid the complexity of managing the conductor connections, and the Hall element itself must be protected from oil, moisture, and other gas atmospheres in which the motor is installed, which has the drawback of limiting the application of the motor. be.

In addition, Hall elements and other conventional detection sensors are
The purpose of the electric motor, for example, is to detect the rotational position of the rotor by fixing it at a specific predetermined position depending on the number of rotations of the drive and the size of the load. When this type of electric motor is used for purposes other than the drive rotation speed, it has the disadvantage that it is difficult to operate with high efficiency.

Furthermore, in some DC motors, it has been practiced for a long time to control the operation of the motor using the back electromotive force generated in the stator windings, but the conventional control method using the back electromotive force Since this is a macroscopic control that compares the back electromotive force generated in proportion to the rotational speed with a reference voltage, the rotational control of the motor becomes a rough control, and the stator winding is adjusted to correspond to the rotational position of the rotor. Because of the lack of energization control, there was a gap between the optimum operating conditions for the motor. Therefore, the size of conventional motors of this kind has to be designed to provide ample driving capacity, making it difficult to make the motors smaller and thinner.

In view of these points, it is an object of the present invention to provide a control method that enables stable and efficient operation of an electric motor without using a special element for detecting the rotational position of the rotor. It is.

(d) Means for Solving the Problems In other words, in the present invention, the back electromotive force generated in the windings on the stator side due to the rotation of the rotor does not affect the rotational position of the rotor, especially the state of this rotational position. The difference between the energization state of the stator winding and the stator winding is detected, and the timing of energization of the next stator winding is set so that the magnitude of this difference matches the optimal operating conditions. It is designed to control the supply of electricity to the

(e) Effect By configuring the electric motor control system of the present invention as described above, there is no need to separately provide a special detector for detecting the rotational position of the rotor, and It is possible to prevent motor defects due to performance and reliability issues.

(F) Embodiment The present invention will be described below based on an embodiment in which the present invention is applied to a three-phase commutatorless DC motor shown in FIGS. 1 and 2. FIG. 3 is a drive control circuit diagram of a three-phase non-commutator motor embodying the present invention, and components similar to those in FIG. 1 are designated by the same figure numbers. The difference from the conventional structure shown in Fig. 3 is that the control circuit 5 has been changed to a control circuit 8 with a completely new concept, and as a result, a position detection sensor such as a Hall element is omitted and is replaced by a star connection. The neutral point N of the stator windings U, V, and W is located at the point connected to the position detection circuit 9 side. Otherwise, the same elements and parts as in FIG. 1 are used, and the functions of the respective elements and parts are the same as those explained with respect to FIGS. The detailed explanation of the electric motor control device according to the present invention will be given below by simplifying the parts already explained as follows.

First, generally when the electric motor shown in FIG. During operation, a back electromotive force is induced in each stator winding U, V, and W. In particular, in the embodiment shown in FIG. 3, since there is a stator winding that is not energized in each ignition mode, a conducting wire 10 is used to connect the neutral point N of the stator winding and the control circuit 8. In this case, a potential due to a back electromotive force appears directly between the stator windings and the stator windings that are not energized. The curves u, v, and w shown by dotted lines as d in FIG. The relationship between this waveform and the mode of energization to each stator winding U, V, and W is as shown in the diagram when the motor is in steady operation, and when the motor is started or when the motor load is increasing. In this case, the rotation of the rotor 7 cannot follow the conduction of each stator winding and is delayed, so if the waveform of the voltage induced also does not change the width of the horizontal axis in Figure 2, then the waveform of the voltage shown in Figure 2 is d.
This will lag behind the dotted line waveform.

The present invention thus provides stator windings U, V,
The rotational position of the rotor 7 is detected by inputting the back electromotive force generated at W, and the optimal ignition output is given to the inverter 3 in relation to the rotational state of the rotor 7.

In other words, U in FIG. 2 showing the operating state of the electric motor
Regarding the phase, the midpoint between the point where the second ignition mode ends and the point where the fourth ignition mode begins, in other words, the middle point in the (third) ignition mode where the U phase is not energized. The direction of the potential of the back electromotive force is reversed at point E (150° position on the scale in the figure), and similarly, the direction of the back electromotive force is reversed at the midpoint F (330° position) of the 6th ignition mode. is reversed. Then, when a load is applied to the rotor 7, these points E and F gradually move to the second ignition mode (or fifth mode), and when the motor starts, point E and F become the second point. Before the end of the arc mode (or the fifth mode), for example, the direction of the potential of the back electromotive force changes at the 120° or 280° position on the scale in the figure, etc., so that the ignition mode and the actual rotation of the rotor 7 Therefore, the timing of ignition of the inverter 3 by the control device 8 such as a microcomputer is made to correspond to the rotational state of the rotor 7, and the stator winding
give the signal in the optimal mode for the necessary time.

The point of change in the direction of the potential of the back electromotive force (hereinafter referred to as the point of change in potential direction) is located at the stator 4, in addition to the point E and point F of the U phase, and is 120° shifted from the U phase in the embodiment shown in FIG. ₁ point E and 1 point F in the V phase, and ₂ points E and ₂ points F in the W phase, which are also arranged ₂₄₀ ° apart, can be detected in the same way.In the present invention, the point of potential direction change from each phase can be detected in the same way. The timing of energization to each stator winding, in other words, the switching of each mode and the time of energization to the inverter 3 are controlled according to the results.

However, unless the load is extremely heavy, the rotor has inertia, and there is no need to detect the rotor position every 60° rotation.In the following explanation, we will simplify the device and detect the potential direction every 120°. Inverter 3 based on the change point
There is no practical problem in using a method that determines the timing of the ignition output.

When the load on the motor is lighter, every 360°,
In other words, the potential direction change point for each rotation of the rotor is U
The inverter may be controlled based on this signal by detecting the winding of phase, V phase, or W phase, but in the following explanation, the rotation position is determined every one-third rotation (120° rotation). A case will be described in which the firing of each of the transistors Tr ₁ to Tr ₆ constituting the inverter 3 is controlled based on the detection signal.

In Fig. 3, 11, 12, 13, and 14 are terminals to which stator windings U, V, and W and conducting wire N are connected, and CU, CV, and CW are the reverse polarities that occur in each stator winding U, V, and W. The microcomputer 8 detects the point of change in position and direction based on the electromotive force and uses it as a position signal for the rotor 7.
a comparator that supplies input terminals I ₁ , I ₂ , I ₃ to
15 is a protection circuit for protecting the transistors Tr ₁ to Tr ₆ from the back electromotive force generated when switching the stator windings U, V, and W; 16, 17, and 18 are connected to one end of the transistors Tr ₁ , Tr ₂ , and Tr _3; an inverting amplifier, 2 connected to the base side of the microcomputer 8 and the other end connected to the output ports ₁ , ₂ , and ₃ of the microcomputer 8;
5, 26, 27 are connected to output ports ₄ , ₅ , ₆ of the microcomputer, and transistors
Transistors forming a Darlington connection together with Tr ₄ , Tr ₅ , and Tr ₆ , 24 is a transistor 25, 2
6, 27, and transistors Tr ₁ to Tr ₆ are output port _1.
Each of them is made conductive in response to the H signal from 6 to ₆ .

Note that 19 is a reset input port to the microcomputer 8, and 20 is a clock input port for inputting the oscillation pulse from the vibrator 21 to the microcomputer 8 for internal control.

FIG. 4 shows changes in the voltage at the terminal 11 shown in FIG. 3. This figure shows a period in which the first mode and second mode shown in Fig. 2 are continuously maintained, and during this period the rotor is rotated through 120°.
Rotate. is the period during which the third mode is maintained, and the rotor rotates by 60°. Similarly, is a period in which the fourth mode and the fifth mode are continuously maintained, and the rotor rotates 120°. is the period during which the 6th mode is maintained, and the rotor is at 60°
Rotate. Therefore, by changing from → to →, the rotor makes one rotation (360°). is followed by again, and then →→→→ are repeated in order.

During the period, the first mode and the second mode are maintained. Therefore, during this period, transistor Tr ₁ is continuously ON, and transistor Tr ₄ is ON continuously.
is continuously OFF and the transistor
Since either Tr ₅ or Tr ₆ is ON, terminal 11
The DC voltage for driving the motor is supplied by a transistor.
Applied via Tr ₁ . That is, during this period, since a DC voltage is applied to the terminal 11, a change in the back electromotive force cannot be detected, and the voltage at the terminal 11 becomes the voltage level of the DC power supply.

The third mode is maintained during the period.
Therefore, since the transistors Tr ₁ and Tr ₄ are continuously OFF, the terminal 11 is substantially in an open state and the stator winding U is in a non-energized state. That is, since the input impedance of the comparator CU is sufficiently high, a change in the back electromotive force generated in the stator winding U can be detected at the terminal 11 in accordance with the rotation of the rotor. The intersection of this back electromotive force and the neutral point voltage is point E during this period. As shown in FIG. 2, the output of the comparator CU is inverted at this point E.

During the period, the fourth mode and the fifth mode are maintained. Therefore, during this period, transistor Tr ₁ is continuously OFF, and transistor
Tr ₄ is continuously ON and the transistor
Since either Tr ₂ or Tr ₃ is ON, terminal 11
is connected to the negative side of the DC voltage for driving the motor via the transistor Tr ₂ or Tr ₃ . That is, during this period, since a DC voltage is applied to the terminal 11, a change in the back electromotive force cannot be detected, and the voltage at the terminal 11 becomes the negative voltage of the DC power supply.

The sixth mode is maintained during the period.
Therefore, since the transistors Tr ₁ and Tr ₄ are continuously OFF, the terminal 11 is substantially in an open state and the stator winding U is in a non-energized state. That is, since the input impedance of the comparator CU is sufficiently high, a change in the back electromotive force generated in the stator winding U can be detected at the terminal 11 in accordance with the rotation of the rotor. The intersection of this back electromotive force and the neutral point voltage is point F during this period. As shown in FIG. 2, the output of the comparator CU is inverted at this point F.

Between the period and the period , the polarity of the magnet changes due to the rotation of the rotor, and the direction of change of the back electromotive force is reversed between negative and positive.

In FIG. 4, T1, T2, and T3 are respectively called reversal time, restart time, and standby time.
As can be seen from this figure, the time T1+T3 is the time from the beginning of the period to point E, and T2 is the time from point E to the end of the period. This E
From point (when the output of comparator CU is inverted)
After time T2, the stator winding energization mode is changed from the third mode to the fourth mode. The basis of the present invention is to change the energization mode to the stator windings after time T2 from the time when the output of the comparator is reversed.

As you can see from the second d, there are three comparators
When CU, CV, and CW are used, there is one point in time when the output of the comparator changes in each energization mode (first mode to sixth mode). That is, in the first mode E ₂ points and in the second mode
_F1 point, E point in the third mode, _F2 point in the fourth mode, _E1 point in the fifth mode, and F point in the sixth mode.

Therefore, in the current energizing mode, by repeating the operation of changing the energizing mode to the next energizing mode after T2 hours from the time when the comparator output is reversed, the energizing mode changes continuously and the motor rotates. You can rotate the child.

Theoretically (when there is no load), the times of T1, T2, and T3 are (T1+T3)=T2. That is, the second
As can be seen from the figure, the time when the output of the comparator is inverted is the intermediate time in each mode. However, when a load is actually driven by an electric motor, (T1+T3)>T2, as can be seen from FIG.
That is, (T1+T3)=kT2. The optimum value of k is set depending on the size of the load connected to the motor, the rotational speed of the motor, the structural operating efficiency of the motor, and the like. During actual operation, the values determined based on the size of the load etc. are corrected based on the actual rotational speed and used. This makes it possible to improve the operating efficiency of the electric motor when accelerating or decelerating. K is T2, which is almost the same as T1.
The value is within the range set below. The time of T2 is determined by the microcomputer 8 based on the time of T1 + T3.
is calculated and found.

Therefore, the time T2 can be determined by determining the time T1+T3, that is, the time from the start of energization in the current mode until the output of the comparator changes. The time from the start of the current mode until the output of the comparator changes is measured by a built-in timer in the microcomputer 8. Since the microcomputer 8 changes the ON/OFF combination of transistors to change the energization mode, this microcomputer remembers the start time of the energization mode, and changes in the comparator output are detected by the input port 11 of the microcomputer 8. The microcomputer 8 can measure the above-mentioned time because it can be known from the change in the voltage of .about.13.

T3 is a standby time, which is used when starting the electric motor, and an initial value is set at the time of starting the motor. When the motor is stopped, the rotor is not rotating and no back electromotive force is generated. In other words, since the output of the comparator does not change and the time cannot be determined, this value is set in a pseudo manner. Therefore, this T3 time is 0 after the start of the electric motor is completed. That is, in a steady state, the relationship T2=kT1 holds true.

Next, the operation at startup will be explained. The greater the output of the motor, the longer the T3 time needs to be, and the higher the design rotation speed at startup, the shorter the T3 time needs to be. That is, it is necessary to set the optimum value for each motor. In the following explanation, the waiting time T3 is temporarily set to 1 second. When energization is started, the time (T1+T3) from the start of energization mode until the output of the comparator changes is at least 1 second.
Also, if the change in the comparator output cannot be detected, use the upper limit of T1 (T1 + T3) = 1 + α
seconds, and even if a change in the output of the comparator cannot be detected, the time T2 can be calculated by calculation as described above. At this time, the time when the time measurement of T1 reaches the upper limit value is the time of point E, for example.
Timing of T2 time starts. Therefore, the energization mode can be changed to the next mode at the end of the T2 time measurement. A state in which a change in the output of the comparator cannot be detected corresponds to a state in which the rotor is not rotating. By doing this, the energization mode changes even when the rotor does not rotate when the motor is started. This state continues until the stop rotational position of the rotor and the energization mode match (within six energization modes at most). Generally, in a DC motor, the rotor will not rotate unless an appropriate energization mode is matched to the rotation angle of the rotor (distribution of the magnetic field by the permanent magnet).
In other words, when starting the electric motor, the rotor will not start unless the rotational position of the rotor and the energization mode match. In the present invention, the energization mode is forcibly changed until the rotational position of the rotor and the energization mode match. The time for changing this energization mode is set based on T3.

The following describes the process from when the rotational position of the rotor and the energization mode match and the rotor begins to rotate until the rotor enters a steady state (completion of startup). When the power is turned on in this mode, the timer T3 is first measured, and the time T1 from the time UP of T3 time to point E (when the comparator output changes) is measured. Timing of T2 is started at the time of point E, and the energization mode is changed to the next mode after the time of T2 has increased. Thereafter, this operation is repeated while decreasing the value of T3.

FIG. 5 is a flowchart showing the operation when the above operation is applied to an actual electric motor. In the flowchart on the left side of Figure 5, first perform initial settings (initial settings of the microprocessor).
Next, the transistor is energized in mode 1 (first energization mode). Next, a timer process to be described later is performed, and then the transistor is energized in mode 2 (second energization mode). Next, timer processing to be described later is performed, and the transistor is energized in mode 6 (sixth energization mode). ……. The operation of changing the energization mode after performing the timer processing in this way is repeated thereafter. In the flowchart of timer processing shown on the right side of FIG. 5, timer T3 is first started to measure time to secure time T3. Next, when the time T3 has elapsed and the timer T3 finishes counting, the timer T1 starts counting, and the time T1 of the input to the comparator (until the output of the comparator changes) is measured. At this time, T3=
Perform (T3-1) and reduce the value of T3. (T3=1 second=
It is assumed to be 1000m seconds. Also, the amount of subtraction is not limited to 1, but 20 to 50.
You can also make it a rank. ) Note that an upper limit value (approximately three times the time T3 time) is set for the time measured by timer T1, and when there is no input from the comparator, timer T1 ends the time measurement at this upper limit value and starts the next step. Proceed to. Therefore, the timer T2 is started to measure time either by an input from the comparator or by the end of the timer T1. The time measured by the timer T2 is calculated by the microprocessor, which is k times the time measured by the timer T1 (or the upper limit time of the timer T1), and is set in the timer T2.
At startup, it is preferable to make T2 time shorter than during steady state to advance the phase of the rotating magnetic field relative to the rotation of the rotor. Therefore, the time of T2 is kT1(k(T1+T3))
), it is possible to change the amount of phase advance between startup and steady state without changing the value of k. In other words, since the T3 time is not added, the T2 time is shortened and the phase of the rotating magnetic field can be advanced. When the timer T2 finishes counting, the timer process ends and the transistor energization mode is changed to the next energization mode.

In addition, in the flowchart shown in Figure 5, the time T3 is subtracted even before the rotor starts rotating, but the amount of subtraction is small compared to the value of T3, and this subtraction is limited to 6 times at most. Therefore, a predetermined energization time is always ensured in each energization mode, so there is no problem during actual startup, and the flowchart can be simplified.

Since the energization mode is switched in this manner, the standby time T3 gradually becomes shorter as the motor starts, and becomes 0 when the rotation of the rotor 7 reaches a steady speed. In addition, since the speed of the rotor 7 gradually increases after the motor starts until it reaches a steady rotation speed, the time T1 until the potential direction change point E at which the direction of the back electromotive force generated in the stator winding changes, As a result, the restart time T2 gradually becomes shorter, and in the end, the time for energizing the windings in each mode (T1 + T2 + T3) is the time required to provide a rotational speed that balances the load on the rotor and the current flowing through the windings. Eventually, each phase repeats a cycle of forward energization for 120° rotation, pause for 60° rotation, reverse energization for 120° rotation, and pause for 60° rotation.

FIG. 6 shows another embodiment in which a single comparator U0 can be used to detect such points of potential direction change due to back electromotive force every 120°.

(G) Effects of the Invention As described above, in the control method of the present invention, the position state of the rotor is detected by the back electromotive force generated in the stator side winding due to the rotation of the stator, and the time until this detection is Since the energization time and timing of the stator windings are controlled using output signals calculated based on The method can be simplified.

In addition, since no position detection element is used, it is possible to easily convert compressors, etc., which were previously difficult to convert into brushless units due to problems such as temperature resistance, humidity resistance, and Freon resistance of position detection devices, making them extremely useful. This method can provide a high level of control.

Further, since the energization mode maintenance time is always set to an optimal value according to the time measured by the timer, that is, the time that changes depending on the rotational status of the motor and load fluctuations, the operating efficiency of the motor can be improved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the basic configuration of a non-commutated DC motor, Figure 2 is a timing chart diagram,
FIG. 3 is a circuit diagram showing an embodiment of the control according to the present invention, FIG. 4 is an explanatory diagram of ignition timing control, FIG. 5 is a flowchart showing an example of control according to the present invention, and FIG. FIG. 2 is a circuit diagram showing another embodiment of the rotor position detection circuit. 1...AC power supply, 4...Stator, 3...Inverter, 7...Rotor, 8...Microcomputer, 9...Position detection circuit.

Claims (1)

[Claims] 1. Energization state of each stator winding of an electric motor having a rotor that rotates with magnetism and a plurality of stator windings that form a magnetic field for rotating the rotor. Alternatively, in a motor control method in which a plurality of energization modes are set by combining de-energized states and the energization modes are sequentially switched so that the rotor rotates, a timer unit for measuring time and a rotor a detection unit that detects an induced voltage generated in the de-energized stator winding due to the rotation, the timer unit starts counting time from the time when the energization mode is switched, and the induced voltage detected by the detection unit is provided. In response to a signal obtained when the voltage reaches a predetermined set voltage, the timer unit finishes measuring time, and the energization is stopped after the time measured by the timer unit has elapsed from the time when the signal was obtained. A control method for an electric motor characterized by switching the mode to the next energization mode. 2. The electric motor control method according to claim 1, wherein the time measured by the timer section is corrected using a predetermined constant.