Power conversion equipment and air conditioning equipment

Abstract

To provide a miniaturized power conversion device. [Solution] A power converter comprising: a rectifier circuit for rectifying AC power from a three-phase AC power supply; an inverse conversion circuit for modulating the voltage rectified by the rectifier circuit based on the carrier frequency, inversely converting it to a predetermined frequency, and applying it to a motor; and a first capacitor provided between the rectifier circuit and the inverse conversion circuit, the capacitance of which satisfies predetermined conditions; a composite coil having common-mode inductance and normal-mode inductance arranged between the three-phase AC power supply and the first capacitor, wherein the coupling coefficient between each winding is 0.85 or more and less than 1, and the carrier frequency is 17.7 kHz or higher.

Description

Technical Field

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

Background Art

[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, 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.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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, the miniaturization of the power conversion device is hindered. An object of this disclosure is to provide a miniaturized power conversion device and the like.

Means for Solving the Problems

[0005] The power converter in the first aspect includes a rectifier circuit that rectifies the AC power of a three-phase AC power supply, an inverse conversion circuit that modulates the voltage rectified by the rectifier circuit based on the carrier frequency fc ([Hz]), inversely converts it to a predetermined frequency, and applies 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]) satisfies equations (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]), and the three-phase AC A composite coil is provided between the power supply and the capacitor, the carrier frequency is 17.7 kHz or higher, the composite coil 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, and the coupling coefficient between the windings of each phase of the composite coil is 0.85 or more and less than 1, and has a normal mode inductance component Ln([H]) that satisfies equation (3). TIFF0007862742000001.tif36150, where K=0.25. In the second aspect of the power conversion device, 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. In this case, by using a composite coil, it is possible to eliminate the coil with only normal mode inductance between the power supply and the capacitor. In the third aspect of the power converter, the (LI) 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. TIFF0007862742000002.tif16150 This value is 90% or more of the normal mode inductance. 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 separately from each other on the winding portion of the core. In this case, the coupling coefficient between the windings of each phase of the composite coil can be reduced. The power conversion device in the fifth aspect is one in which 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 power conversion device of the sixth aspect, if La is the air-core inductance of one phase of the winding of the composite coil, then 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) In this case, by using leakage flux, the normal mode inductance can be made higher than that of an air-core inductor (La). In the seventh aspect, the power conversion device is such that 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 eighth aspect of the air conditioning system can provide an air conditioning system equipped with a power conversion device. In this case, a smaller, lighter, and lower-cost air conditioning unit can be provided. [Brief explanation of the drawing]

[0006] [Figure 1] This diagram illustrates the circuit configuration of the power converter according to this embodiment. [Figure 2] This diagram illustrates the generation of inductance in normal mode. [Figure 3] (A) is a diagram showing the noise terminal voltage of the composite coil 110 of this embodiment and a conventional CMC at an input current of 2.5Arms. (B) is a diagram showing the noise terminal voltage of a conventional CMC and the composite coil of this embodiment at an input current of 29Arms. [Figure 4] (A) is a table showing the calculation conditions for inductance and coupling coefficient, (B) is a figure showing the common mode filter gain G required for each carrier frequency calculated from the withstand voltage test results, and (C) is a figure showing the change in the maximum value of normal mode inductance and the minimum value of common mode inductance according to the carrier frequency. [Figure 5] This figure shows the coupling coefficient with respect to carrier frequency and the volume of the power converter. [Figure 6] (A) is a perspective view of the composite coil according to this embodiment, and (B) is a diagram showing the coil winding method. [Figure 7] (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. [Figure 8] This figure shows an example of a circuit configuration for a power converter in which a second capacitor is placed. [Figure 9] (A) is a diagram showing an air-core coil, and (B) is a diagram illustrating leakage inductance. [Figure 10] This figure shows an example of the circuit configuration of a power conversion device to be compared. [Modes for carrying out the invention]

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

[0008] <Comparison target power converter 11> First, let's describe the power converter 11, which will be used for comparison. Figure 10 shows an example of the circuit configuration of a power converter 11 for comparison. 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 may also be referred to as a 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 provide 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 part between the rectifier circuit 620 and the inverter circuit 650. The DC link section 640 includes a positive (+)-side wiring and a negative (-)-side wiring. A capacitor 635 is provided between the positive (+)-side wiring and the negative (-)-side wiring of the DC link section 640. In the power conversion device 11, a reactor 630 is provided on the positive (+)-side wiring. The reactor 630 is provided between the rectifier circuit 620 and the inverter circuit 650. In the power conversion device 11, it is effective to provide the reactor 630 between the rectifier circuit 620 and the inverter circuit 650 to suppress normal-mode noise. The reactor 630 has an inductance L ([H]). The reactor 630 is also called a normal-mode choke coil. The reactor 630 can suppress normal-mode noise.

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

[0012] The noise generated in the power conversion circuit will be described in detail. The noise generated in the power conversion circuit includes normal mode noise and common mode noise. Common mode noise is the noise that returns from a plurality of power lines to the power converter through the capacitance between the power conversion circuit and the reference ground and the power source connected to the reference ground, from a power conversion circuit that is electrically connected by a power source and a plurality of power lines and generates noise. The common mode choke coil 610 is a noise filter that suppresses common mode noise. The winding directions of the coils in each phase of the common mode choke coil 610 are the same as each other. Therefore, the magnetic fluxes due to normal mode noise cancel each other out between phases. Normal mode noise is the noise that returns from one power line through a power source and a plurality of power lines that are electrically connected and generate noise to the power conversion circuit from the other power line. The reactor 630 is also called a normal mode choke coil and suppresses normal mode noise.

[0013] The capacitor 635 suppresses noise such as switching noise generated by the inverter circuit 650. The capacitor 635 forms a reactor and an LC filter and suppresses the normal mode noise among the switching noises. As described above, in the power conversion device 11, it was necessary to provide the common mode choke coil 610 and the reactor 630. However, if the common mode choke coil 610 and the reactor 630 are provided as separate components, the miniaturization of the power conversion device is hindered. In particular, the reactor 630 is a component in which an electric wire is wound in a coil shape, and the miniaturization of the power conversion device has been hindered due to the need to secure space.

[0014] <Configuration of the power conversion device according to the present embodiment> Figure 1 shows an example of the circuit configuration of a 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 comparative power converter 11 (see Figure 10) is that the common mode choke coil 610 of the comparative power converter 11 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 50Hz or 60Hz.

[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 the composite coil 110, and converts the AC voltage Vac ([V]) output by the AC power supply 100 to 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 in the figure, 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 with voltage fluctuations caused by the AC voltage Vac ([V]). Capacitor 130 does not have the function of smoothing the pulsation of the voltage waveform 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, improvements such as power factor improvement can be achieved.

[0021] The statement above, "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 capacitor 130 does not have the function of smoothing the pulsation of the voltage waveform rectified by the rectifier circuit 120, a small capacitance capacitor can be used for capacitor 130. However, because the capacitance C ([F]) of 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 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 2kW 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]

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[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]

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[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, 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 process, 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 in 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 equation (3) below. Through our research, we have 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]

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[0031] The inverse transform 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 shown in Figure 1, the composite coil 110 was placed between the AC power supply 100 and the rectifier circuit 120. Alternatively, the composite coil 110 may be placed between the rectifier circuit 120 and the capacitor 130. Furthermore, in the circuit configuration of Figure 1, the only coil present between the three-phase AC power supply 100 and the capacitor 130 is the composite coil 110. 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 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 has the added function of a normal mode choke coil by adjusting the coupling coefficient of the common mode choke coil to increase the leakage flux. In general, 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]

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[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 equals the inductance Ln required in normal mode during operation. Therefore, the inductance required for the normal mode component of 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]

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[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 low leakage flux. In a typical common-mode choke coil, 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 required. 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 will become 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] Figure 2 illustrates the generation of normal-mode inductance. In a three-phase coil, if normal-mode current is passed through two phases and the remaining phase is de-energized, a conventional common-mode choke coil would have zero normal-mode inductance due to the cancellation of magnetic flux. In a composite coil, leakage flux forms a magnetic path, generating normal-mode inductance. The graph in Figure 2 shows the small normal-mode inductance values ​​generated by the magnetic path of leakage flux in a coil where the three-phase windings N1, N2, and N3 are arranged in a line around the core. Note that N2 has a larger value than N1 and N3 because N2 is located in the center of the three-phase windings and is influenced by the windings on either side of it.

[0042] Figure 3(A) shows the noise terminal voltage when using the composite coil 110 of this embodiment and when using a conventional CMC at an input current of 2.5 Arms. The horizontal axis represents frequency (MHz), and the vertical axis represents the noise terminal voltage. Waveform W1 is the noise terminal voltage when using the composite coil 110, and waveform W2 is the noise terminal voltage when using a conventional CMC. Comparing waveforms W1 and W2 of the noise terminal voltage, they are almost identical at frequencies above 150 kHz. Therefore, it can be confirmed that the composite coil 110 has the same performance as a conventional CMC at frequencies above 150 kHz. Figure 3(B) shows the noise terminal voltage when using a conventional CMC and when using the composite coil of this embodiment, with an input current of 29Arms. Comparing the noise terminal voltage waveform W3 when using the composite coil with the noise terminal voltage waveform W4 when using a conventional CMC, it can be confirmed that the composite coil performs comparably to the conventional CMC at frequencies above 150kHz. Figures 3(A) and (B) show that the composite coil exhibits performance equivalent to that of a conventional CMC at 150kHz and above, regardless of whether the input current is as low as 2.5Arms or as high as 29Arms.

[0043] Next, we will explain how to calculate the normal mode inductance Ln and common mode inductance Lc of a composite coil. The normal mode inductance Ln is first determined from the maximum power consumption Pmax and the AC voltage Vac to find the normal mode capacitance Cn, and then determined from the calculated capacitance Cn and the carrier frequency fc. Specifically, the capacitor capacitance Cn is determined from equations (1) and (2) above, and the normal mode inductance Ln is determined from equation (3) above.

[0044] The common-mode inductance Lc is first determined from the common-mode capacitance Cc, which is calculated from the test voltage Vt and frequency f during the withstand voltage test, and the specified value I of the leakage current. The withstand voltage test is then determined from the calculated capacitance Cc, the filter gain G, and the filter frequency ff. The withstand voltage test is a constraint that must be satisfied according to the standard. With no power supply voltage applied, a test voltage is applied, and the current flowing must be less than or equal to the specified value. Specifically, first, the capacitor capacitance Cc is determined from equation (8), which is used to calculate the leakage current that flows during the withstand voltage test.

[0045]

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

[0047] Figure 4(B) shows the required common-mode filter gain G 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 sharply in the carrier frequency region 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, at 100 μH or less. On the other hand, as the carrier frequency fc increases, the minimum required common-mode inductance Lc tends to increase. There is an inflection point around a carrier frequency of 17.7 kHz. In the region of carrier frequencies greater than 17.7 kHz, the minimum common-mode inductance increases sharply from 4 mH.

[0050] The relationship between the coupling coefficient k and the carrier frequency fc was determined under the assumption that the constraints of equations (1), (2), and (3) related to the normal mode inductance Ln, and equations (8) and (9) related to the common mode inductance Lc, as well as equation (7) for the coupling coefficient k, were satisfied. Figure 5 shows the coupling coefficient and volume of the power converter with respect to the carrier frequency fc. The horizontal axis represents the carrier frequency fc (kHz), the left vertical axis represents the coupling coefficient k, and the right vertical axis represents the volume. The volume shows the estimated trend, with the upper side being larger and the lower side being smaller. Observing 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. Subsequently, as the carrier frequency increases, the coupling coefficient k asymptotically approaches 1.

[0051] Next, let's consider the change in volume of 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 trends described above, 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 conversion device 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 input current is at its maximum. In a typical coil, the ratio of the inductance when the overcurrent protection is activated to the inductance when the input current is at its maximum 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). TIFF0007862742000010.tif10152 The inductance for the maximum input current I1 is defined as LCA. When overcurrent protection is activated, the input current overcurrent flows for a period shorter than one cycle. Therefore, if the effective value of the sinusoidal current corresponding to the peak value of the input current when overcurrent protection is activated is I2, then the inductance with respect to I2 is defined as LCB. In this case, the LCB / LCA ratio in the composite coil 110 of this embodiment becomes 0.9 or greater.

[0054] As described above, the (LI) 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 inverse converter circuit 150. When magnetic materials are used, such as in reactors, a large current flows when a lightning surge is applied, causing magnetic saturation and making it impossible to maintain inductance. If the inductance is lost, there is no impedance from the power supply to the inverter, so all the energy of the lightning surge is transferred to the inverter. However, when using leakage flux, 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 shown in Figure 1, the inductance generated by leakage flux is used as the inductance of the normal mode component, thereby maintaining the inductance value up to a current even greater than the maximum operating current, and the effect as inductance is maintained even when lightning surges flow in. As described above, in the case of a composite coil, the inductance generated by leakage flux can be used as the inductance of the normal mode component, thus providing a power conversion device that is resistant to large currents when lightning surges are applied.

[0056] Figure 6(A) is a perspective view of the 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 a printed circuit board, as shown in Figure 7(A). The composite coil according to this embodiment can be directly installed on a 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 installed. The power converter in Figure 8 has a circuit configuration in which a second capacitor is installed 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 the 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 coil) Here, the values ​​of the normal mode inductance of the composite coils of the first and second embodiments will be described. Figure 9(A) shows 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 magnetic flux passes through air and magnetic material when nanocrystals are used as the magnetic material for the core of the composite coil. If the inductance of one phase of the winding in the air-core case is La, and the sum of the inductances of two phases in normal mode 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 using leakage inductance than by using air core inductance.

[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 converter 1 of this disclosure includes a rectifier circuit 120 that rectifies the AC power of a three-phase AC power supply 100, an inverse converter 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 converter 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). TIFF0007862742000011.tif35152, where K=0.25. In this case, a miniaturized power converter 1 can be provided. Here, the coil present between the three-phase AC power supply 100 and the capacitor 130 is either the composite coil 110 alone, or a coil with multiple windings wound around a core and the composite coil 110 alone. 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 (LI) 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 the value of the input current I1 to the power converter 1 expressed by equation (4) when the power factor φ = 0.95 at the maximum power consumption. This value is 90% or more of the normal mode inductance value corresponding to TIFF0007862742000012.tif10152. 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 separately from each other on the winding portion of the core. 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 La is the air-core inductance of one phase of the winding of the composite coil 110, 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) In this case, by using leakage flux, the normal mode inductance can be made higher than that of an air-core inductor (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 conditioning system equipped with 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. [Explanation of Symbols]

[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 that rectifies the AC power of a three-phase AC power supply, An inverse conversion circuit modulates the voltage rectified by the rectifier circuit based on the carrier frequency fc ([Hz]), converts it inversely to a predetermined frequency, and applies it to a motor with a maximum power consumption Pmax ([W]) of 2kW or more. A capacitor is provided between the rectifier circuit and the inverse converter circuit, wherein the capacitance Cn ([F]) satisfies equations (1) and (2) with respect to the AC voltage Vac ([V]) of the three-phase AC power supply and the maximum power consumption Pmax, A composite coil is provided between the three-phase AC power supply and the capacitor. The carrier frequency fc is 17.7 kHz or higher. The aforementioned composite coil is Multiple windings are wound around the core, and it 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 is 0.85 or more and less than 1, and it has a normal mode inductance component Ln([H]) that satisfies equation (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 input current 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 ([A]) to the power converter, expressed by equation (4) when the power factor φ = 0.95 at the maximum power consumption. Power converter. 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 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.

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

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

6. The power conversion device according to claim 1, wherein the motor is mounted on the compressor of an air conditioner.

7. An air conditioning system equipped with a power conversion device according to any one of claims 1 to 6.

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