JP2013169141A - Power conversion device and power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that effectively reduces common mode components caused by other stray capacitances even if stray capacitances between midpoints of switching arms and a ground line are not main paths of high frequency leakage currents.SOLUTION: In a power conversion system having a first power conversion device in which a plurality of lines of switching arms each comprising a series connection of two arms each comprising one or more switching elements are connected in parallel and an AC power supply is connected between respective midpoints of at least two lines of switching arms, and a second power conversion device which converts power from a power storage device to feed both ends of the switching arms, the plurality of lines of switching arms include a switching arm having a relatively low impedance connected to the midpoint, the second power conversion device comprises at least one switching element, and a control circuit for controlling the switching element of the second power conversion device is connected via an insulated circuit.

Description

  The present invention relates to a power conversion device and a power conversion system, and particularly to an insulation configuration between a main circuit unit and a control circuit unit in the power conversion device.

  There are various power converters such as a converter, an inverter, or an uninterruptible power supply. The main part of this power conversion is a switching element represented by a transistor such as an IGBT (Insulated Gate Bipolar Transistor). As a power converter including a switching element that interrupts the circuit, noise is applied as regulated by CISPR (International Committee for Radio Interference) and VCCI (Electromagnetic Interference Regulations for Information Processing Equipment). Occurrence is inevitable. Noise is classified into a normal mode component using voltage / current ripple as a noise source and a common mode component using high-frequency leakage current flowing through a stray capacitance with the ground (ground line) as a noise source. In particular, the common mode component is dominant as noise accompanying high-speed switching recently requested, and should be reduced in order to prevent disturbance of conduction noise and radiation noise.

  FIG. 8 shows a speed control system of a three-phase motor as a specific example of the power converter, and simultaneously illustrates a noise terminal voltage measurement system of a general-purpose inverter. The configuration shown in FIG. 8 includes a three-phase power source 1, a pseudo power source network (LISN) 2 for impedance matching, a diode rectifier 3, a smoothing capacitor 4, an IGBT as a switching element, and a diode connected in reverse parallel thereto. Is a general-purpose inverter 5 provided with three switching arms with three arms connected in series with two arms connected in series, a cable 6 derived from the middle point of each switching arm of the general-purpose inverter 5, and switching connected to this cable 6 A spectrum analyzer (interference wave intensity) that includes a three-phase motor 7 that controls the drive current by switching the element and performs speed control, and further obtains the terminal voltage of the resistive element connected to the ground line from each phase line in the LISN 2 8) is provided.

  The stray capacitance that causes the common mode component of noise is mainly stray capacitance between the midpoint of the switching arm and the ground line, stray capacitance between the cable 6 and the ground line in parallel with this stray capacitance, and the three-phase motor 7. There is a stray capacitance between the winding and the motor frame (connected to the ground line). The path consisting of these stray capacitances becomes the main path of the high-frequency leakage current, and the noise terminal voltage measurement system measures and evaluates the noise by extracting the terminal voltage due to this leakage current via the ground line with the spectrum analyzer 8. It is.

  The equivalent circuit of the current path of the high-frequency leakage current exemplified in the speed control system for the three-phase motor shown in FIG. 8 can be displayed by a common mode component equivalent circuit as shown in FIG. In FIG. 9, the neutral point potential fluctuation E (V), the leakage current path inductance L (H), the leakage current path resistance R (Ω), and the stray capacitance C (F) are simply displayed as a series circuit. . Here, the high-frequency leakage current in FIG. 9 can be defined as a current flowing through the ground line via a stray capacitance in the system or apparatus. This stray capacitance is dominated by the stray capacitance consisting of the midpoint of the switching arm and the ground line, and is a stray capacitance to which the high-frequency potential fluctuation E in FIG. 9 is applied. Therefore, by reducing the high-frequency leakage current flowing through the stray capacitance, it is possible to reduce the conduction noise of the common mode component of the noise. In addition, since radiation noise is generated by the flow of conduction noise, reduction of conduction noise also leads to reduction of radiation noise.

  Conventionally, as a measure for reducing the noise of the common mode component flowing in the stray capacitance, in Patent Document 1, a three-phase collective short circuit is connected to the middle point of the switching arm to short-circuit the three phases of the inverter output. Is fixed by a potential fixing circuit to fix the potential fluctuation at the neutral point low and reduce noise.

  Further, in Patent Document 2, a damping impedance is inserted between the motor frame and the ground line, between the cooling fin of the power converter and the ground line, and between the AC reactor and the ground line, so that the noise current is inserted. The thing which suppresses is disclosed.

  Further, Patent Document 3 discloses a device that suppresses noise by interposing a common mode transformer at the next stage of the power source and setting the resonance frequency of the secondary winding and the capacitor to the frequency band of the common mode component. Has been.

Non-Patent Document 1 discloses that a common mode choke, which is a reactor, is connected to each phase of the midpoint of the inverter to suppress noise peaks.
JP 2004-222421 A JP 2006-25467 A JP 2006-136058 A "Modeling and Theoretical Analysis of High Frequency Leakage Current Generated by Voltage-Type PWM Inverter" Ogasawara, Fujita, Akagi, Denki Theory D, Vol. 115, No. 1, pp. 77-83, 1995

  As disclosed in the above-mentioned document, the measure for reducing the noise of the common mode component mainly focuses on the stray capacitance between the midpoint of the switching arm and the ground line, and reduces the high-frequency leakage current flowing through it. It is something to be suppressed.

  Here, the stray capacitance that is the main path of the high-frequency leakage current so far is mainly the stray capacitance between the midpoint of the switching arm and the ground line as described above (the cable and ground line in parallel with this stray capacitance). And the stray capacitance between the winding of the three-phase motor and the ground line (motor frame)), and this stray capacitance has been the main path of high-frequency leakage current. Although there are stray capacitances at other locations, high-frequency potential fluctuations are not applied, and therefore, it is not considered as a main leakage current path.

  For this reason, in the above conventional example, in order to suppress the high-frequency leakage current flowing in the stray capacitance between the midpoint of each switching arm constituting the power conversion device and the ground line, an output short circuit is provided on the output side of the inverter. A potential fixing circuit that fixes the potential of the output short circuit is connected to suppress the potential fluctuation of the motor grounding (Patent Document 1), or the motor frame, the cooling fin of the power converter, the AC reactor, and the ground A damping impedance is inserted between them (Patent Document 2), or the resonance frequency of the LC parallel resonance circuit formed by the secondary winding of the common mode transformer and the capacitor interposed between the power source and the converter is set to the common mode. Set to the frequency band of noise (Patent Document 3), induction motor via a common mode choke and LC filter on the output side of the inverter Connect the neutral point of the filter capacitor of the LC filter via a capacitor are or connected to the DC side of the inverter (N side) (Non-Patent Document 1).

  However, in each of the above conventional examples, as described above, attention is paid to the fact that the main path of the leakage current is the high-frequency leakage current flowing in the stray capacitance between the midpoint of the switching arm and the ground line. Although effective when the converter has a circuit configuration in which a high-frequency leakage current flows through the stray capacitance between the midpoint of each switching arm and the ground line as shown in FIG. 8, the main leakage current path is effective. Unlike the above, when a stray capacitance other than the stray capacitance between the midpoint and the ground line becomes the main leakage current path in a specific switching arm, it may not be applicable or effective. There is an unsolved problem (Patent Document 1 and Patent Document 2, Non-Patent Document 1).

  Therefore, the present invention has been made paying attention to the above-mentioned unsolved problems of the conventional example, and the stray capacitance between the midpoint of the switching arm and the ground line does not become the main path of the high-frequency leakage current, and the specific switching is performed. To provide a power conversion device and a power conversion system that effectively reduce the common mode component of high-frequency noise when a stray capacitance other than the stray capacitance between the midpoint and the ground line is the main leakage current path in the arm. .

  In the power conversion system according to claim 1 of the present invention, a switching arm in which two or more switching elements are connected in series with one or more switching elements as one arm is connected in parallel to each other, and at least between the middle points of the two switching arms. A power conversion system comprising: a first power conversion device connected to an AC power supply; and a second power conversion device that converts power from a power storage device and supplies the power to both ends of the switching arm. The switching power source is connected to the AC power source without connecting a reactor to the midpoint, the impedance is relatively small, and the stray capacitance other than the stray capacitance generated between the midpoint and the ground line is the main leakage current. A switching arm serving as a path is provided, and the second power conversion device is configured to include at least one switching element. A control circuit for controlling a switching element of the second power conversion device is connected via an insulation circuit, and the insulation circuit includes an insulation transformer for supplying control power to a switching unit for controlling the switching element, and the switching unit And a photocoupler for supplying a control signal for the above.

  When the switching arms in a plurality of rows have switching arms with relatively small impedances connected to the midpoint, high-frequency potential fluctuations spread to the positive and negative lines connected to both ends of the switching arms. The stray capacitance between the midpoint of the switching arm and the ground line does not become the main path of the high-frequency leakage current, but the main path of the high-frequency leakage current is formed by another stray capacitance. For this reason, an insulation transformer and a photocoupler are used for the control circuit that controls the switching element of the second power conversion device connected to both ends of the switching arm, and an insulation state is secured in both the power supply system and the control signal system. Thus, stray capacitance between the second power conversion device and the ground can be prevented from becoming a path for high-frequency leakage current, and conduction noise flowing through the ground wire can be reduced.

  A power conversion system according to a second aspect of the present invention is the power conversion system according to the first aspect, wherein the switching control unit includes a switching unit connected to a control terminal of the switching element, and a CPU that determines an on / off timing of the switching element. The photocoupler is inserted between the output side of the CPU and the switching unit, and the insulation transformer has a control power supply connected to the primary side, and one output on the secondary side passes through the rectifier circuit. The other output on the secondary side is supplied to the switching unit as a control power supply to the CPU via a rectifier circuit.

  According to a third aspect of the present invention, there is provided a power conversion system according to the first or second aspect, further comprising a voltage detector that detects an output voltage of the first power conversion device, and the voltage detection value of the voltage detector is used as a photocoupler. Is supplied to the control circuit via the control circuit, and the control circuit is controlled to output a voltage corresponding to the detected voltage value from the second power converter.

  When the control circuit switches from the single-phase PWM converter to the second power conversion device at the time of switching the power supply in order to control the voltage corresponding to the output voltage detected by the voltage detector to be output from the second power conversion device. Voltage fluctuation can be suppressed.

  A power conversion system according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, a control signal for the switching unit is supplied by a pulse transformer.

  According to the present invention, when the power conversion device has a switching arm having a relatively small impedance connected to the midpoint, the control circuit for the switching element included in the power conversion device is provided. By adopting an insulating configuration, the control circuit is used when the main path of the high-frequency leakage current is not used as the main path of the high-frequency leakage current without using the main path of the high-frequency leakage current between the midpoint of the switching arm and the ground line. The stray capacitance between the ground wire and the ground can be prevented from becoming a high-frequency leakage current path, and conduction noise flowing through the ground wire can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings referred to in the following description, the same parts as those in the other drawings are denoted by the same reference numerals.
(First embodiment)
FIG. 1 is a circuit diagram illustrating a single-phase PWM (Pulse Width Modulation) converter as a power converter. The case where the stray capacitance between the midpoint of the switching arm and the ground line found by the present inventor is not the main path of the high-frequency leakage current will be described using this circuit diagram. First, the circuit of FIG. 1 will be described.

  In FIG. 1, single-phase AC power output from a single-phase AC power supply 10 is supplied to a pseudo power supply network (hereinafter referred to as LISN) 11 for impedance matching. The R phase on the output side of the LISN 11 is connected to the single phase PWM converter 13 via the normal reactor 12, and the S phase is directly connected to the single phase PWM converter 13.

  The single-phase PWM converter 13 has two rows of switching arms SA1 and SA2, and the R-phase line and S-phase line of LISN 11 are connected to the midpoints of the switching arms SA1 and SA2 of each row, respectively.

  The switching arm SA1 is composed of switching elements S1 and S2 composed of, for example, IGBTs (Insulated Gate Bipolar Transistors) connected in series, and diodes D1 and D2 individually connected in reverse parallel to the switching elements S1 and S2. Has been.

  Similarly, the switching arm SA2 is composed of switching elements S3 and S4 made of, for example, IGBTs connected in series, and diodes D3 and D4 individually connected in antiparallel to the switching elements S3 and S4. Yes.

  The R phase of the LISN 11 is connected to the midpoint of the switching elements S1 and S2 of the switching arm SA1 via the normal reactor 12, and the midpoint of the switching elements S3 and S4 of the switching arm SA2 is connected to the S phase of the LISN 11. Yes. The collectors of the switching elements S1 and S3 of the switching arms SA1 and SA2 are connected to the positive line P, and the emitters of the switching elements S2 and S4 of the switching arms SA1 and SA2 are connected to the negative line N. A smoothing capacitor Cdc is connected between the positive electrode line P and the negative electrode line N on the output side.

  In this single-phase PWM converter 13, the switching elements S1, S2, and S3, S4 of the same switching arm SA1 and SA2 are simultaneously applied to the switching elements S1 to S4 constituting the switching arms SA1 and SA2 in accordance with the input AC power. DC power is output to the positive line P and the negative line N by performing on / off control by PWM control so as not to be in the on state. In this circuit, power conversion can also be performed for power regeneration from the load side to the power source side of the single-phase PWM converter 13.

  In the circuit shown in FIG. 1, a main path of high-frequency leakage current based on high-speed switching will be described. The high-frequency leakage current that flows through the stray capacitance due to switching at the switching elements S1 and S2 (switching arm SA1) is caused by potential fluctuations at the midpoint of the switching arm due to this switching. Therefore, if this potential fluctuation can be suppressed, the high-frequency leakage current for charging and discharging the stray capacitance can be reduced. This is the principle of outflow of high-frequency leakage current in the prior art shown in FIG.

  However, the switching of the switching arm SA1 connected to the R-phase line and the switching of the switching arm SA2 connected to the S-phase line differ in the presence or absence of the normal reactor 12 due to the circuit configuration. The potential fluctuation at the midpoint of SA2 is different. For this reason, the high-frequency leakage current path that flows when the switching arm SA1 switches and the high-frequency leakage current path that flows when the switching arm SA2 switches are different.

Hereinafter, each will be described in detail.
(Switching of switching arm connected to R phase line)
A high-frequency leakage current generated by switching of the switching element S1 or S2 flows through the stray capacitance Cs2 between the midpoint of the switching arm SA1 and the ground line. That is, the potential of the ground line is a neutral point potential of the R-phase potential and the S-phase potential due to the circuit configuration inside the LISN 11, so that even if a high-frequency potential fluctuation due to switching occurs in the R-phase potential and the S-phase potential, it is large. It is not a thing. Moreover, even if a high-frequency potential fluctuation occurs due to switching in the R phase, the voltage sharing is performed between the normal reactor 12 and the stray capacitance Cs2 for this potential fluctuation. Therefore, the shared potential fluctuation charges / discharges only the stray capacitance Cs2 and flows through the ground line as a high-frequency leakage current. In this respect, the stray capacitance between the midpoint of the switching arm and the ground line becomes the main path of the high-frequency leakage current as in the case of FIG.

(Switching of switching arm connected to S phase line)
The high-frequency leakage current generated by switching of the switching elements S3 and S4 is as follows. As described above, the potential of the ground line is a neutral point potential of the R-phase potential and the S-phase potential due to the circuit configuration inside the LISN 11, and therefore even if a high-frequency potential fluctuation due to switching occurs in the R-phase potential and the S-phase potential. Not big. That is, the midpoint potential of the switching arm SA2 composed of the switching elements S3 and S4 is an S-phase potential that is a stable potential, and a large potential fluctuation does not occur and a large high-frequency leakage current does not occur in the stray capacitance Cs4.

  However, when the entire block including the switching arm SA2 including the switching elements S3 and S4 and the positive line P and the negative line N is viewed, a large potential fluctuation occurs. In this case, the potential fluctuation between the positive electrode line P and the negative electrode line N corresponds to the DC intermediate voltage Vcdc that is the voltage across the terminals of the smoothing capacitor Cdc. That is, the following operation is performed.

<When S3 is on and S4 is off>
The potential fluctuation of the positive line P is the S phase potential, and the potential fluctuation of the N line is S phase potential−DC intermediate voltage Vcdc.

<When S3 is off and S4 is on>
The potential variation of the positive line P is S phase potential + DC intermediate voltage Vcdc, and the potential variation of the negative line N is S phase potential.

Accordingly, the potential at the midpoint of the switching arm SA2 becomes the potential of the positive line P or the negative line N depending on the switching state, and the potential fluctuation becomes the DC intermediate voltage Vcdc.
As a result, when the switching arm SA1 of the switching elements S1 and S2 is switched, the high-frequency leakage current based on the high-frequency potential fluctuation flows through the stray capacitance Cs2 as the main circuit as described above, whereas the switching elements S3 and S4 When the switching arm SA2 is switched, the high-frequency potential fluctuation spreads to the positive line P and the negative line N, and other than the stray capacitance Cs4, for example, stray capacitances Cs1, Cs3 between the collectors of the switching elements S1, S3 and the ground line, A high-frequency leakage current having a stray capacitance between all the switching elements and the ground line E as a main path flows (here, the midpoint potential of the switching arm SA1 composed of the switching elements S1 and S2 is always the positive line P or the negative line) Since this is connected to N, this midpoint and ground Stray capacitance Cs2 generated between the in-E also becomes a high-frequency leakage current path).

  Therefore, even when the stray capacitance between the midpoint of the switching arm SA2 and the ground line does not become the main path of the high-frequency leakage current, the main path of the high-frequency leakage current is formed by another stray capacitance, and this other stray capacitance The largest high-frequency leakage current flows through this.

  Further, the negative electrode line N in FIG. 1 is generally often equal to the reference potential of the control circuit. At this time, the stray capacitance between the wiring of the control circuit and the ground line E also becomes the main path of the high-frequency leakage current, and many circuit configurations and print patterns are affected by the common mode component.

  FIG. 2 illustrates the converter and inverter of the single-phase uninterruptible power supply device taken out. In FIG. 2, (a), (b), and (c) show examples in which the installation positions of the reactors L1 to L3 serving as filters are different. As can be seen from the example of FIG. 1, in FIG. 1, a normal reactor is interposed not only in the R-phase line but also in the S-phase line, so that a countermeasure for preventing high-frequency leakage current due to other stray capacitance is generally considered. is there. However, as a practical problem, installing a plurality of large normal reactors increases the bulk of the power conversion device and goes against the downsizing of the device. Therefore, if the number of reactors is reduced as much as possible, the problem that the main path of the high-frequency leakage current is formed by other stray capacitance as described above becomes obvious. In this respect, the illustration of FIG. 2 is the same, and FIGS. 2A to 2C are those in which at least one switching arm does not connect a reactor (that is, an impedance element) and becomes a switching arm having a relatively low impedance. is there.

  2A to 2C, a LISN 21 is connected to the single-phase power source 20, and the R-phase line of the LISN 21 is connected to the converter 22. The converter 22 includes a switching arm SA1 including switching elements S1 and S2 and diodes D1 and D2 connected in reverse parallel thereto, and a switching arm SA3 including switching elements S5 and S6 and diodes D5 and D6 connected in reverse parallel thereto. Is a structure composed of two rows of switching arms connected in series up and down, each centered on the middle point. The R-phase line and the S-phase line are connected to the midpoint of the switching arms SA1 and SA2. The converter 22 is provided with a smoothing capacitor Cdc.

  An inverter 23 is arranged at the next stage of the converter 22. In this inverter 23, a switching arm SA3 in which two arms, each of which is composed of switching elements S5 and S6 and diodes D5 and D6 connected in antiparallel with each other, are connected in series up and down around the middle point is shared with the converter 22. ing. That is, the inverter 23 has two rows of switching arms SA3 and SA4, and each switching arm SA3 and SA4 has switching elements S5, S6 and S7, S8 and diodes D5, D6 and D7 connected in reverse parallel thereto. Two arms consisting of D8 are connected in series up and down around the midpoint. Here, the midpoint of the switching arm SA4 on the output side of the inverter 23 is connected to the load 24. Further, this circuit is provided with capacitors C1 and C2 serving as filters between the R phase and the S phase on the input side of the converter 22 and the output side of the inverter 23, respectively.

  Further, in FIG. 2A, reactors L1 and L3 are provided at the midpoint of the input side switching arm SA1 of the converter 22 and the midpoint of the output side switching arm SA4 of the inverter 23, respectively. The midpoint of the shared switching arm SA3 is directly connected to the S phase line. 2B, the midpoint of the common switching arm SA3 and the S-phase line are connected via a reactor L2, and the reactor L3 is provided at the midpoint of the output side switching arm SA4 of the inverter 23. Further, in FIG. 2C, a reactor L1 is provided at the midpoint of the input side switching arm SA1 of the converter 22, and the midpoint of the common switching arm SA3 and the S-phase line are connected via the reactor L2. .

  Accordingly, each of the circuits shown in FIGS. 2A to 2C has a switching arm that is not connected to the reactor, that is, a switching arm that has a relatively small impedance. The middle point of the switching arm to which the reactor, that is, the impedance element is not connected, is electrically the middle point where the same voltage fluctuation occurs as the middle point of the switching element S3 of the converter 13 shown in FIG. Become.

  That is, in FIG. 2A, the switching arm SA3 having the switching elements S5 and S6 is switched, in FIG. 2B, the switching arm SA1 having the switching elements S1 and S2 is switched, and in FIG. By switching the switching arm SA4 having the switching elements S7 and S8, the largest high-frequency leakage current flows so that the stray capacitance formed between the midpoint of each switching arm and the ground line E does not become the main path.

  As described above, the negative electrode line N in FIG. 1 is generally often equal to the reference potential of the control circuit. This is because the switching elements S2 and S4 of the lower arm in FIG. 1 can be driven without insulation by making the negative electrode line N the same as the reference potential of the control power supply. Thus, making the negative electrode line N and the reference potential of the control power source equal is often used particularly when a desired operation is realized with a circuit configuration as simple as possible. The circuit configuration that realizes the converter unit and the inverter unit as shown in FIG. 2 using the common arm described in this patent particularly corresponds to this.

  However, in this case, since all the stray capacitance between the control circuit unit (including the printed pattern, switching element, and passive element) and the ground is the main path of the high-frequency leakage current, the conduction noise is greatly increased.

  Therefore, in the present invention, as shown in FIG. 3, the control circuit unit 30 and the single-phase PWM converter 13 as the power converter are connected via an insulating circuit. This insulation circuit employs a configuration in which, for example, the power supply power is insulated by an insulation transformer and the control signal is insulated by a photocoupler. That is, as shown in FIG. 3, a switching arm having at least a relatively small impedance connected via the isolation transformer 33 and the photocoupler 31 (SA2 in FIG. 1, SA3 in FIG. 2A, FIG. A configuration is employed in which the switching element Si (i = 3, 5, 1, 7) on the upper side of SA1 in the case of b) and SA4 in the case of FIG. 2C is driven.

  In this case, the output voltage of the control power supply 32 is transmitted to the secondary side of the insulating transformer 33, and is rectified by the secondary side rectifier diode 34a, the smoothing capacitor 35a, the rectifier diode 34b, and the smoothing capacitor 35b, respectively. The rectified output by the rectifier diode 34a and the smoothing capacitor 35a is applied to the transistors Tr1 and Tr2 that are connected in a complementary manner to drive the switching element S1 and whose midpoint is connected to the gate of the switching element S1.

  On the other hand, the rectified output from the rectifier diode 34b and the smoothing capacitor 35b is applied to the CPU 36 as a power source. The CPU 36 has a function of determining the on / off timing of the switching element S1. The output of the CPU 36 is input to the light emitting side of the photocoupler 31 via the resistor 37. The light receiving side of the photocoupler 31 is connected to the bases of the transistors Tr1 and Tr2.

  According to such a configuration, the CPU 36 controls the on / off states of the transistors Tr1 and Tr2 via the photocoupler 31, and as a result, the switching element S1 is driven. The lower switching element Sj (j = 4, SA2 in FIG. 1, SA3 in FIG. 2A, SA1 in FIG. 2B, SA4 in FIG. 2C). 6, 2, and 8) are also driven through an insulating transformer and a photocoupler with the same configuration.

  By the way, in the prior art, the potential of the negative line N of the main circuit portion and the potential of the negative line M of the control power supply are the same, and the drive signal and the control power supply are not insulated and are located above and below the switching arm. The switching element is driven. On the other hand, in the present invention, the negative electrode line N and the negative electrode line M are not set to the same potential, and the switching element Si on the upper side of the switching arm and the switching element Sj on the lower side are similarly provided with an insulating transformer and a photocoupler (not shown). ) Is driven through. Also for other switching arms (not shown), the upper and lower switching elements are driven via an insulating transformer and a photocoupler (not shown).

  In addition, the configuration using a pulse transformer is not limited to the configuration using a photocoupler as shown in FIG. Further, in the case where a voltage detection unit for detecting the voltage Vdc between the positive electrode line P and the negative electrode line N is provided, insulation is also required for this. When the negative electrode line N and the negative electrode line M are at the same potential, the voltage Vdc can be detected by a voltage dividing resistor. However, when the negative electrode line N and the negative electrode line M are not at the same potential as in the present invention, a transformer, A voltage detector having an insulating circuit including a photocoupler is required.

As described above, in the present invention, when the power conversion device has a switching arm having a relatively small impedance connected to the midpoint, the power conversion device and the control circuit unit for the switching element included in the power conversion device are insulated circuits. Connected through. In this way, by adopting a configuration that insulates the power converter from the control circuit unit, it is possible to reliably prevent the stray capacitance formed between the control circuit unit and the ground from becoming a high-frequency leakage current path. . Thereby, the conduction noise which flows through an earth wire can be reduced. In addition, although the cost is increased due to the addition of an insulating circuit, there is an advantage that noise countermeasure components can be simplified because the high-frequency leakage current can be reduced.
(Second Embodiment)
In the circuit configuration shown in FIGS. 1 and 2, a mode in which a voltage is supplied from a power storage device such as a battery in parallel with the PWM converter 13 or 22 in order to secure the voltage across the switching arms SA1 to SA4 (voltage between PN). The structure which connects the power converter device which has is known. A typical device is an uninterruptible power supply.

  Here, generally, the value of the storage voltage of a power storage device such as a battery and the voltage between the positive line P and the negative line N are different. That is, the voltage value between the positive line P and the negative line N is higher than the output voltage value of a power storage device such as a battery. For this reason, the 2nd power converter device with a transformation function is added between power storage devices, such as a battery, and the power converter device of FIG. 1, FIG.

  That is, as shown in FIG. 4, in the configuration of FIG. 1 in the first embodiment described above, the second power conversion device 40 connected to the power storage device 39 such as a battery is provided on the output side of the single-phase PWM converter 13. Connected in parallel.

  Various main circuit configurations of the second power converter 40 are conceivable. For example, as shown in FIGS. 5A and 5B, a circuit configuration including a transformer can be considered. Referring to FIG. 5A, a second power conversion device 40 includes a capacitor 41 charged by a DC power supply 39 by a power storage device such as a battery, and a transformer 42 that transmits the output of the DC power supply 39 to the secondary side. The switching element S is composed of a transistor connected in series to the transformer 42 and a diode D connected in antiparallel thereto, a rectifier diode 43 connected to the secondary side of the transformer 42, and a smoothing capacitor 44. ing. Both ends of the smoothing capacitor 44 are connected to the positive line P and the negative line N on the output side of the single-phase PWM converter 13.

  Referring to FIG. 5B, the second power converter 40 is connected in reverse parallel to the capacitor 41 charged by a DC power source 39 such as a battery, switching elements SA, SB, SC and SD. A transistor bridge TB composed of diodes DA, DB, DC and DD, a transformer 42 connected to a connection point of the switching elements SA and SB, a connection point of the switching elements SC and SD, and a secondary side of the transformer 42 And a connected diode bridge 45. Then, both ends of the diode bridge 45 are connected to the positive line P and the negative line N on the output side of the single-phase PWM converter 13 in FIG.

  Here, the second power conversion device 40 shown in FIGS. 5A and 5B also includes a switching element. At this time, the negative electrode line N ′ in FIGS. 5A and 5B and the negative electrode line N connected to the first power converter (FIGS. 1 and 2) have the same potential via the control circuit. In many cases.

  This is because the transformer 42 included in the second power conversion device 40 in FIG. 5 is not intended for insulation but for transformation, and is connected to the control circuit in a non-insulated manner. This is because driving the switching element can simplify the control circuit and reduce the cost.

  However, in such a configuration, not only the stray capacitance between the control circuit and the ground described above but also the stray capacitance between the second power conversion device 40 and the ground is a high-frequency leakage that becomes a conduction noise source. There is a problem that noise is greatly increased due to a current path.

  In order to solve this, as described above with reference to FIG. 3, a configuration in which insulation is performed by an insulating transformer and a photocoupler is employed. That is, as shown in FIG. 6, a configuration in which the switching element S in FIG. 5A is driven via the photocoupler 30 is adopted. Similarly, each of the switching elements SA to SD in FIG. 5B adopts a configuration of driving through a photocoupler. That is, the second power conversion device 40 and the control circuit unit for the switching element included in the second power conversion device 40 are connected via the insulating circuit. In this way, by adopting a configuration in which the second power conversion device 40 and the control circuit unit 30 are insulated, the stray capacitance between the control circuit unit 30 of the second power conversion device 40 and the ground is high frequency. A leakage current path can be prevented. Thereby, the conduction noise which flows through an earth wire can be reduced.

  In addition, since there is a stray capacitance between the primary and secondary sides of the insulating transformer 42, it is not insulated in the high frequency region. However, even in this case, the stray capacitance that becomes the high-frequency leakage current path can be greatly reduced. That is, the stray capacitance that becomes the high-frequency leakage current path becomes “a series circuit of the stray capacitance between the primary and secondary sides of the transformer and the stray capacitance between the second power conversion device and the ground”. This is because the combined capacitance becomes smaller because the inter-secondary stray capacitance is smaller.

  In the second embodiment, when the output voltage from the single-phase PWM converter 13 serving as the first power converter cannot be supplied, the output voltage from the second power converter 40 is used. In this case, the voltage fluctuation at the time of switching from the output voltage of the single-phase PWM converter 13 to the output voltage of the second power conversion device 40 is suppressed. Therefore, it is necessary to adjust the output voltage of the second power conversion device 40. For this purpose, as shown in FIG. 7, the output voltage of the single-phase PWM converter 13 is detected by the voltage detector 50, and the switching element S or SA to SD of the second power conversion device 40 based on the detected voltage. The CPU 36 that constitutes a control circuit that controls the frequency of the transistors Tr1 and Tr2 controls the frequency for PWM control.

  At this time, as shown in FIG. 7, the voltage detector 50 includes voltage dividing resistors R1 and R2 connected between the connection lines P1 and N1 connected to the output side of the smoothing capacitor Cdc, and a predetermined DC power source Vcc. A series circuit of a resistor R3 and a constant voltage diode ZD is connected between the connection line N1 and a connection middle point of the voltage dividing resistors R1 and R2 and a connection middle point of the resistor R3 and the constant voltage diode ZD are connected to the input side of the error amplifier 51. The light emitting side of the photocoupler 52 is connected between the output side of the error amplifier 51 and the connection line N1. Then, the light receiving side of the photocoupler 52 is connected to the CPU 36 constituting the control circuit.

  Then, the CPU 36 controls the switching element S or DA to DD so that the output voltage of the single-phase PWM converter 13 detected by the voltage detector 50 matches the output voltage of the second power conversion device 40. Voltage fluctuation when switching from the single-phase PWM converter 13 to the second power conversion device 40 at the time of power source switching can be suppressed.

  The present invention can be used for countermeasures such as conduction noise generated by a power converter.

It is a circuit diagram showing a schematic structure of a converter for explaining an embodiment of the present invention. It is a circuit diagram showing a schematic structure of a power converter as a 1st embodiment of the present invention. It is a figure which shows the structural example of the insulation circuit which connects a control circuit part and a power converter device. It is a circuit diagram which shows schematic structure of the 2nd Embodiment of this invention. It is a figure which shows the structural example of the 2nd power converter device for ensuring the both-ends voltage of a switching arm series circuit. It is a figure which shows the structural example of the insulation circuit which connects a control circuit part and a 2nd power converter device. It is a circuit diagram which added the voltage detector to 2nd Embodiment. It is a circuit diagram which shows a noise terminal voltage measurement system in the speed control of a motor. It is a common mode component equivalent circuit diagram of noise.

DESCRIPTION OF SYMBOLS 1 Three-phase power supply 2 Pseudo power supply network 3 Diode rectifier 4 Smoothing capacitor 5 General-purpose inverter 6 Cable 7 Three-phase motor 8 Spectrum analyzer 10 AC power supply 12 Normal reactor 13, 22 Converter 20 Single-phase power supply 23 Inverter 24 Load 30 Control circuit part 31 Photocoupler 32 Control power supply 33 Transformers 34a, 34b Rectifier diodes 35a, 35b Smoothing capacitor 36 CPU
37 resistor 39 DC power supply 40 second power converter 41 capacitor 42 transformer 43 rectifier diode 44 smoothing capacitor 45 diode bridge L inductances L1 to L3 reactors S, S1 to S8, SA to SC switching element TB transistor bridge

Claims (4)

A first power conversion device in which one or more switching elements are used as one arm, two switching arms connected in series are connected in parallel in a plurality of rows, and an AC power supply is connected between the midpoints of at least two rows of switching arms; A power conversion system having a second power conversion device that converts power from the power storage device and supplies the power to both ends of the switching arm,
The AC power supply is connected to the switching arms of the plurality of rows without connecting a reactor to the midpoint, the impedance is relatively small, and the stray capacitance other than the stray capacitance generated between the midpoint and the ground line is the main. A switching arm serving as a leakage current path is provided, and the second power conversion device includes at least one switching element, and a control circuit that controls the switching element of the second power conversion device includes an insulating circuit. Connected through
The insulation circuit includes an insulation transformer that supplies a control power to a switching unit that controls the switching element, and a photocoupler that supplies a control signal to the switching unit. The switching control unit includes a switching unit connected to a control terminal of the switching element, and a CPU that determines on / off timing of the switching element,
The photocoupler is interposed between the output side of the CPU and the switching unit,
The isolation transformer has a control power supply connected to the primary side, one output on the secondary side is supplied to the switching unit via a rectifier circuit, and the other output on the secondary side is supplied to the CPU via the rectifier circuit. The power conversion system according to claim 1, wherein the power conversion system is supplied as a control power source.   A voltage detector for detecting an output voltage of the first power converter is provided, and a voltage detection value of the voltage detector is supplied to the control circuit via a photocoupler, and the control circuit responds to the voltage detection value. 3. The power conversion system according to claim 1, wherein the voltage is controlled to be output from the second power conversion device. The power conversion system according to any one of claims 1 to 3, wherein a control signal for the switching unit is supplied by a pulse transformer.

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