JP3464930B2 - Power conversion system - Google Patents

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 reducing function of supplying a noise compensation current when a motor is driven at a variable speed based on AC power, and more particularly,
The present invention relates to a power conversion system in which the noise reduction function of each power conversion device is shared and the size can be reduced.

[0002]

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

In recent years, in a drive system of an electric motor 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 attracting attention as a problem.

FIG. 8 is a circuit diagram showing the structure of a drive system of an electric motor for explaining this problem. As for the circuit configuration,
There may be a case where one inverter device drives a plurality of electric motors, but here, a case where each one inverter device drives one electric motor will be described.

In this motor drive system, a three-phase AC voltage is supplied from a common AC power source 1 to a plurality of full-wave rectifier circuits 2, respectively. Since the n sets A1 to An from the full-wave rectifier circuit 2 to the inverter device 3 and the electric motor 4 in 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 is composed of three-phase bridge-connected diode elements D1 to D6, which converts the three-phase AC voltage into a DC voltage, and the DC voltage is the positive side input line P and the negative side input line. It is supplied to the inverter device 3 from between N and N.

The inverter device 3 is composed of switching elements Q1 to Q6 connected in a three-phase bridge, and a pulse whose width is controlled by PWM (pulse width modulation) control of each switching element Q1 to Q6 by a gate drive circuit (not shown). Voltage (rectangular wave) is applied to each phase winding terminal of the electric motor 4. The electric motor 4 is driven by this pulsed voltage. However, the electric motor 4 has a stray capacitance C between itself and the ground. Therefore, when a pulsed voltage is applied to the electric motor 4 as each switching element of the inverter device 3 is turned on / off, the pulsed 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 earth line between the electric motor 4 and the earth terminal of the AC power source 1 and the ground, and flows into or out of the earth terminal of the AC power source 1 depending on the polarity. . Therefore, the leakage current I1 causes malfunction of the leakage breaker, electric shock accident, or the like. From the viewpoint of eliminating the inconvenience caused by the leakage current I1, it is considered to apply the noise reduction device to the power conversion device as shown in FIG.

This noise reducing 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 electrically connecting between the line P and the ground or between the ground and the negative side input line N.

The noise reduction circuit 6 includes amplifiers 7, n
pn type transistor Tr1, pnp type transistor Tr
The transistor Tr1 and Tr2 are required to have high withstand voltage, high frequency, and high current amplification performance.

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

The amplifier 7 amplifies this detection signal and gives an output signal to the bases of the transistors Tr1 and Tr2.

Of the transistors Tr1 and Tr2, n
The pn-type transistor Tr1 has a collector connected to the positive side input line P and an emitter connected to the pnp-type transistor Tr1.
Two emitters and one end of the coupling capacitor. The collector of the pnp type transistor is connected to the negative side input line N. The other end of the coupling capacitor C1 is connected to 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 reverse, and connect the positive side input line P or the negative side input line N to the ground via the coupling capacitor C1.

For example, when the leakage current I1 flows from the electric motor 4 into the earth line of the AC power source 1, the noise reduction device turns on only the pnp type transistor Tr2.

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

Therefore, the noise compensating current i cancels the leakage current I1 flowing into the ground terminal of the AC power supply 1.

When the leakage current I1 flows from the earth 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 compensating current i flows from the diode D1, D2 or D3 of the full wave rectifier circuit 2 to the ground line through the positive side input line P, the npn type transistor Tr1 and the coupling capacitor C1.

Therefore, the noise compensating current i cancels the leakage current I1 flowing from the earth line of the AC power source 1 to the electric motor 4.

[0022]

However, in the above-described power conversion system, in the case of a configuration in which a plurality of inverter devices 3 are connected in parallel, a noise reduction device is required for each number of inverter devices. When the number of noise reduction devices is increased, it is necessary to increase the number of noise reduction devices, which makes it difficult to reduce the size.

The present invention has been made in consideration of the above-mentioned circumstances. Even when a plurality of power conversion devices are connected in parallel, noise associated with driving can be reduced by a common noise reduction device, which facilitates miniaturization. An object is to provide a power conversion system that can be achieved.

[0024]

According to a first aspect of the invention, a common AC power source and AC power supplied from the AC power source are converted into AC power of an arbitrary frequency to individually adjust the speed of the electric motor. A plurality of power conversion devices to be driven, and a power conversion system including a common noise reduction device that detects a leakage current from a power supply line of the AC power source and flows a noise compensation current, wherein the noise reduction device is: An insulating transformer whose primary side is connected between the AC power source and each of the power conversion devices, a rectifying circuit connected to the secondary side of the insulating transformer, a positive output line and a negative output line in the rectifying circuit. And a positive side and negative side capacitors connected in series with each other, and a series connection point between the positive side and negative side capacitors is connected to a grounded common AC input line in front of each power converter. Connection means for connecting, 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, and has an on / off characteristic opposite to that of the positive side switching element. A negative side switching element having, a coupling capacitor arranged between each of the other ends of the positive side and negative side switching elements and the ground, a detection signal of the leakage current is amplified, and the obtained amplified signal is the positive side. And an element control means for giving a control input to the negative side switching element.

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

Further, the invention according to claim 3 is the power conversion system according to claim 1 or 2, wherein the AC power source has a plurality of phases, and one of the plurality of phases is one of the plurality of phases. It is a grounded power conversion system.

The invention according to claim 4 is the power conversion system according to any one of claims 1 to 3, wherein each of the positive side and negative side switching elements is a plurality of switching elements. Is a power conversion system that is electrically connected in parallel.

Further, in the invention corresponding to claim 5, the AC power supply of the Y connection in which the neutral point is grounded, and the AC power supplied from the AC power supply are converted into AC power of an arbitrary frequency and individually. What is claimed is: 1. A power conversion system comprising: a power conversion device for driving an electric 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 causes a noise compensation current to flow, the noise reduction device being Is an insulating transformer whose primary side is connected between the AC power supply and the power converter, a rectifying circuit connected to the secondary side of the insulating transformer, a positive output line and a negative output of the rectifying circuit. A positive and negative side capacitors connected in series with the line, and a Y connection in which one end is individually connected to the 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 side and negative side capacitors, and positive side switching having one end connected to the positive side output line. An element, 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, each other end of the positive side and negative side switching elements, and a ground. Is a power conversion system including a coupling capacitor disposed between the two, and an element control unit that amplifies the detection signal of the leakage current and applies the obtained amplified signal to the control inputs of the positive side and negative side 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 arranged closer to the AC power source side than a connection point between the Y connection capacitor and the AC input line. The power conversion system includes a leakage current detector that equivalently detects a leakage current and applies the obtained detection signal to the element control means.

Further, the invention according to claim 7 is the power conversion system according to claim 5 or 6, wherein a plurality of phases of the AC power source are Y-connected, and the neutrality of the Y connection is neutral. It is a power conversion system whose points are grounded.

The invention according to claim 8 is the power conversion system according to any one of claims 5 to 7, wherein each of the positive side and negative side switching elements has a plurality of switching elements. A power conversion system in which elements are electrically connected in parallel.

(Operation) Therefore, in the invention corresponding to claim 1, by taking the above means, 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. By connecting to the AC input line, the connection points of the noise reduction device are eliminated from each power conversion device and concentrated in the preceding stage.
A common noise reduction device can be realized. Therefore, even when connecting a plurality of power conversion devices in parallel,
The noise associated with driving can be reduced by the common noise reduction device, so that the size can be easily reduced.

The rectified DC voltage is applied to the positive and negative output lines of the rectifier circuit.
This DC voltage is divided by the capacitors on the positive side and the negative side, with the intermediate series connection point fixed to the ground potential.
Therefore, the positive output line can always supply a positive constant voltage to the ground potential, and the negative output line can always supply a negative constant voltage to the ground potential. That is, since the voltage to earth can be always kept constant, the controllability of the noise compensation current can be improved.

When the positive and negative side switching elements are turned on and off by the element control means, the coupling capacitor, the positive side switching element and the positive side output are connected to the AC input line where the noise compensating current is grounded. Since 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, it is possible to cancel the leakage current as noise current, and easily and reliably. Noise can be reduced.

The invention according to claim 2 is characterized in that the leakage current detector is arranged closer to the AC power source than the connection point between the connecting 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 operation can be improved.

Further, the invention according to claim 3 is one in which the alternating-current power supply has a plurality of phases, and one of the plurality of phases is grounded. Therefore, the invention according to claim 1 or 2 It is possible to achieve the same action as the action.

The invention according to claim 4 has a large current capacity because a plurality of switching elements are electrically connected in parallel as the positive-side and negative-side switching elements, respectively. In addition to the action corresponding to any one of claims 1 to 3, even if the leakage current has a large value, a noise compensation current that cancels it can be made to flow.

Further, in the invention corresponding to claim 5, even in the case of the AC power source of the Y connection, the Y connection capacitor is provided in the three-phase AC input line, and the neutral point of the Y connection capacitor is set to the virtual ground. By connecting the positive and negative capacitors of the noise reducing device in series as points, the voltage to the virtual ground (the voltage with respect to the potential at the virtual ground point) is always constant as in the case of the operation corresponding to claim 1. Can be held in
Since the connection points of the noise reduction device can be concentrated in the previous stage of each power conversion device, even when multiple power conversion devices are connected in parallel, the noise due to driving can be reduced by the common noise reduction device, which makes it easy to downsize. Can be achieved.

Similarly, the controllability of the noise compensation current can be improved by keeping the voltage to the virtual ground constant. Further, the ON / OFF control of the positive-side and negative-side switching elements by the element control means causes the noise compensating current to flow through the neutral point of the Y-connection capacitor to the AC input line in the same path as described above. It is possible to cancel the leakage current as a current and easily and surely reduce noise.

The invention according to claim 6 corresponds to claim 5, in which the leakage current detector is arranged closer to the AC power source than the connection point between the Y connection capacitor and the AC input line. In addition to the function, the leakage current can be detected regardless of the inflow or outflow of the noise compensation current at the connection point, so that the reliability of the operation can be improved.

Furthermore, in the invention corresponding to claim 7, as the AC power source, a plurality of phases are Y-connected and the neutral point of the Y-connection is grounded. It is possible to achieve the same action as the action corresponding to.

The invention according to claim 8 has a large current capacity because a plurality of switching elements are electrically connected in parallel as the positive side switching element and the negative side switching element. In addition to the action corresponding to any one of claims 5 to 7, even if the leakage current has a large value, a noise compensation current that cancels it can be passed.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION 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 detailed description thereof is omitted, and here, different parts will be mainly described. In the following embodiments as well, duplicated description will be omitted.

That is, this 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 and T1.
Insulation transformer 9 and rectifier circuit 10 for creating a potential difference between each collector of r2 and ground, and noise compensation current i depending on ON / OFF of each of transistors Tr1 and Tr2.
Is provided with capacitors Cp and Cn for flowing in or out of the input ground terminal of the full-wave rectifier circuit 2.

Here, the insulation transformer 9 has a primary side connected to the power supply line passing through the leakage current detector 5, and a secondary side connected to the rectifying circuit 10.

The rectifier circuit 10 full-wave rectifies the output AC voltage on the secondary side of the insulation transformer 9 to direct the DC voltage between the positive side output line P1 and the negative side output line N1, and the npn type transistors Tr1 and pnp. Has a power supply function of supplying 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 one end of the capacitor Cn. And pnp type 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 series-connected capacitors Cp and Cn having the same capacitance. In addition, 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, a noise reduction operation in the above power conversion system will be described.

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

Therefore, the positive output line P1 can always supply a constant positive voltage with respect to the ground potential. 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.

Specifically, in the noise reduction circuit 8, when each of the transistors Tr1 and Tr2 receives an output signal from the amplifier 7 at its base, the transistors Tr1 and Tr2 turn on / off in reverse, 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 electric motor 4 into the earth line of the AC power source 1, the noise reduction device turns on only the pnp type transistor Tr2.

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

Therefore, the noise compensation current i cancels the leakage current I1 flowing into the ground terminal of the AC power supply 1.

When the leakage current I1 flows from the earth 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 compensating 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-type transistor Tr1 and the coupling capacitor C1.

Therefore, the noise compensating current i cancels the leakage current I1 flowing from the earth line of the AC power source 1 to the electric motor 4.

As described above, according to the present embodiment, the isolation transformer 9 extracts the AC voltage and the noise reduction device performs the inflow / outflow of the noise compensation current i to the common AC input line. Since the connection part of the noise reduction device is eliminated from each power conversion device and concentrated in the preceding stage, the noise reduction device can be shared. For this reason, even when a plurality of power conversion devices 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 insulating transformer 9 is used, it is possible to set a free voltage regardless of the voltage and capacity applied to the inverter device 3. Therefore, a current control element such as a commercially available npn-type transistor or pnp-type transistor can be used for the configuration. Therefore, it is possible to realize a noise reduction device having a simple configuration, a small size, a low cost, and high-speed control.

The DC voltage applied to the positive side output line P1 and the negative side output line N1 is 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 to the ground potential, and the negative output line N1 can be supplied.
Can always supply a constant negative voltage with respect to the ground potential.
In this way, since the voltage to earth can be kept constant at all times, the controllability of the noise compensation current can be improved.

Further, the amplifier 7 allows 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 rectification circuit 2 and the ground, so that the leakage current I1 as the noise current It can be canceled, and noise can be reduced easily and surely.

Further, the noise compensation current i for canceling the leakage current I1 is caused to flow in or out on the full-wave rectification circuit 2 side of the leakage current detector 5 to prevent 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 to the series connection point 11, the AC of the full-wave rectification circuit 2 is changed. Since the leak current can be detected regardless 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 an electric motor to which a power conversion system according to a second embodiment of the present invention is applied.

The present embodiment is a modification of the first embodiment, and aims to control a large value of the noise compensation current i in order to compensate for a large value of the leakage current I1. The noise reduction circuit 8a has a configuration in which the number of series circuits including the npn-type transistor Tr1 and the pnp-type transistor Tr2 is increased, and these series circuits are electrically connected in parallel with each other. The parallel number of the series circuit can be set appropriately 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 that cancels it can be passed.

The current that can flow in each of the transistors Tr1 and Tr2 is limited by the rated current of each of Tr1 and Tr2. However, current controlling elements such as transistors capable of high frequency control generally have only low voltage and small capacitance. 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 the insulation transformer, each transistor Tr is increased so as to increase the current capacity regardless of the voltage.
1 and Tr2 can be arranged in parallel.

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

Usually, even if it is desired to simply apply the first embodiment to an AC power supply with a Y connection, in the case of an AC power supply with a neutral earth grounding with a Y connection, there is no power supply line having a ground line, so noise is generated. There is a problem that the noise compensating current i for canceling cannot be applied. On the other hand, in order to return the leakage current of the power supply ground to the neutral point and compensate it, it is necessary to use the three-phase four-wire power supply wiring. Therefore, there is a problem that the system becomes expensive because the 4-wire wiring or the NFB is used.

The present embodiment is made to include the viewpoint of solving such a problem. Therefore, 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 subsequently, 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 structure of a drive system of an electric motor to which a power conversion system according to a third embodiment of the present invention is applied. In the present embodiment, as shown in the figure, instead of the AC power supply 1, a Y-connection AC power supply 1a having a grounded neutral point 12, a leakage current detector 5, and a full-wave rectification circuit 2 are provided. It is provided with three capacitors C2 to C4 of Y connection, one end of which is individually connected to the phase AC input line and the other end of which is connected to the neutral point Pi. The capacitor C
The neutral point Pi of 2 to C4 is connected to the series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit.

According to the above configuration, the three Y-connected capacitors C2 to C4 are equivalently provided for the Y-connected AC power supply 1a, and the 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 AC power source 1a of the Y connection, is associated with the neutral point Pi of the capacitors C2 to C4 of the Y connection 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, the positive side output line P1 and the negative side output line N1 of the rectifier circuit 10 are applied with the full-wave rectified direct current voltage, and the direct current voltage is applied to the two capacitors Cp, C.
The intermediate series connection point 11 is fixed to the potential of the virtual earth point (neutral point Pi) by n, and the voltage is divided.

Therefore, as described above, the positive output line P1
Can always supply a positive constant voltage with respect to the potential of the virtual ground point. 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.

Specifically, the noise compensating current i passes through the series connection point 11 of the capacitors Cp and Cn of the noise reduction circuit 8b in accordance with ON / OFF of the transistors Tr1 and Tr2, and is connected to the Y connection 3 as described above. Two capacitors C2-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 Y-connected three capacitors C2 to C4 are provided in the three-phase AC input line, and the noise reduction circuit 8b uses the neutral point Pi of the capacitors C2 to C4 as a virtual ground point. By connecting the capacitors Cp and Cn to the serial connection point 11, the same effect as that of the first embodiment can be obtained.

In this embodiment, as shown in FIG.
Even if the number of series circuits of both the transistors Tr1 and Tr2 is increased in the same manner as described above and the configuration is modified such that they are connected in parallel with each other, a large value of the noise compensation current i can be controlled as described above. Furthermore, as shown in FIG. 5 and FIG. 6, even if it is modified to a configuration in which a plurality of inverter devices are connected in parallel,
Similar to the above, size reduction can be achieved by a common noise reduction device.

(Fourth Embodiment) FIG. 7 is a circuit diagram showing the configuration of a drive system of an electric motor to which a power conversion system according to a fourth embodiment of the present invention is applied. This embodiment is the third
This is a modification of the above embodiment and shows an example in which the idea of the third embodiment described above is applied to all AC power supplies having a ground that is not connected to a power supply line. Specifically, instead of the AC power supply 1a, the AC power supply 1b of the three-phase Δ connection grounded at the neutral point 13 of the two phase, and the three-phase between the leakage current detector 5 and the full-wave rectification circuit 2 It is provided with four capacitors C5 to C8, which are connected to the AC input line and are equivalently connected to the AC power supply 1b and are in a Δ connection. In this case, the neutral point Pa of the capacitor is a connection point between C5 and C6 which is equivalent to the ground of the AC power supply 1b, and the capacitors Cp and Cn of the noise reduction circuit 8d are similar to the above.
Is connected to the serial connection point 11.

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

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 two-phase neutral point 13, the same operational effect as that of the above-described third embodiment can be obtained.
Further, in the present embodiment, (1) a plurality of capacitors C5 to C8, which are connected equivalently to the AC power supply 1b, are provided,
(2) The neutral point Pa of each of the capacitors C5 to C8 (virtual ground point corresponding to the ground connection point of the AC power supply 1b) 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 is not limited to the AC power supplies 1a and 1b described in the third or fourth embodiment, but can be applied to any AC power supply having a ground that is not connected to the power supply line.

Although not shown in the figure, T as shown in FIG.
Even if 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 as shown in FIG. 5 are connected in parallel, or a configuration including both as shown in FIG. Then, the same 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 elements for controlling the noise compensation current i has been described, but the present invention is not limited to this. , Tr2 may be replaced by another current control element satisfying the same high withstand voltage, high frequency, and high current amplification performance, and the same effects can be obtained by implementing the present invention in the same manner. .

Besides, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0087]

As described above, according to the present invention, even when a plurality of power conversion devices 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. It is possible to provide a power conversion system capable of performing the above.

[Brief description of 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 an electric 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 of the same embodiment.

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

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

FIG. 7 is a circuit diagram showing a configuration of a drive system of an electric 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 an electric motor to which a conventional power conversion system is applied.

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

[Explanation 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 ... Isolation transformer 10 ... Rectifier circuit 11 ... Series connection point 12, 13, Pi, Pa ... Neutral point D1 to D6 ... Diode Q1-Q6 ... Switching element C1 ... Coupling capacitor Cp, Cn, C2-C8 ... Capacitor Tr1 ... npn type transistor Tr2 ... pnp type transistor P ... Positive side input line N ... Negative side input line P1 ... Positive side output line N1 ... Negative output line C ... stray capacitance I1 ... Leakage current i ... Noise compensation current

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-266677 (JP, A) JP-A 8-98536 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 7/48 H02M 7/12

Claims (8)

(57) [Claims] 1. A common AC power supply, a plurality of power conversion devices 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, and the AC power supply. A power conversion system including a common noise reduction device that detects a leakage current from a power supply line of a power supply and causes a noise compensation current to flow, wherein the noise reduction device is between the AC power supply and each of the power conversion devices. An insulating transformer whose primary side is connected to the rectifying circuit, a rectifier circuit connected to the secondary side of the insulating transformer, a positive side and a positive side connected in series between the positive side output line and the negative side output line in the rectifying circuit, and A negative side capacitor, connection means for connecting a series connection point between the positive side and negative side capacitors to a grounded common AC input line in the preceding stage of each power converter, and the positive side output A positive side switching element whose one end is connected to a power line, one end connected to the negative side output line, and a negative side switching element having an on / off characteristic opposite to that of the positive side switching element; A coupling capacitor arranged between each other end of the negative side switching element and the ground, and an element which amplifies the detection signal of the leakage current and applies the obtained amplified signal to the 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 conversion system is arranged closer to the AC power supply side than a connection point between the connection means and the AC input line, and the leakage current is equivalently detected and obtained. 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 and negative-side switching elements each have a plurality of switching elements electrically connected in parallel. A power conversion system characterized by the above. 5. A Y-connection AC power supply having a neutral point grounded, and power for converting AC power supplied from the AC power supply into AC power having an arbitrary frequency and individually driving the motors at variable speeds. 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 causes a noise compensation current to flow, wherein the noise reduction device includes the AC power supply and the power conversion device. An insulating transformer having a primary side connected between the insulating transformer, a rectifying circuit connected to a secondary side of the insulating transformer, and a rectifying circuit connected in series between a positive side output line and a negative side output line. Positive side and negative side capacitors, a Y-connection capacitor whose one end is individually connected to the AC input line in the preceding stage of the power conversion device, and the other ends are connected to a neutral point, and the Y-connection capacitor. Connection means for connecting a neutral point of the capacitor to a series connection point between the positive and negative side capacitors, a positive side switching element having one end connected to the positive side output line, and the negative side output One end is connected to the line, a negative side switching element having an on / off characteristic opposite to that of the positive side switching element, and a coupling arranged between each other end of the positive side and negative side switching elements and ground. A power conversion system comprising: a capacitor; and an element control unit that amplifies the detection signal of the leakage current and applies the obtained amplified signal to control inputs of the positive side and negative side switching elements. 6. The power conversion system according to claim 5, wherein the leakage current is equivalently detected by being arranged on a side closer to the AC power source than a connection point between the Y connection capacitor and the AC input line. A power conversion system comprising a leakage current detector for providing the 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 each of the positive-side and negative-side switching elements has a plurality of switching elements electrically connected in parallel. A power conversion system characterized by the above.