JP2012253927A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-level power converter having 5 or more levels in which a circuit structure of an inverter is simplified and a wiring inductance having adverse effect on the voltage surge of a semiconductor switching element during current interruption operation can be reduced.SOLUTION: A power converter comprises: a capacitor arm 12 which serially connects four capacitors in parallel with a first switching arm 13 serially connecting eight switching devices; and a second switching arm 14 which serially connects two switching devices between a junction of second stage with third stage of the first switching arm 13 and a junction of sixth stage with seventh stage of the first switching arm 13. DC power supply is connected to both upper and lower ends of the capacitor arm 12 so that an intermediate point of the second switching arm 14 works as an AC output point.

Description

  Embodiments described herein relate generally to a power converter that converts direct current into three-phase alternating current.

  Conventionally, a motor drive that converts a direct current into an alternating current to control a three-phase induction motor at a variable speed, and a converter power conversion device that serves as a direct current power source for an inverter that converts a three-phase alternating current into a direct current and converts the direct current into an alternating current, Three-phase two-level inverters have been applied. Since the three-phase two-level inverter is composed of six semiconductor switching elements that are the minimum necessary for configuring a power converter that outputs three-phase alternating current from direct current, it is possible to reduce the size and cost.

  On the other hand, when the input DC voltage is Vdc, the output voltage waveform is switched between binary values of + Vdc / 2 and -Vdc / 2 for each phase by PWM (pulse width modulation), and pseudo-AC It is a generated waveform, and it uses a high withstand voltage switching frequency and cannot increase the PWM switching frequency, a high voltage motor drive connected to the power distribution system, or for stabilizing the power distribution system In reactive power compensators and the like, electromagnetic noise caused by switching harmonics sometimes becomes a problem. In distribution system connection equipment, a filter consisting of a reactor and a capacitor is inserted at the three-phase AC end so that the harmonics flowing out to the distribution system are below the regulation value, but the capacity of the reactor and the capacitor is large. This has led to cost increases and weight increases.

  On the other hand, a three-level inverter, a five-level inverter, and the like have begun to be studied so that the output voltage waveform is closer to a sine wave by devising the power converter topology. The diode clamp type 5-level inverter is more effective in reducing electromagnetic noise because the output waveform is closer to a sine wave than the 2-level inverter and 3-level inverter, and 3 when applied to equipment connected to the power distribution system. Cost reduction and weight reduction can be achieved by reducing the phase AC output reactor capacity.

JP 2009-219265 A

  However, the diode-clamped 5-level inverter creates a 5-level output voltage, which complicates the circuit configuration and makes it impossible to reduce the wiring inductance of the circuit in terms of component mounting. There is a concern that the voltage jump at the time becomes large and the voltage rating of the semiconductor switching element is exceeded and the element is destroyed. Or, in order to absorb the voltage jumping energy, it is necessary to newly add a snubber auxiliary circuit composed of components such as a resistor, a capacitor, and a diode, which may increase the cost and size of the inverter.

  Embodiments of the present invention provide a multi-level power converter of 5 levels or more that can simplify the circuit configuration of an inverter and reduce the wiring inductance that adversely affects the voltage jump during the current interruption operation of the semiconductor switching element.

  According to the embodiment of the present invention, a power conversion device that converts direct current into three-phase alternating current, comprising a switching element having a self-extinguishing capability and a diode connected in reverse parallel to the switching element. A first switching arm having a plurality of switching devices connected in series; A capacitor arm in which four capacitors are connected in series with the first switching arm; and a connection point between the fourth stage and the fifth stage from the top of the first switching arm and the top of the capacitor arm. A connection point between the second stage and the third stage is short-circuited with a connection wiring. The connection point between the first and second stages from the top of the first switching arm and the connection point between the first and second stages from the top of the capacitor arm are connected from the capacitor arm side to the first switching arm side. A first diode is connected in a direction in which a current flows through the first switching arm; a connection point between the third stage and the fourth stage from the top of the first switching arm; and a first stage and a second stage from the top of the capacitor arm. A second diode is connected to the connection point in a direction in which current flows from the first switching arm side to the capacitor arm side, and the connection point between the fifth stage and the sixth stage from the top of the first switching arm and the capacitor Connect a third diode from the capacitor arm side to the first switching arm side at the connection point between the third stage and the fourth stage from the top of the arm. The fourth diode in the direction in which current flows from the first switching arm side to the capacitor arm side at the connection point between the seventh stage and the eighth stage and the connection point between the third stage and the fourth stage from the top of the capacitor arm. Connect. Further, two switching devices include a connection point between the second and third stages from the top of the first switching arm and a connection point between the sixth and seventh stages from the top of the first switching arm. Are connected in series, a DC power source is connected to the upper and lower ends of the capacitor arm, and an intermediate point of the second switching arm is operated as an AC output point.

The lineblock diagram of an example of the power converter concerning a 1st embodiment of the present invention. The wave form diagram which shows an example at the time of setting it as the output voltage approximated to the sine wave by combining the level of the output voltage of the power converter device which concerns on 1st Embodiment of this invention. FIG. 6 is an explanatory diagram of current paths of switching states of the switching devices Su1, Su2, and Su3 when the output voltage is switched from + Vdc / 4 to + Vdc / 2 in the power conversion device according to the embodiment of the present invention. The lineblock diagram of other examples of the power converter concerning a 1st embodiment of the present invention. The block diagram which shows an example of the power converter device which concerns on 2nd Embodiment of this invention. The block diagram which shows an example of the power converter device which concerns on 3rd Embodiment of this invention. The block diagram which shows another example of the power converter device which concerns on 3rd Embodiment of this invention. The block diagram which shows an example of the power converter device which concerns on 4th Embodiment of this invention.

  Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram of an example of a power conversion apparatus according to the first embodiment of the present invention. The power conversion device according to the first embodiment is an inverter that converts direct current into three-phase alternating current, and is a power conversion device that outputs a voltage of 5 levels in each phase. The direct current obtained by the converter 11 is input to the switching arms 13U, 13V, and 13W of the U-phase, V-phase, and W-phase via the capacitor arm 12 composed of four capacitors C1 to C4, and the three-phase. Converted to alternating current. Since the switching arms 13U, 13V, and 13W have the same configuration, the switching arm 13U will be described.

  The U-phase first switching arm 13U is configured by connecting eight switching devices Su1 to Su8 in series. A first diode Ddu1 is connected between the lower end of the switching device Su1 and the lower end of the capacitor C1 so that conduction from the capacitor C1 to the switching device Su1 is possible. Similarly, a second diode Ddu2 is connected between the lower end of the switching device Su3 and the lower end of the capacitor C1 so that conduction from the switching device Su3 to the capacitor C1 is possible.

  Further, a third diode Ddu3 is connected between the lower end of the switching device Su5 and the lower end of the capacitor C3 so that conduction from the capacitor C3 to the switching device Su5 is possible, and the lower end of the switching device Su7 and the capacitor C3 Between the lower ends, a fourth diode Ddu4 is connected so that conduction from the switching device Su7 to the capacitor C3 is possible.

  Then, the lower end of the switching device Su2 and the lower end of the switching device Su6 are connected by two switching devices Su9 and Su10 to form a second switching arm 14U. That is, the second switching arm 14U has a connection point between the second and third stages from the top of the first switching arm 13U and a connection between the sixth and seventh stages from the top of the first switching arm. The point is formed by connecting in series with two switching devices Su9 and Su10. A U-phase AC output point is drawn from the connection point of the switching devices Su9 and Su10 of the second switching arm 14U. The V phase and the W phase have the same configuration.

Next, the correlation between the output voltage and the on / off state of each switching device will be described. Table 1 is a table showing the correlation between the on / off state of each switching device of the power conversion apparatus shown in FIG. 1 and the output voltage.

  Now, assuming that the intermediate point of the capacitor arm 12, that is, the connection point between the capacitor C2 and the capacitor C3 is the point of the ground point (= potential zero) and the voltage across the capacitor arm 12 is Vdc, the output voltage is + Vdc / 2. , + Vdc / 4, 0, -Vdc / 4, and -Vdc / 2 can be output in five levels.

  When it is desired to output the output voltage + Vdc / 2, as shown in Table 1, the switching device Su1 is turned on, the switching device Su2 is turned on, the switching device Su3 is turned off, the switching device Su4 is turned off, the switching device Su5 is turned off, and the switching device The switching devices Su1 to Su10 are controlled by a combination of switching states in which Su6 is turned off, the switching device Su7 is turned off, the switching device Su8 is turned off, the switching device Su9 is turned on, and the switching device Su10 is turned off.

  When it is desired to output the output voltage + Vdc / 4, the switching device Su1 is turned off, the switching device Su2 is turned on, the switching device Su3 is turned on, the switching device Su4 is turned off, the switching device Su5 is turned off, the switching device Su6 is turned off, and the switching device Su7 Is switched off, the switching device Su8 is turned off, the switching device Su9 is turned on, and the switching device Su10 is turned off to control the switching device.

  Next, when the output voltage 0 is desired to be output, one of the following two switching states can be selected. Each switching state with the smallest switching count is selected taking into account the transition to the next switching state.

  In the first switching state, the switching device Su1 is turned off, the switching device Su2 is turned off, the switching device Su3 is turned on, the switching device Su4 is turned on, the switching device Su5 is turned off, the switching device Su6 is turned off, and the switching device Su7 is turned off. The switching device is controlled by a combination of switching states in which the switching device Su8 is turned off, the switching device Su9 is turned on, and the switching device Su10 is turned off.

  The second switching state includes switching device Su1 off, switching device Su2 off, switching device Su3 off, switching device Su4 off, switching device Su5 on, switching device Su6 on, switching device Su7 off, The switching device is controlled by a combination of switching states in which the switching device Su8 is turned off, the switching device Su9 is turned off, and the switching device Su10 is turned on.

  When the output voltage -Vdc / 4 is to be output, the switching device Su1 is turned off, the switching device Su2 is turned off, the switching device Su3 is turned off, the switching device Su4 is turned off, the switching device Su5 is turned off, and the switching device Su6 is turned on. The switching device is controlled by a combination of switching states in which the switching device Su7 is turned on, the switching device Su8 is turned off, the switching device Su9 is turned off, and the switching device Su10 is turned on.

  When it is desired to output the output voltage −Vdc / 2, the switching device Su1 is turned off, the switching device Su2 is turned off, the switching device Su3 is turned off, the switching device Su4 is turned off, the switching device Su5 is turned off, and the switching device Su6 is turned off. The switching device is controlled by a combination of switching states in which Su7 is turned on, switching device Su8 is turned on, switching device Su9 is turned off, and switching device Su10 is turned on. The same applies to the V phase and the W phase.

  FIG. 2 is a waveform showing an example in which these output voltages, + Vdc / 2, + Vdc / 4, 0, −Vdc / 4, and −Vdc / 2 are combined to obtain an output voltage approximated to a sine wave. FIG.

  Next, a case where the output voltage is switched from + Vdc / 4 to + Vdc / 2 in a state where current flows from the load to the power conversion device (inverter) will be described.

  FIG. 3 is an explanatory diagram of current paths of switching states of the switching devices Su1, Su2, and Su3 when the output voltage is switched from + Vdc / 4 to + Vdc / 2 in the power conversion device according to the embodiment of the present invention. As shown in FIG. 3A, in the state of outputting the output voltage + Vdc / 4, the current becomes a path E1 that flows from the load to the power source (converter) in the order of Su9, Su3, Ddu2, and C1. In this state, when switching to the output voltage + Vdc / 2, the path E2 flows from the load to the power source in the order of Su9, Su2, and Su1. In this case, Su3 cuts off the current for voltage level switching, but the voltage jump at this time depends on the wiring inductance of the current switching path E3. Therefore, in order to reduce the voltage jump, it is necessary to dispose the elements forming the path E3 close to each other so that the inductance of the path E3 is reduced.

  On the other hand, FIG. 3B is an explanatory diagram of a current path when the output voltage is switched from + Vdc / 4 to + Vdc / 2 in the conventional power converter. Similarly, in the conventional clamp diode type five-level inverter, when the output voltage is switched from + Vdc / 4 to + Vdc / 2, the current path E1 is switched to the current path E2. When this voltage level is switched, the fifth switching device Su5 from the top cuts off the current. Since the voltage jump at this time depends on the wiring inductance in the current switching path E3, it is necessary to dispose the elements forming the path E3 close to each other so that the inductance of the path E3 is similarly reduced.

  However, this path includes five switching devices and three clamp diodes, and even if they are arranged close to each other, there is a limit to reducing the wiring inductance. On the other hand, since the number of parts included in the path E3 in the circuit configuration of the embodiment of the present invention is small, a smaller wiring inductance can be achieved.

  In the above description, the switching devices Su9 and Su10 are each described as a single switching device. However, since the withstand voltage is twice as high as that of the switching devices Su1 to Su8, it is more than twice as high. It is necessary to prepare a withstand voltage element.

  Therefore, as shown in FIG. 4, the switching devices Su9 and Su10 are configured by two series switching devices Su9a, Su9b, Su10a, and Su10b, which are the same breakdown voltage elements as the switching devices Su1 to Su8. Thereby, the switching device used for a power converter device is unified, and it becomes possible to make a structure easier.

  According to the first embodiment, the connection point between the second stage and the third stage from the top of the first switching arm 13, and the sixth stage and the seventh stage from the top of the first switching arm 13 Since the second switching arm 14 is formed by connecting the two switching devices SU9 and Su10 in series with the connection point, the inductance of the current switching path formed at the time of voltage level switching can be made smaller.

  Next, a second embodiment of the present invention will be described. FIG. 5 is a configuration diagram illustrating an example of a power conversion apparatus according to the second embodiment of the present invention. In the second embodiment, a third switching arm 15 in which four switching devices Sc1 to Sc4 are connected in series is connected to the capacitor arm 12 in parallel to the first embodiment shown in FIG. A first reactor L1 that connects a connection point between the first stage and the second stage from above 12 and a connection point between the first stage and the second stage from above the third switching arm 15, and a capacitor arm 12 A second reactor L2 for connecting a connection point between the third stage and the fourth stage from the top and a connection point between the third stage and the fourth stage from the top of the third switching arm 15 is provided. The uppermost end of the switching arm 13U and the uppermost end of the capacitor arm 12 are connected, and the lowermost end of the first switching arm 13U and the lowermost end of the capacitor arm 12 are connected. The same elements as those in FIG. 4 are denoted by the same reference numerals, and redundant description is omitted.

  The third switching arm 15, the first reactor L1, and the second reactor L2 operate as a chopper circuit. Switching devices Sc1 and Sc2 and reactor L1 perform a switching operation so as to suppress voltage imbalance of capacitors C1 and C2. Similarly, the switching devices Sc3 and Sc4 and the reactor L2 perform a switching operation in order to suppress voltage imbalance of the capacitors C3 and C4.

  When the voltage of the capacitor C1 is larger than the voltage of the capacitor C2, the energy of the capacitor C1 is accumulated in the reactor L1 by turning on the switching device Sc1. Here, when the switching device Sc1 is turned off, the current flowing through the reactor L1 continues to flow through the capacitor C2 and the reverse conducting diode of the switching device Sc2, so that the capacitor C2 is charged.

  Conversely, when the voltage of the capacitor C2 is larger than the capacitor voltage C1, the energy of the capacitor C2 is stored in the reactor L1 by turning on the switching device Sc2. Here, when the switching device Sc2 is turned off, the current flowing through the reactor L1 continues to flow through the reverse conducting diode and the capacitor C1 of the switching device Sc2, so that the capacitor C1 is charged.

  In the first embodiment, if the capacitor capacity is not sufficiently large, the capacitor voltage may be unbalanced and operation may not be continued. In the second embodiment, however, the capacitor voltage unbalance is controlled in a controlled manner. Thus, the capacitance of the capacitor of the multilevel power conversion device can be reduced, and the size of the device can be reduced.

  Next, a third embodiment of the present invention will be described. FIG. 6 is a configuration diagram illustrating an example of a power conversion apparatus according to the third embodiment of the present invention. In the third embodiment, the second switching arm 14 is applied to a converter, and is a power converter that outputs a voltage of 5 levels for each phase.

  The direct current obtained by the switching arms 13U, 13V, and 13W of the U-phase, V-phase, and W-phase constituting the converter is transferred to the inverter 16 via the capacitor arm 12 that includes four capacitors C1 to C4. Entered. Since the U-phase, V-phase, and W-phase switching arms 13U, 13V, and 13W of the converter have the same configuration, the U-phase first switching arm 13U will be described below.

  The U-phase first switching arm 13U includes four switching devices Su1 to Su4 and four diodes Ddu5 to Ddu8 connected in series.

A first diode Ddu1 is connected between the lower end of the diode Ddu5 and the lower end of the capacitor C1 so that conduction from the capacitor C1 to the diode Ddu5 is possible. A second diode Ddu2 is connected between the lower end of the switching device Su1 and the lower end of the capacitor C1 so that conduction from the switching device Su1 to the capacitor C1 is possible. A third diode Ddu3 is connected between the lower end of the switching device Su3 and the lower end of the capacitor C3 so that conduction from the capacitor C3 to the switching device Su3 is possible. A fourth diode Ddu4 is connected between the lower end of the diode Ddu7 and the lower end of the capacitor C3 so that conduction from the switching device Su7 to the capacitor C3 is possible.

  The lower end of the diode Ddu6 and the lower end of the switching device Su4 are connected by two diodes Ddu9 and Ddu10 to form a second switching arm 14U. That is, the second switching arm 14U includes a connection point between the second stage and the third stage from the top of the first switching arm 13U, and a sixth stage and a seventh stage from the top of the first switching arm 13U. The connection point is formed in series by two diodes Ddu9 and Ddu10. The U-phase AC output point is drawn from the connection point of the diodes Ddu9 and Ddu10 of the second switching arm 14U. The V phase and the W phase have the same configuration.

Next, the correlation between the output voltage and the on / off state of each switching device will be described. Table 2 is a table showing the correlation between the ON / OFF state of each switching device of the power conversion device shown in FIG. 6 and the output voltage.

  Now, assuming that the intermediate point of the capacitor arm 12, that is, the connection point between the capacitor C2 and the capacitor C3 is the point of the ground point (= potential zero) and the voltage across the capacitor arm 12 is Vdc, the output voltage is + Vdc / 2. , + Vdc / 4, 0, -Vdc / 4, and -Vdc / 2 can be output in five levels.

  When it is desired to output the output voltage + Vdc / 2, as shown in Table 2, all the switching devices Su1 to Su4 are turned off. Since the AC voltage is positive and the AC current is positive, + Vdc / 2 is output by energizing the diode.

  When it is desired to output the output voltage + Vdc / 4, the switching device Su1 is turned on, the switching device Su2 is turned off, the switching device Su3 is turned off, and the switching device Su4 is turned off, and the switching device is controlled.

  When it is desired to output 0 output voltage, two switching states can be selected. Each switching state with the smallest switching count is selected taking into account the transition to the next switching state.

  In the first switching state, the switching device Su1 is turned on, the switching device Su2 is turned on, the switching device Su3 is turned off, and the switching device Su4 is turned off to control the switching device.

  In the second switching state (V4), the switching device is controlled by a combination of switching states of Su1 off, Su2 off, Su3 on, and Su4 on.

  When the output voltage -Vdc / 4 is desired to be output, the switching device Su1 is turned off, the switching device Su2 is turned off, the switching device Su3 is turned off, and the switching device Su4 is turned on to control the switching device.

  When it is desired to output the output voltage −Vdc / 2, all the switching devices Su1 to Su4 are turned off. Since the AC voltage is negative and the AC current is negative, -Vdc / 2 is output by energizing the diode. The same applies to the V phase and the W phase.

  According to the third embodiment, similarly to the first embodiment, it is possible to make the wiring inductance smaller in terms of mounting, and it is possible to reduce the number of switching devices used than in the first embodiment. Therefore, a low-harmonic rectifier circuit can be obtained at low cost.

  Although the diode Ddu9 and the diode Ddu10 forming the second switching arm 14 are each described as a single switching device, the withstand voltage is more than twice that of the diodes Ddu1 to Ddu8 because a double voltage is applied. It is necessary to prepare a high breakdown voltage element.

  Therefore, as shown in FIG. 7, the diodes Ddu9 and Ddu10 are configured by two series switching devices Ddu9a, Ddu9b, Ddu10a, and Ddu10b that are the same breakdown voltage elements as the diodes Ddu1 to Ddu8. Thereby, the switching device used for a power converter device is unified, and it becomes possible to make a structure easier.

  Next, a fourth embodiment of the present invention will be described. FIG. 8 is a configuration diagram illustrating an example of a power converter according to the fourth embodiment of the present invention. This fourth embodiment is different from the third embodiment shown in FIG. 7 in that the switching device Sc1 is provided in the first stage, the diodes Dc1 and Dc2 are provided in the second and third stages, and the switching device is provided in the fourth stage. The third switching arm 15 having Sc2 is connected in parallel to the capacitor arm 12, and the connection point between the first stage and the second stage from the top of the capacitor arm 12 and the first stage from the top of the third switching arm 15. A first reactor L1 that connects the connection points between the first and second stages, a connection point between the third and fourth stages from the top of the capacitor arm 12, and a third stage from the top of the third switching arm 12. A second reactor L2 for connecting the connection point with the fourth stage, the uppermost end of the first switching arm 13U and the uppermost end of the capacitor arm 12 are connected, and the first switching arm It is obtained by connecting the lowermost end of the lowermost and a capacitor arm 12. The same elements as those in FIG. 7 are denoted by the same reference numerals, and redundant description is omitted.

  The third switching arm 15, the first reactor L1, and the second reactor L2 operate as a chopper circuit. The switching device Sc1, the diode Dc1, and the first reactor L1 perform a switching operation so as to suppress voltage imbalance of the capacitors C1 and C2. Similarly, the switching device Sc2, the diode Dc2, and the second reactor L2 are switched to suppress voltage imbalance of the capacitors C3 and C4.

  When the voltage of the capacitor C1 is larger than the voltage of the capacitor C2, the energy of the capacitor C1 is accumulated in the first reactor L1 by turning on the switching device Sc1. Here, when the switching device Sc1 is turned off, the current flowing through the first reactor L1 continues to flow through the capacitor C2 and the diode Dc1, and as a result, the capacitor C2 is charged.

  The power conversion device (converter) of the third embodiment is limited to the rectification operation from AC to DC, and cannot convert from DC to AC in principle. Due to this, the balance between the capacitor C1 and the capacitor C2 is always smaller than the capacitor C1. Therefore, the capacitor C2 can be charged by the configuration of the fourth embodiment, and balance control of the capacitor can be achieved.

  If the capacitor capacity is not sufficiently large in the third embodiment, a capacitor voltage imbalance may occur and the operation may not be continued. However, according to the fourth embodiment, the capacitor voltage imbalance can be controlled in a controlled manner. Thus, the capacitance of the capacitor of the multilevel power conversion device can be reduced, and the device can be miniaturized.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Converter, 12 ... Capacitor arm, 13 ... 1st switching arm, 14 ... 2nd switching arm, 15 ... 3rd switching arm

Claims (6)

A power conversion device that converts direct current to three-phase alternating current,
A first switching arm in which eight switching devices including a switching element having a self-extinguishing capability and a diode connected in antiparallel to the switching element are connected in series;
A capacitor arm in which four capacitors are connected in series with the first switching arm;
A connection wiring for short-circuiting a connection point between the fourth stage and the fifth stage from the top of the first switching arm and a connection point between the second stage and the third stage from the top of the capacitor arm;
The connection point between the first and second stages from the top of the first switching arm and the connection point between the first and second stages from the top of the capacitor arm are connected from the capacitor arm side to the first switching arm side. A first diode connected in a direction in which a current flows in
The connection point between the third stage and the fourth stage from the top of the first switching arm and the connection point between the first stage and the second stage from the top of the capacitor arm are moved from the first switching arm side to the capacitor arm side. A second diode connected in the direction of current flow;
The connection point between the fifth stage and the sixth stage from the top of the first switching arm and the connection point between the third stage and the fourth stage from the top of the capacitor arm are moved from the capacitor arm side to the first switching arm side. A third diode connected in the direction of current flow;
The connection point between the seventh stage and the eighth stage from the top of the first switching arm and the connection point between the third stage and the fourth stage from the top of the capacitor arm are moved from the first switching arm side to the capacitor arm side. A fourth diode connected in the direction of current flow;
Two switching devices are connected in series with the connection point between the second and third stages from the top of the first switching arm and the connection point between the sixth and seventh stages from the top of the first switching arm. And a connected second switching arm,
A power conversion apparatus, wherein a DC power source is connected to the upper and lower ends of the capacitor arm, and the intermediate point of the second switching arm is operated as an AC output point. The second switching arm is replaced with a series connection of two switching devices,
The power converter according to claim 1, wherein four switching devices are connected in series. A third switching arm connected in parallel to the capacitor arm and having four switching devices connected in series;
A first reactor connecting a connection point between the first stage and the second stage from the top of the capacitor arm and a connection point between the first stage and the second stage from the top of the third switching arm;
A second reactor connecting a connection point between the third stage and the fourth stage from the top of the capacitor arm and a connection point between the third stage and the fourth stage from the top of the third switching arm;
The uppermost end of the first switching arm and the uppermost end of the capacitor arm are connected, and the lowermost end of the first switching arm and the lowermost end of the capacitor arm are connected. 2. The power conversion device according to 2. A rectifying power conversion device that converts three-phase alternating current into direct current,
Four capacitor arms connected in series;
Four switching devices composed of a switching element having a self-extinguishing capability and a diode connected in reverse parallel to the switching element are connected in series, and the capacitor arm is connected to the top of the capacitor arm from the uppermost end of the series connection of the switching devices. The upper end is connected by a first two series diodes so that current flows from the switching device side to the capacitor arm side, and the switching device is connected from the lowest end of the series connection of the switching device to the lowest end of the capacitor arm from the capacitor arm side. A first switching arm configured to be connected by a second two series diode so that a current flows to the side,
A connection wiring for short-circuiting a connection point between the fourth stage and the fifth stage from the top of the switching arm and a connection point between the second stage and the third stage from the top of the capacitor arm;
A current flows from the capacitor arm side to the first switching arm side through the connection point between the first stage and the second stage from the top of the switching arm and the connection point between the first stage and the second stage from the top of the capacitor arm. A first diode connected in a direction;
Current flows from the first switching arm side to the capacitor arm side at the connection point between the third and fourth stages from the top of the switching arm and the connection point between the first and second stages from the top of the capacitor arm. A second diode connected in the direction;
Current flows from the capacitor arm side to the first switching arm side through the connection point between the fifth and sixth stages from the top of the switching arm and the connection point between the third and fourth stages from the top of the capacitor arm. A third diode connected in the direction;
A current flows from the first switching arm side to the capacitor arm side at the connection point between the seventh stage and the eighth stage from the top of the switching arm and the connection point of the third stage and the fourth stage from the top of the capacitor arm. A fourth diode connected in the direction;
A diode in which two connection points between the second and third stages from the top of the first switching arm and two connection points of the sixth and seventh stages from the top of the first switching arm are connected in series. A second switching arm to be connected,
A power converter, wherein a DC load is connected to both upper and lower ends of the capacitor arm, and an intermediate point of the second switching arm is connected to an AC power source to operate.   5. The power conversion device according to claim 4, wherein the second switching arm includes four diodes connected in series instead of a series connection of two diodes. A third switching arm connected in parallel to the capacitor arm, having a switching device in the first stage, having a diode in the second and third stages, and having a switching device in the fourth stage and connecting them in series;
A first reactor connecting a connection point between the first stage and the second stage from above the capacitor arm and a connection point between the first stage and the second stage from above the third switching arm;
A second reactor connecting a connection point between the third stage and the fourth stage from the top of the capacitor arm and a connection point between the third stage and the fourth stage from the top of the third switching arm;
6. The uppermost end of the first switching arm and the uppermost end of the capacitor arm are connected, and the lowermost end of the first switching arm and the lowermost end of the capacitor arm are connected. Power converter.

Images