Power conversion device and refrigeration apparatus

Abstract

To mitigate magnetic saturation in a common-mode choke coil by means of a digital control unit.SOLUTION: A power conversion device includes a common-mode choke coil, a power converter that performs forward conversion or frequency conversion on AC current inputted via the common-mode choke coil, current measurement means that measures current flowing through the common-mode choke coil in a common mode, and a digital control unit that, if a measurement value of the current or a calculation value based on the measurement value exceeds a threshold, switches operation of the power converter to reduce a peak value of the current at a frequency component the same as the carrier frequency of the power converter, to be lower than that before the switching of the operation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device and a refrigeration device. [Background technology]

[0002] A power conversion device that prevents magnetic saturation of a common-mode reactor connected between an AC power source and the power conversion device is known. This power conversion device includes a magnetic flux detector that detects the magnetic flux flowing through the iron core of the common-mode reactor, compares the magnetic flux detected by the magnetic flux detector with a protection level, and changes the switching frequency of the carrier wave if the detected magnetic flux exceeds the protection level. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-260963 Summary of the Invention [Problem to be solved by the invention]

[0004] One possible method for determining magnetic saturation in a common mode choke coil is to calculate the magnetic flux density based on the voltage across the auxiliary winding wound around the common mode choke coil. However, this method requires measuring the voltage across the auxiliary winding at a measurement frequency that exceeds the carrier frequency of the power conversion device, which increases the calculation load on the control unit. This makes it difficult to achieve digitalization, which is one way to miniaturize power conversion devices.

[0005] An object of the present disclosure is to mitigate magnetic saturation in a common mode choke coil using a digital control unit. [Means for solving the problem]

[0006] The power conversion device of the first aspect is A common mode choke coil, a power converter that performs forward conversion or frequency conversion of the AC input via the common mode choke coil; a current measuring means for measuring a current flowing in a common mode through the common mode choke coil; and a digital control unit that, when the measured value of the current or a calculated value based on the measured value exceeds a threshold, switches the operation of the power converter to reduce the peak value Icp of the current at the same frequency component as the carrier frequency of the power converter to a level lower than before the operation was switched.

[0007] According to the power conversion device of the first aspect, when a measured value of the current flowing in common mode through the common mode choke coil or a calculated value based on the measured value exceeds a threshold, the peak value Icp decreases, thereby alleviating magnetic saturation of the common mode choke coil. The power conversion device of the first aspect reduces the peak value Icp at the same frequency component as the carrier frequency of the power converter, thereby reducing the load on the control unit compared to reducing the peak value of the current at all frequency components. Therefore, magnetic saturation of the common mode choke coil can be alleviated by a digital control unit.

[0008] In addition, when a measured value or calculated value exceeds a threshold value, it may be when a positive measured value or a positive calculated value becomes larger than a positive threshold value, or when a negative measured value or a negative calculated value becomes smaller than a negative threshold value.

[0009] The power conversion device of the second aspect is the power conversion device of the first aspect, The digital control unit may lower the carrier frequency to make the peak value Icp lower than before the operation was switched.

[0010] According to the power conversion device of the second aspect, when the measured value or the calculated value exceeds the threshold value, the carrier frequency decreases, thereby decreasing the peak value Icp, and therefore, the magnetic saturation of the common mode choke coil can be alleviated by the digital control unit.

[0011] A power conversion device of a third aspect is the power conversion device of the second aspect, The digital control unit may change the threshold value after lowering the carrier frequency.

[0012] According to the power conversion device of the third aspect, the measured value or the calculated value after the carrier frequency is lowered is compared with the threshold value changed after the carrier frequency is lowered. If the carrier frequency is lowered, the level at which magnetic saturation occurs in the common mode choke coil also changes. Therefore, according to the power conversion device of the third aspect, the threshold value compared with the measured value or the calculated value after the carrier frequency is lowered can be changed to an appropriate value according to the peak value Icp after the carrier frequency is lowered.

[0013] A fourth aspect of the power conversion device is the third aspect of the power conversion device, The digital control unit may change the threshold value according to a first frequency after the carrier frequency is lowered.

[0014] According to the power conversion device of the fourth aspect, the measured value or the calculated value after the carrier frequency is lowered is compared with the threshold value changed according to the first frequency after the carrier frequency is lowered. When the carrier frequency is lowered to the first frequency, the level at which magnetic saturation of the common mode choke coil occurs also changes according to the first frequency. Therefore, according to the power conversion device of the fourth aspect, the threshold value compared with the measured value or the calculated value after the carrier frequency is lowered can be changed to an appropriate value according to the first frequency after the carrier frequency is lowered.

[0015] A fifth aspect of the power conversion device is the power conversion device of any one of the first to fourth aspects, The power converter may include a converter that converts AC input via the common mode choke coil into DC, a DC link to which the DC output from the converter is supplied, and an inverter that converts the DC from the DC link into AC, The digital control unit may reduce the voltage of the DC link to reduce the peak value Icp to a value lower than that before the operation was switched.

[0016] According to the power conversion device of the fifth aspect, when the measured value or the calculated value exceeds the threshold value, the voltage of the DC link decreases, thereby decreasing the peak value Icp, and therefore, the magnetic saturation can be alleviated by a digital control unit.

[0017] A sixth aspect of the power conversion device is the power conversion device of any one of the first to fifth aspects, The power converter may include a converter that converts AC input via the common mode choke coil into DC, a DC link to which the DC output from the converter is supplied, and an inverter that converts the DC from the DC link into AC, The carrier frequency may be a carrier frequency of the inverter.

[0018] According to the power conversion device of the sixth aspect, when the measured value or the calculated value exceeds the threshold value, the carrier frequency of the inverter is lowered, thereby lowering the peak value of the current, and therefore, the magnetic saturation can be alleviated by the digital control unit.

[0019] A seventh aspect of the power conversion device is the power conversion device of any one of the first to sixth aspects, The common mode choke coil may further include a temperature measuring means for measuring a temperature of the common mode choke coil. The digital control unit may change the threshold value in response to the measured temperature value.

[0020] According to the power conversion device of the seventh aspect, the threshold value to be compared with the measured value or the calculated value of the current can be changed to an appropriate value according to the measured value of the temperature.

[0021] The power conversion device of an eighth aspect is the power conversion device of any one of the first to seventh aspects, The common mode choke coil may include a magnetic core around which a winding is wound, The digital control unit may calculate a magnetic flux density based on information about the magnetism of the magnetic core, the carrier frequency, and the measured value of the current, The threshold value may be a current value at which the magnetic flux density becomes a saturated magnetic flux density, or a saturated magnetic flux density.

[0022] In this disclosure, saturation magnetic flux density refers to the magnetic flux density when a magnetic material is magnetically saturated, and is the magnetic flux density at which the derivative (dB / dH) of the magnetic flux density B with respect to the magnetic field strength H becomes significantly small. The saturation magnetic flux density may be a value close to the magnetic permeability in a vacuum.

[0023] According to the power conversion device of the eighth aspect, when the measured value or the calculated value of the current exceeds the current value at which the magnetic flux density becomes saturated magnetic flux density or exceeds the saturated magnetic flux density, the peak value of the current decreases, and therefore, the magnetic saturation can be alleviated by the digital control unit.

[0024] A power conversion device of a ninth aspect is the power conversion device of the eighth aspect, The digital control unit may derive a relationship between magnetic flux density and magnetic field strength at the carrier frequency based on information about the magnetism of the magnetic core and the carrier frequency.

[0025] According to the power conversion device of the ninth aspect, the relationship at the carrier frequency is derived, and therefore the accuracy of deriving the magnetic flux density or the accuracy of deriving the threshold value is improved.

[0026] A power conversion device of a tenth aspect is the power conversion device of the ninth aspect, The digital control unit may calculate a magnetic field strength based on the measured value of the current, and calculate a magnetic flux density based on the calculated magnetic field strength and the derived relationship.

[0027] According to the power conversion device of the tenth aspect, the magnetic flux density is calculated based on the calculated magnetic field strength and the derived relationship, and therefore the accuracy of calculation of the magnetic flux density is improved.

[0028] A refrigeration device according to an eleventh aspect includes the power conversion device according to any one of the first to tenth aspects.

[0029] The refrigeration device of the eleventh aspect includes the power conversion device of any one of the first to tenth aspects, and therefore, the magnetic saturation of the common mode choke coil can be alleviated by a digital control unit. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a block diagram showing an example of the configuration of a power conversion device according to a first embodiment; [Figure 2] FIG. 1 is a diagram illustrating an example of a configuration of a power converter. [Figure 3] 10 is a diagram illustrating the BH characteristics of a common mode choke coil. [Figure 4] 1 is a diagram illustrating a first example of a power conversion device according to a first embodiment. [Figure 5] 4 is a flowchart showing a first example of a magnetic saturation mitigation method executed by the power conversion device according to the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating an approximate BH curve. [Figure 7] 10 is a diagram illustrating frequency characteristics of the slope μ and the holding force Hc. FIG. [Figure 8] FIG. 10 is a diagram illustrating the temperature characteristics of the saturation magnetic flux density Blim. [Figure 9] 6 is a flowchart showing a second example of the magnetic saturation mitigation method executed by the power conversion device according to the first embodiment. [Figure 10] FIG. 4 is a diagram illustrating a second example of the power conversion device according to the first embodiment. [Figure 11] 10 is a flowchart showing a first example of a magnetic saturation mitigation method executed by a power conversion device according to a second embodiment. [Figure 12]FIG. 2 is a diagram illustrating an example of a hardware configuration of a digital control unit. DETAILED DESCRIPTION OF THE INVENTION

[0031] An embodiment will be described below.

[0032] Fig. 1 is a block diagram showing an example of the configuration of a power conversion device according to the first embodiment. The power conversion device 100 shown in Fig. 1 performs forward conversion or frequency conversion on AC input from a power source 6, and supplies the converted DC or frequency-converted AC to a load 7.

[0033] The power supply 6 is an AC power supply that supplies AC power. When the power supply 6 is a three-phase AC power supply, the three-phase AC power is supplied from the power supply 6 to the power conversion device 100. The power supply 6 is, for example, a commercial power supply.

[0034] When the load 7 is a DC load, the power conversion device 100 is a converter device that converts AC power supplied from the power source 6 into DC power to be supplied to the load 7. In this case, the load 7 operates on DC power supplied from the power conversion device 100. An example of a DC load is an electronic circuit.

[0035] When the load 7 is an AC load, the power conversion device 100 is an inverter device that converts the frequency of AC power supplied from the power source 6 into AC power to be supplied to the load 7. In this case, the load 7 operates on the AC power supplied from the power conversion device 100. An example of an AC load is a motor.

[0036] The power conversion device 100 is provided, for example, in a refrigeration device 200 that includes a load 7. The refrigeration device 200 is a refrigeration cycle device that includes a compressor driven by an AC motor, which is an example of the load 7. An example of the refrigeration device 200 is an air conditioner that conditions the air in a target space. Note that the device in which the power conversion device 100 is provided is not limited to the refrigeration device 200, and may be other equipment that requires a power conversion function.

[0037] The load 7 may be a three-phase AC motor. A three-phase AC motor is used as an electric motor that drives a compressor provided in a refrigerant circuit of the refrigeration device 200. The three-phase AC motor is, for example, a concentrated winding motor with 4 poles and 6 slots or 6 poles and 9 slots.

[0038] The power conversion device 100 includes a common mode choke coil 10, a power converter 30, a current measuring means 20, and a digital control unit 50. The power conversion device 100 may also include a temperature measuring means 40.

[0039] The common mode choke coil 10 is a component inserted in series in the AC wiring between the power supply 6 and the power converter 30, and is a noise filter that acts as an inductor for the common mode.

[0040] The power converter 30 is a circuit that performs forward conversion or frequency conversion on the AC power input via the common mode choke coil 10. When the load 7 is an AC load, the power converter 30 is an inverter circuit that performs frequency conversion on the AC power input via the common mode choke coil 10 to AC power to be supplied to the load 7. When the load 7 is a DC load, the power converter 30 is a converter circuit that performs forward conversion on the AC power input via the common mode choke coil 10 to DC power to be supplied to the load 7.

[0041] Fig. 2 is a diagram showing an example of the configuration of a power converter. The power converter 30 shown in Fig. 2 is an inverter circuit that converts the frequency of three-phase AC power input via the common mode choke coil 10 into three-phase AC power to be supplied to a load 7. The power converter 30 includes a converter 2, a DC link 3, and an inverter 4.

[0042] Converter 2 is a circuit that converts AC input via common mode choke coil 10 into DC, for example, converting three-phase AC into DC. Converter 2 is, for example, a diode bridge circuit in which a plurality of (for example, six) diodes are connected in a bridge configuration. These diodes full-wave rectify the AC voltage input from common mode choke coil 10 and convert it into DC voltage. Converter 2 may also be a voltage conversion circuit with a circuit format other than a diode bridge circuit. Converter 2 supplies the converted DC power to inverter 4 via DC link 3.

[0043] The DC link 3 is a portion to which the DC output from the converter 2 is supplied. The DC link 3 includes, for example, a pair of wires 31 and 32 connecting the converter 2 and the inverter 4, and a capacitor 3a connected between the pair of wires 31 and 32. The voltage Vdc of the DC link 3 is the potential difference between the pair of wires 31 and 32, and is approximately equal to the DC voltage generated across the capacitor 3a. The DC voltage Vdc is input to the inverter 4.

[0044] The wiring 32 refers to a path through which a current flows, and is not limited to a simple conductor. For example, the wiring 32 may be a grounded conductive part or a heat sink for dissipating heat from the inverter 4.

[0045] The inverter 4 is a circuit that converts the DC from the DC link 3 into AC, for example, converting the DC into three-phase AC. The inverter 4 supplies the converted AC power to the load 7. The inverter 4 is, for example, a bridge circuit in which a plurality of (for example, six) switching elements 4a are connected in a bridge shape. The inverter 4 converts the DC power from the DC link 3 into AC power for the load 7 by turning the plurality of switching elements 4a on or off in accordance with a command S generated by the digital control unit 50.

[0046] In FIG. 1, the common mode choke coil 10 is a component with a relatively large volume among the multiple components included in the power conversion device 100. Therefore, reducing the size of the common mode choke coil 10 contributes to reducing the size of the power conversion device 100 and improving design freedom. However, reducing the size of the common mode choke coil 10 may cause a phenomenon called magnetic saturation, in which the inductance (AC resistance) of the common mode choke coil 10 becomes extremely small. When magnetic saturation occurs, noise generated by the switching operation of the power converter 30 tends to leak out to the power supply 6 side. For this reason, a design with a sufficient margin is required.

[0047] Figure 3 is a diagram illustrating the BH characteristics of a common mode choke coil (CMC). The magnetic material used in a CMC has a nonlinear characteristic called the BH characteristic. The BH characteristic is expressed by a BH curve defined by the magnetic flux density B, which changes according to the voltage applied to the CMC, and the magnetic field strength H, which changes according to the current flowing through the CMC. When a large magnetic flux density B occurs in the magnetic material of a CMC, a phenomenon known as magnetic saturation occurs, in which the slope of the BH curve (derivative of B: dB / dH), which represents the inductance of the CMC, becomes smaller. When magnetic saturation occurs, the effectiveness of the CMC as a noise filter is reduced.

[0048] The present disclosure provides a power conversion device that determines magnetic saturation of a CMC and switches the operation of the power converter based on the determination result, thereby mitigating magnetic saturation of the CMC.

[0049] As a first comparative example, a method can be considered in which magnetic flux density B is estimated based on a measurement value of the voltage V across the auxiliary winding wound around the CMC, and magnetic saturation is determined based on the estimated magnetic flux density B. When estimating magnetic flux density B based on the voltage V across the auxiliary winding, magnetic flux density B is estimated using the following equation 1, and therefore a very short measurement interval "dt" is required to measure the voltage V across the winding.

[0050]

number

[0051] As a second comparative example, a method can be considered in which magnetic field strength H is estimated based on a measurement value of a current (common mode current) flowing in a CMC in common mode, and magnetic saturation is determined based on the estimated magnetic field strength H. When estimating magnetic field strength H based on a common mode current, magnetic field strength H is estimated by the following Equation 2.

[0052]

number

[0053] In contrast, the power conversion device 100 according to the first embodiment shown in Fig. 1 reduces the peak value of the common mode current at the same frequency component as the carrier frequency F of the power converter 30. Since magnetic saturation of the common mode choke coil 10 occurs mainly at the carrier frequency F of the power converter 30, limiting the frequency at which the peak value is reduced to the carrier frequency F reduces the memory load of the digital control unit. Therefore, the magnetic saturation of the common mode choke coil 10 can be alleviated by the digital control unit.

[0054] In FIG. 1, current measurement means 20 measures the current (common mode current Ic) flowing in common mode through common mode choke coil 10 and outputs a measurement value I representing the current value of the measured common mode current Ic. For example, current measurement means 20 detects common mode current Ic based on a secondary current flowing through a secondary winding wound around a magnetic core of common mode choke coil 10. Current measurement means 20 may measure common mode current Ic flowing on the power supply 6 side or the power converter 30 side of common mode choke coil 10. A specific example of current measurement means 20 is a current sensor such as a current transformer. Current measurement means 20 may also measure common mode current Ic using other methods.

[0055] When the measured value I of the common mode current Ic or the calculated value C based on the measured value I exceeds the threshold value Th, the digital control unit 50 outputs a command S to switch the operation of the power converter 30. The calculated value C is a value calculated by the digital control unit 50 or the current measuring means 20 using a predetermined formula based on the measured value I, and the calculated value C increases as the measured value I increases (details will be described later). By switching the operation of the power converter 30 using the command S, the digital control unit 50 reduces the peak value Icp of the common mode current Ic at the frequency component that is the same as the carrier frequency F of the power converter 30 to a value lower than before the operation of the power converter 30 was switched.

[0056] According to the power conversion device 100, when the measured value I of the common mode current Ic or the calculated value C based on the measured value I exceeds the threshold value Th, the peak value Icp of the common mode current Ic decreases, thereby alleviating magnetic saturation of the common mode choke coil 10. The power conversion device 100 reduces the peak value Icp of the common mode current Ic at the same frequency component as the carrier frequency F of the power converter 30, thereby reducing the load on the control unit compared to lowering the peak value of the common mode current Ic for all frequency components. Therefore, the magnetic saturation of the common mode choke coil 10 can be alleviated by the digital control unit 50.

[0057] The command S may be a signal that controls a switching frequency for power conversion of the power converter 30, for example, a signal that controls the driving of a switching element within the power converter 30. An example of the command S is a pulse width modulation signal.

[0058] The digital control unit 50 may lower the carrier frequency F of the power converter 30 when the measured value I or the calculated value C exceeds the threshold value Th. When the measured value I or the calculated value C exceeds the threshold value Th, the digital control unit 50 lowers the carrier frequency F, thereby lowering the peak value Icp of the frequency component that is the same as the carrier frequency F compared to before switching the operation of the power converter 30 (more specifically, before lowering the carrier frequency F). By lowering the carrier frequency F, the switching frequency for power conversion of the power converter 30 is lowered by the command S, and therefore the peak value Icp of the frequency component that is the same as the carrier frequency F is also lowered. This makes it possible to alleviate magnetic saturation of the common mode choke coil 10.

[0059] The digital control unit 50 may change the threshold value Th after lowering the carrier frequency F. In this way, the digital control unit 50 compares the measured value I or calculated value C after lowering the carrier frequency F with the threshold value Th that was changed after lowering the carrier frequency F. If the carrier frequency F is lowered, the level at which magnetic saturation occurs in the common mode choke coil 10 also changes. Therefore, by changing the threshold value Th after lowering the carrier frequency F, the threshold value Th that is compared with the measured value I or calculated value C after lowering the carrier frequency F can be changed to an appropriate value according to the peak value Icp after lowering the carrier frequency F.

[0060] The digital control unit 50 may change the threshold value Th according to the first frequency f1 after the carrier frequency F has been lowered. In this way, the digital control unit 50 compares the measured value I or calculated value C after the carrier frequency F has been lowered with the threshold value Th that has been changed according to the first frequency f1 after the carrier frequency F has been lowered. When the carrier frequency F is lowered to the first frequency f1, the level at which magnetic saturation occurs in the common mode choke coil 10 also changes according to the first frequency f1. Therefore, by changing the threshold value Th according to the first frequency f1 after the carrier frequency F has been lowered, the threshold value Th that is compared with the measured value I or calculated value C after the carrier frequency F has been lowered can be changed to an appropriate value according to the first frequency f1 after the carrier frequency F has been lowered.

[0061] The carrier frequency F is, for example, a carrier frequency for determining the switching frequency of the inverter 4 (see FIG. 2). When the measured value I or the calculated value C exceeds the threshold value Th, the digital control unit 50 lowers the carrier frequency F of the inverter 4, thereby lowering the peak value Icp of the common mode current Ic to a value lower than before switching the operation of the power converter 30 (more specifically, before lowering the carrier frequency F). By lowering the carrier frequency F of the inverter 4, the switching frequency for power conversion of the power converter 30 is lowered by command S, and therefore the peak value Icp of the common mode current Ic also lowers. This makes it possible to alleviate magnetic saturation of the common mode choke coil 10.

[0062] When the measured value I or the calculated value C exceeds the threshold value Th, the digital control unit 50 may reduce the voltage Vdc of the DC link 3 (see FIG. 2). For example, if the DC link 3 of the power converter 30 includes a step-up circuit or a step-down circuit, the digital control unit 50 reduces the voltage Vdc by issuing a command S to the step-up circuit or the step-down circuit to reduce the voltage Vdc. When the measured value I or the calculated value C exceeds the threshold value Th, the digital control unit 50 reduces the voltage Vdc, thereby reducing the peak value Icp of the common mode current Ic to a value lower than before switching the operation of the power converter 30 (more specifically, before reducing the voltage Vdc). By reducing the voltage Vdc, the peak value Icp of the common mode current Ic also decreases, thereby alleviating magnetic saturation of the common mode choke coil 10.

[0063] 1, temperature measurement means 40 measures temperature T of common mode choke coil 10 and outputs a temperature measurement value (measured value of temperature T) indicating the measured temperature. Examples of temperature measurement means 40 include a thermocouple, a thermistor, a bimetal, an infrared sensor, and a resistance temperature detector. Temperature measurement means 40 may measure temperature T of common mode choke coil 10 using other methods. Temperature T of common mode choke coil 10 may include the ambient temperature of common mode choke coil 10, and temperature measurement means 40 may be means for measuring the ambient temperature of common mode choke coil 10.

[0064] The digital control unit 50 may change the threshold value Th to be compared with the measured value I or the calculated value C, depending on the temperature measurement value obtained by the temperature measurement means 40. If the temperature T changes, the level at which magnetic saturation occurs in the common mode choke coil 10 also changes. By changing the threshold value Th depending on the temperature measurement value, the threshold value Th can be changed to an appropriate value depending on the temperature measurement value.

[0065] For example, as the temperature T increases, the saturation magnetic flux density Blim of the common mode choke coil 10 decreases. When the temperature T increases from a first temperature to a second temperature, the digital control unit 50 decreases the threshold value Th from the first threshold value to the second threshold value, and when the temperature T decreases from the second temperature to the first temperature, the digital control unit 50 increases the threshold value Th from the second threshold value to the first threshold value. This allows the digital control unit 50 to mitigate magnetic saturation in accordance with changes in the temperature T.

[0066] FIG. 4 is a diagram showing a first example of a power conversion device according to the first embodiment. The power conversion device 101 shown in FIG. 4 is one example of the above-mentioned power conversion device 100. The power conversion device 101 includes a common mode choke coil 10, a power converter 30, current measurement means 20, and a digital control unit 50A. The power conversion device 101 may also include temperature measurement means 40. In the power conversion device 101, descriptions of the same configurations, actions, and effects as those of the above-mentioned power conversion device 100 will be omitted by referencing the above descriptions.

[0067] Common mode choke coil 10 includes a magnetic core 12 around which windings 11 are wound. When common mode choke coil 10 is inserted into three-phase AC wiring, windings 11 are interposed in each of the three-phase AC wiring.

[0068] The digital control unit 50A calculates the magnetic field strength H using Equation 2, where C is a calculated value based on the measured value I of the common mode current Ic. If the calculated magnetic field strength H exceeds a threshold value Hth, the digital control unit 50A outputs a command S to switch the operation of the power converter 30. The threshold value Hth is an example of the threshold value Th. By switching the operation of the power converter 30 using the command S, the digital control unit 50 reduces the peak value Icp of the common mode current Ic at the frequency component that is the same as the carrier frequency F of the power converter 30 compared to before the operation of the power converter 30 was switched. This allows the digital control unit 50A to alleviate magnetic saturation of the common mode choke coil 10.

[0069] The digital control unit 50A includes, for example, a magnetic saturation determination unit 51, a memory 52, and an operation switching unit 53.

[0070] The magnetic saturation determination unit 51 determines whether the magnetic field strength H exceeds the threshold value Hth based on information about the magnetism of the magnetic core 12 stored in the memory 52, the carrier frequency F obtained from the operation switching means 53, and the measurement value I obtained from the current measurement means 20. If the magnetic field strength H does not exceed the threshold value Hth, the magnetic saturation determination unit 51 determines that the common mode choke coil 10 is not magnetically saturated. If the magnetic field strength H exceeds the threshold value Hth, the magnetic saturation determination unit 51 determines that the common mode choke coil 10 is magnetically saturated.

[0071] When the magnetic saturation determination unit 51 determines that the common mode choke coil 10 is not magnetically saturated, the operation switching unit 53 continues the power conversion operation of the power converter 30 by command S without reducing the peak value Icp of the common mode current Ic. When the magnetic saturation determination unit 51 determines that the common mode choke coil 10 is magnetically saturated, the operation switching unit 53 switches the power conversion operation of the power converter 30 by command S so as to reduce the peak value Icp of the common mode current Ic.

[0072] The memory 52 pre-stores information (magnetic information) relating to the magnetism of the magnetic core 12. Examples of the magnetic information of the magnetic core 12 include the frequency characteristics of the slope μ of the BH curve, the frequency characteristics of the coercive force Hc of the BH curve, and the saturation magnetic flux density Blim.

[0073] Fig. 5 is a flowchart showing a first example of the magnetic saturation mitigation method executed by the power conversion device according to Example 1. The magnetic saturation mitigation method shown in Fig. 5 is executed by the digital control unit 50A (Fig. 4).

[0074] In step S10, the digital control unit 50A sets the carrier frequency F to the reference frequency f0.

[0075] In step S11, the digital control unit 50A acquires the measured value I of the common mode current Ic from the current measuring means 20.

[0076] In step S12, the digital control unit 50A calculates the magnetic field strength H by substituting the measurement value I obtained in step S11 into equation 2. In equation 2, N represents the number of turns of the winding 11 of the common mode choke coil 10, and Le represents the magnetic path length of the magnetic core 12 of the common mode choke coil 10. The number of turns N and the magnetic path length Le are known design values ​​of the common mode choke coil 10 used, and may be stored in advance in the memory 52. ​​The number of turns N may be the number of turns for one phase wound around the magnetic core 12.

[0077] In step S13, the digital control unit 50A derives a BH curve (the relationship between magnetic flux density B and magnetic field strength H) at the carrier frequency F based on information about the magnetism of the magnetic core 12 and the carrier frequency F. The digital control unit 50A derives the threshold value Hth according to this relationship, thereby improving the accuracy of deriving the threshold value Hth.

[0078] In step S13, the digital control unit 50A calculates a threshold value Hth to be compared with the magnetic field strength H calculated in step S12, based on the BH curve at the carrier frequency F when the measurement value I was measured in step S11. For example, the digital control unit 50A calculates the threshold value Hth using Equation 3, which is derived based on the BH curve at the carrier frequency F when the measurement value I was measured in step S11. The threshold value Hth is a threshold value for determining magnetic saturation of the common mode choke coil 10, and corresponds to the magnetic field strength H when the magnetic flux density B reaches the saturation magnetic flux density Blim.

[0079] Here, the formula 3 and the threshold value Hth will be explained below.

[0080] As shown in Figure 3 above, the BH curve has frequency characteristics that change in the H-axis direction depending on the frequency, so the magnetic field strength H at magnetic saturation differs for each frequency. Therefore, the threshold value Hth when the carrier frequency F is at frequency a corresponds to the magnetic field strength Ha when the magnetic flux density B reaches the saturation magnetic flux density Blim. Similarly, the threshold value Hth when the carrier frequency F is at frequency b corresponds to the magnetic field strength Hb when the magnetic flux density B reaches the saturation magnetic flux density Blim. Frequency b is higher than frequency a, and magnetic field strength Hb is greater than magnetic field strength Ha.

[0081] Figure 6 illustrates an approximate BH curve. Approximating the BH curve (the relationship between magnetic flux density B and magnetic field strength H) shown in Figure 3 yields an approximate BH curve defined by B = μ × (H ± Hc) and B = ± Blim, as shown in Figure 6. B = μ × (H ± Hc) is a combination of "B = μ × (H - Hc)" in Equation 5 and "B = μ × (H + Hc)" in Equation 6. B = ± Blim is a combination of positive saturation magnetic flux density (B = Blim) and negative saturation magnetic flux density (B = -Blim). The slope μ represents magnetic permeability. Coercivity Hc is the strength of the external magnetic field in the opposite direction required to return a magnetized magnetic material to its unmagnetized state. It is the value of magnetic field strength H when magnetic flux density B is zero on the BH curve.

[0082] 6 corresponds to the magnetic field strength when the magnetic flux density B reaches the saturation magnetic flux density Blim. Therefore, by modifying "B=μ×(H−Hc)" in Equation 5, Equation 3 in step S13 in FIG. 5 is obtained.

[0083] 5, digital control unit 50A determines μ in equation 3 in step S13 of FIG. 5, for example, based on the frequency characteristics of carrier frequency F when measurement value I was measured in step S11 and slope μ stored in advance in memory 52. ​​Digital control unit 50A determines Hc in equation 3 in step S13 of FIG. 5, for example, based on the frequency characteristics of carrier frequency F when measurement value I was measured in step S11 and coercive force Hc stored in advance in memory 52.

[0084] 7 is a diagram illustrating the frequency characteristics of the slope μ and the holding force Hc. The digital control unit 50A identifies the slope μ corresponding to the carrier frequency F when the measurement value I is measured in step S11 from the frequency characteristics of the slope μ shown in FIG. 7. The digital control unit 50A identifies the holding force Hc corresponding to the carrier frequency F when the measurement value I is measured in step S11 from the frequency characteristics of the holding force Hc shown in FIG.

[0085] The frequency characteristics of the slope μ, which indicate the relationship between the slope μ and the carrier frequency F, and the frequency characteristics of the holding force Hc, which indicate the relationship between the holding force Hc and the carrier frequency F, may be defined by a map (table) or by an arithmetic expression.

[0086] In step S13 of FIG. 5, the digital control unit 50A determines Blim in equation 3 in step S13 of FIG. 5, for example, based on the temperature measurement value acquired from the temperature measurement means 40 and the temperature characteristics of the saturation magnetic flux density Blim stored in advance in the memory 52.

[0087] 8 is a diagram illustrating the temperature characteristic of the saturation magnetic flux density Blim. The digital control unit 50A identifies the saturation magnetic flux density Blim corresponding to the temperature measurement value when the measurement value I is measured in step S11 from the temperature characteristic of the saturation magnetic flux density Blim shown in FIG.

[0088] The temperature characteristic of the saturation magnetic flux density Blim, which indicates the relationship between the saturation magnetic flux density Blim and the temperature T, may be defined by a map (table) or by an arithmetic expression.

[0089] 5, the digital control unit 50A compares the magnetic field strength H calculated in step S12 with the threshold value Hth calculated in step S13 to determine whether the common mode choke coil 10 is magnetically saturated. If the magnetic field strength H does not exceed the threshold value Hth, the digital control unit 50A determines that the common mode choke coil 10 is not magnetically saturated. In this case, the digital control unit 50A returns to the process of step S11 and repeats the above-described processes from step S11 onwards. On the other hand, if the magnetic field strength H exceeds the threshold value Hth, the digital control unit 50A determines that the common mode choke coil 10 is magnetically saturated, and executes the process of step S15.

[0090] In step S15, the digital control unit 50A changes the carrier frequency F from the current frequency to a first frequency f1. The first frequency f1 represents a frequency lower than the current frequency. As the carrier frequency F drops to the first frequency f1, the peak value Icp of the frequency component that is the same as the first frequency f1 decreases, thereby alleviating magnetic saturation of the common mode choke coil 10.

[0091] After lowering the carrier frequency F in step S15, the digital control unit 50A returns to the processing of step S11 and repeats the above processing from step S11 onwards. As a result, in steps S11, S12, and S13 from the second time onwards, values ​​after lowering the carrier frequency F (measured value I, magnetic field strength H, and threshold value Hth) are obtained. Therefore, even after lowering the carrier frequency F, the digital control unit 50A can accurately perform the magnetic saturation determination processing (step S14) and the operation switching processing (step S15).

[0092] The threshold value "-Hth" shown in FIG. 6 corresponds to the magnetic field strength when the magnetic flux density B reaches the saturation magnetic flux density "-Blim". Therefore, by modifying "B=μ×(H+Hc)" in Equation 6, Equation 4 shown in FIG. 6 is obtained. The digital control unit 50A may use the threshold value "-Hth" expressed by Equation 4 to determine whether the common mode choke coil 10 is magnetically saturated in step S14 of FIG. 5.

[0093] Furthermore, in step S13, the relationship between the carrier frequency F and the threshold value Hth may be stored in advance in memory 52 as information related to the magnetism of magnetic core 12, and the threshold value Hth corresponding to the carrier frequency F when the measurement value I is measured in step S11 may be determined based on the relationship between the carrier frequency F and the threshold value Hth. In this case, the relationship between the carrier frequency F and the threshold value Hth and the relationship between the temperature T may be stored in memory 52 in advance, and the relationship between the carrier frequency F and the threshold value Hth corresponding to the temperature measurement value acquired from temperature measurement means 40 when the measurement value I is measured in step S11 may be used.

[0094] Fig. 9 is a flowchart showing a second example of the magnetic saturation mitigation method executed by the power conversion device according to Example 1. The magnetic saturation mitigation method shown in Fig. 9 is executed by the digital control unit 50A (Fig. 4).

[0095] In step S20, the digital control unit 50A sets the carrier frequency F to the reference frequency f0.

[0096] In step S21, the digital control unit 50A acquires the measured value I of the common mode current Ic from the current measuring means 20.

[0097] In step S23, the digital control unit 50A derives a BH curve (the relationship between magnetic flux density B and magnetic field strength H) at the carrier frequency F based on information about the magnetism of the magnetic core 12 and the carrier frequency F. The digital control unit 50A derives the threshold value Ith according to this relationship, thereby improving the accuracy of deriving the threshold value Ith.

[0098] In step S23, the digital control unit 50A calculates a threshold value Ith to be compared with the measurement value I measured in step S21, based on the BH curve at the carrier frequency F when the measurement value I was measured in step S21. For example, the digital control unit 50A calculates the threshold value Ith using Equation 7, which is derived based on the BH curve at the carrier frequency F when the measurement value I was measured in step S21. The threshold value Ith is a threshold value for determining magnetic saturation of the common mode choke coil 10, and corresponds to the current value of the common mode current Ic when the magnetic flux density B reaches the saturation magnetic flux density Blim.

[0099] Equation 7 is obtained by modifying "H = (N × I) / Le" in Equation 2 above. In Equation 7, N represents the number of turns of winding 11 of common mode choke coil 10, and Le represents the magnetic path length of magnetic core 12 of common mode choke coil 10. The number of turns N and the magnetic path length Le are known design values ​​of the common mode choke coil 10 used, and may be stored in advance in memory 52. ​​The number of turns N may be the number of turns for one phase wound around magnetic core 12. Hth in Equation 7 is a threshold value calculated in the same way as Hth in step S13 of FIG. 5 above.

[0100] 9, the digital control unit 50A compares the measurement value I measured in step S21 with the threshold value Ith calculated in step S23 to determine whether the common mode choke coil 10 is magnetically saturated. If the measurement value I does not exceed the threshold value Ith, the digital control unit 50A determines that the common mode choke coil 10 is not magnetically saturated. In this case, the digital control unit 50A returns to the processing of step S21 and repeats the above processing from step S21 onwards. On the other hand, if the measurement value I exceeds the threshold value Ith, the digital control unit 50A determines that the common mode choke coil 10 is magnetically saturated, and executes the processing of step S25.

[0101] In step S25, the digital control unit 50A changes the carrier frequency F from the current frequency to a first frequency f1. The first frequency f1 represents a frequency lower than the current frequency. As the carrier frequency F drops to the first frequency f1, the peak value Icp of the frequency component that is the same as the first frequency f1 decreases, thereby mitigating magnetic saturation of the common mode choke coil 10.

[0102] After lowering the carrier frequency F in step S25, the digital control unit 50A returns to the processing of step S21 and repeats the above processing from step S21 onwards. As a result, in steps S21 and S23 from the second time onwards, values ​​(measured value I and threshold value Ith) after lowering the carrier frequency F are obtained. Therefore, the digital control unit 50A can accurately perform the magnetic saturation determination processing (step S24) and the operation switching processing (step S25) even after lowering the carrier frequency F.

[0103] Furthermore, in step S23, the relationship between the carrier frequency F and the threshold value Ith may be stored in advance in memory 52 as information related to the magnetism of magnetic core 12, and the threshold value Ith corresponding to the carrier frequency F when the measurement value I is measured in step S21 may be found based on the relationship between the carrier frequency F and the threshold value Ith. In this case, the relationship between the carrier frequency F and the threshold value Ith and the relationship between the temperature T may be stored in memory 52 in advance, and the relationship between the carrier frequency F and the threshold value Ith corresponding to the temperature measurement value acquired from temperature measurement means 40 when the measurement value I is measured in step S11 may be used.

[0104] FIG. 10 is a diagram showing a second example of the power conversion device according to the first embodiment. The power conversion device 102 shown in FIG. 10 is one example of the above-described power conversion device 100. The power conversion device 102 includes a common mode choke coil 10, a power converter 30, current measurement means 20, and a digital control unit 50B. The power conversion device 102 may also include temperature measurement means 40. In the power conversion device 102, descriptions of the same configurations, actions, and effects as those of the above-described power conversion devices 100 and 101 will be omitted by referencing the above descriptions.

[0105] The digital control unit 50B calculates the magnetic flux density B using the above formula 5, "B = μ × (H - Hc)," as the calculated value C based on the measured value I of the common mode current Ic. If the calculated magnetic flux density B exceeds the saturation magnetic flux density Blim, the digital control unit 50B outputs a command S to switch the operation of the power converter 30. The saturation magnetic flux density Blim is an example of the above threshold value Th. By switching the operation of the power converter 30 using the command S, the digital control unit 50B reduces the peak value Icp of the common mode current Ic at the frequency component that is the same as the carrier frequency F of the power converter 30 compared to before the operation of the power converter 30 was switched. This allows the digital control unit 50B to alleviate magnetic saturation of the common mode choke coil 10.

[0106] The digital control unit 50B includes, for example, a magnetic flux density calculation unit 54, a magnetic saturation determination unit 51, a memory 52, and an operation switching unit 53.

[0107] The magnetic flux density calculation unit 54 calculates the magnetic flux density B generated in the common mode choke coil 10 based on information about the magnetism of the magnetic core 12 stored in the memory 52, the carrier frequency F obtained from the operation switching means 53, and the measurement value I obtained from the current measurement means 20.

[0108] The magnetic saturation determination unit 51 determines whether the magnetic flux density B exceeds the saturation magnetic flux density Blim. If the magnetic flux density B does not exceed the saturation magnetic flux density Blim, the magnetic saturation determination unit 51 determines that the common mode choke coil 10 is not magnetically saturated. If the magnetic flux density B exceeds the saturation magnetic flux density Blim, the magnetic saturation determination unit 51 determines that the common mode choke coil 10 is magnetically saturated.

[0109] Fig. 11 is a flowchart showing a first example of a magnetic saturation mitigation method executed by the power conversion device according to Example 2. The magnetic saturation mitigation method shown in Fig. 11 is executed by the digital control unit 50B (Fig. 10).

[0110] Steps S30, S31, and S32 in FIG. 11 may be the same as steps S10, S11, and S12 in FIG. 5, and therefore the description of steps S30, S31, and S32 will be omitted by referencing the above description of steps S10, S11, and S12.

[0111] In step S33, the digital control unit 50B derives a BH curve (the relationship between magnetic flux density B and magnetic field strength H) at the carrier frequency F based on information about the magnetism of the magnetic core 12 and the carrier frequency F. By deriving the magnetic flux density B according to this relationship, the digital control unit 50B improves the accuracy of deriving the magnetic flux density B.

[0112] In step S33, the digital control unit 50B derives the magnetic flux density B corresponding to the magnetic field strength H calculated in step S32 on the BH curve at the carrier frequency F when the measurement value I was measured in step S31. For example, the digital control unit 50B calculates the magnetic flux density B using Equation 5, which is derived based on the BH curve at the carrier frequency F when the measurement value I was measured in step S31.

[0113] In step S33, the digital control unit 50B may determine μ and Hc in equation 5 in step S33 in the same way as the method for determining μ and Hc in equation 3 in step S13 of FIG.

[0114] 11, the digital control unit 50B compares the magnetic flux density B calculated in step S33 with the saturation magnetic flux density Blim to determine whether the common mode choke coil 10 is magnetically saturated. If the magnetic flux density B does not exceed the saturation magnetic flux density Blim, the digital control unit 50B determines that the common mode choke coil 10 is not magnetically saturated. In this case, the digital control unit 50B returns to the process of step S31 and repeats the above-described processes from step S31 onwards. On the other hand, if the magnetic flux density B exceeds the saturation magnetic flux density Blim, the digital control unit 50B determines that the common mode choke coil 10 is magnetically saturated, and executes the process of step S35.

[0115] In step S34, the digital control unit 50B identifies the saturation magnetic flux density Blim, which is the threshold value in step S34, based on, for example, the temperature measurement value acquired from the temperature measurement means 40 and the temperature characteristics of the saturation magnetic flux density Blim pre-stored in the memory 52. ​​For example, the digital control unit 50B identifies the saturation magnetic flux density Blim corresponding to the temperature measurement value when the measurement value I is measured in step S31, from the temperature characteristics of the saturation magnetic flux density Blim shown in FIG.

[0116] 11, the digital control unit 50B changes the carrier frequency F from the current frequency to a first frequency f1. The first frequency f1 represents a frequency lower than the current frequency. As the carrier frequency F drops to the first frequency f1, the peak value Icp of the frequency component that is the same as the first frequency f1 decreases, thereby alleviating magnetic saturation of the common mode choke coil 10.

[0117] After lowering the carrier frequency F in step S35, the digital control unit 50B returns to the processing of step S31 and repeats the above processing from step S31 onwards. As a result, in steps S31, S32, and S33 from the second time onwards, values ​​after lowering the carrier frequency F (measured value I, magnetic field strength H, and magnetic flux density B) are obtained. Therefore, even after lowering the carrier frequency F, the digital control unit 50B can accurately perform the magnetic saturation determination processing (step S34) and the operation switching processing (step S35).

[0118] As described above, according to this embodiment, the magnetic saturation of the common mode choke coil 10 can be alleviated by the digital control unit 50.

[0119] In this embodiment, the control circuit, control device, controller, or digital control unit is an electronic circuit such as a CPU (Central Processing Unit), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit). The control circuit, control device, controller, or digital control unit may be a computer having a memory and a processor. The control circuit, control device, controller, or digital control unit performs the various control operations described in this specification by executing a program such as instruction code stored in the memory, or by being a circuit designed for a specific application.

[0120] 12 is an example of a hardware configuration diagram of a control circuit, control device, controller, or digital control unit. A computer 500 is an example of a control circuit, control device, controller, or digital control unit. The computer 500 has a drive device 508, an auxiliary storage device 502, a memory device 503, a CPU 504, an interface device 505, and the like, which are all connected to each other via a bus 506.

[0121] A program for realizing processing in computer 500 is provided by recording medium 507. When recording medium 507 on which the program is recorded is set in drive device 508, the program is installed from recording medium 507 to auxiliary storage device 502 via drive device 508. However, the program does not necessarily have to be installed from recording medium 507, but may be downloaded from another computer via a network. Auxiliary storage device 502 stores the installed program as well as necessary files, data, etc.

[0122] When an instruction to start a program is received, the memory device 503 reads the program from the auxiliary storage device 502 and stores it. The CPU 504 is a processor that executes functions related to the computer 500 in accordance with the program stored in the memory device 503. The interface device 505 is used as an interface for connecting to the outside.

[0123] Examples of the recording medium 507 include portable recording media such as a CD-ROM, a DVD disk, or a USB memory. Examples of the auxiliary storage device 502 include a hard disk drive (HDD) or a flash memory. Both the recording medium 507 and the auxiliary storage device 502 correspond to computer-readable recording media.

[0124] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0125] 2 Converter 3 DC Link 3a capacitor 4 inverters 4a Switching element 6 Power supply 7 Load 10 Common mode choke coil 11 Windings 12 Magnetic core 20 Current measurement means 30 Power Converter 31,32 Wiring 40 Temperature measuring means 50 Digital control section 51 Magnetic saturation determination unit 52 memory 53 Operation switching means 54 Magnetic flux density calculation unit 100, 101, 102 Power conversion device 200 Refrigeration equipment 500 computers

Claims

1. A common mode choke coil (10), a power converter (30) for converting the AC current input via the common mode choke coil into a forward or frequency converted AC current; a current measuring means (20) for measuring a current flowing in a common mode through the common mode choke coil; and a digital control unit (50) that, when the measured value of the current or a calculated value based on the measured value exceeds a threshold, switches the operation of the power converter to reduce the peak value of the current at a frequency component that is the same as the carrier frequency of the power converter compared to before the operation was switched.

2. The power conversion device according to claim 1 , wherein the digital control unit reduces the carrier frequency to reduce the peak value to a value lower than that before the operation is switched.

3. The power conversion device according to claim 2 , wherein the digital control unit changes the threshold value after lowering the carrier frequency.

4. The power conversion device according to claim 3 , wherein the digital control unit changes the threshold value in accordance with the first frequency obtained after the carrier frequency is lowered.

5. The power converter includes a converter (2) that converts AC input via the common mode choke coil into DC, a DC link (3) to which the DC output from the converter is supplied, and an inverter (4) that converts the DC from the DC link into AC, The power conversion device according to claim 1 , wherein the digital control unit reduces the voltage of the DC link to reduce the peak value to a value lower than that before the operation is switched.

6. The power converter includes a converter (2) that converts AC input via the common mode choke coil into DC, a DC link (3) to which the DC output from the converter is supplied, and an inverter (4) that converts the DC from the DC link into AC, The power conversion device according to claim 1 , wherein the carrier frequency is a carrier frequency of the inverter.

7. Further provided is a temperature measuring means (40) for measuring the temperature of the common mode choke coil, The power conversion device according to claim 1 , wherein the digital control unit changes the threshold value in accordance with the measured value of the temperature.

8. The common mode choke coil includes a magnetic core (12) around which a winding (11) is wound, the digital control unit calculates a magnetic flux density (B) based on information about the magnetism of the magnetic core, the carrier frequency, and the measured value of the current; The power conversion device according to claim 1 , wherein the threshold value is a current value at which the magnetic flux density becomes a saturation magnetic flux density (Blim), or the saturation magnetic flux density (Blim).

9. The power conversion device according to claim 8, wherein the digital control unit derives a relationship between magnetic flux density (B) and magnetic field strength (H) at the carrier frequency based on information about the magnetism of the magnetic core and the carrier frequency.

10. The power conversion device according to claim 9, wherein the digital control unit calculates a magnetic field strength (H) based on the measured value of the current, and calculates a magnetic flux density (B) based on the calculated magnetic field strength and the derived relationship.

11. A refrigeration device comprising the power conversion device according to any one of claims 1 to 5.

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