JPS5831826B2 - Induction motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in drive circuits for variable speed induction motors.

In a variable speed driving device that includes a forward converter connected to an AC power source, an inverse converter connected to the forward converter for converting into a variable frequency AC output, and an induction motor connected to the inverse converter, Inrush current limiting resistor to limit the inrush current that flows into the smoothing capacitor of the forward converter when the power is turned on, regenerative current consuming resistor to consume regenerative current, braking current limiting resistor, etc. in the DC braking circuit, etc. Since a resistive element with relatively large power is required, the drive circuit becomes large and the cost becomes high.

In view of the fact that two or more of these resistance elements do not operate at the same time, the present invention uses one resistance element as the other two resistance elements to reduce the number of resistance elements, thereby creating a compact and low-cost drive circuit. It provides:

The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 shows a circuit diagram of a drive circuit according to the invention.

In Figure 1, 1 is an AC power supply, 2 is a diode 21 to 2
6 and a smoothing converter 27, 3 is a flywheel of transistors Q1 to Q6, and diodes 31 to 3.
The transistors Q1 to Q6 are turned on and off by an output signal of a well-known inverter control circuit (not shown) to convert the output voltage of the forward converter 2 into alternating current with a variable frequency.

4 indicates an induction motor. rl, r21~r23°r31
, r32 indicate contact points of relays R1 to R3, which will be described later.

28 indicates a regenerative current detection capacitor, 29 indicates a regenerative current detection diode, 41.42 indicates a common resistance, and 4
3 is a regenerative current control circuit, 44 is a switching transistor, and 45 is a DC braking circuit.

In FIG. 1, when the AC power supply 1 is turned on and the forward converter 2 starts operating, the contact r1 is initially turned off for a certain period of time. Until then, the rush current to the capacitor 27 flows through the resistors 41 and 42, and at this time, the inrush current to the capacitor 27 flows through the resistors 4
1.42 acts as an inrush current limiting resistor.

Contact r1 is closed after a certain period of time has passed since the power was turned on.
Resistors 41 and 42 act as regenerative current consumption resistors.

That is, when a regenerative current is generated, it charges the capacitor 28 through the contact r1, and the regenerative current detecting capacitor 28
When the voltage across the terminals of the diode 29 increases, the voltage e1 across the diode 29 increases.

That is, when a regenerative current is generated, the regenerative current is further superimposed on the current supplied to the container/container 28 from the AC power supply 1, so that the capacitor 28 is further charged and the voltage between its terminals increases.

On the other hand, since the diode 29 is connected in the opposite direction to the direction in which the regenerative current flows, the regenerative current flows through the capacitor 27.
There is no flow to capacitor 2 due to regenerative current.
The voltage across terminals 7 does not change.

Therefore, when a regenerative current occurs, the terminal voltages of the capacitors 27 and 28 on the diode 29 side will be different from each other.

In other words, a voltage is generated between both electrodes of the diode 290, and the voltage is higher on the negative side at the point b side than at the point a side of the diode 29.

This voltage e1 between points a and b applies a reverse bias to the diode 29.

This voltage e1 increases as the regenerative current increases.

When this terminal voltage e1 exceeds a certain value, the switching transistor 44 is turned on via the regenerative current control circuit 43, and the regenerative current flows through the resistors 41 and 42 and is consumed.

As a result, the charge in the capacitor 28 is discharged, the voltage e1 becomes zero, and the transistor 44 is turned off.

If the regenerative current continues to occur, the capacitor 2
8 is charged and repeats the same switching operation of the transistor.

When an emergency stop command is given to the motor from the outside and the motor is brought to an emergency stop, contact rl is
, r21 to r23 are opened, contacts r31 and r32 are closed, and the DC output voltage of the forward converter 2 is supplied to two specific primary terminals of the motor 4 via the DC braking circuit 45 to apply DC braking.

That is, the output voltage of the forward converter 2 is determined by the resistors 41, 42, the braking circuit 45, and the contacts r31. Identification of electric motor via r32
given to the next terminal.

In this case, the resistors 41, 42 therefore act as current-limiting resistors in the DC braking circuit.

2 and 3 show the contacts rl, r21 to r23. in FIG. 1.
r31. The opening/closing control circuit diagram of r32 is shown, and FIG. 4 shows an operation time chart.

In Figure 2, X1-X3 are relays, R20-R31 are resistors, Q20-Q26 are transistors, D20-D22
indicates a diode, and ZD indicates a Zener diodexll
indicates the contact point of relay X1, and C20°C21 indicates the capacitor.

When AC power supply 1 is turned on, transistor Q21 is turned on and relay X2 is turned on.

In addition, capacitor C20 is connected via resistor R20 and contact xll.
is charged and exceeds the Zener voltage of Zener diode ZD, transistor Q20 turns on and relay
1 is turned on.

As a result, relays R1 and R2 in FIG. 3 are turned on, and their contacts rl and r21 to r23 shown in FIG. 1 are closed.

Therefore, in FIG. 1, the inrush current to the capacitor C27 flows through the resistors R41 and R42 since the junction r1 from when the power is turned on until the relay R1 is turned on is open, and the resistors 41 and 42 limit the inrush current. Acts as a resistor.

Relays R1 and R2 are turned on and the first fixed contacts 1 and r21~
After r23 is closed, it becomes a normal operating state and the inverter 3
The electric motor 4 is rotated at a speed corresponding to the switching frequency.

When a regenerative current is generated, the capacitor 28 is charged through the contact r1, and the transistor 44 is turned on through the control circuit 43.

At this time, the resistors 41 and 42 act as regenerative current consuming resistors as described above.

- In the power cylinder diagram 2, transistor Q25 is off, Q26
is on and Q22 is off, so relay X3 is off.

When an emergency stop command ESP (high potential) is applied to the terminal T21 in FIG. 2, the transistor Q25. Q26. Q22 is reversed and relay X3 is turned on.

Also, transistors Q23°Q24. Q20. Q21 also reversed and became Lire XI.

X2 is turned off.

Therefore, in FIG. 3, after relays R1 and R2 are restored, relay R3 is turned on.

If this results in an emergency stop, contacts rl and r21 in Figure 1
~ After r23 is opened, contacts r31 and r32 are closed, and the DC braking current is transferred to the forward converter 2, resistors 41 and 42, and circuit 45.
, contact r31, electric motor 4, contact r32, and forward converter 2, and electric motor 4 is braked.

At this time, the resistors 41 and 42 act as braking current limiting resistors.

As described above, according to the present invention, the rush current limiting resistor that flows into the smoothing capacitor of the forward converter when the power is turned on is also used as the regenerative current consumption resistor and the DC braking current limiting resistor. The number of resistive elements can be reduced to reduce the size and cost of the circuit.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is a circuit diagram of a drive circuit according to the present invention, FIG. 2, FIG. 3 is a circuit diagram for controlling the opening and closing of the contacts in FIG. An operation time chart of the circuit is shown. AC power supply, 2: forward converter, 3: inverse converter, 4: induction motor, rl, r21 to r23. r31゜r32: Contact, 41, 42: Common resistance, 43: Regenerative current control circuit, 4
5: DC braking circuit, R1-R3, XI-X3: Relay.

Claims (1)

[Claims] 1 A forward converter connected to an AC power supply, an inverse converter connected to the forward converter for converting into a variable frequency AC output, and an induction motor connected to the inverse converter, the forward converter In an induction motor drive circuit comprising an inrush current limiting resistance element for the smoothing capacitor, a regenerative current consumption circuit, and a DC braking circuit for the induction motor, the inrush current limiting resistance element and the timer contact are connected in parallel. circuit and a parallel circuit of the DC braking circuit and the regenerative current detection capacitor are connected in series to connect the inrush current limiting resistive element to the regenerative current consuming circuit, the regenerative current consuming resistive element, and the DC braking circuit. A drive circuit for an induction motor, characterized in that it is shared as a braking current limiting resistance element in a braking circuit.