Inverter system, noise filter and noise reduction method

Abstract

The invention provides an inverter system, a noise filter, and a noise reduction method capable of improving the effect of reducing conductive noise. An inverter system (1) is provided with: an inverter device (9) having a power conversion unit (41) using switching elements; and a noise filter (7) that inputs, to a primary winding (25p) of a common-mode transformer (25) having the primary winding (25p) and a secondary winding (25s), a current based on a common-mode voltage generated during the switching operation of the switching element.

Description

Technical Field

[0001] Embodiments of this disclosure relate to inverter systems, noise filters, and noise reduction methods. Background Technology

[0002] Patent Document 1 describes a conducted noise filter. This conducted noise filter includes: a common-mode voltage detection unit that detects the common-mode voltage generated during the switching operation of a power semiconductor element via a grounded capacitor connected to a line between an AC power supply and a rectifier; and a cancellation voltage source that, based on the detected common-mode voltage, generates a cancellation voltage of the same magnitude but opposite polarity, such that the cancellation voltage is superimposed between the connection point of the AC power supply and the grounded capacitor in the line to cancel the common-mode voltage.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 5263663. Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In the aforementioned prior art conducted noise filters, when an error occurs between the voltage value superimposed on the line by the canceling voltage source and the voltage value that can cancel the generated common-mode voltage, it is difficult to suppress the common-mode current caused by the generated error voltage, and the effect of reducing conducted noise may become insufficient.

[0008] The embodiments disclosed herein were made in view of the following problems, and the purpose is to provide an inverter system, noise filter, and noise reduction method that can improve the effect of reducing conducted noise.

[0009] Methods for solving problems

[0010] To address the aforementioned issues, according to one aspect of the present invention, an inverter system is provided, comprising: an inverter device including a power conversion section using a switching element; and a noise filter that inputs a current based on the common-mode voltage generated when the switching element is switched on to the primary winding of a common-mode transformer having a primary winding and a secondary winding.

[0011] In addition, according to another aspect of the invention, a noise filter is applied, which is a noise filter provided in an inverter system having an inverter device having a power conversion section using a switching element, and the noise filter inputs a current based on the common-mode voltage generated when the switching element is switched on to the primary winding of a common-mode transformer having a primary winding and a secondary winding.

[0012] In addition, according to another aspect of the present invention, a noise reduction method is applied to an inverter system including an inverter device having a power conversion section using a switching element. The noise reduction method inputs a current based on the common-mode voltage generated when the switching element is switched on to the primary winding of a common-mode transformer having a primary winding and a secondary winding.

[0013] Invention Effects

[0014] According to the disclosed implementation method, the effect of reducing conducted noise can be improved. Attached Figure Description

[0015] Figure 1 This is a diagram illustrating an example of the overall structure of the inverter system involved in the implementation method.

[0016] Figure 2 This is a diagram illustrating an example of the structure of a noise filter according to an implementation method.

[0017] Figure 3 This is a diagram illustrating an example of the common-mode equivalent circuit of a comparative inverter system.

[0018] Figure 4 It means to Figure 3 A diagram of an example of the equivalent circuit after the equivalent circuit transformation.

[0019] Figure 5 This is a diagram illustrating an example of the common-mode equivalent circuit of an inverter system implemented in this way.

[0020] Figure 6 It means to Figure 5 A diagram of an example of the equivalent circuit after the equivalent circuit transformation.

[0021] Figure 7 This is a graph representing an example of the simulation results for the output impedance characteristics.

[0022] Figure 8 This is a diagram illustrating an example of the overall structure of an inverter system involving a variation in which a noise filter is connected between the rectifier section and the power conversion section.

[0023] Figure 9 This is a diagram illustrating an example of the overall structure of an inverter system involving a variation in which a noise filter is connected between the power conversion unit and the motor. Detailed Implementation

[0024] The embodiments will now be described with reference to the accompanying drawings.

[0025] <1. Overall Structure of the Inverter System>

[0026] Reference Figure 1 An example of the overall structure of the inverter system 1 of the implementation method will be described.

[0027] like Figure 1 As shown, the inverter system 1 includes a LISN (Line Impedance Stabilization Network) 3, a power cable 5, a noise filter 7, an inverter device 9, a motor cable 11, and a motor 13.

[0028] LISN3 is an analog power circuit network designed to measure conducted noise in the power lines of inverter system 1.

[0029] Power cable 5 connects LISN3 and noise filter 7. Power cable 5 has power lines 17r, 17s, 17t corresponding to the three-phase AC voltage (R phase, S phase, T phase) input from AC power source 15 via LISN3, and a grounding wire 19. One end of grounding wire 19 is connected to ground or a conductor with high capacitance via LISN3.

[0030] A noise filter 7 is connected between the AC power supply 15 and the inverter device 9. The noise filter 7 includes a common-mode voltage detection circuit 21, a voltage-to-current conversion circuit 23, and a common-mode transformer 25. The common-mode voltage detection circuit 21 (an example of a common-mode voltage detection unit) detects the common-mode voltage generated when the switching elements included in the power conversion unit 41 of the inverter device 9 are switched. The voltage-to-current conversion circuit 23 (an example of a voltage-to-current conversion unit) outputs current based on the common-mode voltage detected by the common-mode voltage detection circuit 21. The common-mode transformer 25 has a primary winding 25p and a secondary winding 25s. One end of the primary winding 25p is connected to the voltage-to-current conversion circuit 23 via an external noise protection circuit 29, and the other end is connected to the ground wire 19. The secondary winding 25s is connected to power lines 17r, 17s, and 17t, respectively. The current output from the voltage-to-current conversion circuit 23 is input to the primary winding 25p of the common-mode transformer 25. According to the above structure, in the noise filter 7, the primary winding 25p of the common-mode transformer 25 is input with a current based on the common-mode voltage.

[0031] Furthermore, the noise filter 7 has an external noise protection circuit 27 connected to the input section of the voltage-to-current conversion circuit 23 and an external noise protection circuit 29 connected to the output section of the voltage-to-current conversion circuit 23. The external noise protection circuits 27 and 29 protect the voltage-to-current conversion circuit 23 from noise (pulse noise, etc.) applied from the AC power supply 15. Alternatively, the external noise protection circuit may be provided only in either the input or output section of the voltage-to-current conversion circuit 23. Additionally, as... Figure 2As shown, in the input section of the voltage-to-current conversion circuit 23, in addition to the external noise protection circuit 27, a high-pass filter 31 and a low-pass filter 33 are also connected, but... Figure 1 Illustrations omitted.

[0032] The inverter device 9 has an input terminal 35, a grounding terminal 37, a rectifier 39, a power conversion unit 41, and an output terminal 43.

[0033] Power lines 17r, 17s, and 17t are connected to input terminals 35 respectively. The three-phase AC voltage input from AC power supply 15 via LISN3, power cable 5, and noise filter 7 is input to inverter device 9 via input terminals 35. The other end of grounding wire 19 and one end of grounding wire 45 are connected to grounding terminal 37.

[0034] The rectifier 39 converts the output of the AC power supply 15, i.e. the AC voltage input from the input terminal 35, into a DC voltage.

[0035] The power conversion unit 41 uses switching elements to convert DC voltage to AC voltage. Switching elements include, for example, semiconductor devices such as IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and SiC-MOSFETs.

[0036] Power lines 47u, 47v, and 47w are connected to the output terminals 43 respectively. The three-phase AC voltage (U-phase, V-phase, and W-phase) converted by the power conversion unit 41 is output from the inverter device 9 via the output terminals 43.

[0037] Motor cable 11 connects inverter unit 9 to motor 13. Motor cable 11 has power lines 47u, 47v, and 47w corresponding to the three-phase AC voltage (U-phase, V-phase, W-phase) output from output terminal 43 of inverter unit 9, and a ground wire 45. One end of ground wire 45 is connected to ground terminal 37 of inverter unit 9, and the other end is connected to motor 13. Motor 13 is driven by drive power supplied from inverter unit 9.

[0038] As described above, the inverter system 1 detects the common-mode voltage through the common-mode voltage detection circuit 21 near the inverter device 9, and the input voltage is obtained from the common-mode transformer 25 on the LISN3 side. That is, it is configured as a feedforward type.

[0039] The rectifier section 39 of the inverter device 9 is mounted on the converter substrate 49, and the power conversion section 41 of the inverter device 9 is mounted on the inverter substrate 51 (an example of the first substrate). Additionally, the common-mode voltage detection circuit 21, voltage-to-current conversion circuit 23, and common-mode transformer 25 of the noise filter 7 are mounted on the noise reduction substrate 53 (an example of the second substrate). The converter substrate 49, inverter substrate 51, and noise reduction substrate 53 are each configured as different substrates and are arranged separately from each other. Furthermore, as long as at least the inverter substrate 51 and the noise reduction substrate 53 are configured as different substrates, a substrate structure other than that described above may also be used. For example, the converter substrate 49 and the inverter substrate 51 may also be constructed from the same substrate.

[0040] Furthermore, the inverter system 1 described above is an example and is not limited to the above content. For example, LISN3 may not be necessary. Additionally, in Figure 1 The diagram shows an example where the noise filter 7 and the inverter device 9 are separate units, but the noise filter 7 and the inverter device 9 can also be integrated (unitized).

[0041] <2. Composition of Noise Filters>

[0042] Reference Figure 2 An example of the construction of noise filter 7 will be explained.

[0043] like Figure 2 As shown, the noise filter 7 includes a common-mode voltage detection circuit 21, a voltage-to-current conversion circuit 23, a common-mode transformer 25, an external noise protection circuit 27, an external noise protection circuit 29, a high-pass filter 31, and a low-pass filter 33.

[0044] The common-mode voltage detection circuit 21 detects the common-mode voltage generated during the switching operation of the switching elements included in the power conversion section 41 of the inverter device 9. The common-mode voltage detection circuit 21 includes a detection capacitor. Figure 2 In the example shown, the common-mode voltage detection circuit 21 has three X capacitors 55 (an example of a detection capacitor) and one Y capacitor 57 (an example of a detection capacitor). The X capacitors 55 are connected between the power supply lines 17r, 17s, and 17t respectively. The Y capacitor 57 is connected between the power supply lines 17r, 17s, and 17t and the ground line 19 (an example of ground). The damping resistor 59 is connected in parallel with the Y capacitor 57.

[0045] The voltage-to-current conversion circuit 23 outputs current based on the common-mode voltage detected by the common-mode voltage detection circuit 21. At this time, the voltage-to-current conversion circuit 23 determines the current such that the voltage induced in the secondary winding 25s of the common-mode transformer 25 is consistent with the common-mode voltage detected by the common-mode voltage detection circuit 21. The term "consistent" does not mean strictly consistent, but rather includes the meaning of "approximately consistent." Specifically, as... Figure 2 As shown, the voltage-to-current conversion circuit 23 has a load analog section 61, an operational amplifier 63, and multiple resistors 65, 67, 69, and 71.

[0046] The load simulation unit 61 is a circuit that simulates the magnetizing impedance of the primary winding 25p of the common-mode transformer 25. Although not shown in the figure, the load simulation unit 61 is constructed by combining passive components such as windings, capacitors, and resistors. Resistor 65 is connected between the input 23i of the voltage-to-current conversion circuit 23 and the non-inverting input terminal of the operational amplifier 63. Resistor 67 is connected between the output terminal and the inverting input terminal of the operational amplifier 63. Resistor 69 is connected between the inverting input terminal of the operational amplifier 63 and the ground wire 19. Resistor 71 is connected between the output terminal of the load simulation unit 61 and the non-inverting input terminal of the operational amplifier 63. According to the above structure, in the voltage-to-current conversion circuit 23, the common-mode voltage detected by the common-mode voltage detection circuit 21 is applied to the two ends of the load simulation unit 61, and the current generated in the load simulation unit 61 is output to the primary winding 25p of the common-mode transformer 25. Furthermore, the voltage-to-current conversion circuit 23 can be configured with a circuit structure other than that described above, as long as it can output the current generated by applying a common-mode voltage to both ends of the load analog unit 61 to the primary winding 25p of the common-mode transformer 25.

[0047] A high-pass filter 31, a low-pass filter 33, and an external noise protection circuit 27 are connected between the input section 23i of the common-mode voltage detection circuit 21 and the voltage-to-current conversion circuit 23. The high-pass filter 31 suppresses low-frequency common-mode voltage caused by three-phase imbalance in power lines 17r, 17s, and 17t, and extracts high-frequency common-mode voltage. The low-pass filter 33 suppresses high-frequency voltage generated when noise (pulse noise, etc.) is applied from the AC power supply 15. The external noise protection circuit 27 reduces the noise current (pulse noise current, etc.) generated when noise is applied from the AC power supply 15 and bypasses it into the protection circuit, protecting the voltage-to-current conversion circuit 23, etc. The high-pass filter 31, the low-pass filter 33, and the external noise protection circuit 27 are examples of external noise protection components.

[0048] An external noise protection circuit 29 is connected between the output 23o of the voltage-to-current conversion circuit 23 and the primary winding 25p of the common-mode transformer 25. When noise (such as pulse noise) is applied from the AC power supply 15, the external noise protection circuit 29 reduces the noise current (such as pulse noise current) generated through the common-mode transformer 25 and bypasses it within the protection circuit, thus protecting the voltage-to-current conversion circuit 23, etc. Although not shown in the figure, the external noise protection circuit 29 is constructed by combining passive components such as resistors and semiconductor components such as diodes. The external noise protection circuit 29 is an example of an external noise protection unit.

[0049] Furthermore, the structure of the noise filter 7 described above is an example and is not limited to the above. For example, any one or two of the high-pass filter 31, low-pass filter 33, and external noise protection circuit 27 can be connected to the input section 23i of the voltage-to-current conversion circuit 23. Alternatively, a band-pass filter can be connected instead of any one of the high-pass filter 31, low-pass filter 33, and external noise protection circuit 27, or on this basis. The band-pass filter removes the voltage in the frequency band suppressed by the high-pass filter 31 or low-pass filter 33.

[0050] <3. Principles for Improving the Effect of Conductive Noise Reduction>

[0051] The inverter system 1 configured as described above can improve the reduction of conducted noise. (Refer to...) Figures 3 to 7 This principle will be explained.

[0052] As a comparative example for comparison with the inverter system 1 according to this embodiment, an inverter system is envisioned as follows: the common-mode voltage is detected in a noise filter, the detected common-mode voltage is amplified to a predetermined ratio using a voltage-type signal source such as an operational amplifier or a transistor, and the amplified voltage is input to the power line using a common-mode transformer, thereby canceling the common-mode voltage. Figure 3 This represents an example of the common-mode equivalent circuit of the inverter system in the comparative example.

[0053] like Figure 3As shown, the common-mode equivalent circuit of the comparative example has a voltage source Vamp of operational amplifier 73 and an output impedance Zoamp of operational amplifier 73. The voltage source Vamp and the output impedance Zoamp are connected in series to form a closed circuit on the primary side of common-mode transformer 75. Additionally, the common-mode equivalent circuit of the comparative example has an impedance Zlisn of LISN, an impedance Zpc of the power cable, an excitation impedance Zcmt of common-mode transformer 75, impedances Zxyc of X capacitor 55 and Y capacitor 57 constituting the common-mode voltage detection circuit, a common-mode voltage source Vcom of the inverter device, and an impedance Zmc of the motor cable. The common-mode voltage source Vcom is connected in series with impedances Zlisn, Zpc, Zcmt, and Zmc, and impedances Zxyc and Zmc are connected in parallel to form a closed circuit on the secondary side of common-mode transformer 75.

[0054] Figure 4 It shows that Figure 3 The equivalent circuit is modeled by a T-type circuit using the common-mode transformer 75, and an example of the equivalent circuit after using Thevenin's theorem to transform the common-mode voltage source Vcom and impedances Zmc and Zxyc, and the voltage source Vamp and impedances Zoamp and Zcmt. For example... Figure 4 As shown, the converted equivalent circuit has impedance Zlisn, impedance Zpc, combined impedance Z1, combined voltage V1 of the operational amplifier, combined voltage V2 of the inverter device, and combined impedance Z2. These impedances Zlisn, Zpc, combined impedances Z1 and Z2, and combined voltages V1 and V2 are connected in series to form a closed circuit.

[0055] The combined impedance Z1 is represented by Equation 1.

[0056] Z1=(Zcmt×Z'oamp) / (Zcmt+Z'oamp)...Equation 1

[0057] The combined voltage V1 is represented by Equation 2.

[0058] V1={Zcmt / (Zcmt+Z'oamp)}×V'amp...Equation 2

[0059] The combined voltage V2 is represented by Equation 3.

[0060] V2={Zxyc / (Zxyc+Zmc)}×Vcom…Equation 3

[0061] The combined impedance Z2 is represented by Equation 4.

[0062] Z2=(Zxyc×Zmc) / (Zxyc+Zmc)…Equation 4

[0063] Furthermore, the voltage V'amp and impedance Z'oamp are obtained by converting the voltage Vamp and impedance Zoamp of operational amplifier 73 to the secondary side of common-mode transformer 75, respectively. For example, when the winding ratio of common-mode transformer 75 is a, V'amp is Vamp × a, and Z'oamp is Zoamp × a. 2 .

[0064] exist Figure 4 In this context, the voltage V'amp used to completely cancel the common-mode voltage Vcom and suppress noise becomes V1 = V2, and is therefore represented by Equation 5.

[0065] {Zcmt / (Zcmt+Z'oamp)}×V'amp={Zxyc / (Zxyc+Zmc)}×Vcom

[0066] V'amp={(Zcmt+Z'oamp) / Zcmt}×{Zxyc / (Zxyc+Zmc)}×Vcom...Equation 5

[0067] If the common-mode voltage detected by the common-mode voltage detection circuit is set as Vcomdet, then the common-mode voltage Vcomdet is represented by Equation 6.

[0068] Vcomdet={Zxyc / (Zxyc+Zmc)}×Vcom-{(Zxyc×Zmc) / (Zxyc+Zmc)×Icom}…Equation 6

[0069] In addition, Icom flows due to common-mode voltage. Figure 4 The common-mode current of a closed circuit.

[0070] If equation 6 is modified, it becomes equation 7.

[0071] {Zxyc / (Zxyc+Zmc)}×Vcom=Vcomdet+{(Zxyc×Zmc) / (Zxyc+Zmc)×Icom}…Equation 7

[0072] Substituting equation 7 into equation 5, we get equation 8.

[0073] V'amp={(Zcmt+Z'oamp) / Zcmt}×[Vcomdet+{(Zxyc×Zmc) / (Zxyc+Zmc)×Icom}]…Equation 8

[0074] Equation 8 becomes the voltage V'amp used to completely cancel the common-mode voltage Vcom to suppress noise.

[0075] However, the impedance Zmc of the motor cable included in the term {(Zxyc×Zmc) / (Zxyc+Zmc)×Icom} in Equation 8 is the impedance between the power supply line and the ground line of the UVW in the motor cable, which is difficult to determine. In addition, the common-mode current Icom is small and high-frequency, making it difficult to detect. Therefore, in the inverter system of the comparative example, the above terms are omitted, and the voltage V'amp is set as Equation 9.

[0076] V'amp={(Zcmt+Z'oamp) / Zcmt}×Vcomdet...Equation 9

[0077] In this case, according to the difference between Equations 8 and 9, an error occurs in the inverter system of the comparative example between the voltage value that can cancel the common-mode voltage and the voltage value input to the power line using the common-mode transformer.

[0078] On the other hand, in the common-mode equivalent circuit of the comparative example, the impedance Zpc is small because it is a cable. Furthermore, the combined impedance Z2 is limited by the impedances of the X and Y capacitors at high frequencies, so their impedances are also small. In addition, the impedance Zlisn is used to measure conducted noise and does not contribute to reducing the common-mode current Icom, so it is not considered here. Furthermore, since the output impedance Zoamp of the operational amplifier is small, the combined impedance Z1 expressed by Equation 1 also becomes small, making it impossible to effectively utilize the magnetizing impedance Zcmt of the common-mode transformer 75. As a result, it is difficult to suppress the common-mode current Icom caused by the generated error voltage, and the effect of reducing conducted noise may become insufficient.

[0079] Figure 5 This illustrates an example of the common-mode equivalent circuit of the inverter system 1 in this embodiment. For example... Figure 5 As shown, the common-mode equivalent circuit of inverter system 1 has a current source Iamp of voltage-to-current conversion circuit 23 and an output impedance Zoamp of voltage-to-current conversion circuit 23. The current source Iamp and the output impedance Zoamp are connected in parallel to form a closed circuit on the primary side of common-mode transformer 25. Furthermore, regarding the closed circuit on the secondary side of common-mode transformer 25, since it is connected with… Figure 3 Since they are the same, the explanation is omitted.

[0080] Figure 6 Indicates will Figure 5 The equivalent circuit is modeled using a T-type circuit for the common-mode transformer 25, and an example of the equivalent circuit after transforming the common-mode voltage source Vcom with impedances Zmc and Zxyc, and the current source Iamp with impedances Zoamp and Zcmt using Thevenin's theorem. For example... Figure 6As shown, the converted equivalent circuit has impedance Zlisn, impedance Zpc, combined impedance Z3, combined voltage V3 of the operational amplifier, combined voltage V4 of the inverter device, and combined impedance Z4. These impedances Zlisn, Zpc, combined impedances Z3 and Z4, and combined voltages V3 and V4 are connected in series to form a closed circuit.

[0081] The combined impedance Z3 is represented by Equation 1 above.

[0082] The combined voltage V3 is represented by Equation 10.

[0083] V3={Zcmt / (Zcmt+Z'oamp)}×Z'oamp×I'amp...Equation 10

[0084] The combined voltage V4 is represented by Equation 3 above.

[0085] The combined impedance Z4 is represented by Equation 4 above.

[0086] Furthermore, the current I'amp and impedance Z'oamp are obtained by converting the current Iamp and impedance Zoamp of the voltage-to-current conversion circuit 23 to the secondary side of the common-mode transformer 25, respectively. For example, when the winding ratio of the common-mode transformer 25 is a, I'amp is Iamp / a, and Z'oamp is Zoamp×a. 2 .

[0087] exist Figure 6 In this context, the current I'amp used to completely cancel the common-mode voltage Vcom to suppress noise becomes V3 = V4, and is therefore represented by Equation 11.

[0088] {Zcmt / (Zcmt+Z'oamp)}×Z'oamp×I'amp={Zxyc / (Zxyc+Zmc)}×VcomI'amp={(Zcmt+Z'oamp) / (Zcmt×Z'oamp)}×{Zxyc / (Zxyc+Zmc)}×Vcom...Equation 11

[0089] If we substitute Equation 7 into Equation 11, we get Equation 12.

[0090] I'amp={(Zcmt+Z'oamp) / (Zcmt×Z'oamp)}×[Vcomdet+{(Zxyc×Zmc) / (Zxyc+Zmc)×Icom}]…Equation 12

[0091] Equation 12 becomes the current I'amp used to completely cancel the common-mode voltage Vcom to suppress noise.

[0092] For the same reason as above, if the term {(Zxyc×Zmc) / (Zxyc+Zmc)×Icom} in Equation 12 is omitted, the current I'amp becomes Equation 13.

[0093] I'amp={(Zcmt+Z'oamp) / (Zcmt×Z'oamp)}×Vcomdet={(Zcmt / Z'oamp+1) / Zcmt}×Vcomdet...Equation 13

[0094] exist Figure 5 and Figure 6 In the equivalent circuit shown, the output impedance Z'oamp of the voltage-to-current conversion circuit 23 is sufficiently large compared to the magnetizing impedance Zcmt of the common-mode transformer 25. Therefore, Equation 13 can be approximated as in Equation 14.

[0095] I'amp≒Vcomdet / Zcmt…Form 14

[0096] Thus, in inverter system 1, most of the common-mode voltage can be offset by the current I'amp specified in Equation 14.

[0097] Furthermore, it is believed that due to the difference between Equation 12 and Equation 14, an error voltage is generated in the inverter system 1 of the embodiment, similar to the comparative example described above. However, as Figure 5 and Figure 6 As shown in the equivalent circuit diagram, due to the use of the current source Iamp, the output impedance Zoamp (Z'oamp converted to the secondary side) of the voltage-to-current conversion circuit 23 is very large. Therefore, the combined impedance Z1 expressed by Equation 1 can be increased, and the magnetizing impedance Zcmt of the common-mode transformer 75 can be effectively utilized. As a result, the common-mode current Icom caused by the generated error voltage can be suppressed, and the effect of reducing conducted noise can be improved.

[0098] Figure 7 An example of simulation results representing the output impedance characteristics. Figure 7 The graph shown is a double logarithmic graph with the horizontal axis representing frequency and the vertical axis representing impedance, and both axes scaled logarithmically. The graph shows the output impedance (zoamp) of the voltage-to-current conversion circuit 23, the magnetizing impedance of the primary side of the common-mode transformer 25, and the combined impedance of these two impedances. Figure 7 As shown, in the frequency region below 1MHz, the output impedance of the voltage-to-current conversion circuit 23 is more than 10 times greater than the magnetizing impedance of the primary side of the common-mode transformer 25, and the combined impedance is approximately the same as the magnetizing impedance of the primary side of the common-mode transformer 25. Therefore, it can be confirmed that the combined impedance Z3 (expressed by Equation 1 above) is... Figure 6 It also gets bigger. In addition, Figure 7The characteristic shown is the output impedance of the primary side of common-mode transformer 25. Converted to the secondary side, if the winding ratio of common-mode transformer 25 is set to 'a', then the impedance is 'a'. 2 This increases the common-mode current Icom suppression effect by a factor of two.

[0099] <4. Effects of the Implementation Method>

[0100] As explained above, in the inverter system 1 of this embodiment, current is input to the primary winding 25p of the common-mode transformer 25 based on the common-mode voltage generated when the switching element included in the power conversion section 41 of the inverter device 9 is switched. This allows the common-mode voltage to be reduced by the voltage induced in the secondary winding 25s of the common-mode transformer 25. By configuring the structure to input current to the primary winding 25p of the common-mode transformer 25, the combined impedance Z3 in the common-mode equivalent closed circuit of the inverter system 1 can be increased. Therefore, even if an error occurs between the voltage value induced in the secondary winding 25s of the common-mode transformer 25 due to the noise filter 7 and the voltage value that can cancel the generated common-mode voltage, the common-mode current Icom caused by the generated error voltage can be suppressed. Thus, the effect of reducing conducted noise can be improved.

[0101] Furthermore, in this embodiment, the current input from the voltage-to-current conversion circuit 23 to the primary winding 25p of the common-mode transformer 25 can be determined such that the voltage induced in the secondary winding 25s of the common-mode transformer 25 is approximately the same as the common-mode voltage detected by the common-mode voltage detection circuit 21. In this case, most of the common-mode voltage generated during the switching operation of the switching element can be offset by the voltage induced in the secondary winding 25s of the common-mode transformer 25.

[0102] Alternatively, in this embodiment, the inverter substrate 51, on which the power conversion section 41 of the inverter device 9 is mounted, and the noise reduction substrate 53, on which the voltage-to-current conversion circuit 23 of the noise filter 7 is mounted, can be set as different substrates. In this case, by separating the inverter substrate 51 and the noise reduction substrate 53, it is possible to suppress the influence of noise generation sources in the inverter substrate 51 on the noise filter function in the noise reduction substrate 53, thus reducing the noise reduction function. In addition, by making the noise reduction substrate 53 on which the voltage-to-current conversion circuit 23 is mounted detachable, the noise filtering function can be changed or added.

[0103] Alternatively, in this embodiment, the voltage-to-current conversion circuit 23 may also have a load simulation unit 61 that simulates the excitation impedance of the primary winding 25p of the common-mode transformer 25. In this case, by using the load simulation unit 61, it is possible to determine a current value that is approximately the same as the voltage induced in the secondary winding 25s of the common-mode transformer 25 and the common-mode voltage detected by the common-mode voltage detection circuit 21.

[0104] In this embodiment, the voltage-to-current conversion circuit 23 can also apply the common-mode voltage detected by the common-mode voltage detection circuit 21 to both ends of the load simulation unit 61, and output the current generated in the load simulation unit 61 to the primary winding 25p of the common-mode transformer 25. In this case, the voltage induced in the secondary winding 25s of the common-mode transformer 25 can be made to match the common-mode voltage detected by the common-mode voltage detection circuit 21 with high precision.

[0105] Alternatively, in this embodiment, the load simulation unit 61 can be constructed from passive components. In this case, the characteristics of the excitation impedance of the primary winding 25p of the common-mode transformer 25 can be reproduced with high accuracy.

[0106] Alternatively, in this embodiment, the common-mode voltage detection circuit 21 can be configured using detection capacitors. In this case, the detection capacitors (X capacitor 55, Y capacitor 57) of the common-mode voltage detection circuit 21 bypass most of the common-mode current flowing from the power conversion unit 41 through the grounding wire 45, thereby suppressing the common-mode current flowing to the LISN3 side and detecting the common-mode voltage with high accuracy.

[0107] Alternatively, in this embodiment, the common-mode voltage detection circuit 21 may be configured to include at least a Y capacitor 57. Thus, by using at least the Y capacitor 57 of the common-mode voltage detection circuit 21 to bypass most of the common-mode current flowing from the power conversion unit 41 through the grounding wire 45, the common-mode current flowing towards the LISN3 side can be suppressed, and the common-mode voltage can be detected with high accuracy.

[0108] In the case where the noise filter 7 includes an LC circuit consisting of windings and capacitors, resonance may occur in a specific frequency band, leading to increased noise. Therefore, in this embodiment, the damping resistor 59 can be connected in parallel with the Y capacitor 57. In this case, the resonance in the LC circuit can be attenuated, and the increase in noise can be prevented.

[0109] In this embodiment, the noise filter 7 may also have external noise protection circuits 27 and 29 in at least one of the input section 23i and the output section 23o of the voltage-to-current conversion circuit 23. In this case, the voltage-to-current conversion circuit 23 can be protected from noise (pulse noise) applied from the AC power supply 15.

[0110] In this embodiment, at least one of a high-pass filter 31, a low-pass filter 33, and a band-pass filter may be connected to the input section 23i of the voltage-to-current conversion circuit 23. In this case, voltages in a specific frequency band can be suppressed or removed, thus preventing malfunctions of the voltage-to-current conversion circuit 23 and enabling high-precision detection of common-mode voltage.

[0111] In this embodiment, the external noise protection circuit 29 connected to the output 23o of the voltage-to-current conversion circuit 23 may also include passive components, semiconductor components such as diodes. In this case, when noise (pulse noise) is applied from the AC power supply 15, the pulse noise current generated via the common-mode transformer 25 can be suppressed. Therefore, malfunctions of the voltage-to-current conversion circuit 23 caused by pulse noise current can be prevented.

[0112] In this embodiment, the noise filter 7 can also be connected between the AC power supply 15 and the power conversion section 41 of the inverter device 9. In this case, the common-mode voltage is detected by the common-mode voltage detection circuit 21 near the inverter device 9, and the input voltage is obtained from the common-mode transformer 25 on the LISN3 side, thereby realizing a feedforward inverter system 1. As a result, oscillations caused by the design of increasing the amplification rate of the amplifier circuit (high-gain design) can be suppressed, and stability can be improved. In addition, the increase in conducted noise caused by voltage overshoot injected into the power lines 17r, 17s, and 17t, and the decrease in conducted noise suppression effect caused by phase delay of the amplifier circuit can be suppressed.

[0113] <5. Variations>

[0114] The disclosed embodiments are not limited to those described above, and various modifications can be made without departing from their spirit and technical concept. Examples of such modifications will be described below.

[0115] (5-1. Case where a noise filter is connected between the rectifier and the power conversion section)

[0116] In the above embodiment, in the inverter system 1, the noise filter 7 is configured to be connected between the AC power supply 15 and the power conversion section 41 of the inverter device 9. However, the connection position of the noise filter 7 can also be other than the above-described position. For example, it can also be as follows: Figure 8 As shown in the inverter system 1A, the noise filter 7A is connected between the rectifier section 39 and the power conversion section 41 of the inverter device 9.

[0117] In the noise filter 7A, the common-mode voltage detection circuit 21 has two X capacitors 55 (an example of a detection capacitor) and one Y capacitor 57 (an example of a detection capacitor). The X capacitors 55 are connected between the power lines 77p and 77n respectively, which are located between the rectifier section 39 and the power conversion section 41. The Y capacitor 57 is connected between the power lines 77p and 77n and the ground line 45 (an example of ground). Although not shown in the figure, a damping resistor 59 is connected in parallel with the Y capacitor 57. The structure of the noise filter 7A other than the above is the same as that of the noise filter 7 in the embodiment, so the description is omitted. In this modified example, the inverter device 9 and the noise filter 7A are integrally formed. Alternatively, the inverter device 9 and the noise filter 7A can also be formed separately. In addition, the converter board 49, the inverter board 51, and the noise reduction board 53 can also be formed as one board or two boards.

[0118] According to this modified example, similarly to the embodiment described above, an inverter system 1A that improves the reduction of conducted noise can be achieved. Furthermore, the inverter device 9 and the noise filter 7A can be integrated, thus simplifying the system structure.

[0119] (5-2. Case where a noise filter is connected between the power conversion unit and the motor)

[0120] In the above embodiment, in the inverter system 1, the noise filter 7 is configured to be connected between the AC power supply 15 and the power conversion section 41 of the inverter device 9. However, the connection position of the noise filter 7 can also be other than the above-described position. For example, it can also be as follows: Figure 9 As shown in the inverter system 1B, the noise filter 7B is connected between the power conversion section 41 of the inverter device 9 and the motor 13.

[0121] The structure of noise filter 7B is the same as that of noise filter 7 in the embodiment. Furthermore, in noise filter 7B, the three X capacitors 55 constituting the common-mode voltage detection circuit 21 are respectively connected between power supply lines 47u, 47v, and 47w. Additionally, a Y capacitor 57 is connected between power supply lines 47u, 47v, and 47w and ground line 45 (an example of ground). Although not shown in the figure, a damping resistor 59 is connected in parallel with the Y capacitor 57.

[0122] According to this modified example, similarly to the above-described embodiment, an inverter system 1B that can improve the reduction effect of conducted noise can be achieved.

[0123] In addition to those already described above, the methods of the above embodiments and their variations can also be appropriately combined. Furthermore, although not all examples have been shown, the above embodiments and their variations can be implemented with various modifications without departing from their spirit.

[0124] The problems and effects to be solved by the implementation methods and modifications described above are not limited to those described above. Through the implementation methods and modifications, problems not described above can also be solved, or effects not described above can also be achieved. Sometimes, only a part of the described problems are solved, or only a part of the described effects are achieved.

[0125] Symbol Explanation

[0126] 1 Inverter System

[0127] 1A Inverter System

[0128] 1B Inverter System

[0129] 5. Power cable

[0130] 7. Noise Filter

[0131] 7A noise filter

[0132] 7B Noise Filter

[0133] 9. Inverter Unit

[0134] 11 Motor cables

[0135] 13 motors

[0136] 15 AC power supply

[0137] 17r power cord

[0138] 17s power cord

[0139] 17t power cord

[0140] 19 Grounding wire

[0141] 21 Common-mode voltage detection circuit

[0142] 23 Voltage-to-current conversion circuit

[0143] 23i Input Section

[0144] 23o Output Section

[0145] 25 Common Mode Transformer

[0146] 25p primary winding

[0147] 25s secondary winding

[0148] 27 External noise protection circuit

[0149] 29 External noise protection circuit

[0150] 31 High-pass filter

[0151] 33 Low-pass filter

[0152] 39 Rectifier Section

[0153] 41 Power Conversion Department

[0154] 45 Grounding wire

[0155] 47u power cord

[0156] 47V power cord

[0157] 47W power cord

[0158] 49 Converter substrate

[0159] 51 Inverter baseboard

[0160] 53 Noise Reduction Substrate

[0161] 55X capacitor

[0162] 57Y capacitor

[0163] 59 Damping resistor

[0164] 61 Load Simulation Department

[0165] 63 Operational Amplifier

[0166] 77n power cord

[0167] 77p power cord

Claims

1. An inverter system, comprising: An inverter device having a power conversion section that uses switching elements; A noise filter inputs a current based on the common-mode voltage generated when the switching element is switched on to the primary winding of a common-mode transformer having a primary winding and a secondary winding.

2. The inverter system according to claim 1, wherein, The noise filter includes: The common-mode voltage detection unit detects the common-mode voltage. A voltage-to-current converter outputs the current based on the common-mode voltage detected by the common-mode voltage detection unit; and The common-mode transformer, wherein the primary winding of the common-mode transformer is input with the current output from the voltage-to-current conversion unit. The voltage-to-current conversion unit determines the current such that the voltage induced in the secondary winding of the common-mode transformer is consistent with the common-mode voltage detected by the common-mode voltage detection unit.

3. The inverter system according to claim 2, wherein, The power conversion unit is mounted on the first substrate. A second substrate is mounted with the voltage-to-current conversion unit, and the second substrate is at least different from the first substrate.

4. The inverter system according to claim 2, wherein, The voltage-to-current conversion unit has a load simulation unit that simulates the excitation impedance of the primary winding of the common-mode transformer.

5. The inverter system according to claim 4, wherein, In the voltage-to-current conversion unit, the common-mode voltage detected by the common-mode voltage detection unit is applied to both ends of the load simulation unit, and the current generated by the load simulation unit is output to the primary winding of the common-mode transformer.

6. The inverter system according to claim 4 or 5, wherein, The load simulation unit has passive components.

7. The inverter system according to claim 2, wherein, The common-mode voltage detection unit includes a detection capacitor.

8. The inverter system according to claim 7, wherein, The detection capacitor includes a Y capacitor connected between the power line and ground, or the Y capacitor and an X capacitor connected between the power line.

9. The inverter system according to claim 8, wherein, The common-mode voltage detection unit has a damping resistor connected in parallel with the Y capacitor.

10. The inverter system according to claim 2, wherein, The noise filter has an external noise protection section on at least one of the input and output sections of the voltage-current converter, which is used to protect the voltage-current converter from noise applied from the AC power supply.

11. The inverter system according to claim 10, wherein, The external noise protection unit connected to the input unit has at least one of a high-pass filter, a low-pass filter, and a band-pass filter.

12. The inverter system according to claim 10 or 11, wherein, The external noise protection unit connected to the output unit has at least one of a passive component and a semiconductor component.

13. The inverter system according to claim 1, wherein, The noise filter is connected between the AC power supply and the power conversion unit.

14. The inverter system according to claim 1, wherein, The inverter device has: The rectifier section converts the AC power output into DC voltage; and The power conversion unit converts the DC voltage into AC voltage; The noise filter is connected between the rectifier and the power conversion unit.

15. The inverter system according to claim 1, wherein, The inverter system also includes a motor driven by drive power supplied from the inverter unit. The noise filter is connected between the power conversion unit and the motor.

16. A noise filter configured in an inverter system including an inverter unit having a power conversion section using switching elements. The noise filter inputs a current based on the common-mode voltage generated when the switching element is switched on to the primary winding of the common-mode transformer, which has a primary winding and a secondary winding.

17. The noise filter according to claim 16, further comprising: The common-mode voltage detection unit detects the common-mode voltage. The voltage-to-current conversion unit outputs current based on the common-mode voltage detected by the common-mode voltage detection unit; as well as The common-mode transformer, wherein the primary winding of the common-mode transformer is input with the primary current output from the voltage-to-current conversion unit. The voltage-to-current conversion unit determines the current such that the voltage induced in the secondary winding of the common-mode transformer is approximately the same as the common-mode voltage detected by the common-mode voltage detection unit.

18. A noise reduction method for an inverter system including an inverter device having a power conversion section using switching elements. In the noise reduction method, a current based on the common-mode voltage generated when the switching element is switched is input to the primary winding of a common-mode transformer having a primary winding and a secondary winding.

19. The noise reduction method according to claim 18, wherein, The input current based on the common-mode voltage includes: Detect the common-mode voltage; The current is determined such that the voltage induced in the secondary winding of the common-mode transformer matches the detected common-mode voltage; and The determined current is input into the primary winding of the common-mode transformer.

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