JP5822773B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device.

  Switching elements and free-wheeling diodes generate switching losses when the switching elements switch. Switching loss generates heat and can cause thermal destruction, thus reducing reliability. As is well known, the switching loss is proportional to the switching frequency. For this reason, in the conventional power converter, in order to ensure the reliability with respect to thermal destruction, the switching frequency was made as low as possible.

  On the other hand, although it varies depending on the person, when the switching frequency is exclusively in the human audible frequency band, electromagnetic noise from a motor or a reactor connected to the power converter may become a problem. In addition, when the switching frequency is lower than the high switching frequency, harmonic components are largely superimposed on the current of the motor and the reactor, and the loss of the motor and the reactor is increased. Therefore, the switching frequency may be increased. It has been desired.

  Therefore, in order to increase the switching frequency while maintaining reliability, adoption is being performed for switching elements and free-wheeling diodes of SiC, which is a power device having a lower loss than Si.

  Although the object of the invention is partly different from the above, for example, in Patent Document 1 below, a SiC-JFET is adopted as a transistor provided in a power converter (inverter) and connected in antiparallel to the SiC-JFET. The structure which employ | adopts SiC-SBD (Schottky barrier diode) as the return | reflux diode to be performed is disclosed.

JP 2000-224867 A

  However, when SiC is used for all the switching elements and freewheeling diodes that constitute the power conversion device, an increase in the cost of the chip itself is a problem. In addition, an increase in noise is expected due to the high-speed operation unique to SiC devices. In the switching waveform when SiC is employed, a unique ringing phenomenon occurs simultaneously with turn-on due to the structure of SiC, leading to an increase in noise.

  The present invention has been made in view of the above, and is configured to reduce electromagnetic noise and motor loss while maintaining reliability against thermal destruction, and further configured to be able to suppress cost increase and noise increase. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, a power conversion device according to the present invention includes a pair of switching elements made of SiC and a freewheeling diode made of Si connected in reverse parallel, and a switching made of Si. A voltage-type bridge circuit having an upper and lower arm configuration in which a pair of elements and SiC freewheeling diodes connected in antiparallel is connected in series.

  According to the power conversion device of the present invention, it is possible to reduce electromagnetic noise and motor loss while maintaining reliability against thermal destruction, and to further suppress an increase in cost and an increase in noise.

FIG. 1 is a diagram illustrating a configuration of the power conversion device according to the first embodiment. FIG. 2 is a diagram showing a turn-on switching waveform when Si and SiC are employed. FIG. 3 is a diagram illustrating a power conversion apparatus in which the upper arm and the lower arm in FIG. 1 are interchanged. FIG. 4 is a diagram illustrating a power conversion device in the step-up / step-down chopper circuit according to the first embodiment. FIG. 5 is a diagram illustrating a power conversion device in which the upper arm and the lower arm in FIG. 4 are interchanged. FIG. 6 is a diagram illustrating a power converter in the single-phase full bridge circuit according to the second embodiment. FIG. 7 is a diagram illustrating a power conversion device in which the upper arm and the lower arm in FIG. 4 are interchanged. FIG. 8 is a diagram illustrating a three-phase power converter according to the second embodiment. FIG. 9 is a diagram illustrating a power conversion device in which the upper arm and the lower arm in FIG. 8 are interchanged. FIG. 10 is a diagram illustrating a configuration of the power conversion device according to the third embodiment. FIG. 11 is a diagram showing details of the polarity discriminator in FIG. FIG. 12 is a diagram illustrating details of a control unit related to switching of the switching frequency using the current polarity. FIG. 13 is a diagram showing a current flow when the current polarity is positive. FIG. 14 is a diagram showing the switching command in FIG. FIG. 15 is a diagram illustrating a power conversion apparatus in which a plurality of voltage source bridge circuits according to Embodiment 3 are connected in parallel. FIG. 16 is a diagram illustrating details of a control unit related to switching of the switching frequency using the current polarity in FIG. 15. FIG. 17 is a diagram showing the switching command in FIG. FIG. 18 is a diagram showing a current polarity discriminating unit different from that of FIG. 10 in the power conversion device according to the third embodiment. FIG. 19 is a diagram illustrating a power polarity discriminating unit different from that of FIG. 10 and FIG. 18 in the power conversion device according to the third embodiment. FIG. 20 is a diagram illustrating details of a control unit related to switching of the switching frequency using the current effective value. FIG. 21 is a diagram illustrating details of a control unit related to switching of the switching frequency using temperature. FIG. 22 is a diagram illustrating details of a control unit related to switching of the switching frequency using a table of switching frequencies with respect to the effective current value. FIG. 23 is a diagram illustrating details of a control unit related to switching of switching frequency using a table of switching frequency with respect to temperature. FIG. 24 is a diagram illustrating details of a control unit related to switching of the switching frequency using the current polarity and the current effective value. FIG. 25 is a diagram illustrating details of a control unit related to switching of a switching frequency using a current polarity, a current effective value, and a table.

  Hereinafter, with reference to an accompanying drawing, a power converter concerning an embodiment of the invention is explained. In addition, this invention is not limited by embodiment shown below.

Embodiment 1 FIG.
1 is a diagram showing a configuration of a power conversion device according to Embodiment 1 of the present invention. The power conversion device according to the first embodiment includes a switching element 3a made of silicon carbide (SiC) and a freewheeling diode 2a made of silicon (Si) connected in reverse parallel (first element pair), and Si A voltage-type bridge circuit 22 having an upper and lower arm configuration in which a switching element 1b configured and a pair (second element pair) of anti-parallel connection of a free-wheeling diode 4b formed of SiC are connected in series, and the voltage-type bridge circuit 22 in parallel And smoothing capacitors 11a and 11b connected in series. Further, a connection point between the upper arm and the lower arm of the voltage-type bridge circuit 22 and a connection point between the smoothing capacitors 11 a and 11 b are connected via an inductive load 12.

  Moreover, the control part 14 converts the speed command given from the outside into the switching command with respect to each switching element, for example, and provides the converted switching command with respect to a corresponding switching element. In the switching element to which each switching command is given, the DC voltage charged in the smoothing capacitors 11a and 11b is modulated into a pulse having an arbitrary width, and the complementary on / off operation is performed by the upper and lower arms, whereby the desired voltage and desired A pseudo sine wave of frequency is supplied to the inductive load 12.

  The main gist of the power conversion device according to the first embodiment is that the switching element of the upper arm is made of SiC, and the free wheel diode of the lower arm is made of SiC. Specifically, in the configuration of FIG. 1, the switching element 1 b made of Si is, for example, a Si-IGBT (Si-Insulated Gate Bipolar Transistor), and the free-wheeling diode 2 a made of Si is, for example, Si-FRD ( The switching element 3a made of SiC is a SiC-MOSFET (SiC-Metal Oxide Semiconductor Field Effect Transistor), for example, and the free-wheeling diode 4b made of SiC is made of SiC-SBD (SiC), for example. -Schottky Barrier Diode). That is, in the power conversion device according to the first embodiment, the switching element that employs SiC and the free-wheeling diode that employs SiC have a configuration in which they are arranged at positions where the task is applied.

  Here, FIG. 2 is a diagram showing a turn-on switching waveform when Si and SiC are employed. More specifically, the upper part (a) is an example of a turn-on switching waveform when Si-IGBT is adopted as a switching element, and the lower part (b) is a turn-on switching when SiC-MOSFET is adopted as a switching element. It is a waveform. When SiC is employed as the switching element, a ringing phenomenon as indicated by a thick line occurs in the lower stage portion. However, when Si is employed as the switching element, no ringing phenomenon such as SiC occurs. For this reason, the power conversion device according to the first embodiment reduces noise compared to the case where SiC is used for both the elements constituting the first element pair and the elements constituting the second element pair. The generation amount can be reduced.

  That is, according to the power conversion device according to the first embodiment, it is possible to reduce the conduction loss and the switching loss of the element by adopting SiC, which is a low-loss power device, and configure the power conversion device. It is possible to suppress an increase in cost and an increase in noise as compared with the case where SiC is used for all the switching elements and the freewheeling diodes.

  In FIG. 1 above, the switching element of the upper arm of the voltage source bridge circuit is composed of SiC, the freewheeling diode of the upper arm is composed of Si, the switching element of the lower arm is composed of Si, and the freewheeling diode of the lower arm. As an example, the power conversion device configured with SiC is described, but the present invention is not limited to this configuration. For example, as shown in FIG. 3, the upper arm switching element is made of Si, the upper arm freewheeling diode is made of SiC, the lower arm switching element is made of SiC, and the lower arm freewheeling diode is made of Si. Even if it comprises, the effect mentioned above is acquired.

  Further, for example, the present invention can be applied to a step-up / step-down chopper circuit as shown in FIG. 4 in which the coil 13 is configured as an inductive load, and the above-described effects can be obtained similarly. In the configuration of FIG. 4, the switching element of the upper arm is composed of SiC and the free wheel diode of the lower arm is composed of SiC. However, the upper and lower relations are switched, and the switching element of the lower arm is changed as shown in FIG. Of course, it may be made of SiC, and the free-wheeling diode of the upper arm may be made of SiC.

  As described above, according to the power conversion device of the first embodiment, since SiC is used for a part of the switching element and the free wheel diode constituting the power conversion device, the reliability against thermal destruction caused by the loss is ensured. However, an increase in cost and an increase in noise peculiar to SiC can be suppressed.

Embodiment 2. FIG.
Next, a second embodiment will be described. FIG. 6 is a diagram showing a configuration of a power conversion device according to Embodiment 2 of the present invention. In the first embodiment, a power converter having a so-called single-phase half-bridge configuration using one voltage-type bridge circuit 22 having an upper and lower arm configuration has been described as an example. FIG. 6 shows a voltage-type bridge circuit having an upper and lower arm configuration. This is a power conversion device having a so-called single-phase full-bridge configuration using two 22. Other configurations are the same as those in the first embodiment.

  Even with such a configuration, the effects described in the first embodiment can be obtained in the same manner. In the configuration of FIG. 6, the switching element composed of SiC is composed only of the switching element of the upper arm, and the free wheeling diode composed of SiC is composed of only the free wheeling diode of the lower arm. Of course, as shown in FIG. 7, the switching element made of SiC may be constituted only by the switching element of the lower arm, and the free wheeling diode constituted by SiC may be constituted only by the free wheeling diode of the upper arm.

  Further, for example, the present invention can be applied to a three-phase power converter as shown in FIG. 8, and the above-described effects can be obtained similarly. In the configuration of FIG. 8, the switching element of the upper arm is made of SiC and the free wheel diode of the lower arm is made of SiC. However, the upper and lower relations are switched, and the switching element of the lower arm is changed as shown in FIG. Of course, it may be made of SiC, and the free-wheeling diode of the upper arm may be made of SiC.

  As described above, according to the power conversion device of the second embodiment, since SiC is used for a part of the switching element and the free wheel diode constituting the power conversion device, the reliability against thermal destruction caused by the loss is ensured. However, an increase in cost and an increase in noise peculiar to SiC can be suppressed.

Embodiment 3 FIG.
Next, a third embodiment will be described. FIG. 10 is a diagram showing a configuration of a power conversion device according to Embodiment 3 of the present invention. The configurations of the voltage source bridge circuit 22, the smoothing capacitors 11 a and 11 b, and the inductive load 12 are the same as those of the first embodiment.

  Further, a current sensor 16 for detecting current information is provided between the connection point between the upper arm and the lower arm of the voltage-type bridge circuit 22 and the inductive load 12, and the current information detected by the current sensor 16 is supplied to the polarity discriminator 15. input. FIG. 11 is a diagram showing details of the polarity discriminator 15. The potential difference between the two input voltages is amplified by the differential amplifier 202, and compared with zero by the comparator 203 to determine the positive or negative current polarity. The determined positive or negative current polarity is input to the control unit 14. Here, the direction of the current flowing from the connection point of the voltage source bridge circuit 22 shown in FIG. 10 toward the inductive load 12 is a positive current polarity.

  FIG. 12 is a diagram illustrating details of the control unit 14 related to switching of the switching frequency using the current polarity. The control unit 14 generates and outputs a preset low switching frequency (first switching frequency), and generates a switching frequency (second switching frequency) higher than the first switching frequency. According to the positive or negative current polarity output from the polarity discriminator 15, a high switching frequency is output as a switching command if the current polarity is positive, and a low switching frequency is output as a switching command if the current polarity is negative. A switch 17 is provided. Thus, the control unit 14 operates as a switching frequency switching unit.

  Here, FIG. 13 is a diagram showing the flow of current when the current polarity is positive, and the thick line shows the flow of current. When the current polarity is positive, under any operating condition, either the drain current 103 flowing through the switching element made of SiC or the forward current 105 flowing through the free wheel diode made of SiC, In any case, the SiC element always flows.

  FIG. 14 is a diagram illustrating a current of the power conversion device illustrated in FIG. 10 and a switching command corresponding to the current. (A) shows the waveform of the load current 301 flowing through the inductive load 12 or the coil 13, and (b) shows the waveform of the switching voltage 302. According to the current polarity of the load current 301, the switching voltage 302 is output at a high switching frequency when the polarity is positive and at a low switching frequency when the polarity is negative.

  According to this, during the period when the load current 301 is positive, that is, when it flows through the switching element or the free wheel diode composed of SiC, the switching frequency becomes high, and the load current 301 is negative, that is, flows through the switching element or the free wheel diode composed of Si. The switching frequency is low during the period. Therefore, the switching frequency can be temporarily increased as the power conversion device. Here, if SiC is used, loss can be tolerated even if the switching frequency is increased due to low loss, so reliability is not deteriorated.

  Further, FIG. 15 is a diagram showing a configuration of a power conversion apparatus in which voltage-type bridge circuits are connected in parallel, and the operation will be described based on this. Specifically, it has a configuration in which three voltage-type bridge circuits 22 having an upper and lower arm configuration are connected in parallel, that is, a three-phase power converter that forms a U phase, a V phase, and a W phase. Further, the switching elements made of SiC are located only in the upper arm of the voltage-type bridge circuit in all of the U phase, the V phase, and the W phase.

  FIG. 16 is a diagram illustrating details of the control unit 14 related to switching of the switching frequency using the current polarity in the case of the three-phase power device. Depending on the current polarity of the U-phase, V-phase, and W-phase output from the polarity discriminator 15, a high switching frequency is used as a switching command for each phase if the current polarity is positive and a low switching frequency if the current polarity is negative. Output each.

  At this time, FIG. 17 is a figure which shows the switching instruction | command corresponding to the electric current of the three-phase power converter device shown in FIG. 15, and an electric current. (A) shows the three-phase current waveforms detected by the current sensors 16a, 16b, and 16c, that is, the U-phase current 303, the V-phase current 304, and the W-phase current 305. (B) is a U-phase switching command 306, which has a high switching frequency when the U-phase current 303 has a positive current polarity and a low switching frequency when the U-phase current 303 has a negative current polarity. (C) is a V-phase switching command 307, which has a high switching frequency when the V-phase current 304 has a positive current polarity and a low switching frequency when the V-phase current 304 has a negative current polarity. (D) is a W-phase switching command 308, which has a high switching frequency when the W-phase current 305 has a positive current polarity and a low switching frequency when the W-phase current 305 has a negative current polarity.

  According to this, since at least one phase always flows in the reverse direction in the three-phase alternating current, if a switching element composed of SiC is arranged only in the upper arm, the current always flows in SiC. Therefore, SiC can always be used in any operating state, and is most efficient.

  As described above, according to the power conversion device of the third embodiment, it is possible to increase the switching frequency according to operating conditions by actively utilizing SiC while maintaining reliability against thermal breakdown. Therefore, reduction of motor loss due to electromagnetic noise and harmonic current due to switching can be realized, and cost and noise can be suppressed as compared with adopting SiC for all switching elements and freewheeling diodes.

  Here, in the third embodiment, as shown in FIGS. 10 and 15, the current polarity is obtained from the current information of the current sensor 16 or 16a, 16b, 16c, but it is not determined only by the current sensor. As shown in FIG. 18, current information can also be detected from the voltage across the terminals of the shunt resistor 18 connected in series to the switching element of the lower arm. Further, as shown in FIG. 19, current information can also be detected from the voltage between the collector and the emitter of the switching element.

  In the third embodiment, the current polarity output from the polarity discriminator 15 is used as a switching frequency switching element as shown in FIGS. 10 and 15. However, the current polarity is not determined only by the current polarity. The effective current value output from the effective value detector 19 may be used as shown in FIG. In that case, if the current effective value <threshold value, a high switching frequency is output as a switching command, and if the current effective value> threshold value, a low switching frequency is output as a switching command. Further, as shown in FIG. 21, the temperature output from the temperature detecting means 20 that measures or estimates the temperature of the switching element and the free wheel diode may be used. In this case, a high switching frequency is output as a switching command if temperature <threshold, and a low switching frequency is output if temperature> threshold with respect to a preset threshold.

  Further, as shown in FIG. 22, the switching frequency is changed based on the relationship of the switching frequency to the current effective value output from the preset effective value detector 19 (the table 21a is illustrated in FIG. 22), This switching frequency may be used as a switching command. Further, as shown in FIG. 23, the switching frequency is changed based on the relationship of the switching frequency with respect to the temperature output from the preset temperature detecting means 20 (the table 21b is illustrated in the figure), and this switching frequency is switched. It may be a command.

  In the third embodiment, only one piece of information is input to the switch 17 as shown in FIGS. 12, 20, and 21, but the number is not limited to one. For example, FIG. 24 is a diagram illustrating details of the control unit 14 related to switching of the switching frequency using the current polarity and the current effective value. In accordance with the positive or negative current polarity determined by the polarity discriminator 15 and the current effective value output by the effective value detector 19, the control unit 14 increases the switching frequency if the current polarity is positive or the current effective value <threshold. Is output as a switching command, and if the current polarity is negative and the current effective value> threshold, a low switching frequency is output as a switching command.

  For example, FIG. 25 is a diagram illustrating details of the control unit 14 related to switching of the switching frequency using the switching frequency table 21a with respect to the current polarity and the current effective value. The control unit 14 outputs a high switching frequency as a switching command when the current polarity is positive according to the positive or negative current polarity determined by the polarity determiner 15 and the effective current value output by the effective value detector 19. When the current polarity is negative, the switching frequency is output as a switching command based on the switching frequency table 21a for the preset current effective value.

  In the first to third embodiments, the configuration employing SiC, which is a low-loss power device, is disclosed, but is not limited to SiC. SiC is an example of a semiconductor called a wide bandgap semiconductor because it captures the characteristic that the bandgap is larger than that of Si (in contrast, Si is an example of a semiconductor called a narrow bandgap semiconductor). In addition to this SiC, for example, a semiconductor formed using a gallium nitride-based material (GaN) or diamond (C) belongs to a wide band gap semiconductor, and their characteristics are also similar to SiC. Accordingly, a configuration using a wide band gap semiconductor other than SiC also forms the gist of the present invention.

  In addition, since the switching element and the diode element formed of such a wide band gap semiconductor have high voltage resistance, the switching element and the free wheel diode can be downsized, and the semiconductor element module can be downsized. . In addition, since an element formed of a wide band gap semiconductor has high heat resistance, the heat sink can be downsized, and the cooling structure for cooling the semiconductor element module can be downsized.

  As described above, the power conversion device according to the present invention is useful as an invention that can reduce electromagnetic noise and motor loss while maintaining reliability against thermal destruction, and can further suppress cost increase and noise increase.

1a-1f Si switching element 2a-2f Si freewheeling diode 3a-3f SiC switching element 4a-4f SiC freewheeling diode 11a, 11b Smoothing capacitor 12 Inductive load 13 Coil 14 Control Unit 15 Polarity discriminator 16, 16a, 16b, 16c Current sensor 17 Switch 18 Shunt resistor 19 RMS detector 20 Temperature detection means 21a, 21b Table 22 Voltage source bridge circuit 103 Drain current 105 Forward current 202 Differential amplifier 203 Comparator 301 Load current 302 Switching command 303 U phase current 304 V phase current 305 W phase current 306 U phase switching command 307 V phase switching command 308 W phase switching command

Claims (12)

  A first element pair in which a switching element formed by a wide band gap semiconductor and a free wheel diode formed by a narrow band gap semiconductor are connected in reverse parallel, and a switching element formed by a narrow band gap semiconductor and a wide band gap semiconductor are formed. A power converter comprising a voltage-type bridge circuit having an upper and lower arm structure in which a second element pair having anti-reflux diodes connected in antiparallel is connected in series.   Two or more voltage-type bridge circuits having the upper and lower arm configurations are connected in parallel, and a switching element formed of the wide band gap semiconductor is disposed only on either the upper arm or the lower arm of the voltage-type bridge circuit. The power converter according to claim 1, wherein It has a configuration unit for generating and outputting a first switching frequency set in advance, and a configuration unit for generating and outputting a second switching frequency higher than the first switching frequency, the first element The switching frequency for controlling on / off of at least one of the pair of switching elements or the switching elements of the second element pair is either the first switching frequency or the second switching frequency. The power converter according to claim 1, further comprising a switching frequency switching unit that switches between the two. The voltage source bridge circuit includes a current detection means,
The said switching frequency switch part switches the said switching frequency by the positive / negative of the current polarity obtained from the said current detection means, The power converter device of Claim 3 characterized by the above-mentioned. The voltage source bridge circuit includes a current detection means,
4. The power converter according to claim 3, wherein the switching frequency switching unit switches the switching frequency based on a magnitude comparison between a current effective value obtained from the current detection unit and a preset threshold value. 5. Comprising a temperature detection means for measuring or estimating at least one of temperature of the switching element and the reflux diode, the switching frequency switching unit, comparison between a threshold value set in advance as the temperature obtained from the temperature detecting means The power conversion device according to claim 3, wherein the switching frequency is switched. The relationship of the switching frequency with respect to the effective current value is determined in advance, and at least one of the switching element formed by the narrow band gap semiconductor or the switching element formed by the wide band gap semiconductor is turned on / off. 6. The power conversion apparatus according to claim 5 , further comprising means for changing a switching frequency at the time of control according to the relationship. The relationship of the switching frequency with respect to the temperature obtained from the temperature detecting means is determined in advance, and at least one of the switching element formed by the narrow band gap semiconductor or the switching element formed by the wide band gap semiconductor The power converter according to claim 6 , further comprising means for changing a switching frequency when the on / off control is performed according to the relationship. Current detection means is provided on the output side,
The said switching frequency switch part switches the said switching frequency by the positive / negative of the current polarity obtained from the said current detection means , The power converter device of Claim 3 characterized by the above-mentioned . The power converter according to claim 4, wherein the current polarity is obtained from a shunt resistor connected in series to a switching element that is turned on. The power converter according to claim 4, wherein the current polarity is obtained from a collector-emitter voltage or a drain-source voltage of a switching element that is turned on. The power converter according to any one of claims 1 to 11, wherein the wide band gap semiconductor is a semiconductor using silicon carbide, a gallium nitride-based material, or diamond.