Power conversion device

Abstract

To provide an electric power convertor making it possible to suppress an increase in size and a rise in cost.SOLUTION: An electric power convertor is connected in parallel with a load connected onto each of power lines of a three-phase ac power supply, and includes plural semiconductor switch elements which are connected to the respective power lines, whose resistible voltage is lower than a line voltage of the three-phase ac power supply, and which are directly attached to a mounting surface of a circuit board, and a convertor that suppresses a harmonic component of a current flowing into the load.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device connected in parallel with a load to each power line of a three-phase AC power supply to which the load is connected.

Background Art

[0002] Power conversion devices such as active filters are known that are connected in parallel with a load to each power line of a three-phase AC power supply to which a load such as an electrical device is connected, and suppress harmonic components included in the current flowing through the load.

[0003] This power conversion device includes a switching element, and supplies a compensation current (a compensation current to be added to the load current) for suppressing harmonic components generated from the load to each power line by switching the switching element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the line voltage of a three-phase AC power supply is 200 V, a semiconductor switching element with a withstand voltage of, for example, 600 V is used as each switching element of the power conversion device. In such a high withstand voltage semiconductor switching element, the amount of heat generation increases, and it is necessary to provide large heat dissipation fins for coping with this and a cooling fan for ventilating the fins, which leads to an increase in the size and complexity of the device and an increase in cost.

[0006] An object of an embodiment of the present invention is to provide a power conversion device capable of suppressing an increase in size and cost.

Means for Solving the Problems

[0007] The power conversion device according to the embodiment is connected in parallel with the load to each power line of a three-phase AC power supply to which the load is connected; and includes a plurality of semiconductor switch elements that are connected to each of the power lines and have a breakdown voltage lower than the line voltage of the three-phase AC power supply and are directly mounted on the mounting surface of the circuit board, and includes a converter that suppresses harmonic components of the current flowing through the load. This converter includes a plurality of unit converters each composed of the plurality of semiconductor switch elements and one capacitor, and selectively generates and outputs DC voltages of three or more levels by switching of each semiconductor switch element, and a cluster formed by connecting these unit converters in series is provided for each phase of each power line. Each semiconductor switch element of at least one of the clusters is directly mounted on the mounting surface of one circuit board. The one circuit board has an upper surface which is the mounting surface of the circuit board and a lower surface opposite to the upper surface, and a positive-side conductive pattern serving as a positive-side current path and a negative-side conductive pattern serving as a negative-side current path between each semiconductor switch element and the capacitor are separately arranged on the upper surface and the lower surface. Furthermore, it includes a control unit provided outside the one circuit board for controlling each semiconductor switch element; and a connector provided on the mounting surface of the one circuit board for relaying signals between the control unit and each unit converter. Each unit converter is arranged in a state of surrounding the connector on the mounting surface of the one circuit board.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0009] One embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, for example, an air conditioner 2 as a load is connected to the U-phase, V-phase, and W-phase power supply lines (first, second, and third power supply lines) Lu, Lv, and Lw of a three-phase AC power supply 1. The air conditioner 2 includes a rectifier circuit 3 that rectifies the power supply voltages Eu, Ev, and Ew of the power supply lines Lu, Lv, and Lw by a plurality of diodes connected in a bridge, a capacitor 5 to which the output voltage of this rectifier circuit 3 is applied via a DC reactor 4, an inverter 6 connected between both ends of this capacitor 5 that converts the DC voltage into an AC voltage of a predetermined frequency and outputs it, a compressor motor 7 that operates by the output of this inverter 6, and the like.

[0010] The power conversion device 10 of this embodiment is connected to the power supply lines Lu, Lv, and Lw to which this air conditioner 2 is connected in a parallel relationship with the air conditioner 2.

[0011] Here, the power conversion device 10 is an active filter (hereinafter also referred to as the active filter 10), and includes a passive filter 11, reactors 14u, 14v, 14w, a multilevel converter 20 connected to the power supply lines Lu, Lv, and Lw via these passive filter 11 and reactors 14u, 14v, 14w, a detection unit 15 disposed at a position closer to the air conditioner 2 than the connection position of the passive filter 11 in the power supply lines Lu, Lv, and Lw to detect the currents Iu, Iv, Iw flowing through the air conditioner 2 (referred to as load currents), a detection unit 16 that detects the currents Icu, Icv, Icw flowing through the energization path between the reactors 14u, 14v, 14w and the multilevel converter 20, a detection unit 17 that detects the phases of the power supply voltages Eu, Ev, Ew of the three-phase AC power supply 1, and a control unit 18 that controls the multilevel converter 20 according to the detection results of these detection units 15, 16, 17.

[0012] The passive filter 11 includes an LC circuit composed of a reactor 12u and a capacitor 13u, an LC circuit composed of a reactor 12v and a capacitor 13v, and an LC circuit composed of a reactor 12w and a capacitor 13w. If the harmonic waves to be suppressed are small, since the reactance generated in the power wiring can be used instead of the reactor, the passive filter 11 and the reactors 14u, 14v, and 14w may not be provided.

[0013] The multilevel converter 20 includes first, second, and third clusters 21u, 21v, and 21w that selectively generate and output DC voltages of three or more levels for each phase of the power lines Lu, Lv, and Lw.

[0014] The active filter 10 is required to have high-speed current controllability in order to cope with the steep current during the commutation of the diode rectifier circuit 3 to be compensated. However, in the active filter 10, reactors 14u, 14v, and 14w are provided as coupling reactors for smoothing the rectangular wave components associated with the switching of the PWM control described later. The larger the inductance of the reactors 14u, 14v, and 14w, the worse the current change rate.

[0015] Therefore, by adopting the clusters 21u, 21v, and 21w that selectively generate and output DC voltages of three or more levels for each phase of the power lines Lu, Lv, and Lw, it becomes possible to reduce the change width of the voltage applied to the reactors 14u, 14v, and 14w. As a result, it becomes possible to adopt reactors 14u, 14v, and 14w with a small inductance. This also contributes to the reduction of EMI noise.

[0016] Cluster 21u is a so-called multi-series converter cluster formed by connecting in series (cascading) a plurality (three) of unit converters (cells) 31u, 32u, and 33u, each of which selectively generates and outputs a DC voltage of multiple levels (multi-level) by switching. By adding the output voltages (cell output voltages) Vcu1, Vcu2, and Vcu3 of the unit converters 31u to 33u, an AC voltage Vcu0 (= Vcu1 + Vcu2 + Vcu3) with a waveform close to a sine wave is generated and output to reduce harmonics.

[0017] Cluster 21v is a so-called multi-series converter cluster formed by connecting in series a plurality (three) of unit converters 31v, 32v, and 33v, each of which selectively generates and outputs a DC voltage of multiple levels by switching. By adding the output voltages Vcv1, Vcv2, and Vcv3 of the unit converters 31v to 33v, an AC voltage Vcv0 (= Vcv1 + Vcv2 + Vcv3) with a waveform close to a sine wave is generated and output to reduce harmonics.

[0018] Cluster 21w is a so-called multi-series converter cluster formed by connecting in series a plurality (three) of unit converters 31w, 32w, and 33w, each of which selectively generates and outputs a DC voltage of multiple levels by switching. By adding the output voltages Vcw1, Vcw2, and Vcw3 of the unit converters 31w to 33w, an AC voltage Vcw0 (= Vcw1 + Vcw2 + Vcw3) with a waveform close to a sine wave is generated and output to reduce harmonics.

[0019] The unit converters 31u, 32u, and 33u of cluster 21u are mounted on one circuit board 40u. Similarly, the unit converters 31v, 32v, and 33v of cluster 21v and the unit converters 31w, 32w, and 33w of cluster 21w are each mounted on one circuit board 40v and 40w, respectively. The control unit 18 composed of a microcomputer and its peripheral circuits, etc., is provided on one control circuit board 60 separate from the circuit boards 40u, 40y, and 40w on which the clusters 21u, 21v, and 21w are mounted.

[0020] Since the configurations of clusters 21u, 21v, and 21w are the same, cluster 21u will be taken as an example for explanation. One end of the series circuit of unit converters 31u, 32u, and 33u is connected to power line Lu via passive filter 11 and reactor 14u. One end of the series circuit of unit converters 31v, 32v, and 33v is connected to power line Lv. One end of the series circuit of unit converters 31w, 32w, and 33w is connected to power line Lw. And the other ends of the series circuits of unit converters 31u, 32u, and 33u, the other ends of the series circuits of unit converters 31v, 32v, and 33v, and the other ends of the series circuits of unit converters 31w, 32w, and 33w are interconnected (N terminal: star connection).

[0021] The specific configuration of unit converters 31u, 32u, and 33u is shown in Figure 2. Unit converter 31u includes a pair of output terminals, semiconductor switch elements Q1a, Q1b, Q1c, Q1d each having a freewheeling diode D, a capacitor (DC capacitor) C1 connected to the output terminals via these semiconductor switch elements Q1a to Q1d, a gate drive circuit 31a that drives semiconductor switch elements Q1a to Q1d according to a control signal from control unit 18, a power supply circuit 31b that obtains the operating voltage of this gate drive circuit 31a from the voltage of capacitor C1 (capacitor voltage), and a voltage detection circuit 31c that detects the voltage of capacitor C1 and notifies control unit 18. It generates and outputs multiple levels of DC voltage by selectively forming multiple conduction paths through the switching (on, off) of semiconductor switch elements Q1 to Q1d. When MOSFETs are used for semiconductor switch elements Q1, the freewheeling diode D can be used as a parasitic diode.

[0022] The unit converter 31v includes a pair of output terminals, semiconductor switch elements Q2a, Q2b, Q2c, Q2d each having a freewheeling diode D, a capacitor (DC capacitor) C2 connected to the output terminals via these semiconductor switch elements Q2a to Q2d, a gate drive circuit 32a that drives the semiconductor switch elements Q2a to Q2d in response to a control signal from the control unit 18, a power supply circuit 32b that obtains the operating voltage of this gate drive circuit 32a from the voltage of the capacitor C2 (capacitor voltage), and a voltage detection circuit 32c that detects the voltage of the capacitor C2 and notifies the control unit 18. It generates and outputs a plurality of levels of DC voltage by selectively forming a plurality of current paths by switching (on, off) of the semiconductor switch elements Q2a to Q2d.

[0023] The unit converter 31w includes a pair of output terminals, semiconductor switch elements Q3a, Q3b, Q3c, Q3d each having a freewheeling diode D, a capacitor (DC capacitor) C3 connected to the output terminals via these semiconductor switch elements Q3a to Q3d, a gate drive circuit 33a that drives the semiconductor switch elements Q3a to Q3d in response to a control signal from the control unit 18, a power supply circuit 33b that obtains the operating voltage of this gate drive circuit 33a from the voltage of the capacitor C3 (capacitor voltage), and a voltage detection circuit 33c that detects the voltage of the capacitor C3 and notifies the control unit 18. It generates and outputs a plurality of levels of DC voltage by selectively forming a plurality of current paths by switching (on, off) of the semiconductor switch elements Q3a to Q3d.

[0024] Fig. 3 shows the pulse width modulation control (PMW control) by the control unit 18 when performing switching by, for example, two-level modulation on the semiconductor switch elements Q1a to Q3d. The control unit 18 sets an AC voltage command value Vcu sinθ for generating an AC voltage having substantially the same waveform as the AC voltage Eu of the three-phase AC power supply 1 in the cluster 12u, and by pulse width modulation that compares the voltage levels of the carrier signals V1, V2, V3 having triangular waveforms with different phases from each other and the voltage level of the AC voltage command value Vcu sinθ, and having the same number as the number of the unit converters 31u, 32u, 33u, it generates control signals for switching (also referred to as gate signals) for the semiconductor switch elements Q1a to Q3d of the unit converters 31u, 32u, 33u.

[0025] When generating this control signal, the control unit 18 ensures a dead time that becomes an off state between the on and off of the switch elements Q1a and Q1b arranged in series with each other and between the on and off of the switch elements Q1c and Q1d arranged in series with each other in the unit converter 31u, respectively, for preventing a short circuit. Similarly, between the on and off of the switch elements Q2a and Q2b arranged with each other and between the on and off of the switch elements Q2c and Q2d arranged in series with each other in the unit converter 31v, respectively, a dead time that becomes an off state is ensured for preventing a short circuit. Between the on and off of the switch elements Q3a and Q3b arranged in series with each other and between the on and off of the switch elements Q3c and Q3d arranged in series with each other in the unit converter 31w, respectively, a dead time that becomes an off state is ensured for preventing a short circuit.

[0026] In the case of switching by two-level modulation, the unit converters 31u, 32u, 33u selectively generate and output DC voltages of two levels, "positive level" and "negative level", respectively. In the case of switching by three-level modulation, the unit converters 31u, 32u, 33u selectively generate and output DC voltages of three levels, "positive level", "zero level", and "negative level", respectively.

[0027] The configurations and switching of the unit converters 31u, 32u, and 33u of the solid cluster 21u described above are the same for the configurations and switching of the unit converters 31v, 32v, and 33v of the cluster 21v, and are also the same for the configurations and switching of the unit converters 31w, 32w, and 33w of the cluster 21w.

[0028] The control unit 18 sets an AC voltage command value Vcv sinθ for generating an AC voltage having substantially the same waveform as the AC voltage Ev of the three-phase AC power supply 1 in the cluster 12v, and sets an AC voltage command value Vcw sinθ for generating an AC voltage having substantially the same waveform as the AC voltage Ew of the three-phase AC power supply 1 in the cluster converter 12w. The AC voltage command values Vcu sinθ, Vcv sinθ, and Vcw sinθ are shifted in phase from each other by 120°.

[0029] [Breakdown Voltage of Semiconductor Switching Element] All semiconductor switching elements Q1a to Q3d in the clusters 21u, 21v, and 21w are silicon semiconductor switching elements such as MOSFETs and IGBTs, and those having a breakdown voltage lower than the line voltages Eu, Ev, and Ew of the three-phase AC power supply 1 are used. For example, when the line voltages Eu, Ev, and Ew of the three-phase AC power supply 1 are 200 V, so-called low-breakdown-voltage semiconductor switching elements Q1a to Q3d having a breakdown voltage of less than 200 V are used. These low-breakdown-voltage semiconductor switching elements Q1a to Q3d are directly attached to and wired to the mounting surfaces of the circuit boards 40u, 40v, and 40w, respectively. The conductive patterns of the circuit boards 40u, 40v, and 40w function as heat dissipation members for the directly attached semiconductor switching elements Q1a to Q3d.

[0030] The low-voltage semiconductor switch elements Q1a to Q3d have a lower on-resistance and a faster switching speed than so-called high-voltage semiconductor switch elements with a breakdown voltage of, for example, 600V, so the power conversion efficiency is high. For this reason, the low-voltage semiconductor switch elements Q1a to Q3d generate less heat than high-voltage semiconductor switch elements, and can be sufficiently cooled by a conductive pattern formed of copper foil or the like on the mounting surface of the element, just by directly mounting them on the mounting surfaces of the circuit boards 40u, 40v, and 40w as described above. Therefore, heat dissipation fins and cooling fans, which are essential when adopting high-voltage semiconductor switch elements, are not required, and thus the increase in the size and cost of the device can be suppressed. Since the operation of attaching heat dissipation fins to each of the semiconductor switch elements is not required, the work efficiency during the manufacture of the device is improved.

[0031] If necessary, a small heat dissipation fin may be soldered as a board mount to the conductive pattern portion to which the semiconductor switch elements Q1a to Q3d of the circuit boards 40u, 40v, and 40w are connected. In this case, since automatic soldering is possible in the same manner as the semiconductor switch elements Q1a to Q3d, the work efficiency is significantly improved compared to the case where an operator manually screws a heat sink to each of the semiconductor switch elements.

[0032] [Switching Frequency] A passive filter 11 composed of reactors 12u, 12v, 12w and capacitors 13u, 13v, 13w, and a reactor 14u, 14v, 14w form an LCL resonance circuit for removing rectangular wave components associated with the switching of PWM control. The gain characteristics of this resonance circuit are shown in FIG. 4. Assuming that the inductance of the reactors 12u, 12v, 12w is Lf, the capacitance of the capacitors 13u, 13v, 13w is Cf, and the inductance of the reactor 14u, 14v, 14w is Lb, the resonance frequency fc of this resonance circuit is expressed by the following formula.

[0033]

Equation

[0034] Generally, in a resonance circuit for removing the rectangular wave component associated with the switching of PWM control, in terms of design, a cut-off frequency, that is, a resonance frequency fc, lower than the switching frequency of the active filter 10 is set. In other words, in a conventional active filter, it is necessary to make its switching frequency higher than the resonance frequency fc. For this reason, the switching frequency of the semiconductor switch element in the active filter has to be increased, resulting in increased losses.

[0035] On the other hand, in the active filter 10 of the present embodiment, since the output voltage for each phase is made multi-level by adopting the clusters 21u, 21v, 21w, even if the actual switching frequency fs, that is, the switching frequency of each semiconductor switch element Q1 in each unit converter 31, is lower than the resonance frequency fc, the equivalent switching frequency can be made higher than the resonance frequency fc as "N × fs" (where N represents the number of stages of the unit converters in one cluster, and is 3 stages in the clusters shown in FIGS. 1 and 3). For example, when the resonance frequency fc is 8 kHz, even if the switching frequency fs is set to 5 kHz, which is lower than this resonance frequency fc, the equivalent switching frequency "N × fs" is 3 × 5 = 15 kHz. Therefore, the actual switching frequency of the active filter 10 can be made higher than the resonance frequency fc to avoid resonance.

[0036] By thus making the actual switching frequency fs of the active filter 10 lower than the resonance frequency fc, the switching losses of the semiconductor switch elements Q1a to Q3d in the clusters 21u, 21v, 21w of the multilevel converter 20 can be reduced. As a result, the temperature rise of the semiconductor switch elements Q1a to Q3d can be suppressed. Since the temperature rise of the semiconductor switch elements Q1a to Q3d can be suppressed, even in a configuration where the circuit boards 40u, 40v, 40w are used as heat dissipation members for the semiconductor switch elements Q1a to Q3d as in the present embodiment, that is, without providing heat dissipation fins or cooling fans, sufficient heat dissipation effect on the semiconductor switch elements Q1a to Q3d can be obtained.

[0037] [Circuit board] In the multilevel converter 20, the clusters 21u, 21v, and 21w are each configured on the same single substrate. Since the configuration of each substrate is common, here, with reference to FIG. 5, the circuit board of the cluster converter 21u will be described as an example. On the upper surface, which is the mounting surface of the circuit board 40u, an elongated connector (first connector) 50 that relays signals between the control unit 18 and the unit converters 31u, 32u, 33u of the cluster 21u is arranged, and external connection terminals (referred to as L terminals) 51a and external connection terminals (referred to as N terminals) 51b of the cluster 21u are arranged.

[0038] The L terminal 51a is connected to one phase of the AC power line, here the U phase, and the N terminal 51b is a wiring connection part that leads to the interconnection point of the cluster converters 21u, 21v, and 21w. The switching elements of each unit converter 31u, 32u, 33u perform on / off operations based on the signal from the control unit 18 sent via the connector 50. Also, the outputs of the voltage detection circuits 31c, 32c, 33c of each unit converter 31u, 32u, 33u are sent to the control unit 18 via the connector 50. And on the upper surface, which is the mounting surface of the circuit board 40u, the unit converters 31u, 32u, 33u and the external connection terminals 51a, 51b are arranged surrounding the connector 50 from around and at positions facing the connector 50 respectively.

[0039] Specifically, the first-stage unit converter 31u is arranged at a position facing one side portion 50a along the longitudinal direction of the connector 50, the second-stage unit converter 32u is arranged at a position facing one end portion 50b along the longitudinal direction of the connector 50, the final-stage (third-stage) unit converter 33u is arranged at a position facing the other side portion 50c along the longitudinal direction of the connector 50, and the L terminal 51a and the N terminal 51b are arranged at a position facing the other end portion 50d along the longitudinal direction of the connector 50.

[0040] In this way, by arranging the unit converters 31u, 32u, 33u and the L terminal 51a and the N terminal 51b in a state surrounding the connector 50, the area of the circuit board 40u can be reduced as much as possible, and each signal line between the connector 50 and the unit converter 31u, between the connector 50 and the unit converter 32u, and between the connector 50 and the unit converter 33u can be shortened respectively.

[0041] Since the first-stage unit converter 31u and the L terminal 51a are close to each other, the length of the external connection energization path (conductive pattern 41a described later) between the unit converter 31u and the L terminal 51a can be shortened as much as possible. Since the last-stage unit converter 33u and the N terminal 51b are close to each other, the length of the external connection energization path (conductive pattern 41b described later) between the unit converter 33u and the N terminal 51b can be shortened as much as possible.

[0042] By shortening these signal lines and energization paths, the influence of external noise can be eliminated as much as possible, and the working efficiency during the manufacture of the device is improved. Since the L terminal 51a and the N terminal 51b are adjacent to each other, when providing a common-mode noise filter, the connection work of the noise filter becomes easy.

[0043] In the region where the unit converter 31u is arranged on the circuit board 40u and its periphery, there are arranged a conductive pattern 41a which is an external connection energization path between the semiconductor switch elements Q1a, Q1b and the L terminal 51a, a positive-side conductive pattern 42 which is a positive-side energization path (+) between the semiconductor switch elements Q1a, Q1c and the positive electrode of the capacitor C1, a negative-side conductive pattern 43 which is a negative-side energization path (-) between the negative electrode of the capacitor C1 and the semiconductor switch elements Q1b, Q1d, and a conductive pattern 44 which is an external connection energization path between the semiconductor switch elements Q1c, Q1d and the subsequent unit converter 32u.

[0044] These conductive patterns 41a, 42, 43, 44 are copper wiring patterns formed by etching or the like on the insulating substrate of the circuit board, and schematically show the existence of the circuit board 40u itself. Actually, as shown in FIG. 6, which is a view looking in the arrow direction along the cross section along the X-X line in FIG. 5, they are separately arranged on the upper surface A, which is the mounting surface of the circuit board 40u, and the lower surface B on the opposite side of the upper surface A. That is, the conductive pattern 41a, which is an energization path for external connection, is arranged on the upper surface A. The positive-side conductive pattern 42 that conducts to the positive electrode of the capacitor C1 is arranged on the upper surface A only for a part that is connected to the semiconductor switch element Q1a, and the remaining almost entire area is arranged on the lower surface B. The negative-side conductive pattern 43 that conducts to the negative electrode of the capacitor C1 is arranged entirely on the upper surface A.

[0045] When using low-breakdown-voltage semiconductor switch elements Q1a to Q1d, since the margin for surge voltage decreases, it is necessary to reduce the stray inductance on the circuit, which is the main cause of the surge voltage. To reduce the stray inductance, it is effective to shorten the conductive pattern between the semiconductor switch elements Q1a to Q1d and the capacitor C1. For this reason, first, the semiconductor switch elements Q1a to Q1d and the capacitor C1 are mounted on the same circuit board 40u. Further, almost the entire area of the positive-side conductive pattern 42 that conducts to the positive electrode of the capacitor C1 and the negative-side conductive pattern 43 that conducts to the negative electrode of the capacitor C1 are arranged on the laminate with the circuit board 40u sandwiched therebetween, and the stray inductance is further reduced by the mutual inductance generated thereby.

[0046] In the region where the unit converter 32u is arranged on the circuit board 40u and its periphery, there are arranged the conductive pattern 44, which is the energization path for external connection between the previous-stage unit converter 31u and the semiconductor switch elements Q2a, Q2b; the positive-side conductive pattern 45, which is the positive-side energization path (+) between the semiconductor switch elements Q2a, Q2c and the positive electrode of the capacitor C2; the negative-side conductive pattern 46, which is the negative-side energization path (-) between the negative electrode of the capacitor C2 and the semiconductor switch elements Q2b, Q2d; and the conductive pattern 47, which is the energization path for external connection between the semiconductor switch elements Q2c, Q2d and the subsequent-stage unit converter 33u.

[0047] These conductive patterns 44, 45, 46, 47 are also copper wirings, which show their existence on the circuit board 40u. Actually, like 41a, 42, 43, 44 of the unit converter 31u, they are separately arranged on the upper surface A and the lower surface B of the circuit board 40u. Regarding the arrangement of this unit converter 32u, similar to the effect described for the unit converter 31u, the stray inductance can be reduced.

[0048] In the region where the unit converter 33u is arranged on the circuit board 40u and its periphery, there are arranged the conductive pattern 47 which serves as an external connection energization path between the previous-stage unit converter 32u and the semiconductor switch elements Q3a, Q3b, the positive-side conductive pattern 48 which serves as a positive-side energization path (+) between the semiconductor switch elements Q3a, Q3c and the positive electrode of the capacitor C3, the negative-side conductive pattern 49 which serves as a negative-side energization path (-) between the negative electrode of the capacitor C3 and the semiconductor switch elements Q3b, Q3d, and the conductive pattern 41b which serves as an external connection energization path between the semiconductor switch elements Q3c, Q3d and the N terminal 51b.

[0049] These conductive patterns 47, 48, 49, 41b are also copper wirings, which show their existence on the circuit board 40u. Actually, like 41a, 42, 43, 44 of the unit converter 31u, they are separately arranged on the upper surface A and the lower surface B of the circuit board 40u. Regarding the arrangement of this unit converter 33u, similar to the effect described for the unit converter 31u, the stray inductance can be reduced.

[0050] The configuration of the solid circuit board 40u described above is the same for the circuit board 40v on which the unit converters 31v, 32v, and 33v of the cluster 21v are implemented, and is also the same for the circuit board 40w on which the unit converters 31w, 32w, and 33w of the cluster 21w are implemented. That is, on the circuit board 40v, an elongated connector (second connector) 50 that relays signals between the control unit 18 and the unit converters 31v, 32v, and 33v is arranged, and conductive patterns 41a, 42 to 49, and 41b are arranged. On the circuit board 40w, an elongated connector (third connector) 50 that relays signals between the control unit 18 and the unit converters 31w, 32w, and 33w is arranged, and conductive patterns 41a, 42 to 49, and 41b are arranged.

[0051] [Regarding the multilevel converter] Since the star-connected clusters 21u, 21v, and 21w are adopted as the multilevel converter 20, the voltage applied to each unit converter of the clusters 21u, 21v, and 21w can be reduced as much as possible. As a result, each semiconductor switch element with low withstand voltage can be used.

[0052] As the multilevel converter 20, as shown in FIG. 7, for each phase, the adoption of a diode-clamped multilevel converter composed of a large number of semiconductor switch elements S, a large number of diodes D, and a large number of capacitors C can be considered. Alternatively, as shown in FIG. 8, for each phase, the adoption of a flying capacitor multilevel converter composed of a large number of semiconductor switch elements S and a large number of capacitors C can be considered. However, these are originally complex in configuration and have a large number of components, and are not suitable for a power conversion device whose purpose is to suppress enlargement and cost increase as in the present embodiment.

[0053] [Modification example] In the above-described embodiment, the case where the number of unit converters in each of the clusters 21u, 21v, and 21w is three for each phase has been described. However, the number can be set as appropriate. This number is preferably odd due to the relationship of the drive signals of the switching elements in each unit converter. For example, when increasing the number of unit converters in each cluster to five or seven, as the circuit board configuration, since the number of terminals of the connector 50 shown in FIG. 5 increases and the shape of the connector 50 extends in the longitudinal direction, additional unit converters 31 can be added and arranged along the longitudinal direction of the connector. That is, in FIG. 5, above each of the unit converters 31u and 33u in the drawing, that is, between the unit converter 31u and the unit converter 32u and between the unit converter 33u and the unit converter 32u, additional symmetric unit converters may be provided with the same circuit element arrangement as the circuit element arrangement of the unit converters 31u to 33u.

[0054] The above-described embodiment and modification examples are presented as examples and are not intended to limit the scope of the invention. These embodiment and modification examples can be implemented in various other forms, and various omissions, rewritings, and changes can be made without departing from the gist of the invention. These embodiment and modification examples are included in the gist of the scope of the invention and are included in the invention described in the claims and its equivalent scope.

Description of Reference Numerals

[0055] 1... Three-phase AC power supply, Lu, Lv, Lw... Power supply lines, 3... Air conditioner (load), 10... Power conversion device (active filter), 11... Passive filter, 14u, 14v, 14w... Reactors, 18... Control unit, 20... Multilevel converter, 21u... First cluster, 21v... Second cluster, 21w... Third cluster, 31u to 31w... Unit converters, Q1a to Q3d... Semiconductor switch elements, C1 to C3... Capacitors

Claims

1. A power conversion device connected in parallel with a load to each power line of a three-phase AC power supply to which the load is connected, including a plurality of semiconductor switch elements connected to each of the power lines and having a breakdown voltage lower than the line voltage of the three-phase AC power supply and directly mounted on the mounting surface of the circuit board, and suppressing harmonic components of the current flowing through the load, a converter, comprising, The converter includes a plurality of unit converters each composed of the plurality of semiconductor switch elements and one capacitor, and selectively generates and outputs DC voltages of three or more levels by switching of each semiconductor switch element, and a cluster formed by connecting these unit converters in series is provided for each phase of each power line, Each semiconductor switch element of at least one of the clusters is directly mounted on the mounting surface of one circuit board, The one circuit board has an upper surface which is the mounting surface of the circuit board and a lower surface opposite to the upper surface, and a positive conductive pattern serving as a positive-side current path and a negative conductive pattern serving as a negative-side current path between each semiconductor switch element and the capacitor are arranged separately on the upper surface and the lower surface, Further, a control unit provided outside the one circuit board for controlling each semiconductor switch element, A connector provided on the mounting surface of the one circuit board for relaying signals between the control unit and each unit converter, comprising, Each unit converter is arranged in a state of surrounding the connector on the mounting surface of the one circuit board, A power conversion device.

2. A passive filter and a reactor are inserted between the converter and each power line, The switching frequency of each semiconductor switch element is lower than the resonance frequency of a resonance circuit formed by the passive filter and the reactor, The power conversion device according to claim 1.

3. The converter is composed of a plurality of first semiconductor switch elements with a breakdown voltage lower than the line voltage of the three-phase AC power supply and one first capacitor, and includes a plurality of first unit converters each selectively outputting a DC voltage of three or more levels. These first unit converters are connected in series and a first cluster directly attached to the mounting surface of one first circuit board, composed of a plurality of second semiconductor switch elements with a breakdown voltage lower than the line voltage of the three-phase AC power supply and one second capacitor, and includes a plurality of second unit converters each selectively outputting a DC voltage of three or more levels. These second unit converters are connected in series and a second cluster directly attached to the mounting surface of one second circuit board, composed of a plurality of third semiconductor switch elements with a breakdown voltage lower than the line voltage of the three-phase AC power supply and one third capacitor, and includes a plurality of third unit converters each selectively outputting a DC voltage of three or more levels. These third unit converters are connected in series and a third cluster directly attached to the mounting surface of one third circuit board, which is a multilevel converter including One end of the series circuit of each first unit converter is connected to the first power line of each power line through the passive filter and the reactor. One end of the series circuit of each second unit converter is connected to the second power line of each power line through the passive filter and the reactor. One end of the series circuit of each third unit converter is connected to the third power line of each power line through the passive filter and the reactor, The other ends of the series circuits of each first unit converter, the other ends of the series circuits of each second unit converter, and the other ends of the series circuits of each third unit converter are interconnected, The power conversion device according to claim 2.

4. The first circuit board has an upper surface which is the mounting surface of the first circuit board and a lower surface opposite to the upper surface. A positive-side conductive pattern serving as a positive-side current path and a negative-side conductive pattern serving as a negative-side current path between each first semiconductor switch element and the first capacitor are arranged separately on the upper surface and the lower surface, The second circuit board has an upper surface which is the mounting surface of the second circuit board and a lower surface opposite to the upper surface, and a positive-side conductive pattern serving as a positive-side current path and a negative-side conductive pattern serving as a negative-side current path between each of the second semiconductor switch elements and the second capacitor are arranged separately on the upper surface and the lower surface. The third circuit board has an upper surface which is the mounting surface of the third circuit board and a lower surface opposite to the upper surface, and a positive-side conductive pattern serving as a positive-side current path and a negative-side conductive pattern serving as a negative-side current path between each of the third semiconductor switch elements and the third capacitor are arranged separately on the upper surface and the lower surface. The power conversion device according to claim 3.

5. The control unit is provided on one control circuit board and controls each of the first semiconductor switch elements, each of the second semiconductor switch elements, and each of the third semiconductor switch elements. The connector includes a first connector provided on the mounting surface of the first circuit board for relaying signals between the control unit and each of the first unit converters, a second connector provided on the mounting surface of the second circuit board for relaying signals between the control unit and each of the second unit converters, and a third connector provided on the mounting surface of the third circuit board for relaying signals between the control unit and each of the third unit converters. Each of the first unit converters is arranged in a state of surrounding the first connector on the mounting surface of the first circuit board. Each of the second unit converters is arranged in a state of surrounding the second connector on the mounting surface of the second circuit board. Each of the third unit converters is arranged in a state of surrounding the third connector on the mounting surface of the third circuit board. The power conversion device according to claim 3.

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