JPS5936517B2 - AC motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for an AC motor driven by a power converter, and more particularly to a control device for an AC motor having an instantaneous current control system that controls the motor current in a sinusoidal manner.

It is common practice to control the motor current of an AC motor driven by a power converter in a sinusoidal manner.

One example is a control system for a non-commutator motor that drives a synchronous motor using a voltage type cycloconverter as shown in FIG. FIG. 1 is a circuit configuration diagram of an example of a conventional voltage type cycloconverter control device.

In Fig. 1, 1 is an AC power supply, and 2 is a cycloconverter that receives AC voltage from the AC power supply 1 and outputs variable voltage, variable frequency three-phase AC, with thyristor groups UP, UN, VP connected in antiparallel. , VN, WP, and WN. 3 is a synchronous motor driven by the cycloconverter 2; 4 is an AC power supply that supplies field power for the synchronous motor 3; 5 is an AC power supply that receives AC voltage from the AC power supply 4 and supplies field current to the field of the synchronous motor 3; A field current control circuit that supplies field current and controls its magnitude.

6 is a speed generator that detects the rotational speed of the synchronous motor 3;
is a position detector that outputs three sine wave signals having a phase difference of 120 degrees from each other, which are sine wave signals whose phases correspond to the relative positions of the field and armature of the synchronous motor 3. For example,
It consists of a permanent magnet rotor and a Hall element attached to a stator facing the rotor.

The sine wave signal (position signal) output from the position detector T is the second
The waveform will be as shown in the figure. 8 is a speed command circuit, 9 is a speed command signal output from the speed command circuit 8 and a speed generator 6
A speed control circuit 10 outputs a signal according to the deviation of the rotational speed signal output from the cycloconverter 2; A multiplier (current command circuit) that outputs a sine wave current reference signal for controlling the output current of the U phase); 12 is a current that outputs a signal according to the deviation between the output signals of the multiplier 10 and the current detector 11; A control circuit, 13 is an automatic pulse phase shifter that controls the firing phase of the thyristor according to the output signal of the current control circuit 12, and 14 is a control circuit that controls the thyristor group UP or UN depending on the direction of the U-phase output current of the cycloconverter 2. This is a gate circuit that sends signals alternately.

Note that the figure shows the thyristor group UP. Although only the control circuit for UN is shown, other thyristor groups P, N and WP,
．． There are also control circuits for WN that are the same as part numbers 10-14. Since they operate in the same way as part numbers 10 to 14, their description will be omitted.Next, the operation of this circuit will be explained.

The position detector 7 emits three sine wave signals having a constant amplitude and a phase difference of 120 degrees, regardless of the rotational speed of the synchronous motor 3.

FIG. 2 shows this output signal Su-Sw. In the multiplier 10, the output signal of the speed control circuit 9, which is a signal corresponding to the rotational speed deviation, is multiplied by the output signal of the position detector 7, and the output signal from the multiplier 10 is in the same phase as the output signal of the position detector 7.
An electric signal having an amplitude proportional to the output signal of the speed control circuit 9 is output.

The automatic pulse phase shifter 13 and the gate circuit 14 are controlled according to the deviation between this signal and the signal from the current detector 11, and the thyristor group UP. The thyristor UN is fired, and the output current of the cycloconverter 2 is controlled to a value according to the output signal of the multiplier 10. That is, the magnitude of the output current is controlled to a value proportional to the output signal of the speed control circuit 9, which is the speed deviation, and the phase of the current is controlled to be in the same phase as the position signal output from the position detector 7. As a result of being controlled by the control circuit as described above, the speed of the synchronous motor 3 is operated at a value commensurate with the speed command signal.

However, this device has the following drawbacks.

That is, since the frequency of the output current varies over a wide range (for example, 0 to 20 Hz), as the operating frequency increases, the response delay of the current control system including the current control circuit 12 causes the sine wave to change as shown in FIG. The phase of the output current lags behind the wave current reference command by a certain angle α.

For this reason, the current is not controlled to a predetermined phase, making it impossible to operate with a predetermined power factor, and the torque decreases, making it impossible to perform a predetermined operation. SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for an AC motor that can eliminate the above-mentioned disadvantages, maintain the current phase at a predetermined value even when the speed changes, and allow the motor to operate in a predetermined manner.

The feature of the present invention is that when obtaining a sine wave current phase reference signal from a multiphase sine wave signal generated by a sine wave generator,
The reason is that the phase of the sine wave current phase reference signal is advanced as the motor speed increases.

The sine wave current reference signal (multiplier 1
Focusing on the fact that the output (0 output) is created based on the position detector signal, the current command signal is set relative to the position detector signal to compensate for the phase delay due to the delay in the current control system.
By controlling the output current to advance according to the speed, it is possible to eliminate fluctuations in the phase of the output current.

FIG. 4 shows an embodiment of the invention.

Items numbered 1 to 14 in FIG. 4 are the same as those shown in FIG. 1, so their explanation will be omitted. 20 is a function generator which receives a signal from the speed generator 6 and outputs a signal having a predetermined relationship therewith.

The function generator 20 generates a phase angle signal α proportional to the speed detection signal of the speed generator 6, as shown by the characteristic a shown by a solid line in FIG. 5, for example. The phase angle signal α is the fifth
It may also be parabolic, as shown by characteristic b indicated by a dotted line in the figure.
Function generators 21 and 22 receive the signals and generate cosine and sine signals therefrom, and multipliers 23 and 24 multiply the position detector signal and the signals from the function generators 21 and 22, respectively.

The control circuit of FIG. 4 has a function generator 2 in addition to the control circuit of FIG.
0, 21, 22 and multipliers 23, 24 are added. In addition, in FIG. 4, the thyristor group UP. UN
Although only the control circuit for the other thyristor groups V is shown,
P. Part number 10-1 also for VN and WP, WN
4 and 21 to 24, but the explanation thereof will be omitted. Next, the operation of the circuit of this embodiment will be explained.

Generally, a sine wave signal whose phase is advanced by a phase angle α with respect to the sine wave signal SINwt can be extracted by calculating the following equation. Note that W is the angular frequency and t is the time. That is, as shown in FIG.
t is detected respectively.

Ten thousand. The function generators 21 and 22 generate a cosine (COSα) signal and a sine (SINα) signal in response to the speed feedback signal. Therefore. A sine wave signal, SIN(Wt+α), can be obtained by multiplying these two signals by multipliers 23 and 24 according to the relationship in the previous equation and adding them. Through such calculations, the sine wave current reference signal (
The output of the multiplier 10) leads the signal phase of the position detector by α.

If the phase angle α is determined to be equal to the phase delay due to the delay of the current control system, as a result, the phase of the current can be made to match the signal of the position detector. That is, if the phase angle α is determined by the function generator 20 in accordance with the phase delay for each frequency. Current phase fluctuations can be prevented. According to the present invention, it is possible to provide a control device for an AC motor that can prevent phase fluctuations in the output current due to speed and can perform predetermined operation without causing a decrease in torque.

In addition, based on the same idea, a possible method to advance the phase of the current reference signal according to the speed is to differentiate the sine wave signal generated by a sine wave generator with a differentiator circuit and advance the phase. In this case, harmonic components are likely to be amplified, so there is a drawback that it is easily affected by noise.

The present invention is not affected by such influences and operates stably.

[Brief explanation of drawings]

Figure 1 is a control block diagram of a conventional non-commutated motor;
, 3 is a diagram for explaining the operation of the circuit shown in FIG. 1,
FIG. 4 is a control block diagram of a commutatorless motor showing an embodiment of the present invention, and FIG. 5 is a diagram showing an example of the characteristics of the function generator in FIG. 1.

Claims (1)

[Claims] 1. An AC motor driven by a power converter, a speed control circuit that outputs a current command signal according to a deviation between a speed command signal of the motor and a speed detection signal, and a speed control circuit for commanding the phase of the motor current flowing through the motor. a sine wave generator that generates a polyphase sine wave signal with a constant amplitude; and a sine wave generator that generates a sine wave current phase reference signal obtained from the polyphase sine wave signal whose amplitude is varied according to the magnitude of the current command signal. a current command circuit that generates a wave current reference signal, an instantaneous current control circuit that performs firing control of the power converter based on the deviation between the sinusoidal current reference signal and the current detection signal, and controls the motor current; and current phase reference adjusting means for advancing the phase of the sinusoidal current phase reference signal in proportion to the motor speed when obtaining the sinusoidal current phase reference signal from the phase sinusoidal signal. Device.