JP2003079169A - Dynamic brake circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic brake circuit wherein damage to contacts is relieved and adhesion of contacts is prevented. SOLUTION: The dynamic brake circuit is provided with an electromagnetic switch 93 having a plurality of contacts 71 and 72; a control portion 100 having an inverter circuit 101 which controls the opening and closing of the contacts 71 and 72 of the electromagnetic switch 93 and further drives a motor 10; and a plurality of resistors 51 and 52 for the dynamic brake circuit. The one-side ends of wires led out of the resistors 51 and 52 and the one-side ends of wires led out of the contacts 71 and 72 are connected with each other, respectively. The resistors 51 and 52 and the contacts 71 and 72 are connected so that both the ends of the connected resistors and both the ends of the connected contacts are in parallel with the motor 10 and the inverter circuit 101, respectively. Thus, adhesion of the contacts 71 and 72 is prevented when the contacts are closed by the electromagnetic switch 93.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic brake circuit of a motor drive control device. 2. Description of the Related Art Conventionally, as a circuit for braking a motor, there is a braking circuit using a so-called dynamic brake for electrically braking using a resistor and a contact point of an electromagnetic switch. When the capacity of the motor is large, there may be no large-capacity electromagnetic switch corresponding thereto. For example, even if there is a large-capacity electromagnetic switch, a small-capacity electromagnetic switch may have to be used due to size and cost restrictions. In this case, a plurality of small-capacity contacts are connected in parallel to make them equivalent to large-capacity contacts. FIGS. 3 and 4 show examples of dynamic brake circuits for single-phase and three-phase motors whose contacts are connected in parallel as described above. As shown in FIG. 3, the contacts 1 and 2 are connected to the motor 3 in parallel with each other. When the motor 3 is driven, the exciting coil 5 of the electromagnetic switch 4 is excited, and the contacts 1 and 2, which are normally closed contacts (B contacts) as shown in FIG. However, when the rotation of the motor 3 is stopped, the excitation of the excitation coil 5 of the electromagnetic switch 4 is cut off, and the contacts 1 and 2 are turned off.
Is closed, and the dynamic brake circuit is operated, and the rotation of the motor 3 is brought into a braking state. The exciting coils 121 and 125, the resistor and contact circuits 122 and 124, and the resistor 123 shown in FIG. 4 constitute a dynamic brake circuit for a three-phase motor, and the contact 1 of the dynamic brake circuit for a single-phase motor shown in FIG. , 2, the excitation coil 5 and the resistor 6. However, when the operation of the contacts is observed in a short time, the parallel contacts are not always closed at the same time. That is, when one of the contacts tries to close first, or when the contact closes once and causes chattering and repeats opening and closing for a short time, the arc discharge current or inrush current May flow. When such a condition is repeated, damage to the contacts is increased, and welding of the contacts may occur. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a dynamic brake circuit for reducing damage to contacts and preventing welding of the contacts. SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an electromagnetic switch having a plurality of contacts, and controls the opening and closing of the contacts of the electromagnetic switch and drives a motor. A control unit having an inverter circuit, and a plurality of resistors for a dynamic brake circuit, wherein one end of a line drawn from the resistor and one end of a line drawn from the contact are connected and connected. The two ends of the resistor and the contact are connected in parallel with the motor and the inverter circuit, and the contact is closed by the electromagnetic switch. As described above, since the resistor having a larger resistance value than the resistance value of the resistor used in the conventional dynamic brake circuit is connected in series to the contact, the arc discharge current and the inrush current are reduced by the resistance value. Smaller in inverse proportion to. In addition, the steady current flowing through each contact is also suppressed by the increased resistance value of each resistor as compared with the prior art. 1 and 2 are views showing an example of an embodiment according to the present invention. FIG. 1 shows a single-phase motor,
FIG. 2 shows a dynamic brake circuit for a three-phase motor. An example of an embodiment according to the present invention will be described with reference to FIG. The dynamic brake circuit according to the present invention, as shown in FIG.
2. It is composed of an electromagnetic switch 93 and a control unit 100. The electromagnetic switch 93 has contacts 71 and 72 and an exciting coil 95 for opening and closing the contacts 71 and 72. Further, the control unit 100
A circuit (not shown) for controlling the electromagnetic switch 93 and an inverter circuit 101 for driving the motor 10 are provided. In the dynamic brake circuit according to the present invention, one end of the lead wire of the resistor 51 and one end of the contact 71 are connected at a connection point 61 shown in FIG. The resistor 52 and the contact 72 are similarly connected at the connection point 62. The other ends 41 and 81 of the resistor 51 and the contact 71 connected as described above are connected to the other end of the resistor 52 and the contact 72 similarly connected.
43, 83 and connected at connection points 42, 82 as shown in the figure,
Further, connection points 31, 91 between the inverter circuit 101 and the circuit of the motor 10 are connected in parallel with the motor 10. With such a circuit, the resistance value can be twice as large as that of a conventional case using one resistor. For this reason, the arc discharge current, the inrush current, and the steady current flowing through the contact to be closed first can be halved. By reducing each of the currents in this manner, damage to the contacts due to arc discharge current or inrush current is suppressed, and welding of the contacts is prevented. Further, since the current is divided into the respective resistors, the current flowing through the respective resistors is reduced, and the resistors themselves are protected. Further, it is possible to reduce the capacity and use an inexpensive electromagnetic switch and resistor. Also, in a steady state, for example, when a 2Ω resistor is connected in parallel as a braking resistor, the equivalent resistance value as viewed from the motor side is 1Ω, which satisfies the required regenerative braking resistance value as viewed from the motor side. Will do. That is, the regenerative braking operation can maintain the conventional operation while increasing the margin of the contact capacity. The dynamic brake circuit of a single-phase motor has been described with reference to FIG. 1. FIG. 2 is a diagram relating to the dynamic brake circuit of a three-phase motor. A control device 120, an inverter circuit 119, a control unit 116, resistors and contact circuits 112 and 114, a resistor 113, and an electromagnetic switch 11 shown in FIG.
The excitation coils 111 and 115 of the motors 7 and 118 and the motor 110 are the control device 20, the inverter circuit 101, the control unit 100, the circuits 51, 52, 71 and 72 of the resistors and the contacts, and the excitation coils of the electromagnetic switch 93 shown in FIG. 95, equivalent to motor 10. According to the present invention, it is possible to suppress the damage to the contacts due to the arc discharge current or the rush current and to prevent the welding of the contacts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a dynamic brake circuit relating to a single-phase motor in an embodiment of the present invention. FIG. 2 is a diagram showing a dynamic brake circuit relating to a three-phase motor in an example of an embodiment of the present invention. FIG. 3 is a diagram showing a dynamic brake circuit for a conventional single-phase motor. FIG. 4 is a diagram showing a dynamic brake circuit for a conventional three-phase motor. [Description of reference numerals] 1, 2 contacts 3 Motor 4 Electromagnetic switch 5 Excitation coil 6 Resistance 10 Motor 20 Control device 31, 41, 42, 43 Connection point 51, 52 Resistance 61, 62 Connection point 71, 72 Contact 81, 82 , 83, 91 Connection point 93 Electromagnetic switch 95 Excitation coil 100 Control unit 101 Inverter circuit 110 Motor 111, 115 Exciting coil 112, 114 Circuit of resistance and contact 113 Resistance 116 Control unit 117, 118 Electromagnetic switch 119 Inverter circuit 120 Control Device 121, 125 Excitation coil 122, 124 Circuit of resistance and contact 123 Resistance

Claims (1)

Claims 1. An electromagnetic switch having a plurality of contacts, a control unit having an inverter circuit for controlling opening and closing of the contacts of the electromagnetic switch and driving a motor, and a dynamic brake circuit. A plurality of resistors, one end of a wire drawn from the resistor and one end of a wire drawn from the contact are connected to each other, and both ends of the connected resistor and both ends of the contact are connected to the motor. And a dynamic brake circuit connected in parallel with the inverter circuit, wherein the contact is closed by the electromagnetic switch.