JP2000236672A - Power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power conversion system in which noise accompanying the driving is reduced through a common noise reducer, even when a plurality of power converters are connected in parallel, and the size can be reduced easily. SOLUTION: A DC voltage is applied from an AC input line via an insulating transformer 9 and a rectifier circuit 10 to a positive side output line P1 and a negative side output line N1. The DC voltage is divided by capacitors Cp, Cn, by fixing the intermediate series joint 11 to the earth potential. Consequently, the positive side output line P1 can supply a positive constant voltage at all times with respect to ground potential, and the negative side output line N1 can supply a negative constant voltage constantly. When transistors Tr1, Tr2 are turned on/off by an amplifier 7, a noise compensation current i flows through the series joint 11 of Cp, Cn between the grounded AC input line and the ground. Joints of a noise reducer are concentrated at the prestage of each power converter through such an operation to more the noise reducer shared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion system having a noise reduction function for passing a noise compensation current when a motor is driven at a variable speed based on AC power.
The present invention relates to a power conversion system that can share a noise reduction function of each power conversion device and can achieve downsizing.

[0002]

2. Description of the Related Art Usually, when a motor is driven, a power conversion system including an AC power supply and a power conversion device for converting the AC power to supply desired power is used. A typical example of this type of power converter is a GT.
O (gate turn-off thyristor) or IGBT (insulated g
There is an inverter device in which a plurality of semiconductor switching elements such as ate bipolar transistors are arranged in series and parallel. This inverter device will be described as a representative example of a power conversion device in the following description.

In recent years, in a motor drive system using this type of inverter device, a ground leakage current (hereinafter referred to as a leakage current) flowing to the ground through a stray capacitance C between a motor winding and a frame ground due to high-speed switching of each switching element. ) Is drawing attention as a problem.

FIG. 8 is a circuit diagram showing a configuration of a drive system of a motor for explaining this problem. As the circuit configuration,
In some cases, a plurality of motors are driven by one inverter device. Here, a case in which one motor is driven by each one inverter device will be described.

In this motor drive system, a three-phase AC voltage is supplied to a plurality of full-wave rectifier circuits 2 from a common AC power supply 1. Since the n sets A1 to An from the full-wave rectifier circuit 2 to the inverter device 3 and the electric motor 4 at the subsequent stage have the same configuration, the circuit of the set A1 will be described as an example.

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.

At this time, the leakage current I1, which is a noise current, flows to the ground through the stray capacitance C between the motor winding and the frame ground due to the voltage change rate dv / dt.

The leakage current I1 passes 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 eliminating 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 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 bases of the transistors Tr1 and Tr2.

In each of the transistors Tr1 and Tr2, n
The pn-type transistor Tr1 has a collector connected to the positive input line P, and an emitter connected to the pnp-type transistor Tr1.
2 and one end of a coupling capacitor. The collector of the pnp 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 of the transistors Tr1 and 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, when the leakage current I1 flows 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.

Thus, 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.

When the leakage current I1 flows from the ground line of the alternating current 1 to the motor 4, the noise reduction device turns on only the npn 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.

[0022]

However, in the above-described power conversion system, when a plurality of inverter devices 3 are connected in parallel, a noise reduction device is required for each number of inverter devices, so that the installation of the inverter devices is required. As the number increases, the number of noise reduction devices also needs to increase, which makes it difficult to reduce the size.

The present invention has been made in consideration of the above-mentioned circumstances, and even when a plurality of power converters are connected in parallel, noise accompanying driving can be reduced by a common noise reduction device, and thus, miniaturization can be easily achieved. An object is to provide a power conversion system that can be achieved.

[0024]

According to a first aspect of the present invention, a common AC power supply and an AC power supplied from the AC power supply are converted into an AC power of an arbitrary frequency to individually control the electric motor at a variable speed. A plurality of power conversion devices to be driven, a power conversion system including a common noise reduction device that detects a leakage current from a power supply line of the AC power supply and supplies a noise compensation current, wherein the noise reduction device includes: An insulating transformer having a primary side connected between the AC power supply and each of the power converters, a rectifying circuit connected to a secondary side of the insulating transformer, a positive output line and a negative output line in the rectifying circuit. And a series connection point between the positive and negative capacitors connected in series between the positive and negative capacitors, and a grounded common AC input line in front of each power converter. Connection means for connection, a positive-side switching element having one end connected to the positive-side output line, and one end connected to the negative-side output line, having an on / off characteristic opposite to that of the positive-side switching element. A negative-side switching element having a coupling capacitor disposed between each of the other ends of the positive-side and negative-side switching elements and ground; amplifying the leakage current detection signal; And a device control means for providing a control input to the negative switching device.

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

Further, according to a third aspect of the present invention, in the power conversion system 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. This is a grounded power conversion system.

According to a fourth aspect of the present invention, in the power conversion system according to any one of the first to third aspects, each of the positive and negative switching elements includes a plurality of switching elements. Is a power conversion system electrically connected in parallel.

Further, according to a fifth aspect of the present invention, a Y-connected AC power supply whose neutral point is grounded and an AC power supplied from the AC power supply are converted into AC power of an arbitrary frequency and individually. A power conversion system comprising: a power conversion device for driving a motor at a variable speed; and a noise reduction device that detects a leakage current from a power supply line of the AC power supply and supplies a noise compensation current. 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, a positive output line and a negative output of the rectifier circuit. Y-connection in which one end is individually connected to a positive-side and a negative-side capacitor connected in series between the line and an AC input line in the preceding stage of the power converter, and the other ends are connected to a neutral point. A capacitor; connecting means for connecting a neutral point of the Y-connection capacitor to a series connection point between the positive and negative capacitors; and a positive switching element having one end connected to the positive output line. An element, one end of which is connected to the negative output line, a negative switching element having an on / off characteristic opposite to that of the positive switching element, and each of the other ends of the positive and negative switching elements and ground. And a device control means for amplifying the leakage current detection signal and providing the obtained amplified signal to control inputs of the positive and negative switching elements. .

According to a sixth aspect of the present invention, in the power conversion system according to the fifth aspect, the power conversion system is disposed closer to the AC power supply than a connection point between the Y connection capacitor and the AC input line. A power conversion system including a leakage current detector that equivalently detects a leakage current and provides an obtained detection signal to the element control unit.

According to a seventh aspect of the present invention, in the power conversion system according to the fifth or sixth aspect, as the AC power supply, a plurality of phases are Y-connected, and the Y-connection is neutral. The point is a grounded power conversion system.

According to an eighth aspect of the present invention, in the power conversion system according to any one of the fifth to seventh aspects, each of the positive and negative switching elements includes a plurality of switching elements. This is a power conversion system in which elements are electrically connected in parallel.

(Operation) Therefore, the invention corresponding to claim 1 employs the above means, so that the extraction of the AC voltage by the insulating transformer and the inflow / outflow of the noise compensation current by the noise reduction device are common. Since the connection point of the noise reduction device is eliminated from each power conversion device and concentrated at the preceding stage,
A common noise reduction device can be realized. Therefore, even when a plurality of power converters are connected in parallel,
Noise due to driving can be reduced by a common noise reduction device, and thus, miniaturization can be easily achieved.

The rectified DC voltage is applied to the positive output line and the negative output line of the rectifier circuit.
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, and the negative output line can always supply a constant negative voltage with respect to the ground potential. That is, since the voltage with respect to the ground can always be kept constant, the controllability of the noise compensation current can be improved.

When the positive and negative switching elements are on / off controlled by the element control means, the noise compensation current is supplied to the grounded AC input line by the coupling capacitor, the positive switching element, and the positive output. It flows through the line and the positive side capacitor, or through the coupling capacitor, the negative side switching element, the negative side output line and the negative side capacitor, so that the leakage current as a noise current can be canceled, and easily and reliably. Noise can be 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 the invention corresponding to claim 3, since the AC power supply has a plurality of phases, and one of the plurality of phases is grounded, the AC power supply corresponds to claim 1 or claim 2. The same operation as the above operation can be achieved.

Further, 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.

Further, in the invention according to claim 5, even in the case of a Y-connection AC power supply, a three-phase AC input line is provided with a Y-connection capacitor, and the neutral point of the Y-connection capacitor is set to a virtual earth. By connecting the positive and negative capacitors in series to the series connection point of the noise reduction device as a point, the virtual earth voltage (voltage with respect to the potential of the virtual earth point) is always constant, similarly to the operation according to the first aspect. Can be held in
The connection point of the noise reduction device can be concentrated at the front stage of each power conversion device, so even when multiple power conversion devices are connected in parallel, the noise associated with driving can be reduced by the common noise reduction device, thereby easily reducing the size. Can be achieved.

Similarly, the controllability of the noise compensation current can be improved by keeping the virtual earth voltage constant. Further, by the on / off control of the positive and negative switching elements by the element control means, the noise compensation current flows through the neutral path of the Y-connection capacitor to the AC input line in the same path as described above. Leakage current as a current can be canceled, and noise can be easily and reliably reduced.

The invention according to claim 6 corresponds to claim 5 in that the leakage current detector is disposed closer to the AC power supply than the connection point between the Y connection capacitor and the AC input line. In addition to the function, since the leakage current can be detected independently 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 the invention corresponding to claim 7, in the AC power supply, a plurality of phases are Y-connected and a neutral point of the Y-connection is grounded. The same operation as the operation corresponding to the above can be achieved.

The invention corresponding to claim 8 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 effect corresponding to any one of the fifth to seventh aspects, even if the leakage current has a large value, a noise compensation current for canceling the leakage current can flow.

[0043]

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 system according to a first embodiment of the present invention is applied. The same reference numerals are given and the detailed description is omitted, and different portions are mainly described here. In the following embodiments, the same description will not be repeated.

That is, the present embodiment is intended to improve the controllability of the noise compensation current. 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 insulating 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 npn transistors Tr1 and pnp. Has a function of supplying power to the 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 a pnp transistor Tr2
Connected to the collector.

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 conversion system will be described.

Now, a DC voltage extracted from the common AC input line by the insulating transformer 9 and full-wave rectified by the rectifier circuit 10 is applied to the positive output line P1 and the negative output line N1. This DC voltage is divided by fixing the intermediate series connection point 11 to the ground potential by two capacitors Cp and Cn.

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, the noise compensation current i can always be 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, when the leakage current I1 flows 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.

When the leakage current I1 flows from the ground line of the alternating 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 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.

Accordingly, 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 extraction of the AC voltage by the insulating transformer 9 and the inflow / outflow of the noise compensation current i by the noise reduction device are performed on the common AC input line. Since the connection point of the noise reduction device is excluded from each power conversion device and concentrated at the preceding stage, the noise reduction device can be shared. For this reason, even when a plurality of power converters are connected in parallel, the noise associated with driving can be reduced by the common noise reduction device, and the size can be easily reduced.

Further, since the voltage passes through the insulating transformer 9, it 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.

The DC voltage applied to the positive output line P1 and the negative output line N1 is controlled by the capacitors Cp and Cn.
Thus, the series connection point 11 is fixed to the ground potential and divided. Therefore, 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 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.

Further, each transistor T
When r1 and Tr2 are on / off controlled, 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, so that the leakage current I1 as the noise current is reduced. The noise can be canceled, and the noise can be reduced easily and reliably.

Further, the detection of the leakage current I1 by the leakage current detector 5 is prevented by flowing the noise compensation current i for canceling the leakage current I1 on the side of the full-wave rectifier circuit 2 rather than the leakage current detector 5. 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 rectifier circuit 2 with respect to the series connection point 11, the AC of the full-wave rectifier 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. 2 is a circuit diagram showing a configuration of a drive system of a motor to which a power conversion system 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, since the parallel circuit of the plurality of npn transistors Tr1 and the parallel circuit of the plurality of pnp transistors Tr2 have a large current capacity, 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 the present embodiment, since the voltage can be set arbitrarily using an insulating transformer, each transistor Tr is set to increase the current capacity irrespective of the voltage.
1 and Tr2 can be arranged in parallel.

(Third Embodiment) Next, a case where the above-described power conversion system according to the present invention is applied to a Y-connection AC power supply will be described from a technical background.

Normally, even if the first embodiment is simply applied to a Y-connection AC power supply, in the case of a Y-connection AC power supply having a neutral ground, since there is no power supply line having an earth line, noise is reduced. There is a problem that the noise compensation current i for canceling out cannot be passed. On the other hand, in order to compensate for the leakage current of the power supply ground to the neutral point, it is necessary to use a three-phase four-wire power supply wiring. Therefore, there is a problem that the system becomes expensive due to the use of the 4-wire wiring or NFB.

This embodiment includes a viewpoint for solving such a problem. For this reason, first, a simple configuration in which there is one set of an inverter device and an electric motor will be described with reference to the drawings, and then this description will be applied to a set of a plurality of inverter devices and the like.

FIG. 3 is a circuit diagram showing a configuration of a drive system of a motor to which a power conversion system according to a third embodiment of the present invention is applied. In this embodiment, as shown in the figure, instead of the AC power supply 1, a Y-connected AC power supply 1a having a grounded neutral point 12 and a three-way circuit between the leakage current detector 5 and the full-wave rectifier circuit 2 are provided. One end is individually connected to the phase AC input line, and the other end includes three Y-connected capacitors C2 to C4 connected to the neutral point Pi. Note that the capacitor C
The neutral points Pi of 2 to C4 are connected to the series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit.

According to the configuration described above, three Y-connected capacitors C2 to C4 are provided for the Y-connected AC power supply 1a, and these capacitors C2 to C4 are connected to the three-phase AC input line. It is connected. Here, the neutral point Pi, which is the ground connection point of the Y-connected AC power supply 1a, is associated with the neutral point Pi of the Y-connected capacitors C2 to C4 as a virtual ground point.

The series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit 8b is connected to this virtual ground point. Therefore, a full-wave rectified DC voltage is applied to the positive output line P1 and the negative output line N1 of the rectifier circuit 10, and this DC voltage is applied to two capacitors Cp and Cp.
The intermediate series connection point 11 is fixed to the potential of the virtual earth point (neutral point Pi) by n and divided.

Therefore, as described above, the positive output line P1
Can always supply a constant positive voltage with respect to the potential of the virtual earth point. Further, the negative output line N1 can always supply a constant negative voltage with respect to the potential of the virtual ground point. Therefore, the noise compensation current i can always be controlled.

More specifically, the noise compensation current i passes through the series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit 8b in accordance with the on / off of the transistors Tr1 and Tr2, and the Y-connection 3 Capacitors C2 to C
4 flows into or out of the AC input line via the neutral point Pi. Therefore, similarly, the leakage current I1 can be canceled.

As described above, according to the third embodiment,
Even in the case of the Y-connected AC power supply 1a, the three-phase AC input line is provided with three Y-connected capacitors C2 to C4, and the neutral point Pi of the capacitors C2 to C4 is used as a virtual ground point to form the noise reduction circuit 8b. By connecting to the series connection point 11 of the capacitors Cp and Cn, the same operation and effect as in the first embodiment can be obtained.

In this embodiment, as shown in FIG.
As described above, even if the number of series circuits of the transistors Tr1 and Tr2 is increased and the configuration is modified to be connected in parallel to each other, the noise compensation current i having a large value can be controlled as described above. Further, as shown in FIG. 5 and FIG. 6, even when the configuration is changed to a configuration in which a plurality of inverter devices are connected in parallel,
As described above, downsizing can be achieved by a common noise reduction device.

(Fourth Embodiment) FIG. 7 is a circuit diagram showing a configuration of a drive system of a motor to which a power conversion system according to a fourth embodiment of the present invention is applied. In the present embodiment, the third
This is a modification of the third embodiment, and shows an example in which the concept of the third embodiment described above is applied to all AC power supplies having a ground connected to no power line. Specifically, instead of the AC power supply 1a, a three-phase Δ-connection AC power supply 1b grounded at a neutral point 13 of a two-phase, and a three-phase AC power supply between the leakage current detector 5 and the full-wave rectifier circuit 2. It is provided with four ΔC-connected capacitors C5 to C8 connected to the AC input line and equivalently connected to the AC power supply 1b. In this case, the neutral point Pa of the capacitor is a connection point between C5 and C6 in an arrangement equivalent to the ground of the AC power supply 1b, and the capacitors Cp and Cn of the noise reduction circuit 8d as described above.
Are connected to the series connection point 11 of

According to the above configuration, four capacitors C5 to C8 equivalently connected to each other are provided for the AC power supply 1b composed of four AC power supplies connected to each other. Connected to three-phase AC input line. Here, with respect to the neutral point 13 between the two power supplies, which is the ground connection point of the Δ-connected AC power supply 1b, the neutral point Pa of the Δ-connected capacitors C5 to C8 is set as a virtual ground point.
Corresponding.

The series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit 8d is connected to this virtual ground point.

Therefore, even in the case of the three-phase Δ-connection AC power supply 1b grounded at the neutral point 13 of the two-phase, the same operation and effect as in the third embodiment can be obtained.
Further, in this embodiment, (1) a plurality of capacitors C5 to C8 connected equivalently to the AC power supply 1b are provided;
(2) The neutral point Pa (virtual ground point corresponding to the ground connection point of the AC power supply 1b) of each of the capacitors C5 to C8 is connected to the series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit 8d.
The method of connecting to the power supply is not limited to the AC power supplies 1a and 1b described in the third or fourth embodiment, and can be applied to any AC power supply having a ground not connected to the power supply line.

Although not specifically shown, T as shown in FIG.
Even when the configuration is changed to a configuration in which a plurality of series circuits of r1 and Tr2 are connected in parallel, a configuration in which a plurality of inverter devices 3 are connected in parallel as shown in FIG. 5, or a configuration having both as shown in FIG. Thus, a similar effect can be obtained.

(Other Embodiments) In 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 compensating current i has been described. , Tr2, and a structure provided with another current controlling element that satisfies the same operation performance of high withstand voltage, high frequency, and high current amplification, the same effect can be obtained by implementing the present invention in the same manner. .

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0087]

As described above, according to the present invention, even when a plurality of power converters are connected in parallel, the noise associated with driving can be reduced by the common noise reduction device, so that the size can be easily reduced. And a power conversion system that can perform the power conversion.

[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 conversion system according to a first embodiment of the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration of a drive system of an electric motor to which a power conversion system according to a second embodiment of the present invention is applied.

FIG. 3 is a circuit diagram showing a configuration of a drive system of a motor to which a power conversion system according to a third embodiment of the present invention is applied.

FIG. 4 is a circuit diagram showing a modified configuration in the embodiment.

FIG. 5 is a circuit diagram showing a modified configuration in the embodiment.

FIG. 6 is a circuit diagram showing a modified configuration in the embodiment.

FIG. 7 is a circuit diagram showing a configuration of a drive system of a motor to which a power conversion system according to a fourth embodiment of the present invention is applied.

FIG. 8 is a circuit diagram showing a configuration of a drive system of a motor to which a conventional power conversion system is applied.

FIG. 9 is a circuit diagram showing a configuration of a drive system of a motor to which a conventional power conversion system is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Full-wave rectifier circuit 3 ... Inverter device 4 ... Electric motor 5 ... Leakage current detector 7 ... Amplifier 8,8a, 8b, 8c, 8d ... Noise reduction circuit 9 ... Insulation transformer 10 ... Rectifier circuit 11 ... Series Connection points 12, 13, Pi, Pa ... Neutral points D1 to D6 ... Diodes Q1 to Q6 ... Switching elements C1 ... Coupling capacitors Cp, Cn, C2 to C8 ... Capacitors Tr1 ... npn transistors Tr2 ... pnp transistors P ... Positive Side input line N ... Negative side input line P1 ... Positive side output line N1 ... Negative side 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 factory of Toshiba Corporation (reference) 5H006 AA01 BB05 CA01 CA12 CA13 CB01 CC01 DA02 DC02 5H007 AA01 AA12 BB06 CA01 CB04 CB05 CC01 CC05 CC23 CC35 DA05 DB01 DB05 DC02 EA02

Claims (8)

[Claims] 1. A common AC power supply, a plurality of power converters for converting AC power supplied from the AC power supply into AC power of an arbitrary frequency and individually driving a motor at a variable speed; A power conversion system comprising: a common noise reduction device that detects a leakage current from a power supply line of a power supply and supplies a noise compensation current; wherein the noise reduction device is provided between the AC power supply and each of the power conversion devices. An insulating transformer whose primary side is connected to a rectifier circuit connected to the secondary side of the insulating transformer; a positive side connected in series between a positive side output line and a negative side output line in the rectifier circuit; and A negative-side capacitor; connecting means for connecting a series connection point between the positive-side and negative-side capacitors to a grounded common AC input line in a preceding stage of each of the power converters; A positive-side switching element having one end connected to a power line; a negative-side switching element having one end connected to the negative-side output line and having an on / off characteristic opposite to that of the positive-side switching element; A coupling capacitor disposed between each other end of the negative-side switching element and ground; an element for amplifying the leakage current detection signal and providing an obtained amplified signal to control inputs of the positive-side and negative-side switching elements A power conversion system comprising a control unit. 2. The power conversion system according to claim 1, wherein the power supply system is disposed closer to the AC power supply than a connection point between the connection unit and the AC input line, and the leakage current is detected and obtained equivalently. A power conversion system comprising a common leakage current detector for providing a detection signal to the element control means. 3. The power conversion system according to claim 1, wherein the AC power supply has a plurality of phases, and one of the plurality of phases is grounded. system. 4. The power conversion system 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 conversion system, characterized in that: 5. A Y-connection AC power supply whose neutral point is grounded, and power for converting AC power supplied from the AC power supply to AC power of an arbitrary frequency and individually driving the motor at a variable speed. A power conversion system comprising: a conversion device; and a noise reduction device that detects a leakage current from a power supply line of the AC power supply and supplies a noise compensation current, wherein the noise reduction device includes the AC power supply and the power conversion device. An insulation transformer having a primary side connected between the rectifier circuit, a rectifier circuit connected to a secondary side of the insulation transformer, and a rectifier circuit connected in series between a positive output line and a negative output line in the rectifier circuit. A positive-side capacitor and a negative-side capacitor; a Y-connection capacitor, one end of which is individually connected to an AC input line in the preceding stage of the power converter, and the other end of which is connected to a neutral point; Connecting means for connecting a neutral point to a series connection point between the positive and negative capacitors; a positive switching element having one end connected to the positive output line; and the negative output. A negative-side switching element having one end connected to the line and having an on / off characteristic opposite to that of the positive-side switching element; and a coupling disposed between each other end of the positive-side and negative-side switching elements and ground. A power conversion system, comprising: a capacitor; and element 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. 6. The power conversion system according to claim 5, wherein the power supply system is disposed closer to the AC power supply than a connection point between the Y connection capacitor and the AC input line, and equivalently detects the leakage current. A power conversion system comprising a leakage current detector for providing an obtained detection signal to the element control means. 7. The power conversion system according to claim 5, wherein a plurality of phases of the AC power supply are Y-connected, and a neutral point of the Y-connection is grounded. Power conversion system. 8. The power conversion system according to claim 5, wherein the positive and negative switching elements each include a plurality of switching elements electrically connected in parallel. A power conversion system, characterized in that: