JP7127582B2 - clamp circuit - Google Patents

Description

The present invention relates to a technique for suppressing overvoltage generated between the output section of an inverter and ground in a clamp circuit of a power converter.

In a system in which a load such as a motor is connected to an inverter, an overvoltage such as a surge voltage may occur between the inverter output section (that is, the load connection section) and ground due to the switching operation of switching elements in the inverter. In order to prevent the load from deteriorating or being destroyed due to this overvoltage, a clamp circuit is provided between the inverter output section and ground to suppress the overvoltage between the inverter output section (that is, the load connection section) and ground. (For example, Patent Documents 1 and 2).

The overvoltage suppression device of Patent Document 1 clamps between the inverter output line and the ground with a diode bridge circuit. The capacitor connected to the DC voltage circuit of the diode bridge circuit absorbs the energy of the overvoltage, and the resistor connected in parallel with the capacitor consumes the absorbed energy, thereby suppressing the ground voltage.

Moreover, the surge voltage suppressing device of Patent Document 2 connects inverter output lines with a three-phase diode bridge circuit. Then, the DC voltage circuit of this diode bridge circuit is connected to the DC voltage circuit inside the inverter, and furthermore, a diode bridge circuit is connected in parallel with this diode bridge circuit, the neutral point of which is grounded, and the ground voltage circuit is connected to the inverter. clamp to a DC voltage of

JP-A-2005-269726 Japanese Patent No. 6299915

The overvoltage suppression device of Patent Literature 1 needs to connect a diode bridge circuit for each inverter output phase, which increases the number of circuit components and increases the size and cost of the clamp circuit and system. In addition, since the clamped voltage is the DC voltage of the inverter circuit, the amount of overvoltage energy that can be absorbed is small, and the overvoltage suppressing effect is weak. If an attempt is made to increase the amount of energy absorption, the capacitance value of the capacitor in the clamp circuit increases, resulting in an increase in the size of the capacitor and the clamp circuit.

The surge voltage suppressing device of Patent Document 2 needs to connect the DC voltage circuit section of the clamp circuit to the DC voltage circuit inside the inverter. The three-phase input section of the clamp circuit must be connected to a location where overvoltage should be suppressed, such as the input terminal section of the motor. Therefore, when the distance between the inverter and the motor is long, an electric wire for connecting the inside of the inverter and the clamp circuit is required according to the distance. Using a long-distance electric wire leads to an increase in man-hours for wiring work. In addition, since the capacitor in the DC voltage circuit inside the inverter has a relatively large amount of charge energy, if the DC voltage circuit of the clamp circuit is short-circuited, a very large short-circuit current will flow through the inverter and the clamp circuit, resulting in serious damage to the inverter and clamp circuit. may cause serious damage.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to reduce the manufacturing cost of a clamp circuit of a power converter and to improve the effect of suppressing overvoltage.

Accordingly, one aspect of the present invention is a clamp circuit of a power conversion device including an inverter connected to a load, comprising a diode bridge circuit connected to an output line of the inverter, and a DC voltage circuit of the diode bridge circuit. a first capacitor connected to the positive electrode of the DC voltage circuit; a first resistor connected to the positive electrode in parallel with the first capacitor; a second capacitor connected to the negative electrode of the DC voltage circuit; and a second resistor connected to the negative electrode, wherein a common connection point of the first capacitor, the first resistor, the second capacitor and the second resistor is connected to ground, and the second capacitor is It has the same capacity as the first capacitor, and the second resistor has the same resistance value as the first resistor.

According to one aspect of the present invention, the clamp circuit further includes a third resistor connected between the common connection point and the ground.

According to one aspect of the present invention, in the clamp circuit, the resistance value of the third resistor is variable.

According to the present invention described above, it is possible to reduce the manufacturing cost of the clamp circuit of the power converter and improve the overvoltage suppression effect.

BRIEF DESCRIPTION OF THE DRAWINGS The circuit diagram of the power converter device which is one Embodiment of this invention. FIG. 4 is a diagram for explaining the operation of the clamp circuit on the positive voltage side in the embodiment; FIG. 4 is a diagram for explaining the operation of the clamp circuit on the negative voltage side in the embodiment; FIG. 4 is a waveform diagram of voltage to ground when the clamp circuit is not provided; FIG. 4 is a waveform diagram of voltage to ground when the clamp circuit is provided.

Embodiments of the present invention will be described below with reference to the drawings.

A power conversion device 1 as one embodiment of the present invention shown in FIG. . Also, the motor 2 is connected to ground 4 .

(Aspect example of each functional unit of the power conversion device 1)
The inverter 3 is a three-phase PWM inverter connected to the inverter DC voltage circuit 7 and connected to the motor 2 via a three-phase output line 8 . Note that the motor 2 is one aspect of the load, and the load of the present invention is not limited to the motor 2 .

The clamp circuit 5 includes a three-phase diode bridge circuit 6 connected to an output line 8 . As the diode bridge circuit 6, a well-known three-phase diode bridge circuit employed in power conversion technology may be applied.

A first capacitor C1 and a second capacitor C2 are connected to the DC voltage circuit of the diode bridge circuit 6 as capacitors for absorbing surge voltage energy.

A first capacitor C1 is connected to the positive pole P of the DC voltage circuit. On the other hand, a second capacitor C2 is connected to the negative pole N of the DC voltage circuit. The second capacitor C2 has the same capacity as the first capacitor C1.

Furthermore, a first resistor R1 and a second resistor R2 are connected to the DC voltage circuit as resistors for consuming surge voltage energy. A first resistor R1 is connected to the positive electrode P in parallel with the first capacitor C1. On the other hand, the second resistor R2 is connected to the negative electrode N in parallel with the second capacitor C2. The second resistor R2 has the same resistance value as the first resistor R1.

The clamp circuit 5 is connected to ground 4 via a third resistor R3 which suppresses leakage current.

A third resistor R3 is connected between the common connection point of the first capacitor C1, the first resistor R1, the second capacitor C2 and the second resistor R2 in the clamp circuit 5 and the ground 4. As the third resistor R3, if a resistor with a variable resistance value is used, it is possible to adjust the frequency component of the ground voltage to be suppressed.

Note that the third resistor R3 is not an essential element in the clamp circuit 5, so it may be appropriately provided according to the specifications and applications of the motor 2 and the inverter 3.

(Example of operation of clamp circuit 5)
An operation example of the clamp circuit 5 will be described below with reference to FIGS.

(1) Suppression operation of the positive side voltage to ground A positive side overvoltage is generated between the output line 8 of the inverter 3 in FIG. When this occurs, the following clamping operation is performed between the phase that produces the maximum positive voltage to ground and the ground 4 among the three phase voltages output from the inverter 3 .

FIG. 2 shows an example of current paths indicated by black arrows when the U-phase on the output side of the inverter 3 has the largest overvoltage on the positive side. In the clamp circuit 5, the energy of the overvoltage is absorbed by the first capacitor C1 and consumed by the first resistor R1, so that the overvoltage on the positive side generated between the output section and the ground 4 is suppressed. be done.

Then, when the phase generating the highest positive voltage is switched, the phase to be clamped is automatically switched and the voltage between that phase and ground 4 is suppressed.

As described above, according to the clamp circuit 5 of this aspect, the positive voltage between the connection point of each of the three phases of the load (motor 2) and the ground 4 can be suppressed to a predetermined voltage or less. In particular, due to the arrangement of the first capacitor C1, the second capacitor C2, the first resistor R1 and the second resistor R2, the circuit for absorbing and consuming the positive overvoltage can be configured with only one phase.

(2) Suppression Operation of Negative Side Voltage to Ground If a negative side overvoltage occurs between the output of inverter 3 and ground 4 shown in FIG. The following clamping action is performed between the phase producing the largest negative voltage to ground and ground 4 .

FIG. 3 shows an example of current paths indicated by white arrows when the U-phase on the output side of the inverter 3 has the largest overvoltage on the negative side. Also in this example, the energy of the overvoltage is absorbed by the second capacitor C2 and consumed by the second resistor R2, so that the overvoltage on the negative side generated between the output section and the ground 4 is suppressed. be.

Then, when the phase generating the highest negative voltage is switched, the clamped phase is automatically switched and the voltage between that phase and ground 4 is suppressed.

As described above, according to the clamp circuit 5 of this aspect, the absolute value of the negative voltage between the connection point of each of the three phases of the load (motor 2) and the ground 4 can be suppressed to a predetermined voltage or less. In particular, the arrangement of the first capacitor C1, the second capacitor C2, the first resistor R1 and the second resistor R2 allows the circuit for absorbing and consuming the overvoltage on the negative side to be configured with only one phase.

(Simulation result of suppression effect of ground voltage)
A simulation result of the effect of suppressing the voltage to ground by the clamp circuit 5 will be described.

FIG. 4 shows the waveform of the voltage to ground at the output of the inverter 3 when the clamp circuit 5 is not provided. FIG. 5 shows the waveform of the voltage to ground at the output of the inverter 3 when the clamp circuit 5 is provided. As is clear from the comparison of the waveforms of FIGS. 4 and 5, the maximum voltage to ground is reduced from 2021 V to 1438 V, so it can be confirmed that the clamp circuit 5 greatly improves the voltage to ground.

(Effect of this embodiment)
According to the clamp circuit 5 described above, since only a single diode bridge circuit, which is a three-phase diode bridge circuit, can be used, compared to the conventional technology (Patent Document 1) that requires three single-phase diode bridge circuits, the diode bridge The number of circuits (number of implementations) is reduced. Therefore, it is possible to reduce the size and cost of the clamp circuit and the device system including the same. In addition, since the voltage can be clamped on the positive and negative sides, the DC voltage of the diode bridge circuit is the sum of the maximum positive voltage to ground and the negative voltage to ground among the three-phase voltages output by the inverter circuit. becomes. Therefore, the amount of overvoltage energy absorbed is increased compared to the above-described prior art (however, the capacitance value of the first capacitor C1 or the second capacitor C2 of the present invention and the capacitor of the clamp circuit of Patent Document 1 have the same capacitance value). case). Therefore, the effect of suppressing overvoltage is increased, and the reliability of the system is improved.

Furthermore, clamp circuit 5 can suppress overvoltage between inverter 3 and ground 4 without being connected to the DC voltage circuit of inverter 3 . Therefore, compared with the prior art such as Patent Document 2, the degree of freedom in selecting the installation position when installing the clamp circuit 5 is increased.

In addition, in the power conversion device as disclosed in Patent Document 2, when the inverter is separated from the motor and the clamp circuit is arranged near the motor, the wires connecting the two become long, requiring a large amount of man-hours for wiring work. requires.

On the other hand, in the power conversion device 1 of this aspect, since the electric wire for connecting the clamp circuit 5 and the DC voltage circuit of the inverter 3 is not required, the work of attaching the electric wire for the clamp circuit is not required. The manufacturing man-hours under the condition of arrangement are reduced.

Furthermore, since the clamp circuit 5 is not connected to the DC voltage circuit of the inverter 3 having a large-capacity capacitor, even if a short-circuit fault occurs in the DC voltage circuit of the clamp circuit 5, the fault current can be reduced and the inverter 3 and the clamp can be Damage to components, wiring, etc. of the circuit 5 can be suppressed.

As described above, according to the clamp circuit 5 of the present embodiment, it is possible to reduce the manufacturing cost of the clamp circuit of the power converter and improve the overvoltage suppression effect. In particular, the clamp circuit 5 absorbs the maximum positive voltage and the maximum negative voltage in each phase on the output side of the inverter 3, thereby suppressing overvoltage between the load motor and ground. Moreover, since only one clamp circuit 5 is required, the size and cost of the system of the power converter 1 can be reduced.

Furthermore, the clamp circuit 5 is connected to the ground 4 through the third resistor R3, thereby suppressing leakage current. In particular, when the third resistor R3 whose resistance value is variable is applied, it is possible to arbitrarily cope with the ground voltage to be suppressed.

REFERENCE SIGNS LIST 1 power converter 2 motor 3 inverter 4 ground 5 clamp circuit 6 diode bridge circuit 7 inverter DC voltage circuit 8 output line R1 first resistor R2 second resistor R3 third resistor C1... first capacitor, C2... second capacitor

Claims (2)

A clamp circuit for a power conversion device having an inverter connected to a load,
a diode bridge circuit connected to the output line of the inverter;
a first capacitor connected to the positive electrode of the DC voltage circuit of the diode bridge circuit;
a first resistor connected to the positive electrode in parallel with the first capacitor;
a second capacitor connected to the negative electrode of the DC voltage circuit;
a second resistor connected to the negative electrode in parallel with the second capacitor;
a third resistor connected between a common connection point of the first capacitor, the first resistor, the second capacitor and the second resistor and ground;
with
The second capacitor has the same capacity as the first capacitor,
The clamp circuit, wherein the second resistor has the same resistance value as the first resistor. 2. A clamp circuit according to claim 1 , wherein said third resistor has a variable resistance value.

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