JPH06351258A - Circuit for dealing with power interruption of inverter - Google Patents

Abstract

PURPOSE:To ensure control power supply for an inverter from a main circuit DC power supply and voltage detection thereof at time of power interruption. CONSTITUTION:In a system where the control power supply for a control circuit 10A is obtained from the DC power supply for main circuit and the voltage thereof is detected in order to control the inverter body 6 and to protect the main circuit, the control power supply for a switching power supply 13 is provided by taking out DC power from the main circuit through a diode 11. Voltage of the main circuit is detected and divided by voltage division resistors 21, 22 to produce a DC voltage, lower than the voltage of the main circuit, for charging a backup capacitor 12. At the time of power interruption, power charged in the backup capacitor is fed to the switching power supply through a diode 23. This constitution allows accurate detection of the main circuit voltage up to the low voltage of the backup capacitor when the main circuit voltage begins to drop due to power interruption while ensuring the control power supply by means of the capacitor 12.

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, the DC power supply circuit rectifies the AC from the AC power supply 1 by the rectifier 2 and directs it to the smoothing capacitor 5 via the parallel circuit of the inrush current suppressing resistor 3 for precharging and the short-circuiting 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.

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

The control circuit 10 obtains DC power from the main circuit DC power source through the backflow prevention diode 11, and obtains a DC power source in which the DC power from the control power source backup capacitor 12 is stepped down by the switching power source 13 and controls it. It controls the inverter body 6 as a power source. 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 for protection calculation.

The diode 11 and the capacitor 12 serve as a countermeasure against a power failure, and the power required for control is secured by the charging power of the capacitor 12 even for an instantaneous power failure of the main circuit DC power supply.

That is, in a normal state, the main circuit voltage V _DCM and the voltage V _{DCB of the} capacitor 12 are almost the same, and the control of the main circuit voltage V _DCM is maintained even if the main circuit voltage V _DCM is lowered due to the occurrence of a power failure to continue the control. to enable.

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

[0008]

In the conventional measures against power failure, the required capacity of the capacitor 12 is about 1/10 as compared with the case where the voltage is secured against the momentary power failure by increasing the capacity of the capacitor 5 of the main circuit. Can be made smaller.

However, since the switching power supply 13 also detects the voltage of the main circuit from the voltage of the capacitor 12, the correct main circuit voltage cannot be detected due to the presence of the diode 11 when a power failure occurs, and the main circuit voltage is detected. The control and protection performed by doing so become impossible. 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 ON-controlled, and when the main circuit voltage drops due to discharge to the braking resistor 8, the switch 9 is turned on.
Is controlled to prevent overvoltage in the main circuit.

However, with respect to the decrease in the main circuit voltage,
Since the decrease of the control power supply voltage is delayed due to the intervention of the power failure countermeasure circuit, the switch 9 for detecting and controlling this is delayed to be turned off, resulting in an excessive decrease of the main circuit voltage and an excessive heating of the resistor 8 due to excessive power consumption.

(2) Switch 4 at the time of starting the inverter
Is turned off to pre-charge the main circuit capacitor 5 via the resistor 3 to suppress the inrush current to the capacitor 5. The switch 4 is off-controlled at a certain voltage or less by the voltage detection by the control circuit 10, and is on-controlled when the capacitor 5 is charged to a certain voltage or more. Further, the off control is also performed when the main circuit voltage drops due to power off or power failure.

In such control, as shown in FIG. 7, when the power is restored from the power failure, the voltage of the main circuit capacitor 5 is quickly lowered due to the occurrence of the power failure, but the control power source is lowered due to the occurrence of the power failure. Is delayed, the switch 4 remains controlled to be in the ON state, and when power is restored in this state, an inrush current flows through the switch 4, which may cause overcurrent damage to the rectifier 2 or burnout of the switch 4.

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

Further, 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 the long power failure time, the switch 4 is controlled to the off state at the time of power restoration. Therefore, the initial charge of the capacitor 5 at the time of power recovery is performed through the resistor 3.

In the charge at the time of power recovery, the electric power is supplied to the electric motor 7 in parallel in addition to the capacitor 5, so that the charging time becomes longer than that at the time of normal start-up, and the resistor 3 is overheated, disconnected or ignited. There is a fear.

(3) The above-mentioned problems are caused even when the main circuit voltage is not detected from the voltage input of the switching power supply 13 and another voltage detection circuit is provided.
Delay of voltage drop of 2 causes similar inconvenience.

It is an object of the present invention to provide a power failure countermeasure circuit for obtaining control power from a main circuit DC power supply and ensuring control power supply and voltage detection at the time of power failure in an inverter for voltage detection.

[0019]

In order to solve the above-mentioned problems, the present invention provides a main circuit having a rectifier, a smoothing capacitor and an inverter main body, and a control power source from the DC power source of the main circuit, and In an inverter equipped with a control circuit for detecting a voltage and controlling an inverter body and protecting a main circuit, 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 receives a DC power output of a diode as an input to obtain a control power supply and detects the voltage of the main circuit; and a DC control circuit that receives a 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,
And a second diode forming a current path for supplying the charging power of the backup capacitor to the DC power supply circuit when the main circuit fails.

[0020]

With the DC control circuit, the backup voltage of the control power supply is maintained at a voltage lower than the main circuit voltage, the control power is supplied from the main circuit through the first diode during normal operation, and the second voltage is supplied from the backup capacitor at a low voltage during backup. Control power is supplied through the diode.

Thus, when the main circuit voltage starts to drop due to the occurrence of a power failure, the main circuit voltage is accurately detected until the voltage of the backup capacitor becomes low, and the control power supply is secured to ensure reliable braking control and preliminary charging. 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 in the control circuit 10A, from the diode 11 to the backup capacitor 12
This is because the voltage dividing resistors 21 and 22 are provided in the charging circuit and the diode 23 that bypasses the resistor 21 is provided 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
Of the DC voltage of the main circuit
_{By dividing the} voltage of the _DCM , the backup capacitor 12 is charged to a low voltage. This voltage is the switching power supply 1
3 is set to a voltage higher than that required for normal operation.

In the present embodiment, the main circuit voltage remains unchanged as it is through the diode 11 in the switching power supply 1
3, the braking control and the preliminary charging control are performed by securing the power source and detecting the voltage as in the conventional example.

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 to the switching power supply 13.

Therefore, in the voltage detection by the switching power supply 13, the main circuit voltage V _DCM is the backup capacitor 1
The voltage V _DCM can be correctly detected until it becomes equal to or lower than the voltage V _{DCB of} 2, and the control at the time of power failure and power recovery is ensured.

FIG. 2 shows the waveform of each part of the braking control in this embodiment. By decelerating the electric motor 7, the main circuit voltage V _DCM
Rises and the switch 9 operates, the voltage V _DCB of the backup capacitor 12 is always kept lower than the voltage V _DCM , so that the input voltage to the switching power supply 13 follows V _DCM and Can obtain a normal overvoltage suppressing operation.

During deceleration of the motor, the main circuit voltage V
_{Since the} voltage of the _DCM is higher than that at the normal time, the voltage V _DCB of the backup capacitor 12 also changes due to the influence, but it does not cause any problem in actual operation.

FIG. 3 shows the waveform of each part of 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 drops.

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

After that, when the voltage V _DCM becomes lower than the voltage V _DCB , the backup function using the backup capacitor 12 as a control power supply operates.

Since the switch 4 is turned off at the time of power recovery, the precharge by power recovery is normally performed. Further, when the switch 4 is turned off, the inverter main body 6 is controlled to reduce the output voltage, and the generation of the inrush current is prevented.

To completely restore the voltage V _DCM , the main circuit voltage V
_{When the DCM} exceeds the ON control voltage V _MCON of the switch 4, the switch 4 is ON-controlled, and the control of the inverter body 6 is also restarted.

Therefore, when a power failure occurs, the switch 4 is turned off by detecting a drop in the main circuit voltage, and it is possible to prevent overheating of the preliminary charging resistor 3 and generation of a rush current to the electric motor 7 when power is restored.

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

In FIG. 3A, the voltage control circuit 24 controls the output voltage of the output transistor 25 to control the backup capacitor 12 to the set voltage V _DCB .

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

In these embodiments as well, in addition to the same effects as the above-mentioned embodiments, the voltage of the backup capacitor 12 is always kept constant during braking control as shown by the broken line in FIG.

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

[0040]

As described above, according to the present invention, the direct-current control circuit keeps the backup voltage of the control power supply lower than the main circuit voltage, the control power is supplied from the main circuit during normal operation, and the backup power is supplied during backup. Since the control power is supplied from the capacitor at a low voltage,
When the main circuit voltage starts to drop due to a power failure, the main circuit voltage can be accurately detected until the voltage of the backup capacitor becomes low, and the control power supply is secured to enable reliable control of braking control and preliminary charging. Has the effect of

Further, since the backup capacitor is charged at a low voltage, it has a lower withstand voltage than the conventional one.

[Brief description of drawings]

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

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

FIG. 3 is an operation waveform diagram during an instantaneous power failure in the embodiment.

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

FIG. 5 is a conventional inverter circuit diagram.

FIG. 6 is a conventional braking control waveform diagram.

FIG. 7 is a waveform diagram of a conventional precharging operation during a power failure.

FIG. 8 is a waveform diagram of a conventional precharging operation during a power failure.

[Explanation of symbols]

 2 ... Rectifier 5 ... Smoothing capacitor 6 ... Inverter body 10A ... Control circuit 12 ... Backup capacitor 13 ... Switching power supply 24 ... Voltage control circuit

Claims (3)

[Claims] 1. A main circuit having a rectifier, a smoothing capacitor, and an inverter main body, and a control power source is obtained from a DC power source of the main circuit, and the voltage of the main circuit is detected to control the inverter main body and protect the main circuit. In a inverter provided with 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 DC power output of the diode as an input to obtain a control power supply and a voltage of a main circuit. A direct current power supply circuit for detecting a direct current, a direct current control circuit for receiving a direct current output of the diode to obtain a direct current having a voltage lower than the direct current voltage, a backup capacitor charged by the output of the direct current 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 at the time of power failure of the circuit. Power failure countermeasure circuit of an inverter, characterized in that it comprises a and. 2. The main circuit has a braking control circuit in which regenerative energy from the electric motor is absorbed by a braking resistor and a braking current path forming switch, and the control circuit has 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 setting value is exceeded and for turning off the switch when the main circuit voltage is equal to or lower than the lower limit setting value. Power failure countermeasure circuit. 3. The main circuit has a pre-charging circuit for supplying a rectified output from a rectifier to the smoothing capacitor through a rush current suppressing resistor and a short-circuiting switch thereof, and the control circuit has a DC power supply circuit. Control means for turning off the switch when the main circuit voltage to be detected exceeds the upper limit set value, and turning on the switch when the main circuit voltage becomes lower than the lower limit set value higher than the charging voltage of the backup capacitor. The power failure countermeasure circuit for an inverter according to claim 1, further comprising: