JPH04111290U - soft start circuit - Google Patents

Abstract

(57) [Summary] (Purpose) By making it possible to short-circuit the soft-start resistor after the motor is powered on and the current in the main circuit that drives the motor becomes sufficiently low, the desired function can be achieved. (Configuration) It has a main circuit that drives the motor 15 using direct current obtained by rectifying an alternating current power source, and a soft start resistor 18 is inserted into the main circuit. At the same time, a switch 17 is inserted which operates to short-circuit the soft start resistor when the voltage of the DC power source rises above a certain voltage after the power is turned on.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention is applicable to, for example, a motor drive circuit having an inverter device etc. as the main circuit. The present invention relates to an applicable soft start circuit.

0002

[Conventional technology]

For example, in a motor drive circuit that has an inverter device etc. as its main circuit, When the power is turned on, an excessive current flows through the smoothing electrolytic capacitor that makes up the controller device. This will destroy the diode in the rectifier circuit installed before the smoothing capacitor. There is a fear. Therefore, in general, a soft-start resistor is used to prevent excessive voltage when the power is turned on. It is designed to prevent flow.

0003 Figure 5 shows an example of a conventional soft start circuit. A rectifier circuit 31 receives a three-phase AC power source as an input, and a DC rectifier rectified by the rectifier circuit 31. A soft start resistor 32 is inserted in series between the capacitor 33 for smoothing the switch 3, which is turned on by inputting a run signal, which is a motor operation command signal. 4 is connected in parallel to the soft start resistor 32. When the power is turned on is prevented by passing current through the smoothing circuit through the soft start resistor 32. prevent the current, then turn on the switch 34 to short-circuit the resistor 32, and during normal operation This is to prevent loss due to the resistor 32.

0004

[Problem that the idea aims to solve]

A soft start resistor 32 and a switch 3 that shorts it as shown in FIG. In the soft start circuit using 4, the terminal voltage of the smoothing electrolytic capacitor 33 is It is necessary to turn on the switch 34 when the current decreases. However, according to the conventional soft start circuit described above, the motor operation command signal is Since the switch 34 is turned on based on the run signal, the motor When the main circuit power is turned on at the same time as the start switch is turned on, the smoothing electrolytic The switch 34 is turned on before the terminal voltage of the capacitor 33 rises sufficiently, and the resistor is turned on. The resistor 32 is short-circuited, and a large current flows from the rectifier circuit 31 to the smoothing capacitor 33. It may not be possible to fulfill its function as a soft start circuit.

[0005] This invention was devised to solve these problems. After turning on the motor, wait until the current in the main circuit that drives the motor has become sufficiently low before turning on the software. By making it possible to short-circuit the starting resistor, it is possible to achieve the intended function. The purpose of this invention is to provide a soft start circuit that can perform

[0006]

[Means to solve the problem]

This invention uses direct current obtained by rectifying alternating current power to drive a motor. A soft start resistor is inserted into this main circuit. After the power is turned on, when the voltage of the DC power supply above rises above a certain voltage, the A feature is that a switch is inserted to short-circuit the foot-start resistor.

[0007]

[Effect]

When the motor is first powered on, current flows through the main circuit through the soft start resistor. The current is throttled to prevent excessive current and provide a soft start. Power on The switch operates when the DC power supply voltage rises and exceeds a certain level. The soft start resistor is short-circuited and there is no loss due to the soft start resistor. Shift to normal operation.

[0008]

【Example】

The implementation of the soft start circuit according to the present invention will be explained below with reference to FIGS. 1 to 4. An example will be explained. The embodiment shown in FIG. and a smoothing capacitor 9, which switches the smoothed DC output to generate AC. an inverter 12 that generates electricity, and a motor 15 that is driven by the output of the inverter 12. have. Configuration including the rectifier circuit 6, capacitor 9 and inverter 12 This portion constitutes a main circuit that drives the motor 15. This main circuit includes a rectifier circuit. A soft start resistor 18 is connected in series between the line 6 and the capacitor 9. . In addition, a relay switch 17 is connected in parallel to the soft start resistor 18. There is.

[0009] The embodiment shown in FIG. Smoothing capacitor 7 and converting smoothed DC output to DC output of different voltage. Switching regulator 10 and DC output from switching regulator 10 It has a control circuit 13 to which power is supplied. Three-phase alternating current leading to the rectifier circuit 6 above A breaker 1 is inserted in each power supply circuit, and a breaker 1 is inserted in each of the two phases of the AC power supply circuit. Fuses 2 and 3 are inserted respectively. The two phases of a three-phase AC power supply, R phase and T phase, After passing through fuses 2 and 3, it is supplied to a rectifier circuit 5 for rectification, and then to a capacitor. 8 and is input to the switching regulator 11. switching legs The regulator 11 outputs a voltage different from the input voltage, and its output is the base driver. is supplied to the eve circuit 14.

The control circuit 13 controls the operation of the base drive circuit 14 . The base drive circuit 14 supplies drive current to the bases of the transistors forming the inverter 12 under the control of the control circuit 13 . Therefore, the base drive circuit 14 has a DC power supply circuit, and a time constant circuit consisting of a resistor 19 and a capacitor 20 is connected between the output terminals of the DC power supply circuit. A relay 16 is connected in parallel to the capacitor 20 of this time constant circuit. The relay switch 17 is a contact that the relay 16 has, and operates when the DC power supply voltage v ₂ of the base drive circuit 14 rises above a certain voltage, turning on the relay switch 17 and turning on the soft star resistor. 18 is short-circuited.

Now, when the three-phase AC power is turned on, each rectifier circuit 4 , 5 , 6 rectifies the AC, each rectified output is smoothed by the capacitors 7 , 8 , 9 , and the switching regulators 10 , 11 and the inverter 12 DC power is supplied to each. When the power is first turned on, a large charging current flows through each of the capacitors 7, 8, and 9, and the terminal voltage of the DC power supply rises rapidly, gradually becomes slower, and eventually reaches a saturated state. FIG. 3 shows changes in the DC power supply voltage v ₁ of the main circuit and changes in the DC power supply voltage v ₂ of the base drive circuit 14.

The operating voltage of the relay 16 of the base drive circuit 14 is set to a voltage slightly lower than the saturation voltage of the DC power supply voltage v ₂ of the base drive circuit 14 . Therefore, while the DC power supply voltage _v1 of the main circuit is rising rapidly, the relay switch 17 is off and current flows through the soft start resistor 18, preventing excessive current and protecting the diode of the rectifier circuit 6. be done. When the DC power supply voltage _v1 of the main circuit rises to a constant voltage close to the saturation voltage, the relay 16 operates and the relay switch 17 is turned on, shorting the soft start resistor 18 to prevent loss and heat generation due to the resistor 18. , in this state, it shifts to normal operation. Ry in FIG. 3 indicates the operation of the relay 16.

[0013] The rising speed of the DC power supply voltage of the main circuit that drives the motor is determined by the DC power supply circuit of the main circuit. It varies depending on the capacity of the smoothing capacitor 9 connected to. Curve a shown in Figure 4 is the case where the capacitance of the smoothing capacitor 9 is the smallest, and curve b is different from curve a. When the capacitance is large, curve c is the case where the capacitance is the largest. Code 2 shown in Figure 2 1, 22, and 23 are smoothing capacitors 9 to increase the capacity of the smoothing capacitor 9. The capacitors connected in parallel with each are shown.

As described above, as the capacity of the smoothing capacitor 9 increases, the rising speed of the DC power supply voltage v ₁ becomes slower. If the settings were made uniformly as when the capacitance is small, the resistor 18 would be short-circuited before the DC power supply voltage _v1 rises sufficiently, and an excessive current would flow, making the soft start ineffective. . In order to solve this problem, as shown in FIG. 4, the relay switch 17 may be set to turn on when the DC power supply voltage _v1 reaches a certain voltage. To do this, when the capacity of the smoothing capacitor 9 is small, the relay switch 17 is turned on at a relatively early time t ₁ from the power-on, and as the capacity of the smoothing capacitor 9 increases, the relay switch 17 is turned on at a relatively early time t ₁ from the power-on. It is only necessary to sequentially delay the ON time of the relay switch 17 as shown in ₃ .

[0015] As mentioned above, the relay switch 17 is turned on depending on the capacity of the smoothing capacitor 9. To change the time, detect the DC power supply voltage itself of the main circuit and make sure that the voltage is a constant voltage. The relay switch 17 may be turned on when the pressure is reached, or as shown in FIG. By changing the time constant of the circuit consisting of the resistor 19 and the capacitor in this embodiment, Good too.

Further, as shown in FIG. 2, a transformer 24 is connected to the AC input side of the rectifier circuit 6 constituting the main circuit, and the output of the transformer 24 is rectified by a diode 25 and then connected to a smoothing capacitor via a resistor 26. The terminal voltage v ₂ of this capacitor 27 may be used to operate the relay 16. The terminal voltage v ₂ of the capacitor 27 increases according to a time constant determined by the resistor 26 and the capacitor 27, and when the terminal voltage v ₂ reaches a certain value, the relay switch 17 is turned on and the resistor 18 is short-circuited. By changing the value of the resistor 26 or capacitor 27, the timing at which the relay switch 17 is turned on can be changed.

[0017]

[Effect of the idea]

According to this invention, the motor is driven by using the DC power obtained by rectifying the AC power supply. Insert a soft start resistor into the main circuit where the It operates when the power supply voltage rises above a certain voltage and shortens the soft start resistance. Because I inserted a switch that causes The soft start resistor is short-circuited after the current in the main circuit becomes sufficiently low. This can reliably prevent excessive current from flowing.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a soft start circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the soft start circuit according to the present invention.

FIG. 3 is a diagram showing the relationship between the increase in DC power supply voltage and the operation of the relay in the above embodiment.

FIG. 4 is a diagram showing the relationship between the rise in DC power supply voltage and the operation of the relay when the capacitance of the smoothing capacitor is changed.

FIG. 5 is a circuit diagram showing an example of a conventional soft start circuit.

[Explanation of symbols]

15 Motor 17 Switch 18 Soft start resistor

Claims (1)

[Scope of utility model registration request] Claim 1: The main circuit has a main circuit that drives the motor using direct current obtained by rectifying an alternating current power source, and a soft start resistor is inserted into this main circuit, and after the power is turned on, A soft start circuit characterized in that a switch is inserted that operates when the voltage of a DC power source rises above a certain voltage to short-circuit the soft start resistor.