Power conversion device, motor drive device, and refrigeration cycle application apparatus

Abstract

This power conversion device (1) comprises a single-switch boost-type AC / DC converter (220) having a rectifier circuit (130) and a single-switch boost-type circuit (140). The single-switch boost-type circuit (140) comprises a reactor (141) and a switching element (142). The switching element (142) operates by varying the switching frequency. In the single-switch boost-type AC / DC converter (220), when the conversion efficiency is η, the AC-side input power factor is λ, the effective value of the AC-side input voltage is VinRMS, the DC-side output voltage is Vout, the DC-side output power is Pout, the inductance of the reactor (141) is L, the current ripple rate, which is the ratio of the maximum value of the pulsation width of the reactor current flowing in the reactor (141) to √(2) times the effective value of the input current from the AC power supply (110), is α, and the switching frequency of the switching element (142) is fsw, the upper limit value or the lower limit value of the switching frequency fsw is defined by an expression using said values.

Description

Power conversion devices, motor drive devices, and refrigeration cycle application equipment

[0001] The present disclosure relates to a power conversion device that performs power conversion, a motor drive device, and a refrigeration cycle application device.

[0002] Conventionally, some power conversion devices include an AC (Alternating Current)-DC (Direct Current) converter that converts AC power into DC power, i.e., an AC-DC converter. For example, Patent Document 1 discloses a technology for a power conversion device that includes a single-transistor step-up AC-DC converter and is capable of reducing losses by varying the switching frequency.

[0003] Patent No. 7109688

[0004] Converter operating modes include a continuous current mode, in which current flows continuously through the reactor; a discontinuous current mode, in which a period of time when no current flows through the reactor occurs; and a critical current mode, which is an operating mode between the continuous current mode and the discontinuous current mode and in which a momentary state of no current flows through the reactor. However, because the circuit response differs between the continuous current mode and the discontinuous current mode, operating in only one of these operating modes contributes to improved control stability. Furthermore, the ripple factor of the reactor current relative to the AC current of AC power also differs between the continuous current mode and the discontinuous current mode. However, while the above-mentioned conventional technology considers reducing losses in a power conversion device by varying the switching frequency, it does not consider the controllability of the power conversion device or the ripple factor of the reactor current. Therefore, in order to perform control that takes into account control stability, the ripple factor of the reactor current, and other characteristics, it is necessary to define the switching frequency range of the switching element used in a single-transistor boost AC / DC converter, taking into account characteristics such as control stability and the ripple factor of the reactor current.

[0005] The present disclosure has been made in view of the above, and aims to provide a power conversion device that is capable of variable control of the switching frequency of a switching element in consideration of at least one of control stability and the ripple rate of the reactor current when variable control of the switching frequency is performed to reduce losses in a configuration including a single-transistor boost AC / DC converter.

[0006] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a single-transistor boost AC / DC converter having a rectifier circuit that rectifies AC voltage supplied from an AC power source and outputs DC voltage, and a single-transistor boost circuit that boosts the DC voltage. The single-transistor boost circuit includes a reactor and a switching element, and the switching element operates by varying the switching frequency. Let η be the conversion efficiency of the single-transistor boost AC / DC converter, λ be the AC-side input power factor of the single-transistor boost AC / DC converter, and V be the effective value of the AC-side input voltage of the single-transistor boost AC / DC converter. ｉｎＲＭＳ The DC output voltage of the single-transistor boost AC / DC converter is V ｏｕｔ The DC output power of the single-transistor boost AC / DC converter is P ｏｕｔ The inductance of the reactor is L, the current ripple factor is the ratio of the maximum value of the pulsation width of the reactor current flowing through the reactor to √(2) times the effective value of the input current from the AC power supply, and the switching frequency of the switching element is f ｓｗ Then, the switching frequency of the switching element is f ｓｗ The upper and lower limits are defined by the formulas using these.

[0007] The power conversion device according to the present disclosure has an advantage that, in a configuration including a single-transistor step-up AC / DC converter, when variable control of the switching frequency is performed to reduce losses, variable control of the switching frequency of the switching element is possible while taking into consideration at least one of the control stability and the ripple rate of the reactor current.

[0008] FIG. 1 is a diagram showing an example of the configuration of a power conversion device according to embodiment 1. FIG. 2 is a diagram showing an example of the operating state of a current continuous mode in a general AC-DC converter. FIG. 3 is a diagram showing an example of the operating state of a current critical mode in a general AC-DC converter. FIG. 4 is a diagram showing an example of the operating state of a current discontinuous mode in a general AC-DC converter. FIG. 5 is a diagram showing the definition of a current ripple factor, which indicates the ratio of the maximum value of the pulsation amplitude of the reactor current flowing through the reactor to √(2) times the effective value of the input current from an AC power source to the power conversion device. FIG. 6 is a diagram showing an example of the control state of the switching frequency of the switching element in the power conversion device according to embodiment 1. FIG. 7 is a diagram showing an example of the hardware configuration realizing a control unit provided in the power conversion device according to embodiment 1. FIG. 8 is a diagram showing an example of the configuration of a refrigeration cycle application device according to embodiment 2.

[0009] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle applied device according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] First Embodiment. Fig. 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 is connected to an AC power supply 110 and a motor 314. The power conversion device 1 converts a first AC voltage, which is a power supply voltage Vs supplied from the AC power supply 110, such as a commercial power supply, into a second AC voltage having a desired amplitude and phase, and supplies the second AC voltage to the motor 314. In the example of Fig. 1, the AC power supply 110 is a single-phase AC power supply, but may be a three-phase AC power supply. The power conversion device 1 includes a single-transistor step-up AC / DC converter 220, an inverter 310, and a control unit 400. The power conversion device 1 and the motor 314 constitute a motor drive device 2.

[0011] The single-transistor step-up AC / DC converter 220 is a power converter that converts the AC voltage of the power supply voltage Vs supplied from the AC power supply 110 into a DC voltage. The single-transistor step-up AC / DC converter 220 includes a rectifier circuit 130, a single-transistor step-up circuit 140, and a capacitor 210.

[0012] The rectifier circuit 130 rectifies a first AC voltage of the power supply voltage Vs supplied from the AC power supply 110 and outputs a DC voltage. When the AC power supply 110 is a single-phase AC power supply as shown in FIG. 1 , the rectifier circuit 130 is a bridge circuit configured with four rectifier elements.

[0013] The single-transistor boost circuit 140 boosts and outputs the DC voltage rectified by the rectifier circuit 130. The single-transistor boost circuit 140 includes a reactor 141, a switching element 142, a freewheeling diode 143, and a diode 144. The switching element 142 is turned on and off under the control of the control unit 400. The switching element 142 can operate by varying its switching frequency under the control of the control unit 400. That is, the switching element 142 operates by varying its switching frequency under the control of the control unit 400. The switching element 142 may be, for example, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), a bipolar transistor, or the like, but is not limited to these. In the following description, the DC voltage rectified by the rectifier circuit 130, boosted by the single-transistor boost circuit 140, and output to the capacitor 210 may be referred to as a first DC voltage.

[0014] The capacitor 210 is connected in parallel to the output terminal of the single-transistor boost circuit 140 and smoothes the first DC voltage into a second DC voltage. The capacitor 210 is, for example, an electrolytic capacitor or a film capacitor.

[0015] The inverter 310 is a power converter connected in parallel across the capacitor 210. The inverter 310 includes, for example, six switching elements and six freewheeling diodes (not shown), and turns on and off the switching elements under the control of the control unit 400 to convert the DC voltage output from the single-transistor boost AC-DC converter 220 into a second AC voltage having a desired amplitude and phase, i.e., generates the second AC voltage, and outputs it to the motor 314. The switching elements included in the inverter 310 include, for example, IGBTs, MOSFETs, bipolar transistors, etc., but are not limited to these. The circuit configuration of the inverter 310 is not particularly limited, and may be a full-bridge circuit, a single-phase bridge circuit, a half-bridge circuit, or the like.

[0016] The control unit 400 performs control calculations to control the on / off of the switching element 142 included in the single-transistor boost AC / DC converter 220 and the switching element included in the inverter 310. Although not shown in the example of FIG. 1 , the control unit 400 controls the on / off of the switching element 142 and the switching elements included in the inverter 310, for example, using a detection result from a voltage detection unit that detects the voltage across the capacitor 210, i.e., the DC bus voltage Vdc, which is the second DC voltage. Note that the control unit 400 can control the on / off of the switching element 142 and the switching elements included in the inverter 310 using one or more physical quantities that indicate the operating state of the power conversion device 1, such as the AC current supplied from the AC power supply 110 and the AC current supplied from the inverter 310 to the motor 314.

[0017] The motor 314 is a load connected to the power conversion device 1. The motor 314 is, for example, a compressor motor for driving a compressor. The motor 314 rotates in accordance with the amplitude and phase of the second AC voltage supplied from the inverter 310 to perform a compression operation. For example, when the compressor is a hermetic compressor, the load torque of the motor 314 that drives the compressor can often be considered a constant torque load. The motor 314 may have a Y-connection or a Δ-connection, or may have a motor winding (not shown) that is switchable between the Y-connection and the Δ-connection. Furthermore, the load connected to the power conversion device 1, i.e., the inverter 310, is not limited to the compressor-driving motor 314, but may also be a fan motor or the like.

[0018] Here, the operation modes of a general AC-DC converter will be described. An AC-DC converter has three operation modes: a continuous current mode in which the reactor current flows continuously, a critical current mode in which a state in which the reactor current does not flow occurs for an instant, and a discontinuous current mode in which a period in which the reactor current does not flow occurs. Fig. 2 is a diagram showing an example of an operation state in the continuous current mode of a general AC-DC converter. Fig. 3 is a diagram showing an example of an operation state in the critical current mode of a general AC-DC converter. Fig. 4 is a diagram showing an example of an operation state in the discontinuous current mode of a general AC-DC converter. Fig. 5 is a diagram showing an example of an input current I from the AC power source 110 to the power conversion device 1. ｉｎ The reactor current I flowing through the reactor 141 for √(2) times the effective value of Ｌ 10 is a diagram showing the definition of a current ripple factor α, which indicates the ratio of the maximum value of the pulsation amplitude of the current.

[0019] 2 to 4, the input current I from the AC power supply 110 to the power conversion device 1 has a slower change period. ｉｎ The faster the period of change, the greater the reactor current I Ｌ The reactor current I of the reactor 141 is Ｌ The period of change of the input current I from the AC power supply 110 to the power conversion device 1 changes depending on the switching frequency of the switching element 142. ｉｎ The maximum value of √(2)・I ｉｎＲＭＳand the reactor current I flowing through the reactor 141 Ｌ The maximum value of the pulsation width is I ＬＲＩＰＰＬＥ Then, as shown in FIG. 5, the current ripple factor α is expressed as "α = I ＬＲＩＰＰＬＥ / √(2)・I ｉｎＲＭＳ That is, the current ripple factor α is defined as follows: ｉｎ The reactor current I flowing through the reactor 141 for √(2) times the effective value of Ｌ For convenience of notation in this specification, the square root of 2 is represented as √(2). The same applies hereinafter.

[0020] As shown in FIGS. 2 to 4, the reactor current I Ｌ If the period of change of current is slow, i.e., if the switching frequency of the switching element 142 is low, the power conversion device 1 will enter the discontinuous current mode. Since the circuit response differs between the continuous current mode and the discontinuous current mode, operation in only one of the operation modes in the power conversion device 1 leads to improved control stability. Since the current ripple factor α deteriorates in the discontinuous current mode, in this embodiment, the switching frequency of the switching element 142 is defined so that the power conversion device 1 can maintain operation in the continuous current mode or the critical current mode.

[0021] Specifically, a description will be given of how to determine the switching frequency of the switching element 142. In a typical AC-DC converter, the switching duty of the switching element 142 is expressed by equation (1).

[0022]

[0023] In formula (1), V ｏｕｔ is the DC side output voltage of the single-transistor step-up AC / DC converter 220, and the instantaneous value of the input voltage is the input voltage V ｉｎ In the single-transistor boost AC / DC converter 220, the switching duty of the switching element 142 is ｉｎ Since the minimum value is reached near the peak of ｍｉｎ is expressed as in equation (2).

[0024]

[0025] In formula (2), V ｉｎＲＭＳ is the effective value of the AC side input voltage of the single-transistor boost AC / DC converter 220. At this time, the ON time of the switching of the switching element 142, that is, the minimum ON time T ｏｎ＿ｍｉｎ is expressed as in equation (3).

[0026]

[0027] In formula (3), f ｓｗ is the switching frequency of the switching element 142. ｏｎ＿ｍｉｎ The current flowing through the reactor 141 defined in FIG. 5 is the reactor current I Ｌ The primary current not including the ripple due to the reactor 141, i.e., the input current I from the AC power supply 110, ｉｎ is the input voltage V from the AC power supply 110 ｉｎ Near the peak, the relationship between current and voltage is expressed as in equation (4).

[0028]

[0029] In formula (4), I ｉｎＰＥＡＫ is the input current I from the AC power supply 110 ｉｎ is the peak value of I ｉｎＲＭＳ is the input current I from the AC power supply 110 ｉｎ is the effective value of P ｏｕｔ is the DC side output power of the single-transistor boost AC / DC converter 220, η is the conversion efficiency of the single-transistor boost AC / DC converter 220, λ is the AC side input power factor of the single-transistor boost AC / DC converter 220, and V ｉｎＲＭＳ is the effective value of the AC side input voltage of the single-transistor boost AC / DC converter 220. Equation (4) is a modified version of the general equation "output power = input voltage effective value x input current effective value x power factor x efficiency" and applies the relationship between the peak value and the effective value. Input voltage V ｉｎ The input voltage V from the AC power supply 110, which is the primary current, is near the peak of ｉｎ Reactor current I ＬAs described above, the ratio of the current ripple factor α is obtained by the equation v=L×di / dt of the reactor 141, and the ripple amount in one switching of the switching element 142, that is, α×I ｉｎＰＥＡＫ Since a current of this magnitude flows, if the inductance of the reactor 141 is L, then equation (5) is obtained.

[0030]

[0031] Equation (5) is used to calculate the switching frequency f ｓｗ Solving this gives us equation (6).

[0032]

[0033] As described above, in the present embodiment, the power conversion device 1 is configured to operate at a switching frequency f ｓｗ The switching element 142 is switched within the range where the upper or lower limit of is defined by the formula (6).

[0034] Specifically, from Figures 2, 3, and 5, in the critical current mode, the current ripple factor α is 2. Also, in the continuous current mode, the current ripple factor α is smaller than the current ripple factor α=2 in the critical current mode. Therefore, the reactor current I Ｌ The current flowing continuously is the continuous current mode or the reactor current I Ｌ In order to maintain the current critical mode, which occurs for a moment when no current flows, the DC side output power P ｏｕｔ The minimum value of P ｏｕｔ＿ｍｉｎ and the current ripple factor α=2, the switching frequency f ｓｗ The lower limit value f ｓｗ＿ｍｉｎ is defined by equation (7).

[0035]

[0036] The power conversion device 1 is configured to set the switching frequency f of the switching element 142 included in the single-transistor boost circuit 140 of the single-transistor boost AC / DC converter 220 within the range defined by the formula (7). ｓｗBy controlling the current, the continuous current mode or critical current mode can be maintained, and stable control can be performed.

[0037] 2 and 5, when the current ripple factor α is set to 50% in the continuous current mode, the current ripple factor α becomes 0.5. Therefore, the reactor current I Ｌ The reactor current I Ｌ In order to maintain the current ripple rate at 50% or less, the DC side output power P ｏｕｔ The minimum value of P ｏｕｔ＿ｍｉｎ and the current ripple factor α=0.5, the switching frequency f ｓｗ The lower limit value f ｓｗ＿ｍｉｎ is defined by equation (8).

[0038]

[0039] The switching frequency f of the switching element 142 ｓｗ The theoretical lower limit of the capacity of the reactor 141 is defined by the formula (7), but the capacity of the reactor 141 may not be the expected capacity due to the influence of temperature dependency, current dependency, product variations, etc. If the capacity of the reactor 141 is different from the expected capacity, the switching frequency f of the switching element 142 may be lowered. ｓｗ If the switching frequency f of the switching element 142 is controlled in accordance with the formula (7), the operation mode of the single-transistor boost AC / DC converter 220 may become a discontinuous current mode, which may cause unstable control. ｓｗ The allowable range of "maintaining the current continuous mode and the reactor current I Ｌ This allows the power conversion device 1 to operate in the continuous current mode even when the operating environment changes.

[0040] 2 and 5, when the current ripple factor α is set to 10% in the continuous current mode, the current ripple factor α becomes 0.1. Therefore, the reactor current I Ｌ In order to maintain a current ripple rate of 10% or more, the DC side output power P ｏｕｔ The maximum value of Pｏｕｔ＿ｍａｘ and the current ripple factor α is set to 0.1, the switching frequency f ｓｗ Upper limit value f ｓｗ＿ｍａｘ is defined by equation (9).

[0041]

[0042] In the power conversion device 1, by increasing the carrier frequency by sequential frequency variable control, the loss of the reactor 141 can be reduced, but the loss of the switching element 142 increases, so there is no need to increase it excessively. ｓｗ Therefore, the switching frequency f of the switching element 142 is set so that the upper limit of the current ripple factor α when operating at maximum power is 10%. ｓｗ By setting an upper limit value for , it is possible to prevent an excessive increase in loss in the switching element 142.

[0043] In this embodiment, the control unit 400 sets a control frequency, which is the reciprocal of the calculation period for performing control calculation, as f ｃｏｎｔ and the control frequency f ｃｏｎｔ The maximum value of f ｃｏｎｔ＿ｍａｘ Then, f ｃｏｎｔ＿ｍａｘ ≧f ｓｗ In the case of control frequency f ｃｏｎｔ = f ｓｗ Control calculation is performed with f ｃｏｎｔ＿ｍａｘ <f ｓｗ In the case of control frequency f ｃｏｎｔ = f ｓｗ / n≦f ｃｏｎｔ＿ｍａｘ Find the smallest integer n that satisfies the control frequency f ｃｏｎｔ = f ｓｗ The control unit 400 may perform control calculations at a control frequency f ｃｏｎｔ and the switching frequency f of the switching element 142. ｓｗ It is best to set the duty cycle for each switching of the switching element 142 to be the same as the switching frequency f ｓｗ When the switching frequency f ｓｗTherefore, the control unit 400 can suppress the increase in the calculation load by, for example, setting n=2 in the above example, performing one calculation for every two switching of the switching element 142, and switching the switching element 142 twice based on the result of one calculation. ｃｏｎｔ The maximum value of f ｃｏｎｔ＿ｍａｘ and the maximum value f ｃｏｎｔ＿ｍａｘ In the above, by performing the calculation once every n times, the calculation load can be reduced.

[0044] In this embodiment, the power conversion device 1 controls the switching frequency f of the switching element 142 so that at least one of the magnetic flux density, the current ripple factor α, and the power loss of the reactor 141 is constant during a specified period including the time when the detected voltage of the AC power supply 110 is at its maximum. ｓｗ 6 is a graph showing the switching frequency f of the switching element 142 in the power conversion device 1 according to the first embodiment. ｓｗ 7 is a first diagram illustrating an example of a control state of the switching frequency f of the switching element 142 in the power conversion device 1 according to the first embodiment. ｓｗ 6 is a second diagram showing an example of the control state of the switching frequency f of the switching element 142. ｓｗ 7 shows the relationship between the switching frequency f of the switching element 142 and the magnetic flux density of the reactor 141. ｓｗ and the AC voltage and AC current supplied from the AC power supply 110. As a result, the power conversion device 1 can effectively reduce the loss of the reactor 141 while preventing an excessive increase in the loss of the switching element 142.

[0045] Next, a description will be given of the hardware configuration of the control unit 400 included in the power conversion device 1. Fig. 8 is a diagram showing an example of a hardware configuration that realizes the control unit 400 included in the power conversion device 1 according to embodiment 1. The control unit 400 is realized by a processor 91 and a memory 92.

[0046] The processor 91 is a CPU (Central Processing Unit, also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). Examples of memory 92 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable Programmable Read Only Memory). Memory 92 is not limited to these, and may also be a magnetic disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0047] As described above, according to this embodiment, the power conversion device 1 controls the switching frequency f ｓｗ The upper limit or lower limit of the switching frequency f of the switching element 142 is controlled within a range defined by a mathematical formula. ｓｗ It is possible to perform variable control of the above.

[0048] Second Embodiment Fig. 9 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to a second embodiment. The refrigeration cycle-applied device 900 according to the second embodiment includes the power conversion device 1 described in the first embodiment. The refrigeration cycle-applied device 900 according to the second embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 9, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0049] The refrigeration cycle application equipment 900 includes a compressor 315 incorporating the motor 314 in embodiment 1, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, which are attached via refrigerant piping 912.

[0050] Inside the compressor 315, a compression mechanism 904 that compresses the refrigerant and a motor 314 that operates the compression mechanism 904 are provided.

[0051] 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 314 that is variably controlled in speed.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 1 Power conversion device, 2 Motor drive device, 91 Processor, 92 Memory, 110 AC power supply, 130 Rectifier circuit, 140 Single-transistor boost circuit, 141 Reactor, 142 Switching element, 143 Freewheeling diode, 144 Diode, 210 Capacitor, 220 Single-transistor boost type AC / DC converter, 310 Inverter, 314 Motor, 315 Compressor, 400 Control unit, 900 Refrigeration cycle applicable equipment, 902 Four-way valve, 904 Compression mechanism, 906 Indoor heat exchanger, 908 Expansion valve, 910 Outdoor heat exchanger, 912 Refrigerant piping.

Claims

1. a single-transistor boost AC / DC converter having a rectifier circuit that rectifies an AC voltage supplied from an AC power source and outputs a DC voltage, and a single-transistor boost circuit that boosts the DC voltage; Equipped with the single-transistor boost circuit includes a reactor and a switching element, the switching element operates by varying a switching frequency; The conversion efficiency of the single-transistor boost AC / DC converter is η, the AC side input power factor of the single-transistor boost AC / DC converter is λ, and the effective value of the AC side input voltage of the single-transistor boost AC / DC converter is V ｉｎＲＭＳ and the DC side output voltage of the single-transistor step-up AC / DC converter is V ｏｕｔ and the DC side output power of the single-transistor step-up AC / DC converter is P ｏｕｔ where L is the inductance of the reactor, α is the current ripple factor, which is the ratio of the maximum value of the pulsation amplitude of the reactor current flowing through the reactor to √(2) times the effective value of the input current from the AC power supply, and f is the switching frequency of the switching element. ｓｗ Then, the switching frequency f of the switching element ｓｗ The upper or lower limit of is defined by the following formula (1): In order to maintain a continuous current mode in which the reactor current flows continuously or a critical current mode in which the reactor current does not flow for a moment, when the minimum value of the DC side output power P out of the single-transistor boost AC / DC converter is P out_min and the current ripple factor α is 2, the lower limit value f sw_min of the switching frequency f sw of the switching element is defined by the following equation (2): Power conversion device. [Equation 1] [Equation 2]

2. A single-transistor boost AC / DC converter having a rectifier circuit that rectifies AC voltage supplied from an AC power source and outputs DC voltage, and a single-transistor boost circuit that boosts the DC voltage; Equipped with the single-transistor boost circuit includes a reactor and a switching element, the switching element operates by varying a switching frequency; Let η be the conversion efficiency of the single-transistor step-up AC-DC converter, λ be the AC side input power factor of the single-transistor step-up AC-DC converter, V inRMS be the effective value of the AC side input voltage of the single-transistor step-up AC-DC converter, V out be the DC side output voltage of the single-transistor step-up AC-DC converter, P out be the DC side output power of the single-transistor step-up AC-DC converter, L be the inductance of the reactor, α be the current ripple factor which is the ratio of the maximum value of the pulsation amplitude of the reactor current flowing through the reactor to √(2) times the effective value of the input current from the AC power source, and f sw be the switching frequency of the switching element, then the upper limit or lower limit of the switching frequency f sw of the switching element is defined by the following equation (3): In order to maintain a continuous current mode in which the reactor current flows continuously and to maintain a current ripple rate of the reactor current of 50% or less, the DC side output power P of the single-transistor step-up AC / DC converter is ｏｕｔ The minimum value of P ｏｕｔ＿ｍｉｎ When the current ripple factor α is set to 0.5, the switching frequency f ｓｗ The lower limit value f ｓｗ＿ｍｉｎ is defined by the following equation (4): Power conversion device. [Equation 3] [Equation 4]

3. In order to maintain a current ripple rate of 10% or more of the reactor current, the DC side output power P of the single-transistor step-up AC / DC converter ｏｕｔ The maximum value of P ｏｕｔ＿ｍａｘ When the current ripple factor α is set to 0.1, the switching frequency f ｓｗ Upper limit value f ｓｗ＿ｍａｘ is defined by the following equation (5): The power conversion device according to claim 1 . [Equation 5]

4. a control unit that performs control calculations to control the switching of the switching element; Equipped with The control unit sets a control frequency, which is the reciprocal of the calculation period for performing control calculation, to f ｃｏｎｔ and the control frequency f ｃｏｎｔ The maximum value of f ｃｏｎｔ＿ｍａｘ Then, f ｃｏｎｔ＿ｍａｘ ≧f ｓｗ In the case of control frequency f ｃｏｎｔ = f ｓｗ Control calculation is performed with f ｃｏｎｔ＿ｍａｘ <f ｓｗ In the case of control frequency f ｃｏｎｔ = f ｓｗ / n≦f ｃｏｎｔ＿ｍａｘ Find the smallest integer n that satisfies the control frequency f ｃｏｎｔ = f ｓｗ / n to perform control calculations. The power conversion device according to claim 1 .

5. sequentially controlling the switching frequency so that at least one of the magnetic flux density of the reactor, the current ripple rate, and the power loss becomes a constant value during a specified period including a time point when the detected voltage of the AC power supply becomes maximum; The power conversion device according to claim 1 .

6. A motor drive device comprising the power conversion device according to any one of claims 1 to 5.

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

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