Power conversion device

Abstract

The purpose of the present invention is to suppress an increase in size and cost in a power conversion device having three or more single-phase inverters. A power conversion device (1) is provided with a control unit (4) that controls a single-phase inverter (2), and three or more single-phase inverters (2) that convert DC power into AC power, each of the three or more single-phase inverters (2). When the absolute value of the output voltage of each single-phase inverter is defined as the absolute value of the voltage and the minimum value of the absolute value of the voltage is defined as the minimum value of the absolute value of the voltage, the absolute value of the voltage of at least one single-phase inverter is set to a value equal to a power of 2 or a power of 3 of the minimum voltage value. The absolute value of the voltage of at least one of the other single-phase inverters is set to a value that is a real multiple, including a decimal, of the minimum voltage value.

Description

Technical Field

[0001] The present application relates to a power conversion device. Background Art

[0002] As one of the power conversion devices, a hierarchical control type power conversion device is known that can output a smooth AC waveform to a load without requiring a large-capacity output filter. The hierarchical control type power conversion device is composed of a plurality of single-phase inverters connected in series. As a conventional hierarchical control type power conversion device, a method of setting the absolute value of the output voltage of each of the plurality of single-phase inverters to approximately 2 K (K=0, 1, 2, ...) times power conversion device, which controls the total voltage of voltages output by a plurality of single-phase inverters in stages and outputs the total voltage to a load (for example, refer to Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2004-7941 Summary of the invention

[0004] In the case of outputting a high voltage sine wave close to the rated value in a conventional power conversion device, a plurality of output voltage levels of a single-phase inverter can be combined to form a waveform, thereby forming a smooth AC waveform close to a sine wave. However, in the case of outputting a low voltage sine wave in a conventional power conversion device, there is a problem as follows: the number of output voltage levels of the single-phase inverter combined to form the waveform decreases, thereby failing to form a smooth AC waveform.

[0005] The present application is proposed to solve the above-mentioned problems, and its object is to provide a power conversion device having a plurality of single-phase inverters, which can form a smooth AC waveform even when outputting a low-voltage AC waveform.

[0006] The power conversion device of the present application has more than or equal to three single-phase inverters and a control unit for controlling the single-phase inverters, wherein the more than or equal to three single-phase inverters convert DC power into AC power respectively. Furthermore, the more than or equal to three single-phase inverters are connected in series, and when the absolute value of the output voltage of each single-phase inverter is taken as the absolute value of the voltage and the minimum value of the absolute value of the voltage is taken as the minimum voltage value, the absolute value of the voltage of at least one single-phase inverter is set to a value of a power of 2 or a power of 3 of the minimum voltage value, and the absolute value of the voltage of at least another single-phase inverter is set to a value of a real number multiple of the minimum voltage value including a decimal.

[0007] Effects of the Invention

[0008] The absolute value of the voltage of at least one single-phase inverter of the power conversion device of the present application that is greater than or equal to three single-phase inverters is set to a value that is a power of 2 or a power of 3 of the minimum voltage value, and the absolute value of the voltage of at least another single-phase inverter is set to a value that is a real number multiple of the minimum voltage value including decimals. Therefore, even when outputting a low-voltage AC waveform, a smooth AC waveform can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a configuration diagram of a power conversion device according to Embodiment 1.

[0010] Figure 2 This is a configuration diagram of a single-phase inverter of the power conversion device according to the first embodiment.

[0011] Figure 3 This is a configuration diagram of a power conversion device according to Embodiment 1.

[0012] Figure 4 It is an explanatory diagram showing the total output voltage of the power conversion device according to the first embodiment.

[0013] Figure 5 It is a configuration diagram of a power conversion device of a comparative example according to the first embodiment.

[0014] Figure 6 It is an explanatory diagram showing the total output voltage of the power conversion device of the comparative example according to the first embodiment.

[0015] Figure 7 It is an explanatory diagram showing the total output voltage of the power conversion device according to the first embodiment.

[0016] Figure 8 This is a configuration diagram of a power conversion device according to Embodiment 1.

[0017] Fig. 9 It is an explanatory diagram showing the total output voltage of the power conversion device according to the first embodiment.

[0018] Fig.10 This is a configuration diagram of a power conversion device according to the second embodiment.

[0019] Fig.11 It is an explanatory diagram showing the total output voltage of the power conversion device according to the second embodiment.

[0020] Fig.12 This is a configuration diagram of a power conversion device according to the third embodiment.

[0021] Fig.13 This is a configuration diagram of a power conversion device according to the third embodiment.

[0022] Fig.14 It is an explanatory diagram showing the total output voltage of the power conversion device according to the third embodiment.

[0023] Fig.15 This is a diagram showing a hardware configuration that realizes a control unit of the power conversion device according to Embodiments 1 to 3. DETAILED DESCRIPTION

[0024] Hereinafter, a power conversion device according to an embodiment of the present application will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals in each figure represent the same or corresponding parts.

[0025] Implementation Method 1

[0026] Figure 1 2 is a block diagram of a power conversion device according to Embodiment 1. In the power conversion device 1 of this embodiment, three or more single-phase inverters 2 are connected in series. Figure 1 In the power conversion device 1 shown, INV1, INV2, INV3, ..., INV n-1 、INV n These n single-phase inverters 2 are connected in series. Here, n is a natural number. The single-phase inverters 2 are connected to the DC power supply 3 respectively. For example, n The output voltage of the DC power supply 3 connected to the single-phase inverter 2 is denoted as Vd n . Each single-phase inverter 2 converts the DC power supplied from the DC power source 3 into AC power after step-by-step control. Each single-phase inverter 2 is connected to a control unit 4. The control unit 4 controls each single-phase inverter 2 and outputs the sum of the output voltages of each single-phase inverter 2 as a total output voltage to a load 10. In the power conversion device 1 of this embodiment, there is an inverter group 5 composed of two or more single-phase inverters connected in series. Figure 1 In the power conversion device 1 shown in FIG. 1 , INV n-1 The single-phase inverter and INV n The single-phase inverters constitute the inverter group 5. The details of the inverter group 5 will be described later.

[0027] Figure 21 is a structural diagram of a single-phase inverter of a power conversion device according to the present embodiment. Each single-phase inverter 2 has a full-bridge circuit composed of four switching elements 11, 12, 21, 22 and a capacitor 23. The four switching elements 11, 12, 21, 22 are respectively connected in reverse parallel with a diode. The switching elements 11, 12, 21, 22 are, for example, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), etc. In the case where MOSFETs are used for the four switching elements 11, 12, 21, 22, the aforementioned reverse-parallel connected diodes can also be removed and replaced with the body diodes of the MOSFETs. The two ends of the capacitor 23 are respectively connected to input terminals 6a and 6b. A DC power supply is connected between the input terminals 6a and 6b. An output terminal 7a is connected between the switching element 11 and the switching element 12 constituting one bridge circuit, and an output terminal 7b is connected between the switching element 21 and the switching element 22 constituting another bridge circuit. Another single-phase inverter 2 or a load 10 is connected between the output terminals 7a and 7b.

[0028] also, Figure 2 The single-phase inverter shown has four switching elements, but is not limited thereto. For example, each switching element may be formed by connecting a plurality of switching elements in series for higher withstand voltage, or may be formed by connecting a plurality of switching elements in parallel for higher current.

[0029] Each single-phase inverter 2 can output a positive voltage, a negative voltage, and a zero voltage between output terminals 7a and 7b. Here, for the direction of the voltage between output terminals 7a and 7b, the situation where the potential of output terminal 7b is higher than the potential of 7a is defined as a positive voltage. For example, the positive terminal of the DC power supply is connected to the input terminal 6b side, and the negative terminal is connected to the input terminal 6a side. By setting the switch elements 11 and 22 to be turned on and the switch elements 12 and 21 to be turned off, the single-phase inverter 2 outputs a positive voltage between output terminals 7a and 7b. In addition, by setting the switch elements 11 and 22 to be turned off and the switch elements 12 and 21 to be turned on, the single-phase inverter 2 outputs a negative voltage between output terminals 7a and 7b. Further, by setting the switch elements 11 and 21 to be turned on or the switch elements 12 and 22 to be turned on, the single-phase inverter 2 outputs a zero voltage between output terminals 7a and 7b.

[0030] In addition, it is assumed that the resistance components of the switch elements, wiring, etc. between the input terminals 6a, 6b and the output terminals 7a, 7b of the single-phase inverter 2 are at a negligible level, so that the output voltage of the single-phase inverter is the same as the voltage of the DC power supply. Therefore, the output voltage of the single-phase inverter is described as the voltage of the DC power supply hereinafter.

[0031] In addition, when describing the ratio of the output voltages of the single-phase inverter 2 , it is assumed that it is the ratio of the absolute values ​​of the output voltages of the single-phase inverter 2 .

[0032] In the power conversion device of the present embodiment, the case where the inverter group 5 is regarded as one single-phase inverter, that is, the case where the total voltage of the DC power source connected to the inverter group 5 is regarded as the voltage of the DC power source connected to one single-phase inverter is considered. In this case, when the ratio of the minimum voltage value is set to 1, the voltage of the DC power source connected to each single-phase inverter is set to a ratio of 2 or 3 times the minimum voltage value. In addition, in the present embodiment, a power conversion device in which the voltage of the DC power source connected to each single-phase inverter is set to a ratio of 3 times is described.

[0033] exist Figure 1 In the power conversion device shown, the following relationship holds true for the voltage of the DC power source connected to each single-phase inverter.

[0034] Vd1:Vd2:Vd3:…:Vd n-1 +Vd n =3 0 :3 1 :3 2 :…:3 n-2

[0035] Here, Vd n-1 +Vd n INV n-1 、INV n The sum of the voltages of the DC power supplies connected to the single-phase inverters. n-1 and Vd n At least one of is set to a ratio such as 4.5 that includes a lower digit than the ratio 1 of the minimum voltage value. For convenience, the ratio that includes a lower digit than the ratio 1 of the minimum voltage value is referred to as a value of a real number multiple of the minimum voltage value including a decimal. Herein, a real number including a decimal refers to a real number having a value other than 0 after the decimal point, such as 1.5, 2.6, 3.65, etc.

[0036] Hereinafter, a power conversion device composed of four single-phase inverters will be described as an example.

[0037] Figure 3 This is a configuration diagram of a power conversion device including four single-phase inverters according to the present embodiment. Figure 3 The power conversion device 1 shown has four single-phase inverters 2, INV1, INV2, INV3, and INV4, and four DC power supplies 3 connected to the single-phase inverters 2, respectively. Furthermore, if the voltages of the four DC power supplies 3 are set to Vd1, Vd2, Vd3, and Vd4, respectively, then Vd1 = V0, Vd2 = 3V0, Vd3 = 4.5V0, and Vd4 = 4.5V0 are set. Here, V0 is the minimum voltage value of the DC power supply connected to the single-phase inverter. That is, Vd1:Vd2:Vd3:Vd4 = 1:3:4.5:4.5. Therefore, in Figure 3 In the power conversion device 1 shown in FIG. 1 , the inverter group 5 is composed of the single-phase inverter of INV3 and the single-phase inverter of INV4. In addition, in the power conversion device 1 , Vd1 : Vd2 : Vd3 + Vd4 = 3 0 :3 1 :3 2 (=1:3:9) holds. In addition, Vd3 and Vd4 are set to values ​​that are real number multiples of the minimum voltage value, including decimals.

[0038] Figure 4 It is an explanatory diagram showing the total output voltage of the power conversion device according to the present embodiment. Figure 4 The voltage output by each single-phase inverter relative to the total output voltage is shown. Figure 4 In , the voltage ratio indicates the voltage ratio of the four DC power supplies, and the total output voltage indicates the ratio of the total output voltage to the minimum ratio 1 of the voltage ratio. Figure 4 In the figure, "+" indicates that a positive voltage is output from the corresponding single-phase inverter, "-" indicates that a negative voltage is output, and a blank column indicates that a zero voltage is output. For example, it is shown that when the total output voltage is 2.5, the INV1 single-phase inverter with a voltage ratio of 1 outputs a positive voltage, the INV2 single-phase inverter with a voltage ratio of 3 outputs a negative voltage, the INV3 single-phase inverter with a voltage ratio of 4.5 outputs a positive voltage, and the INV4 single-phase inverter with a voltage ratio of 4.5 outputs a zero voltage (1-3+4.5+0=2.5).

[0039] Figure 5 1 is a block diagram of a power conversion device according to a comparative example of the present embodiment. When the inverter group is regarded as a single-phase inverter, Figure 3 The power conversion device of the present embodiment shown is composed of three single-phase inverters. Figure 5The power conversion device 1 of the comparative example shown has three single-phase inverters 2, INV1, INV2, and INV3, and three DC power supplies 3 connected to the single-phase inverters 2, respectively. And, if the voltages of the three DC power supplies 3 are respectively set to Vd1, Vd2, and Vd3, then Vd1 = V0, Vd2 = 3V0, and Vd3 = 9V0. That is, in the power conversion device 1 of the comparative example, Vd1: Vd2: Vd3 = 3 0 :3 1 :3 2 (=1:3:9) is established. Figure 6 It is an explanatory diagram showing the total output voltage of the power conversion device of the comparative example according to the present embodiment.

[0040] right Figure 4 The total output voltage of the power conversion device of this embodiment shown is Figure 6 The total output voltage of the power conversion device of the comparative example shown in the figure is compared. The maximum value of the total output voltage is 13 in both the power conversion device of the present embodiment and the power conversion device of the comparative example. However, if the comparison is made based on the grading level, the power conversion device of the present embodiment can output the total output voltage in a grading level of 22 divisions between 0 and 13, while the power conversion device of the comparative example can only output the total output voltage in a grading level of 13 divisions between 0 and 13. That is, in the power conversion device of the comparative example, the total output voltage can only be output in a grading level that is an integer multiple of the minimum voltage value. In contrast, in the power conversion device of the present embodiment, as long as the total output voltage is in the range of 0 to 9, the total output voltage can be output in a grading level that is 0.5 times the minimum voltage value.

[0041] For example, in the power conversion device of the present embodiment and the power conversion device of the comparative example, the case of outputting a sine wave with a peak value of 3V0 is compared. In the power conversion device of the present embodiment, a sine wave can be formed with a total output voltage of 0, ±0.5V0, ±1V0, ±1.5V0, ±2V0, ±2.5V0, ±3V0, a ​​total of 13 gradation levels. In contrast, in the power conversion device of the comparative example, a sine wave can only be formed with a total output voltage of 0, ±1V0, ±2V0, ±3V0, a ​​total of 7 gradation levels.

[0042] The power conversion device of this embodiment has more than or equal to three single-phase inverters that convert DC power into AC power respectively and a control unit that sends hierarchical control signals to the single-phase inverters respectively. When the minimum value of the output voltages of each single-phase inverter is used as the minimum voltage value, the output voltage of at least one single-phase inverter is set to a value that is a power of 3 times the minimum voltage value, and the output voltage of at least one other single-phase inverter is set to a value that is a real number multiple of the minimum voltage value including a decimal. Therefore, the power conversion device of this embodiment can form a smooth AC waveform even when outputting a low-voltage AC waveform.

[0043] In addition, the power conversion device of the present embodiment has an inverter group composed of two or more single-phase inverters connected in series, so the DC voltage applied to each single-phase inverter constituting the inverter group can be reduced. Therefore, electronic components with low withstand voltage can be used as switching elements and capacitors constituting the single-phase inverter. Generally, for electronic components, the lower the withstand voltage, the lower the power loss and the faster the response speed. By using electronic components with low withstand voltage, it is possible to achieve miniaturization, low loss, high speed, etc. of the power conversion device.

[0044] In the power conversion device of the present embodiment, the inverter group is provided at the position of the single-phase inverter having the largest output voltage, but the position of the inverter group is not limited to this position. Figure 3 In the power conversion device of the present embodiment shown in FIG. Figure 5 The inverter group is provided at the position of the single-phase inverter with a voltage ratio of 9 in the power conversion device of the comparative example shown, but the inverter group may also be provided at the position of the single-phase inverter with a voltage ratio of 3 in the power conversion device of the comparative example. However, from the viewpoint of reducing the DC voltage applied to each single-phase inverter constituting the above-mentioned inverter group, the inverter group is preferably provided at the position of the single-phase inverter with the largest output voltage. In addition, the power conversion device of this embodiment has one inverter group, but may also have a plurality of inverter groups. For example, in Figure 3 In the power conversion device of the present embodiment shown, the single-phase inverter with a voltage ratio of 3 may be replaced with an inverter group.

[0045] like Figure 4As shown, in the power conversion device of the present embodiment, when the total output voltage is switched from 1 to 1.5 and from 1.5 to 2, the output of the single-phase inverter INV3 included in the inverter group 5 is switched from zero output to positive voltage output and from positive voltage output to zero voltage output. As described above, in the power conversion device of the present embodiment, it is possible that the number of on-off times of the single-phase inverter included in the inverter group 5 increases, and the on-off loss increases. In the case where the on-off loss becomes a problem, for example, when the load current or the load power increases in heavy load operation, it is also possible to reduce the on-off loss by not using the single-phase inverter included in the inverter group and only using a single-phase inverter whose output voltage is set to a power of 3 times the minimum voltage value. As described above, it is also possible to consider the smoothness of the output waveform and the priority of low on-off loss according to the load condition, and switch the action mode to respond.

[0046] In addition, in the power conversion device of this embodiment, the output voltages of the plurality of single-phase inverters included in the inverter group are made the same. In this case, the single-phase inverters to be switched on and off can also be replaced in the inverter group 5. For example, Figure 4 In the power conversion device of the present embodiment shown, when a sine wave with a peak value of 13V0 is output, the number of on-off times of the single-phase inverter INV3 outputting 4.5V is greater than the number of on-off times of the single-phase inverter INV4 outputting the same 4.5V. In this case, the on-off of the single-phase inverter INV3 with a total output voltage between 0V0 and 5V0 can also be replaced by the on-off of the single-phase inverter INV4 in the next cycle of the sine wave. Alternatively, the single-phase inverters INV3 and INV4 can be alternately turned on and off in the sine wave of the same cycle. By operating as described above, it is possible to prevent the on-off loss from being concentrated on one single-phase inverter.

[0047] In the power conversion device of this embodiment, the output voltages of the plurality of single-phase inverters included in the inverter group may be different. Figure 3 In the power conversion device of the present embodiment shown, what was set to Vd1:Vd2:Vd3:Vd4=1:3:4.5:4.5 may be set to Vd1:Vd2:Vd3:Vd4=1:3:4.33:4.66. Figure 7 1 is an explanatory diagram showing the total output voltage of the power conversion device of this embodiment set as described above. Figure 7As shown, by setting the output voltages of the multiple single-phase inverters included in the inverter group 5 to different values, the total output voltage can be output in a graded level divided into 32 levels between 0 and 13 in the power conversion device of this embodiment. As described above, the power conversion device that sets the output voltages of the multiple single-phase inverters included in the inverter group to different values ​​can increase the number of divisions of the graded level compared to the power conversion device that sets the output voltages of the multiple single-phase inverters included in the inverter group to the same value. In addition, the output voltage is preferably able to be output at equal intervals. For example, by using the value after the decimal point of the real number multiple including the decimal of the minimum voltage value as Figure 3 As shown, it is set to 1 / 2, so that a 1 / 2 scale voltage can be output. Figure 7 As shown, it is set to 1 / 3 or 2 / 3, so that a voltage of 1 / 3 scale can be output.

[0048] The power conversion device of the present embodiment described so far is a power conversion device in which an inverter group is composed of two single-phase inverters. The number of single-phase inverters constituting the inverter group may be three or more. Figure 8 It is a configuration diagram of a power conversion device according to this embodiment. Figure 8 The power conversion device 1 of the present embodiment shown in the figure has five single-phase inverters 2, namely INV1, INV2, INV3, INV4, and INV5, and five DC power supplies 3 connected to the single-phase inverters 2, respectively. Furthermore, if the voltages of the five DC power supplies 3 are respectively set to Vd1, Vd2, Vd3, Vd4, and Vd5, then Vd1=V0, Vd2=3V0, Vd3=2.5V0, Vd4=3V0, and Vd5=3.5V0. That is, in Figure 8 In the power conversion device 1 shown in FIG. 1 , the inverter group 5 is composed of three single-phase inverters, INV3, INV4, and INV5. In the power conversion device 1, Vd1:Vd2:Vd3+Vd4+Vd5=3 0 :3 1 :3 2 (=1:3:9) holds. Vd3 and Vd5 are set to values ​​that are real number multiples of the minimum voltage value, including decimals.

[0049] Fig. 9 1 is an explanatory diagram showing the total output voltage of the power conversion device of this embodiment set as described above. Fig. 9 As shown, by increasing the number of single-phase inverters included in the inverter group 5, the total output voltage can be output in a 24-divided grade between 0 and 13 in the power conversion device of this embodiment. Figure 4As shown, the number of the classification level in the power conversion device including two single-phase inverters in the inverter group 5 is 22 divisions. In this way, the power conversion device including three single-phase inverters in the inverter group can increase the number of divisions of the classification level compared to the power conversion device including two single-phase inverters in the inverter group.

[0050] In addition, Figure 8 In the power conversion device of the present embodiment shown in FIG. 1 , the voltages of the DC power supplies connected to the three single-phase inverters included in the inverter group are set to 2.5V0, 3V0, and 3.5V0, respectively. Figure 8 In the power conversion device shown, one of the three DC power supplies included in the inverter group is set to a voltage that is an integer multiple of the minimum voltage value. In the power conversion device of this embodiment, it is not necessary to set the voltages of all DC power supplies respectively connected to the single-phase inverters included in the inverter group to values ​​that are real multiples of the minimum voltage value, including decimals.

[0051] As described above, in a power conversion device having three or more single-phase inverters that convert DC power into AC power and a control unit that sends hierarchical control signals to the single-phase inverters, an inverter group consisting of a plurality of single-phase inverters is formed, and the ratio of the total value of the output voltages of the single-phase inverters included in the inverter group to the output voltages of the single-phase inverters not included in the inverter group is set to a power of 3. Furthermore, the output voltage of at least one single-phase inverter included in the inverter group is set to a value that is a real number multiple of the minimum voltage value of the output voltage of the single-phase inverter, including a decimal. The power conversion device thus configured can form a smooth AC waveform even when outputting a low-voltage AC waveform.

[0052] In addition, the power conversion device constructed in this way can reduce the DC voltage applied to the single-phase inverter included in the inverter group. Therefore, electronic components with low withstand voltage can be used as switching elements and capacitors constituting the single-phase inverter, which can achieve miniaturization, low loss, high speed, etc. of the power conversion device.

[0053] Implementation Method 2

[0054] In the first embodiment, a power conversion device is described in which the voltage of the DC power source connected to each single-phase inverter is set to a value multiplied by a power of 3. In the second embodiment, a power conversion device is described in which the voltage of the DC power source connected to each single-phase inverter is set to a value multiplied by a power of 2.

[0055] The structure of the power conversion device of this embodiment is similar to that of the first embodiment. Figure 1However, the power conversion device of this embodiment has the same structure as that of the power conversion device shown in FIG. Figure 1 In the power conversion device shown, the following relationship holds true for the voltage of the DC power source connected to each single-phase inverter.

[0056] Vd1:Vd2:Vd3:…:Vd n-1 +Vd n =2 0 :2 1 :2 2 :…:2 n-2

[0057] Here, Vd n-1 +Vd n INV n-1 、INV n The sum of the voltages of the DC power supplies connected to the single-phase inverters. n-1 and Vd n At least one of is set to a value that is a real number multiple of the minimum voltage value, including a decimal.

[0058] Hereinafter, a power conversion device composed of four single-phase inverters will be described as an example.

[0059] Fig.10 This is a configuration diagram of a power conversion device including four single-phase inverters according to the present embodiment. Fig.10 The power conversion device 1 shown has four single-phase inverters 2, INV1, INV2, INV3, and INV4, and four DC power supplies 3 connected to the single-phase inverters 2, respectively. Furthermore, if the voltages of the four DC power supplies 3 are set to Vd1, Vd2, Vd3, and Vd4, respectively, then Vd1 = V0, Vd2 = 2V0, Vd3 = 1.5V0, and Vd4 = 2.5V0 are set. Here, V0 is the minimum voltage value of the DC power supply connected to the single-phase inverter. That is, Vd1:Vd2:Vd3:Vd4 = 1:2:1.5:2.5. Therefore, in Fig.10 In the power conversion device 1 shown, INV3 and INV4 constitute the inverter group 5. In the power conversion device 1, Vd1:Vd2:Vd3+Vd4=2 0 :2 1 :2 2 (=1:2:4) holds. In addition, Vd3 and Vd4 are set to values ​​that are real number multiples of the minimum voltage value, including decimals.

[0060] Fig.11 It is an explanatory diagram showing the total output voltage of the power conversion device according to the present embodiment. Fig.11The voltage output by each single-phase inverter relative to the total output voltage is shown. Fig.11 As shown, it can be seen that in the power conversion device of this embodiment, the total output voltage can be adjusted to the gradation level at a voltage value half of the minimum voltage value until the total output voltage reaches 6. Therefore, in the power conversion device in which the voltage of the DC power supply connected to each single-phase inverter is set to a value multiplied by a power of 2, by providing an inverter group, a smooth AC waveform can be formed even when a low-voltage AC waveform is output.

[0061] As described above, in a power conversion device having three or more single-phase inverters that convert DC power into AC power and a control unit that sends hierarchical control signals to the single-phase inverters, an inverter group consisting of a plurality of single-phase inverters is formed, and the ratio of the total value of the output voltages of the single-phase inverters included in the inverter group to the output voltages of the single-phase inverters not included in the inverter group is set to a power of 2. Furthermore, the output voltage of at least one single-phase inverter included in the inverter group is set to a value that is a real number multiple of the minimum voltage value of the output voltage of the single-phase inverter, including decimals. The power conversion device thus constructed can form a smooth AC waveform even when outputting a low-voltage AC waveform.

[0062] In addition, the power conversion device constructed in this way can reduce the DC voltage applied to the single-phase inverter included in the inverter group. Therefore, electronic components with low withstand voltage can be used as switching elements and capacitors constituting the single-phase inverter, which can achieve miniaturization, low loss, high speed, etc. of the power conversion device.

[0063] Implementation 3

[0064] Fig.12 1 is a block diagram of a power conversion device according to Embodiment 3. In the power conversion device 1 of this embodiment, k+m+1 single-phase inverters 2 are connected in series. Here, k is a natural number, and m is an integer greater than or equal to 0. However, k+m is greater than or equal to 2. The single-phase inverters 2 are connected to the DC power supply 3, respectively. For example, n The output voltage of the DC power supply 3 connected to the single-phase inverter 2 is denoted as Vd n Each single-phase inverter 2 converts the DC power supplied from the DC power source 3 into AC power after step-by-step control. Each single-phase inverter 2 is connected to the control unit 4. The control unit 4 controls each single-phase inverter 2 and outputs the sum of the output voltages of each single-phase inverter 2 as the total output voltage to the load 10.

[0065] In addition, in the power conversion device of this embodiment, the output voltage of the single-phase inverter is the same as the voltage of the DC power supply, as in Embodiment 1. Therefore, the output voltage of the single-phase inverter is described as the voltage of the DC power supply. In the power conversion device of this embodiment, the minimum value of the output voltage of the single-phase inverter is set to V0. And Vd1 = V0.

[0066] For INV1 to INV k The voltage of the DC power supply to which the single-phase inverter is connected, the relationship described below holds true.

[0067] Vd1:Vd2:Vd3:…:Vd k =3 0 :3 1 :3 2 :…:3 K-1

[0068] And, with INV k+1 The output voltage Vd of the single-phase inverter 2 connected to the DC power supply 3 k+1 It is set in the following range.

[0069] Vd1+Vd2+Vd3+…+Vd k <Vd k+1 <Vd1+Vd2+Vd3+…+Vd k +Vd1

[0070] Furthermore, for INV k+1 To INV k+m+1 The voltage of the DC power supply to which the single-phase inverter is connected, the relationship described below holds true.

[0071] Vd k+1 :Vd k+2 :Vd k+3 :…:Vd k+m+1 =3 0 :3 1 :3 2 :…:3 m

[0072] In addition, m is an integer greater than or equal to 0, and m may be 0. In this case, the above INV k+1 The single-phase inverter becomes the single-phase inverter that outputs the maximum output voltage.

[0073] Hereinafter, a power conversion device composed of four single-phase inverters will be described as an example.

[0074] Fig.13 This is a configuration diagram of a power conversion device including four single-phase inverters according to the present embodiment. Fig.13The power conversion device 1 shown is Fig.12 The power conversion device shown has a structure in which k=2 and m=1. Fig.13 The power conversion device 1 shown has four single-phase inverters 2, INV1, INV2, INV3, and INV4, and four DC power supplies 3 connected to the single-phase inverters 2, respectively. Furthermore, if the voltages of the four DC power supplies 3 are set to Vd1, Vd2, Vd3, and Vd4, respectively, then Vd1 = V0, Vd2 = 3V0, Vd3 = 4.5V0, and Vd4 = 13.5V0. Here, V0 is the minimum voltage value of the DC power supply connected to the single-phase inverter. That is, Vd1:Vd2 = 3 0 :3 1 (=1:3). And Vd3 is 4.5V0 which is greater than Vd1+Vd2=4V0 and less than Vd1+Vd2+Vd1=5V0. That is, Vd3 is set to a value that is a real number multiple of the minimum voltage value including decimals. Further, Vd3:Vd4=3 0 :3 1 (=1:3).

[0075] Fig.14 It is an explanatory diagram showing the total output voltage of the power conversion device according to the present embodiment. Fig.14 The voltage output by each single-phase inverter relative to the total output voltage is shown. Fig.14 As shown, it can be seen that in the power conversion device of this embodiment, the grading level can be adjusted with a voltage value half of the minimum voltage value until the total output voltage reaches 18. Therefore, the power conversion device of this embodiment can form a smooth AC waveform even when outputting a low-voltage AC waveform.

[0076] In the power conversion device of this embodiment, Vd3 is set to a value 4.5 times the minimum voltage value. Therefore, the total output voltage is divided into levels at intervals of 0.5 times the minimum voltage value. The value after the decimal point of the value of a real number multiple including a decimal is not limited to 0.5. For example, Vd3 may be set to a value 4.3 times or 4.7 times the minimum voltage value. However, if Fig.14 As shown, it is preferable that the intervals between the graded levels of the total output voltage be constant, and therefore the value after the decimal point of the value of the real number multiple including the decimal is set to 0.5.

[0077] like Fig.14As shown, in the case where the total output voltage is switched from 4.5 to 5 and from 5 to 5.5 in the power conversion device of the present embodiment, the output of the single-phase inverter INV4 outputting the maximum voltage is switched from zero output to positive voltage output and from positive voltage output to zero output. As described above, in the power conversion device of the present embodiment, it is possible that the number of on-off times of the single-phase inverter outputting the maximum voltage increases, and the on-off loss increases. In the case where the on-off loss becomes a problem, such as when the load current or the load power increases in heavy load operation, it is also possible to reduce the on-off loss by not using the single-phase inverter outputting the maximum voltage and only using the single-phase inverter whose output voltage is set to a power of 3 times the minimum voltage value. As described above, it is also possible to consider the smoothness of the output waveform and the priority of low on-off loss according to the load condition, and switch the action mode to respond.

[0078] The power conversion device of the present embodiment described so far is a structure in which the ratio of the output voltage of the single-phase inverter is a power of 3. In the power conversion device of the present embodiment, the ratio of the output voltage of the single-phase inverter may also be a power of 2. In this case, Fig.12 In the power conversion device of the present embodiment shown, the following relationship holds. In this case, the minimum value of the output voltage of the single-phase inverter is also set to V0. And Vd1 = V0.

[0079] For INV1 to INV k The voltage of the DC power supply to which the single-phase inverter is connected, the relationship described below holds true.

[0080] Vd1:Vd2:Vd3:…:Vd k =2 0 :2 1 :2 2 :…:2 k-1

[0081] And, with INV k+1 The output voltage Vd of the single-phase inverter 2 connected to the DC power supply 3 k+1 It is set in the following range.

[0082] Vd1+Vd2+Vd3+…+Vd k <Vd k+1 <Vd1+Vd2+Vd3+…+Vd k +Vd1

[0083] Furthermore, for INV k+1 To INV k+m+1 The voltage of the DC power supply to which the single-phase inverter is connected, the relationship described below holds true.

[0084] Vdk+1 :Vd k+2 :Vd k+3 :…:Vd k+m+1 =2 0 :2 1 :2 2 :…:2 m

[0085] In the power conversion device configured as described above, even when outputting a low-voltage AC waveform, a smooth AC waveform can be formed.

[0086] In addition, an example of the hardware of the control unit 4 is as follows Fig.15 As shown, the processor 100 and the storage device 101 are composed. Although not shown in the figure, the storage device includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. In addition, an auxiliary storage device such as a hard disk may be provided instead of the flash memory. The processor 100 executes a program input from the storage device 101. In this case, the program is input from the auxiliary storage device to the processor 100 via the volatile storage device. In addition, the processor 100 can output data such as calculation results to the volatile storage device of the storage device 101, and can also save data in the auxiliary storage device via the volatile storage device.

[0087] In addition, the control unit 4 may be a digital controller such as FPGA (Field Programmable Gate Array) or MCU (MicroController Unit). Alternatively, the control unit 4 may be a structure in which an analog circuit and a digital controller exist in combination.

[0088] This application describes various exemplary embodiments, but various features, schemes, and functions described in one or more embodiments are not limited to application to specific embodiments, and can be applied to the embodiments alone or in various combinations.

[0089] Therefore, within the technical scope disclosed in the present application, numerous modifications not shown in the examples are conceivable, including, for example, the modification, addition or omission of at least one structural element, and the extraction of at least one structural element and the combination of the structural elements of other embodiments.

[0090] Description of the label

[0091] 1 power conversion device, 2 single-phase inverter, 3 DC power supply, 4 control unit, 5 inverter group, 6a, 6b input terminals, 7a, 7b output terminals, 10 load, 11, 12, 21, 22 switching elements, 23 capacitor, 100 processor, 101 storage device.

Claims

1. A power conversion device comprising three or more single-phase inverters and a control unit for controlling the single-phase inverters, wherein the three or more single-phase inverters convert DC power into AC power respectively. The power conversion device is characterized in that More than or equal to three single-phase inverters are connected in series, and when the absolute values ​​of the output voltages of the respective single-phase inverters are taken as the absolute values ​​of the voltages and the minimum value of the absolute values ​​of the voltages is taken as the minimum voltage value, the absolute value of the voltage of at least one single-phase inverter is set to a value that is a power of 2 or a power of 3 of the minimum voltage value, and the absolute value of the voltage of at least another single-phase inverter is set to a value that is a real number multiple of the minimum voltage value, including decimals.

2. The power conversion device according to claim 1, characterized in that: There is one or more inverter group consisting of two or more single-phase inverters connected in series, the absolute value of the voltage of the single-phase inverter not included in the inverter group is set to a value that is a power of 2 or a power of 3 of the minimum voltage value, and the absolute value of the voltage of at least one single-phase inverter included in the inverter group is set to a real number multiple of the minimum voltage value including decimals.

3. The power conversion device according to claim 2, characterized in that: The absolute value of the voltage of at least one of the single-phase inverters included in the inverter group is the maximum value of the absolute values ​​of the voltages of the single-phase inverters.

4. The power conversion device according to claim 2 or 3, characterized in that: A total value of the absolute values ​​of the voltages of the single-phase inverters constituting the inverter group is larger than the absolute value of the voltages of the single-phase inverters not included in the inverter group.

5. The power conversion device according to any one of claims 1 to 4, characterized in that: The value after the decimal point of the real number multiple including the decimal of the minimum voltage value is 1 / 3, 1 / 2 or 2 / 3.

6. The power conversion device according to claim 1, characterized in that: When k is a natural number and m is an integer greater than or equal to 0, k+m is greater than or equal to 2, and the power conversion device has k+m+1 single-phase inverters. The absolute values ​​of the voltages of k single-phase inverters are set to values ​​that are powers of 2 or 3 of the minimum voltage value, the absolute value of the voltage of another single-phase inverter is set to a value that is greater than the sum of the absolute values ​​of the voltages of the k single-phase inverters and less than a value obtained by adding the minimum voltage value to the sum of the absolute values ​​of the voltages of the k single-phase inverters, and the absolute values ​​of the voltages of the other m single-phase inverters are set to values ​​that are powers of 2 or 3 of the absolute value of the voltage of the other single-phase inverter.

7. The power conversion device according to claim 6, characterized in that: The voltage absolute value of the one single-phase inverter is set to a value obtained by adding 1 / 2 of the minimum voltage value to the sum of the voltage absolute values ​​of the k single-phase inverters.

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