Active filter device and motor compressor provided with the same

Abstract

To provide an active filter device in which an attenuation characteristic of a common mode noise filter can be effectively improved without large increase of the volume and the weight.SOLUTION: An active filter device includes a detection unit 29 that detects a common mode voltage, an inverting amplifier circuit 37 that inverts and amplifies the common mode voltage detected by the detection unit 29, and Y capacitors 21, 22, and an output voltage from the inverting amplifier circuit 37 is applied as a compensation voltage to the Y capacitors 21, 22. An amplifier unit 32 of the inverting amplifier circuit 37 includes an operational amplifier 35, and a current amplifier 40, and an output impedance compensation circuit 56 is provided that compensates a voltage drop associated with an increase of the output impedance of the amplifier unit, according to a voltage difference between input and output of the current amplifier.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an active filter device for suppressing common mode noise, and to an electric compressor including the active filter device. [Background technology]

[0002] A passive common mode noise filter (passive filter) aimed at reducing common mode noise consists of a Y capacitor connected between a pair of power supply lines and a ground potential, and a common mode choke coil inserted in the pair of power supply lines (see, for example, Patent Document 1).

[0003] However, for example, in the case of an inverter device that drives the motor of an electric compressor, if a Y capacitor, which is a component, is used to improve the attenuation characteristics of a common mode noise filter using a passive method, the capacitance value is restricted from the safety standpoint due to an increase in leakage current, and it becomes necessary to use an unrealistic capacitance value. Also, even if a common mode choke coil is used, there is an issue of dimensional restrictions on the coil that can be implemented.

[0004] Therefore, various common mode noise filters that employ an active system have been developed (see, for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-78844 A [Patent Document 2] Patent No. 3044650 [Patent Document 3] Patent No. 5528543 Summary of the Invention [Problem to be solved by the invention]

[0006] However, all of the above documents require a common mode transformer for detecting and compensating for common mode noise, which results in an increase in the size of the active filter device, and therefore improvements have been desired.

[0007] The present invention has been made to solve the above-mentioned conventional technical problems, and has an object to provide an active filter device that can effectively improve the attenuation characteristics of a common mode noise filter without using a common mode transformer and without causing a significant increase in volume or weight compared to a passive type common mode noise filter, and an electric compressor equipped with the same. [Means for solving the problem]

[0008] The active filter device of the present invention comprises a common mode choke coil inserted between a pair of power supply lines, a detection unit that detects a common mode voltage, an inverting amplifier circuit that inverts and amplifies the common mode voltage detected by the detection unit, and Y capacitors connected between the output of the inverting amplifier circuit and the pair of power supply lines, and the amplification unit of the inverting amplifier circuit has an operational amplifier and a current amplifier provided at the output of the operational amplifier, and applies the output voltage of the inverting amplifier circuit to the Y capacitor as a compensation voltage, and is characterized in that it also comprises an output impedance compensation circuit that compensates for the voltage drop associated with an increase in the output impedance of the amplification unit in accordance with the voltage difference between the input and output of the current amplifier.

[0009] The active filter device of the invention of claim 2 is characterized in that in the above invention, the current amplifier is configured separately from the operational amplifier and is connected to the output of the operational amplifier, and the output of the current amplifier is applied to the Y capacitor as a compensation voltage.

[0010] The electric compressor according to the invention in claim 3 is characterized in that the active filter device according to the inventions above and an inverter device are integrally provided with a housing.

[0011] The electric compressor of the present invention according to claim 4 is characterized in that in the above-mentioned invention, the active filter device is configured on a board different from the board on which the inverter device is configured.

[0012] The electric compressor of the present invention according to claim 5 is characterized in that in the above-mentioned invention, the active filter device is shielded from the inverter device. Effect of the Invention

[0013] The active filter device of the present invention includes a common mode choke coil inserted between a pair of power supply lines, a detection unit that detects a common mode voltage, an inverting amplifier circuit that inverts and amplifies the common mode voltage detected by the detection unit, and Y capacitors connected between the output of the inverting amplifier circuit and the pair of power supply lines, and the output voltage of the inverting amplifier circuit is applied to the Y capacitor as a compensation voltage, so that the apparent capacitance value of the Y capacitor increases in accordance with the gain of the inverting amplifier circuit.

[0014] By increasing the apparent capacitance value of the Y capacitor in this way, it is possible to increase the return flow of noise current and reduce the common mode current leaking to the power supply, without using a large-capacity Y capacitor or a large common mode choke coil.

[0015] In addition, it can be applied to a normal passive noise filter consisting of a common mode choke coil and a Y capacitor to improve the attenuation characteristics of common mode noise, making it a very versatile product.

[0016] Furthermore, an output impedance compensation circuit is provided to compensate for the voltage drop that occurs with an increase in the output impedance of the amplifier section, so that it is possible to suppress the deterioration of attenuation characteristics in the high frequency range that occurs with an increase in the output impedance of the amplifier section.

[0017] Here, for example, if an output current detection resistor through which the output current of the amplifier section flows is provided and the voltage difference across the output current detection resistor is used to compensate for the voltage drop associated with an increase in the output impedance of the amplifier section, it is necessary to determine the resistance value of the output current detection resistor while taking into account element variations and temperature characteristics related to the output resistance of the amplifier section, and there is a risk that adverse effects will occur when setting the gain of the output impedance compensation circuit, particularly when the output current is large.

[0018] On the other hand, in the present invention, the amplification section of the inverting amplifier circuit is composed of an operational amplifier and a current amplifier provided at the output of this operational amplifier, and the output impedance compensation circuit compensates for the voltage drop associated with an increase in the output impedance of the amplification section in accordance with the voltage difference between the input and output of the current amplifier, so it is possible to directly read the voltage drop caused by the output impedance of the amplification section and compensate for the output impedance.

[0019] This makes it possible to appropriately set the gain of the output impedance compensation circuit and realize effective output impedance compensation without taking into consideration element variations, temperature characteristics, and the like related to the output resistance of the amplifier section.

[0020] In this case, as in the invention of claim 2, if the current amplifier is configured separately from the operational amplifier and connected to the output of the operational amplifier, and the output of the current amplifier is applied to the Y capacitor as a compensation voltage, it becomes possible to easily read the voltage difference between the input and output of the current amplifier.

[0021] The active filter device of each of the above-mentioned aspects of the invention is extremely suitable when it is integrally provided in the housing of the electric compressor together with the inverter device as in the third aspect of the invention.

[0022] In this case, by configuring the active filter device on a substrate different from that of the inverter device as in the invention of claim 4, it becomes possible to easily change the filter characteristics to any desired ones according to the specifications.

[0023] Furthermore, by shielding the active filter device from the inverter device as in the invention of claim 5, the influence of the noise source (inverter device) can be suppressed, and the intended noise attenuation effect can be achieved. [Brief description of the drawings]

[0024] [Figure 1] 1 is an electric circuit diagram of an electric compressor according to an embodiment to which an active filter device of the present invention is applied and a power supply path to the electric compressor. [Diagram 2] FIG. 2 is an electric circuit diagram of the electric compressor in FIG. [Diagram 3] 2 is a schematic cross-sectional view of an inverter accommodating portion of the electric compressor shown in FIG. 1. [Figure 4] 3 is an equivalent circuit diagram of the active filter device of FIG. 2. [Diagram 5] FIG. 11 is a diagram showing impedance characteristics of a Y capacitor for explaining the common-mode noise reduction effect of the active filter device of the present invention. [Figure 6] 1A to 1C are diagrams illustrating the common-mode noise reduction effect of the active filter device of the present invention. [Figure 7] 3 is an equivalent circuit diagram taking into consideration the component characteristics of an inverting amplifier circuit of the active filter compensation circuit of FIG. 2. [Figure 8] 8 is a diagram showing frequency characteristics of the open loop gain A and output impedance Zout of the operational amplifier of FIG. 7. [Figure 9] FIG. 3 is a diagram showing impedance characteristics of the Y capacitor of FIG. 2. [Figure 10] 2 is an equivalent circuit diagram of an amplifier and an output impedance compensation circuit of the active filter device of the present invention. [Figure 11] FIG. 11 is an electrical circuit diagram of the output impedance compensation circuit of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 shows an electric circuit diagram of an electric compressor 2 and a power supply path to the electric compressor 2 according to an embodiment of the present invention, in which an active filter device 1 of the present invention is applied, Fig. 2 shows an electric circuit diagram of the electric compressor 2, and Fig. 3 shows a schematic cross-sectional view of an inverter accommodating section 4 that accommodates an inverter device 3 of the electric compressor 2.

[0026] The electric compressor 2 of the embodiment constitutes a part of a refrigerant circuit of a vehicle air conditioner that is mounted on a vehicle such as an electric vehicle or a hybrid vehicle and conditions the interior of the vehicle, and an inverter device (PWM inverter) 3 and the active filter device 1 of the present invention are integrally provided with this electric compressor 2. That is, the electric compressor 2 of the embodiment is an inverter-integrated electric compressor.

[0027] The inverter device 3 converts DC voltage from a high voltage battery 7 (HV, for example, DC 350 V) mounted on the vehicle as a DC power source into AC voltage of a given frequency and supplies it to the motor 8 of the electric compressor 2 to operate it, and the active filter device 1 of the embodiment of the present invention is provided to reduce common mode noise generated in the inverter device 3.

[0028] (1) Power supply path for electric compressor 2 In Fig. 1, the inverter device 3 is composed of a plurality of switching elements (IGBTs, Fig. 3) 15 connected to a positive power supply line 11 and a negative power supply line 12 of a high-voltage battery 7. Reference numeral 20 in Fig. 1 denotes a control circuit, and each switching element 15 of the inverter device 3 is subjected to switching control (PWM control) by this control circuit 20. Reference numeral 13 denotes a smoothing capacitor connected between the pair of power supply lines 11, 12.

[0029] Reference numeral 14 denotes the vehicle's ECU, 16 a low-voltage battery (DC 12V), and the control circuit 20 controls the switching of each switching element 15 of the inverter device 3 using the low-voltage battery 16 as a power source based on a command from the ECU 14. Reference numeral 18 denotes a housing (made of aluminum die-cast) of the electric compressor 2. Furthermore, the electric compressor 2 is connected to the high-voltage battery 7 by a shielded HV harness 25 (which constitutes a pair of power supply lines 11, 12), and the housing 18 of the electric compressor 2 is directly fixed to the body of the vehicle. As a result, the housing 18 is at ground potential.

[0030] The active filter device 1 of the embodiment includes a pair of power supply lines 11 and 12 and a Y capacitor (C Y ) 21, 22, an active filter compensation circuit 23 connected between the Y capacitors 21, 22 and the housing 18 (ground potential), and common mode voltage detection capacitors 26, 27 (C sense ) which constitutes a detection unit 29 in the present invention, and a common mode choke coil (CMCC) 28 inserted in a pair of power supply lines 11, 12 on the high-voltage battery 7 side as viewed from the Y capacitors 21, 22, the active filter compensation circuit 23, and the common mode voltage detection capacitors 26, 27.

[0031] (2) Electric circuit of electric compressor 2 Next, Fig. 2 shows only the electric circuit of the electric compressor 2. In this figure, the same reference numerals as in Fig. 1 denote the same things. Insulating paper, refrigerant, and oil are present between the winding 8C of the motor 8 and the housing 18, and the stray capacitance between the winding 8C of the motor 8 and the housing 18 is shown as 31 in Fig. 2. A noise current flows through this stray capacitance 31, generating common mode noise.

[0032] 2 also shows details of the active filter compensation circuit 23 of the active filter device 1. The active filter compensation circuit 23 of the embodiment includes an amplifier 32, a negative feedback resistor (R f ) 33, and a power supply circuit (V CC , V EE ) 34, the above-mentioned common mode voltage detection capacitors 26 and 27, and the common mode voltage detection resistor (R insense )36.

[0033] The amplifier section 32 in the present invention is composed of the above-mentioned operational amplifier 35 and the above-mentioned current amplifier 40 provided at the output of this operational amplifier 35. The current amplifier 40 is a push-pull circuit made up of, for example, two transistors, and amplifies the output current of the operational amplifier 35 with a voltage gain of 1. In the embodiment, the current amplifier 40 is configured separately from the operational amplifier 35 and is connected to the output of the operational amplifier 35.

[0034] The amplifier section 32, negative feedback resistor 33, and common mode voltage detection resistor 36 constitute an inverting amplifier circuit 37 (gain G1 of operational amplifier 35) of the present invention. One ends of the common mode voltage detection capacitors 26, 27 are connected to the pair of power supply lines 11, 12, respectively, and the other ends of the common mode voltage detection capacitors 26, 27 are both connected to one end of a common mode voltage detection resistor 36. The other end of the common mode voltage detection resistor 36 is connected to the inverting input terminal (-) of the operational amplifier 35 of the amplifier section 32. The non-inverting input terminal (+) of the operational amplifier 35 of the amplifier section 32 is connected to a resistor 50 (R inref ) to the circuit ground 30. This ground path 38 serves as the ground path for the detection unit 29. It is assumed that the circuit ground 30 is connected to the housing 18, which is at the ground potential.

[0035] Meanwhile, one ends of the Y capacitors 21 and 22 described above are connected to a pair of power supply lines 11 and 12, respectively. The other ends of the Y capacitors 21 and 22 are both connected to the output terminal of a current amplifier 40 of the amplifier unit 32. A ground path 39 of the power supply circuit 34 of the amplifier unit 32 is connected to the housing 18 (ground potential). This ground path 39 is the ground path of the inverting amplifier circuit 37.

[0036] As a result, each Y capacitor 21, 22 is connected between the pair of power supply lines 11, 12 and the housing 18 (ground potential) via the amplifier section 32 of the active filter compensation circuit 23, and the output voltage of the current amplifier 40 of the amplifier section 32 that constitutes the inverting amplifier circuit 37 is applied to the Y capacitors 21, 22 as a compensation voltage.

[0037] 2, 56 is an output impedance compensation circuit of the present invention. The output impedance compensation circuit 56 includes a resistor 55 (R f ) in series with the output of the current amplifier 40 of the amplifier section 32, the operational amplifier 35 and a resistor 50 (R inref ) and the configuration and operation of this output impedance compensation circuit 56 will be described in detail later. This output impedance compensation circuit 56 is also included in the active filter compensation circuit 23 of the active filter device 1 of the present invention.

[0038] (3) Structure of the electric compressor 2 (inverter housing 4) Here, Fig. 3 shows a schematic cross-sectional view of the electric compressor 2. The motor 8 and the compression mechanism driven by the motor 8 are housed in an aluminum die-cast housing 18 shown in Fig. 3. In the embodiment, the high-voltage circuit 41 (Fig. 3) including the inverter device 3 and the smoothing capacitor 13, and the low-voltage circuit 42 (Fig. 3) including the control circuit 20 are provided on a control board 43 as shown in Fig. 3. On the other hand, the active filter device 1 including the active filter compensation circuit 23, the Y capacitors 21 and 22, and the common mode choke coil 28 is provided on an HV filter board 44 provided separately from the control board 43.

[0039] The control board 43 and HV filter board 44 are disposed in the inverter accommodating section 4 formed at one end of the housing 18 of the electric compressor 2, as shown in Fig. 3. In this case, the inside of the inverter accommodating section 4 is divided into a first accommodating chamber 4A and a second accommodating chamber 4B by a partition wall 46 formed in the housing 18, and the control board 43 is provided in the first accommodating chamber 4A, and the HV filter board 44 is provided in the second accommodating chamber 4B (Fig. 3). This results in the active filter device 1 being shielded from the high-voltage circuit 41 including the inverter device 3 and the like, and the low-voltage circuit 42 including the control circuit 20 and the like.

[0040] 3, reference numeral 47 denotes an HV connector for connecting the high-voltage battery 7 and the active filter device 1. Reference numeral 48 denotes a bus bar for wiring connections of the inverter device 3, the control circuit 20, and the active filter device 1, and has a structure molded from hard synthetic resin. The above-mentioned switching element 15 (IGBT) is disposed in the housing 18 so as to dissipate heat, and is connected to the inverter device 3 (high-voltage circuit 41) through the bus bar 48.

[0041] (4) Function (operation) of the active filter device 1 With the above configuration, the action (operation) of the active filter device 1 of this embodiment will be described with reference to Fig. 2 and Fig. 4 to Fig. 6. Note that in Fig. 4 to Fig. 6, the same reference numerals as in Fig. 1 to Fig. 3 denote the same components. Fig. 4 shows an equivalent circuit of the active filter device 1 (excluding the output impedance compensation circuit 56). Note that in an actual circuit, the Y capacitors 21 and 22 have a parasitic inductance 51 (L strayCy ) (FIG. 4). In FIG. 4, the amplifier section 32 consisting of the operational amplifier 35 and the current amplifier 40 is shown by one circuit symbol.

[0042] The common mode voltage (HV common mode voltage) appearing on the power supply lines 11 and 12 is v HVcom , the compensation voltage of the inverting amplifier circuit 37 is v compcom Since the input terminal of the inverting amplifier circuit 37 to which the common mode voltage detection resistor 36 is connected is a virtual ground, the common mode voltage (HV common mode voltage) v HVcom can be expressed by the following formula (I). insense is the resistance of the common-mode voltage detection resistor 36, C sense is the capacitance value of the common-mode voltage detection capacitors 26 and 27, and C sense (×2) means the combined capacitance value of these. G1 is the gain of the inverting amplifier circuit 37 (actually, the gain of the operational amplifier 35), and G1 = R f / R insense This R f is the resistance value of the negative feedback resistor 33.

[0043] Also, L strayCy is the inductance value of the parasitic inductance 51, and L strayCy (×1 / 2) means their combined inductance value. C Y is the capacitance of the Y capacitors 21 and 22, and C Y (×2) means the combined capacitance of these. Furthermore, I CY is the current flowing through the Y capacitors 21 and 22.

[0044]

number

[0045] From formula (I), the following formula (II) holds.

[0046]

number

[0047] The impedance of the Y capacitors 21 and 22 due to the compensation of the active filter compensation circuit 23 is Z Cy Then, the impedance Z Cy is expressed by the following formula (III).

[0048]

number

[0049] Using formulas (I) to (III), impedance Z Cy The combined capacitance value C of the common mode voltage detection capacitors 26 and 27 is sense (×2), resistance value R of common mode voltage detection resistor 36 insense , the combined capacitance value C of the Y capacitors 21 and 22 Y (×2), inductance value L of parasitic inductance 51 strayCy This is expressed as the following formula (IV).

[0050]

number

[0051] Here, in the high frequency region, the capacitance value C of the common mode voltage detection capacitors 26, 27 is set so that the impedance of the common mode voltage detection capacitors 26, 27 can be ignored compared to the impedance of the common mode voltage detection resistor 36. sense and the resistance value R of the common mode voltage detection resistor 36 insense By selecting the above, formula (IV) can be regarded as the following formula (V).

[0052]

number

[0053] This formula (V) means that it is equivalent to connecting a (1+G1)-fold Y capacitor. That is, the capacitance value of the Y capacitors 21 and 22 appears to be increased by (1+G1)-fold due to the compensation by the active filter compensation circuit 23. The inductance value of the parasitic inductance 51 is equivalently reduced (1 / (1+G1)).

[0054] As described above, the common mode voltage v detected by the detector 29 HVcom The output voltage of the inverting amplifier circuit 37 is converted to a compensation voltage v compcom is applied to the Y capacitors 21 and 22, the apparent capacitance values ​​of the Y capacitors 21 and 22 increase (by a factor of (1+G1)) in accordance with the gain G1 of the inverting amplifier circuit 37.

[0055] The dashed line in FIG. 5 indicates the impedance characteristic of the Y capacitor of a normal passive noise filter, and the solid line indicates the impedance characteristic of the Y capacitor of the active filter device 1 of the present invention. Cy is the impedance of the Y capacitor. As is clear from this figure, according to the active filter device 1 of the present invention, the capacitance value of the Y capacitor appears to increase, and the impedance Z Cy decreases according to the value of gain G1 more than in a conventional passive noise filter (Figure 5 shows the change in impedance when G1=3).

[0056] By increasing the apparent capacitance value of the Y capacitors 21 and 22, it is possible to increase the return flow of the noise current indicated by the dashed arrow in FIG. 2, reduce the common mode current leaking to the power supply, and reduce the common mode noise, without using a large-capacity Y capacitor or a large common mode choke coil.

[0057] 6, the black parts indicate the common mode noise level caused by a conventional passive noise filter, and the shaded parts indicate the common mode noise level caused by the active filter device 1 of the present invention. As is clear from this figure, the common mode noise level is lower in accordance with the reduction in the impedance of the Y capacitor than in a conventional passive noise filter.

[0058] In particular, by adding the active filter compensation circuit 23 to a normal passive type noise filter consisting of a common mode choke coil 28 and Y capacitors 21 and 22, the attenuation characteristics of common mode noise can be improved, making it highly versatile.

[0059] The active filter device 1 of the present invention is extremely suitable when it is provided integrally with the inverter device 3 in the housing 18 of the electric compressor 2 as in the embodiment.

[0060] In addition, in the embodiment, the active filter device 1 is configured with an HV filter board 44 that is different from the control board 43 on which the inverter device 3 is mounted, so that the filter characteristics can be easily changed to any desired characteristics according to the specifications. Furthermore, this HV filter board 44 (active filter device 1) is shielded by a partition wall 46 from the control board 43 on which the inverter device 3 is mounted, so that the influence of the noise source (inverter device 3) can be suppressed, and the intended noise attenuation effect can be achieved.

[0061] (5) Output impedance compensation circuit 56 Here, an equivalent circuit of the inverting amplifier circuit 37 of the active filter compensation circuit 23 constituting the active filter device 1 of each of the above-mentioned embodiments is shown in FIG. insense is the resistance value of the common mode voltage detection resistor 36 mentioned above, R f is the resistance of the negative feedback resistor 33, R o is the resistance value of the output resistance 54 of the current amplifier 40 constituting the amplifying section 32.

[0062] 8 shows the frequency characteristic of the open loop gain A of the amplifier 32 constituting the inverting amplifier circuit 37, and the lower part shows the output impedance Z out The frequency characteristic of the inverting amplifier circuit 37 is shown in FIG. out , output voltage V out Then, the output impedance Z of the amplifier 32 is out is expressed by the following formula (VI). Also, the feedback factor β is expressed by the following formula (VII), so from the relationship between the potential and current in FIG. out is represented by the following formula (VIII). + is the voltage at the non-inverting input terminal (+) of the operational amplifier 35 in the amplifier section 32, and V - is the voltage at the inverting input terminal (−) of the operational amplifier 35 in the amplifier section 32.

[0063]

number

[0064] In addition, the voltage V of the non-inverting input terminal (+) of the operational amplifier 35 of the amplifier unit 32 + and the voltage V of the inverting input terminal (-) - Since the difference between the output impedance and the output impedance is expressed by the following formula (IX), the formula (VIII) can be transformed into the following formulas (X) and (XI), and the output impedance Z out This finally results in equation (XII).

[0065]

number

[0066] From equation (XII), when the open loop gain A decreases, the output impedance Z out It can be seen that the output impedance Z out However, since the open loop gain A has a frequency characteristic as shown in the upper part of Figure 8, the feedback amount decreases as the frequency increases, and the output impedance Z outbecomes higher, and the noise attenuation characteristics deteriorate.

[0067] This situation is shown in Figure 9. In Figure 9, L1 is the frequency characteristic of the passive filter, and L2 is the frequency characteristic when an ideal active filter compensation circuit is applied. In Figure 9, the impedance of the Y capacitor in the case of active filter device 1 is lower than the impedance of the Y capacitor of the passive method up to the resonance point, which is the valley, due to the above-mentioned action, but once the resonance point is passed, the impedance increases, creating a region where the noise attenuation characteristics decrease.

[0068] That is, by using the active filter device 1 as in the above-mentioned embodiment, it is possible to reduce the impedance (common mode impedance) of the Y capacitor. On the other hand, since the inverting amplifier circuit 37 is used in the active filter compensation circuit 23, the output resistance 54 (R o ) may have an effect.

[0069] Therefore, in the present invention, the output impedance is compensated for by feeding back the voltage difference between the input and output of the current amplifier 40 of the active filter compensation circuit 23 using the output impedance compensation circuit 56.

[0070] 10 shows an equivalent circuit in the case where an output impedance compensation circuit 56 is added to an inverting amplifier circuit 37 using the amplifier unit 32. In the figure, the same reference numerals as in Figure 7 denote the same elements. G2 is the gain of another operational amplifier 57.

[0071] In the output impedance compensation circuit 56 of the embodiment, the operational amplifier 57 forms a differential amplifier, and the voltage difference between the input and output (the stage subsequent to the output resistance component 54) of the current amplifier 40 is input to the operational amplifier 57 (gain G2), and the output voltage of this operational amplifier 57 is added to the input voltage of the amplifier section 32.

[0072] 11 shows an actual electric circuit of this output impedance compensation circuit 56. The output impedance compensation circuit 56 is a differential amplifier consisting of an operational amplifier 57 and resistors R1 to R4, and the terminals T1 to T3 in the figure correspond to the terminals T1 to T3 in FIG.

[0073] In this case, the output current of the amplifier 32 is I, and the voltage of the previous stage of the current amplifier 40 of the amplifier 32 is V o , the output voltage of the active filter compensation circuit 23 is V out , input voltage V in Then, the output voltage V out and voltage V o is represented by the following formula (XIII).

[0074]

number

[0075] The voltage output by op-amp 57 is G2(V o -V out ), so the voltage V o can be expressed by the following formula (XIV).

[0076]

number

[0077] From formulas (XIII) and (XIV), V o After eliminating and rearranging, the output voltage V out This is expressed as the following formula (XV).

[0078]

number

[0079] By setting the output current I term in formula (XV) to 0, the output resistance 54 (R o) can be eliminated. As a result, the gain G2 of the operational amplifier 57 of the output impedance compensation circuit 56 can be obtained by the following formula (XVI). That is, the gain G2 of the output impedance compensation circuit 56 can be easily obtained as the reciprocal of the gain G1 of the amplifier unit 32 (operational amplifier 35) of the active filter compensation circuit 23.

[0080]

number

[0081] In this manner, the output impedance compensation circuit 56 is provided to compensate for the voltage drop associated with an increase in the output impedance of the amplifier section 32 constituting the inverting amplifier circuit 37 in accordance with the output current I of the amplifier section 32. This makes it possible to suppress the decrease in attenuation characteristics in the high frequency range associated with an increase in the output impedance of the amplifier section 32.

[0082] This state is also shown in Figure 9. L3 in Figure 9 shows the frequency characteristic of the impedance of the Y capacitor when the output impedance compensation circuit 56 of the present invention is provided and ideal output impedance compensation is in effect. As is clear from this figure, the impedance (L3) of the Y capacitor when the impedance compensation circuit 56 is provided is lower than the impedance (L1) of the Y capacitor in a normal passive filter over the entire frequency range.

[0083] Here, for example, if an output current detection resistor through which output current I of amplifier unit 32 flows is provided downstream of output resistance component 54 in FIG. 10, and the voltage difference before and after this output current detection resistor is input to operational amplifier 57, thereby attempting to compensate for the voltage drop associated with the increase in the output impedance of amplifier unit 32, then when setting gain G2 of operational amplifier 57 in output impedance compensation circuit 56, it is necessary to determine the resistance value of the output current detection resistor while taking into account element variations and temperature characteristics related to output resistance component 54 of amplifier unit 32; this can have a particular impact when output current I is large.

[0084] On the other hand, in the present invention, the amplifier section 32 of the inverting amplifier circuit 37 is composed of an operational amplifier 35 and a current amplifier 40 provided at the output of this operational amplifier 35, and the output impedance compensation circuit 56 compensates for the voltage drop associated with an increase in the output impedance of the amplifier section 32 in accordance with the voltage difference between the input and output of the current amplifier 40. This makes it possible to directly read the voltage drop caused by the output impedance of the amplifier section 32 and compensate for the output impedance.

[0085] This makes it possible to appropriately set the gain G2 of the operational amplifier 57 in the output impedance compensation circuit 56, without taking into consideration element variations and temperature characteristics, etc., related to the output resistance 54 of the amplifier section 32, thereby achieving effective output impedance compensation.

[0086] In this case, in the embodiment, the current amplifier 40 is configured separately from the operational amplifier 35 and is connected to the output of the operational amplifier 35. The output of the current amplifier 40 is applied to the Y capacitors 21 and 22 as a compensation voltage, so that the voltage difference between the input and output of the current amplifier 40 can be easily extracted and read.

[0087] In the embodiment, the active filter device 1 of the present invention is applied to the electric compressor 2 that constitutes the refrigerant circuit of a vehicle air conditioning system, but the invention of claims 1 and 2 is not limited to this, and the present invention is effective in various household / commercial appliances that require reduction of common mode noise. [Explanation of symbols]

[0088] 1. Active filter device 2 Electric compressor 3. Inverter device 4 Inverter housing 7 High voltage battery (DC power source) 8 Motor 11, 12 Power lines 15 Switching elements 18. Cabinet 20 Control circuit 21, 22 Y capacitor 23 Active filter compensation circuit 26, 27 Common mode voltage detection capacitor 28 Common mode choke coil 29 Detection unit 30 Circuit Ground 32 Amplification section 36 Common mode voltage detection resistor 35 Operational Amplifiers 37 Inverting amplifier circuit 40 Current Amplifier 43 Control Board 44 HV filter board 46 Partition Wall 56 Output impedance compensation circuit 57 Operational Amplifiers

Claims

1. A common mode choke coil inserted in a pair of power supply lines; A detection unit for detecting a common mode voltage; an inverting amplifier circuit that inverts and amplifies the common mode voltage detected by the detection unit; a Y capacitor connected between an output of the inverting amplifier circuit and the pair of power supply lines, The amplifier section of the inverting amplifier circuit has an operational amplifier and a current amplifier provided at the output of the operational amplifier, The output voltage of the inverting amplifier circuit is applied to the Y capacitor as a compensation voltage, an output impedance compensation circuit for compensating for a voltage drop caused by an increase in the output impedance of the amplifier section in response to a voltage difference between an input and an output of the current amplifier;

2. The current amplifier is configured separately from the operational amplifier and is connected to the output of the operational amplifier.

2. The active filter device according to claim 1, wherein an output of the current amplifier is applied to the Y capacitor as a compensation voltage.

3. 3. An electric compressor comprising: the active filter device according to claim 1 or 2; and an inverter device, which are integrally provided with a housing.

4. 4. The electric compressor according to claim 3, wherein the active filter device is configured on a substrate different from that of the inverter device.

5. 5. The electric compressor according to claim 4, wherein the active filter device is shielded from the inverter device.

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