JP2013021764A - Power conversion device and inverter device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that protects a load and a power supply against an insulation deterioration due to an excessive surge voltage.SOLUTION: A switching element series circuit having an AC terminal U at a series junction of switching elements Qu, Qx is connected to both ends of a DC voltage supply series circuit having a neutral terminal M at a series junction of DC voltage supplies 1a, 1b, a bidirectional switch Sux is connected between the neutral terminal M and the AC terminal U, and a filter circuit comprising a series connection of a reactor Lf and a capacitor Cf is connected. When the switching elements Qu, Qx are switched between an on state and an off state, the bidirectional switch Sux is turned on for half a resonance period of the filter circuit to output a neutral potential to the AC terminal.

Description

  The present invention relates to a power conversion device capable of suppressing a surge voltage generated due to an on / off operation of a switching element, and an inverter device using the same.

  In general, when driving an AC motor, the voltage of the DC voltage source is converted into a pulse voltage string equivalent to a sine wave voltage by a voltage-type PWM inverter (a voltage waveform that becomes a sine wave when components above the switching frequency are removed). A pulse width modulated sinusoidal voltage is applied to the motor. FIG. 10 is a schematic configuration diagram of a system for driving an electric motor in such a manner. In FIG. 10, 1 is a DC voltage source, 2 is a two-level three-phase voltage source PWM inverter (hereinafter also simply referred to as an inverter) connected to the DC voltage source 1, and 3 is used to turn on / off switching elements constituting the inverter 2. 4 is a motor driven by an inverter 2.

  The inverter 2 includes a U-phase switching arm in which switching elements Su and Sx are connected in series, a V-phase switching arm in which switching elements Sv and Sy are connected in series, and a W-phase switching arm in which switching elements Sw and Sz are connected in series. It consists of a three-phase bridge.

  The inverter 2 and the electric motor 4 are connected by wiring, and a resistance component and an inductance component exist in this wiring. Furthermore, stray capacitance exists between the wirings of each phase between the inverter 2 and the electric motor 4 and between the wirings of each phase and the ground. Ls represents the inductance of the wiring between the inverter 2 and the electric motor 4, and Cs represents the stray capacitance between the wiring of each phase and the ground or the reference potential. Note that the resistance component of each phase wiring is omitted.

  Here, the positive terminal of the DC voltage source 1 is P, and the negative terminal is N. Further, a connection midpoint between the switching elements Su and Sx of the inverter 2 is defined as an AC terminal U, a connection midpoint between the switching elements Sv and Sy is defined as an AC terminal V, and a connection midpoint between the switching elements Sw and Sz is defined as an AC terminal W. The three-phase input terminals of the motor 4 are Um, Vm, and Wm, respectively.

  In such an electric motor drive system, the inverter 2 switches on / off states of the switching elements Su to Sw and Sx to Sz in accordance with a control signal generated by the control device 3, and the voltage of the DC voltage source 1 is a pulse width modulated rectangular shape. Converts to a wavy pulse voltage train. The pulse-width-modulated rectangular wave pulse voltage train is output between the AC terminals U, V, and W of the inverter 2 and applied to the input terminals Um, Vm, and Wm of the electric motor 4 through the wiring.

  When a pulse-width-modulated pulse-wave-shaped pulse voltage train is applied to an LC circuit composed of an inductance Ls and a stray capacitance Cs, a resonance phenomenon occurs between the inverter 2 and the LC circuit. FIG. 11 is a diagram illustrating a resonance voltage generated between the input terminals Um and Vm of the electric motor 4 when the switching element Su of the inverter 2 performs an on / off operation. Hereinafter, the potential reference point of each terminal is N point in FIG.

  This resonant voltage becomes a surge voltage that attenuates and oscillates with time due to a resistance component (not shown) included in the wiring between the inverter 2 and the electric motor 4. The maximum value of the surge voltage reaches about twice the voltage Ed [V] of the DC voltage source 1. It is known that this excessive surge voltage and its time change rate dv / dt cause dielectric breakdown of the electric motor 4.

  Even in a three-level inverter that reduces the harmonic component contained in the output voltage using a power converter that can divide the voltage of the DC voltage source 1 into two and output positive, neutral, and negative potentials. The principle for generating the surge voltage is the same.

  As a measure to prevent the breakdown of the motor due to such an excessive surge voltage, surge voltage suppression is achieved by connecting a rectifier composed of a diode bridge at the input terminal of the motor and a capacitor and a resistor in parallel at both ends of the DC terminal. An apparatus has been proposed (see, for example, Patent Document 1). As an improvement, a surge voltage suppression device has been proposed in which a current flowing through a resistor connected to a DC terminal of a rectifier is controlled by a switching element (see, for example, Patent Document 2). In addition, a surge voltage suppression method has been proposed in which the DC terminal of the rectifier is connected to the input terminal of the inverter and the energy of the surge voltage is regenerated to the power source (for example, see Patent Document 3). Further, a surge voltage suppression method has been proposed in which a reactor is connected between an inverter and an electric motor, and a series body of a resistor and a capacitor is connected in parallel to the reactor (see, for example, Patent Document 4).

JP-A-8-23682 JP 2006-115667 A JP 2010-136564 A JP 2007-166708 A

  However, in the above measures, it is necessary to add a surge voltage suppression device composed of a rectifier, a resistor, a capacitor, and a surge voltage suppression circuit composed of a reactor, a resistor, and a capacitor in order to suppress the surge voltage. This will lead to higher prices.

  The present invention seeks to solve the problems of such a conventional surge voltage suppressor, and its purpose is to add no special parts or a minimum number of parts. An object of the present invention is to provide a power conversion device capable of suppressing a surge voltage applied to a load such as an electric motor and an inverter device using the same.

  In order to achieve the above object, according to the present invention, a power converter is connected to both ends of a DC voltage source series circuit including a first DC voltage source and a second DC voltage source connected in series. Between the side terminal, the negative side terminal, the neutral point terminal connected to the series connection point of the first DC voltage source and the second DC voltage source, and between the positive side terminal and the negative side terminal A switching element series circuit composed of a first switching element and a second switching element connected in series to each other, and an alternating current connected to a series connection point of the first switching element and the second switching element A terminal, a bidirectional switch circuit connected between the neutral point terminal and the AC terminal, one end of a reactor and one end of a capacitor are connected, and the other end of the reactor is connected to the AC terminal The other end of the capacitor Configured to include a filter circuit connected to the neutral terminal.

  A first time from when the first switching element is switched from the on state to the off state until the second switching element is switched from the off state to the on state, and when the second switching element is on. The second time from when the first switching element switches from the off state to the on state after switching from the state to the off state is set to a time that is ½ of the resonance period of the filter circuit. During this period, the bidirectional switch circuit is turned on.

  According to the present invention, when the first or second switching element is turned off and the bidirectional switch circuit is turned on, and when the bidirectional switch circuit is turned off and the second or first switching element is turned on, Two resonance voltages having substantially the same amplitude and opposite phase can be generated in the filter circuit. Since these two resonance voltages are combined and applied to a load such as an electric motor, a surge voltage generated at an input terminal of the electric motor or the like can be suppressed.

  Furthermore, the present invention adjusts the first time and the second time in direct proportion to the resonance period of the filter circuit and the square root of the inductance value of the reactor. Alternatively, the first time and the second time are changed according to the value of the current flowing through the reactor.

  According to the present invention, the two resonance voltages can be surely set to 180 [°] opposite phase voltages, so that a surge voltage generated at an input terminal of a load such as an electric motor can be more effectively suppressed.

  The power conversion device according to the present invention generates two resonance voltages having substantially the same amplitude and opposite phase in a filter circuit section provided on the AC output side of a so-called three-level power conversion circuit, and synthesizes these two resonance voltages. The voltage from which the vibration component is removed is applied to a load such as an electric motor. As a result, it is possible to suppress a surge voltage generated at an input terminal of a load such as an electric motor.

It is a figure for demonstrating embodiment of this invention. (A) It is a figure for demonstrating the other structural example of the switch circuit Sux. (B) It is a figure for demonstrating the other structural example of the switch circuit Sux. (A) It is a figure for _{demonstrating the} control signal _GQU . (B) It is a figure for _{demonstrating the} control signal _GQX . (C) It is a figure for _{demonstrating the} control signal _GSU . (D) It is a figure for _{demonstrating the} control signal _GSX . (A) It is a figure for demonstrating the voltage waveform between U-M. (B) It is a figure for demonstrating the resonant voltage waveform produced by the voltage change of each timing. (C) It is a figure for demonstrating the voltage waveform between U1-M. (A) It is a figure for _{demonstrating the} control signal _GQU . (B) It is a figure for _{demonstrating the} control signal _GQX . (C) It is a figure for _{demonstrating the} control signal _GSU . (D) It is a figure for _{demonstrating the} control signal _GSX . (A) It is a figure for demonstrating the voltage waveform between U-M. (B) It is a figure for demonstrating the resonant voltage waveform produced by the voltage change of each timing. (C) It is a figure for demonstrating the voltage waveform between U1-M. It is a figure for demonstrating the power converter device which concerns on other embodiment of this invention. It is a figure for demonstrating the power converter device which concerns on other embodiment of this invention. It is a figure for demonstrating the relationship between the inductance value of a reactor, and an electric current. It is a figure for demonstrating the power converter device which concerns on a prior art. It is a figure for demonstrating the surge voltage which generate | occur | produces in an electric motor input terminal when an electric motor is driven with the power converter device shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a diagram for explaining a first embodiment according to the present invention. In FIG. 1, reference numerals 1a and 1b are DC voltage sources, 2a is an inverter, 3a is a control device, Lf is a reactor, and Cf is a capacitor. In the following, it is assumed that the inductance value of the reactor Lf is L [H] and the capacitance value of the capacitor Cf is C [F].

  The DC voltage sources 1a and 1b are connected in series to form a DC voltage source series circuit. One end of the DC voltage source series circuit is connected to the positive terminal P, the other end is connected to the negative terminal N, and the series connection point of the DC voltage sources 1a and 1b is connected to the neutral point terminal M. The voltages of the DC voltage sources 1a and 1b are each Ed / 2 [V]. Therefore, the potentials of the positive terminal P and the negative terminal N with respect to the potential (0 [V]) of the neutral point terminal M are Ed / 2 [V] and −Ed / 2 [V], respectively.

  The inverter 2a includes a switching element series circuit formed by connecting switching elements Qu and Qx connected in antiparallel to the diodes Du and Dx in series, and a bidirectional switch circuit Sux formed by connecting switching elements Su and Sx in antiparallel. It is the switching arm comprised by these. As shown in FIGS. 2A and 2B, the bidirectional switch circuit Sux may be configured by connecting in series the switching elements Su and Sx each having a diode connected in antiparallel.

  In addition, the inverter 2a of FIG. 1 is comprised using IGBT which is one of the switching elements. However, the switching element may be any element that can perform an on / off operation at a high frequency, and may be, for example, a transistor, a MOSFET, or a SiC semiconductor.

  A series connection point of the switching elements Qu and Qx is connected to the AC terminal U. One end of the switching element series circuit is connected to the positive terminal P of the DC voltage source series circuit, and the other end is connected to the negative terminal N. One end of the bidirectional switch circuit Sux is connected to the neutral point terminal M, and the other end is connected to the AC terminal U.

  Reactor Lf and capacitor Cf are connected in series to form a filter circuit. One end of the reactor is connected to the AC terminal U, and one end of the capacitor is connected to the neutral point terminal M. A connection point between the reactor Lf and the capacitor Cf is connected to the AC terminal U1.

  Although not shown in FIG. 1, the AC terminal U1 is connected to a load such as the electric motor shown in FIG. Further, wiring inductance Ls and stray capacitance Cs (not shown) exist in the wiring between the AC terminal U1 and the input terminal of the motor. The inductance value of the reactor Lf and the capacitance value of the capacitor Cf are sufficiently large with respect to the wiring inductance Ls and the stray capacitance Cs, for example, each value is about 10 times or larger.

  The control device 3a generates a signal for selectively turning on / off the switching elements Qu, Qx, Su, Sx in the inverter 2a. For example, the control device 3a performs pulse width modulation for comparing the magnitude of a sine wave signal (modulation signal) obtained by normalizing the output voltage command of the inverter 2a with the voltage of the DC voltage source series circuit and a predetermined triangular wave signal (carrier signal). An operation is performed to generate a pulse width modulated signal (hereinafter referred to as a PWM signal). Next, based on the generated PWM signal, a control signal for selectively turning on / off the switching elements Qu, Qx, Su, Sx in the inverter 2a is generated.

  The inverter 2a selectively switches on / off states of the switching elements Qu, Qx, Su, Sx according to the control signal generated by the control device 3a. By the selective ON / OFF operation of the switching elements Qu, Qx, Su, and Sx, the voltage of the DC voltage source series circuit is converted into a pulse voltage train having a pulse width modulated rectangular wave shape. The pulse voltage train having a pulse width modulated rectangular wave is output to the AC terminal U of the inverter 2a. The pulse voltage train output to the AC terminal U is rectified by a filter circuit to form a sine wave, and is output from the AC terminal U1 toward a load such as an electric motor.

  Here, the first mode in which the potential of the AC terminal U of the inverter 2a is switched from the potential of the negative terminal N to the potential of the positive terminal P will be described. In the following, the potential of each part of the inverter 2a is based on the potential of the neutral point terminal M.

FIGS. 3A to 3D are diagrams for explaining the relationship of control signals of the switching elements Qu, Qx, Su, Sx in the first mode.
In this figure, when the respective control signals G _QU , G _QX , G _SU , G _SX are High, the corresponding switching elements Qu, Qx, Su, Sx are in the ON state. On the other hand, when the respective control signals G _QU , G _QX , G _SU , G _SX are Low, the corresponding switching elements Qu, Qx, Su, Sx are in the OFF state. In addition, a pause time Td is provided between the control signals G _QU and G _SX of the switching elements Qu and Sx so that the switching elements Qu and Sx are not turned on simultaneously. Similarly, a pause time Td is also provided between the control signals G _QX and G _SU of the switching element Qx and Su.

First, since the control signal G _QU and the control signal G _SU are Low, both the switching elements Qu and Su are turned off. Further, since the control signal G _QX and the control signal G _SX are High, both the switching elements Qx and Sx are turned on. In this case, the potential −Ed / 2 [V] of the negative terminal N is output to the AC terminal U of the inverter 2a.

Since the control signal G _QX becomes Low from this state (see FIG. 3B), the switching element Qx is turned off. As a result, the potential 0 [V] of the neutral point terminal M is output to the AC terminal U of the inverter 2a. The timing at which this voltage change occurs is the first timing.

Subsequently, the control signal _{G SU} after pause time Td elapses from the control signal _{G QX} is turned Low becomes High (see FIG. 3 (c).) Therefore, the switching element Su is turned on. In this case, the potential of the AC terminal U of the inverter 2a does not change and remains 0 [V].

Subsequently, since the control signal G _SX becomes Low after the time T11 has elapsed since the control signal G _QX became Low (see FIG. 3D), the switching element Sx is turned off. As a result, the potential Ed / 2 [V] of the positive terminal P is output to the AC terminal U of the inverter 2a. The timing at which this voltage change occurs is the second timing.

Subsequently, since the control signal G _QU becomes High after the suspension time Td elapses after the control signal G _SX becomes Low (see FIG. 3A), the switching element Qu is turned on. In this case, the potential of the AC terminal U of the inverter 2a does not change and remains at the potential Ed / 2 [V] of the positive terminal P. The time T12 from when the control signal G _QX becomes Low until the control signal G _QU becomes High is T12 = T11 + Td.

  FIG. 4A is a diagram for explaining a change in potential of the AC terminal U of the inverter 2a in the first mode. The potential of the AC terminal U is changed from the potential −Ed / 2 [V] of the negative terminal N to the potential 0 [V] of the neutral point terminal M to the positive terminal by the above operation of the switching elements Qu, Qx, Su, Sx. The potential changes to P potential Ed / 2 [V]. A time T1 from the first timing to the second timing corresponds to a time T11 in FIG. 3D, and 0 [V] is output to the AC terminal U during this time.

  FIG. 4B shows the resonance voltage Vr1 of the filter circuit generated when the potential of the AC terminal U changes at the first timing, and the resonance voltage of the filter circuit generated when the potential of the AC terminal U changes at the second timing. It is a figure for demonstrating Vr2.

  The resonance voltage Vr1 is a voltage that oscillates sinusoidally with an amplitude of Ed / 2 [V] and a resonance period Tf of the filter circuit centering on 0 [V]. The resonance period Tf is 2π√ (LC) [s]. The initial value of the resonance voltage is the value −Ed / 2 [V] at the first timing.

  The resonance voltage Vr2 is a voltage that performs sinusoidal vibration centering around Ed / 2 [V] with an amplitude of Ed / 2 [V] and a resonance period Tf of the filter circuit. The initial value of the resonance voltage is 0 [V] at the second timing. The resonance voltage Vr2 is in an opposite phase relationship to the resonance voltage Vr1.

  When the angular frequency of the resonance voltages Vr1 and Vr2 is ω (= 2π / Tf) [rad / s], the magnitudes of the resonance voltages Vr1 and Vr2 with respect to the time t [s] are (Ed / 2) sin (ωt− π / 2) [V], Ed / 2 {1 + sin (ωt + π / 2)} [V].

  FIG. 4C is a diagram illustrating a waveform of a voltage output to the AC terminal U1 of the filter circuit. A voltage obtained by synthesizing the resonance voltages Vr1 and Vr2 of the filter circuit shown in FIG. 4B is output to the AC terminal U1. Since the resonance voltages Vr1 and Vr2 have a phase shifted by π [rad], the voltage obtained by combining the resonance voltages Vr1 and Vr2 does not include a vibration component. Therefore, the voltage of the AC terminal U1 becomes a constant voltage of Ed / 2 [V] after changing from -Ed / 2 [V] to Ed / 2 [V] during the time T1.

  The resonance cycle Tf of the resonance voltage Vr1 is sufficiently longer than the resonance cycle of the LC circuit determined by the wiring inductance Ls and the stray capacitance Cs. That is, the voltage change rate of the AC terminal U1 generated during the time T1 is sufficiently small to cause resonance in the LC circuit. Even when such a voltage having a change rate is applied to the LC circuit including the inductance Ls of the wiring connected to the motor and the stray capacitance Cs, voltage resonance does not occur in the LC circuit. As a result, a surge voltage generated at the input terminal of the electric motor can be suppressed.

Next, a second mode in which the potential of the AC terminal U of the inverter 2a is switched from the potential of the positive terminal P to the potential of the negative terminal N will be described.
FIGS. 5A to 5D are diagrams for explaining the relationship between the control signals of the switching elements Qu, Qx, Su, Sx in the second mode.

First, since the control signal G _QU and the control signal G _SU are High, both the switching elements Qu and Su are turned on. Further, since the control signal G _QX and the control signal G _SX are Low, both the switching elements Qx and Sx are off. In this case, the potential Ed / 2 [V] of the positive terminal P is output to the AC terminal U of the inverter 2a.

Since the control signal G _QU becomes Low from this state (see FIG. 5A), the switching element Qu is turned off. As a result, the potential 0 [V] of the neutral point terminal M is output to the AC terminal U of the inverter 2a. The timing at which this voltage change occurs is the third timing.

Subsequently, since the control signal G _SX becomes High after the suspension time Td has elapsed after the control signal G _QU becomes Low (see FIG. 5D), the switching element Sx is turned on. In this case, the potential of the AC terminal U of the inverter 2a does not change and remains at the potential 0 [V] of the neutral point terminal M.

Subsequently, the control signal _{G SU} from when the control signal _{G QU} is Low the time T21 after the elapse becomes Low (FIG. 5 (c) reference.) Therefore, the switching element Su is turned off. As a result, the potential -Ed / 2 [V] of the negative terminal N is output to the AC terminal U of the inverter 2a. The timing at which this voltage change occurs is the fourth timing.

Subsequently, the control signal _{G QX} after pause time Td elapses from the control signal _{G SU} is turned Low becomes High (see FIG. 5 (b).) Therefore, the switching element Qx is turned on. In this case, the potential of the AC terminal U of the inverter 2a does not change and remains at the potential -Ed / 2 [V] of the negative terminal N. The time T22 from when the control signal G _QU becomes Low until the control signal G _QX becomes High is T22 = T21 + Td.

  FIG. 6A is a diagram for explaining a change in potential of the AC terminal U of the inverter 2a in the second mode. The potential of the AC terminal U is changed from the potential Ed / 2 [V] of the positive terminal P to the potential 0 [V] of the neutral point terminal M to the negative terminal N by the above operation of the switching elements Qu, Qx, Su, Sx. The potential changes to −Ed / 2 [V]. A time T2 from the third timing to the fourth timing corresponds to a time T21 in FIG. 5C, and 0 [V] is output to the AC terminal U during this time.

  FIG. 6B shows the resonance voltage Vr3 of the filter circuit generated when the potential of the AC terminal U changes at the third timing and the resonance voltage of the filter circuit generated when the potential of the AC terminal U changes at the fourth timing. It is a figure for demonstrating Vr4.

  The resonance voltage Vr3 is a voltage that oscillates sinusoidally with an amplitude of Ed / 2 [V] and a resonance period Tf of the filter circuit with 0 [V] as the center. The resonance period Tf is 2π√ (LC) [s]. The initial value of the resonance voltage is the value Ed / 2 [V] at the third timing.

  The resonance voltage Vr4 is a voltage that performs sinusoidal oscillation centered on -Ed / 2 [V] with an amplitude of Ed / 2 [V] and a resonance period Tf of the filter circuit. The initial value of the resonance voltage is 0 [V] at the fourth timing. The resonance voltage Vr4 is in an antiphase relationship with the resonance voltage Vr3.

  When the angular frequency of the resonance voltages Vr3 and Vr4 is ω (= 2π / Tf) [rad / s], the magnitudes of the resonance voltages Vr3 and Vr4 with respect to time t [s] are (Ed / 2) sin (ωt− π / 2) [V], −Ed / 2 {1 + sin (ωt + π / 2)} [V].

  FIG. 6C is a diagram illustrating a waveform of a voltage output to the AC terminal U1 of the filter circuit. A voltage obtained by synthesizing the resonance voltages Vr3 and Vr4 of the filter circuit shown in FIG. 6B is output to the AC terminal U1. Since the resonance voltages Vr3 and Vr4 are in a phase shifted by π [rad], the voltage obtained by combining the resonance voltages Vr3 and Vr4 does not include a vibration component. Therefore, the voltage of the AC terminal U1 becomes a constant voltage of -Ed / 2 [V] after changing from Ed / 2 [V] to -Ed / 2 [V] during the time T2.

  The resonance period Tf of the resonance voltage Vr3 is sufficiently longer than the resonance period of the LC circuit determined by the wiring inductance Ls and the stray capacitance Cs. That is, the voltage change rate of the AC terminal U1 generated during the time T2 is sufficiently small to cause resonance in the LC circuit. Even when such a voltage having a change rate is applied to the LC circuit including the inductance Ls of the wiring connected to the motor and the stray capacitance Cs, voltage resonance does not occur in the LC circuit. As a result, a surge voltage generated at the input terminal of the electric motor can be suppressed.

  FIG. 7 is a diagram for explaining the second embodiment. In the second embodiment, the switching arm and the filter circuit shown in the first embodiment are applied to a single-phase inverter to reduce the surge voltage generated at the input terminal of the motor.

  In FIG. 7, reference numerals 1a and 1b are DC voltage sources, 2b is a single phase inverter, 3b is a control device, Lf is a reactor, Cf is a capacitor, Ls is a wiring inductance, Cs is a stray capacitance, 4b is an electric motor, and 5b is a current detection. It is a vessel.

The DC voltage source series circuit composed of the DC voltage sources 1a and 1b is the same as the DC voltage source series circuit shown in the first embodiment.
The voltage of the DC voltage source series circuit is converted into a pulse voltage string equivalent to a sine wave voltage by the selective on / off operation of the switching element in the single-phase inverter 2b. This pulse voltage train is shaped into a sine wave by a filter circuit including a reactor Lf and a capacitor Cf, and then applied to the motor 4b.

The current detector 5b detects a current flowing through the motor 4b and outputs a signal corresponding to the motor current.
Control device 3b generates a control signal for selectively turning on / off switching elements in single-phase inverter 2b. The control signal generated by the control device 3b is adjusted so that the current supplied to the motor 4b becomes a predetermined value with reference to the signal corresponding to the motor current output from the current detector 5b.

Next, the detailed configuration of the single-phase inverter 2b and the reduction of the surge voltage generated at the input terminal of the electric motor 4b will be described.
The single-phase inverter 2b is a single-phase inverter in which the inverter 2a shown in the first embodiment is used as a switching arm for one phase and a two-phase switching arm is configured using the two switching arms.

  The first phase switching arm is composed of a first switching element series circuit formed by connecting switching elements Qu and Qx connected in antiparallel with diodes Du and Dx in series, and a bidirectional switching circuit Sux. The series connection point of the switching elements Qu and Qx is an AC terminal U.

  The second phase switching arm includes a second switching element series circuit formed by connecting switching elements Qv and Qy in which diodes Dv and Dy are connected in antiparallel to each other in series, and a bidirectional switch circuit Svy. The series connection point of the switching elements Qv and Qy is an AC terminal V.

One end of each of the first phase switching arm and the second phase switching arm is connected to the positive side terminal P, and the other end is connected to the negative side terminal N.
One end of the bidirectional switch circuit Sux is connected to the AC terminal U. One end of the bidirectional switch circuit Svy is connected to the AC terminal V. The other ends of the bidirectional switch circuits Sux and Svy are connected to the neutral point terminal M.

Note that the bidirectional switch circuits Sux and Svy are abbreviated to the bidirectional switch circuit shown in FIG. 1, and may be the bidirectional switch circuits shown in FIGS. 2 (a) and 2 (b).
Moreover, the single phase inverter 2b of FIG. 7 is configured using an IGBT which is one of switching elements. However, the switching element may be any element that can perform an on / off operation at a high frequency, and may be, for example, a transistor, a MOSFET, or a SiC semiconductor.

  Between the AC terminals U and V and the neutral point terminal M of the single-phase inverter 2b, a filter circuit in which a reactor Lf and a capacitor Cf are connected in series is connected. The series connection points of the filter circuits are AC terminals U1 and V1.

The AC terminals U1 and V1 are connected to an electric motor 4b that is a load. A wiring inductance Ls and a stray capacitance Cs exist in the wiring between the AC terminals U1 and V1 and the electric motor 4b.
The control device 3b includes control signals G _QU , G _QX , G _SU , G _SX , for selectively turning on / off the switching elements Qu, Qx, Qv, Qy, Su, Sx, Sv, Sy in the single-phase inverter 2b. G _QV , G _QY , G _SV , and G _SY are generated. The relationship between the control signals G _QU , G _QX , G _SU , G _SX generated by the control device 3b and the relationship between the control signals G _QV , G _QY , G _SV , G _SY are shown in FIG. To (d) and the relationship of the control signals shown in FIGS.

  Therefore, the voltage output to the AC terminals U and V, the waveform of the resonance voltage generated at each step, and the voltage output to the AC terminals U1 and V1 are shown in FIGS. 4 (a) to 4 (c) and 6 (a), respectively. It becomes the same as the voltage shown in (c).

  That is, the potential of the AC terminals U and V once becomes 0 [V] when changing from the potential of the negative terminal to the potential of the positive terminal or changing from the potential of the positive terminal to the potential of the negative terminal. Go through the period. The period in which the potentials of the AC terminals U and V are 0 [V] is a half time of the resonance period Tf of the filter circuit including the reactor Lf and the capacitor Cf. Thereby, the potential change of the AC terminals U1 and V1 changes from the potential of the negative side terminal to the potential of the positive side terminal or from the potential of the positive side terminal to the potential of the negative side terminal in a half time of the resonance period Tf. To do. The rate of change of the voltage generated at the AC terminals U1, V1 at this time is sufficiently small to cause resonance in the LC circuit composed of the wiring inductance Ls and the stray capacitance Cs.

As a result, the surge voltage generated at the input terminal of the electric motor 4b can be suppressed.
FIG. 8 is a diagram for explaining the third embodiment. In the third embodiment, the switching arm and the filter circuit shown in the first embodiment are applied to a three-phase inverter to reduce the surge voltage generated at the input terminal of the motor.

  In FIG. 8, reference numerals 1a and 1b are DC voltage sources, 2c is a three-phase inverter, 3c is a control device, Lf is a reactor, Cf is a capacitor, Ls is wiring inductance, Cs is stray capacitance, 4c is an electric motor, and 5c is current detection. It is a vessel.

The DC voltage source series circuit composed of the DC voltage sources 1a and 1b is the same as the DC voltage source series circuit shown in the first embodiment.
By the selective on / off operation of the switching element in the three-phase inverter 2c, the voltage of the DC voltage source series circuit is converted into a pulse voltage string equivalent to a sine wave voltage. The pulse voltage train is shaped into a sine wave by a filter circuit including a reactor Lf and a capacitor Cf, and then applied to the motor 4c.

The current detector 5c detects the current flowing through the electric motor 4c and outputs a signal corresponding to the electric motor current.
The control device 3c generates a control signal for selectively turning on / off the switching elements in the three-phase inverter 2c. The control signal generated by the control device 3c is adjusted so that the current supplied to the motor 4c becomes a predetermined value with reference to a signal corresponding to the motor current output from the current detector 5c.

Next, the detailed configuration of the three-phase inverter 2c and the reduction of the surge voltage generated at the input terminal of the electric motor 4c will be described.
The three-phase inverter 2c is a three-phase inverter in which the inverter 2a shown in the first embodiment is used as a switching arm for one phase, and a three-phase switching arm is configured using the three switching arms.

  The first phase switching arm is composed of a first switching element series circuit formed by connecting switching elements Qu and Qx connected in antiparallel with diodes Du and Dx in series, and a bidirectional switching circuit Sux. The series connection point of the switching elements Qu and Qx is an AC terminal U.

  The second phase switching arm includes a second switching element series circuit formed by connecting switching elements Qv and Qy in which diodes Dv and Dy are connected in antiparallel to each other in series, and a bidirectional switch circuit Svy. The series connection point of the switching elements Qv and Qy is an AC terminal V.

  The third phase switching arm includes a third switching element series circuit formed by connecting switching elements Qw and Qz connected in reverse parallel to the diodes Dw and Dz in series, and a bidirectional switch circuit Swz. The series connection point of the switching elements Qw and Qz is an AC terminal W.

  One end of each of the first phase switching arm, the second phase switching arm and the third phase switching arm is connected to the positive terminal P, and the other end is connected to the negative terminal N.

  One end of the bidirectional switch circuit Sux is connected to the AC terminal U. One end of the bidirectional switch circuit Svy is connected to the AC terminal V. One end of the bidirectional switch circuit Swz is connected to the AC terminal W. The other end of each of the bidirectional switch circuits Sux, Svy, Swz is connected to a neutral point terminal M.

  Note that the bidirectional switch circuits Sux, Svy, and Swz are abbreviated to the bidirectional switch circuit shown in FIG. 1, and the bidirectional switch circuits shown in FIGS. good.

  Further, the three-phase inverter 2c in FIG. 8 is configured using an IGBT which is one of the switching elements. However, the switching element may be any element that can perform an on / off operation at a high frequency, and may be, for example, a transistor, a MOSFET, or a SiC semiconductor.

  Between the AC terminals U, V and W of the three-phase inverter 2c and the neutral point terminal M, a filter circuit in which a reactor Lf and a capacitor Cf are connected in series is connected. The series connection points of the filter circuits are AC terminals U1, V1, W1.

AC terminals U1, V1, and W1 are connected to an electric motor 4c that is a load. A wiring inductance Ls and a stray capacitance Cs exist in the wiring between the AC terminals U1, V1, W1 and the motor 4c.
The control device 3c controls the switching elements Qu, Qx, Qv, Qy, Qw, Qz, Su, Sx, Sv, Sy, Sw, Sz in the three-phase inverter 2c to selectively turn on / off the control signals G _QU , G _{QX, G SU, G SX,} G QV, G QY, G SV, G SY, G QW, G QZ, G SW, generates the _{G SZ.} The relationship between the control signals G _QU , G _QX , G _SU , G _SX generated by the control device 3c, the relationship between the control signals G _QV , G _QY , G _SV , G _SY and G _QW , G _QZ , G _SW , G _SZ are the same as the control signals shown in FIGS. 3A to 3D and 5A to 5D, respectively.

  Therefore, the voltage output to the AC terminals U, V, W, the waveform of the resonance voltage generated in each step, and the voltage output to the AC terminals U1, V1, W1 are respectively shown in FIGS. It becomes the same as the voltage shown to 6 (a)-(c).

  That is, the potential of the AC terminals U, V, and W is once 0 [V] when changing from the potential of the negative terminal to the potential of the positive terminal or when changing from the potential of the positive terminal to the potential of the negative terminal. It goes through the period. The period in which the potentials of the AC terminals U, V, and W are 0 [V] is a time that is ½ of the resonance period Tf of the filter circuit including the reactor Lf and the capacitor Cf. As a result, the potential change of the AC terminals U1, V1, and W1 changes from the potential of the negative terminal to the potential of the positive terminal or from the potential of the positive terminal to the potential of the negative terminal in a half time of the resonance period Tf. To change. At this time, the rate of change of the voltage generated at the AC terminals U1, V1, and W1 is sufficiently small to cause resonance in the LC circuit including the wiring inductance Ls and the stray capacitance Cs.

As a result, the surge voltage generated at the input terminal of the electric motor 4c can be suppressed.
Even in the case of a multi-phase inverter having more than three phases, the switching arm and the filter circuit of each phase are configured as in the third embodiment, and the control signals of the switching elements are shown in FIGS. 5A to 5D, the surge voltage generated at the input terminal of the motor can be suppressed by generating and switching on / off each switching element.

  By the way, the time of the resonance period Tf of the filter circuit composed of the reactor Lf and the capacitor Cf is 2π√ (LC) [s]. That is, the time of the resonance period Tf is directly proportional to the square root of the inductance value L [H] of the reactor Lf.

  Further, a magnetic material typified by a ferrite magnet or an amorphous alloy is used for the core material of the reactor Lf. As shown in FIG. 9, a reactor using such a magnetic material for the iron core has a characteristic that the inductance value L [H] decreases as the value of the current If flowing through the coil increases.

  Accordingly, if the resonance period Tf of the filter circuit is uniquely determined from the specification values of the reactor Lf and the capacitor Cf, the effect of canceling the AC components of the resonance voltages Vr1 and Vr2 and the resonance voltages Vr3 and Vr4 may not be sufficiently exhibited. is there. That is, when the inductance value L [H] decreases as the value of the current If [A] flowing through the coil increases, the resonance of the preset resonance frequency Tf of the filter circuit and the actually generated resonance voltages Vr1 to Vr4. Deviation occurs between cycles. As a result, the resonance voltage is not sufficiently canceled, and the effect of suppressing the surge voltage is reduced.

Therefore, it is necessary to adjust the lengths of the times T1 and T2 in direct proportion to the resonance period Tf of the filter circuit so that the resonance voltage is surely canceled.
As described above, the resonance period Tf of the filter circuit is directly proportional to the square root of the inductance value L [H] of the reactor Lf. Therefore, if the times T1 and T2 are adjusted so as to be directly proportional to the square root of the inductance value L [H] of the reactor Lf, the resonance voltage is effectively canceled. Even if the square value of the time T1 and T2 is adjusted to be directly proportional to the inductance value L [H] of the reactor Lf, the resonance voltage is effectively canceled.

  The inductance value L [H] of the reactor Lf is, for example, the relationship between the inductance value L [H] of the reactor Lf shown in FIG. 9 and the value of the current If [A] flowing through the coil in the control devices 3a, 3b, 3c. By providing the data table shown, it can be obtained based on the value of the current flowing through the reactor Lf.

  Further, the resonance period Tf of the filter circuit is calculated from the inductance value L [H] of the reactor Lf obtained above and the capacitance value C [F] of the capacitor Cf, and the time T1, T1 is directly proportional to the calculated resonance period Tf. T2 can also be adjusted.

  Further, a data table indicating the phase between the resonance period Tf of the filter circuit obtained as described above and the current value flowing through the reactor is prepared in advance and provided in the control device 3a, and this table is referred to based on the current value flowing through the reactor Lf. The times T1 and T2 can be adjusted in direct proportion to the resonance period obtained by referring to the table.

  Note that the current detected by the current detectors 5b and 5c shown in FIGS. 7 and 8 can be used as the current flowing through the reactor Lf. The currents detected by the current detectors 5b and 5c are currents flowing through the electric motors 4b and 4c. However, if the current flowing through the capacitor Cf is ignored, the current flowing through the reactor Lf can be substantially set. In order to detect the current flowing through the reactor Lf more accurately, the current detectors 5b and 5c may be provided between the inverters 2b and 2c and the reactor Lf or between the reactor Lf and the capacitor Cf.

  In the above-described embodiment, the electrical components added to suppress the surge voltage are the reactor Lf and the capacitor Cf. As in the prior art, a resistor that consumes energy of the surge voltage, a diode bridge circuit, and the like There is no need to add. Therefore, an increase in size and cost of the power conversion device can be suppressed.

  In addition, if the half of the resonance period of the resonance circuit composed of the wiring inductance Ls and the stray capacitance Cs is a time that can be controlled by the inverter, the wiring inductance Ls instead of the filter circuit composed of the reactor Lf and the capacitor Cf. The present invention can be implemented with respect to a resonance circuit composed of a floating capacitance Cs.

  In the above-described embodiment, the operation and effect of the present invention have been described with reference to an example in which an electric motor is driven by a three-phase and single-phase inverter. However, the load of the inverter is not limited to the electric motor, and an electric circuit other than the electric motor is used. Alternatively, even when an electrical component is used as a load, similar actions and effects can be exhibited.

  Further, the inverter may be replaced with a converter that exchanges power with a generator. In this case, the surge voltage generated at the AC terminal of the generator can be suppressed by applying the present invention.

  1, 1a, 1b ... DC voltage source, 2, 2a, 2b, 2c ... inverter, 3, 3a, 3b, 3c ... control device, 4, 4a, 4b, 4c ... electric motor, 5b , 5c ... current detector, Qu to Qw, Qx to Qz ... switching element, Su to Sw, Sx to Sz ... switching element, Ls ... inductance of wiring, Cs ... floating of wiring Capacity, Lf: Reactor, Cf: Capacitor

Claims (16)

A positive terminal and a negative terminal connected to both ends of a DC voltage source series circuit composed of a first DC voltage source and a second DC voltage source connected in series;
A neutral point terminal connected to a series connection point of the first DC voltage source and the second DC voltage source;
A switching element series circuit comprising a first switching element and a second switching element connected in series between the positive terminal and the negative terminal;
An AC terminal connected to a series connection point of the first switching element and the second switching element;
A bidirectional switch circuit connected between the neutral point terminal and the AC terminal;
A filter circuit in which one end of a reactor and one end of a capacitor are connected, the other end of the reactor is connected to the AC terminal, and the other end of the capacitor is connected to the neutral point terminal;
A power conversion device comprising: When the potential of the AC terminal switches from the potential of the positive terminal to the potential of the negative terminal,
The potential of the AC terminal switches from the potential of the positive terminal to the potential of the neutral point terminal. After being at the potential of the neutral point terminal for a first time, the potential of the negative terminal is changed to the potential of the negative terminal. The power converter according to claim 1, wherein the power converter is switched. When the potential of the AC terminal switches from the potential of the negative terminal to the potential of the positive terminal,
The potential of the AC terminal is switched from the potential of the negative terminal to the potential of the neutral point terminal, and after being at the potential of the neutral point terminal for a second time, the potential of the positive terminal The power converter according to claim 1, wherein the power converter is switched. When the second switching element switches from the off state to the on state after the first switching element switches from the on state to the off state,
The bidirectional switch circuit is turned on after the first switching element is switched from an on state to an off state, and the bidirectional switch circuit is kept in a conductive state for a first time and then switched to a non-conductive state. Thereafter, the second switching element is switched from an off state to an on state, and the power converter according to claim 1. When the first switching element switches from the off state to the on state after the second switching element switches from the on state to the off state,
The bidirectional switch circuit is turned on after the second switching element is switched from an on state to an off state, and the bidirectional switch circuit is maintained in a conductive state for a second time and then switched to a non-conductive state. Then, the power switching device according to claim 1, wherein the first switching element is switched from an off state to an on state.   6. The power converter according to claim 2, wherein the first time is ½ of a resonance period of the filter circuit.   6. The power converter according to claim 2, wherein the second time is ½ of a resonance period of the filter circuit.   The first time and / or the second time is 1/2 of the resonance period of the filter circuit, and is proportional to either the resonance period of the filter circuit or the square root of the inductance value of the reactor. The power conversion device according to claim 6, wherein the power conversion device changes.   The first time and / or the second time is a half of a resonance period of the filter circuit, and changes according to a current value flowing through the reactor constituting the filter circuit. The power converter according to any one of claims 6 and 7.   The power converter according to any one of claims 1 to 9, wherein the bidirectional switch circuit is configured by connecting switching elements having reverse breakdown voltage in antiparallel.   The power converter according to any one of claims 1 to 9, wherein the bidirectional switch circuit includes switching elements connected in reverse parallel to each other in reverse series.   12. The power conversion device according to claim 10, wherein switching elements constituting the switching element series circuit and the bidirectional switch circuit are SiC semiconductors.   The single phase inverter apparatus which comprises a two-phase switching arm using the power converter device of any one of Claims 1 thru | or 12.   The single phase converter apparatus which comprises a two-phase switching arm using the power converter device of any one of Claims 1 thru | or 12.   The multiphase inverter apparatus which comprises the switching arm of 3 or more phases using the power converter device of any one of Claims 1 thru | or 12.   A multiphase converter device comprising a switching arm of three or more phases using the power conversion device according to any one of claims 1 to 12.