JP2002044958A - Ac-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC-DC converter, capable of easily changing a capacity of a switching-means element of a regenerative-power discharging circuit, corresponding to the change in connected motor, operating conditions and the like. SOLUTION: In the regenerative-power discharging circuit 2, that detects regenerative power fed to the AC-DC converter 1 from a motor M, switching means, i.e., MOSFETs Q1 to Q3, which start the discharging of the regenerative power by a resistor 4 detecting a voltage rise, are connected in parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifying AC input,
Smoothing to supply DC output, voltage rise detecting means for detecting a rise in voltage generated by regenerative power from the DC output side, and switching for starting discharge of regenerative power by detecting the voltage rise The present invention relates to an AC-DC converter provided with a regenerative power discharging circuit constituted by the means.

[0002]

2. Description of the Related Art For example, a DC output terminal of an AC-DC converter (AC-DC converter) for rectifying and smoothing an AC input from an AC power supply and converting it to a DC output is connected to a DC-A.
When a power failure occurs in a motor drive system of a textile machine connected to a motor via an inverter, which is a C conversion device, the motor that is being driven is rapidly decelerated by the inverter, so that the motor enters a regenerative operation state. The generated regenerative energy is returned to the inverter and the converter. Then, this energy becomes regenerative power, and even during a power outage, the motor and the like are continuously controlled by the regenerative power so that no abnormality occurs in the running of the yarn. The converter has a regenerative power discharging circuit. This is to prevent a voltage exceeding a withstand voltage from being applied to a circuit element for performing the rectification and smoothing due to a voltage rise due to regenerative power from the DC output side terminal, thereby preventing the element from being damaged. The regenerative power is discharged to maintain the DC bus voltage of the converter at a predetermined value or less.

[0003] The regenerative power discharging circuit is an IC circuit as voltage rise detecting means for detecting a voltage rise (high voltage equal to or higher than a predetermined voltage) between DC buses in an AC-DC converter.
The switching circuit is activated when the IC circuit detects a voltage rise, and includes a resistance element that starts discharging regenerative power by the operation of the switching unit.

[0004]

The magnitude of the regenerative power varies depending on the motor connected to the converter, the operating conditions, and the like. The elements used for the switching means are designed so that the elements are not destroyed by the magnitude of the regenerative power. It is necessary to select an appropriate capacity. Here, as the switching means, for example, a bipolar transistor capable of self-turning on and off the switching by a base current may be used. In the case where the capacity of the bipolar transistor is changed depending on a motor, operating conditions, and the like, this may be used. Accordingly, the design of the converter itself may be changed.

The present invention has been made in view of the above problems, and has an AC-DC converter capable of easily changing the capacity of an element of a switching means in a regenerative power discharge circuit in response to a difference in a connected motor, operating conditions, and the like. The purpose is to provide.

[0006]

In order to achieve the above object, the invention according to claim 1 rectifies and smoothes an AC input and supplies a DC output, wherein the regenerative power from the DC output side is supplied. In an AC-DC converter equipped with a regenerative power discharge circuit configured by voltage rise detecting means for detecting a rise in voltage generated by and switching means for starting discharge of regenerative power by detecting the rise in voltage,
The switching means is constituted by a switching element that performs a switching operation by applying a voltage to a gate. In the present invention, the switching means is constituted by a switching element that performs a switching operation by applying a voltage to the gate, so that even when large regenerative power is generated, the rated current of one switching element is considered. By connecting a plurality of switching elements in parallel while increasing the number of connected elements, it is possible to shunt the current accompanying the regenerative power and adjust the current so as not to exceed the rated current of each element.

Here, for example, when a plurality of bipolar transistors, which are self-turning on and off by a base current, are connected in parallel, the current amplification factor of the transistor (defined by the ratio between the base current and the collector current)
The current shunted to each transistor tends to be biased due to the variation of the current, and the biased shunted current may exceed the rated current of the transistor, resulting in damage to the transistor.

According to a second aspect of the present invention, in the regenerative power discharging circuit, a plurality of switching elements for performing a switching operation by applying a voltage to a gate are connected in parallel. In the present invention, a plurality of switching elements that perform a switching operation by applying a voltage to the gate are connected in parallel to the transistor,
If the current shunted to each element tends to be biased to one side, the on-resistance at the time of switching increases and the current is suppressed, so that the current is less likely to be biased and the element can be reliably prevented from being damaged.

The invention according to claim 3 is characterized in that the switching element is a MOS field effect transistor. In the present invention, the switching element is a MOS field effect transistor,
A switching operation can be performed by applying a voltage to the gate, and high-speed switching can be realized.

According to a fourth aspect of the present invention, the switching element is an IGBT. According to the present invention, by using an IGBT as the switching element, it is possible to perform a switching operation by applying a voltage to the gate, and to realize a higher breakdown voltage and a larger current than a MOS field-effect transistor. Becomes

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the embodiments unless it departs from the gist of the present invention.

FIG. 1 is a circuit diagram showing an AC-DC converter 1, an inverter INV, and a motor M according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a MOSFE of a regenerative power discharging circuit 2 shown in FIG.
It is a figure showing switching characteristics of TQ1-Q3. FIG. 3 is a circuit diagram showing a modification of the regenerative power discharging circuit 2 of FIG.

As shown in FIG. 1, the AC-DC converter 1 is connected to a three-phase AC power supply AC via terminals R, S, and T. The AC-DC converter 1 has a rectifier D1 for rectifying an AC input. An electrolytic capacitor C1 is a smoothing element for smoothing the rectified output. The electrolytic capacitor C1 is connected between a bus P and a bus N of a DC line from which a waveform rectified by the rectifier D1 is output. I have. Also, A
The C-DC converter 1 has an inverter IN on the DC output side.
It is connected to the motor M via V.

Here, in the AC-DC converter 1,
A regenerative power discharging circuit 2 for discharging regenerative power from the DC output side is provided. IC circuit 3 of the discharge circuit 2
Is a voltage rise detecting means for detecting a rise in voltage generated by the regenerative power from the DC output side, and the IC circuit 3 is a switching means for starting discharge of the regenerative power via the resistors R1 to R3. A certain MOSFET (MOS
Type field effect transistors) Q1 to Q3. The sources of the MOSFETs Q1 to Q3,
The drain is connected to the bus N and the resistor R4, and the MOSFETs Q1 to Q3 are connected in parallel between the bus P and the bus N. A diode D2 is connected in parallel with the resistor R4, and the bus P side is a cathode.

Further, in the discharge circuit 2, resistors (current suppressing elements) R7 and R8 are connected in series between the bus P and the bus N,
The IC circuit 3 is branched and connected between the resistors R7 and R8. The IC circuit 3 uses a terminal Vcc as a power supply, and a resistor R5 is connected between the IC circuit 3 and the terminal Vcc, and a resistor R6 is connected between the IC circuit 3 and the bus N.

FIG. 1 shows a drive system of a motor M, which is used, for example, when a textile machine is driven by an inverter. The AC power supplied from the three-phase AC power supply AC is temporarily converted to DC by the AC-DC converter 1, and the DC output is converted to DC by the inverter INV via the buses P and N, and then to the motor M. Supply.
Through the above conversion, the power is supplied to the motor M at a constant power supply frequency at a frequency corresponding to the operating condition of the motor M (stopping, forward rotation, reverse rotation, etc. of the motor M). That is, by adjusting the output frequency of the inverter INV,
The rotation speed of the motor M can be arbitrarily changed.

In the AC-DC converter 1, the rectifier D1 uses a plurality of bridge-connected diodes to perform full-wave rectification on an AC waveform supplied from a three-phase AC power supply. Further, the smoothing electrolytic capacitor C1
Reduces the ripples by smoothing the output after rectification by the rectification unit D1. As described above, the rectifier D1 and the smoothing electrolytic capacitor C1 perform AC-DC conversion.

In the regenerative power discharging circuit 2 in the AC-DC converter 1, the bus P and the bus N are connected by resistors R7 and R8.
The divided voltage is taken into the IC circuit 3, and based on the divided voltage, the bus P-the bus N
The voltage between them is detected. This is the bus P
-The voltage between the buses N is applied as it is,
This is to prevent the C circuit 3 from being damaged.

Here, when a power failure occurs in the drive system shown in FIG. 1, the inverter INV causes the motor M to rapidly decelerate to generate regenerative power. As shown in FIG. 2A, the voltage between the bus P and the bus N of the AC-DC converter 1 increases due to the regenerative power from the motor M, and when the voltage reaches a predetermined value Von, the IC circuit 3 turns on the MOSF.
Switching control is performed on the gates of the ETQ1 to ETQ3. Thereby, MOSFETQ
The drain currents ID1 to ID3 flow because the gate-source voltage of the transistors 1 to Q3 increases and the drain-source conduction resistance decreases. That is, as shown in FIG. 2B, the gate switching of the MOSFETs Q1 to Q3 is turned on. M
When the gate switching of the OSFETs Q1 to Q3 is turned on and the drain currents ID1 to ID3 flow, a current flows to the resistor R4, so that the regenerative power is discharged at the resistor R4. The voltage rise between N can be suppressed.

When the voltage between the bus P and the bus N decreases and reaches a predetermined value Voff due to the discharge of the regenerative power, I
The C circuit 3 performs switching OFF control on the gates of the MOSFETs Q1 to Q3. MO
When the gate switching of the SFETs Q1 to Q3 is turned off, the conduction resistance between the drain and the source increases, and the drain currents ID1 to ID3 do not flow. Here, when the power regeneration state from the motor M continues, when the voltage between the bus P and the bus N increases again and reaches Von in FIG. 2, the IC circuit 3 connects the gates of the MOSFETs Q1 to Q3 with each other. Perform switching control. Therefore, the drain
As the conduction resistance between the sources decreases and the drain currents ID1 to ID3 flow, a current flows through the resistor R4. That is, the gate switching of the MOSFETs Q1 to Q3 is O
The state becomes N, and the regenerative power is discharged by the resistor R4.

As described above, the regenerative power discharge circuit 2 repeats the above-described operation characteristics, thereby maintaining the voltage between the bus P and the bus N at Von or less, and rectifying the voltage between the bus P and the bus N by the regenerative power. The device does not exceed the breakdown voltage of the diode constituting the section D1, the smoothing electrolytic capacitor C1, and the transistor for driving the motor of the inverter INV, so that the device is not damaged.

Here, when the gate switching of the MOSFETs Q1 to Q3 is turned on, a surge voltage is generated due to the stray inductance near the resistor R4. If the surge voltage exceeds the withstand voltage of the MOSFETs Q1 to Q3, the MOSFETs Q1 to Q3 may be damaged. Could be reached. Therefore, the current caused by the surge voltage is supplied to the diode D
2 in the direction from the anode to the cathode, the influence of the surge voltage on the MOSFETs Q1 to Q3 is suppressed.
1 to Q3 are prevented from being damaged.

In FIG. 1, three Ms are used as switching means.
The OSFETs Q1 to Q3 are connected in parallel. However, in consideration of the rated current of one MOSFET, when a large regenerative power is generated, the current accompanying the regenerative power is divided to exceed the rated current of each MOSFET. The number of mounted MOSFETs differs depending on the voltage between the bus P and the bus N and the value of the resistor R4.
That is, the current value (determined by the voltage between the bus P and the bus N and the value of the resistor R4) flowing through one FET when the gate switching is ON must be provided to be always smaller than the rated current value of the FET. .

The MOSFETs Q1 to Q3 are switching elements that perform a switching operation by applying a voltage to the gates.
If the current shunted to TQ1 to Q3 tends to be biased to one side, the ON resistance (drain-source conduction resistance) at the time of switching increases and the current is suppressed. Damage due to the above current flowing can be reliably prevented.

As a modification of the embodiment of the present invention, M in FIG.
Similar effects can be obtained by providing IGBTs (insulated gate bipolar transistors) Q1 'to Q3' for performing a switching operation by applying a voltage to the gate and flowing a collector current, as shown in FIG. 3, instead of the OSFETs Q1 to Q3. Can play. However, by using the IGBT as the switching means of the regenerative discharge circuit 2, it becomes easier to increase the breakdown voltage and increase the current as compared with the case where the MOSFETs Q1 to Q3 are used. FIG. 2 shows MOSFETs Q1 to Q3 of FIG. 1 replaced by IGBTs Q1 'to Q3'.
Since it has the same effect,
Other circuit elements and the like are denoted by the same reference numerals as in FIG. 1 and will not be described in detail.

[0026]

The present invention is configured as described above.
The following effects are obtained.

According to the first aspect of the present invention, a DC output is supplied by rectifying and smoothing an AC input, and a voltage for detecting a rise in voltage generated by regenerative power from the DC output side. In an AC-DC converter provided with a regenerative power discharging circuit including a rise detecting means and a switching means for starting discharge of regenerative power by detecting a voltage rise, the switching means is switched by applying a voltage to a gate. Even when a large regenerative power is generated by configuring the switching elements to perform operations, a plurality of switching elements are connected in parallel while considering the rated current of one switching element,
By increasing the number of connections, it is possible to shunt the current accompanying the regenerative power and adjust the current so that it does not exceed the rated current of each element.

According to the second aspect of the present invention, in the regenerative power discharging circuit, when a plurality of the switching elements are connected in parallel, if the current shunted to each element tends to be biased to one side, the ON resistance at the time of switching is reduced. Since the current is increased to suppress the current, the current is less likely to be biased, and damage to the element can be prevented.

According to the third aspect of the present invention, since the switching element is a MOS field effect transistor, it is possible to perform a switching operation by applying a voltage to a gate and realize high-speed switching. It becomes possible.

According to the fourth aspect of the invention, by using an IGBT as the switching element, it is possible to perform a switching operation by applying a voltage to the gate,
It is possible to realize a higher breakdown voltage and a larger current than a MOS type field effect transistor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an AC-DC converter, an inverter, and a motor according to an embodiment of the present invention.

FIG. 2 is a MOSFET in the regenerative power discharge circuit of FIG.
FIG. 5 is a diagram showing switching characteristics of the switching device.

FIG. 3 is a circuit diagram showing a modified example of the regenerative power discharge circuit of FIG.

[Explanation of symbols]

 1 AC-DC converter 2 Regenerative power discharge circuit 3 IC circuit Q1, Q2, Q3 MOSFET Q1 ', Q2', Q3 'IGBT

Claims (4)

[Claims] A DC output is supplied by rectifying and smoothing an AC input, wherein a voltage rise detecting means for detecting a rise in a voltage generated by regenerative power from a DC output side; In an AC-DC converter provided with a regenerative power discharging circuit constituted by a switching means for starting discharge of regenerative power by detection, the switching means is constituted by a switching element which performs a switching operation by applying a voltage to a gate. An AC-DC converter characterized by the above-mentioned. 2. The AC-DC converter according to claim 1, wherein a plurality of the switching elements are connected in parallel in the regenerative power discharging circuit. 3. The AC / DC converter according to claim 1, wherein the switching element is a MOS field effect transistor. 4. The AC-DC converter according to claim 1, wherein the switching element is an IGBT.