Power conversion device and refrigeration cycle application apparatus

Abstract

A power conversion device (1) is equipped with a power supply unit (100) comprising: a rectifying / boosting unit (170) that has a switching element (142) capable of pulse width modulation driving and that converts AC power into DC power; and a reactor (120) that is disposed between an AC power supply (110) for supplying AC power and a smoothing unit (200) for smoothing DC power. The capacity of the reactor (120) is set from the power factor of the power supply unit (100) and the reactor peak current flowing through the reactor (120) during non-pulse width modulation driving in which a current flows through a diode connected in parallel to the switching element (142), and the drive frequency of the switching element (142) is set from the magnetic characteristics of the reactor (120).

Description

Power conversion equipment and refrigeration cycle application equipment

[0001] The present disclosure relates to a power conversion device that converts AC power into DC power and a refrigeration cycle device.

[0002] Conventionally, power conversion devices operate to reduce losses generated in inverters, motors, etc. For example, Patent Document 1 discloses a technology for minimizing motor losses without using a complex control mechanism, arithmetic circuit, etc., when a motor drive device performs PWM (Pulse Width Modulation) control to generate AC power and supply it to a motor. In the motor drive device described in Patent Document 1, the carrier frequency to be used is determined based on the relationship between the motor loss and the carrier frequency, which is the frequency of the carrier signal used in PWM control.

[0003] JP 2012-10513 A

[0004] Devices such as the motor drive device described in Patent Document 1 typically include a reactor on the AC power supply side to which AC power is supplied. Reactors have a larger volume than other electronic components, and one method for reducing the volume of the reactor is to increase the drive frequency when the device is PWM-driven. Increasing the drive frequency when the device is PWM-driven allows for a reduction in reactor capacity, thereby reducing the reactor volume. However, when the device stops PWM drive and switches to non-PWM drive due to an abnormality or other reason, a free resonance waveform is generated in the device by the reactor and smoothing capacitor. Therefore, with a reactor capacity designed for PWM drive at a high drive frequency, there is a problem in that current rapidly increases during non-PWM drive, potentially damaging elements used in power conversion.

[0005] The present disclosure has been made in consideration of the above, and aims to provide a power conversion device that can prevent damage to elements used in power conversion when a PWM-drivable switching element is not performing PWM driving.

[0006] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a power supply unit having a switching element capable of Pulse Width Modulation driving, and including a rectifier / boost unit that converts AC power to DC power, and a reactor arranged between an AC power supply that supplies the AC power and a smoothing unit that smooths the DC power, wherein the capacity of the reactor is set from the reactor peak current that flows in the reactor and the power factor of the power supply unit during non-Pulse Width Modulation driving in which current flows in a diode connected in parallel to the switching element, and the driving frequency of the switching element is set from the magnetic characteristics of the reactor.

[0007] The power conversion device according to the present disclosure has an advantage that it is possible to prevent damage to elements used in power conversion when PWM-drivable switching elements are not PWM-driven.

[0008] FIG. 1 is a diagram showing a configuration example of a power conversion device according to embodiment 1. FIG. 2 is a diagram showing a configuration example of a power supply unit included in a power conversion device according to embodiment 1. FIG. 3 is a diagram showing a configuration example of a power supply unit included in a power conversion device according to embodiment 1. FIG. 4 is a diagram showing a difference in reactor current depending on the capacity of the reactor when a single-phase AC voltage is input in a general power conversion device. FIG. 5 is a diagram showing a difference in reactor current depending on the capacity of the reactor when a three-phase AC voltage is input in a general power conversion device. FIG. 1 shows an example of the relationship between the drive frequency of the switching element of the power supply unit provided in the power conversion device according to embodiment 1 and the current ripple width of the reactor. FIG. 2 shows a first diagram that schematically illustrates the structure of the reactor used in the power conversion device according to embodiment 2. FIG. 3 shows a second diagram that schematically illustrates the structure of the reactor used in the power conversion device according to embodiment 2. FIG. 4 shows, as a comparative example, the difference in volume when the effective cross-sectional area is the same between a case where the width is smaller than the depth and a case where the width is larger than the depth for a reactor of the same height. FIG. 5 shows an example of the configuration of a refrigeration cycle application device according to embodiment 3.

[0009] Hereinafter, a power conversion device and a refrigeration cycle application device according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0010] 1 is a diagram showing an example of the configuration of a power conversion device 1 according to a first embodiment. The power conversion device 1 includes a power supply unit 100, a smoothing unit 200, and a load unit 300. The load unit 300 is configured with a motor, an inverter that drives the motor, and the like. The smoothing unit 200 uses a smoothing capacitor, etc.

[0011] FIG. 2 is a first diagram illustrating a configuration example of the power supply unit 100 included in the power conversion device 1 according to the first embodiment. In the example of FIG. 2, the power supply unit 100 includes an AC power supply 110, a reactor 120, a rectifier unit 130, and a boost unit 140. The rectifier unit 130 and the boost unit 140 form a rectifying / boosting unit 170. The rectifier unit 130 has a bridge-connected configuration of diodes 131 to 134. The boost unit 140 has a boost function, and FIG. 2 illustrates a single-transistor boost chopper circuit including a reactor 141, a switching element 142, and a diode 143 as an example. The boost unit 140 may be replaced with a step-down unit (not shown) including a single-transistor step-down chopper circuit with a step-down function. The AC power supply 110 is, for example, a commercial power supply. Note that the AC power supply 110 may be located outside the power supply unit 100, i.e., outside the power conversion device 1. The same applies hereafter.

[0012] 3 is a second diagram showing a configuration example of the power supply unit 100 included in the power conversion device 1 according to the first embodiment. In the example of FIG. 3, the power supply unit 100 includes an AC power supply 110, a reactor 120, and a rectifying / boosting unit 150. The rectifying / boosting unit 150 is configured to integrate the functions of the rectifying unit 130 and the boosting unit 140 shown in FIG. 2, and is configured as a bridgeless circuit using four active switching elements 151 to 154. The switching elements 151 to 154 may be configured using four discrete elements, or a module in which four elements are mounted in the same package may be used.

[0013] 4 is a third diagram showing a configuration example of the power supply unit 100 included in the power conversion device 1 according to the first embodiment. In the example of FIG. 4, the power supply unit 100 includes an AC power supply 110, which is a three-phase power supply system, three reactors 120 corresponding to each of the three phases, and a rectifying / boosting unit 160. The rectifying / boosting unit 160 is configured to integrate the functions of a rectifying unit and a boosting unit, and is configured as a converter circuit using six switching elements 161 to 166, which are active elements. The switching elements 161 to 166 may be configured using six discrete elements, or a module in which six elements are mounted in the same package may be used.

[0014] For the reactor 120 used in the power supply unit 100 shown in Figures 2 to 4, a core made of a non-oriented electrical steel sheet material, a dust-based material, a ferrite-based material, or the like is selected depending on the application. These core materials are often selected mainly depending on the drive frequency of the switching elements provided in the power supply unit 100 of the power conversion device 1, from the viewpoint of loss in the reactor 120. In terms of frequency ranges, the non-oriented electrical steel sheet material, the dust-based material, and the ferrite-based material are used in order from the low frequency range. In terms of unit price per unit volume, the cheapest is the non-oriented electrical steel sheet material, the dust-based material, and the ferrite-based material in that order.

[0015] Generally, the reactor 120 accounts for a large proportion of the power supply unit 100. Therefore, in order to miniaturize the power supply unit 100 in the power conversion device 1, it is necessary to miniaturize the reactor 120. To miniaturize the reactor 120, it is necessary to PWM-drive the power conversion device 1 and increase the drive frequency. By increasing the drive frequency when PWM-driving the power conversion device 1, the capacity of the reactor 120 can be reduced, and therefore the volume of the reactor 120 can be reduced. However, excessively increasing the drive frequency of the power conversion device 1 increases the heat generation density, raising concerns about thermal destruction of the device. Therefore, to increase the drive frequency of the power conversion device 1 to a higher frequency, it is necessary to set an appropriate drive frequency and then apply a reactor 120 structure that achieves low loss and low heat generation.

[0016] Furthermore, when an abnormality occurs in the power conversion device 1 and the PWM drive stops to switch to non-PWM drive, a free resonance waveform is formed in the power conversion device 1 by the reactor 120 and the capacitors provided in the smoothing unit 200. Non-PWM drive is a drive state in the power conversion device 1 in which current flows through the diodes connected in parallel to the switching elements shown in Figures 2 to 4. With the capacity of the reactor 120 assuming PWM drive at a high-frequency drive frequency, the current increases sharply during non-PWM drive, raising concerns about damage to elements used in the power supply unit 100 in the power conversion device 1.

[0017] In this embodiment, the power conversion device 1 is configured to include a reactor 120 with a capacity that takes into account non-PWM drive, while improving the trade-off between the loss of the reactor 120 and the volume of the reactor 120. As shown in FIGS. 2 to 4 , the power conversion device 1 includes a power supply unit 100 that includes a rectifier / boost unit having a PWM-driveable switching element and converting AC power to DC power, and a reactor 120 that is arranged between an AC power supply 110 that supplies the AC power and a smoothing unit 200 that smoothes the DC power. In the power conversion device 1, the capacity of the reactor 120 is set based on the reactor peak current that flows through the reactor 120 and the power factor of the power supply unit 100 during non-PWM drive, in which a current flows through a diode connected in parallel with the switching element. In the power conversion device 1, the drive frequency of the switching element included in the rectifier / boost unit is set based on the magnetic characteristics of the reactor 120.

[0018] First, the capacity L of the reactor 120 will be described taking into consideration the non-PWM drive state, using the current flowing through the reactor 120, the power factor of the power supply unit 100, and the like. In the power conversion device 1, when non-PWM drive occurs, such as when an abnormality occurs in the device, the component current is determined by the capacity of the reactor 120. If the capacity of the reactor 120 is small, when high power factor control in the power conversion device 1 fails, that is, when PWM control is switched to non-PWM control, the increase in the current flowing inside the power conversion device 1 is large, heat generation increases, and there is a risk of damage to the elements used in the power supply unit 100 if no countermeasures are taken.

[0019] 2 to 4, since the reactor 120 generally accounts for a large proportion of the power supply unit 100, a significant effect can be achieved by reducing the size of the reactor 120. In order to reduce the size of the reactor 120, it is preferable to increase the drive frequency of the switching element provided in the rectifying / boosting unit, and it is common to perform an operation in which the switching element is turned on and off at a frequency of several hundred Hz to several hundred kHz, as in PWM drive.

[0020] If a malfunction occurs in a control unit (not shown) that controls the on / off of the switching elements during operation of the power conversion device 1, the control unit responsible for PWM driving of the switching elements will stop. In such a case, the power conversion device 1 will no longer be able to control the current using the switching elements, and will enter non-PWM driving, generating a free resonance waveform determined by the capacity of the reactor 120 and the capacity of the capacitor included in the smoothing unit 200. If the capacity of the capacitor included in the smoothing unit 200 is sufficiently large, the peak of the free resonance waveform will change depending on the capacity of the reactor 120.

[0021] FIG. 5 shows the difference in reactor current depending on the reactor capacity when a single-phase AC voltage is input to a typical power conversion device. In FIG. 5, FIG. 5(a) shows the state when the reactor capacity is 1000 μH, and FIG. 5(b) shows the state when the reactor capacity is 100 μH. In both FIG. 5(a) and FIG. 5(b), the upper graph shows the input voltage to the typical power conversion device, and the lower graph shows the current flowing through the reactor. FIG. 6 shows the difference in reactor current depending on the reactor capacity when a three-phase AC voltage is input to a typical power conversion device. In FIG. 6, FIG. 6(a) shows the state when the reactor capacity is 1000 μH, and FIG. 6(b) shows the state when the reactor capacity is 100 μH. In both FIG. 6(a) and FIG. 6(b), the upper graph shows the state when the reactor capacity is 100 μH, and FIG. 6(b) shows the state when the reactor capacity is 100 μH. In both FIG. 6(a) and FIG. 6(b), the upper graph shows the state when the reactor capacity is 100 μH, and the lower graph shows the current flowing through the U-phase reactor. As shown in Figures 5 and 6, as the reactor capacity decreases, the waveform peaks tend to increase during non-PWM drive. Since reducing the reactor capacity is inevitable in order to reduce the reactor size, it is necessary to be aware of the trends shown in Figures 5 and 6.

[0022] Furthermore, when non-PWM driving occurs, the power conversion device 1 is unable to control the output voltage and the high power factor of the input current. When the load unit 300 is a motor load and an inverter driving the motor load, the load unit 300 becomes a constant power load, and therefore in the power supply unit 100 of the power conversion device 1, the circuit current increases during non-PWM driving compared to PWM driving due to a decrease in output voltage and an increase in reactive current. When the power conversion device 1 switches from PWM driving to non-PWM driving, the increase amount ΔI of the reactor peak current flowing through the reactor 120 is ｐｅａｋ is shown in equation (1).

[0023]

[0024] In formula (1), P ｍａｘ is the maximum output power of the power supply unit 100, and V ｒｅｆ is the DC voltage applied to the smoothing unit 200 connected in parallel to the rectifying / boosting unit, pf is the overall power factor of the power supply unit 100, and V ａｃ＿ｐｅａｋ is the peak value of the input voltage from the AC power supply 110 that supplies AC power. When the AC power supply 110 is a three-phase AC power supply, the peak value of the line voltage is V ａｃ＿ｐｅａｋ The relationship between the capacity L of the reactor 120 and the overall power factor pf of the power supply unit 100 is expressed by equation (2).

[0025]

[0026] In formula (2), a １ is the first coefficient of a defined positive real number, and a ２ is the second coefficient of the specified positive real number. １ and a ２ is a coefficient determined from the relationship between the capacity L of the reactor 120 and the overall power factor pf of the power supply unit 100 when the power conversion device 1 is not PWM driven. １ and a ２Since L varies depending on the input voltage from the AC power supply 110, the load power of the load unit 300, and the like, it is desirable to perform analysis in advance, during the design stage, to determine L in accordance with the worst-case conditions for actual operation of the power conversion device 1. In the power conversion device 1, an increase in the circuit current of the power supply unit 100 increases the loss of elements used in the power supply unit 100 and increases heat generation. If the capacity L of the reactor 120 is set based on high power factor control in PWM drive, abnormal heat generation will occur when a malfunction occurs in the power conversion device 1, i.e., when non-PWM drive occurs. Therefore, by setting the capacity L of the reactor 120 so as to satisfy equation (3), which is obtained by modifying equation (1) and combining it with equation (2), it is possible to determine the capacity L of the reactor 120 taking into account abnormal heat generation when a malfunction occurs in the power conversion device 1.

[0027]

[0028] In this way, in the power conversion device 1, the amount of change between the reactor current peak value during PWM driving and the reactor current peak value during non-PWM driving under the same operating conditions is defined as ΔI ｐｅａｋ and the peak value of the input voltage from the AC power supply 110 that supplies AC power is V ａｃ＿ｐｅａｋ and the maximum output power of the power supply unit 100 is P ｍａｘ and the DC voltage applied to the smoothing unit 200 connected in parallel to the rectifying / boosting unit is V ｒｅｆ Let a １ Let a be the first coefficient of a defined positive real number, and a ２ is a specified positive real second coefficient, the capacity L of the reactor 120 is expressed as ΔI ｐｅａｋ , V ａｃ＿ｐｅａｋ , P ｍａｘ , V ｒｅｆ , a １ , and a ２ Specifically, the capacity L of the reactor 120 satisfies the above-described formula (3).

[0029] As a result, even if the power conversion device 1 unintentionally switches from PWM driving to non-PWM driving, by using the capacity L of the reactor 120 that satisfies formula (3), it is possible to prevent damage to the elements of the power supply unit 100. Note that even if the power conversion device 1 intentionally switches from PWM driving to non-PWM driving, by using the capacity L of the reactor 120 that satisfies formula (3), it is possible to prevent damage to the elements of the power supply unit 100.

[0030] Next, the capacity L of the reactor 120 will be described taking into consideration the non-PWM drive mode while using the maximum rated current squared time product γ. As mentioned above, when it is desired to reduce the size of the power supply unit 100 shown in Figures 2 to 4, the size of the reactor 120 generally accounts for a large proportion, and therefore, a significant effect can be achieved if the reactor 120 can be reduced in size. In order to reduce the size of the reactor 120, it is preferable to increase the drive frequency of the switching element provided in the rectifying / boosting unit, and it is common to operate the switching element by turning it on and off at a frequency of several hundred Hz to several hundred kHz, as in PWM drive.

[0031] However, when control power is supplied from the capacitor of the smoothing unit 200 to a control unit (not shown) that controls the on / off of the switching elements, the power conversion device 1 starts operating in non-PWM drive mode because power is not supplied to the control unit during startup, recovery from a sudden stop, or other such situations. In such cases, an inrush current flows through an LC circuit when charging the capacitor of the smoothing unit 200. The inrush current flows through diodes 131 to 134 of the rectifier unit 130 that constitute the power supply unit 100, diodes connected in parallel to the switching elements 151 to 154 if the switching elements 151 to 154 of the rectifier boost unit 150 are IGBTs, and diodes connected in parallel to the switching elements 161 to 166 if the switching elements 161 to 166 of the rectifier boost unit 160 are IGBTs.

[0032] The current limit of these elements is the maximum rated current squared time product γ [A ２ When the capacity L of the reactor 120 is derived from the relationship between the circuit constant and the maximum rated current squared time product γ, the equation (4) is obtained.

[0033]

[0034] In equation (4), γ is the squared time product of the maximum rated current based on the current flowing through the power supply unit 100 during non-PWM driving, L is the capacity of the reactor 120, C is the capacity of the capacitor that is the smoothing unit 200 connected in parallel to the rectifying / boosting unit, and P ｍ is the rated output power of the power supply unit 100, and V ａｃ is the input voltage from the AC power supply 110 that supplies AC power, and a is a derating constant. The derating constant a provides a margin for the maximum rated current squared time product γ. In reality, there is variation in the capacity L of the reactor 120, the capacity C of the capacitor, etc., and when taking into account the wiring and other parasitic capacitances, if a = 1, the capacity L of the reactor 120 will be set to the threshold value at which element damage occurs, increasing the risk of element damage. Therefore, by setting a = 0.7, damage to the element can be prevented.

[0035] In this way, in the power supply unit 100, the maximum rated current squared time product based on the current flowing through the power supply unit 100 during non-PWM driving is defined as γ, the capacitance of the capacitor that is the smoothing unit 200 connected in parallel to the rectifying / boosting unit is defined as C, and the rated output power of the power supply unit 100 is defined as P ｍ and the input voltage from the AC power supply 110 that supplies AC power is V ａｃ and the derating constant is a, the capacity L of the reactor 120 is calculated by γ, C, P ｍ , V ａｃ , and a. Specifically, the capacity L of the reactor 120 satisfies the formula (4).

[0036] As a result, by setting the capacity L of the reactor 120 to satisfy the formula (4), the power conversion device 1 can prevent damage to the elements of the power supply unit 100 even during non-PWM driving.

[0037] Next, the drive frequency f of the switching element provided in the power supply unit 100, taking into consideration the loss of the reactor 120, is calculated as follows: ｓｗAs described above, when miniaturizing the power supply unit 100 shown in Figs. 2 to 4, the reactor 120 generally accounts for a large proportion of the size, and therefore, if the reactor 120 can be miniaturized, a significant effect can be obtained. In order to miniaturize the reactor 120, the drive frequency f of the switching element provided in the rectifying / boosting unit is set to a value smaller than the drive frequency f of the switching element provided in the rectifying / boosting unit. ｓｗ It is preferable to increase the frequency of the switching element, and it is common to operate the switching element to turn on and off at a frequency ranging from several hundred Hz to several hundred kHz, as in PWM driving.

[0038] However, when miniaturizing reactor 120, reducing loss is important because, unless the loss density is reduced, the reactor 120 will exceed its allowable heat generation, resulting in damage. The losses in reactor 120 include iron loss P_fe and copper loss P_cu. Iron loss P_fe is loss generated in the core of reactor 120, and copper loss P_cu is loss generated in the windings of reactor 120. Iron loss P_fe is expressed by equation (5) from the Steinmetz equation.

[0039]

[0040] In formula (5), B ｍ is the maximum magnetic flux density of the reactor 120, and f ｓｗ is the driving frequency of the switching element, and k １ , a, b are constants. In general core materials, a>b. B ｍ is expressed by equation (6) based on the relationship between the capacity L of the reactor 120 and the current ripple width.

[0041]

[0042] In formula (6), B ｍ is the maximum magnetic flux density of the reactor 120, L is the capacity of the reactor 120, Δi is the current ripple amplitude in the reactor 120, N is the number of turns of the winding of the reactor 120, and A ｅ is the cross-sectional area of ​​the reactor 120. From the formulas (5) and (6), the iron loss P_fe of the reactor 120 is expressed as ｓｗIt can be seen that the sensitivity to the current ripple width Δi is higher than that of the case where the copper loss P_cu is expressed by the equation (7) using the effective current value and the resistance value of the winding.

[0043]

[0044] In formula (7), R ｄｃ is the DC component of the winding resistance of the reactor 120, and I ｄｃ is the DC component of the current flowing through the reactor 120, and R ａｃ＿ｆ is the AC component of the winding resistance of the reactor 120, and I ａｃ is the AC component of the current flowing through the reactor 120.

[0045] 7 is a diagram showing an example of the current waveform of the reactor current flowing through the reactor 120 of the power conversion device 1 according to the first embodiment and an example of the result of FFT analysis of the reactor current. In FIG. 7, the upper diagram shows the current waveform of the reactor current flowing through the reactor 120, with the horizontal axis representing time and the vertical axis representing current. Also, in FIG. 7, the lower diagram shows the result of FFT analysis of the current waveform of the reactor 120 shown in the upper diagram, with the horizontal axis representing frequency and the vertical axis representing current. R ｄｃ corresponds to the DC component of the winding resistance shown in FIG. 7, and I ｄｃ corresponds to the system frequency component of the current FFT shown in FIG. 7, and R ａｃ＿ｆ corresponds to the AC component of the winding resistance shown in FIG. ａｃ corresponds to the carrier frequency component of the current FFT shown in Fig. 7. As shown in the lower diagram of Fig. 7, when the switching element is PWM driven, the frequency components of the current flowing through the reactor 120 are mainly the system frequency component and the carrier frequency component. The system frequency component is based on the AC voltage supplied from the AC power supply 110, and is calculated from the DC component of the winding resistance of the reactor 120. The carrier frequency component is based on the carrier signal used when the switching element is PWM driven, and is calculated from the AC component of the winding resistance of the reactor 120. The AC component of the current I ａｃ Since the main component is a triangular waveform ripple component, it can be expressed by equation (8).

[0046]

[0047] From the equations (7) and (8), the copper loss P_cu of the reactor 120 also varies with the drive frequency f of the switching element, similarly to the iron loss P_fe of the reactor 120. ｓｗ It can be seen that the sensitivity to the current ripple width Δi is higher than that of the switching element. ｓｗ The relation between these is shown in equation (9).

[0048]

[0049] In equation (9), Δi ｆｎ is the nth driving frequency f ｓｗｎ is the current ripple width in the reactor 120 during PWM drive, and V Ｌ is the applied voltage of the reactor 120, D is the duty ratio when the switching element is PWM driven, and L is the capacity of the reactor 120. From the viewpoint of the loss of the reactor 120, it is possible to calculate the driving frequency f of the switching element from the equation (9). ｓｗ However, the higher the driving frequency of the switching element, f ｓｗ The increase in the current ripple width Δi and the driving frequency f of the switching element leads to an increase in the loss of the switching element. ｓｗ It is known that the relationship between the drive frequency f of the switching element of the power supply unit 100 included in the power conversion device 1 according to the first embodiment is inversely proportional as shown in FIG. ｓｗ 8 is a diagram showing an example of the relationship between the drive frequency f of the switching element and the current ripple width Δi of the reactor 120. In FIG. ｓｗ 8, the vertical axis represents the current ripple width Δi of the reactor 120. As shown in FIG. ｓｗ Increasing the drive frequency f reduces the sensitivity to the current ripple width Δi. ｓｗ It is important to drive the power conversion device 1 with the drive frequency f ｓｗ Δi represents the ratio of the change in the current ripple width Δi to the change in the current ripple width Δi.

[0050]

[0051] In equation (10), Δiｆ１ is the first driving frequency f ｓｗ１ is the current ripple width at ｆ２ is the first driving frequency f ｓｗ１ A second driving frequency f that is one higher than ｓｗ２ X [%] is the current ripple width at the driving frequency f of the switching element. ｓｗ ga f ｓｗ１ From f ｓｗ２ This is the ratio of the change in the current ripple width Δi when the driving frequency f of the switching element is changed to Δi. Experimentally, if the ratio shown by X*100 on the left side of the formula (10) is 10% or less, there is no significant change in the loss of the reactor 120. ｓｗ By determining the above, it is possible to operate the power conversion device 1 at an optimum point for the loss increase of the switching elements and the loss reduction effect of the reactor 120.

[0052] In this way, in the power conversion device 1, the nth drive frequency when the switching element is PWM driven is set to f where n is a positive integer. ｓｗｎ and the applied voltage of the reactor 120 is V Ｌ When the duty ratio of the switching element during PWM drive is D and the capacity of the reactor 120 is L, the switching element operates at the n-th drive frequency f ｓｗｎ The current ripple width Δi in the reactor 120 during PWM driving is ｆｎ is calculated by the formula (9). In the power conversion device 1, the driving frequency f of the switching element is ｓｗ is the first driving frequency f ｓｗ１ to the second drive frequency f ｓｗ２ When the ratio X of the change in the current ripple width Δi in the reactor 120 when the voltage Vcc is changed to Δi is calculated from the equation (10), the driving frequency f during PWM driving of the switching element is set so that X falls within a specified range. ｓｗ For example, as described above, the driving frequency f during PWM driving of the switching element is set so that the ratio indicated by X*100 is 10% or less. ｓｗ is set.

[0053] As a result, in the power conversion device 1, the driving frequency f during PWM driving of the switching elements is set to satisfy the formulas (9) and (10).ｓｗ The lower limit is set.

[0054] In the power conversion device 1, the driving frequency f during PWM driving of the switching elements is set so that the iron loss P_fe is larger than the copper loss P_cu in the loss occurring in the reactor 120. ｓｗ is set. Generally, the core loss of the electromagnetic steel sheet core used in the reactor 120 is lower as the temperature increases, so it is possible to suppress the increase in loss based on such temperature characteristics. When eddy currents are included in the iron loss, the ripple width is approximately equal to the driving frequency of the switching element. Furthermore, copper loss is calculated as follows: I ２ The ripple width becomes dominant from the calculation formula for R. That is, the higher the drive frequency of the switching element, the larger the iron loss P_fe becomes compared to the copper loss P_cu.

[0055] Next, the driving frequency f of the switching element provided in the power supply unit 100 is calculated by taking into consideration the magnetic characteristics of the reactor 120. ｓｗ As described above, when miniaturizing the power supply unit 100 shown in Figs. 2 to 4, the reactor 120 generally accounts for a large proportion of the size, and therefore, if the reactor 120 can be miniaturized, a significant effect can be obtained. In order to miniaturize the reactor 120, the drive frequency f of the switching element provided in the rectifying / boosting unit is set to 1 / f. ｓｗ It is preferable to increase the frequency of the switching element, and it is common to operate the switching element to turn on and off at a frequency ranging from several hundred Hz to several hundred kHz, as in PWM driving.

[0056] However, when miniaturizing the reactor 120, if the loss density is not reduced, the reactor 120 will exceed its allowable heat generation, resulting in damage, so reducing the loss is important. Here, when the core material of the reactor 120 is made of non-oriented electromagnetic steel sheet material, which is made by stacking thin steel sheets, the driving frequency f of the switching element is ｓｗ When the driving frequency f of the switching element becomes high, high frequency magnetic flux is generated in each steel plate, causing the skin effect. The skin effect is a phenomenon in which when magnetic flux is generated in a conductor, the density of the magnetic flux is high on the surface of the conductor and decreases as it goes from the surface to the inside. ｓｗThe higher the skin depth t, the more the magnetic flux concentrates on the surface, and the higher the AC resistance of the conductor. This skin depth t is expressed by equation (11).

[0057]

[0058] In equation (11), ρ is the resistivity of the steel sheet, μ is the magnetic permeability of the steel sheet, and f ｓｗ is the driving frequency of the switching element. If the skin depth is small relative to the thickness of the steel plate, only the skin depth portion of the thickness of the steel plate is effectively utilized. Therefore, the AC resistance component increases, and the iron loss P_fe increases. Furthermore, if the skin depth is extremely small, a magnetic path cannot be formed, and the reactor 120 enters an air-core state. In this state, the reactor 120 cannot have the desired magnetic characteristics, and the power conversion device 1 will malfunction. From the above, in the power conversion device 1, it is necessary to set the driving frequency f of the switching element so that the skin depth is large relative to the thickness of the steel plate. ｓｗ It is necessary to set the equation (11) to the driving frequency f of the switching element. ｓｗ This is transformed into equation (12).

[0059]

[0060] In this way, in the power conversion device 1, when the resistivity of the core of the reactor 120 is ρ, the magnetic permeability of the core of the reactor 120 is μ, and when a non-oriented electromagnetic steel sheet is used for the core of the reactor 120, the thickness of the non-oriented electromagnetic steel sheet is t, the driving frequency f during PWM driving of the switching element is ｓｗ is set to satisfy equation (12).

[0061] As a result, in the power conversion device 1, the driving frequency f during PWM driving of the switching elements is set to satisfy the formula (12). ｓｗ An upper limit is set.

[0062] Here, a specific calculation example is shown. The core material of the reactor 120 is 0.35 mm thick and has a resistivity of 57*10 －８A non-oriented electrical steel sheet with a magnetic permeability of Ω·m is used. The magnetic permeability varies depending on the size of the air gap provided in the reactor 120, but for high frequency reactor applications, it is approximately 50 to 100. When formula (12) is calculated under the above conditions, formula (13) is obtained. From the result of formula (13), the driving frequency f of the switching element is calculated. ｓｗ Therefore, operation at approximately 10 kHz is appropriate. ｓｗ The driving frequency f ｓｗ This is because, in this case, the loss of the reactor 120 increases, and it may not be possible to tolerate the heat generation density resulting from the miniaturization of the reactor 120 .

[0063]

[0064] As described above, according to this embodiment, the power conversion device 1 includes, as the power supply unit 100, a rectifying / boosting unit having a PWM-driveable switching element, and a reactor 120. In the power conversion device 1, the capacity L of the reactor 120 is set based on the reactor peak current flowing in the reactor 120 and the power factor of the power conversion device 1 during non-PWM drive in which a current flows through a diode connected in parallel to the switching element. In addition, in the power conversion device 1, the drive frequency f of the switching element provided in the rectifying / boosting unit is set based on the drive frequency f of the switching element. ｓｗ is set based on the magnetic characteristics of the reactor 120. This allows the power conversion device 1 to prevent damage to elements used in power conversion when the PWM-drivable switching elements are not PWM-driven.

[0065] Second Embodiment In a second embodiment, a description will be given of constraints on the structure of the reactor 120. In the second embodiment, the configuration of the power conversion device 1 is the same as the configuration of the power conversion device 1 shown in Figs. 1 to 4 .

[0066] 9 is a first diagram schematically illustrating the structure of the reactor 120 used in the power conversion device 1 according to the second embodiment. As described in the first embodiment, the drive frequency f of the switching element is required to reduce the size of the power conversion device 1. ｓｗ However, the driving frequency f of the switching element is ｓｗIn order to improve the trade-off relationship between loss and heat generation, a structure of reactor 120 that can suppress loss and heat generation in core 401 of reactor 120 will be described in the second embodiment.

[0067] As shown in FIG. 9 , the reactor 120 has a three-leg core 401, which may be, for example, an EE core or an EI core. The reactor 120 has a shell-type structure in which the winding 402 is arranged in the central leg and the core 401 surrounds the winding 402. The reactor 120 also has a core 401 whose aspect ratio increases in the order of a < b < c. Generally, when the window of the core 401 faces the front, a represents the height, b represents the width, and c represents the depth. By configuring the reactor 120 as shown in FIG. 9 , it is possible to achieve lower loss and improved heat dissipation compared to reactors 120 of the same volume. In other words, by configuring the reactor 120 as shown in FIG. 9 , it is possible to reduce the size of the reactor 120 when the effective cross-sectional area and the number of turns of the winding 402 are the same. By configuring reactor 120 to have the lowest height, that is, to be smallest, reactor 120 can efficiently release heat from the center of core 401, which is the most difficult place to release heat.

[0068] Furthermore, as shown in FIG. 10 , by mounting a heat sink 403 on the core 401, it is possible to increase the heat dissipation area, thereby improving the heat dissipation performance of the reactor 120. FIG. 10 is a second diagram schematically illustrating the structure of the reactor 120 used in the power conversion device 1 according to the second embodiment. The reactor 120 shown in FIG. 10 is obtained by mounting a heat sink 403 on the core 401 of the reactor 120 shown in FIG. 9 . The heat sink 403 is a metal plate and serves as a base for the core 401. As shown in FIGS. 9 and 10 , the reason for shaping the core 401 of the reactor 120 in the order of width < depth is to reduce the volume of the core 401 for the same effective cross-sectional area. If the width is increased to obtain the same effective cross-sectional area, the outer legs of the core 401 must be expanded outward to maintain the same space factor of the winding 402, which increases the total volume of the core 401.

[0069] Fig. 11 is a comparative example showing the difference in volume when the effective cross-sectional area is the same for reactors of the same height, with width < depth and width > depth. Considering the same winding space factor, the core outer frame becomes larger, so as shown in Fig. 11, a reactor with width < depth can be configured to be more compact and with lower loss.

[0070] As described above, in the power conversion device 1, the reactor 120 has a three-legged core 401, the winding 402 is located on the central leg of the core 401, the core 401 is located so as to surround the winding 402, and the aspect ratio of the core 401 when the core window faces forward is such that the width is greater than the height, and the depth is greater than the width. Furthermore, the core 401 of the reactor 120 is in contact with the heat sink 403, i.e., a metal plate serving as a base, and the metal plate is in contact with a product to which the power conversion device 1 is applied. An example of a product to which the power conversion device 1 is applied is an air conditioner. By arranging the heat sink 403, which is a metal plate, so that it is in contact with the cover of the housing of the air conditioner, the reactor 120 can further improve its heat dissipation effect.

[0071] Third Embodiment. Fig. 12 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to a third embodiment. The refrigeration cycle-applied device 900 according to the third embodiment includes the power conversion device 1 described in the first embodiment. The refrigeration cycle-applied device 900 according to the third embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 12, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment. In Fig. 1 and other figures, the load unit 300 included in the power conversion device 1 is considered to include a motor. However, in Fig. 12, the motor 916 is located outside the power conversion device 1 due to the configuration in which the motor 916 is included in the compressor 914.

[0072] The refrigeration cycle applied device 900 includes a compressor 914 , a four-way valve 902 , an indoor heat exchanger 906 , an expansion valve 908 , and an outdoor heat exchanger 910 attached via refrigerant piping 912 .

[0073] Inside the compressor 914, a compression mechanism 904 that compresses the refrigerant and a motor 916 that operates the compression mechanism 904 are provided.

[0074] The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by a motor 916 that is variably controlled in speed.

[0075] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, passes through the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910 and the four-way valve 902 and returns to the compression mechanism 904.

[0076] During cooling operation, as shown by the dashed arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, and returns to the compression mechanism 904 through the four-way valve 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906 and the four-way valve 902.

[0077] During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant to expand it.

[0078] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0079] 1 Power conversion device, 100 Power supply unit, 110 AC power supply, 120, 141 Reactor, 130 Rectification unit, 131 to 134, 143 Diode, 140 Boost unit, 142, 151 to 154, 161 to 166 Switching elements, 150, 160, 170 Rectification boost unit, 200 Smoothing unit, 300 Load unit, 401 Core, 402 Winding, 403 Heat sink, 900 Refrigeration cycle application equipment, 902 Four-way valve, 904 Compression mechanism, 906 Indoor heat exchanger, 908 Expansion valve, 910 Outdoor heat exchanger, 912 Refrigerant piping, 914 Compressor, 916 Motor.

Claims

1. a rectifying / boosting unit that has a switching element capable of being driven by pulse width modulation and converts AC power into DC power; a reactor disposed between an AC power supply that supplies the AC power and a smoothing unit that smooths the DC power; a power supply unit comprising: Equipped with a capacity of the reactor is set based on a reactor peak current flowing through the reactor and a power factor of the power supply unit during non-pulse width modulation driving in which a current flows through a diode connected in parallel to the switching element; The drive frequency of the switching element is set based on the magnetic characteristics of the reactor. Power conversion device.

2. The amount of change between the reactor current peak value when driven with Pulse Width Modulation and the reactor current peak value when driven without Pulse Width Modulation under the same operating conditions is defined as ΔI ｐｅａｋ The peak value of the input voltage from the AC power supply is V ａｃ＿ｐｅａｋ and the maximum output power of the power supply unit is P ｍａｘ and the DC voltage applied to the smoothing section is V ｒｅｆ Let a １ Let a be the first coefficient of a defined positive real number, and a ２ is a specified positive real second coefficient, the capacity L of the reactor is ｐｅａｋ , the V ａｃ＿ｐｅａｋ , the P ｍａｘ , the V ｒｅｆ , the a １ and the a ２ is set using The power conversion device according to claim 1 .

3. The capacity L of the reactor satisfies the following formula: The power conversion device according to claim 2 . [Equation 1]

4. The maximum rated current squared time product based on the current flowing in the power supply unit during non-Pulse Width Modulation driving is γ, the capacitance of the smoothing unit is C, and the rated output power of the power supply unit is P. ｍ and the input voltage from the AC power supply is V ａｃ and the derating constant is a, the capacity L of the reactor is ｍ , the V ａｃ , and is set using the a The power conversion device according to claim 1 .

5. The capacity L of the reactor satisfies the following formula: The power conversion device according to claim 4. [Equation 2]

6. The nth driving frequency when the switching element is driven by Pulse Width Modulation is defined as f ｓｗｎ and the applied voltage of the reactor is V Ｌ When the switching element is driven by Pulse Width Modulation at the drive frequency n, the duty ratio is D and the capacity of the reactor is L, and the current ripple width Δi in the reactor when the switching element is driven by Pulse Width Modulation at the drive frequency n is ｆｎ is calculated using the following formula: When the drive frequency of the switching element is changed from a first drive frequency to a second drive frequency, a ratio X of a change in current ripple width in the reactor is calculated from the following formula, and the drive frequency during Pulse Width Modulation drive of the switching element is set so that the ratio X falls within a specified range. The power conversion device according to claim 1 . [Equation 3] [Equation 4]

7. When the resistivity of the core of the reactor is ρ, the magnetic permeability of the core of the reactor is μ, and when a non-oriented electromagnetic steel sheet is used for the core of the reactor, the thickness of the non-oriented electromagnetic steel sheet is t, the drive frequency during Pulse Width Modulation drive of the switching element is set to satisfy the following formula: The power conversion device according to claim 1 . [Equation 5]

8. The reactor has a three-legged core shape, a winding is present on the central leg of the core, the core is present so as to surround the winding, and the aspect ratio of the core when the core window is facing forward is such that the width is greater than the height and the depth is greater than the width. The power conversion device according to claim 1 .

9. The core of the reactor is in contact with a metal plate serving as a base, and the metal plate is in contact with a product to which the power conversion device is applied. The power conversion device according to claim 8.

10. a drive frequency during Pulse Width Modulation driving of the switching element is set so that iron loss is larger than copper loss in the loss generated in the reactor; The power conversion device according to claim 1 .

11. A refrigeration cycle device comprising the power conversion device according to any one of claims 1 to 10.

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