JP2000092861A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve controllability of noise compensation current by keeping ground voltage resistance all the time. SOLUTION: In this power converter, rectified DC voltage is applied to the positive side output line P1 and the negative side output line N1 of a rectifying circuit 10, however, the DC voltage is divided with a middle serial-connection point 11 fixed to a ground potential by two capacitors Cp, Cn, so that the positive side output line P1 can always supply positive constant voltage to a ground potential, and the negative side output line N1 can always supply negative constant voltage to the ground potential. When respective transistors Tr1, Tr2 are on/off-controlled by an amplifier 7, noise compensation current (i) passes through a noise suppressing circuit 8 between the input ground terminal of a full wave rectifying circuit 2 and the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device having a noise reduction function of flowing a noise compensation current so as to cancel a leakage current when a motor is driven at a variable speed based on AC power.

[0002]

2. Description of the Related Art Usually, when a motor is driven, a power converter capable of supplying a desired power is used. A typical example of this type of power converter is a GTO (gate
turn-off thyristor) or IGBT (insulated gate bipo)
There is an inverter device in which a plurality of semiconductor switching elements such as lar transistors are arranged in series. This inverter device will be described as a representative example of a power conversion device in the following description.

In recent years, in a drive system of a motor using this type of inverter device, a ground leakage current (hereinafter referred to as a leakage current) accompanying high-speed switching of each switching element has been attracting attention as a problem.

FIG. 5 is a circuit diagram showing a configuration of a drive system of a motor for explaining this problem. In the drive system of the electric motor, a three-phase AC voltage is supplied from an AC power supply 1 to a full-wave rectifier circuit 2.

The full-wave rectifier circuit 2 includes three-phase bridge-connected diode elements D1 to D6, converts the three-phase AC voltage into a DC voltage, and converts the DC voltage into a positive input line P and a negative input line. And N to the inverter device 3.

The inverter device 3 includes switching elements Q1 to Q6 connected in a three-phase bridge, and has a pulse whose width is controlled by PWM (pulse width modulation) control of each of the switching elements Q1 to Q6 by a gate drive circuit (not shown). Is applied to each phase winding terminal of the motor 4. The electric motor 4 is driven by the pulse voltage. However, the electric motor 4 has a stray capacitance C between itself and the ground. For this reason, when a pulse-like voltage is applied to the electric motor 4 as each switching element of the inverter device 3 is turned on and off, a pulse-like voltage is also applied between the terminal of the electric motor 4 and the ground.

Due to the voltage change rate dv / dt at this time, a leakage current I1 as a noise current flows to the ground through the stray capacitance C between the motor winding and the frame ground. The leakage current I1 flows through each ground line between the electric motor 4 and the ground terminal of the AC power supply 1 and the ground, and flows according to the polarity so as to flow into or out of the ground terminal of the AC power supply 1. For this reason, the leakage current I1 causes a malfunction or an electric shock accident of the leakage breaker. From the viewpoint of solving the inconvenience caused by the leakage current I1, it is considered to apply a noise reduction device to a power conversion device as shown in FIG.

This noise reduction device includes a leakage current detector 5 for detecting a leakage current I1 from a power supply line between an AC power supply 1 and a full-wave rectifier circuit 2, and a positive-side input based on the detected leakage current. A noise reduction circuit 6 is provided for conducting a noise compensation current by conducting between the line P and the ground or between the ground and the negative input line N.

The noise reduction circuit 6 includes an amplifier 7, n
pn-type transistor Tr1, pnp-type transistor Tr
2 and a coupling capacitor C1, and each of the transistors Tr1 and Tr2 is required to have an operating performance of high withstand voltage, high frequency, and high current amplification.

Here, the leakage current detector 5 is a zero-phase current transformer CT having, for example, an annular core made of ferrite, and the leakage current I1 flowing through the full-wave rectifier circuit 2 is equivalent to the difference between the power line currents. And a detection signal is given to the amplifier 7.

The amplifier 7 amplifies the detection signal and provides an output signal to the base of each of the transistors Tr1 and Tr2. Among the transistors Tr1 and Tr2, the npn transistor Tr1 has a collector connected to the positive input line P, and an emitter connected to the emitter of the pnp transistor Tr2 and one end of a coupling capacitor. pn
The collector of the p-type transistor is connected to the negative input line N. The other end of the coupling capacitor C1 is connected to the ground.

That is, each transistor Tr1, Tr2
When receiving the output signal from the amplifier 7 at the base, they turn on and off in opposite directions, and connect the positive input line P or the negative input line N to the ground via the coupling capacitor C1.

For example, as shown in FIG.
Is flowing from the motor 4 to the ground line of the AC power supply 1, the noise reduction device turns on only the pnp transistor Tr2.

As a result, the noise compensation current i passes through the coupling capacitor C1, the pnp transistor Tr2, and the negative input line N, and passes through the diode D4 of the full-wave rectifier circuit 2.
It flows into a closed circuit consisting of D5 or D6.

Therefore, the leakage current I1 flowing into the ground terminal of the AC power supply 1 is canceled by the noise compensation current i. Further, as shown in FIG. 8, when the leakage current I1 flows from the ground line of the AC current 1 to the electric motor 4, the noise reduction device turns on only the npn-type transistor Tr1.

As a result, the noise compensation current i flows from the diode D1, D2 or D3 of the full-wave rectifier circuit 2 to the ground line via the positive input line P, the npn transistor Tr1 and the coupling capacitor C1. Therefore, the leakage current I1 flowing out from the ground line of the AC power supply 1 to the electric motor 4 is canceled by the noise compensation current i.

[0017]

However, in the above-described power converter, when the elements D3 and D4 become conductive in the full-wave rectifier circuit 2, for example, the positive input line P of the full-wave rectifier circuit 2 is grounded. And the same potential as. At this time, even when the npn-type transistor Tr1 is turned on, there is no potential difference between the positive input line P and the ground.

Conversely, when the elements D6 and D1 of the rectifier circuit 2 conduct, the negative input line N of the full-wave rectifier circuit 2
Similarly, it has the same potential as the ground. At this time, the noise reduction device turns on the pnp transistor Tr2,
Since there is no potential difference between the negative input line N and ground,
The noise compensating current i does not flow, and control becomes impossible.

The present invention has been made in view of the above circumstances, and has as its object to provide a power converter capable of always maintaining a constant voltage with respect to the ground and improving controllability of a noise compensation current.

[0020]

According to a first aspect of the present invention, an AC power from an AC power supply is converted into an AC power having an arbitrary frequency, a motor is driven at a variable speed, and a power supply line of the AC power supply is provided. What is claimed is: 1. A power converter having a noise reduction function of detecting a leakage current and flowing a noise compensation current, comprising: an insulating transformer having a primary side connected between the AC power supply and the power converter; Rectifier circuit connected to the positive and negative side capacitors connected in series between the positive side output line and the negative side output line in the rectifier circuit, and between the positive side and negative side capacitors. Connection means for connecting the series connection point of the power conversion device to a grounded AC input line, a positive switching element having one end connected to the positive output line, and the negative output line. One end is connected, a negative switching element having on / off characteristics opposite to the positive switching element, and a coupling capacitor disposed between each other end of the positive and negative switching elements and ground. And a device control means for amplifying the leakage current detection signal and supplying the resulting amplified signal to control inputs of the positive and negative switching elements.

According to a second aspect of the present invention, in the power converter according to the first aspect, the leakage current is arranged closer to the AC power supply than a connection point between the connection means and the AC input line. Is a power conversion device provided with a leakage current detector that detects equivalently.

Further, according to a third aspect of the present invention, in the power converter according to the first or second aspect, the AC power supply has a plurality of phases, and one of the plurality of phases is one of the plurality of phases. It is a grounded power converter.

According to a fourth aspect of the present invention, in the power converter according to any one of the first to third aspects, each of the positive and negative switching elements includes a plurality of switching elements. Are power converters electrically connected in parallel. (Operation) Accordingly, in the invention corresponding to claim 1, the rectified DC voltage is applied to the positive output line and the negative output line of the rectifier circuit by taking the above means. This DC voltage is divided by fixing the intermediate series connection point to the ground potential by positive and negative side capacitors.

Therefore, the positive output line can always supply a constant positive voltage with respect to the ground potential. Further, the negative output line can always supply a constant negative voltage with respect to the ground potential. As described above, since the voltage with respect to the ground can always be kept constant, the controllability of the noise compensation current can be improved unlike the related art.

When the positive and negative switching elements are controlled to be turned on and off by the element control means, the noise compensation current is supplied to the grounded AC input line of the power converter by the coupling capacitor and the positive switching element. Since the current flows through the positive output line and the positive capacitor, or through the coupling capacitor, the negative switching element, the negative output line and the negative capacitor, it is possible to cancel the leakage current as a noise current, Noise can be easily and reliably reduced.

According to a second aspect of the present invention, the leakage current detector is disposed closer to the AC power supply than the connection point between the connection means and the AC input line. In addition, since the leakage current can be detected regardless of the inflow or outflow of the noise compensation current at the connection point, the reliability of the operation can be improved.

Further, according to a third aspect of the present invention, the AC power supply has a plurality of phases, and one of the plurality of phases is grounded. The same operation as the above operation can be achieved.

The invention corresponding to claim 4 has a large current capacity because a plurality of switching elements are electrically connected in parallel as the positive and negative switching elements, respectively. In addition to the operation corresponding to any one of the first to third aspects, even if the leakage current has a large value, a noise compensation current for canceling the leakage current can be passed.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a circuit diagram showing a configuration of a drive system of an electric motor to which a power conversion device according to a first embodiment of the present invention is applied. The detailed description is omitted here, and different portions are mainly described here. In the following embodiments, the same description will not be repeated.

That is, in the present embodiment, the controllability of the noise compensation current is improved. Specifically, a noise reduction circuit 8 which is an improvement of the conventional noise reduction circuit 6 is provided.
The noise reduction circuit 8 includes transistors Tr1, T
An insulation transformer 9 and a rectifier circuit 10 for creating a potential difference between each collector of r2 and the ground, and a noise compensation current i according to ON / OFF of each of the transistors Tr1 and Tr2.
And capacitors Cp and Cn for flowing out or flowing into the input ground terminal of the full-wave rectifier circuit 2.

Here, the insulation transformer 9 has a primary side connected to a power supply line passing through the leakage current detector 5, and a secondary side connected to the rectifier circuit 10. The rectifier circuit 10 performs full-wave rectification on the output AC voltage on the secondary side of the insulating transformer 9 and converts the DC voltage between the positive output line P1 and the negative output line N1 into an npn transistor Tr1 and a pnp transistor Tr2. Specifically, the positive output line P1 is connected to one end of the capacitor Cp and the collector of the npn transistor Tr1, and the negative output line N1 is connected to one end of the capacitor Cn and the pnp type. It is connected to the collector of the transistor Tr2.

More specifically, the positive output line P1 of the rectifier circuit 10 is connected to the negative output line N1 via capacitors Cp and Cn having the same capacitance in series. A series connection point (neutral point) 11 between the capacitors Cp and Cn
Is connected to the input ground terminal of the full-wave rectifier circuit 2.

Next, the operation of noise reduction in the above power converter will be described. Now, a DC voltage subjected to full-wave rectification is applied to the positive side output line P1 and the negative side output line N1 of the rectifier circuit 10, and this DC voltage is connected to an intermediate series connection point 11 by two capacitors Cp and Cn. The voltage is fixed at the earth potential.

Therefore, the positive output line P1 can always supply a constant positive voltage with respect to the ground potential. Further, the negative output line N1 can always supply a constant negative voltage with respect to the ground potential. Therefore, unlike the related art, the noise compensation current i can be constantly controlled.

More specifically, in the noise reduction circuit 8, when each of the transistors Tr1 and Tr2 receives the output signal from the amplifier 7 as a base, the transistors Tr1 and Tr2 perform on / off operations in reverse to each other, and the positive side output line P1 or the negative side The output line N1 is connected to ground via a coupling capacitor C1.

For example, as shown in FIG.
Is flowing from the motor 4 to the ground line of the AC power supply 1, the noise reduction device turns on only the pnp transistor Tr2.

As a result, the noise compensation current i passes through the coupling capacitor C1, the pnp transistor Tr2, the negative output line N1, and the capacitor Cn, and passes through the full-wave rectifier circuit 2.
Flows into the input ground terminal.

Therefore, the leakage current I1 flowing into the ground terminal of the AC power supply 1 is canceled by the noise compensation current i. Further, as shown in FIG. 3, when the leakage current I1 flows out from the ground line of the alternating current 1 to the electric motor 4, the noise reduction device turns on only the npn transistor Tr1.

Thus, the noise compensation current i flows from the input ground terminal of the full-wave rectifier circuit 2 to the ground line through the capacitor Cp, the positive output line P1, the npn transistor Tr1, and the coupling capacitor C1.

Therefore, the leakage current I1 flowing out from the ground line of the AC power supply 1 to the electric motor 4 is canceled by the noise compensation current i. As described above, according to the present embodiment, the rectified DC voltage is applied to the positive output line P1 and the negative output line N1 of the rectifier circuit 10, and the DC voltage is applied to the two capacitors Cp and Cn. As a result, the intermediate series connection point 11 is fixed to the ground potential and divided, so that the positive output line P1 can always supply a constant positive voltage with respect to the ground potential, and the negative output line N1 can supply the ground potential with respect to the ground potential. Thus, a constant negative voltage can always be supplied.

As described above, since the voltage with respect to the ground can be kept constant, the controllability of the noise compensation current can be improved unlike the conventional case. Also, by the amplifier 7,
When the transistors Tr1 and Tr2 are controlled to be turned on and off, the noise compensation current i flows through the noise reduction circuit 8 between the input ground terminal of the full-wave rectifier circuit 2 and the ground. I1 can be canceled and noise can be reduced easily and reliably.

Further, since the voltage passes through the insulating transformer 9, the voltage can be set to a free voltage irrespective of the voltage and capacity applied to the inverter device 3. Therefore, it can be configured using a current control element such as a generally available npn transistor or pnp transistor. Therefore, it is possible to realize a small, inexpensive, and high-speed controllable noise reduction device having a simple configuration.

Further, the noise compensation current i for canceling the leakage current I1 is caused to flow in or out on the full-wave rectifier circuit 2 side from the leakage current detector 5, thereby preventing the leakage current detector 5 from detecting the leakage current I1. I try not to.

In other words, since the leakage current detector 5 is arranged closer to the AC power supply 1 than the connection point of the AC input line of the full-wave rectification circuit 2 with respect to the series connection point 11, the AC of the full-wave rectification circuit 2 is changed. Since the leakage current can be detected irrespective of the inflow or outflow of the noise compensation current i in the input line, the reliability of the operation can be improved. (Second Embodiment) FIG. 4 is a circuit diagram showing a configuration of a drive system of a motor to which a power converter according to a second embodiment of the present invention is applied.

This embodiment is a modification of the first embodiment, and is intended to control a large value noise compensation current i in order to compensate for a large value leakage current I1. The noise reduction circuit 8a has a configuration in which the number of series circuits including the npn transistor Tr1 and the pnp transistor Tr2 is increased, and these series circuits are electrically connected in parallel to each other. The number of series circuits connected in parallel can be set as appropriate in proportion to the magnitude of the leakage current.

With the above configuration, the parallel circuit of the plurality of npn-type transistors Tr1 and the parallel circuit of the plurality of pnp-type transistors Tr2 have a large current capacity, so that even if the leakage current I1 has a large value, A noise compensation current i for canceling the current can flow.

The current that can flow through each of the transistors Tr1 and Tr2 is limited by the rated current of each of the transistors Tr1 and Tr2. However, such a current control element as a transistor capable of high frequency control generally has only a low voltage and a small capacity. Even if a high-voltage, large-capacity current control element is manufactured, its use is limited, resulting in an increase in cost.

However, in this embodiment, since the voltage can be set arbitrarily by using an insulating transformer, each transistor Tr is increased so as to increase the current capacity irrespective of the voltage.
1 and Tr2 can be arranged in parallel.

In each of the above embodiments, the case where the npn-type transistor Tr1 and the pnp-type transistor Tr2 are used as the element for controlling the noise compensation current i has been described. However, the present invention is not limited to this. The present invention can be implemented in the same manner and the same effect can be obtained with a configuration in which another current control element that satisfies the operation performance of the same high withstand voltage, high frequency, and high current amplification is provided. In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[0050]

As described above, according to the present invention, it is possible to provide a power converter capable of always keeping the ground voltage constant and improving the controllability of the noise compensation current.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a drive system of an electric motor to which a power converter according to a first embodiment of the present invention is applied.

FIG. 2 is a schematic diagram for explaining an operation in the embodiment.

FIG. 3 is a schematic diagram for explaining the operation in the embodiment.

FIG. 4 is a circuit diagram showing a configuration of a drive system of an electric motor to which a power converter according to a second embodiment of the present invention is applied.

FIG. 5 is a circuit diagram showing a configuration of a drive system of a conventional electric motor.

FIG. 6 is a circuit diagram showing a configuration of a drive system of a motor to which a conventional power converter is applied.

FIG. 7 is a schematic diagram for explaining an operation of noise reduction in a conventional power converter.

FIG. 8 is a schematic diagram for explaining an operation of noise reduction in a conventional power converter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 AC power supply 2 Full-wave rectifier circuit 3 Inverter device 4 Motor 5 Leakage current detector 7 Amplifier 8 and 8 a Noise reduction circuit 9 Insulation transformer 10 Rectifier circuit 11 Series connection points D1 to D6 Diode Q1 to Q6 Switching element C1 Coupling capacitor Cp, Cn Capacitor Tr1 npn transistor Tr2 pnp transistor P Positive input line N Negative input line P1 Positive output line N1 Negative output line C: stray capacitance I1: leakage current i: noise compensation current

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Dai Dai Karasawa 1 Toshiba-cho, Fuchu-shi, Tokyo F-term in the Fuchu Plant of Toshiba Corporation 5H007 AA01 AA08 BB06 CA01 CA05 CB04 CB05 CC12 CC23 DA03 DA05 DB01 DC02 EA02 5H740 BA02 BA11 BB05 BB08 BB10 NN01 NN17

Claims (4)

[Claims] 1. A noise reduction device for converting an AC power from an AC power supply into an AC power having an arbitrary frequency, driving a motor at a variable speed, detecting a leakage current from a power supply line of the AC power supply, and supplying a noise compensation current. In a power converter having a function, an insulation transformer having a primary side connected between the AC power supply and the power converter, a rectifier circuit connected to a secondary side of the insulation transformer, and a positive side in the rectifier circuit. A positive-side and a negative-side capacitor connected in series between an output line and a negative-side output line; and a series connection point between the positive-side and the negative-side capacitors connected to a grounded AC input of the power converter. A connection means for connecting to a line, a positive switching element having one end connected to the positive output line, and a positive switching element having one end connected to the negative output line. A negative switching element having an on / off characteristic opposite to that of the element; a coupling capacitor disposed between each of the other ends of the positive and negative switching elements and ground; and amplifying the leakage current detection signal. And an element control means for supplying the obtained amplified signal to control inputs of the positive and negative switching elements. 2. The leakage current detection device according to claim 1, wherein the leakage current is disposed equivalently to the AC power supply from a connection point between the connection means and the AC input line, and is equivalent to the leakage current. A power conversion device comprising a device. 3. The power conversion device according to claim 1, wherein the AC power supply has a plurality of phases, and one of the plurality of phases is grounded. apparatus. 4. The power converter according to claim 1, wherein the positive side switching element and the negative side switching element each include a plurality of switching elements electrically connected in parallel. A power converter characterized by the above-mentioned.