JP2013116020A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion apparatus that can obtain three-level AC voltage and causes less power loss.SOLUTION: A power conversion apparatus includes: a positive electrode terminal P and a negative electrode terminal N to which a DC voltage is applied; a terminal C at a neutral point between the positive electrode terminal P and the negative electrode terminal N; and an AC terminal A to which an AC voltage is applied. First and second capacitors 11 and 12 that have the same polarity and are connected in series are connected between the positive electrode terminal P and the negative electrode terminal N. A first series body including: first and second switching elements 1 and 2 that have the same polarity and are connected in series; and reflux diodes 1D and 2D connected in reverse parallel to the first and second switching elements 1 and 2 is connected between the positive electrode terminal P and the negative electrode terminal N. A second series body including: third and fourth switching elements 3 and 4 that have the reverse polarity and are connected in series; and reflux diodes 3D and 4D connected in reverse parallel to the third and fourth switching elements 3 and 4 is connected between the terminal C at the neutral point and the AC terminal A. The first and second reflux diodes 1D and 2D and the third and fourth reflux diodes 3D and 4D have different voltage drop characteristics.

Description

  The present invention relates to a power converter, and more particularly, to a power converter for converting DC power into AC power or converting AC power into DC power.

  A two-level power converter capable of obtaining a two-level AC voltage is conventionally known, but a power conversion system in which two such two-level power converters are connected back to back at a DC section has been proposed (for example, , See Patent Document 1). In the power conversion system, the occupied area of the self-extinguishing semiconductor element, which is a component of the power device constituting the power converter, and the free-wheeling diode connected in reverse parallel to the self-extinguishing semiconductor element is the total occupied area. In this case, the occupation ratio of the self-extinguishing semiconductor element in one power conversion device is different from the occupation ratio of the self-extinguishing semiconductor element in the other power conversion device. By doing so, a more appropriate power conversion device can be selected according to various loads. For example, a larger motor can be driven by connecting the one with a lower occupancy rate to an AC power supply and connecting the one with a higher occupancy rate to an electric motor.

  In recent years, a three-level power converter capable of obtaining a three-level output has also been proposed.

  As a conventional three-level power converter, two switching element series bodies connected in series with the same polarity are connected between a positive electrode and a negative electrode of a DC terminal, and a connection point between the two switching elements and the DC There is a power conversion device that can obtain a three-level AC voltage by connecting two anti-series switching elements connected in anti-series between the neutral point of a terminal. Here, the switching element constituting the anti-series body has a lower withstand voltage than the switching element constituting the series body (see, for example, Patent Document 2).

  As another conventional three-level power conversion device, there is a device using a wide band gap semiconductor only for a diode that generates recovery (see, for example, Patent Document 3).

Japanese Patent No. 3621659 JP 2002-247862 A JP 2011-78296 A

  However, in any of the conventional power converters as described above, the power loss of the return diode connected in reverse parallel to the switching element is not optimized, and as the switching frequency is increased in recent years, the return power is reduced. Since the ratio of the time during which diode power loss occurs (short-circuit protection period (dead time) described later) increases, it affects the overall efficiency of the power converter, making it possible to increase the efficiency and size of the entire power converter. There was no problem.

  The present invention has been made to solve such a problem, and it is an object of the present invention to obtain a power conversion device capable of obtaining a three-level AC voltage and reducing power loss generated in a freewheeling diode. Objective.

  The present invention is connected in series with the same polarity, connected between the positive terminal and the negative terminal to which a DC voltage is applied, the AC terminal to which an AC voltage is applied, and the positive terminal and the negative terminal. The first and second capacitors, the first and second switching elements connected between the positive electrode terminal and the negative electrode terminal, connected in series with the same polarity, and the first and second switching elements thereof A first series body composed of first and second free-wheeling diodes connected in antiparallel to each of the elements, the AC terminal as a connection point of the first and second switching elements, and the first Third and fourth switching elements connected in series with opposite polarity and connected between the neutral point which is a connection point of the first and second capacitors, and each of the third and fourth switching elements Connected in antiparallel to the second And a second series body composed of a fourth reflux diode, and the first and second reflux diodes included in the first series body and the second series body included in the second series body. The power converter is characterized in that the third and fourth freewheeling diodes have different voltage drop characteristics.

  The present invention is connected in series with the same polarity, connected between the positive terminal and the negative terminal to which a DC voltage is applied, the AC terminal to which an AC voltage is applied, and the positive terminal and the negative terminal. The first and second capacitors, the first and second switching elements connected between the positive electrode terminal and the negative electrode terminal, connected in series with the same polarity, and the first and second switching elements thereof A first series body composed of first and second free-wheeling diodes connected in antiparallel to each of the elements, the AC terminal as a connection point of the first and second switching elements, and the first Third and fourth switching elements connected in series with opposite polarity and connected between the neutral point which is a connection point of the first and second capacitors, and each of the third and fourth switching elements Connected in antiparallel to the second And a second series body composed of a fourth reflux diode, and the first and second reflux diodes included in the first series body and the second series body included in the second series body. Since the power converter is characterized in that the third and fourth freewheeling diodes have different voltage drop characteristics, a three-level AC voltage can be obtained, and power loss generated in the freewheeling diode can be reduced.

It is a circuit diagram which shows the main circuit of the power converter device which concerns on Embodiment 1 of this invention. FIG. 4 is a circuit diagram showing first to third switching states of the main circuit of FIG. 1. FIG. 7 is a circuit diagram showing fourth to sixth switching states of the main circuit of FIG. 1. FIG. 3 is a circuit diagram showing a current path during a first to second dead time period of the main circuit of FIG. 1. FIG. 6 is a circuit diagram illustrating a current path during a fourth to fifth dead time period of the main circuit of FIG. 1. It is the figure which showed an example of the simulation result of the power converter device which concerns on Embodiment 1 of this invention. It is the figure which showed an example of the characteristic of the switching element and freewheeling diode which are used for the power converter device which concerns on Embodiment 1 of this invention. It is an example of the simulation result of the power converter device which concerns on Embodiment 2 of this invention. It is a circuit diagram which shows an example which made the main circuit of the power converter device which concerns on Embodiment 1 of this invention the three-phase structure.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a main circuit of the power conversion device according to Embodiment 1 of the present invention. In the power conversion device according to Embodiment 1 of the present invention, as shown in FIG. 1, a capacitor 11 and a capacitor 12 are connected in series with the same polarity, a positive electrode terminal P as a positive electrode, a negative electrode terminal N as a negative electrode, and a neutral A terminal C is formed at the point. The positive electrode terminal P and the negative electrode terminal N are terminals to which a DC voltage is applied, and constitute a DC voltage source that applies a three-level potential (P point, neutral point, N point). The positive terminal P is, for example, a high potential terminal that gives a positive potential, the negative terminal N is a potential that is lower than the potential of the positive terminal P, for example, a low potential terminal that gives a negative potential, and the neutral point terminal C is This is an intermediate potential terminal that applies an intermediate potential between the potential of the positive terminal P and the potential of the negative terminal N. Further, as shown in FIG. 1, between the positive electrode terminal P and the negative electrode terminal N, the switching element 1 and the switching element 2 are connected in series with the same polarity. A first series body configured by connecting freewheeling diodes 1D and 2D in reverse parallel is connected. In addition, an AC terminal A for taking out an AC voltage is provided at a connection point where the switching element 1 and the switching element 2 are connected. Between the AC terminal A and the terminal C, the switching element 3 and the switching element 4 are connected in series with reverse polarity, and further, the free-wheeling diodes 3D and 4D are connected in antiparallel to the switching elements 3 and 4, respectively. The 2nd serial body comprised as mentioned above is connected. Hereinafter, for convenience, the switching elements 1 and 2 and the freewheeling diodes 1D and 2D are referred to as “bridge side” elements, and the switching elements 3 and 4 and the freewheeling diodes 3D and 4D are referred to as “neutral point side” elements.

  In the following description, it is assumed that the switching elements 1 to 4 are unipolar elements such as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and JFET (Junction Gate Field-Effect Transistor). Further, it is assumed that the free-wheeling diodes 1D to 4D are Schottky barrier diodes, PiN diodes, or parasitic diodes that are parasitic on the switching elements 1 to 4.

  In the power conversion device according to the first embodiment, it is assumed that the switching elements 1 to 4 are unipolar elements that can energize currents in both directions. In this case, current flows mainly through the freewheeling diodes 1D to 4D, and power loss occurs in the freewheeling diodes 1D to 4D. As the switching frequency increases in recent years, the proportion of dead time in the switching cycle increases. Therefore, in order to reduce the size and increase the efficiency of power converters in the future, Although a reduction in loss is essential, this can be realized by the present invention.

  The circuit of FIG. 1 used in the power conversion device according to the first embodiment has an average power flow direction from the DC side to the AC side. Therefore, in the power conversion device, the DC power is converted to AC power. It is assumed that the operation time for converting to AC is longer than the operation time for converting AC power to DC power. Further, regarding the voltage drop of the freewheeling diode when the average current or the rated current handled by the power converter is applied, the freewheeling diodes 1D and 2D on the bridge side and the freewheeling diodes 3D and 4D on the neutral point side have different voltage drops. It has the characteristics. Specifically, the first embodiment is characterized in that the voltage drop of the freewheeling diodes 3D and 4D on the neutral point side is smaller than the voltage drop of the freewheeling diodes 1D and 2D on the bridge side. Here, the voltage drop is a voltage drop of the freewheeling diode when an average current or a rated current handled by the power converter is applied.

  Note that the power conversion circuit according to Embodiment 1 of the present invention has a DC / AC or vice versa between a DC three terminal (positive terminal P, neutral point terminal C, negative terminal N) and an AC terminal A. This is a three-level power conversion circuit that can convert a three-level AC voltage. In the power conversion circuit of the present invention, the three-level potential provided by the three DC terminals (the positive terminal P, the neutral point terminal C, and the negative terminal N) is caused to appear at the AC terminal A sequentially, and the three-level AC voltage is generated. obtain. As a method for obtaining a three-level AC voltage, according to whether the voltage command value V_ref is positive or negative, a conduction command is given to at least one of the switching elements 1 to 4 to turn on / off each of the switching elements 1 to 4. By switching, a three-level AC voltage can be obtained.

  Hereinafter, both the voltage between the positive terminal P and the terminal C and the voltage between the terminal C and the negative terminal N are Vdc, the terminal C is a reference potential, and the potential of the AC terminal A is an output voltage Vout.

  FIG. 2 illustrates a switching pattern when the output voltage Vout is a positive voltage. In FIG. 2A, the switching elements 1 and 2 are off, the switching elements 3 and 4 are on, and the output voltage Vout is zero. In FIG. 2B, the switching elements 1 and 4 are on, the switching elements 2 and 3 are off, and the output voltage Vout is Vdc. Therefore, when the voltage command value V_ref is a positive voltage, the average voltage of the output voltage Vout is set to a voltage in the range of 0 to Vdc by controlling the time ratio between the states of FIG. 2 (a) and FIG. 2 (b). The command value V_ref can be followed. Actually, when switching between FIG. 2A and FIG. 2B, the state shown in FIG. 2C (that is, the switching element 4 is turned on and switched) in an infinitely short time with respect to the switching cycle. Element 1, 2, 3 is turned off).

  FIG. 3 illustrates a switching pattern when the output voltage Vout is a negative voltage. In FIG. 3D, the switching elements 1 and 2 are off, the switching elements 3 and 4 are on, and the output voltage Vout is zero. In FIG. 3E, the switching elements 1 and 4 are off, the switching elements 2 and 3 are on, and the output voltage Vout is -Vdc. Therefore, when the voltage command value V_ref is a negative voltage, the average voltage of the output voltage Vout is set to a voltage in the range from −Vdc to 0 by controlling the time ratio between the states of FIG. 3D and FIG. The command value V_ref can be followed. Actually, when switching between FIG. 3D and FIG. 3E, the state shown in FIG. 3F (that is, the switching element 3 is turned on and switched) in an infinitely short time with respect to the switching cycle. The switching operation is performed via the elements 1, 2, and 4).

  The reason why switching is performed via the states shown in FIG. 2C and FIG. 3F, which is called the dead time, is that the capacitors 11 and 12 are short-circuited due to characteristic variations of the switching elements when switching the switching state. This is to prevent it from being done.

  4 (g) and 4 (h) indicate the current paths in the dead time period (FIG. 2 (c)) when the voltage command value V_ref is a positive voltage by bold lines. When the output current Iout is in the direction of flowing out from the AC terminal A in the direction of the load (not shown), the positive current is used. Conversely, when the output current Iout is in the direction of flowing into the AC terminal A from the load (not shown). It will be described as a negative current. FIG. 4G shows a case where the output current Iout is a positive current, and FIG. 4H shows a case where the output current Iout is a negative current. As shown in FIG. 4G, when the output current Iout is a positive current, the freewheeling diode 3D becomes conductive. On the other hand, as shown in FIG. 4H, when the output current Iout is a negative current, the freewheeling diode 1D is turned on.

  On the other hand, FIG. 5 (i) and FIG. 5 (j) show current paths in the dead time period (FIG. 3 (f)) when the voltage command value V_ref is a negative voltage. FIG. 5 (i) shows a case where the output current Iout is a positive current, and FIG. 5 (j) shows a case where the output current Iout is a negative current. As shown in FIG. 5I, when the output current Iout is a positive current, the freewheeling diode 2D is turned on. On the other hand, as shown in FIG. 5 (j), when the output current Iout is a negative current, the freewheeling diode 4D is turned on.

  Therefore, when the voltage command value V_ref or the output voltage Vout and the output current Iout are of the same polarity, the freewheeling diode 3D or 4D is conductive, and when the voltage command value V_ref or the output current Iout is different, the freewheeling diode 1D or 2D is conductive.

  FIG. 6 shows a simulation result when electric power is transmitted from the DC side to the AC side and the power factor of the output voltage Vout and the output current Iout is approximately 1. The voltage command value V_ref is given as a sine wave having an effective value of 115.5 V, and an output voltage Vout in which the average voltage of one period of switching follows V_ref is output at three levels. The DC voltage Vdc is 175V. The output current Iout is a voltage command value Vref or a sine wave current having substantially the same phase as the output voltage Vout and an effective value of 25A.

  Currents that flow through the switching elements 1, 2, 3, and 4 are I_1, I_2, I_3, and I_4, respectively, and currents that flow through the freewheeling diodes 1D, 2D, 3D, and 4D are I_1D, I_2D, I_3D, and I_4D. The direction from the drain to the source is the positive direction for the current of the switching elements 1, 2, 3, 4 and the direction from the anode to the cathode is the positive direction for the current of the freewheeling diodes 1D, 2D, 3D, and 4D.

  According to FIG. 6, the currents I_1D and I_2D flowing in the freewheeling diodes 1D and 2D on the bridge side are substantially 0, whereas the currents I_3D and I_4D flowing in the freewheeling diodes 3D and 4D on the neutral point side are in the dead time period. The current value corresponds to the output current Iout. This is because when the output voltage Vout and the output current Iout have the same polarity as described with reference to FIGS. 4 and 5, the current always flows through the free-wheeling diode 3D or 4D on the neutral point side during the dead time period.

  In the simulation, the power factor is approximately 1 as an example. However, when the power factor is approximately 1, the voltage and current are completely the same polarity (or different polarity in the case of the second embodiment). As a result, the present invention becomes more effective. Even when the power factor is other than approximately 1, when power is transmitted from the DC side to the AC side, the period in which the output voltage Vout and the output current Iout have the same polarity is longer than the period in which the polarity is different. Therefore, the currents I_3D and I_4D flowing through the neutral point freewheeling diode are larger than the currents I_1D and I_2D flowing through the freewheeling diode on the bridge side. Therefore, regarding the voltage drop of the freewheeling diode that has passed the average current or the rated current handled by the power converter, the voltage drop of the freewheeling diodes 3D and 4D on the neutral point side is lower than the voltage drop of the freewheeling diodes 1D and 2D on the bridge side. If the selection is made to be smaller, the loss will be low. In order to make the voltage drop of the freewheeling diodes different, for example, the chip areas of the freewheeling diodes 1D and 2D may be different from the chip areas of the freewheeling diodes 3D and 4D. When the switching elements 1 to 4 and the freewheeling diodes 1D to 4D are provided in the same module, the chip area of the freewheeling diodes 1D and 2D with respect to the total area of the switching elements 1 and 2 and the freewheeling diodes 1D and 2D on the bridge side The ratio (occupancy ratio) may be different from the ratio (occupancy ratio) of the chip area of the free-wheeling diodes 3D and 4D to the total area of the switching elements 3 and 4 and the free-wheeling diodes 3D and 4D on the neutral point side. Alternatively, one of the freewheeling diodes on the bridge side and the neutral point side may be constituted by a parasitic diode of the switching element, and the other freewheeling diode may be an external freewheeling diode. Alternatively, the freewheeling diode on the bridge side and the freewheeling diode on the neutral point side may be composed of different types of diodes.

  In the above simulation, a unipolar element that allows current to flow bidirectionally through the switching element is assumed, but a bipolar element such as an IGBT (Insulated Gate Bipolar Transistor) that allows current to flow only in one direction is used. However, if the dead time is more dominant in the conduction loss of the return diode, the same effect can be obtained. In particular, if the direction of power is from direct current to alternating current and the power factor is close to 1, the current flowing through the freewheeling diode during the period other than the dead time is extremely small.

  In the above simulation, it is assumed that the voltage drop of the switching element is sufficiently smaller than the voltage drop of the freewheeling diode, and no current flows through the freewheeling diode when the switching element is on. FIG. 7 shows, as an example, the relationship between the voltage drop and the current of the MOSFET used for the switching element, the Schottky barrier diode used for the freewheeling diode, and the parasitic diode of the MOSFET. A unipolar element typified by a MOSFET functions as a resistor in the on state, so that the voltage drop at 0 A is approximately 0 V, whereas the diode voltage drop is a voltage drop equal to or higher than a voltage value called a saturation voltage. In the case of FIG. 7, the saturation voltage of the Schottky barrier diode is approximately 0.8V, and the saturation voltage of the parasitic diode of the MOSFET is approximately 2.6V. Usually, when the purpose is to reduce the loss, the on-resistance of the MOSFET is set sufficiently small, so that even if a shunt occurs, the current flowing through the MOSFET is dominant. That is, when each of the switching elements 1 to 4 is turned on, the rated current of the power converter is set in a direction in which the free wheel diodes 1D to 4D corresponding to the switching elements 1 to 4 (connected in antiparallel) are conducted. In the case of current flow, the current diverted to the switching elements 1 to 4 is larger than the current diverted to the freewheeling diodes 1D to 4D. Therefore, the effects described in the present embodiment can be obtained even when a diversion occurs.

  As described above, according to the first embodiment, between the positive terminal P and the negative terminal N to which a DC voltage is applied, the AC terminal A to which an AC voltage is applied, and between the positive terminal P and the negative terminal N. The first and second capacitors 11 and 12 connected in series with the same polarity and connected in series with each other, and connected between the positive terminal P and the negative terminal N, and connected in series with the same polarity. A first series body composed of first and second free-wheeling diodes 1D and 2D connected in antiparallel to the second switching elements 1 and 2 and the switching elements 1 and 2, respectively. 2 is connected between the AC terminal A, which is the connection point of the switching elements 1 and 2, and the neutral point terminal C, which is the connection point of the first and second capacitors 11, 12, and is connected in series with the opposite polarity. Third and fourth switching elements 3, 4 and switches A second series body composed of third and fourth free-wheeling diodes 3D and 4D connected in antiparallel to each of the switching elements 3 and 4, and first and second free-wheeling diodes 1D and 2D, The third and fourth free-wheeling diodes 3D and 4D have different voltage drop characteristics. Specifically, since the power conversion device according to the first embodiment assumes a long operation time for converting DC power to AC power, the voltage drop of the first and second freewheeling diodes 1D and 2D is reduced. The third and fourth free-wheeling diodes 3D and 4D are configured to be larger than the voltage drop. As a result, the power conversion device according to the first embodiment can obtain a three-level AC voltage, reduce the power loss generated in the freewheeling diode, and improve the efficiency and size of the entire power conversion device. be able to.

Embodiment 2. FIG.
Hereinafter, a power converter according to Embodiment 2 of the present invention will be described. The circuit of the power conversion device according to the second embodiment has the same circuit configuration as that of FIG. 1 shown in the first embodiment. Therefore, here, reference is made to FIG. 1 of Embodiment 1 and the description thereof, and detailed description thereof is omitted. However, in the second embodiment, contrary to the first embodiment, the average power flow is in the direction from the AC side to the DC side, and therefore the operation time for converting AC power to DC power is It is assumed that the operation time is longer than the operation time for converting DC power to AC power. Further, regarding the voltage drop of the freewheeling diode when the average current or the rated current handled by the power converter is applied, the voltage drop of the freewheeling diodes 1D and 2D on the bridge side is higher than that of the freewheeling diodes 3D and 4D on the neutral point side. It is characterized by being smaller than the voltage drop. Other configurations and operations are the same as those in the first embodiment.

  FIG. 8 shows a simulation result in a state where the power flow is in the direction from the AC side to the DC side and the power factor of the output voltage Vout and the output current Iout is approximately 1. In this case, in contrast to FIG. 6, since the output voltage and the output current have different polarities, almost no current flows through the freewheeling diodes 3D and 4D, and current flows through the freewheeling diode 1D or 2D. Therefore, if the voltage drop of the freewheeling diodes 1D and 2D on the bridge side is made smaller than the voltage drop of the freewheeling diodes 3D and 4D on the neutral point side, low loss can be realized. In order to make the voltage drop of the freewheeling diodes different, for example, the chip areas of the freewheeling diodes 1D and 2D may be different from the chip areas of the freewheeling diodes 3D and 4D. When the switching elements 1 to 4 and the freewheeling diodes 1D to 4D are provided in the same module, the chip area of the freewheeling diodes 1D and 2D with respect to the total area of the switching elements 1 and 2 and the freewheeling diodes 1D and 2D on the bridge side The ratio (occupancy ratio) may be different from the ratio (occupancy ratio) of the chip area of the free-wheeling diodes 3D and 4D to the total area of the switching elements 3 and 4 and the free-wheeling diodes 3D and 4D on the neutral point side. In addition, either the freewheeling diode on the bridge side or the neutral point side may be composed of a parasitic diode of the switching element, and the other freewheeling diode may be composed of an external freewheeling diode, or Different types of diodes on the neutral point side may be used as the freewheeling diode.

  In addition, when a bipolar element that allows current to flow only in one direction is used as the switching element, the negative current portions of the currents I_1 and I_2 of the switching element flow to the freewheeling diodes 1D and 2D. Since 1D and 2D have the characteristic that a voltage drop is small, they become a low loss.

  As described above, according to the second embodiment, between the positive terminal P and the negative terminal N to which a DC voltage is applied, the AC terminal A to which an AC voltage is applied, and between the positive terminal P and the negative terminal N. The first and second capacitors 11 and 12 connected in series with the same polarity and connected to each other in series, and connected between the positive terminal P and the negative terminal N and connected in series with the same polarity. First and second switching elements 1 and 2 and first and second free-wheeling diodes 1D and 2D connected in antiparallel to first and second switching elements 1 and 2, respectively. Connected between the series body and an AC terminal A, which is a connection point between the first and second switching elements 1 and 2, and a neutral point terminal C, which is a connection point between the first and second capacitors 11 and 12. And the third and fourth switching elements 3 connected in series with opposite polarity 4 and a second series body composed of freewheeling diodes 3D and 4D connected in antiparallel to each of the third and fourth switching elements, and first and second freewheeling diodes 1D and 2D, The third and fourth free-wheeling diodes 3D and 4D have different voltage drop characteristics. Specifically, in Embodiment 2, since it is assumed that the operation time for converting AC power to DC power is long, the voltage drop of the first and second freewheeling diodes 1D and 2D is The voltage drop of the third and fourth freewheeling diodes 3D and 4D was made smaller. As a result, as in the first embodiment, a three-level AC voltage can be obtained, power loss generated in the freewheeling diode can be reduced, and the entire power conversion device can be made highly efficient and downsized. .

  In the first and second embodiments described above, the single-phase configuration shown in FIG. 1 is shown as an example. However, the configuration is not limited to this, and a three-phase configuration may be used as shown in FIG. That is, the switching element 1 of FIG. 1 is composed of three switching elements 1U, 1V, and 1W in FIG. 9, and the switching element 2 of FIG. 1 is composed of three switching elements 2U, 2V, and 2W in FIG. Similarly, the switching element 3 in FIG. 1 includes three switching elements 3U, 3V, and 3W in FIG. 9, and the switching element 4 in FIG. 1 includes three switching elements 4U, 4V, and 4W in FIG. ing. In the configuration of FIG. 9 as well, as in FIG. 1, one free-wheeling diode is connected in antiparallel to each switching element. Also in the configuration of FIG. 9, as in the first and second embodiments, the voltage drop characteristics of the freewheeling diode connected to the switching elements 1U, 1V, 1W and the switching elements 2U, 2V, 2W on the bridge side, and the neutral point The voltage drop characteristics of the freewheeling diodes connected to the switching elements 3U, 3V, 3W on the side and the freewheeling diodes connected to the switching elements 4U, 4V, 4W are different (that is, the voltage drop of the freewheeling diode on the bridge side is neutral) Smaller than the voltage drop of the freewheeling diode on the point side (or vice versa). Therefore, it goes without saying that the same effects as those of the first and second embodiments are obtained in this case.

  Note that the configuration of FIG. 9 will be described in more detail while supplementing. Capacitor 11 and capacitor 12 are connected in series with the same polarity, and positive electrode is formed as positive electrode terminal P, negative electrode is formed as negative electrode terminal N, and terminal C is formed at a neutral point. Between positive electrode terminal P and negative electrode terminal N, a series body in which switching elements 1U and 2U are connected in series with the same polarity, a series body in which switching elements 1V and 2V are connected in series with the same polarity, and switching element 1W and A total of three series bodies of 2W connected in series with the same polarity are connected. Further, an AC terminal U for taking out an AC voltage is provided at a connection point between the switching elements 1U and 2U, an AC terminal V for taking out an AC voltage is provided at a connection point between the switching elements 1V and 2V, and the switching element 1W and An AC terminal W for taking out an AC voltage is provided at a connection point of 2W. Further, switching elements 3U and 4U are connected in series with reverse polarity between AC terminal U and terminal C, and switching elements 3V and 4V are connected in series with reverse polarity between AC terminal V and terminal C. The switching elements 3W and 4W are connected in series with opposite polarity between the AC terminal W and the terminal C. Furthermore, free-wheeling diodes 1DU, 1DV, and 1DW are connected in antiparallel to switching elements 1U, 1V, and 1W, respectively, and free-wheeling diodes 2DU, 2DV, and 2DW are connected in antiparallel to switching elements 2U, 2V, and 2W, respectively. Has been. The switching elements 3U, 3V, and 3W are connected in reverse parallel to the free-wheeling diodes 3DU, 3DV, and 3DW, respectively. The switching elements 4U, 4V, and 4W are connected in reverse-parallel to the free-wheeling diodes 4DU, 4DV, and 4DW, respectively. Has been. As described above, the configuration of FIG. 9 is obtained by changing the single-phase configuration shown in FIG. 1 into a three-phase configuration, and basically has the same circuit configuration.

  In addition, when connecting to a system | strain power supply (not shown), it connects via a reactor (not shown) etc.

  In the description of the first and second embodiments, the semiconductor material constituting the semiconductor element used for the switching elements 1 to 4 and the free wheel diodes 1D to 4D is not particularly limited, but generally silicon can be used. .

  Further, as another semiconductor material, a wide band gap semiconductor material having a larger band gap than silicon may be used. Examples of the wide band gap semiconductor include silicon carbide, a gallium nitride-based material, and diamond.

  When a wide bandgap semiconductor is used, the power loss of the switching element and the freewheeling diode can be reduced compared with the case of using silicon, so that the switching element is highly efficient while maintaining the above-described effects of the present invention. In addition, since it is possible to reduce the power loss of the return diode during the dead time, it is possible to increase the efficiency of the entire power converter.

  In addition, switching elements and freewheeling diodes formed of wide bandgap semiconductors have high voltage resistance and high allowable current density, so that the switching elements and freewheeling diodes can be miniaturized. By using a freewheeling diode, it is possible to reduce the size of a power conversion device incorporating these elements.

  In addition, wide bandgap semiconductor elements have high heat resistance, so they can operate at high temperatures, and heat sink fins can be downsized and water cooling units can be air cooled. Is possible.

  In addition, since the switching element formed of a wide band gap semiconductor can perform high-speed switching, the switching frequency can be increased. In that case, since the ratio of the dead time to a switching period increases, this invention becomes more effective.

  It is desirable that both the switching element and the free wheel diode are formed of a wide band gap semiconductor, but only one of the switching element and the free wheel diode may be formed of a wide band gap semiconductor. Even in this case, the effects described in the first and second embodiments can be obtained.

  1, 2, 3, 4, 1U, 2U, 3U, 4U, 1V, 2V, 3V, 4V, 1W, 2W, 3W, 4W Switching elements, 1D, 2D, 3D, 4D, 1DU, 2DU, 3DU, 4DU, 1DV, 2DV, 3DV, 4DV, 1DW, 2DW, 3DW, 4DW Freewheeling diode, 11, 12 capacitor, A AC terminal, C neutral point terminal, I_1, I_2, I_3, I_4 Current flowing through the switching element, I_1D, I_2D, I_3D, I_4D Current flowing through the freewheeling diode, Iout output current, N negative terminal, P positive terminal, U, V, W AC terminal, Vdc DC voltage, Vout output voltage, V_ref voltage command value.

Claims (10)

A positive terminal and a negative terminal to which a DC voltage is applied;
An AC terminal to which an AC voltage is applied;
First and second capacitors connected in series with the same polarity, connected between the positive terminal and the negative terminal;
The first and second switching elements connected between the positive electrode terminal and the negative electrode terminal and connected in series with the same polarity and each of the first and second switching elements are connected in antiparallel. A first series body composed of first and second free-wheeling diodes;
A first terminal connected between the AC terminal, which is a connection point of the first and second switching elements, and a neutral point, a connection point of the first and second capacitors, and connected in series with a reverse polarity. A second series body composed of three and fourth switching elements and third and fourth free-wheeling diodes connected in antiparallel to each of the third and fourth switching elements,
The first and second freewheeling diodes included in the first series body and the third and fourth freewheeling diodes included in the second series body have different voltage drop characteristics. Power conversion device. A power conversion device that converts DC power to AC power,
A voltage drop of the first and second freewheeling diodes included in the first series body is larger than a voltage drop of the third and fourth freewheeling diodes included in the second series body. The power conversion device according to claim 1. A power conversion device that converts AC power into DC power,
A voltage drop of the first and second freewheeling diodes included in the first series body is smaller than a voltage drop of the third and fourth freewheeling diodes included in the second series body. The power conversion device according to claim 1.   The power conversion device according to claim 1, wherein the power conversion device operates at a power factor of approximately 1. 5.   The first and second free-wheeling diodes included in the first series body and the third and fourth free-wheeling diodes included in the second series body are composed of different types of diodes. The power conversion device according to any one of claims 1 to 4, wherein the power conversion device is characterized. The first, second, third and fourth switching elements are composed of unipolar elements;
When the rated current of the power converter is passed in the direction in which the free-wheeling diode connected in antiparallel with the switching element is turned on when each switching element is turned on, from the current shunted to the free-wheeling diode 6. The power conversion device according to claim 1, wherein a current shunted to the switching element is larger.   The chip areas of the first and second freewheeling diodes included in the first series body and the chip areas of the third and fourth freewheeling diodes included in the second series body are different. The power conversion device according to claim 1, wherein the power conversion device is a power conversion device.   Of the freewheeling diode included in the first serial body and the freewheeling diode included in the second serial body, the freewheeling diode included in either one of the serial bodies is composed of only a parasitic diode parasitic to the switching element, The power conversion device according to any one of claims 1 to 7, wherein the freewheeling diode included in the other series body includes a diode other than the parasitic diode parasitic on the switching element.   At least one of the first, second, third and fourth switching elements and the semiconductor elements constituting the first, second, third and fourth free-wheeling diodes is formed of a wide band gap semiconductor material. The power converter according to claim 1, wherein the power converter is provided.   The power converter according to claim 9, wherein the wide band gap semiconductor material is any one of silicon carbide, a gallium nitride-based material, and diamond.

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