JPH0723040Y2 - Surge voltage suppressor - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a device for suppressing a surge voltage generated on the load side of an inverter.

B. Outline of the Invention The present invention is a device for suppressing the surge voltage of a circuit in which a load is connected to each branch line by branching the middle of the power supply line connected to the output side of the inverter. A surge voltage is suppressed by providing a reactor between the branch point of the electric wire and connecting a filter composed of a series circuit of a resistor and a capacitor to the branch point.

C. Conventional technology For example, in a PWM inverter using a power transistor, the switching speed of the main circuit is high, so when the cable length on the load side becomes large, a reflected voltage due to the distributed constant of the cable causes a surge voltage. .

As a means for suppressing this surge voltage, as shown in FIG. 3, a circuit in which a reactor L is installed at the output end of the inverter I and a filter including a resistor R and a capacitor C is connected between the reactor L and ground. Have already been proposed (Japanese Utility Model Application No. 58-103779).

D. Problem to be Solved by the Invention Although this circuit has an advantage that the structure is simple, the midway of the power supply line is branched so that the motors M _{1 to} M _n
When connecting, there are the following problems. That is, since there is a difference between the distribution constant of the cable from the filter end to the branch board forming the branch point and the distribution constant from the branch board to the motor end, a part of the reflected voltage from the motor side is reflected by the branch board and Returning to the side, the surge voltage becomes higher and the peak value of the cable termination voltage becomes higher than in the case of a single cable. Here, as shown in FIG. 4, from the output end of the inverter I (which can be regarded as the same position as the filter end) to the branch point.
l _1, until the motor end from the branch point and l _2, shows the results of examining the peak value of the cable termination voltage the l _1, l ₂ as a parameter in Figure 5. In the figure, for A and A ′, l ₁ is 200
m, B, B'when l ₁ is 140 m and C, C'is l ₁ at 80 m. For the symbols without dashes there are 3 branch cables and for the symbols with dashes there is 1 branch cable. This is the case. FIG. 6 is a graph showing the relationship between the number of branch cables, l ₂ and the peak value, where l ₁ is 140 m, and A _{1 to} A ₃ are the cases where the branch cables are 1 to 3 lines, respectively. is there. As can be seen from FIGS. 5 and 6, when the cable forming the power supply line on the output side of the inverter I is branched in the middle, the surge voltage tends to be higher than in the case of a single cable. As the number of branch cable lines increases, the effect of taking the measures according to the above application decreases. However, when the surge voltage becomes large, the insulation deterioration of the motor coil is promoted, which eventually leads to burnout.

The present invention is to solve such a problem.

E. Means for Solving Problems The present invention considers a combination of the cable inductance from the output end of the inverter to the branch point and the reactor provided at the output end of the inverter as one inductance component, and determines the branch point. This is done by paying attention to the fact that by providing a filter, it can be handled in the same way as when a single cable is used in the circuit of FIG. Specifically, as shown in FIG. 1, the present invention provides a reactor L between an output end of an inverter I and a branch point of the feeder line, and a resistor R and a capacitor between the branch point and, for example, ground. The configuration is such that a filter composed of a C series circuit is connected.

F. Action According to such a configuration, the steepness of rising of the output voltage of the inverter I is suppressed by the reactor L, and
The reflected waves from the motors M _{1 to} M _n side flow to the ground through the filter composed of the above series circuit at the branch point, and as a result, the surge voltage is suppressed. In this case, assuming that the cable inductance up to the branch point is L ′ and the total inductance with the inductance of the reactor L is (L + L ′), the constant relationship between the resistance R and the capacitor C is expressed by equation (1), It is preferable to set it in a non-vibrating manner.

G. Example Cable termination voltage peak value and branch cable length when the number of branch cable lines is 3 in the circuit configuration of FIG.
The result of examining the relationship with l ₂ is shown in FIG. Fig. 2 1a, 2
In a, the cable length l ₁ to the branch point is 140 m and 80 m, respectively.
From this graph, it is understood that according to the present invention, even if there are a plurality of branch cables, the surge voltage can be suppressed without being substantially affected by the length of the branch cable. In addition, as for the result when the filter including the resistor R and the capacitor C is not provided at the same time in FIG. 2, 1b (l ₁ = 140 m),
It is shown as 2b = (l ₁ = 80 m). In this case, the surge voltage also increases as the length of the branch cable increases.

H. Effect of the Invention According to the present invention, a reactor is provided on the output side of the inverter to suppress the rise of the output voltage, and a filter composed of a resistor and a capacitor is provided at the cable branch point to absorb the reflected wave from each load. Therefore, even if a plurality of branch cables are provided, surge voltage can be suppressed, and insulation breakdown of the motor coil or the like can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the present invention, FIG. 2 is a relationship diagram between branch cable length and surge voltage, FIG. 3 is a circuit diagram showing a conventional example, FIG. 4 is a circuit diagram showing line length, and FIG. FIG. 6 and FIG. 6 are relationship diagrams between the branch cable length and the surge voltage. I ... Inverter, L ... Reactor, C ... Capacitor, R
… Resistors, M _{1 to} M _n … Motors.

Claims (1)

[Scope of utility model registration request] 1. An apparatus for suppressing a surge voltage of a circuit in which a load is connected to each branch line by branching the middle of a power supply line connected to an output side of an inverter, wherein a branch between the output end of the inverter and the power supply line. A surge voltage suppressing circuit characterized in that a reactor is provided between the branch point and a filter formed by connecting a series circuit of a resistor and a capacitor to the branch point.