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

Abstract

The power conversion device (1) includes: a rectifier (130) that rectifies a first AC power supplied from a commercial power source (110); a capacitor (210) connected to the output terminal of the rectifier (130); an inverter (310) connected to both ends of the capacitor (210) that converts the power output from the rectifier (130) and the capacitor (210) into a second AC power and outputs it to a load having a motor (314); and a control unit (400) that controls the operation of the inverter (310) so that the inverter (310) outputs a second AC power to the load, which includes a pulse corresponding to the pulse of the power flowing from the rectifier (130) to the capacitor (210), suppresses the current flowing to the capacitor (210), and does not provide a discharge circuit or overvoltage protection circuit for the capacitor (210).

Description

Technical Field

[0001] This disclosure relates to power conversion devices, motor drive devices, and refrigeration cycle application equipment for converting alternating current into desired power. Background Technology

[0002] Conventionally, there exists a power conversion device that converts AC power supplied from an AC power source into desired AC power and supplies it to loads such as air conditioners. For example, Patent Document 1 discloses a technology in which a power conversion device serving as a control device for an air conditioner uses a diode stack as a rectifier to rectify the AC power supplied from an AC power source, and then uses an inverter composed of multiple switching elements to convert the power smoothed by a smoothing capacitor into the desired AC power, and outputs it to the compressor motor serving as a load.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 7-71805 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, according to the aforementioned prior art, the flow of a large current into the smoothing capacitor leads to an accelerated degradation of the smoothing capacitor over time. To address this issue, methods have been considered such as increasing the capacitance of the smoothing capacitor to suppress voltage ripple variations, or using a smoothing capacitor with a high capacitance that reduces degradation caused by ripple. However, these methods increase the cost of the capacitor components and lead to a larger device size.

[0008] This disclosure was made in view of the above, and its object is to provide a power conversion device capable of suppressing the deterioration of the capacitor used for smoothing and suppressing the enlargement of the device.

[0009] means for solving problems

[0010] To solve the above problems and achieve the objective, the power conversion device disclosed herein includes: a rectifier that rectifies a first AC power supplied from a commercial power source; a capacitor connected to the output terminal of the rectifier; an inverter connected to both ends of the capacitor that converts the power output from the rectifier and the capacitor into a second AC power and outputs it to a load having a motor; and a control unit that controls the operation of the inverter so that the inverter outputs a second AC power to the load, which includes pulsations corresponding to the pulsations of the power flowing from the rectifier to the capacitor, suppresses the current flowing to the capacitor, and does not provide a discharge circuit or overvoltage protection circuit for the capacitor.

[0011] The effects of the invention

[0012] The power conversion device disclosed herein has the effect of suppressing the deterioration of the capacitor used for smoothing and suppressing the enlargement of the device. Attached Figure Description

[0013] Figure 1 This is a diagram showing a structural example of the power conversion device according to Embodiment 1.

[0014] Figure 2 This is a diagram showing, as a comparative example, an example of the currents and the capacitor voltage of the smoothing section's capacitor when the smoothing section smooths the current output from the rectifier section and keeps the current flowing to the inverter constant.

[0015] Figure 3 This diagram illustrates an example of the currents and capacitor voltages of the smoothing section's capacitors when the control unit of the power conversion device in Embodiment 1 controls the operation of the inverter to reduce the current flowing to the smoothing section.

[0016] Figure 4 This is a flowchart illustrating the operation of the control unit included in the power conversion device of Embodiment 1.

[0017] Figure 5 This is a diagram showing an example of the equivalent circuit when the inverter stops in the power conversion device of Embodiment 1.

[0018] Figure 6 This is a diagram showing an example of the capacitor voltage in the power conversion device of Embodiment 1 when the inverter is stopped.

[0019] Figure 7 This is a graph showing the difference in the current flowing to the capacitor in the power conversion device of Embodiment 1 when the control to reduce the current flowing to the capacitor is not applied and when the control is applied.

[0020] Figure 8 This is a diagram showing an example of the hardware structure of the control unit included in the power conversion device implementing Embodiment 1.

[0021] Figure 9 This is a diagram showing a structural example of the power conversion device according to Embodiment 2.

[0022] Figure 10 This is a flowchart showing the operation of the control unit included in the power conversion device of Embodiment 2.

[0023] Figure 11 This is a graph showing the difference in the current flowing to the capacitor in the power conversion device of Embodiment 2 when the control to reduce the current flowing to the capacitor is not applied and when the control is applied.

[0024] Figure 12 This is a diagram showing a structural example of the power conversion device according to Embodiment 3.

[0025] Figure 13 This is a diagram showing a structural example of the power conversion device according to Embodiment 4.

[0026] Figure 14 This is a diagram showing a structural example of the refrigeration cycle application device according to Embodiment 5. Detailed Implementation

[0027] Hereinafter, the power conversion device, motor drive device, and refrigeration cycle application equipment of the present disclosure will be described in detail based on the accompanying drawings.

[0028] Implementation method 1.

[0029] Figure 1 This diagram illustrates a structural example of the power conversion device 1 according to Embodiment 1. The power conversion device 1 is connected to a commercial power supply 110 and a compressor 315. The power conversion device 1 converts a first AC power supply voltage Vs from the commercial power supply 110 into a second AC power supply with a desired amplitude and phase, and supplies it to the compressor 315. The power conversion device 1 includes a voltage and current detection unit 501, a reactor 120, a rectifier 130, a voltage detection unit 502, a smoothing unit 200, an inverter 310, current detection units 313a and 313b, and a control unit 400. Furthermore, a motor drive device 2 is constructed using the power conversion device 1 and the motor 314 included in the compressor 315.

[0030] The voltage and current detection unit 501 detects the voltage and current values ​​of the first AC power supply Vs from the commercial power supply 110 and outputs the detected voltage and current values ​​to the control unit 400. A reactor 120 is connected between the voltage and current detection unit 501 and the rectifier unit 130. The rectifier unit 130 has a bridge circuit composed of rectifier elements 131 to 134, which rectifies the first AC power supply Vs from the commercial power supply 110 and outputs it. The rectifier unit 130 performs full-wave rectification. The voltage detection unit 502 detects the voltage value of the power rectified by the rectifier unit 130 and outputs the detected voltage value to the control unit 400. The smoothing unit 200 is connected to the output terminal of the rectifier unit 130 via the voltage detection unit 502. The smoothing unit 200 has a capacitor 210 as a smoothing element to smooth the power rectified by the rectifier unit 130. The capacitor 210 is, for example, an electrolytic capacitor or a film capacitor. Capacitor 210 smooths the power rectified by rectifier 130. The voltage generated in capacitor 210 due to this smoothing is not the full-wave rectified waveform of the power supply 110, but rather a waveform with a voltage ripple corresponding to the frequency of the power supply 110 superimposed on the DC component, thus avoiding significant pulsation. The frequency of this voltage ripple is twice the frequency of the power supply voltage Vs when the power supply 110 is single-phase, and six times the frequency becomes the dominant component when the power supply 110 is three-phase. When the power input from the power supply 110 and the power output from the inverter 310 remain constant, the amplitude of this voltage ripple is determined by the capacitance of capacitor 210. For example, the voltage ripple generated in capacitor 210 pulsates within a range where the maximum value is less than twice the minimum value.

[0031] The inverter 310 is connected to the two ends of the smoothing section 200, i.e., the capacitor 210. The inverter 310 includes switching elements 311a-311f and freewheeling diodes 312a-312f. The inverter 310, under the control of the control unit 400, switches the switching elements 311a-311f on and off, converting the power output from the rectifier section 130 and the smoothing section 200 into a second AC power with the desired amplitude and phase, and outputting it to the compressor 315. Current detection units 313a and 313b detect the current value of one phase of the three-phase current output from the inverter 310 and output the detected current value to the control unit 400. Furthermore, the control unit 400 can calculate the current value of the remaining phase output from the inverter 310 by obtaining the current values ​​of two phases of the three-phase current output from the inverter 310. The compressor 315 is a load containing a compressor drive motor 314. The motor 314 rotates in accordance with the amplitude and phase of the second AC power supplied from the inverter 310 to perform a compression operation. For example, in the case where the compressor 315 is a hermetic compressor used in air conditioners, the load torque of the compressor 315 is mostly considered a constant torque load.

[0032] In addition, in power conversion device 1, Figure 1 The configurations of the structures shown are examples, and the configurations of the structures are not limited to... Figure 1 The example shown. For example, reactor 120 can also be configured after rectifier 130. In the following description, voltage and current detection units 501, voltage detection unit 502, and current detection units 313a and 313b are sometimes collectively referred to as detection units. Furthermore, the voltage and current values ​​detected by voltage and current detection unit 501, the voltage value detected by voltage detection unit 502, and the current value detected by current detection units 313a and 313b are sometimes referred to as detection values.

[0033] The control unit 400 obtains the voltage and current values ​​of the first AC power supply voltage Vs from the voltage and current detection unit 501, the voltage value of the power rectified by the rectifier unit 130 from the voltage detection unit 502, and the current value of the second AC power with the desired amplitude and phase converted by the inverter 310 from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the inverter 310, specifically the switching on and off of the switching elements 311a to 311f of the inverter 310. In this embodiment, the control unit 400 controls the operation of the inverter 310 so that the inverter 310 outputs a second AC power to the compressor 315, which is a load, such that the second AC power includes pulsations corresponding to the pulsations of the power flowing from the rectifier unit 130 to the capacitor 210 of the smoothing unit 200. The pulsation corresponding to the pulsation of the power flowing into the capacitor 210 of the smoothing section 200 is, for example, a pulsation that varies according to the frequency of the pulsation of the power flowing into the capacitor 210 of the smoothing section 200. Therefore, the control unit 400 suppresses the current flowing into the capacitor 210 of the smoothing section 200. Furthermore, the control unit 400 may not use all the detection values ​​obtained from each detection unit, or it may use only a portion of the detection values ​​for control. In the power conversion device 1 of this embodiment, the capacitor 210 is connected in parallel with the inverter 310, and no discharge circuit or overvoltage protection circuit is provided for the capacitor 210.

[0034] Here, the discharge circuit includes active components such as switching elements and resistors, and controls the connection between the resistor and capacitor 210 by switching the active components on and off. Therefore, a resistor connected in parallel with capacitor 210 is not included, as it is used to balance the voltages of the series-connected capacitors and to detect capacitor voltages. The resistor in the discharge circuit is used to discharge the charge from capacitor 210 over a certain period; therefore, in one example, it is not a large resistance value of 1kΩ or more, but rather a resistance value of a few Ω to several hundred Ω. As an example of a discharge circuit, a circuit with a series-connected switching element and a resistor connected in parallel with capacitor 210 is given.

[0035] On the other hand, the overvoltage protection circuit protects the equipment from voltage rise above a certain level due to regenerative power from the motor 314, disturbances from the commercial power supply 110, etc., and is not a buffer circuit to protect switching elements from damage caused by surge voltages generated when the switching elements are switched. Examples of buffer circuits include RC buffers consisting of a resistor and a capacitor, and C buffers consisting of only a capacitor. As an example of an overvoltage protection circuit, a circuit consisting of a diode, a resistor, and a protective capacitor connected in series with capacitor 210 is provided. In addition, to suppress the rise of the capacitor voltage, a capacitor with a larger capacitance than that used in the buffer circuit is required, such as a capacitor of 10uF or more. Furthermore, a resistor is not necessarily required; it is also possible to use only a diode connected in series with the protective capacitor.

[0036] Next, the operation of the control unit 400 provided in the power conversion device 1 will be explained. In this embodiment, in the power conversion device 1, the load generated by the inverter 310 and the compressor 315 can be regarded as a fixed load. The following explanation assumes that the smoothing unit 200 is connected to a constant current load when observing the current output from the smoothing unit 200. Here, as... Figure 1 As shown, let the current flowing from the rectifier section 130 be current I1, the current flowing to the inverter 310 be current I2, and the current flowing from the smoothing section 200 be current I3. Current I2 is the combined current of current I1 and current I3. Current I3 can be expressed as the difference between current I2 and current I1, i.e., current I2 - current I1. For current I3, let the discharge direction of the smoothing section 200 be the positive direction, and the charging direction of the smoothing section 200 be the negative direction. That is, sometimes the current flows into the smoothing section 200, and sometimes the current flows out of the smoothing section 200.

[0037] Figure 2 This diagram illustrates, as a comparative example, an example of currents I1 to I3 and the capacitor voltage Vdc of capacitor 210 in the smoothing unit 200 when the current output from rectifier 130 is smoothed by smoothing unit 200 and the current I2 flowing to inverter 310 is fixed. Currents I1, I2, and I3, and the capacitor voltage Vdc of capacitor 210 corresponding to current I3 are shown sequentially from top to bottom. The vertical axis of currents I1, I2, and I3 represents the current value, and the vertical axis of capacitor voltage Vdc represents the voltage value. The horizontal axis represents time t. Furthermore, the carrier component of inverter 310 is actually superimposed on currents I2 and I3, but this is omitted here. The same applies thereafter. Figure 2As shown, in the power conversion device 1, assuming that the current I1 flowing from the rectifier 130 is sufficiently smoothed by the smoothing unit 200, the current I2 flowing to the inverter 310 becomes a fixed current value. However, a large current I3 flows to the capacitor 210 of the smoothing unit 200, which becomes the main cause of degradation. Therefore, in this embodiment, in the power conversion device 1, the control unit 400 controls the current I2 flowing to the inverter 310, that is, controls the operation of the inverter 310, so as to reduce the current I3 flowing to the smoothing unit 200.

[0038] Figure 3 This diagram illustrates an example of how the control unit 400 of the power conversion device 1 in Embodiment 1 controls the operation of the inverter 310 to reduce the current I3 flowing to the smoothing section 200, specifically the currents I1 to I3 and the capacitor voltage Vdc of the capacitor 210 in the smoothing section 200. From top to bottom, the diagram shows the currents I1, I2, I3, and the capacitor voltage Vdc of the capacitor 210 corresponding to the current I3. The vertical axis for currents I1, I2, and I3 represents the current value, and the vertical axis for capacitor voltage Vdc represents the voltage value. The horizontal axis represents time t. The control unit 400 of the power conversion device 1 controls the operation of the inverter 310, thereby reducing the currents I1 to I3 and the capacitor voltage Vdc of the smoothing section 200. Figure 3 The current I2 shown flows to inverter 310, thus, with Figure 2 Compared to the previous example, the frequency component of the current flowing from the rectifier section 130 into the smoothing section 200 can be reduced, thus reducing the current I3 flowing into the smoothing section 200. Specifically, the control section 400 controls the operation of the inverter 310 so that a current I2 containing a pulsating current with the frequency component of the current I1 as the main component flows into the inverter 310.

[0039] The frequency component of current I1 is determined by the frequency of the AC current supplied from commercial power supply 110 and the structure of rectifier 130. Therefore, control unit 400 can set the frequency component of the pulsating current overlapping with current I2 to a component with a predetermined amplitude and phase. The frequency component of the pulsating current overlapping with current I2 becomes a similar waveform to the frequency component of current I1. By bringing the frequency component of the pulsating current overlapping with current I2 closer to the frequency component of current I1, control unit 400 can reduce the current I3 flowing to smoothing unit 200 and reduce the pulsating voltage generated in capacitor voltage Vdc.

[0040] The control unit 400 controls the pulsation of the current flowing to the inverter 310 by controlling the operation of the inverter 310, which is the same as controlling the pulsation of the second AC power output from the inverter 310 to the compressor 315. The control unit 400 controls the operation of the inverter 310 such that the pulsation contained in the second AC power output from the inverter 310 is less than the pulsation of the power output from the rectifier unit 130. The control unit 400 controls the amplitude and phase of the pulsation contained in the second AC power output from the inverter 310 such that the voltage ripple of the capacitor voltage Vdc, i.e., the voltage ripple generated in the capacitor 210, is less than the voltage ripple generated in the capacitor 210 when the second AC power output from the inverter 310 does not contain pulsations corresponding to the pulsation of the power flowing into the capacitor 210. When the second AC power output from the inverter 310 does not contain pulsations corresponding to the pulsation of the power flowing into the capacitor 210, it means... Figure 2 The controls shown.

[0041] Furthermore, the AC current supplied from the commercial power supply 110 is not particularly limited; it can be single-phase or three-phase. The control unit 400 determines the frequency component of the pulsating current overlapping with the current I2 based on the first AC power supplied from the commercial power supply 110. Specifically, when the first AC power supplied from the commercial power supply 110 is single-phase, the control unit 400 controls the pulsating waveform of the current I2 flowing to the inverter 310 to be a shape obtained by adding a DC component to a pulsating waveform whose main component is a frequency component that is twice the frequency of the first AC power. Alternatively, when the first AC power supplied from the commercial power supply 110 is three-phase, the control unit 400 controls the pulsating waveform of the current I2 flowing to the inverter 310 to be a shape obtained by adding a DC component to a pulsating waveform whose main component is a frequency component that is six times the frequency of the first AC power. The pulsating waveform can be, for example, the shape of the absolute value of a sine wave or the shape of a sine wave. In this case, the control unit 400 may also add at least one frequency component of the sine wave whose frequency is an integer multiple of the sine wave to the pulsating waveform with a predetermined amplitude. Furthermore, the pulsating waveform may be a rectangular wave or a triangular wave. In this case, the control unit 400 may also set the amplitude and phase of the pulsating waveform to predetermined values.

[0042] The control unit 400 can also use the voltage applied to the capacitor 210 or the current flowing to the capacitor 210 to calculate the amount of pulsation contained in the second AC power output from the inverter 310, and can also use the voltage or current of the first AC power supplied from the commercial power supply 110 to calculate the amount of pulsation contained in the second AC power output from the inverter 310.

[0043] The operation of the control unit 400 is explained using a flowchart. Figure 4This is a flowchart illustrating the operation of the control unit 400 included in the power conversion device 1 according to Embodiment 1. The control unit 400 obtains detection values ​​from each detection unit of the power conversion device 1 (step S1). Based on the obtained detection values, the control unit 400 controls the operation of the inverter 310, thereby reducing the current I3 flowing to the smoothing unit 200 (step S2).

[0044] Here, in Figure 1 In the power conversion device 1 shown, let the inductance component in the power conversion device 1 be L[H], let the capacitance of capacitor 210 be C[F], let the inductance component of one phase of motor 314 be Lm[H], let the maximum voltage of capacitor 210 under steady state be Vcmax[V], let the maximum current of motor 314 be Im[A], let the maximum current of commercial power supply 110 be Is[A], and let the withstand voltage of the component to which capacitor voltage Vdc is applied be Vdclim[V]. At this time, the capacitance C of capacitor 210 is determined by the range of equation (1).

[0045] [Formula 1]

[0046]

[0047] Furthermore, the inductive component L within the power conversion device 1 is the inductive component La of the reactor 120 plus the system impedance Lk. The system impedance Lk includes transformer leakage, parasitic inductance components contained in the wiring, etc. The larger the value of L, the greater the rise in capacitor voltage Vdc. Therefore, the maximum value assumed under actual operating conditions is used for the system impedance Lk. The same applies thereafter. Additionally, the reactor 120 can be positioned as described above, after the rectifier 130, i.e., between the rectifier 130 and the voltage detection unit 502.

[0048] Figure 5 This is a diagram showing an example of the equivalent circuit when the inverter 310 is stopped in the power conversion device 1 of Embodiment 1. Figure 5 The equivalent circuit shown is a simplified circuit and does not simulate the voltage of commercial power supply 110, the induced voltage of motor 314, etc. Figure 5 In this context, the inverter 310 is set to stop at 50ms, and the current and voltage values ​​are the values ​​at 50ms. Figure 6 Various waveforms are shown for the cases where the inverter 310 is stopped within and outside the range shown in Equation (1). Figure 6 This is a diagram showing an example of the capacitor voltage Vdc when the inverter 310 is stopped in the power conversion device 1 of Embodiment 1. (The upper paragraph...) Figure 6 (a) Shows the inverter stop signal from control unit 400, the lower section Figure 6(b) shows the capacitor voltage Vdc. As an example, the parameters are L = 2 [mH], Is = 15 [A], Lm = 9 [mH], Im = 15 [A], Vdclim = 400 [V], and Vcmax = 310 [V]. The capacitance C of capacitor 210 is 20 [uF] outside the range of equation (1), 55 [uF] as a condition for the right side to be equal to the left side in equation (1), and 100 [uF] as a condition for the right side to be larger within the range of equation (1).

[0049] according to Figure 6 It can also be seen that by setting the capacitance C of capacitor 210 to be within the range of equation (1), the power conversion device 1 can prevent the voltage rise within the withstand voltage Vdclim of the component, thus preventing component damage. Furthermore, L in equation (1) can be added to... Figure 1 The inductive component and system impedance included in filters not shown in the figure. In addition, Equation (1) is a simple equation, and the induced voltage of motor 314 and the voltage rise caused by the voltage of commercial power supply 110 can be further added.

[0050] In this embodiment, as described above, in the power conversion device 1, the control unit 400 pulsates the output power of the inverter 310 based on the frequency of the commercial power supply 110, thereby reducing the current of the capacitor 210. Therefore, compared to a control method where the output power pulsates at a fixed rate as in a conventional inverter, the ripple voltage of the capacitor 210 can be reduced. Pulsating the power means pulsating the current of the inverter 310; therefore, in other words, the capacitance C of the capacitor 210 can be reduced based on the pulsation of the output current of the inverter 310. Furthermore, pulsating the output of the inverter 310 is the same as pulsating the input current input to the inverter 310.

[0051] Here, according to Figure 3 It can also be seen that in power conversion device 1, Figure 1 In the structure shown, the current of capacitor 210 pulsates at a frequency of 2fs, which is twice the frequency of commercial power supply 110, and the ripple voltage of capacitor 210 also pulsates accordingly with the frequency of 2fs. Therefore, regarding the ripple voltage of capacitor 210, the allowable ripple voltage can be determined based on the frequency of 2fs, and the capacitance C of capacitor 210 is determined by the value of the allowable ripple voltage. Let the allowable ripple voltage of capacitor 210 in the frequency 2fs component be ΔV_2fs, let the current of capacitor 210 in the frequency 2fs component when there is no pulsation of the frequency 2fs component in the output current of inverter 310 under normal control be Ic_2fs, and let the pulsation of the input current of inverter 310 in the frequency 2fs component under the control of this embodiment be Im_2fs. In this case, the capacitance C of capacitor 210 under the control of this embodiment becomes the range of equation (2).

[0052] [Formula 2]

[0053]

[0054] Furthermore, in equation (2), the frequency 2fs is defined as twice the frequency of the commercial power supply 110. However, it is not limited to this; the frequency 2fs can also be set as an integer multiple of the frequency 2fs. Therefore, in the power conversion device 1, if the above conditions (1) and (2) are met, there is no need to add a discharge circuit or overvoltage protection circuit to the capacitor 210, and a capacitor 210 with a smaller capacitance can be used.

[0055] Thus, in the power conversion device 1, the capacitance C of capacitor 210 is greater than or equal to the capacitance of capacitor 210 when an overvoltage protection circuit is connected to capacitor 210. The capacitance C of capacitor 210 is determined by the following values, calculated using the impedance of reactor 120 configured in the power conversion device 1, system impedance Lk, maximum current Is of commercial power supply 110, inductive component Lm of one phase of motor 314, maximum current Im of motor 314, withstand voltage Vdclim of the element to which voltage is applied from capacitor 210, and maximum voltage Vcmax of capacitor 210 in a steady state. The capacitance C of capacitor 210 can also be further limited by the system voltage of commercial power supply 110 when inverter 310 is stopped, the induced voltage of motor 314, etc. Furthermore, the capacitance C of capacitor 210 is less than the capacitance C of capacitor 210 set when the control unit 400 does not perform the first control. The first control is to control the operation of inverter 310 so that the inverter 310 outputs a second AC power to the load, which includes a pulsation corresponding to the pulsation of the power flowing into capacitor 210 from rectifier 130. The capacitance C of capacitor 210 is determined by the following values: a frequency 2fs, which is twice the frequency of commercial power supply 110 when the current of capacitor 210 pulsates; the allowable ripple voltage ΔV_2fs of capacitor 210 at twice the frequency 2fs; the capacitor current Ic_2fs of capacitor 210 at twice the frequency when the control unit 400 does not perform the first control; and the input current pulsation Im_2fs of inverter 310 at twice the frequency 2fs when the control unit 400 performs the first control.

[0056] In addition, Figure 1 In the power conversion device 1 shown above, the ripple current pulsation caused by the switching of the switching elements 311a to 311f of the inverter 310 was not simulated in the above description. However, in the actual case of driving the inverter 310, Figure 7 The current of the frequency component shown flows into capacitor 210. Figure 7This is a graph showing the difference in the current flowing to capacitor 210 in the power conversion device 1 of Embodiment 1 when the control to reduce the current flowing to capacitor 210 is not applied and when the control is applied. (The upper paragraph...) Figure 7 (a) shows the case where control measures to reduce the current flowing to capacitor 210 are not applied in the power conversion device 1, the upper section Figure 7 (b) shows the application of control measures to reduce the current flowing to capacitor 210 in the power conversion device 1. Figure 7 As can be seen, when the control of this embodiment is applied, the capacitor current Ic_2fs in the frequency component twice the frequency of the commercial power supply 110 is equal to or lower than the first capacitor current Ic_2fcinv in the frequency component twice the switching frequency fcinv of the switching elements 311a to 311f of the inverter 310. In this case, the current flowing to the capacitor 210 is limited as shown in equation (3).

[0057] [Formula 3]

[0058] Ic_2fs≤Ic_2fcinv…(3)

[0059] Furthermore, in equation (3), the frequency 2fs is set to twice the frequency of the commercial power supply 110, but it is not limited to this; the frequency 2fs can also be set to an integer multiple of the frequency 2fs. Therefore, if the power conversion device 1 satisfies the above-mentioned condition equation (3), a capacitor 210 with a small ripple current tolerance can be used. In this way, the capacitor current Ic_2fs, which is twice the frequency of the commercial power supply 110 in the current flowing to the capacitor 210, is less than or equal to the first capacitor current Ic_2fcinv, which is twice the frequency of the switching elements 311a to 311f of the inverter 310. The first capacitor current Ic_2fcinv may also include a current component caused by the rotation of the motor 314.

[0060] Next, the hardware structure of the control unit 400 of the power conversion device 1 will be described. Figure 8 This diagram illustrates an example of the hardware structure of the control unit 400 included in the power conversion device 1 implementing Embodiment 1. The control unit 400 is implemented by a processor 91 and a memory 92.

[0061] Processor 91 is a CPU (also known as a Central Processing Unit, Central Processing Device, Processing Device, Arithmetic Device, Microprocessor, Microcomputer, Processor, DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). Memory 92 can exemplify non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (Electrically Erasable Programmable ROM). However, memory 92 is not limited to these and can also be a magnetic disk, optical disk, high-density disk, mini-disk, or DVD (Digital Versatile Disc).

[0062] As explained above, according to this embodiment, in the power conversion device 1, the control unit 400 controls the operation of the inverter 310 based on the detection values ​​obtained from each detection unit. It superimposes the pulsation of a frequency component corresponding to the frequency component of the current I1 flowing from the rectifier unit 130 onto the current I2 flowing to the inverter 310, thereby reducing the current I3 flowing to the smoothing unit 200. As a result, in the power conversion device 1, by reducing the current I3 flowing to the smoothing unit 200, a capacitor with a low ripple current tolerance can be used compared to the case without the control of this embodiment. Furthermore, in the power conversion device 1, by reducing the pulsating voltage of the capacitor voltage Vdc, the capacitance of the mounted capacitor 210 can be reduced compared to the case without the control of this embodiment. For example, in the case where the smoothing unit 200 is composed of multiple capacitors 210, the power conversion device 1 can reduce the number of capacitors 210 constituting the smoothing unit 200.

[0063] Furthermore, by performing the control described in this embodiment, the power conversion device 1 can suppress the vibration of the compressor 315 caused by the pulsation of the current I2.

[0064] Implementation method 2.

[0065] In Embodiment 2, the case where the power conversion device boosts the voltage of the first AC power supplied from the commercial power source 110 is described.

[0066] Figure 9This diagram illustrates a structural example of the power conversion device 1a according to Embodiment 2. The power conversion device 1a is connected to a commercial power supply 110 and a compressor 315. The power conversion device 1a converts a first AC power supply voltage Vs from the commercial power supply 110 into a second AC power supply with a desired amplitude and phase, and supplies it to the compressor 315. The power conversion device 1a includes a voltage and current detection unit 501, a rectifier 130, a reactor 120, a boost unit 600, a voltage detection unit 502, a smoothing unit 200, an inverter 310, current detection units 313a and 313b, and a control unit 400. Furthermore, in the power conversion device 1a, the rectifier 130, the reactor 120, and the boost unit 600 constitute a rectifier-boost unit 700. Additionally, the motor 314 provided in the power conversion device 1a and the compressor 315 constitutes a motor drive device 2a.

[0067] The voltage and current detection unit 501 detects the voltage and current values ​​of the first AC power supply voltage Vs supplied from the commercial power supply 110 and outputs the detected voltage and current values ​​to the control unit 400. The rectifier unit 130 has a bridge circuit composed of rectifier elements 131-134, which rectifies the first AC power supply voltage Vs supplied from the commercial power supply 110 and outputs it. The reactor 120 is connected between the rectifier unit 130 and the boost unit 600. The boost unit 600 has a switching element 611 and a rectifier element 621. The boost unit 600, under the control of the control unit 400, switches the switching element 611 on and off, boosting the power output from the rectifier unit 130 and outputting the boosted power to the smoothing unit 200. In this embodiment, the boost unit 600 is controlled by the control unit 400 using full PAM (Pulse Amplitude Modulation) with the switching element 611 continuously switching on and off. The power conversion device 1a performs power factor improvement control on the commercial power supply 110 via the boost unit 600, making the capacitor voltage Vdc of the capacitor 210 in the smoothing unit 200 higher than the power supply voltage Vs. The rectifier-boost unit 700, through the rectifier unit 130 and the boost unit 600, rectifies the first AC power supplied from the commercial power supply 110 and boosts the voltage of the first AC power supplied from the commercial power supply 110. In this embodiment, the rectifier unit 130 and the boost unit 600 are connected in series in the rectifier-boost unit 700.

[0068] The voltage detection unit 502 detects the voltage value of the power boosted by the boost unit 600 and outputs the detected voltage value to the control unit 400. The smoothing unit 200 is connected to the output terminal of the boost unit 600 via the voltage detection unit 502. The smoothing unit 200 has a capacitor 210 as a smoothing element to smooth the power boosted by the boost unit 600. The capacitor 210 is, for example, an electrolytic capacitor or a film capacitor. The capacitor 210 is a capacitor that smooths the power rectified by the rectifier unit 130 and boosted by the boost unit 600. The voltage generated by the smoothing on the capacitor 210 is not the full-wave rectified waveform of the commercial power supply 110, but a waveform with a voltage ripple corresponding to the frequency of the commercial power supply 110 superimposed on the DC component, without large fluctuations. The frequency of this voltage ripple is twice the frequency of the power supply voltage Vs when the commercial power supply 110 is single-phase, and six times the frequency becomes the main component when the commercial power supply 110 is three-phase. When the power input from commercial power supply 110 and the power output from inverter 310 remain unchanged, the amplitude of the voltage ripple is determined by the capacitance of capacitor 210. For example, the voltage ripple generated in capacitor 210 pulsates within a range where the maximum value is less than twice the minimum value.

[0069] The inverter 310 is connected to the two ends of the smoothing section 200, i.e., the capacitor 210. The inverter 310 has switching elements 311a-311f and freewheeling diodes 312a-312f. Under the control of the control unit 400, the inverter 310 switches the switching elements 311a-311f on and off, converting the power output from the rectifier boost section 700 and the smoothing section 200 into a second AC power with the desired amplitude and phase, and outputting it to the compressor 315. Current detection units 313a and 313b detect the current value of one phase of the three-phase current output from the inverter 310, and output the detected current value to the control unit 400. Furthermore, the control unit 400 can calculate the current value of the remaining phase output from the inverter 310 by obtaining the current values ​​of two phases of the three-phase current output from the inverter 310. The compressor 315 is a load having a compressor drive motor 314. The motor 314 rotates in accordance with the amplitude and phase of the second AC power supplied from the inverter 310 to perform a compression operation. For example, in the case where the compressor 315 is a hermetic compressor used in air conditioners, the load torque of the compressor 315 is mostly considered a constant torque load.

[0070] In addition, in the power conversion device 1a, Figure 9 The configurations of the structures shown are examples, and the configurations of the structures are not limited to... Figure 9The example shown. The rectifier boost unit 700 may also omit the reactor 120 depending on its configuration. In the following description, the voltage and current detection units 501, 502, and 313a and 313b will sometimes be collectively referred to as detection units. Furthermore, the voltage and current values ​​detected by the voltage and current detection unit 501, the voltage value detected by the voltage detection unit 502, and the current value detected by the current detection units 313a and 313b will sometimes be referred to as detection values.

[0071] The control unit 400 obtains the voltage and current values ​​of the first AC power supply voltage Vs from the voltage and current detection unit 501, the voltage value of the power boosted by the boost unit 600 from the voltage detection unit 502, and the current value of the second AC power with the desired amplitude and phase converted by the inverter 310 from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​from each detection unit to control the operation of the boost unit 600 of the rectifier boost unit 700, specifically the switching elements 611 of the boost unit 600. Furthermore, the control unit 400 uses the detection values ​​from each detection unit to control the operation of the inverter 310, specifically the switching elements 311a to 311f of the inverter 310. In this embodiment, the control unit 400 controls the operation of the rectifier boost unit 700. The control unit 400 controls the operation of the rectifier boost unit 700, performing power factor improvement control on the first AC power supplied from the commercial power supply 110, and average voltage control on the capacitor 210 of the smoothing unit 200. Furthermore, the control unit 400 controls the operation of the inverter 310, causing it to output a second AC power to the compressor 315, which is a load, containing pulsations corresponding to the pulsations of the power flowing from the rectifier 130 to the capacitor 210 of the smoothing unit 200. These pulsations, for example, are pulsations that vary according to the frequency of the pulsations flowing into the capacitor 210 of the smoothing unit 200. Thus, the control unit 400 suppresses the current flowing into the capacitor 210 of the smoothing unit 200. Additionally, the control unit 400 may use only a portion of the detection values ​​obtained from each detection unit for control, rather than all of them.

[0072] Next, the operation of the control unit 400 provided in the power conversion device 1a will be described. The operation of the control unit 400 is the same as that of the control unit 400 in Embodiment 1. In Embodiment 2, the current flowing from the rectifier 130 is changed to the current flowing from the boost unit 600.

[0073] The frequency component of current I1 is determined by the frequency of the AC current supplied from commercial power supply 110, the structure of rectifier 130, and the switching speed of switching element 611 in boost unit 600. Therefore, control unit 400 can set the frequency component of the pulsating current overlapping with current I2 to a component with a predetermined amplitude and phase. The frequency component of the pulsating current overlapping with current I2 becomes a similar waveform to the frequency component of current I1. By bringing the frequency component of the pulsating current overlapping with current I2 closer to the frequency component of current I1, control unit 400 can reduce the current I3 flowing to smoothing unit 200 and reduce the pulsating voltage generated in capacitor voltage Vdc.

[0074] The control unit 400 controls the pulsation of the current flowing to the inverter 310 by controlling the operation of the inverter 310, which is the same as controlling the pulsation of the second AC power output from the inverter 310 to the compressor 315. The control unit 400 controls the operation of the inverter 310 such that the pulsation contained in the second AC power output from the inverter 310 is less than the pulsation of the power output from the rectifier boost unit 700. The control unit 400 controls the amplitude and phase of the pulsation contained in the second AC power output from the inverter 310 such that the voltage ripple of the capacitor voltage Vdc, i.e., the voltage ripple generated in the capacitor 210, is less than the voltage ripple generated in the capacitor 210 when the second AC power output from the inverter 310 does not contain pulsations corresponding to the pulsation of the power flowing into the capacitor 210. When the second AC power output from the inverter 310 does not contain pulsations corresponding to the pulsation of the power flowing into the capacitor 210, it means... Figure 2 The controls shown.

[0075] Furthermore, when the control unit 400 controls the inverter 310 to output a second AC power containing a frequency component different from the frequency component of the first AC power supplied from the commercial power supply 110 to the compressor 315, the frequency component of the second AC power output from the inverter 310 to the compressor 315 can also be superimposed on the drive signal used to turn the switching element 611 of the boost unit 600 on and off. That is, the control unit 400 controls the operation of the rectifier-boost unit 700, specifically the operation of the switching element 611 of the boost unit 600, so that, when the first AC power supplied from the commercial power supply 110 is single-phase, the rectifier-boost unit 700 outputs power with a variable frequency component other than twice the frequency of the first AC power during the power pulsation of the second AC power output from the inverter 310 to the compressor 315; or, when the first AC power supplied from the commercial power supply 110 is three-phase, the rectifier-boost unit 700 outputs power with a variable frequency component other than six times the frequency of the first AC power during the power pulsation of the second AC power output from the inverter 310 to the compressor 315. The control unit 400 can control the variable frequency component using command values ​​for the commercial power supply 110, or it can control the variable frequency component to be a component that is not an integer multiple of the 40th order of the frequency of the first AC power supplied from the commercial power supply 110, or to be a predetermined value, such as a desired specification value or lower.

[0076] The operation of the control unit 400 is explained using a flowchart. Figure 10 This is a flowchart illustrating the operation of the control unit 400 included in the power conversion device 1a according to Embodiment 2. The control unit 400 obtains detection values ​​from each detection unit of the power conversion device 1a (step S1). Based on the obtained detection values, the control unit 400 controls the operation of the inverter 310, thereby reducing the current I3 flowing to the smoothing unit 200 (step S2). Based on the obtained detection values, the control unit 400 controls the operation of the boost unit 600, thereby performing power factor improvement control of the commercial power supply 110 and average voltage control of the capacitor voltage Vdc of the capacitor 210 of the smoothing unit 200 (step S3).

[0077] Furthermore, similar to the power conversion device 1 of Embodiment 1, the power conversion device 1a of Embodiment 2 also determines the capacitance C of the capacitor 210 within the range of the above-described formulas (1) and (2). When the power conversion device 1a is... Figure 9 In that structure, the inductance component L in the power conversion device 1a is the inductance component Lc of the boost reactor 120 plus the system impedance Lk.

[0078] Furthermore, similar to the power conversion device 1 of Embodiment 1, the power conversion device 1a of Embodiment 2 also limits the current flowing to the capacitor 210. Figure 9 In the power conversion device 1a shown, as described above, when the inverter 310 is actually driven, Figure 7 The current flowing through capacitor 210 represents the frequency component shown. Furthermore, in... Figure 9 In the power conversion device 1a shown, when the boost unit 600 is actually driven, Figure 11 The current of the frequency component shown flows into capacitor 210. Figure 11 This is a graph showing the difference in the current flowing to capacitor 210 in the power conversion device 1a of Embodiment 2 when the control to reduce the current flowing to capacitor 210 is not applied and when the control is applied. (The upper paragraph...) Figure 11 (a) shows the case where no control to reduce the current flowing to capacitor 210 is applied in the power conversion device 1a, the next paragraph Figure 11 (b) shows a case where control to reduce the current flowing to capacitor 210 is applied in power conversion device 1a. Additionally, in Figure 11 In the middle, the following was omitted. Figure 7 The current ripple component caused by inverter 310 is shown. According to... Figure 11 As can be seen, when the control of this embodiment is applied, the capacitor current Ic_2fs in the frequency component twice the frequency of the commercial power supply 110 is equal to or lower than the second capacitor current Ic_fccnv in the frequency component of the switching frequency fccnv of the switching element 611 provided in the boost unit 600. In this case, the current flowing to the capacitor 210 is limited as in equation (4).

[0079] [Formula 4]

[0080] Ic_2fs≤Ic_fccnv…(4)

[0081] Furthermore, in equation (4), a frequency twice the frequency of the commercial power supply 110 is defined as frequency 2fs, but it is not limited to this; a portion of frequency 2fs can also be defined as an integer multiple of frequency 2fs. Therefore, in the power conversion device 1a, if equation (3) above is satisfied and the conditional equation (4) above is further satisfied, a capacitor 210 with low ripple current tolerance can be used. Thus, when the power conversion device 1a is equipped with a boost unit 600 that boosts the voltage of the first AC power, the capacitor current Ic_2fs, which is a frequency component twice the frequency of the commercial power supply 110, flowing into the capacitor 210, is less than or equal to the second capacitor current Ic_fccnv, which is a frequency component twice the switching frequency of the switching element 611 provided in the boost unit 600. The second capacitor current Ic_fccnv may also include a current component caused by the rotation of the motor 314.

[0082] As explained above, according to this embodiment, in the power conversion device 1a, the control unit 400 controls the operation of the inverter 310 based on the detection values ​​obtained from each detection unit. It superimposes the pulsation of a frequency component corresponding to the frequency component of the current I1 flowing from the rectifier unit 130 onto the current I2 flowing to the inverter 310, thereby reducing the current I3 flowing to the smoothing unit 200. As a result, in the power conversion device 1a, by reducing the current I3 flowing to the smoothing unit 200, a capacitor with a small ripple current tolerance can be used compared to the case without the control of this embodiment. Furthermore, in the power conversion device 1a, by reducing the pulsating voltage of the capacitor voltage Vdc, the capacitance of the mounted capacitor 210 can be reduced compared to the case without the control of this embodiment. For example, in the case where the smoothing unit 200 is composed of multiple capacitors 210, the power conversion device 1a can reduce the number of capacitors 210 constituting the smoothing unit 200.

[0083] Furthermore, by performing the control described in this embodiment, the power conversion device 1a can suppress the vibration of the compressor 315 caused by the pulsation of the current I2.

[0084] Furthermore, the power conversion device 1a performs a boost operation via the boost unit 600, which increases the capacitor voltage Vdc of the capacitor 210 and expands the output voltage range of the inverter 310. In the power conversion device 1a, the control unit 400 reduces the pulsation of the current I3 and the capacitor voltage Vdc caused by the pulsating frequency component contained in the second AC power output from the inverter 310 by superimposing it onto the drive signal of the switching element 611 of the boost unit 600.

[0085] Implementation method 3.

[0086] In Embodiment 3, a power conversion device will be described, which includes a rectifier and boost section with a circuit structure different from that of the rectifier and boost section 700 of the power conversion device 1a in Embodiment 2.

[0087] Figure 12 This is a diagram showing a structural example of the power conversion device 1b according to Embodiment 3. The power conversion device 1b is relative to... Figure 9 The power conversion device 1a of Embodiment 2 shown replaces the rectifier-boost unit 700 with a rectifier-boost unit 701. Furthermore, the motor drive unit 2b is composed of the power conversion device 1b and the motor 314 included in the compressor 315. The rectifier-boost unit 701 includes switching elements 611-614 and rectifier elements 621-624 connected in parallel with one of the switching elements 611-614. The rectifier-boost unit 701, under the control of the control unit 400, turns the switching elements 611-614 on and off, rectifies and boosts the first AC power output from the commercial power supply 110, and outputs the boosted power to the smoothing unit 200. In this embodiment, the rectifier-boost unit 701 is controlled by the control unit 400 using full PAM (Power Actuation and Activation) with continuous switching operations of the switching elements 611-614. The power conversion device 1b performs power factor improvement control on the commercial power supply 110 through the rectifier boost unit 701, so that the capacitor voltage Vdc of the capacitor 210 of the smoothing unit 200 becomes a voltage higher than the power supply voltage Vs.

[0088] The control unit 400 obtains the voltage and current values ​​of the first AC power supply voltage Vs from the voltage and current detection unit 501, the voltage value of the power boosted by the rectifier boost unit 701 from the voltage detection unit 502, and the current value of the second AC power with the desired amplitude and phase converted by the inverter 310 from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the inverter 310, specifically the switching elements 311a to 311f of the inverter 310. Furthermore, the control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the rectifier boost unit 701, specifically the switching elements 611 to 614 of the rectifier boost unit 701. By controlling the operation of the rectifier boost unit 701 and the inverter 310, the control unit 400 achieves the same effects as described in Embodiment 1.

[0089] Other operations in the power conversion device 1b are the same as those in the power conversion device 1a of Embodiment 2. In this case, the power conversion device 1b can also achieve the same effect as the power conversion device 1a of Embodiment 2.

[0090] Furthermore, in the power conversion device 1b of Embodiment 3, the range of capacitance C of capacitor 210 and the current flowing to capacitor 210 are limited to the same extent as in the power conversion device 1a of Embodiment 2. In the power conversion device 1b... Figure 12 In that configuration, the inductive component L within the power conversion device 1b is equal to the inductive component La of the reactor 120 plus the system impedance Lk. Thus, when the power conversion device 1b includes a rectifier / boost unit 701 that rectifies and boosts the voltage of the first AC power supplied from the commercial power supply 110, the capacitor current Ic_2fs, which contains a frequency component twice the frequency of the commercial power supply 110 in the current flowing to the capacitor 210, is less than or equal to the second capacitor current Ic_fccnv, which contains a frequency component equal to the switching frequency of the switching elements 611-614 included in the rectifier / boost unit 701. The second capacitor current Ic_fccnv may also include a current component caused by the rotation of the motor 314.

[0091] Implementation method 4.

[0092] In Embodiment 4, a power conversion device will be described, which includes a rectifier and boost converter with a circuit structure different from that of the rectifier and boost converter 700 of the power conversion device 1a in Embodiment 2 and the rectifier and boost converter 701 of the power conversion device 1b in Embodiment 3.

[0093] Figure 13 This is a diagram showing a structural example of the power conversion device 1c according to Embodiment 4. The power conversion device 1c is relative to... Figure 9In the power conversion device 1a of Embodiment 2 shown, the rectifier boost unit 700 is replaced with a rectifier boost unit 702. Furthermore, the motor drive device 2c is composed of the power conversion device 1c and the motor 314 included in the compressor 315. The rectifier boost unit 702 includes a reactor 120, a rectifier 130, and a boost unit 601. In Embodiment 2, the boost unit 600 is connected in series with the rectifier 130 after the rectifier 130, i.e., inside the power conversion device 1a. However, in Embodiment 4, the boost unit 601 is connected in parallel with the rectifier 130 inside the power conversion device 1c. The boost unit 601 includes rectifier elements 621-624 and a switching element 611. The boost unit 601, under the control of the control unit 400, turns the switching element 611 on and off to boost the first AC power output from the commercial power supply 110, and outputs the boosted power to the rectifier 130. In this embodiment, the boost unit 601 of the rectifier boost unit 702 is controlled by the control unit 400 to perform a simple switch operation of the switching element 611 once or more within half a cycle of the frequency of the first AC power supplied from the commercial power supply 110. The power conversion device 1c performs power factor improvement control of the commercial power supply 110 through the boost unit 601, so that the capacitor voltage Vdc of the capacitor 210 of the smoothing unit 200 becomes a voltage higher than the power supply voltage Vs.

[0094] The control unit 400 obtains the voltage and current values ​​of the first AC power supply voltage Vs from the voltage and current detection unit 501, the voltage value of the power rectified by the rectifier unit 130 from the voltage detection unit 502, and the current value of the second AC power with the desired amplitude and phase converted by the inverter 310 from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the inverter 310, specifically the switching on / off of the switching elements 311a to 311f of the inverter 310. Furthermore, the control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the boost unit 601, specifically the switching on / off of the switching element 611 of the boost unit 601. The control unit 400 controls the operation of the boost unit 601 and the inverter 310 to achieve the same effect as described in Embodiment 2.

[0095] Other operations in the power conversion device 1c are the same as those in the power conversion device 1a of Embodiment 2. In this case, the power conversion device 1c can also achieve the same effect as the power conversion device 1a of Embodiment 2. Furthermore, compared with the power conversion device 1a of Embodiment 2 and the power conversion device 1b of Embodiment 3, the power conversion device 1c suppresses the number of switching operations, thus reducing losses and achieving low noise. In addition, the rectifier section 130 and the boost section 601 of the power conversion device 1c are connected in parallel, so the boost section 601 does not switch when the switching element 611 is not required, thereby reducing the number of current-carrying elements and achieving low losses.

[0096] Furthermore, in the power conversion device 1c of Embodiment 4, the range of capacitance C of capacitor 210 and the current flowing to capacitor 210 are limited to the same extent as in the power conversion device 1a of Embodiment 2. In the power conversion device 1c... Figure 13 In that structure, the inductive component L in the power conversion device 1c is the inductive component La of the reactor 120 plus the system impedance Lk.

[0097] Implementation method 5.

[0098] Figure 14 This is a diagram illustrating a structural example of the refrigeration cycle application device 900 according to Embodiment 5. The refrigeration cycle application device 900 of Embodiment 5 includes the power conversion device 1 described in Embodiment 1. Alternatively, instead of the power conversion device 1, the refrigeration cycle application device 900 may include the power conversion device 1a described in Embodiment 2, the power conversion device 1b described in Embodiment 3, and the power conversion device 1c described in Embodiment 4. The refrigeration cycle application device 900 of Embodiment 5 can be applied to products with refrigeration cycles, such as air conditioners, cold storage facilities, freezers, and heat pump water heaters. Furthermore, in Figure 14 In the text, structural elements that have the same function as in Embodiment 1 are labeled with the same reference numerals as in Embodiment 1.

[0099] In the refrigeration cycle application equipment 900, a compressor 315 with a built-in motor 314, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, as described in Embodiment 1, are installed via refrigerant piping 912.

[0100] Inside the compressor 315, there is a compression mechanism 904 for compressing refrigerant and a motor 314 for actuating the compression mechanism 904.

[0101] The refrigeration cycle application equipment 900 can operate in heating or cooling mode by switching the four-way valve 902. The compressor 904 is driven by a motor 314 that is controlled to have a variable speed.

[0102] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, then returns to the compression mechanism 904 through the four-way valve 902, indoor heat exchanger 906, expansion valve 908, outdoor heat exchanger 910, and the four-way valve 902.

[0103] During refrigeration operation, as shown by the dashed arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, then 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.

[0104] During heating operation, the indoor heat exchanger 906 acts as a condenser, releasing heat, while the outdoor heat exchanger 910 acts as an evaporator, absorbing heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser, releasing heat, while the indoor heat exchanger 906 acts as an evaporator, absorbing heat. The expansion valve 908 depressurizes the refrigerant, causing it to expand.

[0105] The structure shown in the above embodiments is an example, and it can also be combined with other known technologies, and the embodiments can be combined with each other. Some parts of the structure can also be omitted or changed without departing from the spirit.

[0106] Explanation of reference numerals in the attached figures

[0107] 1. Power conversion devices (1a, 1b, 1c); 2. Motor drive devices (2a, 2b, 2c); 110 Commercial power supply; 120 Reactor; 130 Rectifier; 131-134, 621-624 Rectifier elements; 200 Smoothing section; 210 Capacitor; 310 Inverter; 311a-311f, 611-614 Switching elements; 312a-312f Freewheeling diodes; 313a, 313b Current detection sections; 314 Motor; 315 Compressor; 400 Control section; 501 Voltage and current detection section; 502 Voltage detection section; 600, 601 Boost section; 700, 701, 702 Rectifier and boost section; 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.

Claims

1. A power conversion device, wherein the power conversion device is provided with: a rectifying section that rectifies first alternating-current power supplied from a commercial power source; a capacitor connected to an output terminal of the rectifying section; an inverter connected to both ends of the capacitor, that converts power output from the rectifying section and the capacitor into second alternating-current power and outputs the second alternating-current power to a load having a motor; and a control section that controls only an operation of the inverter such that the second alternating-current power containing a ripple corresponding to a ripple of power flowing from the rectifying section to the capacitor is output from the inverter to the load, and a current flowing to the capacitor is suppressed, no discharge circuit or overvoltage protection circuit is provided for the capacitor, a capacitance of the capacitor is equal to or greater than a capacitance of the capacitor set in a case where an overvoltage protection circuit is connected to the capacitor, the capacitance of the capacitor is determined using a value calculated using an impedance of a reactor provided in the power conversion device, a system impedance, a current maximum value of the commercial power source, an inductive component of one phase of the motor, a current maximum value of the motor, a withstand voltage of an element to which a voltage from the capacitor is applied, and a maximum voltage of the capacitor in a steady state.

2. The power conversion device according to claim 1, wherein the capacitance of the capacitor is further defined by a system voltage of the commercial power source and an induced voltage of the motor at a time when the inverter is stopped.

3. The power conversion device according to claim 1 or 2, wherein the capacitance of the capacitor is smaller than a capacitance of the capacitor set in a case where a first control is not performed by the control section, the first control being a control of the operation of the inverter such that the second alternating-current power containing a ripple corresponding to a ripple of power flowing from the rectifying section to the capacitor is output from the inverter to the load.

4. The power conversion device according to claim 3, wherein the capacitance of the capacitor is determined using a value calculated using a frequency that is twice a frequency of the commercial power source, an allowable ripple voltage of the capacitor at the frequency that is twice, a capacitor current of the capacitor at the frequency that is twice at a time when the first control is not performed by the control section, and an input current ripple of the inverter at the frequency that is twice at a time when the first control is performed by the control section.

5. The power conversion device according to claim 1 or 2, wherein a capacitor current of a frequency component of the frequency that is twice of the commercial power source in the current flowing to the capacitor is equal to or smaller than a first capacitor current of a frequency component of twice a switching frequency of a switching element provided in the inverter.

6. The power conversion device according to claim 5, wherein a current component due to rotation of the motor is contained in the first capacitor current.

7. The power conversion device according to claim 5, wherein The power conversion device has a voltage step-up section that steps up the voltage of the first AC power, or has a rectification step-up section that rectifies the first AC power supplied from a commercial power supply and steps up the voltage of the first AC power instead of the rectification section, A capacitor current of a frequency component of 2 times the frequency of the commercial power supply in the current flowing to the capacitor is a second capacitor current of a frequency component of 2 times the switching frequency of a switching element included in the voltage step-up section or the rectification step-up section.

8. The power conversion device according to claim 7, wherein A current component due to rotation of the motor is included in the second capacitor current.

9. The power conversion device according to claim 1 or 2, wherein The capacitor is an electrolytic capacitor or a film capacitor.

10. The power conversion device according to claim 1 or 2, wherein A maximum value of the voltage ripple generated in the capacitor is less than 2 times a minimum value.

11. The power conversion device according to claim 1 or 2, wherein The rectification section performs full-wave rectification, and a voltage generated in the capacitor is not a full-wave rectified waveform shape of the commercial power supply.

12. The power conversion device according to claim 1 or 2, wherein The discharge circuit has an active element and a resistor, and the connection of the resistor to the capacitor is switched by turning on and off the active element.

13. The power conversion device according to claim 1 or 2, wherein The overvoltage protection circuit is a circuit that performs protection of an apparatus to avoid the voltage of the capacitor from rising above a certain voltage, and is not a snubber circuit that protects a switching element from damage by a surge voltage generated at the time of switching of the switching element.

14. A motor drive device, wherein The motor drive device has the power conversion device according to claim 1 or 2.

15. A refrigeration cycle application apparatus, wherein The refrigeration cycle application apparatus has the power conversion device according to claim 1 or 2.

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