JPH053236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a PWM control inverter device whose load is an AC motor that can suppress magnetic noise of the motor.

[Prior art]

FIG. 1 shows an example of a schematic block configuration of a conventional voltage-controlled sine wave PWM inverter using an induction motor as a load using a slip frequency control method. In the figure, 1 is a three-phase commercial AC power supply,
2 and 3 are converter circuits composed of power switches such as thyristors, 4 is a DC smoothing circuit mainly composed of power capacitors, 5 is an inverter circuit composed of power switches such as power transistors, and 6 is a load. 7 is an induction motor, and 7 is a speed detector. Further, 8 is a speed detection circuit that receives a signal from the speed detector and generates a speed feedback signal, 9 is a slip control amplifier, 10 is a voltage command sine wave generation circuit that generates a command sine wave of the inverter output voltage, and 11 is a V/
F pattern generation circuit, 12 is a voltage detection circuit that detects the inverter output voltage, 13 is a PWM control circuit, 14 is a base amplifier circuit, 15 is a converter voltage command circuit, 16 is a voltage detection circuit that detects the converter output voltage, 17 is a phase control circuit, 1
8 is a gate amplifier circuit.

The control operation will be briefly explained below. Speed command Nr and speed detection signal Nf from speed detection circuit 8
The deviation from this is amplified by the slip amplifier 9, and the output signal of the slip amplifier 9 becomes the slip frequency command signal ω _S corresponding to the slip frequency. This slip frequency command signal and the speed detection signal are added to form a frequency command signal ω _r , which is input to the voltage command sine wave generation circuit 10 and the V/F pattern generation circuit 11. When operating an AC motor at different frequencies, as is well known, in order to avoid magnetic flux saturation of the iron core within the motor, the voltage applied to the motor must be varied while maintaining a certain relationship with the frequency according to the required output characteristics. There is. The V/F pattern generation circuit 11 generates a pattern that defines the relationship between voltage and frequency for this purpose, and its output is generated as shown in curve a in Figure 2, for example, in response to the input frequency command signal ω _r . Become.

In FIG. 2, the region is a region where a constant torque is required, and the region is a region where the torque decreases as the frequency increases and a constant output is required. On the other hand, the voltage command sine wave generation circuit 10 generates a three-phase sine wave signal with a frequency proportional to the frequency command signal ω _r and an amplitude proportional to the signal from the V/F pattern generation circuit 11. First, it becomes each phase voltage command signal Vr of the inverter. This voltage command signal Vr is a voltage feedback signal from the voltage detection circuit 12.
The difference between the two is input to the PWM control circuit 13, where the deviation amount is integrated. FIG. 3 depicts one phase of these operating waveforms as a representative. In Fig. 3, c is a sine wave voltage command signal Vr, and d is a voltage feedback signal Vf. In this figure, the voltage at the output terminal seen from the midpoint of the DC voltage Vd is fed back, and (+)
When the upper switch connected to the side DC bus is on, +Vd/2 is fed back, and when the lower switch is on, -Vd/2 is fed back. Here, the integral value of the deviation of both c and d corresponds to the shaded area,
A signal is generated to turn on and off the upper switch and the lower switch so that this area is kept at a certain value, and is amplified by the base amplifier 14 to control the power switch on and off. The area value (integral value of deviation) that is controlled to be constant here is the number of on/off times allowed for the power switch (this is called the PWM chopper frequency or switching frequency, and is considered from both current ripple suppression and power switch switching loss). It is a value determined from (constrained).

Furthermore, as is clear from Fig. 3, when outputting the same voltage value, when the converter voltage Vd is high, the on/off frequency of the above-mentioned switch becomes higher, which causes an increase in motor magnetic noise, an increase in iron loss, and an increase in iron loss. Furthermore, this has the disadvantage of increasing the switching loss of the inverter device. Therefore, over the entire operating frequency range,
In order to keep this switching frequency substantially constant, the converter voltage Vd is also controlled in accordance with the inverter output voltage, as shown in FIG. 2b, for example. In FIG. 1, a converter voltage command circuit 15 generates a command signal as shown in FIG. 2b from the output of the V/F pattern generation circuit 11. Here, the difference between a and b in FIG. 2 is a value corresponding to the difference between the peak value of the sinusoidal voltage command signal c and the peak value Vd/2 of the voltage feedback signal d in FIG. b
If the difference is small, the on/off frequency of the power switch will be low, as explained above, and as a result, the ripple in the current flowing to the motor will be large.
In FIG. 3, when Vd falls to the peak value of c>Vd/2, the on/off control of the power switch is no longer performed normally, the current ripple becomes even larger, and three-phase phase imbalance may occur. Therefore, in order to properly perform on/off control and suppress current ripple, the difference between a and b in FIG. 2 must be at least a certain value.

The phase control circuit 17 receives the output signal of the converter voltage command circuit 15 and the converter voltage detection circuit 1.
This circuit determines the firing phase of converter 2 or 3 based on the difference between the output of converter 6 and converter 6, but it also has the function of switching the signal to converters 2 and 3 based on the magnitude relationship between the two signals. That is, when the load motor is in a power running state, energy is supplied from the three-phase commercial power supply 1 to the motor via the converter circuit 2, the smoothing circuit 4, and the inverter circuit 5. On the other hand, when the load motor decelerates, the rotational energy of the motor is regenerated to the three-phase commercial power supply 1 via the inverter circuit 5 - smoothing circuit 4 - converter circuit 3.

The inverter device whose configuration is controlled as described above is
Since the voltage drop when the power switch of the inverter circuit 5 is turned on is also taken into consideration and corrected, the DC voltage component included in the output voltage is also very small, and an output voltage close to a sine wave with little harmonic distortion can be obtained. It has high motor efficiency and high response, making it a useful motor drive device.

Next, consider a case where positioning and stop control is performed in the above-mentioned inverter device. FIG. 4 is an example of a conventional schematic block configuration when positioning and stopping control is performed. In FIG. 4, 19 is a position detector such as a pulse encoder, 20, 21, 22 are signal changeover switches, 23 is a positioning sequence circuit that controls switching of these switches, 24 is a positioning speed command circuit, and 25 is a position control amplifier. , 26
is a position detection circuit. FIG. 5 shows an example of the operation when positioning is performed in the circuit configured as shown in FIG. 4. When the positioning signal is input, first the switch 20 is turned off, and the switch 21 is turned on to switch the speed command to a signal from the positioning speed command circuit 24. Next, it is detected that the motor speed has followed the command value, and switch 21 is turned off;
2 switches to a position control loop, approaches the target point at a speed commensurate with the positional deviation from the target stop point, and comes to a stop. When stopped, excitation is applied commensurate with the required servo torque, and a position loop is set up.

However, the conventional positioning control performed as described above has the following drawbacks. That is, the PWM mentioned above
The control method can also compensate for differences in the voltage drop of the power switch itself, so it is useful for reducing motor torque ripple and suppressing motor vibration. Since the on/off frequency changes over time, the magnetic noise from the motor is not a constant sound, but the tone changes slightly, causing discomfort. During normal operation, this is not a problem as it is muffled by noise such as wind noise during motor operation and machine noise, but it becomes particularly noticeable when the motor is stopped due to the positioning stoppage, as the motor operation noise disappears.

[Summary of the invention]

This invention was made to solve these drawbacks, and its purpose is to provide an inverter device that suppresses the converter voltage lower than the value during normal operation and operates at a lower chopper frequency only during positioning stops. There is.

[Embodiments of the invention]

FIG. 6 is a block diagram showing one embodiment of the present invention, in which a voltage correction circuit 27 is added to FIG. 4. The positioning signal and the slip frequency command signal ω _S are input to the voltage correction circuit 27, and the output thereof is input to the converter voltage command circuit 15.
It is configured to correct the converter voltage command. When positioning and stopping is performed here, the voltage correction circuit 27
When the positioning signal is input, it responds to the slip frequency wave command signal ω _S and changes the voltage command from the converter voltage command circuit, for example, from the normal converter voltage command so that the converter voltage command is lower than the value in the normal operating state. The output signal of the voltage correction circuit 27 at this time is corrected to be multiplied, and the converter voltage is lowered. As a result, the on/off frequency of the power switch is lowered, the magnetic noise frequency of the electric motor is lowered, and the discomfort can be reduced. When the on/off frequency decreases, the current ripple increases, but the above correction value of the converter voltage is within the range that allows the current ripple during positioning and stopping, and ensures that the magnetic noise caused by the on/off frequency does not cause discomfort. Select the value of the area that is not given. In this case,
Magnetic noise is largely related to the resonance frequency of the machine in which the motor is assembled, and the correction value is selected to avoid this machine resonance frequency. 7 and 8, in response to the slip frequency command signal ω _S , the difference between the converter voltage and the inverter voltage corresponding to the difference between b and a in FIG. 2 is calculated as the slip frequency command signal ω _B becomes smaller. Voltage correction circuit 2 designed to be small
7 shows the output signal of No. 7. FIG. 9 depicts the above-mentioned correction control of the converter voltage command, and shows how the converter voltage decelerates over time and lowers the converter voltage immediately before or after stopping, as indicated by the transition in the direction of the arrow. If you do it like this,
During deceleration, it is the same as the normal operating state, and there is almost no concern that the previous operating performance will be impaired. FIGS. 10 and 11 are enlarged views of the part marked with the ninth circle. FIG. 10 corresponds to the example shown in FIG. 7, and the line portion in the figure is the corrected portion. In this example, the voltage correction circuit 27 outputs a signal that increases as the slip frequency command signal (ω _{S )} increases when the slip frequency command signal (ω _S becomes less than a predetermined value immediately before stopping). .Also the 11th
The figure corresponds to the example in FIG. 8, and the broken line portion in the figure is the corrected portion. In this example, as the output signal of the voltage correction circuit 27, a signal having a constant value is generated when the slip frequency command signal ω _S becomes equal to or less than a predetermined value immediately before stopping.

〔Effect of the invention〕

This invention lowers the on/off frequency of the power switch during positioning and stopping, so compared to conventional inverter devices, the magnetic noise of the load motor is reduced and discomfort is eliminated, which is a special effect.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram of a conventional voltage-controlled sine wave PWM inverter using a slip frequency control method, and Fig. 2 is a diagram showing an example of the output characteristics of a V/F pattern generation circuit and a converter voltage command generation circuit.
Fig. 3 is a diagram showing PWM operation, Fig. 4 is a block diagram of a conventional device when performing positioning stop control,
Fig. 5 is a time chart showing the positioning and stop control operation, Fig. 6 is a block diagram of an inverter device showing an embodiment of the present invention, Figs. 7, 8, 9,
FIG. 10 and FIG. 11 are characteristic diagrams showing the control operation of the present invention. 1: Commercial power supply, 2, 3: Converter circuit, 5:
An inverter circuit consisting of a power switch,
6: Load AC motor, 10: Voltage command sine wave generation circuit, 11: V/F pattern generation circuit, 13:
PWM control circuit, 15: converter voltage command circuit, 16: converter output voltage detection circuit, 17:
Phase control circuit, 23: positioning sequence circuit,
24: Positioning speed command circuit, 27: Voltage correction circuit, ω _S : Slip frequency command signal. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. An inverter device that uses an AC motor as a load to perform positioning and stop control, and includes a converter section that converts commercial power to direct current, an inverter section that converts direct current to alternating current output at a desired frequency, and an inverter section that converts commercial power to direct current. A PWM control circuit that detects the output voltage of the converter and outputs a pulse width modulation signal for on/off control by matching this detected value with the voltage command value, and a converter voltage that generates the output voltage command signal of the converter section. A command circuit, a speed detection means for detecting the speed of the AC motor, and a slip frequency command signal and a positioning signal generated based on a speed deviation signal that is a difference between the speed command and the speed detection signal of the AC motor are inputted. and a voltage correction circuit that outputs a voltage correction command to the converter voltage command to lower the output voltage of the converter when the slip frequency command signal becomes less than a predetermined value when the positioning signal is input. An inverter device characterized in that the on/off frequency of the power switch of the inverter section is low. 2. The inverter device according to claim 1, wherein the voltage correction circuit always generates an output signal of a constant value when the slip frequency command signal becomes equal to or less than a predetermined value. 3. The inverter according to claim 1, wherein the voltage correction circuit generates an output signal as the slip frequency command signal increases when the slip frequency command signal becomes less than a predetermined value. Device.