Power conversion device and air-conditioning device

Abstract

[Problem] To provide a power conversion device having a reduced size. [Solution] This power conversion device has: a rectifier circuit that rectifies the AC power of a three-phase AC power supply; an inverse conversion circuit that modulates a voltage rectified by the rectifier circuit on the basis of a carrier frequency, inversely converts the voltage into a predetermined frequency, and applies the predetermined frequency to a motor; and a first capacitor that is provided between the rectifier circuit and the inverse conversion circuit and has a capacitance satisfying a predetermined condition. The coupling coefficients between the respective windings of a composite coil disposed between the three-phase AC power supply and the first capacitor and having a common mode inductance and a normal mode inductance are 0.85 or more and less than 1, and the carrier frequency is 17.7 kHz or more.

Description

Power conversion device and air conditioner

[0001] The present disclosure relates to a power conversion device and an air conditioner.

[0002] Patent Document 1 describes a power conversion device including a rectifier circuit, an inverter circuit, a capacitor, and a reactor. The rectifier circuit rectifies an AC power supply, and the inverter circuit inversely converts the voltage rectified by the rectifier circuit into an AC voltage of a predetermined frequency and applies it to a motor with a maximum power consumption of 2 kW or more.

[0003] Japanese Patent Application Laid-Open No. 2019-88090

[0004] In a power conversion device, it is necessary to remove common-mode noise and normal-mode noise. If a common-mode choke coil for removing common-mode noise and a normal-mode choke coil for removing normal-mode noise are provided as separate components, miniaturization of the power conversion device is hindered. The present disclosure aims to provide a miniaturized power conversion device and the like.

[0005] The power conversion device according to the first aspect includes a rectifier circuit that rectifies AC power of a three-phase AC power supply, an inverter circuit that modulates the voltage rectified by the rectifier circuit based on a carrier frequency fc ([Hz]), inversely converts it to a predetermined frequency, and applies it to a motor with a maximum power consumption Pmax ([W]) of 2 kW or more, a capacitor provided between the rectifier circuit and the inverter circuit, having a capacitance Cn ([F]) that satisfies Expressions (1) and (2) with respect to the AC voltage Vac ([V]) of the three-phase AC power supply and the maximum power consumption Pmax ([W]), a composite coil between the three-phase AC power supply and the capacitor, the carrier frequency being 17.7 kHz or more, the composite coil having a plurality of windings wound around a winding portion of a core, having a component of common-mode inductance having a function of a common-mode choke coil and a component of normal-mode inductance having a function of a normal-mode choke coil, and a coupling coefficient between windings of each phase of the composite coil being 0.85 or more and less than 1 and having a component of normal-mode inductance Ln ([H]) that satisfies Expression (3). However, K = 0.25. In this case, a miniaturized power converter can be provided. In the power converter according to the second aspect, the coil between the three-phase AC power supply and the capacitor is either the composite coil only, or a coil with multiple windings wound around a core and the composite coil only. In this case, by using a composite coil, a coil with only normal mode inductance between the power supply and the capacitor can be eliminated. In the power converter according to the third aspect, the (L-I) characteristic of the normal mode inductance of the composite coil is such that the value of the normal mode inductance corresponding to the value of the input current to the power converter when the overcurrent protection of the inverse converter circuit is activated is the value of the input current I1 ([A]) to the power converter, expressed by equation (4) when the power factor φ = 0.95 at the maximum power consumption. The value of the normal mode inductance is 90% or more of the corresponding value. In this case, even when a current twice the rated current flows through the composite coil, magnetic saturation does not occur and the normal mode inductance can be maintained. In the fourth aspect of the power converter, the windings of each phase of the composite coil are made of the same material and have the same wire diameter, and are wound on the winding part of the core, separated from each other. In this case, the coupling coefficient between the windings of each phase of the composite coil can be reduced. In the fifth aspect of the power converter, the capacitor is a film capacitor or a ceramic capacitor. In this case, a capacitor with excellent high-frequency characteristics can be provided. In the sixth aspect of the power converter, if the air-core inductance of one phase of the winding of the composite coil is La, the sum of the inductances of two phases of the normal mode inductance of the composite coil, Lb, is given by equation (5). Lb > 2 × La … (5) In this case, by using leakage flux, the normal mode inductance can be made higher than the air-core La. In the seventh aspect of the power converter, the motor is mounted on the compressor of an air conditioner. In this case, a smaller, lighter, and lower-cost air conditioner can be provided. The air conditioning system in the eighth aspect can be an air conditioning system equipped with a power converter. In this case, a smaller, lighter, and lower-cost air conditioner can be provided.

[0006] This diagram illustrates the circuit configuration of the power converter according to this embodiment. This diagram illustrates the generation of normal mode inductance. (A) is a diagram showing the noise terminal voltage between the composite coil 110 of this embodiment and a conventional CMC at an input current of 2.5 Arms. (B) is a diagram showing the noise terminal voltage between a conventional CMC and the composite coil of this embodiment at an input current of 29 Arms. (A) is a table showing the calculation conditions for inductance and coupling coefficient, (B) is a diagram showing the gain G of the common mode filter required for each carrier frequency calculated from the withstand voltage test results, and (C) is a diagram showing the change in the maximum value of normal mode inductance and the minimum value of common mode inductance according to the carrier frequency. This diagram shows the coupling coefficient and the volume of the power converter with respect to the carrier frequency. (A) is a perspective view of the composite coil according to this embodiment, and (B) is a diagram showing the winding method of the coil. (A) is a diagram illustrating the case where the composite coil is not directly connected to the printed circuit board, and (B) is a diagram illustrating the case where it is directly connected to the printed circuit board. This diagram shows an example of the circuit configuration of a power converter in which a second capacitor is arranged. (A) is a diagram showing an air-core coil, and (B) is a diagram illustrating leakage inductance. This is a diagram showing an example of the circuit configuration of a power conversion device for comparison.

[0007] The embodiments will be described in detail below with reference to the attached drawings.

[0008] <Comparison of Power Converter 11> First, the comparison of power converter 11 will be explained. Figure 10 is a diagram showing an example of the circuit configuration of the comparison of power converter 11. The power converter 11 comprises a rectifier circuit 620, a DC link section 640, and an inverse converter circuit 650. The power converter 11 converts the power supplied from a three-phase AC power supply 600 to a predetermined frequency and supplies it to a motor 660. Here, the motor 660 is a so-called DC motor. As an example, the motor 660 drives a compressor provided in the refrigerant circuit of an air conditioner.

[0009] The rectifier circuit 620 is connected to the AC power supply 600 via a common mode choke coil 610, which will be described later. The common mode choke coil is sometimes referred to as CMC. The rectifier circuit 620 rectifies the AC voltage output by the AC power supply 600 and converts it into a DC voltage, which is then output to the DC link section 640. The rectifier circuit 620 is composed of, for example, a diode bridge circuit. In the power conversion device 11, it is effective to place the common mode choke coil 610 between the AC power supply 600 and the rectifier circuit 620 to suppress common mode noise.

[0010] The DC link section 640 is the DC portion between the rectifier circuit 620 and the inverse conversion circuit 650. The DC link section 640 includes positive (+) wiring and negative (-) wiring. A capacitor 635 is provided between the positive (+) and negative (-) wiring of the DC link section 640. In the power converter 11, a reactor 630 is provided on the positive (+) wiring. The reactor 630 is provided between the rectifier circuit 620 and the inverse conversion circuit 650. In the power converter 11, providing the reactor 630 between the rectifier circuit 620 and the inverse conversion circuit 650 is effective in suppressing normal mode noise. The reactor 630 has an inductance L ([H]). The reactor 630 is also called a normal mode choke coil. Normal mode noise can be suppressed by the reactor 630.

[0011] Capacitor 635 is provided between the rectifier circuit 620 and the inverse converter circuit 650, and is connected in parallel with the rectifier circuit 620 and the inverse converter circuit 650. One end of capacitor 635 is connected to the positive output terminal of the rectifier circuit 620 via reactor 630, and the other end is connected to the negative output terminal of the rectifier circuit 620. The DC voltage generated across capacitor 635 is then applied to the input terminal of the inverse converter circuit 650. The input node of the inverse converter circuit 650 is connected in parallel with capacitor 635 of the DC link section 640.

[0012] This section provides a detailed explanation of the noise generated in power conversion circuits. The noise generated in power conversion circuits includes normal mode noise and common mode noise. Common mode noise is noise that returns to the power converter from the power conversion circuit, which is electrically connected to the power source via multiple power lines, through the capacitance between the power conversion circuit and the reference ground, and through the power source connected to the reference ground. The common mode choke coil 610 is a noise filter that suppresses common mode noise. The winding direction of each phase of the common mode choke coil 610 is the same. Therefore, the magnetic flux due to normal mode noise cancels out between phases. Normal mode noise is noise that returns to the power conversion circuit from one power line and the other power line, through the power source, from the power conversion circuit, which is electrically connected to the power source via multiple power lines. The reactor 630, also called a normal mode choke coil, suppresses normal mode noise.

[0013] Capacitor 635 suppresses noise such as switching noise generated by the inverse conversion circuit 650. Capacitor 635 forms an LC filter with the reactor and suppresses normal mode noise among the switching noise. As described above, the power converter 11 required the provision of a common mode choke coil 610 and a reactor 630. However, providing the common mode choke coil 610 and the reactor 630 as separate components hinders the miniaturization of the power converter. In particular, the reactor 630 is a component made by winding electric wire into a coil, and the need to secure space hinders the miniaturization of the power converter.

[0014] <Configuration of the power converter according to this embodiment> Figure 1 is a diagram showing an example of the circuit configuration of the power converter 1 according to this embodiment. The power converter 1 comprises a composite coil 110, a rectifier circuit 120, a DC link section 140, and an inverse conversion circuit 150. The difference between the circuit configuration of the power converter 1 and the circuit configuration of the power converter 11 (see Figure 10) is that the common mode choke coil 610 of the comparison device is replaced by the composite coil 110, and the reactor 630 of the DC link section 140 is absent. The power converter 1 converts the power supplied from the three-phase AC power supply 100 to a predetermined frequency and supplies it to the motor 160. Here, the motor 160 is a DC motor.

[0015] The AC power supply 100 supplies power to the power converter 1 via a harness or the like. Specifically, the AC power supply 100 is a so-called commercial three-phase AC power supply and supplies an AC voltage Vac ([V]) with a frequency such as 50 Hz or 60 Hz.

[0016] The composite coil 110 primarily functions as a common-mode choke coil, but its leakage flux becomes the inductance of the normal-mode component, allowing it to function as a normal-mode choke coil as well. As shown in the equivalent circuit of the composite coil 110 in Figure 1, the composite coil 110 combines the functions of both a common-mode choke coil 112 and a normal-mode choke coil 114. By giving the composite coil 110 the function of a normal-mode choke coil, the reactor 630, which is a normal-mode choke coil in the power converter 11, can be eliminated. Therefore, the space occupied by the conventional reactor 630 can be reduced, allowing the power converter to be miniaturized.

[0017] The composite coil 110 adds the function of a normal mode choke coil by adjusting the coupling coefficient of the common mode choke coil to increase the leakage flux. The physical configuration of the composite coil 110 will be described later.

[0018] The rectifier circuit 120 is connected to the AC power supply 100 via a composite coil 110 and converts the AC voltage Vac ([V]) output by the AC power supply 100 into a DC link voltage Vdc ([V]). The rectifier circuit 120 is composed of, for example, a diode bridge circuit. The diode bridge circuit is composed of a diode bridge circuit in which six diodes (D1 to D6), not shown, are connected in a bridge configuration. The rectifier circuit 120 rectifies the AC voltage Vac output from the AC power supply 100 and outputs it to the DC link section 140.

[0019] The DC link section 140 is provided between the rectifier circuit 120 and the inverter circuit 150 and is constructed using a capacitor 130. The capacitor 130 is connected in parallel with the rectifier circuit 120 and the inverter circuit 150. One end of the capacitor 130 is connected to the positive output terminal of the rectifier circuit 120, and the other end is connected to the negative output terminal of the rectifier circuit 120. The DC voltage generated across the capacitor 130 (hereinafter also referred to as the DC link voltage Vdc ([V])) is then applied to the input terminal of the inverter circuit 150. The inverter circuit 150 may be, for example, the inverter of a compressor.

[0020] When AC is rectified by the rectifier circuit 120, it becomes a pulsating current where the voltage fluctuates due to the AC voltage Vac ([V]). Capacitor 130 does not have the function of smoothing the pulsation of the waveform of the voltage rectified by the rectifier circuit 120. On the other hand, capacitor 130 has the function of smoothing the normal mode noise among the switching noise from the inverter circuit 150. This reduces the capacitance of capacitor 130. Furthermore, by controlling the switching of the inverter circuit 150, it is possible to improve the power factor, etc.

[0021] The statement above that "it does not have the function of smoothing the pulsation of the waveform of the voltage rectified by the rectifier circuit 120" means that when the motor is driven at its rated output, more than 80% of the pulsation component contained in the waveform of the rectified AC voltage remains across the capacitor. Since the capacitor 130 does not have the function of smoothing the pulsation of the waveform of the voltage rectified by the rectifier circuit 120, a small capacitance capacitor can be used for the capacitor 130. However, because the capacitance C ([F]) of the capacitor 130 is small, the DC link voltage Vdc ([V]) of the DC link section 140 pulsates. For example, when the AC power supply 100 is a three-phase AC power supply, the DC link voltage Vdc ([V]) pulsates at a frequency six times that of the power supply frequency. Such a capacitor 130 can be realized by a capacitor other than an electrolytic capacitor, such as a film capacitor or a ceramic capacitor.

[0022] The inventors investigated the optimization of the capacitance C ([F]) of the capacitor 130 and obtained the following findings. First, for a three-phase AC motor with a maximum power consumption Pmax ([W]) of 2 kW or more, it was found that by adopting a capacitance Cn ([F]) of the capacitor 130 that satisfies the conditions of equation (1), the fifth and seventh harmonics from the rectifier circuit 120 can be reduced.

[0023]

[0024] Furthermore, the inventors have found that by adopting a capacitor 130 with a capacitance C ([F]) that satisfies the conditions of equation (2), the function of smoothing the normal mode noise among the switching noise from the inverse conversion circuit 150 can be maintained even if the capacitance C ([F]) of the capacitor 130 is reduced. Moreover, they have found that with such a capacitor 130, the normal mode choke coil can be miniaturized.

[0025]

[0026] The inverse conversion circuit 150, based on the input of the gate control signal, inversely converts the DC link voltage Vdc rectified by the rectifier circuit 120 into an AC voltage of a predetermined frequency and applies it to the motor 160. The input node of the inverse conversion circuit 150 is connected in parallel to the capacitor 130 of the DC link section 140. The inverse conversion circuit 150 switches the output of the DC link section 140 to convert it into three-phase AC.

[0027] The inverse conversion circuit 150 is equipped with six switching elements SW1 to SW6 (not shown) to output three-phase AC to the motor 160. The inverse conversion circuit 150 switches the DC link voltage Vdc input from the DC link section 140 by switching these switching elements SW1 to SW6 on and off, converting it into a three-phase AC voltage and supplying it to the motor 160. Each of the switching elements SW1 to SW6 is implemented, for example, by an insulated-gate bipolar transistor (IGBT).

[0028] The on / off operation of the switching elements in the inverse converter circuit 150 is controlled by a control circuit (not shown). The control circuit drives the motor 160 by controlling the on / off operation of each switching element. In this case, the control circuit outputs gate control signals that turn each switching element of the inverse converter circuit 150 on or off so that the currents of each phase (U phase, V phase, W phase) flowing through the motor 160 pulsate in synchronization with the pulsation of the DC link voltage Vdc. The control circuit generates the gate control signals using a carrier with a carrier frequency fc ([Hz]).

[0029] Furthermore, in the above embodiment, the values ​​of the inductance Ln ([H]) of the normal mode component of the composite coil 110 and the capacitance Cn ([F]) of the capacitor 130 may be set to satisfy the condition of the following equation (3). Through the inventors' studies, it has been found that when this condition is satisfied, the normal mode noise among the switching noise generated by the inverse conversion circuit 150 can be suppressed. Note that fc ([Hz]) is the carrier frequency, and the value of the constant K is 0.25.

[0030]

[0031] The inverse transformer circuit 150 of this embodiment can suppress harmonics through waveform control, and therefore inherently has the function of miniaturizing the reactor. Miniaturization of the reactor is possible by increasing the carrier frequency. On the other hand, increasing the carrier frequency of a common mode choke coil worsens common mode noise, so the common mode choke coil itself needs to be made larger. As the frequency increases, the reactor tends to become smaller, while the common mode choke coil tends to become larger. Miniaturizing the reactor allows it to be mounted on a circuit board. Furthermore, by using the composite coil of this embodiment, the inductance of the normal mode component can be used, making it possible to replace the reactor.

[0032] In the circuit configuration of Figure 1, the composite coil 110 was placed between the AC power supply 100 and the rectifier circuit 120. The composite coil 110 may also be placed between the rectifier circuit 120 and the capacitor 130. Furthermore, in the circuit configuration of Figure 1, the composite coil 110 is the only coil present between the three-phase AC power supply 100 and the capacitor 130. In addition to the composite coil 110, a detection coil acting as a CT (Current Transfer) with multiple windings wound around a core may also be present between the three-phase AC power supply 100 and the capacitor 130. Therefore, in the circuit configuration of the power converter 1 of this embodiment, the only coil present between the three-phase AC power supply 100 and the capacitor 130 is either the composite coil 110 only, or a coil with multiple windings wound around a core and the composite coil 110 only. When winding the wires around the core, a case such as a bobbin may be used.

[0033] The composite coil 110 is equipped with the function of a normal mode choke coil by adjusting the coupling coefficient of the common mode choke coil to increase the leakage flux. Generally, a mutual induction circuit in which two windings are formed on a single annular core is a magnetically coupled circuit in which the magnetic flux of the primary winding links with the secondary winding. The coupling coefficient k, which is the degree of magnetic coupling between the primary and secondary windings, is defined by equation (6).

[0034]

[0035] M represents the mutual inductance (inductance due to magnetic flux passing through both the primary and secondary sides). L1 is the inductance due to magnetic flux passing through the primary side, and consists of the sum of the inductance due to magnetic flux passing through both the primary and secondary sides and the inductance due to magnetic flux passing through only the primary side. L2 is the inductance due to magnetic flux passing through the secondary side, and consists of the sum of the inductance due to magnetic flux passing through both the primary and secondary sides and the inductance due to magnetic flux passing through only the secondary side.

[0036] The composite coil 110 is set so that the leakage inductance of two phases during operation equals the inductance Ln required in normal mode. Therefore, the inductance of the normal mode component required for one phase is Ln / 2. Thus, substituting L1 = L2 = Lc + Ln / 2 and M = Lc into equation (6), the coupling coefficient is expressed by equation (7).

[0037]

[0038] When there is no magnetic flux leakage (leakage flux = 0), the leakage inductance Ln is 0 (Ln = 0), and the coupling coefficient k is 1. The composite coil 110 is set up so that leakage flux is formed (Ln > 0), and the coupling coefficient becomes less than 1. Typical common-mode choke coils are designed to have a large coupling coefficient k and small leakage flux. In typical common-mode choke coils, the leakage inductance component is about 0.2% of the common-mode inductance value.

[0039] In contrast, the composite coil 110 intentionally reduces the coupling coefficient k and utilizes the inductance due to leakage flux as a substitute for the reactor. In the composite coil 110, about 1% of the common-mode inductance value becomes the leakage inductance component, which is used as the reactor. In order to reduce the coupling coefficient k, the core needs to be made larger. On the other hand, reducing the coupling coefficient lowers the value of the common-mode inductance Lc, but in order to secure the same common-mode inductance as a conventional common-mode choke coil, additional windings of the coil are necessary. For this reason, the composite coil 110 will be somewhat larger in order to achieve the same common-mode inductance as a conventional common-mode choke coil. In particular, in high-current applications, the composite coil becomes large, which may pose a challenge for board mounting. As will be described later, the normal-mode inductance value can be reduced by increasing the carrier frequency of the inverse conversion circuit 150. In order to balance this with meeting the requirement for miniaturization of components, it is best to set the leakage flux of the composite coil 110 to about 1%.

[0040] Conventionally, two coils with different purposes, a common-mode choke coil and a normal-mode choke coil, existed within the power converter. However, a composite coil can achieve both the functions of a conventional common-mode choke coil and a normal-mode choke coil. Therefore, even if the composite coil 110 is slightly larger to achieve the same common-mode inductance as a conventional common-mode choke coil, the power converter 1 as a whole can be made smaller because it can be made reactor-less.

[0041] FIG. 2 is a diagram for explaining the generation of normal-mode inductance. When a normal-mode current is passed through two-phase coils out of three-phase coils and the remaining one-phase coil is de-energized, in the case of a conventional common-mode choke coil, the magnetic fluxes cancel each other out and the normal-mode inductance becomes zero. In the case of the composite coil, leakage magnetic fluxes form a magnetic path and normal-mode inductance is generated. The graph in FIG. 2 shows the value of the minute normal-mode inductance generated by the magnetic path of the leakage magnetic fluxes in the case of a coil in which the three-phase windings N1, N2, and N3 are arranged side by side in a row on the core. Note that N2 has a larger value than the other N1 and N3 because N2 is arranged in the center among the three-phase windings and N2 is affected by the windings on both sides.

[0042] FIG. 3(A) is a diagram showing the noise terminal voltages when the composite coil 110 of the present embodiment is used and when a conventional CMC is used at an input current of 2.5 Arms. The horizontal axis is the frequency (MHz), and the vertical axis is the noise terminal voltage. Waveform W1 is the noise terminal voltage when the composite coil 110 is used, and waveform W2 is the noise terminal voltage when a conventional CMC is used. When comparing waveform W1 and waveform W2 of the noise terminal voltage, they almost coincide at frequencies of 150 kHz or higher. Therefore, it can be confirmed that the composite coil 110 has the same performance as the conventional CMC at frequencies of 150 kHz or higher. FIG. 3(B) is a diagram showing the noise terminal voltages when a conventional CMC is used and when the composite coil of the present embodiment is used in the case of an input current of 29 Arms. When comparing waveform W3 of the noise terminal voltage when the composite coil is used and waveform W4 of the noise terminal voltage when a conventional CMC is used, it can be confirmed that the composite coil has the same performance as the conventional CMC with respect to frequencies of 150 kHz or higher. From FIGS. 3(A) and 3(B), it can be confirmed that the composite coil has the same performance as the conventional CMC at frequencies of 150 kHz or higher, even when the input current is as small as 2.5 Arms or as large as 29 Arms.

[0043] Next, the calculation of the normal mode inductance Ln and the common mode inductance Lc of the composite coil will be described. The normal mode inductance Ln is first determined from the maximum power consumption Pmax and the AC voltage Vac to obtain the capacitor capacitance Cn in the normal mode, and is determined from the obtained capacitor capacitance Cn and the carrier frequency fc. Specifically, the capacitor capacitance Cn is determined from the above-mentioned equations (1) and (2), and the normal mode inductance Ln is determined from the above-mentioned equation (3).

[0044] The common mode inductance Lc is first determined from the test voltage Vt, the frequency f, and the standard value I of the leakage current during the withstand voltage test to obtain the capacitor capacitance Cc in the common mode, and is determined from the obtained capacitor capacitance Cc, the gain G of the filter, and the filter frequency ff. The withstand voltage test is a constraint condition that must be satisfied according to the standard. The test voltage is applied in a state where the power supply voltage is not applied, and it is required that the flowing current be below the standard value. Specifically, first, the capacitor capacitance Cc is determined from the equation (8) for calculating the leakage current flowing during the withstand voltage test.

[0045] Next, the common mode inductance Lc is determined from the equation (9) for the gain of the common mode filter.

[0046] Once the normal mode inductances Ln and Lc of the above-mentioned composite coil are calculated, the coupling coefficient k is calculated by Equation (7). Figure 4(A) is a table showing the parameters that are the calculation conditions for performing the above-mentioned calculation. Here, as parameters related to the normal mode equation, Pmax is the maximum power consumption of the motor, Vac is the AC voltage of the AC power supply 100, Cn is the capacitance of the normal mode capacitor, and K is a dimensionless constant. As parameters related to the common mode equation, I is the standard value during the withstand voltage test, Vt is the test condition voltage of the withstand voltage test, f is the frequency of the applied voltage during the withstand voltage test, Cc is the capacitance of the common mode filter (second capacitor), ff is the frequency at which the gain of the common mode filter is designed (the limit value is defined by the standard for 150 kHz or higher), and G is the gain of the common mode filter.

[0047] Figure 4(B) shows the common-mode filter gain G required for each carrier frequency, calculated from the withstand voltage test results. From Figure 4(B), it can be seen that the common-mode filter gain G decreases rapidly when the carrier frequency exceeds 17.7 kHz. The presence of an inflection point around 17.7 kHz affects the common-mode inductance Lc to increase rapidly in the carrier frequency range above 17.7 kHz.

[0048] Figure 4(C) shows the changes in the maximum normal mode inductance and the minimum common mode inductance as the carrier frequency fc changes. The maximum normal mode inductance and the minimum common mode inductance are determined in order to find the minimum coupling coefficient.

[0049] In Figure 4(C), the left vertical axis represents normal mode inductance, the right vertical axis represents common mode inductance, and the horizontal axis represents carrier frequency fc (kHz). The maximum value of normal mode inductance Ln decreases as the carrier frequency fc increases (see equation (3)). In the region where the carrier frequency fc is less than 17.7 kHz, the normal mode inductance Ln is large, but in the region where the carrier frequency fc is 17.7 kHz or higher, the maximum value of normal mode inductance Ln remains small, less than 100 μH. On the other hand, as the carrier frequency fc increases, the minimum value of the required common mode inductance Lc tends to increase. There is an inflection point around the carrier frequency of 17.7 kHz. In the region where the carrier frequency is greater than 17.7 kHz, the minimum value of the common mode inductance increases sharply from 4 mH.

[0050] Under the assumption that the constraints of equations (1), (2), and (3) related to normal mode inductance Ln, and equations (8) and (9) related to common mode inductance Lc, and equation (7) for the coupling coefficient k are satisfied, the relationship between the coupling coefficient k and the carrier frequency fc was determined. Figure 5 shows the relationship between the coupling coefficient and the volume of the power converter with respect to the carrier frequency fc. The horizontal axis is the carrier frequency fc (kHz), the left vertical axis is the coupling coefficient k, and the right vertical axis is the volume. Note that the volume shows the estimated trend, with the upper side being larger and the lower side being smaller. Focusing on the change in the coupling coefficient k, at a carrier frequency fc of 5.9 kHz, the coupling coefficient k is approximately 0.02, and at a carrier frequency of 11.8 kHz, the coupling coefficient k is approximately 0.09. When the carrier frequency reaches 17.7 kHz, the coupling coefficient k increases sharply to 0.85. Thereafter, as the carrier frequency increases, the coupling coefficient k asymptotically approaches 1.

[0051] Next, we consider the change in volume of the power converter 1 as the carrier frequency fc increases. In the region where the carrier frequency fc is less than 17.7 kHz, the smaller the carrier frequency fc, the smaller the coupling coefficient, so the volume of the composite coil increases, and the power converter becomes larger. Also, in the region where the carrier frequency is greater than 17.7 kHz, the volume gradually increases. As the carrier frequency increases, the required common-mode inductance increases, so the composite coil becomes larger. From the above trends, it can be seen that in the region where the carrier frequency is 17.7 kHz or higher and the coupling coefficient is 0.85 or higher, the composite coil can be miniaturized, and therefore the power converter can also be miniaturized.

[0052] Here, we will explain the characteristics of the normal mode inductance of the composite coil. Generally, the inductance of a coil decreases as the current value increases. In a composite coil, the degree of decrease in inductance with respect to current is less than that of a typical coil. This rate of decrease in inductance is clearly expressed as the difference in the ratio of inductance under two conditions: when the coil has its maximum input current and when the overcurrent protection of the inverse converter circuit is activated. The rated current of the coil is greater than the maximum input current of the coil, and the input current when the overcurrent protection is activated is greater than the rated current of the coil. Therefore, the inductance when the overcurrent protection is activated is smaller than the inductance when the maximum input current is activated. In a typical coil, the ratio of the inductance when the overcurrent protection is activated to the inductance when the maximum input current is activated is a small value of less than 90%, whereas in the composite coil 110 of this embodiment, it is 90% or more.

[0053] To add a more quantitative explanation, for a three-phase AC power supply with AC voltage Vac (effective voltage) and maximum power consumption Pmax, the maximum input current I1 from the three-phase AC power supply when the power factor φ = 0.95 is expressed by equation (4). Let LCA be the inductance with respect to the maximum input current I1. When overcurrent protection is activated, the input current is overcurrent for a period shorter than one cycle. Therefore, if I2 is the effective value of the sinusoidal current that corresponds to the peak value of the input current when overcurrent protection is activated, then LCB is the inductance with respect to I2. In this case, for the composite coil 110, LCB / LCA is 0.9 or more.

[0054] As described above, the (L-I) characteristic of the normal mode inductance of the composite coil 110 is such that the value of the normal mode inductance corresponding to the input current I2 to the power converter when the overcurrent protection of the inverse converter circuit is activated is 90% or more of the value of the normal mode inductance corresponding to the input current I1 to the power converter, which is expressed by equation (4) when the power factor φ = 0.95 at the maximum power consumption.

[0055] If the normal-mode inductance of the reactor 630 in the power converter 11 in Figure 10 is reduced, the coil will become magnetically saturated when a lightning surge is applied, and the surge energy will flow directly into the inverter circuit 150. When a magnetic material such as a reactor is used, a large current flows when a lightning surge is applied, causing magnetic saturation and making it impossible to maintain the inductance. When the inductance is gone, there is no impedance from the power source to the inverter circuit, so all the energy of the lightning surge is transmitted to the inverter. However, when leakage flux is used, the magnetic flux passes through the air, so magnetic saturation does not occur, and the inductance can be maintained. In the power converter 1 according to this embodiment in Figure 1, the inductance generated by the leakage flux is used as the normal-mode component inductance, so the inductance value is maintained even when the current is larger than the maximum operating current, and the effect as inductance is maintained even when a lightning surge flows in. As described above, if a composite coil is used, the inductance generated by the leakage flux can be used as the normal-mode component inductance, so a power converter that is resistant to large currents when a lightning surge is applied can be provided.

[0056] Figure 6(A) is a perspective view of a composite coil according to this embodiment. Figure 6(B) is a diagram showing the coil winding method. In the composite coil of Figure 6(A), three phase coils are wound around a core material. All three phase windings use the same material and wire diameter. By using the same material and wire diameter for the windings, it becomes easier to adjust the inductance and set the coupling coefficient.

[0057] Furthermore, regarding winding methods, Figure 6(B) shows the winding methods for two phases, with cross-sections where the direction of the diagonal lines is different. From left to right in Figure 6(B), there are overlapping winding, separation method (also called split winding or section winding), bifilar winding, and sandwich winding. In the separation method, the windings of different phases are separated from each other and do not overlap. In the separation method, the windings are separated from each other and wound around the winding section of the core. Winding methods other than the separation method tend to have a large coupling coefficient. In the separation method, the distance between the windings of different phases is large and there is no overlap, so the coupling coefficient is small. For this reason, the composite coil according to this embodiment employs a winding method using the separation method.

[0058] Next, a method for mounting the composite coil on a circuit board will be described. Figure 7(A) illustrates the case where the composite coil is not directly connected to the printed circuit board, and Figure 7(B) illustrates the case where it is directly connected to the printed circuit board. Because the composite coil according to this embodiment is miniaturized, it can be mounted on a printed circuit board. If the composite coil is large, it cannot be mounted on the printed circuit board, as shown in Figure 7(A). The composite coil according to this embodiment can be directly installed on the printed circuit board using vias 72 (left figure) and tab terminals 74 (right figure) provided on the printed circuit board, as shown in Figure 7(B). Therefore, because it can be mounted on a printed circuit board, the power conversion device can be miniaturized.

[0059] (Second Embodiment) Figure 8 shows an example of a circuit configuration of a power converter in which a second capacitor is arranged. The power converter in Figure 8 has a circuit configuration in which a second capacitor is provided before and after each phase of the composite coil 110, with one end connected to the composite coil and the other end grounded. In this case, the second capacitor may also be grounded via a third capacitor (not shown). The presence of a common-mode capacitor (second capacitor) as a common-mode filter has the effect of preventing common-mode noise from flowing out to the power supply side.

[0060] The power conversion device of this disclosure uses a capacitor other than an electrolytic capacitor. For example, the capacitor is a film capacitor or a ceramic capacitor. Film capacitors and ceramic capacitors have excellent high-frequency characteristics, which can extend the lifespan and increase the reliability of the power conversion device.

[0061] (Normal Mode Inductance of Composite Coils) Here, the values ​​of the normal mode inductance of the composite coils of the first and second embodiments will be explained. Figure 9(A) is a diagram of an air-core coil. Figure 9(B) is a diagram illustrating leakage inductance. Figure 9(A) is a conceptual diagram of inductance assuming that the composite coil is air-core. Figure 9(B) is a conceptual diagram showing that when nanocrystals are used as the magnetic material for the core of the composite coil, the magnetic flux passes through the air and the magnetic material. If the inductance of one phase of the winding when it is air-core is La, and the sum of the inductances of the two phases of the normal mode inductance is Lb, then the following equation (5) holds: Lb > 2 × La …(5) Equation (5) shows that the normal mode inductance can be made larger by creating the inductance with leakage inductance than by creating the inductance with air core.

[0062] The power conversion device according to this embodiment is used, for example, in an air conditioner. The motor of the air conditioner's compressor is, for example, provided to drive the compressor located in the air conditioner's refrigerant circuit. By installing the power conversion device according to this embodiment in an air conditioner, it is possible to achieve miniaturization, weight reduction, and cost reduction of the air conditioner.

[0063] <Effects> The power conversion device 1 of the present disclosure includes a rectifier circuit 120 that rectifies the AC power of a three-phase AC power supply 100, an inverse conversion circuit 150 that modulates the voltage rectified by the rectifier circuit 120 based on the carrier frequency fc, inversely converts it to a predetermined frequency, and applies it to a motor 160 having a maximum power consumption Pmax of 2kW or more, a capacitor 130 provided between the rectifier circuit 120 and the inverse conversion circuit 150, the capacitance Cn of which satisfies equations (1) and (2) with respect to the AC voltage Vac of the three-phase AC power supply 100 and the maximum power consumption Pmax, and the three-phase AC power supply 100 A composite coil 110 is provided between the capacitor 130 and the carrier frequency is 17.7 kHz or higher. The composite coil 110 has multiple windings wound around the core winding portion and has a common mode inductance component that functions as a common mode choke coil and a normal mode inductance component that functions as a normal mode choke coil. The coupling coefficient between the windings of each phase of the composite coil 110 is 0.85 or more and less than 1, and it has a normal mode inductance component Ln that satisfies equation (3). However, K = 0.25. In this case, a miniaturized power converter 1 can be provided. Here, the coil between the three-phase AC power supply 100 and the capacitor 130 is either the composite coil 110 only, or a coil with multiple windings wound around a core and the composite coil 110 only. In this case, by using the composite coil 110, it is possible to eliminate the coil with only normal mode inductance between the AC power supply 100 and the capacitor 130. Furthermore, the (L-I) characteristic of the normal mode inductance of the composite coil 110 is such that the value of the normal mode inductance corresponding to the value of the input current to the power converter 1 when the overcurrent protection of the inverse converter circuit 150 is activated is expressed by equation (4) when the power factor φ = 0.95 at the maximum power consumption is the value of the input current I1 to the power converter 1. This is 90% or more of the normal mode inductance value corresponding to the above. In this case, even when a current twice the rated current flows through the composite coil 110, the leakage flux passes through the air, so magnetic saturation does not occur and the normal mode inductance can be maintained. Furthermore, the windings of each phase of the composite coil 110 are made of the same material and have the same wire diameter, and are wound on the winding portion of the core, separated from each other. In this case, the coupling coefficient between the windings of each phase of the composite coil 110 can be reduced. Here, the capacitor 130 is a film capacitor or a ceramic capacitor. In this case, a capacitor with excellent high-frequency characteristics can be provided. Furthermore, if the air-core inductance of one phase of the winding of the composite coil 110 is La, then the sum of the inductances of two phases of the normal mode inductance of the composite coil, Lb, is given by equation (5). Lb > 2 × La … (5) In this case, by using the leakage flux, the normal mode inductance can be made higher than that of the air-core La. Furthermore, the motor 160 is mounted on the compressor of an air conditioner. In this case, a smaller, lighter, and lower-cost air conditioner can be provided. Furthermore, an air conditioner equipped with a power converter 1 can be provided. In this case, a smaller, lighter, and lower-cost air conditioner can be provided.

[0064] Although embodiments have been described above, the technical scope of this disclosure is not limited to the embodiments described above. It is clear from the claims that combinations of two or more of the above embodiments, as well as various modifications or improvements to the above embodiments, are also included in the technical scope of this disclosure.

[0065] 1...Power converter, 11...Conventional power converter, 72...Via, 74...Tab terminal, 100...AC power supply, 110...Composite coil, 112...Common mode choke coil, 114...Normal mode choke coil, 120...Rectifier circuit, 130...Capacitor, 140...DC link section, 150...Inverse conversion circuit, 160...Motor, 600...AC power supply, 610...Common mode choke coil, 620...Rectifier circuit, 630...Reactor, 635...Capacitor, 640...DC link section, 650...Inverse conversion circuit, 660...Motor

Claims

1. A rectifier circuit for rectifying the AC power of a three-phase AC power supply; an inverse conversion circuit for modulating the voltage rectified by the rectifier circuit based on a carrier frequency fc ([Hz]), inversely converting it to a predetermined frequency, and applying it to a motor having a maximum power consumption Pmax ([W]) of 2kW or more; a capacitor provided between the rectifier circuit and the inverse conversion circuit, wherein the capacitance Cn ([F]) of the AC voltage Vac ([V]) of the three-phase AC power supply and the maximum power consumption Pmax satisfy equations (1) and (2); and a composite coil between the three-phase AC power supply and the capacitor, wherein the carrier frequency fc is 17.7kHz or more, and the composite coil has multiple windings wound around the winding portion of the core, and has a common-mode inductance component that functions as a common-mode choke coil and a normal-mode inductance component that functions as a normal-mode choke coil, A power converter having a normal mode inductance component Ln([H]) that satisfies equation (3), wherein the coupling coefficient between the windings of each phase of the composite coil is 0.85 or more and less than 1. However, assume K = 0.

25.

2. The power conversion device according to claim 1, wherein the coil between the three-phase AC power supply and the capacitor is either the composite coil alone, or a coil with multiple windings wound around a core and the composite coil alone.

3. The (L-I) characteristic of the normal mode inductance of the composite coil is such that the value of the normal mode inductance corresponding to the value of the input current to the power converter when the overcurrent protection of the inverse converter circuit is activated is the value of the input current I1 ([A]) to the power converter, expressed by equation (4) when the power factor φ = 0.95 at the maximum power consumption. The power conversion device according to claim 1, wherein the value of the normal mode inductance corresponding to is 90% or more.

4. The power conversion device according to claim 1, wherein the windings of each phase of the composite coil are made of the same material and have the same wire diameter, and are wound separately from each other on the winding portion of the core.

5. The power conversion device according to claim 1, wherein the capacitor is a film capacitor or a ceramic capacitor.

6. The power conversion device according to claim 1, wherein when the air-core inductance of one phase of the winding of the composite coil is La, the sum of the inductances of the two phases of the normal mode inductance of the composite coil, Lb, is given by equation (5). Lb > 2 × La …(5) 7. The power conversion device according to claim 1, wherein the motor is mounted on the compressor of an air conditioner.

8. An air conditioning system equipped with the power conversion device described in any one of claims 1 to 7.

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