JPS5822959B2 - Control device for instantaneous voltage drop of input power supply of inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device used when an inverter input becomes abnormal in a configuration in which AC power is supplied to a load by an inverter output.

When operating the electric motor based on the output from the inverter,
2. Description of the Related Art There is a known method for continuing operation by regenerating the mechanical energy of an electric motor into an inverter in the event of an abnormality such as a momentary voltage drop in an input power source or a momentary power outage.

That is, this conventional means disables the forward converter when there is an abnormality in the voltage drop tube of the input power supply to the impark, lowers the frequency of the impark, and allows the motor to continue operating with power regeneration. During a voltage drop or instantaneous power outage, the voltage regulator cannot be used because the voltage control loop is not formed due to the inoperation of the forward converter and the amplifier becomes saturated. It had to be disabled.

However, if this voltage controller is disabled, the rise of the output voltage of the forward converter will be delayed due to the time lag of the damping circuit of the voltage controller when the power is restored, resulting in a delay of approximately several hundred meters.
There will be a time delay of about 5 minutes.

This means that the voltage controller of the inverter is equipped with a damping circuit as a compensation circuit in order to stabilize the voltage control system, and even if the input changes stepwise based on the response delay of this damping circuit, the voltage controller This is clear from the fact that there is a delay in the rise of the output.

Therefore, if the voltage drop compensation circuit due to frequency reduction is immediately disconnected even after the power is restored, there will be a problem that the inverter output voltage will drop before the output of the voltage controller rises.

Therefore, it is necessary to delay switching of the frequency reduction circuit until the output of the voltage controller rises.

Further, this switching time becomes longer as the response speed of the voltage control system becomes slower.

In this way, even if the drop time is about several 100 m5, the open wave number reduction circuit must be operated for about several 100 m5, so the voltage drop time from the inverter to the load will apparently be longer, and The drawback was that a large amount of rotational energy was required from the electric motor to continue operation, and the amount of rotational speed drop was also low.

For example, in the textile industry, if the rotation speed falls outside the accuracy of ±0.1%, the product becomes defective, and if the rotation speed falls for a long time, the defective product also becomes a dog.

The purpose of the present invention is to eliminate all of the above-mentioned drawbacks by configuring a circuit so that the operation of a forward conversion circuit that supplies variable voltage to an inverter can be continued even in the case of a momentary power outage or voltage drop. An object of the present invention is to provide a control device for an inverter when an input power supply abnormality occurs without control delay.

The illustrated embodiment will be described in detail below.

In the figure, 1 is a converter, an AC power source P is connected to its input terminal 1a, and a variable DC voltage is applied to output terminals 1c, i based on a gate command applied to a control input terminal 1b.
Obtained at c'.

2 is an inverter, and its DC input terminal 2a r 2a'
The current outflow terminal 1c of the converter is connected to the current inflow terminal 2a through a smoothing reactor 3 and a diode 4, and the current outflow terminal 23' is connected to the current inflow terminal 1c of the converter 1. 10' are directly connected.

The frequency of the AC power appearing at the output terminal 2c is controlled by the gate signal applied to the control input terminal 2b.

A voltage detection resistor 5 is connected to the series circuit of the converter 1 and the smoothing reactor 3, and detects the position of the intermediate tap 5a as a voltage proportional to the output voltage of the converter 1.

6 is a smoothing capacitor, which is connected to the input terminal 2a of the inverter 2.
, 2a'.

M is a synchronous motor as a controlled object, and the inverter 2
It is driven by AC power supplied from the output terminal 2c of.

? , 8.9 are voltage detection circuits, and voltage detection circuit I
receives the voltage of the AC power supply P at its input terminal 7a and supplies a command having a level proportional to the voltage of the AC power supply P from its output terminal 7b.

On the other hand, the voltage detection circuit 8 receives the voltage at the intermediate tap 5a of the resistor 5 at its input terminal 8a, and supplies a command having a level proportional to the voltage from its output terminal 8b.

Further, the voltage detection circuit 9 receives the output voltage of the inverter 2 at its input terminal 9a, and obtains a command having a level proportional to the input voltage at its output terminal 9b.

10 is a converter driver that controls the phase at the time of pulse generation based on a command applied to an input terminal 10a, and supplies an output command to a control input terminal 1b of the converter 1 from an output terminal 10b.

A voltage controller 11 supplies a signal corresponding to a command applied to an input terminal 11a to an input terminal 10a of the driver 10 from an output terminal 11b.

Feedback control is performed by a command applied to the feedback signal input terminal 11c.

Reference numeral 12 denotes a minimum value selection circuit, which functions to guide the command with a lower input level among the commands applied to the input terminals 12a and 12b to the output terminal 12c;
are the output terminals 8b and 9 of the voltage detection circuits 8 and 9, respectively.
b, and the output terminal 12c is connected to the feedback input terminal 11c of the voltage controller 11.

13 is a multiplier, which functions to supply a command proportional to the multiplied value of the commands applied to input terminals 13a and 13b from an output terminal 13c, and the output terminal of the voltage detector 7 is connected to the input terminal 13a. Terminal 13c is connected to input terminal 11a of voltage controller 11.

14 is an oscillator which receives the signal from the frequency setter 15 at the input terminal 14a and outputs pulses of a predetermined frequency to the output terminal 1.
4b, and has the effect of reducing the oscillation frequency according to a command given to the control terminal 14c.

16 is an F-V converter, and the above oscillator 1 is connected to the input terminal 16a.
The output terminal 16b is connected to the input terminal 13b of the multiplier 13.

Reference numeral 17 denotes a pulse distributor, which supplies a gate signal from an output terminal 17b to a control input terminal 2b of the impark 2 in response to an input from the oscillator 14 received at its input terminal 17a, thereby performing an inverse conversion operation of the inverter 2.

Reference numeral 18 denotes a frequency reducer in which the command level applied to the input terminal 18a is smaller than the command level applied to the other input terminal 18b, and when the command level is input to the control input terminal 18c, the frequency reducer outputs the signal from the output terminal 18d to the oscillator. Each input terminal 18a is connected to the control terminal 14c.

It is configured to send a frequency reduction command according to the difference in the command level given to the frequency reduction command 18b.

At this time, the output terminal 9b of the voltage detection circuit 9 and the output terminal 16b of the F--■ converter 16 are connected to the input terminals 18a and 18b, respectively.

19 is a command device, and a voltage detector 8 received at an input terminal 19a
output terminal 8b, and the other input terminal 19b is F-
The output terminals 16c of the V converters 16 are connected to each other, and when the command level to the input terminal 19a becomes small enough to cause the motor M to become out of synchronization compared to the command level given to the input terminal 19b, the output terminals A command is supplied from 19c to the control terminal 18c of the frequency reducer 18.

In the configuration of the above embodiment, first, when a normal voltage is obtained from the AC power source P, this voltage is supplied to the converter 1, and at the same time, a command corresponding to the rated speed of the electric motor M is issued from the frequency setting device 15. is given to the oscillator 14, and the pulses from the oscillator 14 are passed through the distributor 17 to give ignition signals to each of the sirisks constituting the inverter circuit 2 in a fixed order.

Then, the multiplier 13 is activated by each output command from the F-V converter 16 and the input voltage detector 7, and the voltage controller 11,
Based on the action of the driver 10, phase control of the sirisk that constitutes the converter 1 is performed, and a DC voltage is obtained from the output terminal ICIc'.
is applied to input terminals 2a + 2a' of .

In this way, power at a predetermined frequency is supplied to the synchronous motor M.

On the other hand, the voltage detectors 8 and 9 supply each output command to each input terminal 12a and 12b of the minimum value selection circuit 12, but during normal operation, the level of the output command of the voltage detection circuit 9 is 8, the output command of the voltage detection circuit 9 is supplied to the feedback input terminal 11c of the voltage controller 11 through the minimum value selection circuit 12, and feedback control is performed.

It goes without saying that during normal operation of the synchronous motor M, there is no room for the command device 19, and hence the frequency reducer 18, to operate, and the diode 4 becomes conductive.

Next, if we consider a case where the voltage of the AC power supply P slightly drops, the output command of the input voltage detector 7 will also drop accordingly, and the output command of the multiplier 13 will also drop.

Accordingly, the ignition phase of the converter 1 is narrowed down, the output voltage of the converter 1 is lowered, and the output voltage of the inverter 2 is also lowered to supply electric power of the same frequency to the electric motor M to continue operation.

This operation is to suppress the rush current to the smoothing capacitor 6 and the synchronous motor when the voltage of the AC power supply P returns to normal.

In this way, the synchronous motor M can continue to operate up to a voltage that does not cause synchronization, which is of great benefit in the textile industry.

In the process of normal operation of the inverter as described above, if the voltage drop of the power source P is now large, the output voltage of the inverter 2 will also drop significantly, and the synchronous motor M will become out of synchronization at the rated operating frequency.

For this reason, when the voltage drop of the AC power supply P is particularly large, the command level from the voltage detection circuit 8 immediately decreases due to the fact that the voltage at the smoothing capacitor 6 is cut by the diode 4.

Therefore, only the command level applied to the input terminal 19a of the command unit 19 suddenly decreases.
9 issues a command from the output terminal 19c, and the frequency reducer 18
operate.

As a result, the oscillation frequency of the oscillator 14 is lowered to recover the rotational energy of the synchronous motor, and the smoothing capacitor 6
to prevent further drop in output voltage.

In this way, even if the input voltage to the converter drops due to an abnormal voltage drop of the AC power source P, the voltage on the input side of the inverter, ie, the voltage of the smoothing capacitor 6, is prevented from dropping by the above-mentioned regeneration, and the diode 4 becomes non-conductive.

On the other hand, since the command level from the voltage detection circuit 8 is lower than the command level from the voltage detection circuit 9 due to the voltage drop of the AC power supply P, the minimum value selection circuit 12 selects the minimum value from the voltage detection circuit 8. The output command is given to the voltage control circuit 11 as a feedback command, and the output voltage of the converter 1 is lowered in relation to the reduction in the command level applied to each input terminal 13a, 13b of the multiplier 13 compared to the case when the AC power supply P is normal. Feedback control is performed in a state where the power is narrowed down.

At this time, as a reverse voltage is applied to the diode 4, the converter 1 side and the inverter 2 side continue to operate independently in an electrically isolated state.

In addition, when the AC power supply P has a momentary power outage, the input of the input voltage detector 7 disappears, but the converter 1 uses the input from the F-V converter 16 to maintain a voltage approximately equal to the charging voltage of the smoothing capacitor 6 upon power restoration. It continues to operate at a flow angle that allows voltage to be obtained.

Now, when the AC power supply P is restored to the specified voltage under such a state of instantaneous voltage drop, the flow angle cannot change suddenly due to the inertia of the driver 10, and the output voltage of the converter 1 immediately changes to almost the output of the inverter 2. A voltage is reached depending on the frequency.

To explain more specifically, for example, if the voltage of the AC power supply P applied to the converter 1 drops to 70%, the frequency reduction circuit 18 operates to reduce the frequency of the output voltage of the inverter 2, and the frequency decreases according to this low frequency. The voltage is controlled to 100%.

On the other hand, at this time, the output voltage of the converter 1 is controlled so that the output command level from the multiplier 13 becomes a voltage of 70%.

When the AC power supply P is restored to the specified voltage, the flow angle of the converter 1 does not suddenly change, but the output voltage of the converter 1 immediately changes suddenly to 100% voltage with respect to the reduced frequency.

At this time, the smoothing capacitor 6 is charged to 100% voltage according to the frequency by regeneration from the synchronous motor M, so even if the voltage suddenly changes to 100% of the converter frequency, the smoothing capacitor 6, inverter 2,
There is no risk of inrush current flowing through the synchronous motor M, and the command level of the voltage detector 8 increases.

Therefore, the frequency reducer 18 controls the operation of the command unit 19, that is,
With the disappearance of the command from the output terminal 19c, the impark 2 becomes inactive and the frequency of the impark 2 returns to the value regulated by the frequency setter 15 again.

At the same time, the minimum value selection circuit 12 is regulated by a command from the voltage detection circuit 9 applied to the input terminal 12b, and feedback control is performed.

As described above, in a circuit that drives an AC load such as a synchronous motor from an AC power source through a converter, a smoothing circuit, and an inverter, the converter and inverter are electrically connected by a diode when the voltage of the AC power source drops. The converter is operated continuously based on the action of the minimum value selection circuit.

This configuration completely eliminates control lag when power is restored, and the practical advantage is that there is no room for inrush current to flow to the smoothing capacitor and inverter side.

In addition, with the action of the command unit and frequency reducer, there are control modes in which the motor continues to operate without changing the frequency within a voltage range that does not cause synchronization of the motor under load, and control in which the motor continues to operate at a lower frequency. The switching between modes can be made extremely smoothly, and the operation of the voltage control loop can be maintained even during a voltage drop in the power supply, so even when the frequency is lowered, the frequency lowering period can be set to a minimum. It has characteristics.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Converter, 2... Impark, 3... Smoothing reactor, 4... Diode, 6... Smoothing capacitor, I... Input voltage detector, 8, 9...・・・
Voltage detector, 10... Driver, 11... Voltage controller, 12... Minimum value selection circuit, 13... Multiplier,
14... Oscillator, 18... Frequency reducer, 19...
・Command unit, P... AC power supply, M... synchronous motor.

Claims (1)

[Claims] 1. In a circuit in which power is supplied from an AC power supply to a motor by sequentially valving a converter, a DC intermediate circuit including a smoothing circuit, and an impark, a smoothing capacitor is connected to the inverter input side, and the smoothing capacitor and smoothing capacitor are connected to the inverter input side. A diode is provided between the smoothing reactors that act to electrically isolate impark and the converter when the voltage on the inverter side becomes higher than the voltage on the converter side.
A multiplication command of a command proportional to the input voltage to the converter and a command proportional to the frequency of the impark side; thus, the conduction angle of the converter is controlled, and the lower of the electronic detection commands of each output side of the conbake and impark side An instantaneous voltage drop in the input power supply of Impark, which is characterized by having a means for selecting one command and configuring a feedback circuit to reduce the frequency of the inverter when the output voltage of the converter drops below a certain value. Time control device.