JPH01259791A - Power converter - Google Patents

Abstract

PURPOSE:To control a motor in the direction of acceleration in a minimum time after the recovery of service power by detecting motor speed from the terminal voltage of a load motor during service interruption and controlling a power converter. CONSTITUTION:The terminal voltage (residual voltage) of a load motor 10 is detected by a transformer 16 as the operation of an inverter circuit 14 during service interruption, and the speed of the load motor 10 and voltage phase are arithmetically operated by a reference generator 31 by the detecting signal of the terminal voltage. The arithmetic value is transmitted over an oscillator 22 through a switch 34, and the frequency and phase of the inverter circuit 14 are controlled. The DC voltage of an inverter device and the terminal voltage of the load motor 10 are controlled in linear relationship at that time. When service power is recovered, the re-excitation of the motor after the recovery of service power is unnecessitated, and the motor can be transferred to the state of acceleration in a minimum time.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a variable speed control technology for an AC motor using a variable frequency power converter, and particularly relates to a power converter that takes measures against instantaneous power outages. Regarding.

(Prior Art) A typical conventional example of operating an AC motor at variable speed using a power conversion device such as an inverter device will be described with reference to the drawings.

As shown in FIG. 2, a load motor 10 and an AC power source 11
and a rectifier 12 that converts AC power from the AC power into DC power.

A DC smoothing circuit 13, an inverter circuit 14 that converts DC into an arbitrary frequency, a current transformer 15 that detects the primary current of the load motor 10, a transformer 16 that detects the input voltage of the load motor 10, and an AC power supply voltage. Transformer 17 for detection
, a power failure detection circuit 18 that detects a drop in input voltage, a speed reference generator 19 that provides a speed command for the load motor 10, and a voltage control circuit 20 that controls the output voltage of the inverter device using this output signal as a voltage reference. , a phase shifter 21 that controls the firing phase of the power converter (SCR) of the rectifier 12 in synchronization with the AC input voltage, and a speed base and the output signal of the generator 19 at the frequency J! An oscillator 22 generates a pulse that determines the output frequency of the inverter device by inputting power from the priest, a ring counter 23 controls the firing phase of each element in the inverter circuit, and the output from the current transformer 15 is monitored to control the load. The motor includes a stop circuit 24 that stops the operation of the inverter device when an overcurrent flows through the electric motor 10.

In FIG. 2, when there is a power outage in the AC input voltage, the power outage detection circuit 18 detects the drop, and the phase shifter 21 shifts or shifts/blocks the gate signal of the rectifier 12 to stop the inverter device.

Thereafter, the power failure detection circuit 18 detects the power restoration, and the voltage control circuit 20 and the first oscillator 22 detect the power restoration.

To prevent the inverter from overcurrent, load motor 1
After confirming that the terminal voltage of 0 is below the specified value,
The M-turn was restarted.

(Problem to be Solved by the Invention) However, in conventional power converters, in order to secure the output voltage during a power outage, the capacitor capacity of the DC smoothing means becomes large, so the power converter stops control upon detection of a power outage. Since the motor was started after power restoration, if the motor terminal voltage remains, overcurrent is likely to occur depending on the motor terminal voltage phase, the power converter output phase, and the DC voltage level. After the voltage falls below the specified value, the output frequency must be gradually increased while suppressing overcurrent by delicately controlling the output voltage and frequency, which lengthens the restart time and reduces the motor speed more than necessary. There was such a problem.

Therefore, in view of the above problems, the present invention controls the DC voltage and the power converter output frequency according to the speed reduction of the motor during a power outage, and also controls the output phase, thereby improving the motor terminal voltage phase and power conversion. It is an object of the present invention to provide a power converter device equipped with a control means in which the device output phase is always controlled to be constant, and restarting after the power is restored can be restarted in the shortest possible time without having to wait for the motor terminal voltage to drop. shall be.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in order to achieve the above object, the present invention provides
By detecting the motor speed from the terminal voltage of the load motor and controlling the output frequency of the power converter using this detection signal, the DC voltage is controlled to follow the motor speed, thereby ensuring the magnetic flux of the motor even during power outages. Then, by increasing the DC voltage according to a predetermined function by the power recovery machine and the DC voltage control circuit, the control circuit that controls the DC voltage during a power outage increases the output frequency in an attempt to decrease the DC voltage. Provided is a power conversion device equipped with a control means capable of controlling an electric motor in the direction of acceleration in the shortest time.

(Function) In the power conversion device configured as described above, during a power outage, the ratio of the motor terminal voltage to the motor speed is controlled to be constant,
After the power is restored, the motor speed is controlled smoothly and in the shortest possible acceleration direction by increasing the DC voltage, which is the output voltage of the rectifier, by a predetermined function using the control described above.

(Actual Example) An embodiment of the present invention is shown in FIG. 1 and will be described below. Note that in FIG. 1, the same reference numerals as in FIG. 2 represent the same elements, and the explanation thereof will be omitted.

As shown in FIG. 1, this embodiment uses an isolation amplifier 30 for detecting DC voltage, an output signal of this circuit, and a terminal voltage detection signal of the load motor to determine the output frequency standard until the start of power failure control. a reference generator 31 that generates a signal, a comparator 32 that compares the signal from the speed reference generator 19 and the output signal of the reference generator circuit 31 and detects that they match, and a It includes a switching circuit 33 that outputs a reference switching signal based on a signal from the detection circuit 18, and a switch 34 that switches the reference based on this output signal.

In such a configuration, when the AC power supply 11 has a power outage, the power outage detector 18 detects the power outage, sends the detection signal to the voltage control circuit 20 and the phase shifter 21, and shifts or shifts the gate signal of the rectifier 12. Then, control of the rectifier 12 is stopped.

In parallel with the above operations, the power failure detection signal from the power failure detector 18 is applied to the switching circuit 33, the reference changeover switch 34 is switched, the signal from the speed reference setting device 19 that has been used so far is disconnected, and the reference signal is generated. The output signal of the generator 31 is transmitted to the oscillator 22.
Connect to.

As a result, the operation of the inverter circuit 14 is to detect the terminal voltage (residual voltage) of the load motor 10 by the transformer 16, calculate the speed and voltage phase of the load motor 10 by the reference generator 31 based on this detection signal, and .

This reference generator 34 compares the DC voltage detection signal from the isolation amplifier 30 with the speed of the load motor lO calculated by the reference generator 31, and determines the operating frequency of the inverter circuit 14 such that the ratio becomes a predetermined value. A reference signal corresponding to 1 is sent to the oscillator 22 via the switch 34.

The frequency and phase of the inverter circuit 14 are controlled. At this time, the DC voltage of the inverter device and the terminal voltage of the load motor 10 are controlled in a proportional relationship, and by this control, the terminal voltage and speed of the load motor 10 always maintain a predetermined relationship, and the load motor 10 The magnetic flux is always maintained at a predetermined value even during a power outage.

Thereafter, when power restoration is detected by the power outage detector 18, the power restoration detection signal is transmitted to the phase shifter 21. The voltage is sent to the voltage control circuit 20 and these controls are restarted, and the DC voltage control in the rectifier 12 is started. At this time, the DC voltage reference signal given to the voltage control circuit 20 is the setting signal of the speed reference setter 19, and the voltage control circuit 20 causes the DC voltage to follow the setting value of the speed reference setter 19, for example. , when the set value is larger than the DC voltage at the time of power restoration, the reference generator 31 explained in the control during power outage.

The frequency and phase of the inverter circuit 14 are controlled in the direction of lowering the DC voltage, and the input current of the load motor 10 is increased.

In order to lower the DC voltage, it is sufficient to allow more current to flow through the load motor 10. Therefore, by advancing the phase of the inverter circuit 140, the current increases and attempts to lower the DC voltage, but since the power supplied from the VI current converter 12 is sufficiently secured by the restoration of the AC power supply 11, the inverter circuit The frequency of 14 increases as the phase changes, and the load motor lO moves in the acceleration direction. Thereafter, the comparator 3 detects that the output amount of the reference generator 31 matches that of the speed reference setter 19.
2, and the switch 34 is set to the steady operation mode via the switching circuit 83.

Switch to.

It goes without saying that the same effect can be obtained by using a mechanical detector to detect the speed and phase of the motor.

(Effect of the invention) The present invention detects the motor speed and voltage phase during a power outage,
By controlling the output frequency and phase of the power converter in accordance with this signal, and also controlling the DC voltage in proportion to the motor speed, the following effects can be achieved.

(D After power is restored, control is possible immediately regardless of the presence or absence of motor terminal voltage.

■ During a power outage, the motor magnetic flux is established, so there is no need to re-excite the motor after power is restored, allowing the system to shift to acceleration in the shortest possible time.

■ After the power is restored, the engine accelerates to the speed reference setting value, and when the set value and the reference generator output match, the reference is switched, allowing a smooth transition to steady operation mode. Ru.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing a conventional power conversion device. 10...Load motor 11...AC power supply 12
... Rectifier 13 ... DC smoothing circuit 14
... Inverter circuit 20 ... Voltage control circuit 21
... Phase shifter 22 ... Oscillator 30 ...
Isolation amplifier 31...Reference generator 32...Comparator 33...Switching circuit 34...Switch

Claims (1)

[Claims] a forward conversion means for converting AC power into DC power; an inverse conversion means for converting the DC power from the forward conversion means into arbitrary AC power; and a forward conversion means provided between the forward conversion means and the inverse conversion means. a DC smoothing means, a phase control means for controlling the firing phase of the power conversion element constituting the forward conversion means, a voltage control means for generating a phase reference for controlling the DC power according to an output voltage reference, and an output voltage. oscillation means for generating a pulse signal corresponding to an output frequency according to a power conversion device for controlling an electric motor, comprising: a frequency detection means for detecting a frequency of a terminal voltage of the motor; and an output signal of the frequency detection means. and a DC voltage detection signal to calculate the amount of deviation and add the output signal of the frequency detection means, and the output signal of the addition means and the voltage/frequency reference signal from the speed setting device. Comparing means for comparing levels, drop detection means for detecting a drop in input voltage, and switching means for switching the input signal of the oscillation means based on the output signal of the drop detection means and the output signal of the comparison means. A power conversion device characterized by: