JPH0471392A - Inverter and its restart method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to an inverter that converts DC power supplied from a rectifier back into AC power and supplies power to an AC motor to drive the motor. The present invention relates to a method for restarting an inverter as quickly as possible after such occurrence.

[Prior art] As a method of operating a current type inverter during a power outage, (A)
As described in Japanese Patent Publication No. 58-14160, two of the thyristors constituting the rectifier are ignited in series, and the frequency of the inverter is controlled so that the motor current etc. match the target value. , A method of continuing the operation of the inverter even during a power outage in the external system that supplies AC power to the rectifier (B) As described in the above publication as a conventional example, as soon as a power outage is detected, the operation of the rectifier is stopped and the inverter is operated. and then restore the AC power supply (hereinafter referred to as
There are methods for restarting the system when power is confirmed (known as power restoration).

Regarding method (A), while detecting direct current,
It is necessary to detect the rotation speed of the motor with high precision, which poses the problem of complicated control.

On the other hand, method (B) has the problem that the inverter can be restarted only after charging the commutating capacitor, which is a component of the inverter, resulting in dead time and hindering the operation of the entire facility.

[Problem to be solved by the invention] In order to reduce the wasted time of this method (B), (C)
As described in Japanese Unexamined Patent Publication No. 58-93474, when the motor stops, the commutation capacitor remains charged, and after the power is restored, electricity is restarted from the thyristor of the inverter that was firing immediately before the stop. Method to eliminate the need for recharging after power restoration (D) Set the charging time constant of the commutation capacitor charging circuit to -;3
- A method has been proposed in which the charging circuit is set shorter than before, and the charging circuit is connected to the commutating capacitor only at the time of startup using a thyristor switch, etc., to quickly recharge the commutating capacitor.

In this method (D), the reason why the charging circuit is separated from the commutating capacitor with a thyristor switch etc. except when starting is because the polarity of the commutating capacitor is constantly changing depending on the firing phase of the thyristor during operation. This is because, when looking at the phase at a certain moment, the charging circuit acts to reduce the charge on the commutating capacitor. In particular, when the charging time constant of the charging circuit is shortened, the effect on the charge of the commutating capacitor cannot be ignored.

Reducing dead time in method (B) (C) and (D)
Of the methods described above, method (C) has the disadvantage that it cannot be restarted normally if the inverter fails to commutate during a power outage and there is no charge left, or if the ignition thyristor cannot be detected immediately before a power outage. there were. Furthermore, the method (D) has the disadvantage that the operation becomes impossible due to malfunction of the thyristor switch during operation.

That is, all of the conventional methods lack consideration for reliability, and cannot reliably restart the inverter and continue operation after a power outage or the like.

An object of the present invention is to provide an inverter equipped with a means for quickly restarting the inverter when power is restored after a momentary power outage, and minimizing interference with the operation of the entire facility, and a method for restarting the inverter.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an inverter for driving an AC motor that converts power converted from AC to DC by a rectifier into AC and supplies it to the motor. A method for determining the induced voltage value of an AC motor when power supply is stopped or the inverter control system is switched, and a means for determining the induced voltage value by comparing the induced voltage value with the voltage value required to charge the commutating capacitor in the inverter. The present invention proposes an inverter equipped with means for immediately commanding the inverter to restart when the voltage is high, and for commanding the inverter to restart after waiting for charging of the commutating capacitor by the charging circuit when the induced voltage is low. It is.

Means for determining the induced voltage value of the AC motor include an inverter output voltage detector that directly detects the voltage at the connection point between the inverter and the AC motor, an inverter output voltage detector that directly detects the voltage at the connection point between the AC motor, and an AC motor rotation speed and AC power supply stop or inverter control system. Either means for calculating the induced voltage value based on the elapsed time since switching, means for calculating the induced voltage value based on the magnetic flux and rotational speed of the AC motor, etc. are employed.

In order to achieve the above object, the present invention also provides a method for restarting an inverter for driving an AC motor, in which power converted from AC to DC by a rectifier is reversely converted to AC and supplied to the motor. If the induced voltage of the AC motor exceeds a predetermined value when restarting after a stop or a change in the inverter control system, the inverter immediately resumes operation, and if it falls below the predetermined value, the inverter's commutation capacitor is charged. This paper proposes a method for restarting an inverter that resumes operation of the inverter after charging from a circuit is completed.

[Operation] In the present invention, since the commutating capacitor and the motor are connected in parallel, if there is an induced voltage in the motor, the thyristor of the inverter is ignited and current flows through the motor, so that the induced voltage can be reduced up to the value of the induced voltage. This was developed with the focus on the ability to charge commutating capacitors.

In the present invention, the induced voltage of the motor is detected or calculated from other parameters, and this value is compared with the voltage value required to charge the commutating capacitor, and whether restarting can be performed immediately or charging by the charging circuit is performed. It has a function that determines whether to wait and then restart.

Therefore, when the power is restored after a short power outage in which the induced voltage of the motor does not drop below the voltage required to charge the commutating capacitor, the inverter can be restarted immediately, reducing trouble to the entire equipment.

[Embodiment] Next, an embodiment of an inverter and a restarting method thereof according to the present invention will be described with reference to the drawings.

1 is a block diagram showing a system configuration of an embodiment of an inverter equipped with restart means according to the present invention. In the figure, a three-phase bridge-connected thyristor rectifier 2 is connected to a three-phase AC power source 1.

A three-phase bridge type self-excited inverter 4 is connected to the DC output side of the rectifier 2 via a smoothing reactor 3. For example, a stator winding of a three-phase induction motor 5 is connected to the AC output side of the self-excited inverter 4.

The firing pulses of the individual thyristors of the self-excited inverter 4 are:
It is given from ring counter 6. A pulse train from a V/F (voltage/frequency) converter 7 is input to the ring counter 6 . The V/F converter 7 converts a voltage commanding a frequency into a pulse train having a frequency corresponding to the voltage. A frequency command voltage for the inverter is given from a command converter 8. The command converter 8 creates a frequency command voltage according to the speed command, and its output voltage is also given to the voltage controller 9. The voltage controller 9 is connected to the output voltage detector 1
It acts to match the detected voltage value from 0 to the value from the command converter 8, and its output is given to the current controller 11.

The current controller 11 acts to match the current detection value from the current detector 12 with the value from the voltage controller 9, and its output is given to the phase adjuster 13. The phase regulator 13 generates firing pulses for the individual thyristors in the regulator 2 with a firing angle depending on this command.

Now, the voltage of the AC power supply 1 is monitored by a momentary power failure detection circuit 15 via an input voltage detector 14, and its output is guided to an operation command device 16. Momentary power failure detection circuit 15
determines that there is a power outage on the AC power supply side when the power supply voltage falls below a predetermined value. Depending on the determination result, the operation command device 16 stops the pulse output of the phase adjuster 13 and the ring counter 6. Next, when the power supply voltage reaches a predetermined value of 111 or more, the instantaneous power failure detection circuit 15 determines that the power has been restored. According to the power restoration determination of the instantaneous power failure detection circuit 15 and the determination result of the output determination circuit 17, the operation command device 16 controls the phase adjuster 13 and the ring counter 6 regardless of whether or not the commutating capacitor in the self-excited inverter 4 is charged. restart the pulse output immediately, or
It is determined whether to restart the pulse output after waiting for the charging of the commutating capacitor by the initial charging circuit 18 to be completed.

Figure 2 shows the charging route of the commutating capacitor during restart. The self-excited inverter 4 of this embodiment is a series diode type three-phase inverter consisting of a three-phase bridge-connected thyristor 21, a diode 23 connected in series to each thyristor, and six commutating capacitors 22. be. For example, the thyristor 21 of such a self-excited inverter 4
When a and 21b are ignited and current flows from the rectifier 2, the current flows to the motor 5 along the route shown by the solid line. When the motor 5 is rotating and there is an induced voltage, the peak value of the induced voltage is applied to the commutating capacitor 22 due to the rotation of the motor 5. Current flows and charging occurs. At this charging voltage, the thyristor is able to commutate and the next thyristor can be fired.

FIG. 3 is a flowchart showing the operation of the operation command device 16 after the power is restored.6 When the instantaneous power failure detection circuit 1-5 detects the power restoration, the output voltage determination circuit 17 determines that the motor voltage is equal to or higher than a predetermined value. If it is determined that the motor voltage is lower than a predetermined value, the inverter is restarted immediately after charging by the initial charging circuit 18 is completed. If the inverter is to be restarted immediately, the commutating capacitor 22 is recharged by the induced voltage of the motor 5, as already explained with reference to FIG.

The induced voltage value of the output voltage determination circuit 17 is determined by the motor 5.
In addition to the method of directly detecting the voltage, there are other methods that can be considered, such as a method of calculating it based on the rotation speed of the motor and the time since an instantaneous power failure, a method of calculating it based on the magnetic flux and the rotation speed of the motor, etc.

In addition, the application of the present invention is not limited to instantaneous power outages on the AC power supply 1 side, but in order to improve the reliability of the entire equipment, for example, multiple inverter control systems are installed as shown by dotted lines in Fig. 1, and so-called multiplexing In such a system, events such as a short-term loss of power supplied to the electric motor 5 when switching the inverter control system are also included.

[Effects of the Invention] According to the present invention, when the induced voltage of the motor is relatively high, that is, the motor is at a high rotation speed, and when power is restored after a relatively short power outage or switching of the inverter control system, normal operation can be resumed. Since prompt recovery is possible, disruption to the operation of the entire facility can be reduced.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the system configuration of an inverter equipped with restart means according to the present invention, Fig. 2 is a diagram showing the charging route of the commutating capacitor at the time of restart, and Fig. 3 is a diagram showing the power restoration around the operation command device. FIG. 1...AC power supply, 2...rectifier, 3...smoothing reactor. 4... Self-excited inverter, 5... Electric motor, 6... Ring counter, 7... V/F converter, 8... Command converter, 9... Voltage controller, 10... - Output voltage detector, 11... Current controller, 12... Current detector, 18
...Phase adjuster, 14...Input voltage detector, 15...
・Momentary power failure detection circuit, 16... Operation command device, 17...
Output voltage determination circuit, 18... Initial charging circuit, 21...
Thyristor, 22... Commutation capacitor, 23... Diode.

Claims (1)

[Scope of Claims] 1. In an inverter for driving an AC motor, which converts power converted from AC to DC by a rectifier into AC and supplies it to the electric motor, the supply of AC power is stopped or the control system of the inverter is switched. means for determining the induced voltage value of the AC motor when the induced voltage occurs, and comparing the induced voltage value with a voltage value necessary for charging a commutating capacitor in the inverter, and restarting the inverter if the induced voltage is high. 1. An inverter comprising: means for immediately commanding the inverter to restart the inverter after waiting for charging of the commutating capacitor by a charging circuit when the induced voltage is low. 2. The inverter according to claim 1, wherein the means for determining the induced voltage value of the AC motor is an inverter output voltage detector that directly detects the voltage at a connection point between the inverter and the AC motor. . 3. In the inverter according to claim 1, the means for determining the induced voltage value of the AC motor is based on the rotational speed of the AC motor and the elapsed time since the supply of AC power is stopped or the control system of the inverter is switched. An inverter comprising means for calculating the induced voltage value. 4. The inverter according to claim 1, wherein the means for calculating the induced voltage value of the AC motor comprises means for calculating the induced voltage value based on the magnetic flux and rotational speed of the AC motor. . 5. In the method for restarting an inverter for driving an AC motor, the power converted from AC to DC by the rectifier is reversely converted to AC and supplied to the electric motor, when the supply of AC power is stopped or the control system of the inverter is switched. If the induced voltage of the AC motor is equal to or higher than a predetermined value when the AC motor is restarted later, the operation of the inverter is immediately restarted, and if it is lower than the predetermined value, after charging from the circuit that charges the commutating capacitor of the inverter is completed. A method for restarting an inverter, characterized by restarting the operation of the inverter.