JP3309494B2 - Inverter power failure countermeasure circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter power failure countermeasure circuit for obtaining control power from a main circuit DC power supply.

[0002]

2. Description of the Related Art FIG. 5 shows an example of an inverter configuration. In the inverter main circuit, a DC power supply circuit rectifies an AC from an AC power supply 1 by a rectifier 2, and supplies a direct current to a smoothing capacitor 5 through a parallel circuit of a rush current suppression resistor 3 for preliminary charging and a short-circuit switch 4. Get power. Using this DC power as a power source, an AC output controlled by the inverter body 6 is obtained to drive the induction motor 7.

A braking resistor 8 and a braking current path forming switch 9
When the main circuit DC voltage exceeds a certain level, the braking control circuit absorbs the regenerative energy from the electric motor 7 by turning on the switch 9 and suppresses the braking and the increase of the main circuit voltage.

A control circuit 10 obtains DC power from a main circuit DC power supply through a backflow prevention diode 11, obtains a DC power supply obtained by stepping down a DC from a control power supply backup capacitor 12 by a switching power supply 13, and controls the DC power supply. It controls the inverter body 6 as a power supply. Further, the switching power supply 13 is also used for detecting the voltage of the main circuit, and uses the input voltage as a detection voltage for controlling the switch 9 and performing a protection operation.

[0005] The diode 11 and the capacitor 12 serve as a countermeasure against power failure, and the power required for control is secured by the charging power of the capacitor 12 even in the event of a momentary power failure of the main circuit DC power supply.

That is, at normal times, the main circuit voltage V _DCM becomes almost the same as the voltage _VDCB of the capacitor 12, and the continuation of control is maintained by maintaining the voltage of the capacitor 12 even when the main circuit voltage V _DCM drops due to a power failure. enable.

The continuation of the control is a time until the voltage of the capacitor 12 becomes the lower limit of the operation range of the switching power supply 13, and it is possible to cope with a power failure during this time.

[0008]

In the conventional power failure countermeasures, the required capacity of the capacitor 12 is reduced to about 1/10 as compared with a case in which the voltage of the capacitor 5 in the main circuit is increased to secure the voltage even during an instantaneous power failure. Can be smaller.

However, since the switching power supply 13 also detects the voltage of the main circuit from the voltage of the capacitor 12, when the power failure occurs, it becomes impossible to detect the correct main circuit voltage due to the presence of the diode 11, and the main circuit voltage is detected. Control and protection cannot be performed. This will be described in detail below.

(1) For braking by controlling the switch 9,
As shown in FIG. 6, when the main circuit voltage exceeds a certain level due to the deceleration of the electric motor 7, the switch 9 is turned on, and when the main circuit voltage is lowered by discharging to the braking resistor 8, the switch 9 is turned on.
To prevent overvoltage of the main circuit.

However, when the main circuit voltage decreases,
Since the reduction of the control power supply voltage is delayed due to the intervention of the power failure countermeasure circuit, the turning off of the switch 9 for detecting and controlling the delay is delayed, causing an excessive decrease in the main circuit voltage and an excessive heating due to excessive power consumption to the resistor 8.

(2) When starting the inverter, switch 4
Is turned off to precharge the main circuit capacitor 5 via the resistor 3 to suppress a rush current to the capacitor 5. The switch 4 is turned off at a certain voltage or lower by voltage detection by the control circuit 10, and is turned on when the capacitor 5 is charged to a certain voltage or higher. Also, when the main circuit voltage is reduced due to power off or power failure, the off control is performed.

In such control, as shown in FIG. 7, when the power is restored from the occurrence of the power failure, the voltage of the main circuit capacitor 5 drops rapidly due to the occurrence of the power failure, but the voltage of the control power supply decreases when the power failure occurs. , The switch 4 is kept in the ON state, and if power is restored in this state, an inrush current flows through the switch 4, which may result in overcurrent damage to the rectifier 2 or burnout of the switch 4.

Further, a voltage is rapidly applied to the electric motor 7 due to the restoration of power, and an inrush current to the electric motor may cause an overcurrent stop operation of the control.

As shown in FIG. 8, when power is restored when the voltage of the control power supply becomes lower than the set value due to a longer power failure time, the switch 4 is controlled to be turned off at the time of power restoration. Thus, the initial charging of the capacitor 5 at the time of power restoration is performed through the resistor 3.

At the time of power recovery, power is supplied to the motor 7 in parallel in addition to the capacitor 5, so that the charging time is longer than at the time of normal startup, and the resistor 3 is overheated, disconnected, or ignited. There is fear.

(3) The above problem is that the capacitor 1 is also used in a case where the main circuit voltage is not detected from the voltage input of the switching power supply 13 and another voltage detection circuit is provided.
The same disadvantage is caused by the delay of the voltage drop of 2.

An object of the present invention is to provide a power failure countermeasure circuit which secures control power and ensures voltage detection at the time of a power failure in an inverter that obtains control power from a main circuit DC power supply and detects voltage.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a main circuit having a rectifier, a smoothing capacitor, and an inverter body, a control power supply from a DC power supply of the main circuit, and a control circuit for the main circuit. A first diode for detecting a voltage and controlling the inverter body and protecting the main circuit, wherein a first diode for preventing backflow to the DC power supply and extracting DC power from the DC power supply; A DC power supply circuit that obtains a control power supply with the DC output of the diode as an input and detects the voltage of the main circuit, a DC control circuit that receives the DC output of the diode as an input, and obtains a DC voltage lower than the DC voltage, A backup capacitor charged by the output of the DC control circuit,
A second diode that forms a current path for supplying the charging power of the backup capacitor to the DC power supply circuit when the main circuit loses power.

[0020]

The backup voltage of the control power supply is maintained at a voltage lower than the main circuit voltage by the DC control circuit. Normally, the control power is supplied from the main circuit through the first diode. Control power is supplied through the diode.

Thus, when the main circuit voltage starts to decrease due to the occurrence of a power failure, the main circuit voltage is accurately detected until the voltage of the backup capacitor becomes low, the control power source is also secured, and the braking control and the preliminary charging are ensured. Control is possible.

[0022]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 5 is different from FIG. 5 in that the control circuit 10A includes a diode 11 and a backup capacitor 12
And a diode 23 for bypassing the resistor 21 for supplying power from the backup capacitor 12 to the switching power supply 13.

The voltage dividing resistors 21 and 22 are connected to the diode 11
Is a DC control circuit that receives the DC output of the DC input and obtains a DC of a voltage lower than the DC voltage.
_The backup capacitor 12 is charged to a low voltage by dividing the voltage of the _DCM . This voltage is the switching power supply 1
3 is higher than the voltage required for normal operation.

In this embodiment, the main circuit voltage is normally supplied to the switching power
3 to perform braking control and pre-charging control by securing power and detecting voltage as in the conventional example.

Here, when a power failure occurs, the main circuit voltage V _DCM
There is supplied DC power from the main circuit to drop to a low voltage V _DCB with back-up capacitor 12 to the switching power supply 13, the diode from the backup capacitor 12 when the voltage V _DCM was lower than the voltage V _DCB 2
3 and is supplied to the switching power supply 13.

Therefore, the voltage detected by the switching power supply 13 is determined by the main circuit voltage V _DCM when the backup capacitor 1 is used.
Until the following second voltage V _DCB correctly detect the voltage V _DCM, to ensure control of the time when a power failure occurs and power recovery.

FIG. 2 shows waveforms at various points in the braking control in this embodiment. The main circuit voltage V _{DCM due to} the deceleration of the motor 7
There rises, when the switch 9 is operated, the voltage V _DCB backup capacitor 12 is always kept lower than the voltage V _DCM, the input voltage to the switching power supply 13 to follow the V _DCM, the switch 9 Can obtain a normal overvoltage suppression operation.

During the deceleration of the motor, the main circuit voltage V
_{Since the} voltage of the _DCM becomes higher than usual, the voltage _VDCB of the backup capacitor 12 also changes due to the influence, but this does not cause any problem in actual operation.

FIG. 3 shows waveforms at various points in the precharge control in this embodiment. When an instantaneous power failure of the AC power supply 1 occurs, the main circuit voltage V _DCM decreases toward zero voltage. Following this, the input voltage to the switching power supply 13 also decreases.

In the process of this voltage drop, the switch 4
When the voltage drops to the voltage V _MCOFF for turning off the control circuit 1
0A turns off the switch 4 to prepare for power recovery. At this time, the voltage V _MCOFF is set to a level higher than the voltage V _DCB of the backup capacitor 12.

[0031] Then, the voltage V _DCM backup function of the back-up capacitor 12 and the control power supply when lower than the voltage V _DCB works.

Since the switch 4 is off at the time of power recovery, the preliminary charging by the power recovery is normally performed. Further, when the switch 4 is turned off, the inverter body 6 is controlled to reduce the output voltage, thereby preventing occurrence of an inrush current.

To completely recover the voltage V _DCM , the main circuit voltage V
_{When the DCM} exceeds the ON control voltage _VMCON of the switch 4, the switch 4 is turned on, and the control of the inverter body 6 is restarted.

Therefore, when a power failure occurs, the switch 4 is controlled to be off by detecting a drop in the main circuit voltage, so that the overheating of the pre-charge resistor 3 and the occurrence of a rush current to the motor 7 at the time of power recovery can be prevented.

FIG. 4 is a main part circuit diagram showing another embodiment of the present invention. FIG. 1 shows a case where a constant voltage power supply circuit is provided as a DC control circuit that receives a DC output of a diode as an input and obtains a DC voltage lower than the DC voltage.

In FIG. 3A, the output voltage of the output transistor 25 is controlled by the voltage control circuit 24, and the backup capacitor 12 is controlled to the set voltage _VDCB .

In FIG. 3B, the Zener diode 2
This is a case where a constant voltage circuit that holds the voltage of the capacitor 12 at the set voltage by the resistor 6 and the resistor 27 is used.

In these embodiments, in addition to having the same operation and effect as those of the above-described embodiment, the voltage of the backup capacitor 12 is always kept constant during braking control as shown by a broken line in FIG.

In the embodiment, the control power supply is not limited to the switching power supply 13, but may be an analog constant voltage power supply.

[0040]

As described above, according to the present invention, the backup voltage of the control power source is maintained at a voltage lower than the main circuit voltage by the DC control circuit. Since the control power is supplied at a low voltage from the capacitor,
When the main circuit voltage starts dropping due to a power failure, the main circuit voltage can be accurately detected until the backup capacitor voltage becomes low, and the control power supply is also secured, enabling reliable control of braking control and pre-charging. Has the effect of doing

Further, since the backup capacitor is charged at a low voltage, the backup capacitor can have a withstand voltage lower than that of the conventional capacitor.

[Brief description of the drawings]

FIG. 1 is an inverter circuit diagram showing one embodiment of the present invention.

FIG. 2 is a braking control waveform diagram in the embodiment.

FIG. 3 is an operation waveform diagram at the time of a momentary power failure in the embodiment.

FIG. 4 is a main part circuit diagram of another embodiment.

FIG. 5 is a conventional inverter circuit diagram.

FIG. 6 is a conventional braking control waveform diagram.

FIG. 7 is a conventional precharge operation waveform diagram at the time of a power failure.

FIG. 8 is a conventional precharge operation waveform diagram at the time of a power failure.

[Explanation of symbols]

 2 rectifier 5 smoothing capacitor 6 inverter main body 10A control circuit 12 backup capacitor 13 switching power supply 24 voltage control circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 H02P 7/63 302

Claims (3)

(57) [Claims] 1. A main circuit having a rectifier, a smoothing capacitor, and an inverter main body, a control power supply is obtained from a DC power supply of the main circuit, and a voltage of the main circuit is detected to control the inverter main body and protect the main circuit. An inverter including a control circuit, a first diode for preventing backflow to the DC power supply and extracting DC power from the DC power supply; and a control power supply with a DC output of the diode as an input to obtain a control power supply and a voltage of a main circuit. A DC control circuit that receives a DC output of the diode as an input to obtain a DC voltage lower than the DC voltage; a backup capacitor that is charged by an output of the DC control circuit; A second diode for forming a current path for supplying the charging power of the backup capacitor to the DC power supply circuit when a circuit power failure occurs Power failure countermeasure circuit of an inverter, characterized in that it comprises a and. 2. The main circuit includes a braking control circuit that absorbs regenerative energy from the electric motor with a braking resistor and a braking current path forming switch, and the control circuit controls a main circuit voltage detected by the DC power supply circuit. 2. The inverter according to claim 1, further comprising control means for turning on the switch when the upper limit value is exceeded and turning off the switch when the main circuit voltage falls below the lower limit value. Power failure countermeasure circuit. 3. The main circuit includes a preliminary charging circuit that supplies a rectified output from a rectifier to the smoothing capacitor via an inrush current suppressing resistor and a short-circuit switch thereof, and the control circuit includes a DC power supply circuit. control means for the main circuit voltage to be detected is the switch-on control when exceeding the upper limit set value, off controls the switch when the main circuit voltage falls below a higher lower limit set value than the charging voltage of the backup capacitor 2. The inverter power failure countermeasure circuit according to claim 1, further comprising: