JPH0681547B2 - Control method of voltage type PWM inverter in AC servo motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method for a voltage-type PWM (Pulse Width Modulation) inverter for current control in an AC servomotor, and more particularly to a steady-state method. It can be used as a method to drive a control motor for industrial robots and other automatic machine tools, etc., as long as it suppresses harmonics and is capable of high-speed current follow-up to a sudden change in current command in a transient state. .

[Background technology and its problems]

In a high-performance servo system for an AC motor, it is required to reduce torque ripple and noise in the steady state.
In order to meet this requirement, it is necessary to reduce the harmonic components of the current, and for that purpose it is necessary to implement switching that suppresses the harmonics in the voltage-type PWM inverter. And various switching control methods have been devised to date (for example, G. Pfaff et al; “Design and Experimen
tal Results of a Brushless AC Servo-Drive "in Conf.
Rec.1982 17th Annu.Meet.IEEE IA S; J. Holtz et al;
“A Predictive Controller for the Stator Current V
ector of AC Machines Fed from a Switched Voltage S
ource "in Conf.Rec.1983 Annu.Meet.IPEC; DMBrod et
al; "Crrent Control of VSI-PWM Inverters" in Conf.R
ec.1984 Annual.Meet.IEEE IAS).

However, although these methods are theoretically excellent, they have a drawback that they are not practical for general industrial use because of complicated operations and complicated circuits for implementation. is doing.

In addition, in the high-performance servo system of the AC motor,
High-speed current followability is required for a sudden change in the current command in the transient state. However, in a voltage-type PWM inverter, high-speed current tracking and the above-mentioned harmonic current suppression are contradictory, so it is very difficult to realize a switching system that satisfies both of them at the same time. Actually, there are trade-offs depending on the purpose of application of the servo system, so when both are requested together, system versatility is low.

[Object of the Invention]

The present invention can suppress harmonics in a steady state, can follow a high-speed current in an excessive state, and can control a voltage-type PWM inverter in an AC servomotor in which a control circuit to be executed is relatively simple. Is to provide.

[Means and Actions for Solving Problems]

The present invention When is less than the specified value (at steady state) Select a switching mode in which is always small, Is above the specified value (in the transient state), it is located diagonally to the region to which the deviation current vector belongs The switching mode that produces the largest value is selected, and harmonics can be suppressed in the steady state, and high-speed current tracking can be performed in the transient state.

Specifically, 6 types of voltage vectors and 2 types of zero voltage vectors determined by the switching state of the voltage type PWM inverter for current control are made to correspond to 8 types of switching modes, and by selecting this switching mode, alternating current A method for controlling a voltage-type PWM inverter in an AC servomotor for controlling a servomotor, wherein the inductance and resistance of the servomotor winding are L,
R, And when To In this case, the deviation current vector, which is the difference between the current command vector and the current vector, and the rate of change of the deviation current vector are obtained, and in accordance with the switching mode of the inverter, the central angle 60 ° is divided into six areas. In the current complex plane divided into six equal parts, to which area the deviation current vector belongs is determined, while the zero voltage vector is the origin, and the zero voltage vector is one vertex, and the six types In the voltage complex plane that is equally divided into six equilateral triangular regions I to VI having two sides of two adjacent voltage vectors of the voltage vector, the motor terminal voltage is calculated using the rate of change of the deviation current vector. It is determined which equilateral triangle region I to VI the vector belongs to, and if the deviation current vector is equal to or smaller than a predetermined magnitude, the next switching mode is selected. In determining, among the four switching modes corresponding to two types of voltage vectors and two types of zero voltage vectors which are two sides of the equilateral triangular regions I to VI to which the motor terminal voltage vector belongs in the voltage complex plane. From the equilateral triangular region I to VI to which the motor terminal voltage vector belongs and the region of the current complex plane to which the deviation current vector belongs to.
While selecting from the combination with, when the deviation current vector exceeds a predetermined magnitude,
In determining the next switching mode, a switching mode corresponding to a region to which the deviation current vector belongs on the current complex plane and a region diagonally located on the current complex plane, and which produces the largest change rate component of the deviation current vector Select the configuration.

〔Example〕

1 to 14 are views for explaining an embodiment of the present invention.

Now, consider a load having an internal induced voltage, an inductance L, and a resistance R as shown in FIG. This voltage-current equation is Given in. However, Represents In equation (1), Holds and the following equation is obtained.

Next, the switching mode (switching state) Table 6 shows the relationship with.

Here, k = 0, 7 is a zero voltage mode in which three phases are short-circuited below or above. A vector diagram is shown in FIG.
The left side of the equation (8) is the rate of change of the deviation current, and the current responsiveness is determined by this magnitude and direction. With this, to follow the high-speed current To select a large mode and suppress harmonics You can choose the smaller mode of. in this way It is not necessary to know the load constant value if the switching state is determined by focusing on only the above.

To make the current follow, In contrast, this is 180 degrees out of phase To generate Is required. Shown in FIG. In the case of It is possible to follow the current by selecting the output voltage that causes the component. On the other hand, considering that the inverter output voltage is in seven states including zero voltage, as shown in FIG. 4, the central angle of 60 ° corresponds to the switching mode of the inverter.
In the current complex plane, which is divided into 6 regions by 6 in (6), it is detected to which region the deviation current vector belongs. Here, since the deviation current of each phase is positioned as shown in the figure, it can be easily detected by the comparator.

To suppress harmonic components It is necessary to select a small mode (including zero voltage mode) of.

Therefore, as shown in FIG. Is the origin, and One vertex, the above 6 types In the voltage complex plane that is equally divided into six equilateral triangular regions I to VI having two adjacent voltage vectors on two sides, using the change rate dΔi / dt of the deviation current vector, To which of the equilateral triangle regions I to VI belongs is detected, and the following restrictions are applied to the selection of the switching mode. That is Is small, and I want the current to follow, so The output voltage is selected only from the four modes (zero voltage is the two modes) corresponding to the vertices of the triangle to which is belongs. This is shown in Table 1.

In addition, in FIG. Is in the region of I, and its representative example is at the center of gravity of an equilateral triangle, Indicates. In Figure 6, And the area of the deviation current vector shown in FIG. 4 (FIG. 4). In this case, in order to follow the current in the four triangular modes, When is in or, k = 2 is selected, when is in, k = 1 is selected, and when is in, k = 0, 7 (the one with the smaller number of switching times is selected).
In addition, But in I, III, V Is as shown in FIG. On the other hand, in II, IV and VI, 60
° The phase is delayed and it becomes as shown in FIG. The above
Table 2 shows all the areas considered.

Also, inside the hexagon of Fig. 4, When there is, switching is not performed and the output voltage is held. From this, feedback control of the switching frequency fsw is possible by changing the width Δε of the hexagon. This block diagram is shown in FIG.

Given in. Here, if the coordinates of the current deviation of each phase are delayed by 30 ° and the new coordinate axes are represented by Δx, Δy, and Δz, And can be shown in FIG. Therefore By detecting the sign of the differential dΔx / dt, dΔy / dt, dΔz / dt of Δx, Δy, and Δz The region to which is belongs is uniquely determined.

In this method, as described above, The switching state is determined only from the four modes at the vertices of the triangle to which the. Therefore, Is output, I is either VI or Can be considered to belong to. Therefore, it can be determined from the sign of dΔz / dt from FIG. The other modes are considered in the same manner, and Table 3 shows the results.

By the above method, Can be detected, but the differential signal is easily affected by noise. So actually Think about how you want to do it. Constant (do not use a switching method that can suppress harmonics when transient) Since the expression (7) is satisfied, the expression (9) is defined.
On the other hand, the current command is Therefore, the following equation is obtained by substituting into equation (9).

Than this, It can be seen that has a phase relationship delayed by φ with respect to the current command and rotates at the same angular velocity ω. Therefore, By inserting LPF (Low Pass Filter) into the output of, it is possible to remove the effect of noise generated in the differentiating circuit.

In the case of alternating current, the position is detected, so Can be easily calculated. The circuit configuration diagram is shown in FIG. 10 from the equations (14) and (15).

In order to follow the high-speed current, it must be located diagonally to the area to which the deviation current vector belongs. It suffices to select the switching mode that produces the largest component. In the case of FIG. 3, since the deviation current vector is in the area of, it is located diagonally to this area. Has the largest directional component of K = 2, that is, Should be selected. From equation (8), It is represented by. Therefore, for each region, the largest The output voltage that produces It is uniquely determined regardless of This is shown in Table 4.

This switching method is a comparator method in which the sign of the deviation current of each phase is directly used as a gate signal, and high-speed current tracking is possible.

Both types are switched by the size of. For example, a set value Δh ^* as shown by the dotted line in FIG. 11 is given, and a switching method capable of suppressing harmonics within this hexagon is used. FIG. 12 shows this circuit configuration.

FIG. 13 shows the control circuit.

Is detected using the method as described above in consideration of versatility. Further, FIG. 14 shows a speed control system using a permanent magnet synchronous motor, and Table 5 shows the ratings of the permanent magnet synchronous motor used in this case.

Next, experimental results of a case where the permanent magnet synchronous motor having the rating shown in Table 5 is controlled by the control method according to the embodiment of the present invention and a case where the conventional permanent magnet synchronous motor is controlled by the control method using a known comparator. Will be explained.

In the experiment, as a circuit for implementing the control method of the present embodiment, the circuit shown in FIG. 10, FIG. 12, FIG. 13 and FIG.
Although not shown in the figure, an apparatus for implementing the conventional control method using a comparator using the one shown in the figure is a known general apparatus.

FIG. 15 and FIG. 16 show the results of measurement of the current responsiveness in the steady state by the oscilloscope in the above experiment. FIG. 15 shows the case of fo = OHz, and FIG. In the case of the conventional control method, FIG. 15 (b) shows the case of the above embodiment. In the figure, the vertical axis represents current (A), one scale of the figure is 6 A, the horizontal axis represents time (ms), and one scale is 2 ms.

16 shows the case of fo = 20 Hz, FIG. 16 (a) shows the case of the conventional control method, and FIG. 16 (b) shows the case of the method of the above embodiment. In the figure, the vertical axis represents current (A), one scale in the figure is 6 A, the horizontal axis represents time (ms), and one scale in the figure is 5 ms.

In both the case of the method of the embodiment and the case of the conventional method, the feedback control of Δε is performed so that the switching frequency fsw = 2 KHz.

In this case, in the method of the above-mentioned embodiment in FIG. 15 (b), fsw is limited to about 800 Hz at fo = OHz due to the dead time of the main circuit.

As apparent from FIGS. 15 and 16, the method according to the embodiment of the present invention is always , The harmonic current is significantly suppressed as compared with the conventional method.

Further, FIG. 17 shows the measurement results of the relationship between the rotation speed and the noise during no-load operation in the case of the method of the present embodiment and the case of the conventional method.

In the figure, the vertical axis represents noise (db), and the horizontal axis represents rotation speed (rpm).

In FIG. 17, the curve I is obtained by the conventional method,
Curve II is the case according to the method of this embodiment.

As is clear from FIG. 17, the method according to the present embodiment produces extremely low noise, especially in the low speed region, as compared with the conventional method.

This is in the low speed range This is because the zero voltage mode greatly contributes to the noise reduction since

In addition, the noise increases relatively in the high speed range Increase in zero voltage mode Because it becomes larger.

18 to 19 show the results of measuring the current responsiveness in the transient state.

FIG. 18 shows the case of the conventional method, and FIG. 19 shows the case of the method of the present embodiment.

In this case, the current command of the permanent magnet synchronous motor is id ^* =
It was given by 0, iq = iτ ^* .

Also, in Figures 18 to 19, the horizontal axis represents time (ms).
In each of FIGS. 18 and 19, (a) and (b) show the rotation speed (rpm), and (c) and (d) show the current (A).

In each of the figures, (a) shows a change in the rotation speed control command (ω ^* ), and (b) shows an actual rotation speed (ω) of the electric motor changed based on the command. In the case of, the response is about 15 msec to the command of ω ^* = − 600 → + 600 rpm. In this case, the acceleration torque is about 4.7 times the rated value.

Further, in each of the above figures, (c) and (d) show the current command (iu ^* ) and the current (iu), respectively.

As apparent from FIGS. 18 (d) and 19 (d), there is no difference in the current responsiveness of the two due to the switching of the switching method, and the control method of this embodiment enables high-speed current tracking.
Moreover, the harmonic current is suppressed in the steady state.

As described above, according to the control method of the present embodiment, high-speed response is possible while suppressing harmonics.

Therefore, torque ripple and noise are extremely small. Also,
The control method of this embodiment is Since the switching mode is selected only from the above, there is no need to know the load constant of the motor without depending on the load constant of the motor.

Furthermore, there is no complicated calculation and the control circuit is simple.

For this reason, the control method of this embodiment has an advantage of being extremely versatile.

〔The invention's effect〕

As described in detail above, the present invention is in the voltage complex plane in the steady state. From the four switching modes corresponding to the two types of voltage vectors and the two types of zero voltage vectors on the two sides of, the switching mode in which the deviation current vector change rate is small is selected. Since a switching mode that can be followed is selected, high-speed response is possible while suppressing harmonics, there is little torque ripple and noise, and there is no complicated calculation, so the control circuit can be simplified, and further, Since it does not depend on the load constant, it has excellent effects such as versatility.

[Brief description of drawings]

1 to 14 are views for explaining an embodiment of the present invention, and FIGS. 15 to 16 are for a case where a permanent magnet synchronous motor is controlled by the control method of the embodiment of the present invention and a conventional control method. FIG. 17 is a diagram showing measurement results of torque ripple in the case of control, FIG. 17 is a measurement result of noise in the case of controlling the permanent magnet synchronous motor by the control method of the embodiment of the present invention and in the case of controlling by the conventional control method. FIG. 18 and FIG. 19 are diagrams showing current responsiveness in the transient state by the control method of the embodiment of the present invention and by the conventional example, respectively.

Claims (1)

[Claims] 1. Six types of voltage vectors and two types of zero voltage vectors determined by the switching state of a voltage type PWM inverter for current control are made to correspond to eight types of switching modes, and alternating current is selected by selecting these switching modes. A method for controlling a voltage-type PWM inverter in an AC servomotor for controlling a servomotor, wherein the inductance and resistance of the servomotor winding are L,
R, And when To In this case, the deviation current vector, which is the difference between the current command vector and the current vector, and the rate of change of the deviation current vector are obtained, and in accordance with the switching mode of the inverter, the central angle 60 ° is divided into six areas. In the current complex plane divided into six equal parts, to which area the deviation current vector belongs is determined, while the zero voltage vector is the origin, and the zero voltage vector is one vertex, and the six types In the voltage complex plane that is equally divided into six equilateral triangular regions I to VI having two sides of two adjacent voltage vectors of the voltage vector, the motor terminal voltage is calculated using the rate of change of the deviation current vector. It is determined which equilateral triangle region I to VI the vector belongs to, and if the deviation current vector is equal to or smaller than a predetermined magnitude, the next switching mode is selected. In determining, among the four switching modes corresponding to two types of voltage vectors and two types of zero voltage vectors which are two sides of the equilateral triangular regions I to VI to which the motor terminal voltage vector belongs in the voltage complex plane. From the equilateral triangular region I to VI to which the motor terminal voltage vector belongs and the region of the current complex plane to which the deviation current vector belongs to.
While selecting from the combination with, when the deviation current vector exceeds a predetermined magnitude,
In determining the next switching mode, a switching mode corresponding to a region to which the deviation current vector belongs on the current complex plane and a region diagonally located on the current complex plane, and which produces the largest change rate component of the deviation current vector Voltage source PWM in AC servo motor characterized by selecting
Inverter control method.