JPS5953800B2 - AC motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for operating an AC motor at variable speed using an inverter drive device, and more specifically, the invention relates to a control device for operating an AC motor at variable speed using an inverter drive device. This invention relates to means for preventing the phenomenon of unstable operation (referred to as disturbance).

FIG. 1 is a block diagram showing an example of a conventional AC motor control device equipped with a disturbance prevention circuit, which was already proposed by the present inventor (Japanese Patent Application No. 49808 of 1982).

The principle of this control device is to detect signs of disturbance due to changes in the internal magnetic flux of the motor, and then, depending on the rate of change of the internal magnetic flux,
By changing the output frequency of the power converter that supplies power to the electric motor, changes in internal magnetic flux are damped to prevent disturbances.

In Figure 1, 1 is a commercial three-phase AC power supply, 2 is a converter configured with a controlled rectifier, 3 is an inverter configured with a controlled rectifier, 4 is an induction motor that is the load of the inverter 3, and 5 is a current smoothing reactor. , 6 is a converter phase shifter that controls the output voltage of the converter 3, 7 is a current detector composed of a current transformer and a rectifier, and 8 and 9 are current control computing units that control the converter phase shifter. 10 is a voltage detector composed of a transformer and a rectifier; 11 is an inverter control circuit composed of a logic circuit and an amplification circuit for controlling the thyristor of the inverter 3; 12 is a voltage/frequency conversion circuit; 13 is a speed setting device that can arbitrarily set the load voltage and inverter output frequency.

The torque generated by the induction motor 4 is the output voltage V of the inverter 3.
ac, the current is given as a function of 1ac or Idc, the output frequency, the sweep frequency, etc.

In the control system described above, the frequency wave number of the inverter 3 is controlled by the speed setting value e, and the load voltage is controlled by comparing the detected value of the output voltage with the voltage reference value (speed setting value e,). Closed-loop control is performed, and the load power factor (ratio of magnetizing current to generate magnetic flux and secondary current that contributes to torque generation) is not controlled, so under certain load conditions, the torque generated by the induction motor will decrease. It is known that an unstable phenomenon in which the output voltage and current of the inverter and the inverter oscillate at low frequencies, so-called "disturbance", occurs.
Therefore, in FIG. 1, the following measures S are taken. That is, the motor terminal voltages VR, V5, and VT which are isolated and detected via the transformer 14 are led to the magnetic flux detector 20, where the magnitude of the magnetic flux lφl is calculated. That is, the three-phase voltages VR, V, VT are first converted to the known three-phase/two-phase converter 15.
It is converted into two-phase voltages V and hVβ by . The output voltages Va and Vlj are respectively integrated by an integrator 16 and converted into signals corresponding to two-phase magnetic fluxes φA and φβ, which are then guided to an amplitude calculator 17, where 1φ1=4T
According to the relational expression d1. φ1/Dt is introduced to the adder 19 at the input section of the voltage/frequency converter 12 with the polarity matched to the operating mode (whether the motor is in the motor operating mode or the generator operating mode) each time by the polarity switch 22. and is superimposed on the speed setting signal e1, which is the original frequency command value. The operation mode is determined by comparing the level of output voltage Ea of current control calculator 8, which is a firing angle command signal that determines the output voltage of converter 2, with a reference level in comparator 21. Generally, when the value of the firing angle control signal Ea is at zero level, the firing angle of the converter 2 is 90° and the converter DC output voltage is zero, and this is the boundary between the forward conversion operation and the inverse conversion operation of the converter 2. Converter 2 performs a forward conversion operation in the motor operation mode, and reverse conversion operation in the generator operation mode, so in this case, the comparator 21 changes the firing angle control signal. The operation mode is determined by the polarity. This makes it possible to determine the operating mode of the motor without detecting the rotational speed of the motor, the output voltage of converter 2, or the input voltage of inverter 2. By choosing the polarity relationship correctly for each mode, it is possible to give a damping effect to changes in the internal magnetic flux.
A damping effect occurs due to the mutual interference between the secondary current and the magnetizing current, and unstable phenomena can be prevented over a wide speed control range. As described above, the control device proposed by the present inventor is as follows:
Although it is very effective as a disturbance prevention circuit, it has the following drawbacks.

1 As the load becomes lighter (the motor power factor becomes worse), the effect of preventing disturbance becomes weaker.

It is necessary to switch the polarity of the feedback signal depending on the polarity of the two converter output voltages, that is, whether the motor power factor angle is larger or smaller than 90°. Even if the average power factor angle is always 90 degrees or less since it is only an acceleration, the power factor angle may temporarily exceed 90 degrees, and this switching is necessary.

This will be explained below.

Now, to simplify the explanation, assuming that the leakage reactance and primary resistance of the induction machine are zero, the vector relationship between current and voltage is shown as shown in FIG. Here, i1 is the primary current, I2 is the secondary current, IM is the magnetizing current, V1 is the primary voltage, and φ2 is the effective magnetic flux. Here, the motor power factor is the cosine of the angle θ formed by the current vector and the voltage vector, and the second
In the figure, ゛ is indicated by COsθ. Now, suppose that a disturbance such as a load change is applied to the induction machine, causing mutual interference between the secondary current 12 and the magnetizing current 1M, and the power factor angle changes by ±Δθ degrees. Figures 3A and 3B are vector diagrams showing the situation at this time. Figure 3A is when the load is large (good power factor), and Figure 3B is when the load is light (poor power factor). It shows the vector relationship of .

As can be seen from these figures, the amount of change ΔIM in magnetizing current 1M becomes smaller as the load becomes smaller for the same change in power factor angle Δθ, and this is true because the magnitude of magnetizing current and magnetic flux are proportional. indicates that as the load decreases, the amount of change in magnetic flux, that is, the amount of feedback signal, decreases with respect to a change in the same power factor angle Δθ. Furthermore, in FIG. 3b, even though the average power factor COsθ is positive, in the shaded region the power factor angle (θ−Δθ) is 90° or more, and the power factor is negative. Therefore, in this region, the polarity of the amount of change in magnetic flux must be reversed and returned. If it is not inverted, positive feedback will occur in this region, resulting in increased disturbance. FIG. 4 is a block diagram showing another example of a conventional AC motor control device equipped with a disturbance prevention circuit, which was already proposed by the present inventor as (Japanese Patent Application No. 53239 of 1982).

In this control device as well, the basic configuration of the control system is the same as that shown in FIG. 1, and the same components are given the same reference numbers.

The disturbance prevention circuit added according to this proposal is based on the control input signal E of the phase shifter 6 representing the output voltage &k of the converter 2.
A divider 23 outputs a signal corresponding to the motor power factor COsθ by dividing a by the speed setting signal e1 of the setting device 13 representing the inverter frequency f, and converts the output signal of this divider into a power factor angle θ. Linearization circuit 25 for converting into a corresponding signal
A differentiating circuit 24 that differentiates the output signal of this linearization circuit, and an adder 19 that superimposes the output signal of the differentiating circuit 24 on the speed setting signal e1 that becomes the frequency command value in the input circuit of the voltage/frequency converter. It is configured. For example, when the power factor angle θ changes in the increasing direction due to torque disturbance, the input voltage of the voltage/frequency converter 12 is made higher than the original frequency command value e1 by the power factor angle change rate DO/Dt.

This increases the inverter frequency, that is, the motor primary current frequency, and has the effect of preventing an increase in the power factor angle.
Conversely, in the direction of decreasing the power factor angle, the inverter is operated at a frequency that is lower than the original frequency command value by the rate of change in the power factor angle, thereby creating an effect that prevents the decrease in the power factor angle. According to the disturbance prevention circuit according to the present proposal, when looking at changes in the output voltage of the differentiating circuit 24 in response to minute changes in the input voltage of the voltage/frequency converter, the gain in the signal transmission section has no frequency dependence and has a constant gain. Therefore, an optimum amount of compensation can be obtained over the entire speed control range. However, on the other hand, it has the following drawbacks.

1 The amount of change in power factor COsθ differs depending on the power factor because the amount of change in power factor COsθ is different when θ is around 0° (good power factor) and around 90° (poor power factor) for the same change in power factor angle Δθ. The amount of feedback changes.

2 Therefore, the power factor COsθ is changed to the power factor COsθ by the linearization circuit.
It is necessary to change the power factor angle θ from sθ and feed back the amount of change DO/Dt.

This invention was made in order to solve the drawbacks of the conventionally proposed control devices as described above, and the purpose of this invention is to improve the power factor by making use of the advantages of the two previously proposed control devices. An object of the present invention is to provide a control device for an AC motor that can always obtain the same disturbance prevention effect without depending on.

The main point of the configuration of the present invention is that, in a control device that operates an AC motor at variable speed using an inverter drive device, a calculation circuit that calculates the internal magnetic flux of the AC motor and a phase controller that controls the output voltage of the inverter drive device are provided. A division circuit that divides the control human power signal by the speed setting signal, and a first signal that is the internal magnetic flux signal obtained by the arithmetic circuit and a second signal that is the division result obtained by the division circuit are differentiated. The present invention is characterized in that a differential circuit for outputting the output and a means for superimposing the differential output on the speed setting signal of the inverter drive device are provided. FIG. 5 is a block diagram showing one embodiment of the present invention.

The configuration shown in FIG. 1 corresponds to the circuit shown in FIG. This corresponds to a circuit obtained by removing the linearization circuit 15 from the corresponding circuit.

As a result, when the load is large (good power factor), the circuit consisting of the magnetic flux detection circuit 20 described in the circuit of FIG. An additional circuit for feeding back changes in the power factor, which includes the differential circuit 24 and the adder 25, provides the effect of preventing disturbances, so that the same effect of preventing disturbances as a whole can be obtained regardless of the power factor. FIG. 6 is a plotter diagram showing a modified embodiment of FIG. 5.

The difference between FIG. 6 and FIG. 5 is a comparator 21 and a polarity switch 2.
2 and the differentiating circuit 24 are omitted, and the adder 25 is replaced by the amplitude calculator 1.
7 and the differentiating circuit 18, the divider 2
The output signal of 3 and the output signal of the amplitude calculator 17 are added to form an input signal of the differentiating circuit]8. As a result, in the case of one-quadrant operation such as pump drive, the power factor COs
Even if θ enters the shaded area in Figure 3b at light load and the signal that feeds back the amount of change in magnetic flux becomes a positive feedback, the amount is small, so the signal that feeds back the amount of change in power factor COsθ is Since the amount of positive feedback can be sufficiently canceled by the feedback, a sufficient effect of preventing disturbance can be obtained as a whole.

Therefore, the comparator 21 and the polarity switch 22 can be omitted, and furthermore, by moving the adder 25, the differentiating circuit 24 can also be omitted, so that the overall circuit configuration can be simplified. According to this invention, the magnitude of magnetic flux is 1φl and the power factor COs
Since θ is added and the change is fed back to the frequency command value, it is possible to always obtain the same disturbance prevention effect regardless of changes in the power factor without using a linearization circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a conventional AC motor control device equipped with a disturbance prevention circuit, Fig. 2 is a vector diagram showing the vector relationship between current and voltage in an induction machine, and Fig. 3 is a similar diagram when the disturbance occurs. In this vector diagram, a shows that when the load is relatively heavy, and b shows that when the load is relatively light. FIG. 4 is a block diagram showing another example of a conventional AC motor control device equipped with a disturbance prevention circuit, FIG. 5 is a block diagram showing an embodiment of the present invention, and FIG. FIG. Code explanation, 1...
...AC power supply, 2...Converter, 3...
...Inverter, 4...Induction motor, 5...
... Current smoothing reactor, 6... Phase shifter for converter, 7... Current detector, 8...
・Current control computing unit, 9...Voltage control computing unit, 10...Voltage detector, 11...Inverter control circuit, 12...Voltage /Frequency converter, 13... Speed setter, 14... Motor terminal voltage detector, 15... 2-phase/3-phase converter, 16...・Integrator, 17... Arithmetic unit,
18... Differential circuit, 19... Adder,
20... Magnetic flux detector, 21... Comparator, 22... Polarity switch, 23... Division circuit, 24... Differentiation circuit, 25... Linearization circuit.

Claims (1)

[Claims] 1. In a control device for variable speed operation of an AC motor using an inverter drive device, a control input signal of a calculation circuit that calculates the internal magnetic flux of the AC motor and a phase controller that controls the output voltage of the inverter drive device is controlled by the speed control device. a division circuit that divides by a setting signal; and a differentiation circuit that differentiates and outputs a first signal that is the internal magnetic flux signal obtained by the arithmetic circuit and a second signal that is the division result obtained by the division circuit. , and means for superimposing the differential output on a speed setting signal of an inverter drive device.