JP2002051570A - Noise reduction device of converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a noise current in a wide band from a low frequency to a high frequency. SOLUTION: This noise reduction device has a noise reduction circuit 9 which is provided with a rectifying circuit 14 for rectifying an AC input via an insulating transformer 13, two capacitors C2, C3 which are connected in series between output terminals of the rectifying circuit 14 and whose connection central point is connected with a ground side input power source line of a converter 5, and current control elements Tr1, Tr2 in which a noise compensation current flows with an output of the rectifying circuit 14 acting as an operation voltage. The current control elements Tr1, Tr2 are driven by using a signal in which a signal formed from a driving signal of a switching element in the converter 5 and a noise current detection signal of a noise detecting means 8 are synthesized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter, such as an inverter or a converter, which is capable of greatly reducing a noise current, which is a ground leakage current flowing to the ground side of an input power supply during a conversion operation. It relates to a reduction device.

[0002]

2. Description of the Related Art In recent years, harmonics generated by switching elements such as inverters and converters have increased, and the EMI (electromagnetic interference) problem has been highlighted. Generally, when power is supplied to a load by an inverter device, a leakage current, which is a noise current, flows through a stray capacitance C between a load circuit and a frame ground and between a cable wiring to a load and a ground by high-speed switching.

FIG. 6 shows a mechanism of leakage current flowing in an inverter device. In the figure, 1 is an AC power supply, and 2 is a full-wave rectifier circuit (P
Although there is a WM converter, a full-wave rectifier circuit will be described here for simplicity.) Reference numeral 3 denotes an output terminal P · N of the full-wave rectifier circuit 2.
DC capacitor 4 connected between, DC capacitor 3
A DC power source such as a battery connected in parallel to the power supply, 5 an inverter circuit for converting DC to AC, 6 an inverter circuit 5
The load is driven by When each of the switching elements Q _{1 to} Q _{6 of the} inverter circuit 5 is turned on / off, a pulse voltage is applied between the terminal of the load 6 and the frame ground. The leakage current I1 flows through the stray capacitance C according to the voltage change rate (dv / dt) at this time. The leakage current I1 flows through a circuit including the DC power supply 4, such as a battery, the load 6, and the ground via the inverter circuit 5, and causes a malfunction of the leakage breaker, an electric shock accident, and the like. Further, dv / dt, when the switching elements Q _{1 to} Q ₆ are turned on / off,
There are also new problems such as dielectric breakdown of the load circuit, which is considered to be caused by di / dt, and electromagnetic induction disturbance to other electronic devices.

A noise reduction circuit of a conventional inverter device will be described with reference to FIG. The configurations of the AC power supply 1 to the inverter circuit 5 and the load 6 are the same as those in FIG. The inverter circuit 5 is an inverter of a general three-phase bridge composed of switching elements Q ₁ to Q _6. Switching elements Q _{1 to} Q ₆
Is turned on / off by a PWM pulse from a control circuit (not shown). The output from the inverter circuit 5 is input to each phase circuit terminal of the load 6. Since the load 6 has a stray capacitance C between itself and the ground, when a pulsed voltage output from the inverter circuit 5 is applied to the load 6, a leakage current I1, which is a noise current, flows through the ground. In such an inverter device, a line filter 7 called an EMI filter is provided as a noise reduction circuit. Although line filter 7 has the effect of noise removal, to obtain a sufficient with noise removal effect to increase the on-off frequency of the switching elements Q ₁ to Q ₆ becomes difficult.

[0005]

Heretofore, a line filter called an EMI filter has been used as a noise reduction circuit in a converter such as an inverter. However, it has been difficult for the line filter to obtain a sufficient noise removing effect as the on / off frequency of the switching element in the converter increases. On the other hand, by adding a noise reduction circuit composed of a reactor or a combination of a reactor and a capacitor, it is possible to remove noise in a high frequency range to some extent, but a large reactor is used to enhance the noise removal effect. Therefore, there is a problem that the noise reduction circuit becomes large and expensive.

[0006] The present invention has been made in view of the above,
An object of the present invention is to provide a noise reduction device for a converter that can remove a noise current in a wide band from a low frequency range to a high frequency range, and that can be reduced in size and cost.

[0007]

According to a first aspect of the present invention, there is provided a noise reduction apparatus for a converter including an inverter, comprising: a noise detection means for detecting a noise current; A rectifier circuit for rectifying the AC input input through the rectifier circuit, two capacitors connected in series between the positive and negative output terminals of the rectifier circuit, and having a connection midpoint connected to the ground-side input power supply line of the converter; and A noise reduction circuit including a current control element to which an output voltage of the rectifier circuit is applied as an operation voltage and a noise compensation current flows, wherein a signal generated from a drive signal of a switching element included in the converter and the noise detection The gist is that the current control element is driven by a signal obtained by combining the detection signals of the means. With this configuration, when power is supplied to the load by a converter such as an inverter, a leakage current, which is a noise current, is generated through high-speed switching through a stray capacitance between the load circuit and the frame ground. This noise current flows through the noise reduction circuit to the input power line on the ground side of the converter. At this time, the current control element of the noise reduction circuit is driven by the signal generated from the drive signal of the switching element in the converter and the signal obtained by synthesizing the detection signal of the noise detection means. As a result, the noise current is reduced in a feedforward manner at high speed, and a noise compensation current for suppressing the noise current is generated by the feedback control based on the detection signal from the noise detection means, and the noise current is canceled by the noise compensation current. By adding a feedforward control element, it is possible to suppress a high-frequency noise current that is difficult to remove due to a delay element of the feedback control system. In addition, the noise reduction circuit connects the midpoint of the connection of the two capacitors to the ground-side input power supply line of the converter, so that an operating voltage with a constant voltage difference is always ensured with respect to the ground-side input power supply line. Therefore, the noise compensation current for canceling the noise current can be arbitrarily controlled, and the control cannot be disabled. Further, the operating voltage can be set to any voltage value irrespective of the voltage and capacity applied to a converter such as an inverter, because the noise reduction circuit is connected to the AC input system via an insulating transformer. .

According to a second aspect of the present invention, in the noise reduction device for a converter according to the first aspect, the noise detecting means is provided between the two capacitors from a connection point from a connection middle point of the converter. The point is that it is arranged on the input power supply side. With this configuration, the noise current reduced by the noise reduction circuit is detected by the noise detection unit.

According to a third aspect of the present invention, in the noise reduction device for a converter according to the first aspect, a signal generated from a drive signal of the switching element is supplied to a plurality of switching elements corresponding to each phase of the converter. The gist is to provide the sum of the drive signals. With this configuration, it is possible to reduce the noise current at a higher speed and more reliably in a feedforward manner.

According to a fourth aspect of the present invention, in the noise reduction device for a converter according to the first aspect, the signal generated from the driving signal of the switching element is a pattern triggered by a change in the driving signal of the switching element. The main point is to become a signal. With this configuration, the current control element of the noise reduction circuit is triggered by a change in the drive signal of the switching element, so that the
The noise current can be reduced at high speed and reliably.

According to a fifth aspect of the present invention, in the converter noise reducing apparatus according to the first aspect, a connection midpoint between the two capacitors in the noise reduction circuit is connected to a ground-side input power supply line of the converter. Instead, the gist is that two other capacitors are connected in series between the input power supply lines of the converter and connected to a connection midpoint of the other two capacitors. With this configuration, when the stray capacitance of the input power supply line of the converter, the converter, and its load system is large, the middle point of connection of the other two capacitors becomes a virtual ground point, and a noise compensation current flows through this virtual ground point. This makes it possible to cancel the noise current.

[0012]

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

FIG. 1 shows a first embodiment of the present invention.
FIG. In this embodiment, the noise reduction device of the inverter is used.
Has been applied to First, the converter of the present embodiment has
The configuration of the noise reduction device will be described. AC power supply 1-Invar
The configurations of the load circuit 5 and the load 6 are substantially the same as those in FIG.
The noise reduction device has a leakage current detection
Output circuit 8, noise reduction circuit 9, and inverter circuit 5
Switching element Q ₁~ Q₆Generate output from drive signals
The arithmetic circuit 10 performs the following operations. Leakage current detector 8
Is the zero-phase CT of an annular core made of ferrite, for example.
Yes, and detects the leakage current that is the difference between the input power line currents.
Put out. The noise reduction circuit 9 is connected to the
Rectifying the full-wave rectified AC from the AC power supply 1
Circuit 14, the positive output terminal P of the rectifier circuit 14.₁And the negative side
Output terminal N₁Are connected in series between the
Input power line (negative output terminal of full-wave rectifier circuit 2)
N) two capacitors C connected to_Two, C_ThreeAnd rectification
The output voltage of the circuit 14 is applied as the operating voltage,
Two transformers as current control elements through which compensation current flows
Jista Tr₁, Tr_TwoIs provided. 2 transi
Star Tr₁, Tr_TwoHave opposite polarities and have transistors
Tr₁Is an NPN type transistor Tr_TwoIs a PNP type
You. Transistor Tr₁, Tr_TwoBoth bases (control terminals)
The switch of the inverter circuit 5 from the control circuit 11
Element Q₁~ Q₆Generated by the arithmetic circuit 10 based on the drive signal of
The output signal and the detection output of the leakage current detector 8 also serve as an adder.
The signal synthesized by the flip amplifier 12 is given, and the transistor
Data Tr₁, Tr_TwoWork in reverse to each other. Transistor T
r₁, Tr_TwoEmitters are connected in common and coupled capacitors
Sa C₁Grounded through. This noise reduction circuit
9 in the transistor Tr₁, Tr_TwoIs high frequency, high power
It is necessary to be flow amplification. Note that the noise reduction circuit
9 returns to the DC power supply 4 reduces the leakage current I1
The leakage current detector 8 detects the leakage current
To detect the current with I1 reduced, the DC power supply 4 side
It is necessary to arrange. The arithmetic circuit 10 is an invar
(-) Signal when the output of each phase of the
Is output, and the signal of (+) is output when it becomes the N side.
You. Here, Q, which is the upper arm of the inverter circuit 5,₁
~ Q_ThreeThe drive signal of each switching element of
Q_Four~ Q₆The drive signal of each switching element is
to add.

Next, the operation of the noise reduction device configured as described above will be described. The AC power supply 1 is rectified to DC by the full-wave rectifier circuit 2 and connected to the DC capacitor 3 and the DC power supply 4. This DC voltage becomes the input voltage of the inverter circuit 5. The switching element Q ₁ to Q ₆ of the inverter circuit 5 is on-off controlled by PWM pulses from the control circuit 11, the load 6 is driven by the output of the inverter circuit 5. As described above, the load 6 has a stray capacitance C between itself and the ground.
have. Therefore, when a pulse-like voltage output from the inverter circuit 5 is applied to the load 6, a leakage current I1, which is a noise current, flows to the ground via the grounded terminal of the DC power supply 4. At this time, the combined signal to the drive signal of the switching element Q ₁ to Q _6, a leakage current detector 8 is added equivalently detected signal leakage current I1 flowing to the DC circuit, the transistor Tr of the noise reduction circuit 9
₁ and Tr ₂ are driven. Therefore, the drive current obtained by amplifying the output of the leakage current detector 8 by the amplifier 12 is
r ₁ , Tr ₂ flows into the base, is amplified and leaks current I1
Is injected to cancel out the current.

Here, the detection signal from the leakage current detector 8
And the switching element Q ₁~ Q₆Drive signal
The operation of the noise reduction circuit 9 by the signal generated from the
Will be described.

[0016] In the former, when the leakage current I1 flows to the earth line of the DC power source 4 from the load 6, to turn on the transistor Tr _2, the input of the inverter circuit 5 from the coupling capacitor C ₁ through the transistor Tr ₂ The noise compensation current flows in the closed circuit connected to the line N, and cancels the leakage current I1 flowing through the ground line to the ground terminal of the DC power supply 4. When the leakage current I1 flows from the ground line of the DC power supply 4 to the load 6,
The transistor Tr ₁ turns on, the DC input line P of the inverter circuit 5, the transistor Tr ₁ , and the coupling capacitor C ₁
Leakage current I1 of the DC power supply 4 flowing therethrough is canceled out.

In the latter case, when the switching element Q ₁ of the inverter circuit 5 is turned on, a positive voltage is applied to the load 6, and the leakage current I 1 flows from the load 6 toward the ground line of the DC power supply 4. Then, the transistor Tr ₂ is turned on by the arithmetic circuit 10, a noise compensation current flows from the coupling capacitor C ₁ through the transistor Tr ₂ to the closed circuit connected to the input line N of the inverter circuit 5, and the DC power supply 4 The leakage current I1 flowing into the ground terminal is canceled. Conversely, when the switching element Q ₂ of the inverter circuit 5 is turned on, a negative voltage is applied to the load 6, the leakage current I1 flows toward the load 6 from the DC power supply 4 of the earth line, when the arithmetic circuit The transistor Tr ₁ is turned on by 10, a noise compensation current flows from the coupling capacitor C ₁ through the transistor Tr ₁ to the closed circuit connected to the input line P of the inverter circuit 5, and passes through the ground line to the ground terminal of the DC power supply 4. The leakage current I1 flowing in is canceled out.

As described above, the feedback control based on the leakage current detection from the leakage current detector 8 suppresses the leakage current, and the inverter circuit 5 whose operation response is predicted in advance.
By driving the transistors Tr ₁ and Tr ₂ of the noise reduction circuit 9 with a signal in accordance with the switching signal, the leakage current can be reduced in a feedforward manner. By adding a feedforward element, it becomes possible to suppress a high-frequency leakage current that is difficult to remove due to a delay element of the feedback control system.

In the present embodiment, the positive side P of the rectifier circuit 14
₁ can always supply a constant positive voltage with respect to the ground potential. The negative side N ₁ of the rectifier circuit 14 can also always supplying a constant negative voltage with respect to ground potential. Therefore, a constant voltage difference can always be ensured with respect to the input power supply line, so that arbitrary control is possible. Further, since the voltage is applied via the insulating transformer 13, the operating voltage can be freely set irrespective of the voltage and capacity applied to the inverter circuit 5. Therefore, a commercially available current control element can be used, and it is possible to provide a small, inexpensive, and high-speed converter noise reduction device with a simple configuration.

FIG. 2 shows a second embodiment of the present invention. In FIG. 2 and the drawings showing each of the following embodiments of a third embodiment, the same or equivalent components as those in FIG. 1 are denoted by the same reference numerals, and
A duplicate description will be omitted. In the present embodiment, the signal generated from the drive signals of the switching elements Q _{1 to} Q ₃ in the arithmetic circuit 10 is changed to a signal pattern triggered by a change in the drive signal in the switching elements Q _{1 to} Q ₃ of the inverter circuit 5. I do. Outputs a negative pulse signal of the switching element Q ₁ to Q ₃ in the upper arm of the inverter circuit 5 from the off when shifts into the ON state, changed to turn on the switching element Q ₄ to Q ₆ of the lower arm from off conversely The arithmetic circuit 10 sometimes outputs a positive pulse signal. by this,
An effect similar to that of the first embodiment can be expected. The leakage current is suppressed by feedback control based on the detection output of the leakage current detector 8, and the noise reduction circuit 9 is driven by a signal in accordance with the switching signal of the inverter circuit 5, thereby suppressing a high-frequency leakage current in a feedforward manner. It becomes possible to do.

FIG. 3 shows a third embodiment of the present invention. The DC power supply 4 is used when the neutral point is grounded or not grounded, but when the installation location is far away and cables such as wiring and stray capacitance of the device itself are large, the DC power supply 4
And capacitors 15 and 16 connected in series to the DC power supply line between the inverter circuit 5 and the inverter. The capacitors 15 and 16 connected in series are installed closer to the inverter circuit 5 than the noise reduction circuit 9. These capacitors 15,1
The neutral point 6 and the capacitor C ₂ , which is the noise reduction circuit 9,
Connecting the series connection point C _3.

According to this connection method, a virtual ground point is formed at the neutral point of the capacitors 15 and 16 in which the neutral point which is the ground connection point of the DC power supply 4 is connected in series equivalently, and a noise reduction circuit is provided at the virtual ground point. 9, the capacitor C ₂ ,
By connecting the connection point C _3, it can flow noise compensation current for canceling the noise current. Even when the DC power supply 4 is insulated and connected by a stray capacitance such as wiring, a noise compensation current can flow through the virtual ground point of the neutral point of the additional capacitors 15 and 16.

Even with the DC power supply 4 grounded at the neutral point, the capacitor 1 divided from the DC input power supply line by series connection
By connecting the connection point of the capacitors C ₂ and C ₃ in the noise reduction circuit 9 to the neutral points of 5 and 16, the leakage current is suppressed by feedback control based on the detection signal from the leakage current detector 8 and the inverter is controlled. Driving the noise reduction circuit 9 with a signal that matches the switching signal of the circuit 5 makes it possible to suppress high-frequency leakage current in a feedforward manner.

The positive side P ₁ of the rectifier circuit 14 in the noise reduction circuit 9 can always supply a constant positive voltage with respect to the ground potential, and the negative side N ₁ of the rectifier circuit 14 is also always constant with respect to the ground potential. Negative voltage can be supplied. Therefore, a noise reduction circuit 9 can be used which can be set to a free operating voltage irrespective of the voltage applied to the inverter circuit 5 and the capacity even with the DC power supply 4 having a neutral ground. Therefore, a commercially available current control element can be used, and it is possible to provide a small, inexpensive, and high-speed converter noise reduction device with a simple configuration.

FIG. 4 shows a fourth embodiment of the present invention. The current that can flow through the transistors Tr ₁ and Tr ₂ is limited by the rated current of the element. Therefore, when the leakage current I1, which is a noise current, is large, it is possible to control the flowing leakage current I1 by connecting the transistors Tr _n-1 and Tr _n of the noise reduction circuit 9 in parallel as shown in FIG. it can. It should be noted that there are generally only low-voltage and small-capacity current control elements capable of such control. Even if a high-voltage large-capacity transistor is manufactured, the purpose of use is limited and the cost is extremely low. Will be expensive. As described above, the noise reduction circuit 9 includes the insulating transformer 13.
The operating voltage can be set freely through
By setting the transistors Tr _n-1 and Tr _n in parallel, the current capacity can be increased regardless of the operating voltage.

FIG. 5 shows a fifth embodiment of the present invention. A line filter 17 as an EMI filter is added between the DC power supply 4 and the inverter circuit 5 and on the DC power supply 4 side outside the noise reduction circuit 9.

As a result, it is possible to remove higher frequency components together with the operation and effect of the first embodiment.
Further, since the leakage current in the low frequency range is attenuated by the noise reduction circuit 9, the EMI filter 17 can be reduced in size.

[0028]

As described above, according to the first aspect of the present invention, a noise detecting means for detecting a noise current;
A rectifier circuit for rectifying an AC input input through an isolation transformer, two capacitors connected in series between the positive and negative output terminals of the rectifier circuit and having a connection midpoint connected to a ground-side input power supply line of the converter. And a noise reduction circuit including a current control element to which an output voltage of the rectifier circuit is applied as an operation voltage and a noise compensation current flows, and a signal generated from a driving signal of a switching element included in the converter and the noise. Since the current control element is driven by a signal obtained by synthesizing the detection signal of the detection means, the current control element of the noise reduction circuit is controlled and driven in a feedforward manner by the signal generated from the drive signal of the switching element. By adding elements, it is possible to suppress high-frequency noise currents that are difficult to remove due to delay elements in the feedback control system. And it is, can be removed broadband noise current from the low frequency range to high frequency range. Also,
Since the noise reduction circuit is connected to the AC input system via the insulating transformer, the operating voltage of the current control element can be set to a free voltage value regardless of the voltage and capacity applied to a converter such as an inverter. . Therefore, a general commercially available current control element can be used, and the cost and size of the noise reduction circuit can be reduced.

According to the second aspect of the present invention, the noise detecting means is arranged closer to the input power supply side of the converter than the connection point from the connection middle point of the two capacitors.
The noise detection means detects the noise current reduced by the noise reduction circuit, and the noise current can be reliably removed by feedback control based on the detected signal of the noise current.

According to the third aspect of the present invention, since the signal generated from the drive signal of the switching element is an added value of the drive signals for the plurality of switching elements corresponding to each phase of the converter, the signal is feedforward. In addition, the noise current can be reduced at higher speed and reliably.

According to the fourth aspect of the present invention, the signal generated from the drive signal for the switching element is a signal having a pattern triggered by a change in the drive signal for the switching element. The element is
By triggering when the drive signal of the switching element changes, the noise current can be reduced in a feedforward manner at high speed and reliably.

According to the fifth aspect of the present invention, the midpoint of the connection of the two capacitors in the noise reduction circuit is replaced with the connection of the converter to the ground-side input power supply line, and the input power supply of the converter is changed. Since two other capacitors were connected in series between the lines and connected to the connection midpoint of the other two capacitors, if the stray capacitance of the converter's input power supply line or converter and its load system is large, Is a virtual ground point, and a noise compensation current flows through this virtual ground point to cancel the noise current. This virtual ground point method is particularly effective when the DC power supply, which is the input power supply of the converter, is grounded to a neutral point.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a converter noise reduction device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram according to a fifth embodiment of the present invention.

FIG. 6 is a circuit diagram for explaining a mechanism of leakage current flowing in a conventional inverter device.

FIG. 7 is a circuit diagram showing a noise reduction circuit of a conventional inverter device.

[Explanation of symbols]

2 Full-wave rectifier circuit (input power supply) 4 DC power supply (input power supply) 5 Inverter circuit (converter) 6 Load 8 Leakage current detector (noise detection means) 9 Noise reduction circuit 10 Operation circuit 11 Control circuit 12 Also serves as adder amplifier 13 isolation transformer 14 a rectifier circuit 15, 16 the other two capacitors 17 EMI filter C _2, C ₃ two capacitors Q ₁ to Q ₆ switching elements Tr _1, Tr ₂ transistor (current control element)

Claims (5)

[Claims] 1. A noise reduction device for a converter including an inverter, comprising: a noise detection means for detecting a noise current; a rectifier circuit for rectifying an AC input input via an insulating transformer; Two capacitors connected in series between output terminals and having a connection midpoint connected to the ground-side input power supply line of the converter, and a current control element through which an output voltage of the rectifier circuit is applied as an operating voltage and a noise compensation current flows. A noise reduction circuit comprising: a driving circuit for driving the current control element by a signal obtained by combining a signal generated from a driving signal of a switching element included in the converter and a detection signal of the noise detection unit. Converter noise reduction device. 2. The converter according to claim 1, wherein said noise detecting means is arranged closer to an input power supply side of said converter than a connection point from a connection middle point of said two capacitors. Device noise reduction device. 3. The converter according to claim 1, wherein a signal generated from the drive signal of the switching element is a sum of drive signals for a plurality of switching elements corresponding to each phase of the converter. Noise reduction device. 4. The converter according to claim 1, wherein the signal generated from the driving signal of the switching element is a signal having a pattern triggered by a change in the driving signal of the switching element. apparatus. 5. The connection between the two capacitors in the noise reduction circuit, instead of connecting the converter to the ground-side input power line, and connecting the other two capacitors between the input power lines of the converter. 2. The noise reduction device for a converter according to claim 1, wherein a capacitor is connected in series and is connected to a connection midpoint between the other two capacitors.