Noise filter

Abstract

A noise filter (50) includes a voltage detector (7) that detects a common-mode voltage (Vci) generated by a power converter (2); a voltage dividing circuit (9) that outputs a divided voltage (Vd) obtained by dividing the common-mode voltage (Vci) detected by the voltage detector (7); a plurality of common-mode transformers (11a, 11b) that superimpose an injection voltage (Vs) having a polarity opposite to the common-mode voltage (Vci) on an output or an input of the power converter (2); and an injection waveform generator (10) that generates an output voltage (Vp) output to a primary side of the plurality of common-mode transformers (11a, 11b) based on the divided voltage (Vd). The injection waveform generator (10) generates the output voltage (Vp) such that a difference between a total injection voltage obtained by adding the injection voltages (Vs) superimposed by the plurality of common-mode transformers (11a, 11b) and the common-mode voltage (Vci) becomes equal to or less than an allowable value.

Description

TECHNICAL FIELD

[0001] The present application relates to a noise filter. BACKGROUND

[0002] In recent years, in a power conversion device such as a voltage type PWM (Pulse Width Modulation) inverter, with the development of power semiconductor elements, the high frequency of the carrier frequency has been developed. However, with the high frequency of the carrier frequency, electromagnetic disturbance caused by the common mode voltage generated at the time of switching operation of the power semiconductor element becomes a problem. As a countermeasure for this problem, a method of using a common mode transformer to superimpose and cancel the voltage (canceling voltage) generated by the power conversion device, and suppressing the leakage current, that is, the common mode current, due to the flow of the common mode voltage to the ground, has been proposed (for example, Patent Literature 1).

[0003] The common mode suppression circuit of Patent Literature 1 has a common mode transformer in which a secondary side coil, that is, a secondary winding, is provided in a three-phase cable connecting an inverter and a motor; a capacitor connected in series with a primary side coil, that is, a primary winding, of the common mode transformer; a capacitor group that detects a common mode voltage; and an emitter follower circuit that outputs a canceling voltage, which is power-amplified with respect to the common mode voltage, to the primary winding of the common mode transformer. In the common mode suppression circuit of Patent Literature 1, the turns ratio of the primary winding and the secondary winding of the common mode transformer is 1:1, and by canceling the common mode voltage above the switching frequency, the common mode transformer for superimposing and canceling the voltage is miniaturized compared to the case where the common mode voltage is set to 0.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 6491349 SUMMARY

[0007] However, in the case where the switching frequency is low in the common mode suppression circuit of Patent Literature 1, the time integral of the magnetic flux generated in the core becomes large, and thus there is a problem in that the core used in the common mode transformer becomes large.

[0008] The present application relates to a noise filter.

[0009] The noise filter disclosed in one example of the present application is a noise filter that reduces common-mode voltage generated by a power converter that performs power conversion through switching operation of a semiconductor element. The noise filter includes a voltage detector that detects common-mode voltage generated by the power converter, a voltage dividing circuit that outputs a divided voltage obtained by dividing the common-mode voltage detected by the voltage detector, a plurality of common-mode transformers that superimpose injection voltage having a polarity opposite to the common-mode voltage on an output or an input of the power converter, and an injection waveform generator that generates output voltage to be output to a primary side of the plurality of common-mode transformers in accordance with the divided voltage. The injection waveform generator generates output voltage in which a difference between total injection voltage obtained by adding the injection voltage superimposed by the plurality of common-mode transformers and the common-mode voltage becomes equal to or less than an allowable value.

[0010] The noise filter disclosed in one example of the present application includes a plurality of common-mode transformers, and an injection waveform generator generates output voltage in which a difference between total injection voltage obtained by adding injection voltage superimposed by the plurality of common-mode transformers and common-mode voltage becomes equal to or less than an allowable value, so that even in a case where a switching frequency is low, a small common-mode transformer can be used to suppress common-mode voltage. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a diagram showing a structure of a first noise filter and a motor drive system according to Embodiment 1.

[0012] Figure 2 is a diagram showing a structure of a power converter of Figure 1 .

[0013] Figure 3 is a diagram showing a structure of a voltage dividing circuit of Figure 1 .

[0014] Figure 4 is a diagram showing a first example of an injection waveform generator of Figure 1 .

[0015] Figure 5 is a diagram showing a second example of an injection waveform generator of Figure 1 .

[0016] Figure 6 is a diagram showing a third example of an injection waveform generator of Figure 1 .

[0017] Figure 7 is a diagram showing a structure of a second noise filter and a motor drive system according to Embodiment 1.

[0018] Figure 8 is a diagram showing a structure of a third noise filter and a motor drive system according to Embodiment 1.

[0019] Figure 9 This is a diagram showing the structure of the noise filter and the motor drive system of the comparative example.

[0020] Figure 10 This is a diagram showing the core of the noise filter according to Embodiment 1.

[0021] Figure 11 It is along Figure 10 The cross-sectional view shown by the dashed line AA.

[0022] Figure 12 This is a perspective view showing the core of the noise filter according to Embodiment 1.

[0023] Figure 13 This is a perspective view showing the core of a noise filter for a comparative example.

[0024] Figure 14 This is a diagram showing the structure of the fourth noise filter and the motor drive system according to Embodiment 1.

[0025] Figure 15 This is a diagram showing the structure of the fifth noise filter and the motor drive system according to Embodiment 1.

[0026] Figure 16 This is a diagram showing the structure of the sixth noise filter and the motor drive system according to Embodiment 1.

[0027] Figure 17 This is a diagram showing the structure of the first noise filter and the motor drive system according to Embodiment 2.

[0028] Figure 18 It is shown Figure 17 The first example of the first injected waveform generator is shown in the figure.

[0029] Figure 19 It is shown Figure 17 The first example of the second injected waveform generator is shown in the figure.

[0030] Figure 20 It is shown Figure 17 The second example of the first injected waveform generator is shown in the figure.

[0031] Figure 21 It is shown Figure 17 The second example of the second injected waveform generator is shown in the figure.

[0032] Figure 22 It is shown Figure 17 The figure shows the third example of the first injected waveform generator.

[0033] Figure 23 It is shownFigure 17 The figure shows the third example of the second injected waveform generator.

[0034] Figure 24 It is shown Figure 17 The fourth example of the first injected waveform generator is shown in the figure.

[0035] Figure 25 It is shown Figure 17 The fourth example of the second injected waveform generator is shown in the figure.

[0036] Figure 26 It is shown Figure 17 The figure shows the fifth example of the first injected waveform generator.

[0037] Figure 27 It is shown Figure 17 The figure shows the fifth example of the second injected waveform generator.

[0038] Figure 28 It is shown Figure 17 The sixth example of the first injected waveform generator is shown in the figure.

[0039] Figure 29 It is shown Figure 17 The sixth example of the second injected waveform generator is shown in the figure.

[0040] Figure 30 This is a diagram showing the structure of the second noise filter and the motor drive system according to Embodiment 2.

[0041] Figure 31 This is a diagram showing the structure of the third noise filter and the motor drive system according to Embodiment 2.

[0042] (Symbol Explanation)

[0043] 2: Power converter; 7: Voltage detector; 9: Voltage divider circuit; 10: Injection waveform generator; 10a, 10b: Injection waveform generator (waveform generator); 11a, 11b, 11c: Common mode transformer; 12: Bandwidth limiter; 13: Amplifier; 28: Core; 32, 32a, 32b, 32c: Bandwidth limiter; 33: Bandwidth limiter; 34: Bandwidth limiter; 50: Noise filter; 52, 52a, 52b: Output terminals; Gi: Gain; l: Inner diameter; L: Outer diameter; Nt: Number of transformers connected; Q1, Q2, Q3, Q4, Q5, Q6: Semiconductor elements; Rr: Turns ratio; S: Section area; Vci: Common mode voltage; Vd: Voltage divider voltage; Vp, Vpa, Vpb, Vpc: Output voltage; Vs, Vsa, Vsb, Vsc: Injection voltage; Vst: Total injection voltage. Detailed Implementation

[0044] A noise filter and a motor drive system will be described with reference to the drawings. The same or equivalent portions are denoted by the same reference symbols throughout the respective drawings.

[0045] Embodiment 1

[0046] Figure 1 is a view showing the structure of a first noise filter and a motor drive system according to Embodiment 1. Figure 2 is a view showing the structure of a power converter of Figure 1 Figure 3 is a view showing the structure of a voltage dividing circuit of Figure 1 Figure 4 is a view showing a first example of an injection waveform generator of Figure 1 Figure 5 is a view showing a second example of an injection waveform generator of Figure 1 Figure 6 is a view showing a third example of an injection waveform generator of Figure 1 Figure 7 is a view showing the structure of a second noise filter and a motor drive system according to Embodiment 1, Figure 8 is a view showing the structure of a third noise filter and a motor drive system according to Embodiment 1. Figure 9 is a view showing the structure of a noise filter and a motor drive system according to a comparative example. Figure 10 is a view showing a core of a noise filter according to Embodiment 1, Figure 11 is a cross-sectional view taken along the dotted line A-A of Figure 10 Figure 12 is a perspective view showing a core of a noise filter according to Embodiment 1, Figure 13 is a perspective view showing a core of a noise filter according to a comparative example. Figure 14 is a view showing the structure of a fourth noise filter and a motor drive system according to Embodiment 1, Figure 15 is a view showing the structure of a fifth noise filter and a motor drive system according to Embodiment 1. Figure 16 is a view showing the structure of a sixth noise filter and a motor drive system according to Embodiment 1. The noise filter 50 according to Embodiment 1 is applied to a motor drive system 60 which is a system in which an induction motor 3 is controlled by a power converter 2 such as a voltage type PWM inverter in which a plurality of semiconductor elements perform switching operations.

[0047] ​​​​​​The motor drive system 60 includes an electric power system, an alternating current power source 1 such as an independent voltage source, a power converter 2 that converts alternating current power of the alternating current power source 1 into direct current power and converts the direct current power into alternating current power, a three-phase power line 4 that connects between the alternating current power source 1 and the power converter 2, a three-phase power line 5 that connects between the power converter 2 and an induction motor 3, and a noise filter 50. The induction motor 3 is grounded through a ground line 6. A potential of the ground GND, that is, a ground potential becomes a reference potential of the noise filter 50. The three-phase power line 4 includes a u-phase three-phase power line 4u, a v-phase three-phase power line 4v, and a w-phase three-phase power line 4w. The three-phase power line 5 includes a u-phase three-phase power line 5u, a v-phase three-phase power line 5v, and a w-phase three-phase power line 5w.

[0048] The noise filter 50 includes a voltage detector 7, a voltage dividing circuit 9, an injection waveform generator 10, common mode transformers 11a, 11b. The power converter 2 includes a forward conversion circuit 21 composed of semiconductor elements, a capacitor 22 that is an electric power storage element that stores direct current power, and a reverse conversion circuit 23 composed of semiconductor elements that converts direct current power into alternating current power. The forward conversion circuit 21 is, for example, a rectifier circuit that includes six diodes D1, D2, D3, D4, D5, D6. The reverse conversion circuit 23 includes six semiconductor elements Q1, Q2, Q3, Q4, Q5, Q6. One ends of the three-phase power lines 4u, 4v, 4w connected to the alternating current power source 1 are connected to alternating current input terminals 41u, 41v, 41w of the power converter 2, respectively. The other ends of the three-phase power lines 5u, 5v, 5w connected to the induction motor 3 are connected to alternating current output terminals 42u, 42v, 42w of the power converter 2, respectively.

[0049] The forward converter circuit 21 has a first series connection of diodes D1 and D2 (connected in series), a second series connection of diodes D3 and D4 (connected in series), and a third series connection of diodes D5 and D6 (connected in series) between the high-potential side wiring 44p and the low-potential side wiring 44s. The connection point n1 of diodes D1 and D2 is connected to the AC input terminal 41u. The connection point n2 of diodes D3 and D4 is connected to the AC input terminal 41v, and the connection point n3 of diodes D5 and D6 is connected to the AC input terminal 41w. A capacitor 22 is connected between the high-potential side wiring 44p and the low-potential side wiring 44s. The reverse converter circuit 23 has a fourth series connection of semiconductor elements Q1 and Q2 (connected in series), a fifth series connection of semiconductor elements Q3 and Q4 (connected in series), and a sixth series connection of semiconductor elements Q5 and Q6 (connected in series) between the high-potential side wiring 44p and the low-potential side wiring 44s. The connection point n4 between semiconductor elements Q1 and Q2 is connected to the AC output terminal 42u. The connection point n5 between semiconductor elements Q3 and Q4 is connected to the AC output terminal 42v, and the connection point n6 between semiconductor elements Q5 and Q6 is connected to the AC output terminal 42w.

[0050] Semiconductor components Q1, Q2, Q3, Q4, Q5, and Q6 use power semiconductor components such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors). Figure 2 The diagram illustrates an example of a MOSFET. Semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6 each possess a MOS transistor M and a diode D. The diode D can be a different element from the MOS transistor M, or it can be a parasitic diode. The drain d of semiconductor elements Q1, Q3, and Q5 is connected to the high-potential side wiring 44p, and the source s of semiconductor elements Q2, Q4, and Q6 is connected to the low-potential side wiring 44s. The source s of semiconductor element Q1 and the drain d of semiconductor element Q2 are connected, the source s of semiconductor element Q3 and the drain d of semiconductor element Q4 are connected, and the source s of semiconductor element Q5 and the drain d of semiconductor element Q6 are connected. A control signal (not shown) is input to the gate g of semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6. The inverting converter circuit 23, based on the control signal from the control circuit, switches semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6 to convert DC power into AC power.

[0051] The voltage detector 7 that detects the common mode voltage Vci has three capacitors 8 with mutually equal capacitances, one end of each of the capacitors 8 being connected to each phase of the three-phase power line 5. The other ends of the capacitors 8 are connected to each other at a connection point n7. An input terminal 94 of a voltage dividing circuit 9 is connected to the connection point n7 to which the other ends of the capacitors 8 are connected, and an output terminal 95 is connected to an input terminal 51 of an injection waveform generator 10. The voltage dividing circuit 9 divides the input voltage, that is, the common mode voltage Vci between the wiring 24 that is a ground potential and the input terminal 94, and outputs the divided voltage Vd as an output voltage.

[0052] The voltage dividing circuit 9 has, for example, a capacitor 91 and a series body of a resistor 92 and a resistor 93 connected in parallel to the capacitor 91. One end of the capacitor 91 and one end of the resistor 92 are connected to the input terminal 94, and the other end of the capacitor 91 and one end of the resistor 93 are connected to the wiring 24 that is a ground potential. A connection point at which the other end of the resistor 92 and the other end of the resistor 93 are connected is connected to the output terminal 95. The voltage dividing circuit 9 outputs the divided voltage Vd obtained by dividing the common mode voltage Vci input to the input terminal 94 from the output terminal 95. The detected common mode voltage Vci is divided by the resistance ratio of the resistor 92 and the resistor 93. The voltages of the three-phase power lines 5u, 5v, 5w that are the respective phases of the three-phase power line 5 are divided by the impedance ratio of the capacitors 8 and the capacitor 91, and then divided by the resistance ratio of the resistor 92 and the resistor 93, and output as the divided voltage Vd from the voltage dividing circuit 9.

[0053] The divided voltage Vd is input to the input terminal 51 of the injection waveform generator 10. The injection waveform generator 10 outputs a voltage whose frequency band is limited and whose voltage value is adjusted from the output terminal 52 in accordance with the input divided voltage Vd. The output from the output terminal 52 of the injection waveform generator 10 is input to the primary side, that is, the primary winding, of the common mode transformers 11a, 11b. The common mode transformers 11a, 11b have a primary winding on the primary side and a secondary winding on the secondary side, and the secondary winding is inserted to the three-phase power lines 5u, 5v, 5w that are the respective phases of the three-phase power line 5. The voltage, that is, the output voltage Vp output from the injection waveform generator 10 is applied to the primary winding of each of the common mode transformers 11a, 11b, the polarity of which is opposite to that of the common mode voltage Vci, and a voltage corresponding to the turns ratio of the primary side and the secondary side, that is, an injection voltage Vs is generated in the secondary winding.

[0054] The power converter 2 generates a common-mode voltage Vci that changes in stages each time the semiconductor elements Q1 to Q6 switch. This common-mode voltage Vci is detected by the voltage detector 7, and is divided into a divided voltage Vd by the voltage dividing circuit 9. The output voltage Vp, which is output by the injection waveform generator 10 by limiting the frequency band and adjusting the voltage value of the divided voltage Vd, is input to the primary winding of the common-mode transformer 11a, 11b. The voltage generated in the secondary winding of the common-mode transformer 11a, 11b, that is, the injection voltage Vs, is adjusted in such a manner as to reduce the common-mode voltage Vci generated in the power converter 2. Therefore, the noise filter 50 of Embodiment 1 is able to suppress the common-mode voltage Vci by inputting the voltage, that is, the output voltage Vp, which is adjusted in polarity to be opposite to the common-mode voltage Vci and detected by the voltage detector 7, to the common-mode transformer 11a, 11b, and superimposing the injection voltage Vs on each phase of the three-phase power line 5. It is explained that the noise filter 50 of Embodiment 1 is able to suppress the common-mode voltage Vci using a small common-mode transformer 11a, 11b even in the case where the switching frequency of the power converter 2 is low.

[0055] Figures 4-6 First to third examples of the injection waveform generator 10 are shown. Figure 4 The injection waveform generator 10 of the first example shown is provided with a frequency band limiter 12, an amplifier 13, control power supplies 15a, 15b. The control power supply 15a supplies a positive-side voltage, and the control power supply 15b supplies a negative-side voltage. By the frequency band limiter 12, it is possible to apply only the reduced frequency band of the common-mode voltage Vci to the common-mode transformer 11a, 11b, so it is possible to downsize the common-mode transformer 11a, 11b. The frequency band limiter 12 can pass the frequency band as an object, and any one of a band-pass filter, a low-pass filter, and a high-pass filter can be applied. For example, in the case where the switching frequency is 2 kHz, by setting the frequency band as an object of the frequency band limiter 12 to a frequency band higher than 2 kHz, and connecting a high-pass filter having a cutoff frequency at a frequency lower than 2 kHz, it is possible to attenuate the low-frequency component of the voltage applied to the common-mode transformer 11a, 11b, and downsize the common-mode transformer 11a, 11b. Also, in the case where the frequency band as an object of the frequency band limiter 12 is set to a frequency band higher than 10 kHz, by connecting a high-pass filter having a cutoff frequency between 2 kHz and 10 kHz, it is possible to further downsize the common-mode transformer 11a, 11b. Figure 4The amplifier 13 shown is an example of a reverse amplification circuit. The amplifier 13 is provided with an operational amplifier 19, resistors 16, 17, 18. A ground potential is input to the positive-side input terminal of the operational amplifier 19 via the resistor 17. To the negative-side input terminal of the operational amplifier 19, the output of the band limiter 12 is input via the resistor 16, and the output of the operational amplifier 19 is input via the resistor 18.

[0056] When the resistance values of the resistor 16 and the resistor 18 are set to r1, r2, respectively, the gain Gi of the operational amplifier 19 is expressed by Expression (1). In addition, the output voltage Vp is expressed by Expression (2).

[0057] Gi = r2 / r1... (1)

[0058] Vp = -Gi x Vd... (2)

[0059] The gain Gi of the operational amplifier 19 is set in accordance with the voltage division ratio Rv of the voltage division circuit 9, the turns ratio Rr of the common-mode transformers 11a, 11b, and the number of connected transformers Nt which is the number of the connected common-mode transformers 11a, 11b. The gain Gi, the voltage division ratio Rv, the turns ratio Rr, and the number of connected transformers Nt are set in such a manner that the voltage, i.e., the injection voltage Vs, of the secondary windings of the common-mode transformers 11a, 11b superimposed on the voltages of the u-phase, the v-phase, and the w-phase of the three-phase power line 5 is reduced, i.e., in such a manner that Expression (3) is satisfied.

[0060] |Vci - Vst| ≤ Vto... (3)

[0061] Here, Vto is an allowable value of the voltage difference. Expression (3) indicates that the absolute value of the difference between the common-mode voltage Vci and the total injection voltage Vst is equal to or less than the allowable value Vto. The total injection voltage Vst is a voltage obtained by adding the injection voltages Vs generated by the common-mode transformers 11a, 11b.

[0062] In the case where the voltage values of the injection voltages are the same and the number of connected transformers Nt is 2, the total of the voltages superimposed on the u-phase, the v-phase, and the w-phase of the three-phase power line 5, i.e., the total injection voltage Vst, becomes 2 x Vs. In the case where the number of connected transformers Nt is used, the total of the voltages superimposed on the u-phase, the v-phase, and the w-phase of the three-phase power line 5, i.e., the total injection voltage Vst, is expressed by Expression (4). Figure 1 The number of connected transformers Nt in the case where the voltage values of the injection voltages are the same is 2.

[0063] Vst = Nt x Vs... (4)

[0064] The voltage division ratio Rv of the voltage division circuit 9 is expressed by Expression (5). When the number of turns of the primary winding and the secondary winding are set to N1, N2, respectively, the turns ratio Rr of the common-mode transformers 11a, 11b is expressed by Expression (6).

[0065] Rv = Vci / Vd... (5)

[0066] Rr = N2 / N1... (6)

[0067] The more the number Nt of the connecting transformers is, the smaller the voltage input to one common mode transformer, that is, the output voltage Vp of the injection waveform generator 10 and the voltage output to the secondary winding of the common mode transformer, that is, the injection voltage Vs become, for a value of the common mode voltage Vci. By having the plurality of common mode transformers 11a, 11b, the noise filter 50 of Embodiment 1 can superimpose the total injection voltage Vst on the u-phase, the v-phase, and the w-phase of the three-phase power line 5 with the small common mode transformers 11a, 11b. Therefore, the noise filter 50 of Embodiment 1 can suppress the common mode voltage using the small common mode transformers even in the case where the switching frequency is low. The content that the common mode transformer can be downsized by reducing the injection voltage Vs will be described later.

[0068] The injection waveform generator 10 of the second example is described. The injection waveform generator 10 of the second example is different from the injection waveform generator 10 of the first example in that the current buffer 14 is added between the output terminal of the amplifier 13 and the output terminal 52. Further, the output terminal of the amplifier 13 is the connection point of the wiring that transmits the output of the operational amplifier 19 and the resistor 18. The injection waveform generator 10 of the second example can increase the current capacity that indicates the current supply amount more than the injection waveform generator 10 of the first example. The current buffer 14 has, for example, two transistors BT1, BT2 connected in series. The collector c of the transistor BT1 is connected to the control power supply 15a, the emitter e of the transistor BT1 is connected to the emitter e of the transistor BT2, and the collector c of the transistor BT2 is connected to the control power supply 15b. The output of the amplifier 13 is input to the base b of the transistors BT1, BT2, and the emitter e of the transistors BT1, BT2 is connected to the output terminal 52.

[0069] The example in which the amplifier 13 is the inverting amplification circuit is shown in the injection waveform generator 10 of the first example and the injection waveform generator 10 of the second example, but the amplifier 13 can also be a non-inverting amplification circuit. Figure 6 The injection waveform generator 10 of the third example shown is an example of a non-inverting amplification circuit. The output of the band limiter 12 is input to the positive-side input terminal of the operational amplifier 19 via the resistor 17. The ground potential is input to the negative-side input terminal of the operational amplifier 19 via the resistor 16, and the output of the operational amplifier 19 is input via the resistor 18.

[0070] When the resistance values of the resistor 16 and the resistor 18 are set to r1 and r2, respectively, the gain Gi of the operational amplifier 19 of the non-inverting amplification circuit is represented by Equation (7). In addition, the output voltage Vp is represented by Equation (8).

[0071] Gi = 1 + r2 / r1... (7)

[0072] Vp = Gi x Vd... (8)

[0073] In the case where the amplifier 13 is a non-inverting amplification circuit, as shown in Figure 7 the connection to the primary winding of the common-mode transformer 11a, 11b is changed in reverse to set in a manner in which the voltage output to the secondary winding, that is, the injection voltage Vs, reduces the common-mode voltage Vci. Next, the noise filter 50 of Embodiment 1 is described while comparing with the noise filter 100 of the comparative example.

[0074] Figure 9 The noise filter 100 of the comparative example shown in FIG. 10 has one common-mode transformer 101, and the motor drive system 110 of the comparative example has the noise filter 100. In the noise filter 100 of the comparative example, the output voltage Vpe is output from the injection waveform generator 102 to the primary winding of the common-mode transformer 101, and the injection voltage Vse is overlapped to the u-phase, the v-phase, and the w-phase of the three-phase power line 5. The noise filter 100 of the comparative example differs from the noise filter 50 of Embodiment 1 in that it has one common-mode transformer 101 and the injection waveform generator 10 is changed to the injection waveform generator 102. The structure of the injection waveform generator 102 is the same as that of the injection waveform generator 10, but differs in the gain Gi and the like according to the value of the output voltage Vpe. The number of connection transformers Nt of the noise filter 100 of the comparative example is one. In order to achieve the same reduction of the common-mode voltage even if the number of common-mode transformers differs, the same value of the total injection voltage Vst is required. Therefore, as is clear from Equation (4), the noise filter 100 of the comparative example cannot achieve the same reduction of the common-mode voltage if the injection voltage Vse, which is twice the injection voltage Vs of the noise filter 50 of Embodiment 1 overlapped to each phase of the three-phase power line 5, is not overlapped to each phase of the three-phase power line 5. Therefore, in order to achieve the same reduction of the common-mode voltage as the noise filter 50 of Embodiment 1, the noise filter 100 of the comparative example requires Equation (9) to be satisfied.

[0075] Vse = 2 x Vs... (9)

[0076] In order to achieve Equation (9), two methods are considered, for example. In the first method, the turns ratio Rr of the common-mode transformer 101 is made twice by setting the output voltage Vpe to be the same as the output voltage Vp. In the second method, the output voltage Vpe is made twice the output voltage Vp by setting the turns ratio Rr of the common-mode transformer 101 to be the same as the turns ratio Rr of the common-mode transformer 11a, 11b.

[0077] The common mode transformers 11a, 11b have one primary winding and three secondary windings. The core of the common mode transformers 11a, 11b is, for example, a ring-shaped core 28 as shown in FIG. 2. The noise filter 50 of Embodiment 1 has two common mode transformers 11a, 11b, and thus has two cores 28 as shown in FIG. 2. Figure 10 The noise filter 50 of Embodiment 1 has two common mode transformers 11a, 11b, and thus has two cores 28 as shown in FIG. 2. Figure 12 The noise filter 100 of the comparative example has one common mode transformer 101, and thus has one core 29 as shown in FIG. 6. Figure 13 The noise filter 100 of the comparative example has one common mode transformer 101, and thus has one core 29 as shown in FIG. 6.

[0078] In the first method, in order to increase the turns ratio Rr of the common mode transformer 101, there are a method of reducing the number of turns of the primary winding and a method of increasing the number of turns of the secondary winding. In the case of reducing the number of turns of the primary winding, the excitation current of the common mode transformer 101 increases, and the magnetic flux also increases. In order to avoid magnetic saturation of the core used in the common mode transformer 101, it is necessary to increase the cross-sectional area of the core. In contrast, in the case of increasing the number of turns of the secondary winding, the secondary winding is wound with three-phase windings having the same wire diameter as the three-phase power lines 5, and thus the inner diameter of the core becomes large, and as a result, the core becomes large-sized. When a voltage above the voltage of the control power supply 15a, 15b is generated in the secondary winding of the common mode transformer 101 as an injection voltage Vse, it is not possible to avoid the large-sizing of the core.

[0079] On the other hand, in the second method, in order to apply a high voltage to the common mode transformer 101, a control power supply that outputs a high voltage, a high-voltage element are required. In addition, the voltage-time product in the common mode transformer 101 becomes large, and thus in order to avoid magnetic saturation of the core, it is necessary to increase the cross-sectional area of the core and the number of turns of the primary winding. In order to keep the turns ratio Rr constant, the number of turns of the secondary winding also increases, and as a result, the large-sizing of the core also occurs in the case of applying a high voltage to the common mode transformer 101.

[0080] According to the above, the noise filter 50 of Embodiment 1 has a plurality of common mode transformers 11a, 11b, thereby being able to reduce the injection voltage Vs generated in one common mode transformer. Therefore, the noise filter 50 of Embodiment 1 is different from the noise filter 100 of the comparative example, and the common mode transformers 11a, 11b do not need to increase the cross-sectional area of the core, and do not need to increase the inner diameter of the core in order to increase the number of turns, and are able to downsize the core. In addition, in the noise filter 50 of Embodiment 1, the voltage applied to the common mode transformers 11a, 11b, that is, the output voltage Vp can be a low voltage, and the voltage time product is able to be reduced, so downsizing of the core is achieved. In addition, in the noise filter 50 of Embodiment 1, the voltage applied to the control power supplies 15a, 15b of the injection waveform generator 10 can be a low voltage, and the injection waveform generator 10 is able to be configured with low-voltage elements.

[0081] In the common mode suppression circuit of Patent Document 1, the common mode transformer with a turn ratio Rr of 1 is one. As described above, in the case where the switching frequency is low, the time product of the magnetic flux generated in the core becomes large, so in order to generate the same voltage in the secondary winding, the core used in the common mode transformer becomes large. In one common mode transformer, this increase in size becomes significant. The noise filter 50 of Embodiment 1 has two common mode transformers 11a, 11b, so in the case where the total injection voltage Vst overlapped to the three-phase power line 5 in the common mode suppression circuit of Patent Document 1 is the same, the injection voltage Vs overlapped by each common mode transformer 11a, 11b is able to be Vst / 2. The injection voltage Vs is Vst / 2, so the voltage time product is able to be reduced, and furthermore, the magnetic flux generated in the core is also able to be reduced, and the cross-sectional area of the core is able to be reduced. Therefore, the noise filter 50 of Embodiment 1 is able to use a common mode transformer having a smaller core than the common mode suppression circuit of Patent Document 1.

[0082] The size of the core in the noise filter 50 of Embodiment 1 will be described using Figures 10-13 . The core in the noise filter 50 of Embodiment 1 is a ring-type core 28 as described above, for example, as shown in Figure 10 . The noise filter 50 of Embodiment 1 has two common mode transformers 11a, 11b, so as shown in Figure 12 , two cores 28 are provided. The noise filter 100 of the comparative example has one common mode transformer 101, so as shown in Figure 13 , one core 29 is provided. The inner diameter of the core 28 is l, the outer diameter is L, and the width (thickness) is h. The cross-sectional area of the core 28 is S. In Figure 11 , the left side is the inner side of the core 28, and the right side is the outer side of the core 28. First, a case where the same voltage value of the output voltage Vp is applied to the two common mode transformers 11a, 11b as shown in Figure 1 will be considered. The magnetic flux density B generated in the core 28 is represented by Equation (10).

[0083] B = (Vp x t) / (N1 x S)... (10)

[0084] t is the time at which the output voltage Vp is applied.

[0085] By reducing the voltage-time product (Vp x t) according to Equation (10), it is possible to reduce the cross-sectional area S while keeping the magnetic flux density B and the number of turns N1 of the primary side constant. If the magnetic flux density generated in the core 29 of the common-mode transformer 101 of the comparative example and the total magnetic flux density generated in the cores 28 of the two common-mode transformers 11a, 11b of Embodiment 1 are considered to be the same, the relationship between the cross-sectional area S of the core 28 and the cross-sectional area Se of the core 29 is shown in Equation (11).

[0086] Se = 2 x S... (11)

[0087] The cross-sectional area Se of the core 29 and the volume vl are expressed by Equations (12) and (13). The cross-sectional area Se of the core 29 is the area of the cross section along the broken line indicated by A-A in the case where the core 28 is set as the core 29. The width of the core 29 is h, which is the same as the width of the core 28. Figure 10

[0088] Se = h x (Le - l) / 2... (12)

[0089] vl = π x h x (Le - l) / 4... (13) 2 2

[0090] The cross-sectional area S of the core 28 and the volume v2 are expressed by Equations (14) and (15).

[0091] S = h x (L - l) / 2... (14)

[0092] v2 = π x h x (L - l) / 4... (15) 2 2

[0093] When Equations (12) and (14) are substituted into Equation (11) and are transformed, it is shown as Equation (16).

[0094] L = (Le + l) / 2... (16)

[0095] When the volume v2 of Equation (15) is transformed using Equation (16), it is shown as Equation (17).

[0096] v2 = π x h x (Le + 2Le x l - 3l) / 16... (17) 2 2

[0097] ​​​​​​​According to formula (13) and formula (17), a relationship of formula (18) holds with respect to the volume v1 of the core 29 and the total volume 2 x v2 of the 2 cores 28.

[0098] v1>2 x v2 … (18)

[0099] Thus, in a case where the output voltage Vp of the same voltage value as the one-core common mode transformer 101 is divided by the 2 common mode transformers 11a, 11b and the injection voltage Vs of the same voltage value is superimposed to the three-phase power line 5, the following is described. In the common mode transformers 11a, 11b in the noise filter 50 of Embodiment 1, by making the outer diameter L in the 1 core 28 smaller than the outer diameter Le under the condition that the magnetic flux density B and the inner diameter l are constant, it is possible to reduce the total volume, i.e., the total size, of the cores 28 while maintaining the cross-sectional area S in the 1 core 28 to be 1 / 2 of the cross-sectional area Se of the core 29. Here, the inner diameter l being constant depends on the number of turns N1 being constant and the required inner diameter being constant.

[0100] In addition, as shown in Figure 8 in a case where the common mode transformers 11a, 11b superimpose the injection voltages Vsa, Vsb of different voltage values to the three-phase power line 5, unlike the common mode transformer of Patent Literature 1, it is possible to perform an operation of reducing the total voltage in matching with the allowable value, so it is possible to reduce the cross-sectional area S of the core 28 and to reduce the total volume (total size) of the 2 cores 28.

[0101] In the noise filter 50 of Embodiment 1, it is possible to make the total size of the 2 common mode transformers smaller than the common mode transformer of Patent Literature 1. In the noise filter 50 of Embodiment 1, by using 2 small common mode transformers, the degree of freedom of arrangement of the common mode transformers becomes higher than that of the common mode suppression circuit of Patent Literature 1. Therefore, the noise filter 50 of Embodiment 1 can realize a more efficient component arrangement than the common mode suppression circuit of Patent Literature 1 and can realize a small noise filter. Furthermore, in the noise filter 50 of Embodiment 1, by performing the band limitation of the frequency excluding the frequency having a large influence on the core increase by the injection waveform generator 10 to the divided voltage Vd, it is possible to reduce the common mode transformers 11a, 11b more than the common mode transformer of Patent Literature 1. That is, in a case where the injection voltage Vs generated by the plurality of common mode transformers 11a, 11b is sufficiently low voltage, even if the band limitation of the frequency excluding the frequency having a large influence on the core increase is not performed, it is possible to reduce the common mode transformers 11a, 11b more than the common mode transformer of Patent Literature 1.

[0102] In the common mode suppression circuit of Patent Literature 1, since the electric power of the control power source is the electric power of the input side direct current power source of the inverter, a transistor with high withstand voltage is required. In contrast, in the noise filter 50 of Embodiment 1, the injection voltage Vs becomes 1 / 2 of the injection voltage of the common mode suppression circuit of Patent Literature 1, and the output voltage Vp output from the injection waveform generator 10 can be made lower than that of the common mode suppression circuit of Patent Literature 1. Therefore, the injection waveform generator 10 can be configured with a low withstand voltage element.

[0103] As for the common mode transformers 11a, 11b, a case where the core material, the outer diameter L, the inner diameter 1, the cross-sectional area S, and the number of turns N1, N2 of the core 28 are the same is shown, but any one of the core material, the outer diameter L, the inner diameter 1, the cross-sectional area S, and the number of turns N1, N2 of the core 28 can be different. In this case, as shown in Figure 8 even if the output voltage Vp of the injection waveform generator 10 input to the common mode transformers 11a, 11b is the same, there is a case where the injection voltage Vsa generated by the common mode transformer 11a and the injection voltage Vsb generated by the common mode transformer 11b are different. In this case, the total injection voltage Vst uses Equation (19) instead of Equation (4).

[0104] Vst = Vsa + Vsb... (19)

[0105] Even in the case where the injection voltage Vsa and the injection voltage Vsb are different, the injection voltage Vs to be compared with the comparative example and the common mode suppression circuit of Patent Literature 1 can be considered to be 1 / 2 of the total injection voltage Vst. Therefore, the noise filter 50 of Embodiment 1 can miniaturize the common mode transformers 11a, 11b compared to the noise filter 100 of the comparative example and the common mode transformers of the common mode suppression circuit of Patent Literature 1.

[0106] Further, an example where the voltage detector 7 shown in Figure 1 is connected to the three-phase electric power line 5 is shown, but the voltage detector 7 can also be connected to the three-phase electric power line 4 as shown in Figure 14 The power converter 2 also generates the common mode voltage Vci on the three-phase electric power line 4. Even in this case, the common mode voltage Vci detected from the three-phase electric power line 4 is equivalent to the common mode voltage Vci detected from the three-phase electric power line 5, so Equation (3) is satisfied. In addition, an example where the common mode transformers 11a, 11b are inserted to the three-phase electric power line 5 is shown, but the common mode transformers 11a, 11b can also be inserted to the three-phase electric power line 4 as shown in Figure 15 By reducing the common mode voltage Vci in the three-phase electric power line 4, the common mode voltage Vci in the three-phase electric power line 5 can be reduced. In Figure 15The voltage detector 7 is connected to the three-phase power line 4 in the example shown, but the voltage detector 7 can also be connected to the three-phase power line 5. Furthermore, the positions of the common-mode transformers 11a, 11b and the voltage detector 7 can be exchanged as shown in Figure 16 Figure 1 The noise filter 50 of the first example shown is a feed-forward structure, but Figure 16 The noise filter 50 of the sixth example shown is a feedback structure.

[0107] A structure in which only the capacitor 91 is provided is also possible as the example of the voltage dividing circuit 9, but the voltage dividing circuit 9 is not limited to this. The voltage dividing circuit 9 can also be a structure in which only the resistors 92, 93 are provided, a structure in which two capacitors are connected in series, and furthermore, a structure in which the number of capacitors and resistors is increased.

[0108] As described above, the noise filter 50 of Embodiment 1 is a noise filter that reduces the common-mode voltage Vci generated by the power converter 2 that performs power conversion by the switching operation of the semiconductor elements Q1 to Q6. The noise filter 50 includes a voltage detector 7 that detects the common-mode voltage Vci generated by the power converter 2, a voltage dividing circuit 9 that outputs a divided voltage Vd obtained by dividing the common-mode voltage Vci detected by the voltage detector 7, a plurality of common-mode transformers 11a, 11b that superimpose an injection voltage Vs (Vsa, Vsb) having a polarity opposite to the common-mode voltage Vci on the output or input of the power converter 2, and an injection waveform generator 10 that generates an output voltage Vp output to the primary side of the plurality of common-mode transformers 11a, 11b in accordance with the divided voltage Vd. The injection waveform generator 10 generates the output voltage Vp in which the difference between the total injection voltage Vst obtained by adding the injection voltages Vs (Vsa, Vsb) superimposed by the plurality of common-mode transformers 11a, 11b and the common-mode voltage Vci becomes equal to or less than the allowable value Vt. According to this structure, the noise filter 50 of Embodiment 1 includes the plurality of common-mode transformers 11a, 11b, and the injection waveform generator 10 generates the output voltage Vp in which the difference between the total injection voltage Vst obtained by adding the injection voltages Vs (Vsa, Vsb) superimposed by the plurality of common-mode transformers 11a, 11b and the common-mode voltage Vci becomes equal to or less than the allowable value Vt, so even in the case where the switching frequency is low, a small common-mode transformer 11a, 11b can be used to suppress the common-mode voltage Vci.

[0109] Embodiment 2.

[0110] Figure 17 is a diagram showing the structure of the first noise filter and the motor drive system according to Embodiment 2. Figure 18 is a diagram showing Figure 17 is a diagram showing the first example of the first injection waveform generator of Figure 19 is a diagram showing​Figure 17 The first example of the second injected waveform generator is shown in the figure. Figure 20 It is shown Figure 17 The second example of the first injected waveform generator is shown in the figure. Figure 21 It is shown Figure 17 The second example of the second injected waveform generator is shown in the figure. Figure 22 It is shown Figure 17 The diagram shows the third example of the first injected waveform generator. Figure 23 It is shown Figure 17 The figure shows the third example of the second injected waveform generator. Figure 24 It is shown Figure 17 The fourth example of the first injected waveform generator is shown in the figure. Figure 25 It is shown Figure 17 The fourth example of the second injected waveform generator is shown in the figure. Figure 26 It is shown Figure 17 The fifth example of the first injected waveform generator is shown in the figure. Figure 27 It is shown Figure 17 The figure shows the fifth example of the second injected waveform generator. Figure 28 It is shown Figure 17 The sixth example of the first injected waveform generator is shown in the figure. Figure 29 It is shown Figure 17 The sixth example of the second injected waveform generator is shown in the figure. Figure 30 This is a diagram illustrating the structure of the second noise filter and the motor drive system according to Embodiment 2. Figure 31 This is a diagram showing the structure of the third noise filter and the motor drive system according to Embodiment 2.

[0111] Figure 17 The noise filter 50 of Embodiment 2 differs from the noise filter 50 of Embodiment 1 in that it outputs output voltages Vpa, Vpb, and Vpc to three common-mode transformers 11a, 11b, and 11c through two injection waveform generators 10a and 10b. The three common-mode transformers 11a, 11b, and 11c generate injection voltages Vsa, Vsb, and Vsc on each phase of the three-phase power line 5. Figure 18 The first example of the first injected waveform generator 10a shown is compared to Figure 4 The difference in the injected waveform generator 10 shown is that the bandwidth limiter 12 is changed to a bandwidth limiter 32 that allows the low-frequency bandwidth to pass through and reduces the high-frequency bandwidth, and has two output terminals 52a and 52b. Figure 19 The first example of the second injected waveform generator 10b shown is compared to Figure 4The difference of the illustrated injection waveform generator 10 is that the band limiter 12 is changed to a band limiter 33 that passes a high frequency band and reduces a low frequency band. The injection waveform generator 10a outputs an output voltage Vpa from an output terminal 52a and an output voltage Vpb from an output terminal 52b. The injection waveform generator 10b outputs an output voltage Vpc from an output terminal 52. Further, in Figure 18 , Figures 20-29 in the wiring 24 that becomes a ground potential is omitted. In Figure 20 in the wiring 24 that becomes a ground potential is omitted. Further, the noise filter 50 of Embodiment 2 can also be provided with an injection waveform generator having two waveform generators (the injection waveform generators 10a, 10b).

[0112] The part different from the noise filter 50 of Embodiment 1 is mainly described. The injection waveform generator 10a is set to amplify only a low frequency band and reduce a high frequency band. On the other hand, the injection waveform generator 10b is set to amplify only a high frequency band and reduce a low frequency band. That is, the injection waveform generator 10a outputs output voltages Vpa, Vpb of a low frequency band to the common mode transformers 11a, 11b, and the injection waveform generator 10b outputs an output voltage Vpc of a high frequency band to the common mode transformer 11c. The frequency band of the output voltages Vpa, Vpb is different from the output voltage Vpc. Thereby, a voltage of a low frequency band is applied to the common mode transformers 11a, 11b connected to the injection waveform generator 10a, and a voltage of a high frequency band is applied to the common mode transformer 11c connected to the injection waveform generator 10b. In addition, the output voltages Vpa, Vpb and the output voltage Vpc can also differ in voltage value according to the frequency band.

[0113] Generally, the higher the frequency band of the voltage applied to a transformer, the less the magnetic flux generated in the core due to the property of the core material. That is, the voltage time product in the transformer becomes small as the magnetic flux becomes less, so the cross-sectional area of the core required for the transformer becomes small. Therefore, the common mode transformer 11c to which a high frequency band is applied can be downsized compared to the common mode transformers 11a, 11b.

[0114] In addition, instead of reducing the cross-sectional area S of the core 28, the number of turns Nl, N2 of the common mode transformer 11c can also be reduced to downsize the common mode transformer 11c. In the case of reducing the number of turns Nl, N2, the inner diameter 1 required in the core 28 becomes small. In the case of making the cross-sectional area S of the core 28 constant, the outer diameter L can also be reduced when the inner diameter 1 is reduced, so as a result, the common mode transformer 11c can be downsized. These can also be performed simultaneously, and in the case of the voltage time product in the transformer being small, the number of turns Nl, N2 can be reduced and the outer diameter L and the inner diameter 1 of the core 28 can be reduced while reducing the cross-sectional area S of the core 28.

[0115] Generally, transformers are affected by self-resonance due to inductance and parasitic capacitance, resulting in decreased impedance and increased magnetizing current in high-frequency bands. This self-resonance frequency varies depending on the core material; therefore, by using a core material with a high self-resonance frequency and high impedance in the high-frequency band in the common-mode transformer 11c, which is subjected to voltages in the high-frequency band, the magnetizing current can be reduced. This, in turn, reduces the power supply capacity representing the amount of power supplied to the control power supplies 15a and 15b that supply power to the injected waveform generator 10b.

[0116] Thus, in this second embodiment, by setting the two injected waveform generators 10a and 10b to different structures and the three common-mode transformers 11a, 11b, and 11c to different structures, the applied voltage is separated into low-frequency and high-frequency bands, thereby enabling miniaturization of the common-mode transformer core and reduction of the power supply capacity of the control power supplies 15a and 15b. With the power supply capacity of the control power supplies 15a and 15b reduced, by increasing, for example, the gain Gi of amplifier 13, the output voltages Vpa, Vpb, and Vpc can be made the same as in the case where the power supply capacity of the control power supplies 15a and 15b is not reduced.

[0117] Figure 5 The second example of the first injected waveform generator 10a shown is compared to Figure 21 The difference in the injected waveform generator 10 shown is that the bandwidth limiter 12 is changed to a bandwidth limiter 32 that allows the low-frequency bandwidth to pass through and reduces the high-frequency bandwidth, and has two output terminals 52a and 52b. Figure 5 The second example of the second injected waveform generator 10b shown is compared to Figure 22 The difference in the injected waveform generator 10 shown is that the bandwidth limiter 12 is changed to a bandwidth limiter 33 that allows high-frequency bandwidth to pass and reduces low-frequency bandwidth. The injected waveform generator 10a outputs an output voltage Vpa from output terminal 52a and an output voltage Vpb from output terminal 52b. The injected waveform generator 10b outputs an output voltage Vpc from output terminal 52. Furthermore, the second example of the first injected waveform generator 10a differs from the first example in that a current buffer 14 is added between the output terminal of the amplifier 13 and the output terminals 52a and 52b. The second example of the second injected waveform generator 10b differs from the first example in that a current buffer 14 is added between the output terminal of the amplifier 13 and the output terminal 52. The second examples of the first injected waveform generator 10a and the second example of the second injected waveform generator 10b, through the current buffer 14, can increase the current capacity representing the current supply compared to the first examples of the injected waveform generators 10a and 10b.

[0118] Figure 18 The third example of the first injected waveform generator 10a shown is compared to Figure 23 The difference in the first example of the first injected waveform generator 10a shown is that there is no bandwidth limiter 32 on the input terminal 51 side, and bandwidth limiters 32a and 32b are respectively arranged between the output terminal of the amplifier 13 and the output terminals 52a and 52b. The frequency bands of bandwidth limiter 32a and bandwidth limiter 32b can be the same or different. When the frequency bands of bandwidth limiter 32a and bandwidth limiter 32b are different, output voltages Vpa and Vpb with different frequency bands can be output. Furthermore, the frequency bands of output voltages Vpa and Vpb are lower than the frequency bands of output voltage Vpc. Figure 19 The third example of the second injected waveform generator 10b shown is compared to Figure 24 The difference between the first example of the second injected waveform generator 10b shown is that there is no bandwidth limiter 33 on the input terminal 51 side, and a bandwidth limiter 33 is arranged between the output terminal and the output terminal 52 of the amplifier 13.

[0119] Figure 25 The fourth example of the first injected waveform generator 10a shown differs from the third example in that a current buffer 14 is added between the output terminal of the amplifier 13 and the input side of the bandwidth limiters 32a and 32b. Figure 24 The fourth example of the second injected waveform generator 10b shown differs from the third example in that a current buffer 14 is added between the output terminal of the amplifier 13 and the input side of the bandwidth limiter 33. The fourth example of both the first injected waveform generator 10a and the fourth example of the second injected waveform generator 10b are able to increase the current capacity representing the current supply compared to the third examples of the injected waveform generators 10a and 10b through the current buffer 14.

[0120] Figure 26 The fourth example of the first injected waveform generator 10a shown is an example in which a current buffer 14 is configured between the output terminal of the amplifier 13 and the input side of the band limiters 32a and 32b, but the current buffer 14 can also be configured between the output side of the band limiters 32a and 32b and the output terminals 52a and 52b. Figure 25The fifth example of the first injection waveform generator 10a shown differs from the third example of the first injection waveform generator 10a in that a current buffer 14a is added between the output side of the band limiter 32a and the output terminal 52a, and a current buffer 14b is added between the output side of the band limiter 32b and the output terminal 52b. The fifth example of the first injection waveform generator 10a is able to increase the current capacity, which indicates the current supply amount, by the current buffers 14a, 14b, as compared with the third example of the injection waveform generator 10a.

[0121] Likewise, Figure 27 The fourth example of the second injection waveform generator 10b shown is an example in which the current buffer 14 is disposed between the output terminal of the amplifier 13 and the input side of the band limiter 33, but the current buffer 14 can also be disposed between the output side of the band limiter 33 and the output terminal 52. Figure 28 The fifth example of the second injection waveform generator 10b shown differs from the third example of the second injection waveform generator 10b in that the current buffer 14 is added between the output side of the band limiter 33 and the output terminal 52. The fifth example of the second injection waveform generator 10b is able to increase the current capacity, which indicates the current supply amount, by the current buffer 14, as compared with the third example of the injection waveform generator 10b.

[0122] Figure 29 The sixth example of the first injection waveform generator 10a shown differs from the third example of the first injection waveform generator 10a in that the band limiter 32c is disposed between the input terminal 51 and the input side of the amplifier 13. Figure 17 The sixth example of the second injection waveform generator 10b shown differs from the third example of the second injection waveform generator 10b in that the band limiter 34 is disposed between the input terminal 51 and the input side of the amplifier 13. The frequency band of the band limiter 32c is likewise a lower frequency band than the band limiters 33, 34 in the second injection waveform generator 10b, as is the frequency band of the band limiters 32a, 32b. The frequency band of the band limiter 34 is likewise a higher frequency band than the band limiters 32a, 32b, 32c in the first injection waveform generator 10a, as is the frequency band of the band limiter 33.

[0123] The sixth example of the first injection waveform generator 10a has the band limiter 32c on the input side as well, so the band limiters 32a, 32b on the output side can be downsized. Thus, the sixth example of the first injection waveform generator 10a can reduce the total power consumption of the band limiters by the small band limiters 32a, 32b, 32c, as compared with the third example of the first injection waveform generator 10a having two band limiters 32a, 32b. The sixth example of the second injection waveform generator 10b has the band limiter 34 on the input side, so the band limiter 33 on the output side can be downsized. Thus, the sixth example of the second injection waveform generator 10b can reduce the total power consumption of the band limiters by the small band limiters 33, 34, as compared with the third example of the second injection waveform generator 10b having one band limiter 33.

[0124] In Figure 30 , the case where the injection waveform generators are two and the common-mode transformers are three is shown, but the number of each is not limited. For example, as shown in Figure 30 , the output voltages Vpa, Vpc can be output from the two injection waveform generators 10a, 10b to the two common-mode transformers 11a, 11c. Figure 1 The second noise filter 50 of Embodiment 2 shown in Figure 31 is different from the noise filter 50 of Embodiment 1 shown in

[0125] In addition, for example, as shown in Figure 22 , the output voltages Vpa, Vpc can be output from the one injection waveform generator 10a to the two common-mode transformers 11a, 11c. The injection waveform generator 10a in this case can be applied to the Figure 24 , Figure 26 , Figure 28 , ​ injection waveform generator 10a shown in

[0126] In addition, the case where the frequency bands of the injection waveform generators 10a, 10b are different, that is, the frequency characteristics are different, is shown, but even if the same gain and frequency characteristics are used, the noise filter 50 of Embodiment 2 can be configured. The noise filter 50 of Embodiment 2 in this case produces the same effect as the noise filter 50 of Embodiment 1, so the same effect as the noise filter 50 of Embodiment 1 is exerted. Furthermore, the injection waveform generators 10a, 10b can each have an amplifier 13 with a different gain, and output the output voltages Vpa, Vpc with different voltage values.

[0127] As for the common mode transformers 11a, 11b, 11c, cases where the core material, the outer diameter L, the inner diameter 1, the sectional area S, and the number of turns N1, N2 of the core 28 are different are shown, but even if the core material, the outer diameter L, the inner diameter 1, the sectional area S, and the number of turns N1, N2 of the core 28 are the same, the common mode transformers can be configured.

[0128] Further, an example in which the noise filter 50 of Embodiment 1 and Embodiment 2 is applied to a motor drive system 60 in which the power converter 2 that converts three-phase alternating-current power into three-phase alternating-current power via direct-current power is mounted is shown, but is not limited to this example. The noise filter 50 of Embodiment 1 and Embodiment 2 can also be applied to a system in which a power converter that generates a common mode voltage through switching operation of a semiconductor element is mounted. For example, the power converter 2 can also be an isolated DC-DC converter. In this case, the alternating-current power supply 1 becomes a direct-current power supply, and the induction motor 3 becomes a direct-current motor.

[0129] As described above, the noise filter 50 of Embodiment 2 is provided with the common mode transformer 11a to which the output voltage Vpa of the low frequency band is input and the common mode transformer 11c to which the output voltage Vpc of the high frequency band is input, so the common mode transformer 11c for the high frequency band can be downsized compared to the common mode transformer 11a for the low frequency band. Therefore, the noise filter 50 of Embodiment 2 can be downsized compared to the common mode transformer of Patent Document 1, and a small common mode transformer can be used to suppress the common mode voltage even in the case where the switching frequency is low. In addition, the noise filter 50 of Embodiment 2 is provided with a plurality of common mode transformers for the low frequency band that are larger than the common mode transformer 11c for the high frequency band, so the injection voltage Vsa, Vsb of each 1 is small as explained in Embodiment 1, and thus each common mode transformer 11a, 11b can be further downsized, and can be downsized compared to the common mode transformer of Patent Document 1.

[0130] Further, various exemplary embodiments and examples are described in the present application, but the various features, modes, and functions described in one or more embodiments are not limited to the application of a specific embodiment, and can be applied to an embodiment alone or in various combinations. Therefore, an infinite number of modifications that are not exemplified are assumed within the scope of the technology disclosed in the present application. For example, cases where at least one component is modified, cases where something is added or omitted, and further cases where at least one component is extracted and combined with a component of another embodiment are included.

Claims

1. A noise filter that reduces common-mode voltage generated by a power converter that performs power conversion through switching operation of a semiconductor element, wherein, The noise filter includes: a voltage detector that detects the common-mode voltage generated by the power converter; a voltage dividing circuit that outputs a divided voltage obtained by dividing the common-mode voltage detected by the voltage detector; a plurality of common-mode transformers connected in series that superimpose an injection voltage having a polarity opposite to the common-mode voltage on an output or an input of the power converter; and an injection waveform generator that generates an output voltage to be output to primary sides of the plurality of common-mode transformers connected in series based on the divided voltage, the injection waveform generator generates the output voltage in which a difference between a total injection voltage obtained by adding the injection voltages superimposed by the plurality of common-mode transformers connected in series and the common-mode voltage becomes equal to or smaller than an allowable value, the injection waveform generator includes a frequency band limiter that changes a frequency band of the divided voltage, and the frequency band limiter is configured to pass only a frequency band of interest.

2. The noise filter according to claim 1, wherein the injection waveform generator outputs the same output voltage to the primary sides of all the common-mode transformers.

3. The noise filter according to claim 1, wherein the injection waveform generator has a plurality of output terminals, and outputs different output voltages to the primary sides of the corresponding common-mode transformers from the respective output terminals.

4. The noise filter according to claim 1, wherein the injection waveform generator includes a plurality of waveform generators, the waveform generators each output different output voltages to the primary sides of the corresponding common-mode transformers.

5. The noise filter according to claim 3 or 4, wherein the different output voltages output by the injection waveform generator differ in voltage value.

6. The noise filter according to claim 3 or 4, wherein the different output voltages output by the injection waveform generator differ in frequency band.

7. The noise filter according to any one of claims 1 to 4, wherein the injection waveform generator includes an amplifier that amplifies the divided voltage, a gain of the amplifier is set in accordance with the number of the common-mode transformers and a turns ratio.

8. The noise filter according to claim 1, wherein the plurality of common-mode transformers include a first common-mode transformer and a second common-mode transformer, at least one of a core material, a cross-sectional area of a core, an outer diameter of a core, an inner diameter of a core, and a turns ratio is different between the first common-mode transformer and the second common-mode transformer.

9. The noise filter according to any one of claims 2 to 4, wherein the plurality of common-mode transformers include a first common-mode transformer and a second common-mode transformer, at least one of a core material, a cross-sectional area of a core, an outer diameter of a core, an inner diameter of a core, and a turns ratio is different between the first common-mode transformer and the second common-mode transformer.

10. The noise filter according to claim 8, wherein the injection waveform generator includes a first waveform generator and a second waveform generator, the first waveform generator outputs a first output voltage to the first common-mode transformer, the second waveform generator outputs a second output voltage to the second common-mode transformer. The second waveform generator outputs a second output voltage to the second common-mode transformer.

11. The noise filter according to claim 10, wherein The voltage value of the first output voltage is different from the voltage value of the second output voltage.

12. The noise filter according to claim 10 or 11, wherein The first waveform generator and the second waveform generator are provided with the frequency band limiter, The frequency band of the first output voltage is different from the frequency band of the second output voltage.

13. The noise filter according to claim 10 or 11, wherein The first waveform generator and the second waveform generator are provided with an amplifier that amplifies the divided voltage, The gain of the amplifier is set in accordance with the number and the turns ratio of the common-mode transformers.

14. The noise filter according to any one of claims 1 to 4, wherein The voltage detector detects the common-mode voltage generated by the power converter that outputs three-phase alternating current power, The common-mode transformer is provided with three windings on the secondary side.

Images