Three-phase inverter apparatus

Abstract

To further improve a suppression function in a three-phase inverter apparatus in which a common mode voltage is suppressed using a transformer.SOLUTION: A three-phase inverter apparatus 14 includes an input-side transformer device 18, a three-phase PWM converter 20, and an output-side transformer device 22 in this order from an input side to an output side. The input-side transformer 18 and the output-side transformer device 22 respectively suppress a common mode voltage at the input side and the output side in accordance with input-side and output-side secondary voltages generated from input-side and output-side primary voltages corresponding to the common mode voltage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a three-phase inverter device with a common-mode voltage suppression function. [Background technology]

[0002] In a three-phase circuit incorporating a three-phase inverter, the sum of the phase voltages is not necessarily zero, and a common-mode voltage occurs. Common-mode voltages cause ground fault currents and generate noise, so it is desirable to eliminate them.

[0003] Patent Document 1 discloses a three-phase inverter device that includes a transformer as a passive common-mode noise canceller (PCC). This three-phase inverter device includes a detector that detects common-mode voltages on the output side of the three-phase inverter, and a transformer that generates a primary voltage corresponding to the common-mode voltage detected by the detector and generates secondary voltages on each of the three output lines of the three-phase inverter to suppress the common-mode voltage. This three-phase inverter device also includes a residual common-mode voltage detection circuit to compensate for a decrease in the common-mode voltage suppression function due to leakage flux from the transformer windings, and corrects the primary voltage of the transformer according to the detected residual common-mode voltage.

[0004] Non-Patent Document 1 discloses a three-phase inverter device in which three transformers are connected in series on the output side of a three-phase inverter. In this three-phase inverter device, each transformer has a secondary winding on each of the three output lines on the output side of the three-phase inverter, and one end of the primary winding is inserted between the corresponding output terminal of the three-phase inverter and the midpoint of the DC power supply. In addition, the turns ratio between the primary winding and the secondary winding in each transformer is 3:1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6803478 [Non-patent literature]

[0006] [Non-Patent Document 1] Shunsuke Obara, Yuto Kawada, Satoshi Ogasawara, and Koji Orikawa: "Passive Common Noise Canceller Capable of Canceling Common-Mode Voltage Generated by Inverters," Transactions on Industrial Applications, IEEJ, Vol. 142, No. 11, pp. 825-834, DOI: 10,541 / ieejias.142,825 (Received May 10, 2022, Reaccepted July 11, 2022) Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors have found that the three-phase inverter devices of Patent Document 1 and Non-Patent Document 1 have room for further improvement in terms of suppressing common-mode voltage (this finding will be described later with reference to FIGS. 6A to 6C, etc.).

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a three-phase inverter device that has an improved suppression function when a transformer is used to suppress a common-mode voltage. [Means for solving the problem]

[0009] The three-phase inverter device of the present invention comprises: a three-phase inverter that converts a DC voltage input from a DC power supply via a first input line and a second input line into a three-phase AC voltage and outputs the three-phase AC voltage to a first output line, a second output line, and a third output line; an input transformer device that generates an input primary voltage corresponding to a common mode voltage and generates an input secondary voltage on each input line that reduces the common mode voltage; an output transformer device that generates an output primary voltage corresponding to the common mode voltage and generates an output secondary voltage that reduces the common mode voltage on each output line; Equipped with. [Effects of the Invention]

[0010] According to the present invention, a transformer is provided on each of the input and output sides of a three-phase inverter, and a primary voltage corresponding to the common-mode voltage is generated in each of the input and output transformers. A secondary voltage is then applied to the input and output sides of the three-phase inverter to suppress the common-mode voltage. This makes it possible to further reduce the common-mode voltage that cannot be sufficiently suppressed by the output transformer alone. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a three-phase electrical system including a three-phase inverter device according to an embodiment; [Figure 2] FIG. 1 is a circuit diagram of a three-phase PWM converter. [Figure 3] FIG. 2 is a diagram showing waveforms of a common mode (CM) voltage in a three-phase PWM converter. [Figure 4] FIG. 1 is a schematic diagram of a comparative model for a three-phase electrical system. [Figure 5A] FIG. 1 shows, as a baseline, the changes in the time domain of the CM voltage and CM current when no measures against CM voltage are taken, i.e., when the DC voltage of a DC power supply is directly input to a three-phase PWM converter and directly output to a three-phase AC motor. [Figure 5B] This is a CM voltage diagram when a common mode inductor (CMI) is provided in each phase line on the output side of a DC power supply as a countermeasure against CM voltage. [Figure 5C] FIG. 10 is a time-domain waveform diagram of the CM voltage and CM current in the comparison model. [Figure 6A] 10 is an experimental graph comparing the input-side CM current of a three-phase PWM converter between a comparison model and a three-phase electrical system. [Figure 6B] 10 is an experimental graph comparing the output side CM current of a three-phase PWM converter between a comparison model and a three-phase electrical system. [Figure 6C] 10 is an experimental graph comparing the heat sink CM current of a three-phase PWM converter between a comparison model and a three-phase electrical system. [Figure 7A]6B is a comparison graph in which only the characteristic lines of the comparison model and the three-phase electrical system are extracted from the upper and lower graphs of FIG. 6A and combined into a single graph. [Figure 7B] 6B. FIG. 6C is a comparison graph in which only the characteristic lines of the comparison model and the three-phase electrical system are extracted from the upper and lower graphs of FIG. 6B and combined into a single graph. [Figure 7C] 6C. This is a comparison graph in which only the characteristic lines of the comparison model and the three-phase electrical system are extracted from the upper and lower graphs of FIG. 6C and combined into a single graph. [Figure 8] FIG. 1 is an equivalent circuit diagram of a three-phase electrical system that considers CM currents through the heat sink of a three-phase PWM converter as well as the motor case of a three-phase AC motor. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described. It goes without saying that the present invention is not limited to this embodiment. Note that components common to multiple figures are denoted by the same reference numerals.

[0013] (Embodiment / Configuration) FIG. 1 is a configuration diagram of a three-phase electrical system 10 including a three-phase inverter device 14 according to an embodiment. The three-phase electrical system 10 is applied to, for example, a three-phase motor drive system mounted on an electric vehicle. The three-phase electrical system 10 includes, in order from input side to output side, a DC power supply 12, a three-phase inverter device 14, and a three-phase AC motor 16. The three-phase inverter device 14 has input terminals 24a and 24b and output terminals 26u, 26v, and 26w. The three-phase inverter device 14 includes, in order from input side to output side, an input-side transformer device 18, a three-phase PWM converter 20, and an output-side transformer device 22.

[0014] The DC power supply 12 is a battery with a voltage across it of E (e.g., 200 V) that can be repeatedly charged and discharged. The positive and negative terminals are connected to input terminals 24a, 24b of a three-phase inverter device 14. The three-phase AC motor 16 is connected to output terminals 26u, 26v, and 26w of the three-phase inverter device 14. The input terminals 24a and 24b are connected to positive and negative input terminals of a three-phase PWM converter 20 via input lines 28a and 28b. The three-phase PWM converter 20 converts the DC voltage input between input line 28a and input line 28b into a three-phase AC voltage and outputs U-phase, V-phase, and W-phase AC voltages to output terminals 42u, 42v, and 42w. The output lines 30u, 30v, and 30w are wired between output terminal 42u and output terminal 26u, between output terminal 42v and output terminal 26v, and between output terminal 42w and output terminal 26w, respectively.

[0015] The capacitors 32a and 32b are connected in series and are interposed between the input terminals 24a and 24b. The junction of the input terminals 24a and 24b forms a power supply midpoint 34. The power supply midpoint 34 is also a terminal of half the voltage (E / 2) of the DC voltage E of the DC power supply 12.

[0016] The input-side transformer device 18 includes three transformers 36a, 36b, and 36c. Each of the transformers 36a, 36b, and 36c has one primary winding 38 and two secondary windings 40. One end of the primary winding 38 of each of the transformers 36a, 36b, and 36c is connected to output terminals 42u, 42v, and 42w, respectively, and the other end is connected to the power supply midpoint 34 via respective Y capacitors 44. The two secondary windings 40 of each of the transformers 36a, 36b, and 36c are inserted into the input lines 28a and 28b, respectively.

[0017] The three-phase PWM converter 20 includes three transformers 46a, 46b, and 46c. Each of the transformers 46a, 46b, and 46c has one primary winding 48 and three secondary windings 50. One end of the primary winding 48 of each of the transformers 46a, 46b, and 46c is connected to the output terminals 42u, 42v, and 42w, respectively, and the other end is connected to the power supply midpoint 34 via a corresponding Y capacitor 52. The three secondary windings 50 of each of the transformers 46a, 46b, and 46c are inserted into the output lines 30a, 30b, and 30c, respectively.

[0018] The input side transformer 18 and the output side transformer 22 both function as a PCC (passive common noise canceller).

[0019] (Three-phase PWM converter) 2 is a circuit diagram of the three-phase PWM converter 20. The three-phase PWM converter 20 is configured with three half-bridges 60, each of which has an upper arm switching element and a lower arm switching element connected in series. The carrier frequency f of the PWM (Pulse Width Modulation) is C is, for example, 100 MHz.

[0020] 3 is a diagram showing waveforms of common mode (CM) voltage in the three-phase PWM converter 20. The waveforms were generated by performing a simulation under conditions where there is no CM voltage. In FIG. 3, waveforms V(u), V(v), V(w), and (V(u)+V(v)+V(w)) / 3 are shown from top to bottom. V(u), V(v), and V(w) indicate that they are simulation waveforms corresponding to the U phase, V phase, and W phase, respectively.

[0021] A CM voltage of (V(u)+V(v)+V(w)) / 3 appears sequentially with a phase difference of 120° over time between the output terminals 42u, 42v, 42w and the power supply midpoint 34. The CM voltage has a step-like waveform that changes by E / 3 in steps according to PWM switching.

[0022] (Comparative model / configuration) 4 is a schematic diagram of a three-phase electrical system 100 as a comparative model to the three-phase electrical system 10. The comparative model is provided for the convenience of explaining the significance of the three-phase electrical system 10, and is not included in the embodiments of the present invention.

[0023] The three-phase electrical system 100 in Figure 4 is illustrated in an experimental configuration for measuring data related to CM voltage, which will be described later, and for the purpose of the experiment, a line impedance stabilization network (LISN) 102 has been added. The LISN 102 has the functions of maintaining constant impedance on the DC power supply 12 side and preventing the inflow of external noise other than that being evaluated, and is interposed between the DC power supply 12 and the three-phase inverter device 114 to ensure the reproducibility of noise measurements. In the three-phase electrical system 10 according to the embodiment of the present invention, the LISN 102 is appropriately inserted in the same position as the three-phase electrical system 100 during experiments for data collection, but the installation of the LISN 102 can be omitted in compatible products of the three-phase inverter device 14 manufactured by the manufacturer.

[0024] In the three-phase electrical system 100, elements common to the three-phase electrical system 10 are given the same reference numerals as the corresponding elements in the three-phase electrical system 10, and explanations thereof will be omitted; only the differences from the three-phase electrical system 10 will be described.

[0025] Three-phase electrical system 100 differs from three-phase electrical system 10 in that three-phase electrical system 100 omits input transformer device 18, which is provided on the input side of three-phase PWM converter 20 in three-phase electrical system 10. Note that in three-phase electrical system 100, primary winding 48 of each of transformers 46a, 46b, 46c is connected to both input lines 28a, 28b via a pair of Y-capacitors 104. This connection is functionally identical to the connection of primary winding 48 of each of transformers 46a, 46b, 46c of three-phase electrical system 10 to power supply midpoint 34 via Y-capacitor 52.

[0026] (Comparative model / effect) With reference to the graphs in Figures 5A to 5C, the effects (advantages) of the three-phase electrical system 100 as a comparative model compared to a case where no common-mode voltage countermeasures are implemented and a case where a common-mode inductor (CMI) separate from a transformer is used as a common-mode voltage countermeasure will be described.

[0027] FIG. 5A is a diagram showing, as a baseline, changes in the time domain of the CM voltage and the CM current when no countermeasures against common-mode voltage are taken, that is, when the DC voltage of the DC power supply 12 is input directly to the three-phase PWM converter 20 and output directly to the three-phase AC motor 16.

[0028] 5B is a diagram showing changes in the CM voltage and CM current over time when a common-mode inductor (CMI) is provided as a countermeasure against common-mode voltage in each phase line on the output side of DC power supply 12. Comparing Fig. 5A with Fig. 5B, it can be seen that the CMI has the effect of reducing the common-mode voltage and CM current.

[0029] 5C is a time domain waveform diagram of the CM voltage and CM current in the three-phase electrical system 100. Comparing FIG. 5B with FIG. 5C, it can be seen that the output-side transformer 22 in the three-phase electrical system 100 has a higher suppression effect on the CM voltage and CM current than on the CMI.

[0030] (Insights on improvements) Fig. 6A is an experimental graph comparing the input-side CM current of the three-phase PWM converter 20 between the three-phase electrical system 100 (comparison model) and the three-phase electrical system 10 (embodiment). Fig. 6B is an experimental graph comparing the output-side CM current of the three-phase PWM converter 20 between the three-phase electrical system 100 and the three-phase electrical system 10. Fig. 6C is an experimental graph comparing the heatsink CM current of the three-phase PWM converter 20 between the three-phase electrical system 100 and the three-phase electrical system 10. The heatsink of the three-phase PWM converter 20 will be described in Fig. 8.

[0031] In the experiment of Figures 6A-6C, the switching frequency (PWM frequency) of the three-phase PWM converter 20 was 100 kHz, the three-phase AC output frequency was 50 Hz, the input DC voltage was 200 V, and the three-phase AC motor 16 was rated at 0.75 kW and was driven without load.

[0032] 6A-6C, the upper graphs relate to the three-phase electrical system 100 (comparison model), and the lower graphs relate to the three-phase electrical system 10 (embodiment). In both the upper and lower graphs, the upper and lower graphs show not only the characteristic lines (solid lines) of the three-phase electrical system 100 and the three-phase electrical system 10, but also the characteristic lines (dashed lines) without an EMI (electromagnetic interference) filter and with a CMI.

[0033] 6A to 6C, the "AC" in "AC-CMI" and "AC-PCC" (passive common-mode noise canceller / transformer) means that measurements were taken with the CMI and PCC installed only on the output side (AC side) of the three-phase PWM converter 20. In the lower graphs of Figures 6A to 6C, the "W" in "W-CMI" and "W-PCC" means that measurements were taken with the CMI and PCC installed on both the input side (DC side) and output side (AC side) of the three-phase PWM converter 20.

[0034] Figures 7A, 7B, and 7C are comparison graphs in which only the characteristic lines of three-phase electrical system 100 (comparison model) and three-phase electrical system 10 (embodiment) are extracted from the upper and lower graphs of Figures 6A, 6B, and 6C, respectively, and combined into a single graph. Note that in Figures 7A, 7B, and 7C, the line style of the characteristic line of three-phase electrical system 10 is shown as the solid line in Figures 6A-6C, but the line style of the characteristic line of three-phase electrical system 100 has been changed from the solid line in Figures 6A-6C to a dashed line.

[0035] The upper graphs in Figures 6A-6C reveal the following about the three-phase electrical system 100: (a) The input CM current is attenuated relative to the CMI, although not significantly so, up to about 1 MHz (Figure 6A). (b) The output CM current is attenuated significantly relative to the CMI up to about 2 MHz (Figure 6B). (c) The attenuation of the heat sink CM current is similar to the CMI (Figure 6C).

[0036] A further explanation will be given regarding the heat sink of the three-phase PWM converter 20. Although not shown in Fig. 1, the three-phase PWM converter 20 has a heat sink, and a heat sink current flows from the three-phase PWM converter 20 to the ground 62 via the heat sink (Fig. 6C).

[0037] From the above analysis, it can be concluded that implementing measures to reduce input CM current and heat sink current in the three-phase electrical system 100 is likely to result in a reduction in the overall CM voltage.

[0038] 8 is an equivalent circuit diagram of the three-phase electrical system 10, taking into account the CM currents through the heat sink of the three-phase PWM converter 20 as well as the motor case of the three-phase AC motor 16. The upper circuit diagram shows the stray capacitance C due to the heat sink of the three-phase PWM converter 20. cm,i and C due to the motor case of the three-phase AC motor 16 cm,o In the lower circuit diagram, for simplicity, the upper circuit diagram is converted to a delta-y transform and the two are combined into one C sum (=C cm,i +C cm,o ) is represented.

[0039] The definitions of the symbols in FIG. 8 are as follows: V cm : Common mode voltage C cm,i : Stray capacitance due to the heat sink of the three-phase PWM converter 20 C cm,o : Stray capacitance due to the motor case of the three-phase AC motor 16 Z cm,lisn : Impedance of LISN102 Z cm,motor : Impedance of three-phase AC motor 16 i cm.i : Input side CM current i cm,o : Output side CM current C sum :=C cm,i +C cm,o k:=C cm,o / C sum

[0040] (Improvement structure based on knowledge) The differences between the three-phase electrical system 100 and the three-phase electrical system 10 have already been described, but conversely, the differences between the three-phase electrical system 100 and the three-phase electrical system 100 are improvements to the three-phase electrical system 10. That is, as an improvement, the three-phase inverter device 20 of the three-phase electrical system 10 has an input-side transformer device 18 added to the three-phase inverter device 114 of the three-phase electrical system 100.

[0041] The illustrated change is that the turns ratio between the primary winding 48 and the secondary winding 50 in the output-side transformer 22 differs between the three-phase electrical system 100 and the three-phase electrical system 10. Here, the ratio of the number of turns of the primary winding 38 to the number of turns of the secondary winding 40 in each of the transformers 36a, 36b, and 36c in the input-side transformer 18 is set to mi:1. The ratio of the number of turns of the primary winding 48 to the number of turns of the secondary winding 50 in each of the transformers 46a, 46b, and 46c in the output-side transformer 22 is set to mo:1. In the three-phase electrical system 100, the heat sink current of the three-phase PWM converter 20 is not taken into consideration, so mo is set to 3, which is the number of output lines. In contrast, in the three-phase electrical system 10, mo / mi increases as k increases. When k=1 / 2, mi=mo=6.

[0042] 7A, 7B, and 7C, the three-phase inverter device 14 of the three-phase electrical system 10 has the following effect relative to the three-phase inverter device 114 of the three-phase electrical system 100: the heat sink CM current is sufficiently reduced, and the input-side CM current is also sufficiently reduced. As a result, the CM voltage in the three-phase electrical system 10 can be significantly reduced compared to the three-phase electrical system 100.

[0043] (supplement) In the embodiment of the present invention, a three-phase PWM converter 20 is used as the three-phase converter, but the three-phase converter of the present invention is not limited to this. The three-phase converter of the present invention can also use other three-phase modulation inverters such as PAM (pulse amplitude modulation) and PFM (pulse frequency modulation).

[0044] The three-phase electrical system 10 is mounted on, for example, an electric vehicle. In addition to electric vehicles, electrical systems equipped with the three-phase inverter device of the present invention can also be applied to aircraft, industrial machinery, elevators, transportation vehicles, etc. [Explanation of symbols]

[0045] 10... Three-phase electrical system, 12... DC power supply, 14... Three-phase inverter device, 16... Three-phase AC motor, 18... Input side transformer device, 20... Three-phase PWM converter (three-phase PWM converter), 22... Output side transformer device, 24a, 24b... Input terminal, 26u, 26v, 26w... Output terminal, 28a, 28b... Input line, 30u, 30v, 30w... Output line, 34... Power supply midpoint, 36a, 36b, 36c... Transformer, 38... Primary winding, 40... Secondary winding, 44... Y capacitor, 48... Primary winding, 50... Secondary winding, 52... Y capacitor.

Claims

1. a three-phase inverter that converts a DC voltage input from a DC power supply via a first input line and a second input line into a three-phase AC voltage and outputs the three-phase AC voltage to a first output line, a second output line, and a third output line; an input transformer device that generates an input primary voltage corresponding to a common mode voltage and generates an input secondary voltage on each input line that reduces the common mode voltage; an output transformer device that generates an output primary voltage corresponding to the common mode voltage and generates an output secondary voltage that reduces the common mode voltage on each output line; A three-phase inverter device comprising:

2. 2. The three-phase inverter device according to claim 1, a power supply midpoint of the DC power supply; a U-phase terminal, a V-phase terminal, and a W-phase terminal which are output terminals of the three-phase inverter and are connected to the first output line, the second output line, and the third output line, respectively; Equipped with the input transformer device includes a first input transformer, a second input transformer, and a third input transformer; a primary winding of each of the first input side transformer, the second input side transformer, and the third input side transformer has one end connected to the U-phase terminal, the V-phase terminal, and the W-phase terminal, respectively, and the other end connected to the power supply midpoint via an input side Y capacitor; A three-phase inverter device, wherein each input-side transformer has a secondary winding on each of the first input line and the second input line.

3. 3. The three-phase inverter device according to claim 2, the output transformer device includes a first output transformer, a second output transformer, and a third output transformer; a primary winding of each of the first output side transformer, the second output side transformer, and the third output side transformer has one end connected to the U-phase terminal, the V-phase terminal, and the W-phase terminal, respectively, and the other end connected to the power supply midpoint via an output side Y capacitor; a three-phase inverter device, wherein each output-side transformer has a secondary winding on each of the first output line, the second output line, and the third output line;

4. 4. The three-phase PWM inverter device according to claim 3, C ｃｍ，ｉ : stray capacitance of the three-phase inverter C ｃｍ，ｏ : Stray capacitance of a three-phase device connected as a load to the three-phase inverter device C ｓｕｍ :=C ｃｍ，ｉ +C ｃｍ，ｏ k:=C ｃｍ，ｏ / C ｓｕｍ mi: mi when the turns ratio between the primary winding and the secondary winding in each input transformer is mi:1 mo: mo when the turns ratio between the primary winding and the secondary winding in each output transformer is mo:1 If we define A three-phase inverter device in which mi is set to be smaller and mo is set to be larger as k is larger.

5. 5. The three-phase PWM inverter device according to claim 4, A three-phase inverter device in which mi = mo = 6 when k = 1 / 2.

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