Matrix converter

A matrix converter includes input terminals, output terminals, a power conversion circuit, and a snubber circuit. The power conversion circuit includes bidirectional switches of which each includes antiparallel connection circuits connected serially. The snubber circuit is connected to the bidirectional switches. The snubber circuit includes first diodes, a capacitor, a second diode, and third diodes. The first diodes are respectively corresponded to the bidirectional switches. A first connecting point of each the first diode is connected to a connection point between the two unidirectional switching elements constituting the bidirectional switch. A first connecting point of the capacitor is connected to a second connecting point of each the first diode. First and second connecting points of the second diode are connected to a second connecting point of the capacitor and the corresponding output terminal. The bidirectional switches, the first diodes, and the second diode are arranged in one power module.

FIELD

The embodiments discussed herein are directed to a matrix converter.

BACKGROUND

A matrix converter is capable of suppressing a harmonic current and effectively using regenerative power and hence, the matrix converter has received attention as a new power converter. The matrix converter includes, in some cases, a plurality of bidirectional switches for connecting each phase line of an alternating current source and each phase line of a dynamo-electric machine to perform power conversion by controlling the bidirectional switches.

Furthermore, the matrix converter includes, in some cases, a snubber circuit for ensuring the commutation passage (conduction passage bypassing the bidirectional switch) of a current having flowed immediately before the bidirectional switch is switched over from the ON-state to the OFF-state.

For example, Japanese Patent Application Laid-open No. H11-262264 discloses a matrix converter in which a snubber circuit is provided to each of a plurality of bidirectional switches. However, the conventional matrix converter has room for improvement with respect to the optimization of the snubber circuit.

SUMMARY

A matrix converter according to one aspect of an embodiment includes a plurality of input terminals, a plurality of output terminals, a power conversion circuit, and a snubber circuit. The power conversion circuit includes bidirectional switches of which each includes antiparallel connection circuits that are serially connected to each other. Each of the antiparallel connection circuits includes a unidirectional switching element and a diode. The bidirectional switches are arranged between the input terminals and the corresponding output terminal. The snubber circuit is connected to the bidirectional switches. The snubber circuit includes a plurality of first diodes, a capacitor, a second diode, and a plurality of third diodes. The first diodes are respectively corresponded to the bidirectional switches. A first connecting point of each of the first diodes is connected to a point of connection between the two unidirectional switching elements constituting the bidirectional switch. A first connecting point of the capacitor is connected to a second connecting point of each of the first diodes. A first connecting point of the second diode is connected to a second connecting point of the capacitor and a second connecting point of the second diode is connected to the corresponding output terminal. The third diodes are respectively corresponded to the bidirectional switches. A first connecting point of each of the third diodes is connected to the second connecting point of the capacitor. A second connecting point of each of the third diodes is connected to the corresponding input terminal. Furthermore, the bidirectional switches connected between at least one of the output terminals and each of the input terminals, the first diodes connected to the respective bidirectional switches, and the second diode are arranged in one power module. The power module is provided for the corresponding output terminal.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, the following describes embodiments of a matrix converter disclosed in the present application in detail. Here, the present application is not limited to these embodiments.

First Embodiment

FIG. 1is an explanatory view illustrating a matrix converter1according to the first embodiment. The following embodiment is explained by taking the matrix converter1, as an example, that converts a three-phase alternating voltage input from a power source2into an arbitrary alternating voltage by pulse width modulation (PWM) control and outputs the alternating voltage to an AC motor3. As illustrated inFIG. 1, the matrix converter1according to the first embodiment is provided between the three-phase AC power source2and the AC motor3, and performs power conversion between the power source2and the AC motor3.

The matrix converter1includes three input terminals R1, S1, and T1, three output terminals U1, V1, and W1, an LC filter4, a power conversion circuit5, and a controller6. The input terminals R1, S1, and T1are connected with the R-phase line, the S-phase line, and the T-phase line of the power source2, respectively. Furthermore, the output terminals U1, V1, and W1are connected to the U-phase line, the V-phase line, and the W-phase line of the AC motor3, respectively.

The LC filter4is provided between the R-phase line, the S-phase line, and the T-phase line of the power source2and the power conversion circuit5, and constituted of three reactors and three capacitors. The LC filter4removes a high frequency component (PWM component) attributed to switching by the below-mentioned bidirectional switch units (hereinafter, referred to as “switch units”) Su1to Su9included in the power conversion circuit5.

Here, one end of each of the three reactors is connected to each the corresponding one of the three input terminals R1, S1, and T1in the matrix converter1, and the other ends of the three reactors are connected to respective terminals R2, S2, and T2of the power conversion circuit5. The three capacitors are connected between the other ends of two different reactors. Here, a constitution of the LC filter4is not limited to the constitution illustrated inFIG. 1. For example, the LC filter4may have a constitution in which the three capacitors are connected among the input terminals R1, S1, and T1in Y-connection.

The power conversion circuit5includes three input terminals R2, S2, and T2, three output terminals U2, V2, and W2, three power modules MD1, MD2, and MD3, a capacitor C1(the capacitor C1may be constituted of a plurality of capacitors parallel-connected), and a clamp circuit CL. The input terminals R2, S2, and T2are connected via the LC filter4to the input terminals R1, S1, and T1, respectively. Furthermore, the output terminals U2, V2, and W2of the power conversion circuit5are connected to the output terminals U1, V1, and W1of the matrix converter1, respectively.

Each of the power modules MD1, MD2, and MD3includes input terminals R3, S3, and T3connected with the input terminals R2, S2, and T2of the power conversion circuit5, respectively. Furthermore, the power modules MD1, MD2, and MD3respectively include output terminals U3, V3, and W3connected with the output terminals V2, U2, and W2of the power conversion circuit5, respectively.

Furthermore, the power module MD1includes the three switch units Su1, Su2, and Su3. The switch unit Su1is connected between the input terminal R3and the output terminal U3of the power module MD1. The switch unit Su2is connected between the input terminal S3and the output terminal U3of the power module MD1. The switch unit Su3is connected between the input terminal T3and the output terminal U3of the power module MD1.

The power module MD2includes the switch units Su4, Su5, and Su6. The power module MD2has the identical constitution with the power module MD1except that the output terminal V3is connected to the corresponding output terminal V2of the power conversion circuit5. Furthermore, the power module MD3includes the switch units Su7, Su8, and Su9. The power module MD3has the identical constitution with the power module MD1except that the output terminal W3is connected to the corresponding output terminal W2of the power conversion circuit5.

Here, the power module MD1selectively connects any one of the R-phase line, the S-phase line, and the T-phase line of the power source2and the U-phase line of the AC motor3based on the control of the controller6. In the same manner as above, the power module MD2selectively connects any one of the R-, S-, and T-phase lines of the power source2and the V-phase line of the AC motor3. The power module MD3selectively connects any one of the R-, S-, and T-phase lines of the power source2and the W-phase line of the AC motor3.

Each of the switch units Su1to Su9includes the bidirectional switch constituted of serially connected antiparallel connection circuits each of which has a unidirectional switching element and a diode. Here, one example of the specific constitution of each of the switch units Su1to Su9is explained later in reference toFIG. 2.

In these nine switch units Su1to Su9, the two unidirectional switching elements constituting the bidirectional switch are individually turned on and off by PWM control based on the control of the controller6and hence, the direction of the current, voltage, and the current value are controlled.

Here, as will be specifically explained later, the switch units Su1to Su9include diodes for the snubber circuit so as to ensure the commutation passage (conduction passage bypassing the bidirectional switch) of a current having flowed immediately before the bidirectional switch is switched over from an ON-state to an OFF-state.

The current flow bypassing the bidirectional switch is output from a terminal P of each of the switch units Su1to Su9, input to a terminal N of each of the switch units Su1to Su9via the capacitor C1for the snubber circuit, and output from each of the output terminals U3, V3, and W3, or each of the input terminals R3, S3, and T3. Accordingly, in the matrix converter1, when the bidirectional switch is turned off to interrupt a passage in which a current flows, the occurrence of switching surge voltage can be suppressed.

In this manner, in the matrix converter1, the snubber circuit is constituted of the diodes and the capacitor C1therefor, the diodes being included in the switch units Su1to Su9. Furthermore, in the matrix converter1, some of the switch units Su1to Su9share some of the diodes for the snubber circuit and additionally, the diodes for the snubber circuit is provided in the inside of the power modules MD1, MD2, and MD3thus optimizing the snubber circuit. One example of the specific constitution of the snubber circuit will be explained later in reference toFIG. 2.

The clamp circuit CL includes a resistor and a transistor that are connected with each other in series and connected with the capacitor C1in parallel. The clamp circuit CL restricts a voltage between terminals of the capacitor C1to the predetermined voltage or lower based on the control of the controller6thus preventing the breakage of the capacitor C1caused by overvoltage.

The controller6generates a switch driving signal for outputting a voltage corresponding to the desired-voltage instruction by the known PWM control method of a matrix converter and outputs the signal to the power conversion circuit5.

The power conversion circuit5performs power conversion in a way that the unidirectional switching elements included in the switch units Su1to Su9are turned on and off by PWM control in response to the switch driving signal input from the controller6.

Furthermore, the controller6applies, when a voltage between the terminals of the capacitor C1is increased to the predetermined threshold, a gate voltage to the gate of the transistor in the clamp circuit CL and turns on the transistor thus preventing the breakage of the capacitor C1. Here, the voltage between the terminals of the capacitor C1is detected by a voltage detector that is not illustrated in the drawings.

In reference toFIG. 2, the following describes the power modules MD1, MD2, and MD3included in the power conversion circuit5. Here, the three power modules MD1, MD2, and MD3have identical constitutions. Therefore, hereinafter, only the power module MD1is explained, and the explanations of the other two power modules MD2and MD3are omitted.

FIG. 2is an explanatory view illustrating the power module MD1according to the first embodiment. As illustrated inFIG. 2, the power module MD1includes the three switch units Su1, Su2, and Su3. Each of the switch units Su1, Su2, and Su3includes a bidirectional switch in which an antiparallel circuit having a unidirectional switching element Q1and a diode D1and an antiparallel circuit having a unidirectional switching element Q2and a diode D2are serially connected with each other.

Each of the unidirectional switching elements Q1and Q2is, for example, a semiconductor device such as an insulated gate bipolar transistor (IGBT). Here, although the present embodiment is explained by taking, as an example, a bidirectional switch in which the collectors of the unidirectional switching elements Q1and Q2are connected to each other, the bidirectional switch may adopt, as explained later in reference toFIG. 4, a constitution such that emitters of the unidirectional switching elements Q1and Q2are connected to each other.

Furthermore, each of the switch units Su1, Su2, and Su3includes a diode (first diode) D5whose anode is connected to the point of connection between the two unidirectional switching elements Q1and Q2of which the bidirectional switch is constituted and cathode is connected to an upper electrode P1of the capacitor C1. Each of the switch units Su1, Su2, and Su3includes a diode (third diode) D3whose anode is connected to a lower electrode N1of the capacitor C1and cathode is connected to the corresponding input terminal R, S, or T.

Any one of the three switch units Su1, Su2, and Su3(the switch unit Su2inFIG. 2) includes a diode (second diode) D4whose anode is connected to the lower electrode N1of the capacitor C1and cathode is connected to an output terminal U. In this manner, the three switch units Su1, Su2, and Su3have identical constitutions except that the switch unit Su2includes the diode4.

In the power module MD1, for example, when a current flows from an R3-phase line to a U3-phase line (when an output current is a positive current), the unidirectional switching element Q2of the switch unit Su1is turned on to flow the current through a first passage. Thereafter, when a current flows from a S3-phase line to the U3-phase line, the unidirectional switching element Q2of the switch unit Su1is first turned off and a short time later, the unidirectional switching element Q2of the switch unit Su2is turned on.

In this case, the current having flowed through the switch unit Su1immediately before the unidirectional switching element Q2of the switch unit Su1is turned off flows from the point of connection between the two unidirectional switching elements Q1and Q2to the output terminal U3via a second passage bypassing the unidirectional switching element Q2. To be more specific, the current input from the input terminal R3is output from the output terminal U3via the diode D1, the diode D5, the capacitor C1, and the diode D4.

In this manner, in the power module MD1, after the unidirectional switching element Q1of the switch unit Su1is switched over from an on-state to an off-state, the previous current flow is maintained, which suppresses a surge voltage that occurs by turning off the switch unit Su1.

Furthermore, in the power module MD1, to consider a case where a current flows from the U3-phase line to the R3-phase line (an output current is a negative current), when the unidirectional switching element Q1of the switch unit Su1is turned off, the current is maintained by flowing through the output terminal U3, the diodes D2and D5of the switch unit Su1, the capacitor C1, the diode D3, and the input terminal R3. Here, when each of the other two switch units Su2and Su3is switched over from an on-state to an off-state, the current flows through the passage same as above thus maintaining the previous current flow.

In this manner, with respect to the power module MD1, the snubber circuit is constituted of the diodes D3and D5of each of the switch units Su1, Su2, and Su3, the capacitor C1, and the diode D4of the switch unit Su2.

Furthermore, in the power module MD1, as a diode for outputting a current input from the capacitor C1to the output terminal U3, the diode D4of the switch unit Su2is shared by the three switch units Su1, Su2, and Su3. Therefore, according to the power module MD1, it is unnecessary to provide the diode D4for outputting a current input from the capacitor C1to the output terminal U to each of the switch units Su1, Su2, and Su3thus reducing the costs of the switch units Su1, Su2, and Su3.

In the power module MD1, the diodes D3, D4, and D5for the snubber circuit are all provided in the inside of the power module and hence, it is also unnecessary to provide the diodes D3, D4, and D5for the snubber circuit as separate modules thus realizing the downsizing and cost reduction of the matrix converter1.

As mentioned above, a matrix converter according to the first embodiment includes a plurality of input terminals and a plurality of output terminals. In addition, the matrix converter includes a power conversion circuit in which each of bidirectional switches is arranged between each input terminal and each output terminal, and a snubber circuit connected to the bidirectional switch. Here, each of the bidirectional switches is constituted of serially connected antiparallel connection circuits each of which has a unidirectional switching element and a diode.

The snubber circuit includes the first diode and the capacitor, in which one end of the first diode is connected to the point of connection between the two unidirectional switching elements that constitute the bidirectional switch, and one end of the capacitor is connected to the other end of the first diode. The snubber circuit includes a second diode whose one end is connected to the other end of the capacitor and the other end is connected to an output terminal.

In the snubber circuit, the other end of the second diode is connected to only a part of the bidirectional switches. The bidirectional switches connected between one of the output terminals and each of the input terminals, the first diodes connected to the respective bidirectional switches, and the second diode are arranged in one power module. The power module is provided to the corresponding output terminal.

In the power module, the second diode connected to only a part of the bidirectional switches is arranged. According to the first embodiment, the snubber circuit is optimized thus realizing the downsizing and cost reduction of the matrix converter. Furthermore, inFIG. 2(also inFIG. 1,FIG. 4,FIG. 11,FIG. 13, andFIG. 14), although terminals P or terminals N of the three bidirectional switches are connected in common outside the power module MD1, the terminals P or the terminals N may be connected in common inside the power module MD1so as to provide a pair of the terminal P and the terminal N outside the power module.

The constitution of the power module according to the first embodiment is not limited to the example illustrated inFIG. 2. Here, in reference toFIG. 3, a power conversion circuit including a power module MD1aaccording to a modification 1 is explained.

FIG. 3is an explanatory view illustrating a part of the power conversion circuit according to the modification 1. InFIG. 3, a power module MD1afor a U-phase line and a power module MD2afor a V-phase line are illustrated. Here, a power module for a W-phase line has the same constitution as the power modules MD1aand MD2a, and the illustration thereof is omitted. Furthermore, out of constitutional parts illustrated inFIG. 3, parts having the identical functions with those of the parts illustrated inFIG. 2are given same numerals as those of the parts illustrated inFIG. 2and their explanations are omitted.

As illustrated inFIG. 3, the power module MD1aprovided to the power conversion circuit according to the modification 1 includes parts other than the three diodes D3in the power module MD1illustrated inFIG. 2in the inside thereof. Here, the three diodes D3in the power module MD1illustrated inFIG. 2is replaced by diodes D3r, D3s, and D3tprovided outside the power module MD1a. The constitutions of the two power modules MD1aand MD2aare identical with each other.

In the power conversion circuit, for example, when a current flows from a V3-phase line to a T3-phase line (when an output current is a negative current), the current flows through a first passage via an output terminal V3, a diode D2, a unidirectional switching element Q1, and an input terminal T3in the power module Md2a.

Thereafter, when the unidirectional switching element Q1of the power module MD2ais turned off, the current having flowed immediately before the unidirectional switching element Q1is turned off is maintained by flowing through a second passage illustrated inFIG. 3. To be more specific, the current is maintained by flowing through the second passage via the output terminal V3and diodes D2and D5of the power module MD2a, a capacitor C1, and the diode D3t.

Here, when a current has flowed from the U3-phase line to the T3-phase line immediately before the unidirectional switching element Q1is turned off, in the same manner as the case where a current has flowed from the V3-phase line to the T3-phase line immediately before the unidirectional switching element Q1is turned off, the current is maintained by flowing through the second passage via the diodes D2and D5, the capacitor C1, and the diode D3t.

When a current has flowed from the U3-phase line, the V3-phase line, or the W3-phase line to the R3-phase line, and when a current has also flowed from the U3-phase line, the V3-phase line, or the W3-phase line to the S3-phase line, the current having flowed immediately before the unidirectional switching element Q1is turned off is maintained.

According to the power conversion circuit, the diodes D3r, D3s, and D3tcan be shared as diodes for the snubber circuit by the power module MD1afor the U-phase line, the power module MD2afor the V-phase line, and a power module for the W-phase line. Therefore, as the whole matrix converter, for example, the number of diodes is reduced by six compared with the case that the three power modules MD1illustrated inFIG. 2are provided so as to optimize the snubber circuit thus realizing the cost reduction. Furthermore, to consider that the diode D4is shared, the following advantageous effect can be achieved; that is, one kind of power module is sufficient (as the whole matrix converter, three power modules identical with each other are sufficient) while maximizing the effect of reducing the number of diodes (reducing by 12).

Furthermore, each of the power modules MD1aand MD2aillustrated inFIG. 3includes one diode D4and three diodes D5in the inside thereof. In this manner, for example, compared with the case that all of the diodes D3, D4, and D5for the snubber circuit are provided outside the power module as a different module, manufacturing costs as the whole matrix converter can be lowered.

In this manner, in the power conversion circuit according to the modification 1, a third diode whose one end is connected to the other end of the capacitor and the other end is connected to the input terminal is provided outside the power module, and the other end of the corresponding third diode is connected to the input terminals of only a part of the three power modules. According to the modification 1, the cost of the whole matrix converter can be lowered by optimizing the snubber circuit.

Next, in reference toFIG. 4toFIG. 6, a power module MD1baccording to a modification 2 is explained.FIG. 4toFIG. 6are explanatory views each illustrating the power module MD1baccording to the modification 2. To be more specific,FIG. 4is the explanatory view illustrating the circuit constitution of the power module MD1b,FIG. 5is the explanatory view of the power module MD1bas viewed in a plan view, andFIG. 6is the explanatory view illustrating the sectional view of the power module MD1btaken along a line A-A inFIG. 5. Here, inFIG. 4toFIG. 6, parts having the identical functions with those illustrated inFIG. 2are given same numerals as those illustrated inFIG. 2.

As illustrated inFIG. 4, the power module MD1bincludes three switch units Su1a, Su2a, and Su3a. In the three switch units Su1a, Su2a, and Su3a, the direction of each of the anode and the cathode of each diode D1, D2, D3, or D4, as well as the direction of each of the collector and the emitter of each unidirectional switching element, is opposite to the direction of that illustrated inFIG. 2.

That is, in the switch units Su1a, Su2a, and Su3a, the emitters of the unidirectional switching elements Q1and Q2of which each bidirectional switch is constituted are connected to each other. Furthermore, the cathode of the diode D5(first diode) is connected to the point of connection between the two unidirectional switching elements Q1and Q2, and the anode of the diode D5(first diode) is connected to the lower electrode N1of the capacitor C1.

In the power module MD1b, for example, when a current flows from the U3-phase line to the R3-phase line (an output current is a negative current), the current flows through a first passage via the output terminal U3, the unidirectional switching element Q2, and the diode D1in the switch unit Su1a. Thereafter, when the unidirectional switching element Q2of the switch unit Su1ais turned off, the current having flowed immediately before the unidirectional switching element Q2is turned off is maintained by flowing through a second passage via the output terminal U3, the diode D4of the switch unit Su2a, the capacitor C1, and the diodes D5and D1of the switch unit Su1a.

Furthermore, when the current has flowed from the U3-phase line to the S3-phase line immediately before the switching element Q2is turned off, as well as when the current has flowed from the U3-phase line to the T3-phase line, the current is maintained by flowing through a passage via the diode D4, the capacitor C1, and the diodes D5and D1. Here, when a current has flowed from the R3-phase line, the S3-phase line, or the T3-phase line to the U3-phase line immediately before the unidirectional switching element Q2is turned off (an output current is a positive current), the current is maintained by flowing through a passage via the diode D3of each of the switch units Su1a, Su2a, and Su3a, the capacitor C1, and the diodes D5and D2.

In this manner, also in the power module MD1b, the diode D4of the switch unit Su2ais shared as a diode that outputs a current input from the U3-phase line to the capacitor C1by the three switch units Su1a, Su2a, and SU3a. Therefore, the snubber circuit can also be optimized by the use of the power module MD1baccording to the modification 2.

Here, in a state that a current flows from the U3-phase line to the R3-phase line, when the unidirectional switching element Q2of the switch unit Su1ais turned off, the current having flowed between the output terminal U3and the collector of the unidirectional switching element Q2immediately before the unidirectional switching element Q2is turned off loses the destination thereof. In a state that a current flows from the U3-phase line to the T3-phase line, when the unidirectional switching element Q2of the switch unit Su3ais turned off, the current having flowed between the output terminal U and the collector of the unidirectional switching element Q2also loses the destination thereof. The current that loses the destination thereof may result in a surge voltage.

Consequently, in the power module MD1baccording to the modification 2, the collector-sides of the three of IGBTs or silicon carbide (SiC) transistors Q2are connected to the U3-phase line in common thus constituting the three unidirectional switching elements Q2. Furthermore, the power module MD1bincludes, as illustrated inFIG. 5, a planar-shaped conductor MT with which the collector sides (a bottom surface of a transistor-Q2chip) of a plurality of (three, in this case) unidirectional switching elements Q2connected to the output terminal U3in common are brought into contact in common. Here, inFIG. 5, each diode is arranged in a posture with the cathode side thereof down. In this case, the collectors are connected by the common planar-shaped conductor on a side opposite to a side on which the emitters are connected to each other.

The power module MD1bincludes, for example, as illustrated inFIG. 6, a heat radiation fin FN arranged on the lowermost layer thereof, a copper base plate BS arranged on the heat radiation fin FN, and a ceramic substrate SM for insulation on the copper base plate BS. The planar-shaped conductor MT (a foil pattern or a block plate that is made of copper or aluminum, for example) is provided on the ceramic substrate SM, and the three unidirectional switching elements Q2are provided on the planar-shaped conductor MT directly or by way of a heat spreader HS comprised of a metal block.

Each of the unidirectional switching elements Q2is arranged in a state that the lower surface thereof that constitutes a collector is brought into contact with the upper surface of the heat spreader HS, and a gate and an emitter are extended from the upper surface side of each of the unidirectional switching elements Q2. Here, each circuit element including the unidirectional switching elements Q2is covered with a cover CV.

In this manner, in the power module MD1b, the output terminal U3and the collector of the unidirectional switching element Q2are connected to each other with the use of the planar-shaped conductor MT while making the connection therebetween thick and short. In this manner, an inductance of the connecting part between the output terminal U3and the unidirectional switching element Q2(see the passage indicated by a bold line inFIG. 4) can be reduced, which suppresses the occurrence of the surge voltage attributed to the current that loses the destination thereof in the passage indicated by the bold line inFIG. 4.

Next, in reference toFIG. 7toFIG. 10, an additional modification of a switch unit is explained. A switch unit Su1baccording to a modification 3 is explained.FIG. 7andFIG. 8are explanatory views each illustrating the flow of current in the switch unit Su1illustrated inFIG. 1.FIG. 9andFIG. 10are explanatory views each illustrating the switch unit Su1baccording to the modification 3.

As illustrated inFIG. 7, in the switch unit Su1, in a state that a current flows from a R3-phase line to a U3-phase line through a first passage, when a unidirectional switching element Q2is turned off, the current is maintained by flowing through a second passage. However, in this case, the current having flowed between the anode of a diode D5and the collector of the unidirectional switching element Q2immediately before the unidirectional switching element Q2is turned off loses the destination thereof.

On the other hand, as illustrated inFIG. 8, in a state that a current flows from the U3-phase line to the R3-phase line through a first passage, when a unidirectional switching element Q1is turned off, the current is maintained by flowing through a second passage. However, in this case, the current having flowed between the collector of the unidirectional switching element Q1and the anode of the diode D5immediately before the unidirectional switching element Q1is turned off loses the destination thereof. The current that loses the destination thereof may, as described above, result in the occurrence of surge voltage.

Consequently, as illustrated inFIG. 9, a bidirectional switch of the switch unit Su1baccording to the modification 3 includes a first conductor L1that connects the two unidirectional switching elements Q1and Q2in series. The bidirectional switch includes a second conductor L2that connects the unidirectional switching element Q1and a diode D2in series, and a second conductor L2that connects the unidirectional switching element Q2and a diode D1in series. In the bidirectional switch, the anode of the diode D5is connected to the first conductor L1.

In this manner, as illustrated inFIG. 9, in a state that a current flows from an R3-phase line to a U3-phase line through a first passage, when the flow of the current is switched so that the current flows through a second passage, it is possible to reduce the size of a section where the current loses the destination thereof by the first conductor L1that connects the two unidirectional switching elements Q1and Q2in series. Furthermore, as illustrated inFIG. 10, in a state that a current flows from the U3-phase line to the R3-phase line through a first passage, when the flow of current is switched so that the current flows through a second passage, in the same manner as above, it is possible to reduce the size of a section where the current loses the destination thereof. Therefore, according to the switch unit Su1bin the modification 3, the occurrence of the surge voltage can be suppressed.

Furthermore, as illustrated inFIG. 11, the occurrence of the surge voltage can also be suppressed by constituting switch units Su1c, Su2c, and Su3c.FIG. 11is an explanatory view illustrating a power module MD1cprovided with the switch units Su1c, Su2c, and Su3caccording to a modification 4.

As illustrated inFIG. 11, the power module MD1caccording to the modification 4 differs from that illustrated inFIG. 2in that each of the switch units Su1c, Su2c, and Su3cincludes diodes D51and D52in place of the diode D5(seeFIG. 2).

To be more specific, as illustrated inFIG. 11, the switch unit Su1cincludes a third conductor L3that serially connects an antiparallel connection circuit constituted of a unidirectional switching element Q1and a diode D1, and a antiparallel connection circuit constituted of a unidirectional switching element Q2and a diode D2.

A bidirectional switch of the switch unit Su1cis constituted by connecting anodes of the separate diodes51and D52(first diodes) to both ends of the third conductor L3. Here, the switch unit Su3cis identical with the switch unit Su1cwith respect to the constitution. Furthermore, the switch unit Su2cis identical with the switch unit Su1cwith respect to the constitution except that the switch unit Su2cincludes a diode D4.

In this manner, in the power module according to the modification 4, for example, in a state that a current flows from the R3-phase line to the U3-phase line through the first passage illustrated inFIG. 11, when the flow of current is switched so that the current flows through a second passage, the size of a section where the current loses the destination thereof is reduced, which suppresses the occurrence of the surge voltage.

Here, in the case of a switch unit in which emitters of the two unidirectional switching elements Q1and Q2of which the bidirectional switch is constituted are connected to each other, for example, as illustrated inFIG. 12, the occurrence of the surge voltage can be suppressed by constituting a switch unit Su1d.FIG. 12is an explanatory view illustrating the switch unit Su1daccording to a modification 5.

As illustrated inFIG. 12, the bidirectional switch of the switch unit Su1daccording to the modification 5 includes a fourth conductor L4that serially connects the emitters of the two unidirectional switching elements Q1and Q2. In addition, the bidirectional switch includes a fifth conductor L5that serially connects the unidirectional switching element Q1and a diode D2, and a fifth conductor L5that serially connects the unidirectional switching element Q2and a diode D1.

Furthermore, in the bidirectional switch, a cathode of the diode D5is connected to the fourth conductor L4. In this manner, even in the case of the switch unit Su1din which the emitters of the unidirectional switching elements Q1and Q2are connected to each other, in a state that a current flows between the R3-phase line and the U3-phase line, when the unidirectional switching elements Q1and Q2are turned off, in the same manner as the case illustrated inFIG. 9andFIG. 10, the size of the section where the current loses the destination thereof is reduced. Therefore, the occurrence of the surge voltage can be suppressed.

Second Embodiment

Next, in reference toFIG. 13andFIG. 14, a matrix converter1aaccording to the second embodiment is explained.FIG. 13is an explanatory view illustrating the matrix converter1aaccording to the second embodiment.FIG. 14is an explanatory view illustrating a power module MD4according to the second embodiment. Here, out of constitutional parts illustrated inFIG. 13andFIG. 14, parts identical with those illustrated inFIG. 1andFIG. 2are given same numerals as those of the parts illustrated inFIG. 1andFIG. 2, and their explanations are omitted.

As illustrated inFIG. 13, the matrix converter1adiffers from the matrix converter illustrated inFIG. 1with respect to the constitution of a power conversion circuit5a. To be more specific, the power conversion circuit5aincludes three power modules MD4, MD5, and MD6.

The power module MD4includes three switch units Su11, Su12, and Su13that selectively connect between an R-phase line of a power source2and each of a U-phase line, a V-phase line, and an R-phase line of an AC motor3based on the control of a controller6a. The power module MD5includes three switch units Su14, Su15, and Su16that selectively connect an S-phase line of the power source2and each of the U-phase, the V-phase line, and the R-phase line of the AC motor3based on the control of the controller6a. The power module MD6includes three switch units Su17, Su18, and Su19that selectively connect a T-phase line of the power source2and each of the U-phase line, the V-phase line, and the R-phase line of the AC motor3based on the control of the controller6a.

The controller6agenerates a switch driving signal so as to output a voltage corresponding to the desired-voltage instruction to the AC motor3by the known PWM control method of a matrix converter and outputs the signal to the power conversion circuit5athus allowing the power conversion circuit5ato perform a power conversion operation.

Here, the three power modules MD4, MD5, and MD6are identical with each other with respect to the constitution. Accordingly, hereinafter, the power module MD4is explained, and the explanations of the power modules MD5and MD6are omitted.

As illustrated inFIG. 14, each of the three switch units Su11, SU12, and Su13included in the power module MD4includes a bidirectional switch, which is identical with that illustrated inFIG. 2, constituted of two unidirectional switching elements Q1and Q2and two diodes D1and D2.

Furthermore, each of the three switch units Su11, Su12, and Su13includes a diode D5(first diode) and a diode D4(second diode) that are identical with the diodes D4and D5included in the switch unit Su2illustrated inFIG. 2. In addition, any one of the three switch units Su11, Su12, and Su13(switch unit Su12in this case) includes a diode D3(third diode) identical with the diode D3included in the switch units Su1, Su2, and Su3.

In the power module MD4, for example, when a current flows from a U3-phase line to an R3-phase line, the current flows through a first passage. Thereafter, when the unidirectional switching element Q1of the switch unit Su11is turned off, the current having flowed immediately before the unidirectional switching element Q1is turned off is maintained by flowing through a second passage and output to an input terminal R3via the diode D3included in the switch unit Su12.

Furthermore, in a state that a current flows from a V3-phase line to the R3-phase line, or in a state that the current flows from a W3-phase line to the R3-phase line, when the unidirectional switching element Q1that flows the current is turned off, the current is also output to the input terminal R3via the diode D3.

That is, in the power module MD4, the diode D3of the switch unit Su12is shared as a diode for a snubber circuit that outputs a current input from a capacitor C1to the input terminal R3by the switch units Su11, Su12, and Su13.

In this manner, the matrix converter according to the second embodiment includes a plurality of input terminals and a plurality of output terminals. In addition, the matrix converter includes a power conversion circuit in which each of the bidirectional switch constituted of serially connected antiparallel connection circuits each constituted of a unidirectional switching element and a diode is arranged between each input terminal and each output terminal, and a snubber circuit connected to the bidirectional switch.

The snubber circuit includes the first diode whose one end is connected to the point of connection between the two unidirectional switching elements constituting the bidirectional switch, and a capacitor (a capacitor constituted of a plurality of capacitors are connected to each other in parallel is also applicable) whose one end is connected to the other end of the first diode. In addition, the snubber circuit includes the third diode whose one end is connected to the other end of the capacitor and other end is connected to the input terminal.

In the snubber circuit, the other end of the corresponding third diode is connected to only a part of (the input-terminal sides of) the bidirectional switches. The bidirectional switches connected between one of the input terminals and each of the output terminals, and the first diodes connected to the respective bidirectional switches are arranged in one power module. The power module is provided to the corresponding input terminal.

Furthermore, in the power module, the third diode connected to only a part of the bidirectional switches is arranged. According to the second embodiment, the downsizing and cost reduction of the matrix converter can be achieved by the optimization of the snubber circuit.

Here, the power module MD4illustrated inFIG. 14is one example, and various modifications are conceivable. For example, it may be possible to adopt the constitution in which a second diode whose one end is connected to the other end of the capacitor and other end is connected to the corresponding output terminal is provided outside the power module, and the other end of the second diode is connected to only a part of the output terminals of the power modules.

In this manner, for example, in the matrix converter including three power modules each having the identical constitution with the power module MD4illustrated inFIG. 14, nine diodes D4required for the power module is reduced into three diodes thus optimizing the snubber circuit.

Furthermore, a first conductor L1and a second conductor L2identical with those in the case of the switch unit Su1billustrated inFIG. 9may be provided to each of the switch units Su11, Su12, and Su13and the anode of the first diode D5may be connected to the first conductor L1. In this manner, in the same manner as the case of the first embodiment, the occurrence of a surge voltage can be suppressed.

Furthermore, a third conductor L3identical with that in the case of the switch unit Su1cillustrated inFIG. 11may be provided to each of the switch units Su11, Su12, and Su13illustrated inFIG. 14and the separate first diodes D51and D52may be connected to both ends of the third conductor L3. In this manner, the occurrence of the surge voltage can also be suppressed.

In the second embodiment, the bidirectional switch in each of the switch units Su11, Su12, and Su13may also be a bidirectional switch constituted of the two unidirectional switching elements Q1and Q2whose emitters are connected to each other. In this case, for example, a power module MD4ais constituted as illustrated inFIG. 15.FIG. 15is an explanatory view illustrating the power module MD4aaccording to a modification 1 of the second embodiment as viewed in a plan view.

To be more specific, for example, in the power module MD4a, each of three unidirectional switching elements Q1connected to an input terminal R3is constituted of an IGBT or a SiC transistor. As illustrated inFIG. 15, collectors each provided to the bottom surface of each of the unidirectional switching elements Q1are brought into contact with and connected to the top surface of a planar-shaped conductor MT directly or by way of a heat spreader.

In this manner, an inductance can be lowered between the input terminal R3and the collector of each of the unidirectional switching elements Q1. Hence, when the unidirectional switching element Q1that flows a current is turned off, the occurrence of the surge voltage can be suppressed.

Here, each of the present embodiments is explained by taking the matrix converter that converts a three-phase AC input voltage into a three-phase AC output voltage as an example. However, the snubber circuit described in each of the embodiments can also be applied to a matrix converter that converts the three-phase AC input voltage into a single-phase AC output voltage.