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

Abstract

This power conversion device (1) comprises an AC / DC converter (100) that includes a reactor (141) and a switching element (142) that can operate while changing the switching frequency, the AC / DC converter (100) boosting and rectifying a power supply voltage applied from an AC power supply (110), converting the voltage into a DC voltage, and applying the converted DC voltage to a load (2). The switching frequency is controlled within a range between a set upper limit value and a set lower limit value, in a successively variable manner on the basis of a formula that is defined by using a command value Bref of the magnetic flux density of the reactor (141), the number of turns N of a winding of the reactor (141), the effective cross-sectional area Ae of a magnetic core of the reactor (141), the power supply voltage vac, a bus voltage Vdc that is the voltage value of the DC voltage, and the switching frequency fsw. The average switching frequency, which is the average value of the switching frequency fsw, is modified according to the operation state of the load (2) or the operation environment of the load (2).

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-DC converter that rectifies and boosts a power supply voltage applied from an AC power supply to convert it into a DC voltage, and applies the converted DC voltage to a load. For example, Patent Document 1 listed below discloses a technology for a power conversion device that is capable of reducing losses in a configuration that includes a single-transistor step-up AC-DC converter.

[0003] Patent No. 7109688

[0004] However, the technology of Patent Document 1 has a problem in that the loss and heat generation burden cannot be changed according to the load current, bus voltage, and component state, so that the loss and heat generation are unevenly concentrated in one component, resulting in uneven component deterioration. For this reason, it is desirable to be able to change the loss or heat generation burden of a component according to the load current, bus voltage, and component state.

[0005] The present disclosure has been made in view of the above, and aims to provide a power conversion device that can change the loss or heat generation load of components depending on the load current, bus voltage, and component state.

[0006] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes an AC-DC converter having a reactor and a switching element operable while changing a switching frequency, rectifying and boosting a power supply voltage applied from an AC power supply to convert it into a DC voltage, and applying the converted DC voltage to a load. The switching frequency is sequentially variably controlled within a range between set upper and lower limits based on a prescribed mathematical formula that uses a command value Bref for the magnetic flux density of the reactor, the number of turns N of the reactor winding, the effective cross-sectional area Ae of the reactor's magnetic core, the power supply voltage vac, a bus voltage Vdc that is a voltage value of the DC voltage, and a switching frequency fsw, and the average switching frequency, which is the average value of the switching frequency, is changed according to the operating state or operating environment of the load.

[0007] The power conversion device according to the present disclosure has an advantage in that it is possible to change the loss or heat generation load of components according to the load current, bus voltage, and component state.

[0008] FIG. 1 is a diagram showing an example of the configuration of a motor drive device including a power conversion device according to embodiment 1; FIG. 2 is a diagram showing an example of the configuration of a control system constructed in a control unit provided in the power conversion device according to embodiment 1; FIG. 3 is a diagram used to explain a first control operation in the power conversion device according to embodiment 1; FIG. 4 is a diagram showing an example of operation when the upper limit value of the switching frequency is lowered from the operating state of FIG. 3; FIG. 5 is a diagram used to explain a second control operation in the power conversion device according to embodiment 1; FIG. 6 is a diagram used to explain a third control operation in the power conversion device according to embodiment 1; FIG. 7 is a diagram showing an example of a hardware configuration realizing a control unit provided in the power conversion device according to embodiment 1; FIG. 8 is a diagram used to explain the control operation in the power conversion device according to embodiment 2;

[0009] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle application device according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. For the sake of simplicity, "switching" will be abbreviated as "SW" below.

[0010] Embodiment 1. Fig. 1 is a diagram showing an example of the configuration of a motor drive device 3 including a power conversion device 1 according to embodiment 1. The motor drive device 3 includes a power conversion device 1 connected to an AC power supply 110 and a load 2 connected to the power conversion device 1. The power conversion device 1 includes an AC-DC converter 100 that rectifies and boosts the power supply voltage applied from the AC power supply 110 to convert it into a DC voltage and applies the converted DC voltage to the load 2, and a control unit 400 that controls the operation of the AC-DC converter 100. The load 2 is a DC load that operates by receiving DC power from the power conversion device 1, and includes an inverter 310 and a motor 314. In the example of Fig. 1, the AC power supply 110 is a single-phase AC power supply, but may also be a three-phase AC power supply.

[0011] The inverter 310 is connected to the output terminal of the AC-DC converter 100. The inverter 310 includes a plurality of SW elements 312, which are turned on and off under the control of the control unit 400 to convert the DC voltage output from the AC-DC converter 100 into an AC voltage having a desired amplitude and phase, and apply the converted AC voltage to the motor 314. The SW elements 312 may be, for example, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), or a bipolar transistor, but are not limited to these. The circuit configuration of the inverter 310 may be a full-bridge circuit, a single-phase bridge circuit, a half-bridge circuit, or any other suitable configuration.

[0012] The motor 314 is, for example, a compressor motor for driving the compressor. The motor 314 rotates in accordance with the amplitude and phase of the AC voltage applied from the inverter 310 to perform compression. 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 motor windings (not shown) that are Y-connected, Delta-connected, or switchable between Y-connection and Delta-connection. The motor 314 is not limited to a compressor motor and may also be a fan motor, etc.

[0013] The AC-DC converter 100 includes a rectifier circuit 130 , a boost circuit 140 , a capacitor 210 , voltage detectors 501 and 502 , and a current detector 503 .

[0014] The rectifier circuit 130 includes a plurality of rectifier elements 132, and rectifies the power supply voltage applied from the AC power supply 110 and outputs the rectified voltage to the boost circuit 140. When the AC power supply 110 is the single-phase AC power supply shown in FIG. 1 , the rectifier circuit 130 configures a bridge circuit using four rectifier elements 132.

[0015] The boost circuit 140 boosts the rectified voltage rectified by the rectifier circuit 130 and outputs the boosted voltage to the capacitor 210 and the inverter 310. The boost circuit 140 includes a reactor 141, a SW element 142, a freewheeling diode 143, and a boost diode 144. The freewheeling diode 143 is connected in parallel to the SW element 142. The SW element 142 is turned on and off under the control of the control unit 400. The SW element 142 can operate while changing its SW frequency under the control of the control unit 400. The SW element 142 is, for example, an IGBT, a MOSFET, a bipolar transistor, or the like, but is not limited to these.

[0016] The capacitor 210 is connected to electrical wiring 212, 214 that electrically connects the boost circuit 140 and the inverter 310. The electrical wiring 212, 214 are also called DC buses. The electrical wiring 212 is a high-potential DC bus, and the electrical wiring 214 is a low-potential DC bus. The capacitor 210 is, for example, an electrolytic capacitor or a film capacitor. The capacitor 210 smoothes the rectified voltage. In this document, the voltage between the electrical wiring 212, 214, which is the DC voltage value applied by the boost circuit 140 to the inverter 310, is referred to as the "bus voltage," and is appropriately indicated with the symbol "Vdc."

[0017] The voltage detector 501 detects the power supply voltage vac that the AC power supply 110 applies to the rectifier circuit 130. The voltage detector 502 detects the bus voltage Vdc that the boost circuit 140 applies to the inverter 310. The current detector 503 detects the reactor current IL that flows through the reactor 141. The detected values ​​of the power supply voltage vac, the bus voltage Vdc, and the reactor current IL are input to the control unit 400.

[0018] The control unit 400 performs control calculations to control the on / off of the SW element 142 included in the boost circuit 140. The control unit 400 generates a SW signal Vsw1 for controlling the on / off of the SW element 142 included in the boost circuit 140 based on the detected values ​​of the power supply voltage vac, the reactor current IL, and the bus voltage Vdc, and outputs the SW signal Vsw1 to the boost circuit 140.

[0019] 1 , a SW signal for controlling the on / off of the SW element 312 included in the inverter 310 is not shown, but this SW signal may be generated by the control unit 400 or by a control unit (not shown) included in the inverter 310. This SW signal may be generated based on the detected value of the bus voltage Vdc, a current detector (not shown) for detecting the motor current flowing through the motor 314, a current detector (not shown) for detecting the inverter current supplied from the boost circuit 140 to the inverter 310, or the like.

[0020] 1, the reactor 141 is arranged between the rectifier circuit 130 and the boost diode 144, but the present invention is not limited to this configuration. The reactor 141 may be arranged between the AC power supply 110 and the rectifier circuit 130.

[0021] 2 is a diagram showing an example of the configuration of a control system 420 built in the control unit 400 included in the power conversion device 1 according to embodiment 1. As shown in FIG. 2 , the control system 420 includes adder-subtractors 401 and 404, PI (Proportional Integral) controllers 402 and 405, a current command generator 403, a duty ratio calculator 406, and a SW signal generator 407.

[0022] The PI controller 402 has a voltage control proportional gain Kvp, which is a proportional gain of voltage control, and a voltage control integral gain Kvi, which is an integral gain of voltage control. The PI controller 405 has a current control proportional gain Kip, which is a proportional gain of current control, and a current control integral gain Kii, which is an integral gain of current control.

[0023] An adder / subtractor 401 calculates a voltage deviation, which is the deviation between a bus voltage command value Vdc_ref and the detected value of the bus voltage Vdc. The bus voltage command value Vdc_ref is generated inside the control unit 400 or is commanded from outside the control unit 400. A PI controller 402 performs PI control on the voltage deviation and outputs the result to a current command generator 403. The current command generator 403 generates a reactor current command value IL_ref based on the output of the PI controller 402.

[0024] The adder / subtractor 404 calculates a current deviation, which is the deviation between the reactor current command value IL_ref and the detected value of the reactor current IL. The reactor current command value IL_ref is generated inside the control unit 400 or is commanded from outside the control unit 400. The PI controller 405 performs PI control on the current deviation and outputs it to the duty ratio calculator 406.

[0025] The duty ratio calculator 406 calculates a duty ratio based on the detected value of the power supply voltage vac, the detected value of the bus voltage Vdc, and the output of the PI controller 405. The SW signal generator 407 generates a SW signal Vsw1 based on the detected value of the power supply voltage vac, a command value Bref for the magnetic flux density of the reactor 141, and the duty ratio calculated by the duty ratio calculator 406. The command value Bref for the magnetic flux density is generated inside the control unit 400 or is commanded from outside the control unit 400.

[0026] Next, a description will be given of the main points of the operation of the power conversion device 1 according to embodiment 1. First, the control unit 400 controls the SW frequency fsw, which is the frequency of the SW signal Vsw1, based on the following equation (1).

[0027]

[0028] In the above formula (1), "Bref" is the command value of the magnetic flux density of the reactor 141, "vac" is the power supply voltage, and "Vdc" is the bus voltage. Also, "N" is the number of turns of the winding of the reactor 141, and "Ae" is the effective cross-sectional area of ​​the magnetic core of the reactor 141.

[0029] In the above formula (1), "(Vdc-|vac|) / Vdc" represents the duty ratio calculated by the duty ratio calculator 406. As a basic operation, the power conversion device 1 controls the SW frequency fsw using the above formula (1) so that the magnetic flux density of the reactor 141 is constant.

[0030] Fig. 3 is a diagram illustrating the first control operation of the power conversion device 1 according to the first embodiment. The horizontal axis of Fig. 3 represents time, the upper side of Fig. 3 shows the waveform of the magnetic flux density of the reactor 141, and the lower side of Fig. 3 shows the waveform of the SW frequency fsw. Furthermore, in Fig. 3, "T" represents one cycle of the power supply voltage. Therefore, a period of T / 4 is a period of 1 / 4 cycle of the power supply voltage.

[0031] As shown in FIG. 3 , the power conversion device 1 according to the first embodiment controls the SW frequency fsw so that the magnetic flux density of the reactor 141 is constant, except for a portion of one cycle T of the power supply voltage. To maintain the magnetic flux density of the reactor 141 constant, the magnetic flux density command value Bref is set to a constant value. Meanwhile, during a portion of one cycle T of the power supply voltage, i.e., a period around times t1 and t2 at which the power supply voltage vac crosses zero, |vac| ≈ 0. Therefore, if the SW frequency fsw is brought infinitely close to zero according to the above equation (1), the magnetic flux density of the reactor 141 theoretically diverges to infinity. To prevent this, as shown in FIG. 3 , a lower limit is set for the SW frequency fsw so that the SW frequency fsw does not fall below the lower limit. By setting a lower limit for the SW frequency fsw, an increase in the size and capacity of the reactor 141 can be suppressed.

[0032] In addition, in the first embodiment, the concept of an "average SW frequency" is introduced. The average SW frequency is the average value of one cycle T of the variably controlled SW frequency fsw. In FIG. 3, if either the upper limit or the lower limit of the SW frequency fsw is increased, or if both are increased, the average SW frequency increases. Also, in FIG. 3, if either the upper limit or the lower limit of the SW frequency fsw is decreased, or if both are decreased, the average SW frequency decreases. FIG. 4 is a diagram showing an example of operation when the upper limit of the SW frequency fsw is decreased from the operating state of FIG. 3. When the upper limit of the SW frequency fsw is decreased as shown in FIG. 4, the average SW frequency decreases. Also, FIG. 5 is a diagram showing an example of operation when the lower limit of the SW frequency fsw is increased from the operating state of FIG. 3. When the lower limit of the SW frequency fsw is increased as shown in FIG. 5, the average SW frequency increases.

[0033] Next, the relationship between losses in the power conversion device 1 according to the first embodiment and the SW frequency fsw will be described. In this paper, the reactor loss, the SW element loss, and the diode loss are focused on as losses in the power conversion device 1. The reactor loss is the loss in the reactor 141, and the SW element loss is the loss in the SW element 142. The diode loss is the loss in the boost diode 144, which is considered to have the largest loss among the rectifier element 132, the freewheel diode 143, and the boost diode 144.

[0034] The following four points should be considered when changing the SW frequency fsw. (a1) When changing the SW frequency fsw, the power factor improves as the average SW frequency, which is the average value of the changed SW frequency fsw, increases. Therefore, the higher the average SW frequency, the smaller the copper loss in the reactor loss, as well as the SW element loss and the diode loss. (a2) The greater the change range of the SW frequency fsw, the more dispersed the spectrum of the reactor current IL. Therefore, the greater the change range of the SW frequency fsw, the smaller the copper loss in the reactor loss. (a3) ​​The higher the average SW frequency, the smaller the magnetic flux density in the reactor 141. Therefore, the higher the average SW frequency, the smaller the iron loss in the reactor loss. (a4) The lower the average SW frequency, the fewer the number of switches. Therefore, the lower the average SW frequency, the smaller the SW loss and diode loss in the SW element loss.

[0035] Furthermore, when changing the SW frequency fsw, it is necessary to consider the operating state of the load 2. Here, as the operating state of the load 2, attention is focused on the load current, which is the current flowing through the load 2.

[0036] There are two possible relationships between the load current and the losses in the power conversion device 1: (b1) The smaller the load current, the smaller the copper loss in the reactor loss, the conduction loss in the SW element loss, and the diode loss. (b2) The iron loss in the reactor loss hardly changes depending on the load current.

[0037] Furthermore, when changing the SW frequency fsw, it is necessary to consider the operating environment of the load 2. Here, as the operating environment of the load 2, attention is focused on the bus voltage Vdc.

[0038] The following three points can be cited regarding the relationship between the bus voltage Vdc and the losses of the power conversion device 1. (c1) As the bus voltage Vdc decreases, the VT product, which is the product of the voltage applied to the reactor 141 (Voltage) and the application time (Time) of this voltage, and the current ripple of the reactor current IL both decrease. Therefore, as the bus voltage Vdc decreases, the iron loss and copper loss in the reactor loss decrease. (c2) As the bus voltage Vdc decreases, the duty ratio applied to the SW element 142 decreases, and the effective value of the current flowing through the SW element 142 decreases. Therefore, as the bus voltage Vdc decreases, the conduction loss and SW loss in the SW element loss decrease. (c3) The bus voltage Vdc is the voltage on the cathode side of the freewheel diode 143. Therefore, as the bus voltage Vdc decreases, the effective value of the current through the freewheel diode 143 increases. Therefore, the lower the bus voltage Vdc, the greater the diode loss.

[0039] In the first embodiment, the control unit 400 included in the power conversion device 1 controls the SW frequency fsw by taking into account the above-described relationship. FIG. 6 is a diagram illustrating a second control operation in the power conversion device 1 according to the first embodiment. FIG. 6 shows the relationship between the reactor loss, the element loss, and the total loss, which change depending on the load current. The element loss is the sum of the SW element loss and the diode loss, and the total loss is the sum of the reactor loss and the element loss. FIG. 7 is a diagram illustrating a third control operation in the power conversion device 1 according to the first embodiment. FIG. 7 shows the relationship between the reactor loss, the element loss, and the total loss, which change depending on the bus voltage Vdc. In FIGS. 6 and 7, the horizontal axis represents the average SW frequency, and the vertical axis represents the loss.

[0040] First, as shown in FIG. 6 , the respective proportions of reactor loss and element loss in the total loss change depending on the load current. For example, when the load current decreases, losses other than iron loss in the reactor loss decrease, and iron loss becomes dominant. Therefore, the proportion of reactor loss in the total loss increases. In this case, the intersection point between the reactor loss curve and the element loss curve moves to the right, and therefore the minimum point of the total loss also moves to the right. Therefore, by increasing the average SW frequency, the operating point on each loss curve can be moved to the minimum point of the total loss. Note that, as described above, the average SW frequency can be increased by increasing either the upper limit or the lower limit of the SW frequency fsw, or by increasing both.

[0041] Conversely, when the load current increases, the proportion of iron loss in the reactor loss becomes relatively smaller, and the proportion of reactor loss in the total loss decreases. In this case, the intersection point between the reactor loss curve and the element loss curve moves to the left, and therefore the minimum point of the total loss also moves to the left. Therefore, by lowering the average SW frequency, the operating point on each loss curve can be moved to the minimum point of the total loss. As mentioned above, to lower the average SW frequency, it is sufficient to lower either the upper limit or the lower limit of the SW frequency fsw, or to lower both.

[0042] As described above, if the average SW frequency is controlled in accordance with the load current so as to minimize the total loss, the total loss can be minimized and the operating efficiency of the power conversion device 1 can be maximized.

[0043] As shown in FIG. 7 , the respective proportions of reactor loss and element loss in the total loss change depending on the bus voltage Vdc. For example, when the bus voltage Vdc increases, the proportions of iron loss and element loss in the reactor loss relatively increase. In this case, the upper limit of the SW frequency fsw is increased, or the lower limit of the SW frequency fsw is decreased, or the upper limit is increased and the lower limit is decreased. By controlling in this manner, both iron loss and element loss in the reactor loss decrease. Therefore, by setting the average SW frequency at a point where the total loss is minimized, the total loss can be minimized and the operating efficiency of the power conversion device 1 can be maximized.

[0044] Conversely, when the bus voltage Vdc decreases, the proportion of iron loss and element loss in the reactor loss relative to the total loss decreases. In this case, the upper limit of the SW frequency fsw is lowered, or the lower limit of the SW frequency fsw is raised, or the upper limit is lowered and the lower limit is raised. By controlling in this manner, the proportion of iron loss and element loss in the reactor loss changes, so by setting the average SW frequency at a point where the total loss is minimized, the total loss can be minimized and the operating efficiency of the power conversion device 1 can be maximized.

[0045] It is also possible to change either or both of the upper and lower limits of the SW frequency fsw to control the components of the AC-DC converter 100 so that they operate within their rated temperatures. This control has the effect of reducing the possibility that the components of the AC-DC converter 100 will exceed their temperature protection thresholds.

[0046] Specifically, the control unit 400 performs the following control based on the temperatures of the components. The component temperatures are examples of the operating states of the load 2. The component temperatures include the SW element temperature, the reactor temperature, and the diode temperature. The SW element temperature is the temperature of the SW element 142, and the reactor temperature is the temperature of the reactor 141. Furthermore, the diode temperature is the temperature of the boost diode 144, which is considered to have the greatest temperature rise among the rectifying element 132, the freewheeling diode 143, and the boost diode 144.

[0047] First, when the control unit 400 prioritizes suppressing an increase in reactor temperature over the SW element temperature and diode temperature, it increases the average SW frequency by increasing either one or both of the upper and lower limits of the SW frequency. Also, when the control unit 400 prioritizes suppressing an increase in SW element temperature or diode temperature over the reactor temperature, it decreases the average SW frequency by decreasing either one or both of the upper and lower limits of the SW frequency.

[0048] The determination of which of the reactor temperature, the SW element temperature, and the diode temperature is to be given priority can be made based on the estimated values ​​of the respective temperatures or the values ​​measured by the temperature sensors.

[0049] Furthermore, the control unit 400 may change the average SW frequency depending on the deterioration state of the SW element 142 and the reactor 141. Specifically, the control unit 400 performs the following control.

[0050] When the degree of deterioration of the reactor 141 is greater than the degree of deterioration of the SW element 142, the control unit 400 increases the average SW frequency by increasing either or both of the upper and lower limits of the SW frequency.

[0051] In addition, when the degree of deterioration of the SW element 142 is greater than the degree of deterioration of the reactor 141, the control unit 400 lowers the average SW frequency by lowering either or both of the upper and lower limits of the SW frequency.

[0052] By performing the above control, it is possible to change the loss or heat generation burden of the components of the power conversion device 1, thereby preventing the deterioration of some components from progressing and shortening the lifespan of the power conversion device 1.

[0053] The deterioration state of a component can be determined based on the ambient temperature, which is the temperature of the environment in which the component is placed, and the component temperature relative to the value of the current flowing through the component. A data set showing the relationship between the ambient temperature and the component temperature relative to the current value may be stored in advance by the control unit 400, or the data set may be constructed based on measurement values ​​obtained during operation.

[0054] As a more specific degradation determination method, the following method can be used for the reactor 141. Generally, when the stress fastening the core changes, the iron loss and inductance change. Therefore, the degradation state can be determined from the peak value or its slope of the reactor current. Furthermore, when the core cracks, leakage flux increases eddy current loss, reducing inductance, increasing iron loss, and increasing the peak current. Furthermore, when the physical distance between the adhesive bonds in the gap changes, inductance decreases, iron loss increases, and the peak current increases. Therefore, the degradation state can be determined from the reactor temperature, the peak value of the reactor current, the slope of the reactor current, etc.

[0055] Furthermore, WO 2022 / 144986 and WO 2022 / 153520 disclose highly accurate methods for determining deterioration of SW elements. Therefore, when determining the deterioration state of the SW element 142, the techniques disclosed in these documents may be used.

[0056] 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 realizing the control unit 400 included in the power conversion device 1 according to the first embodiment. The above-described functions of the control unit 400 and the functions of a second embodiment, which will be described later, can be realized by a processor 91 and a memory 92 as shown in Fig. 8.

[0057] The processor 91 is a CPU (Central Processing Unit, also referred to as 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 the 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). The memory 92 is not limited to these, and may also be a magnetic disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0058] The memory 92 stores a program that executes the functions of the control unit 400. The processor 91 exchanges necessary information via an interface including an analog-to-digital converter and a digital-to-analog converter (not shown), and executes the program stored in the memory 92 to perform required processing. The results of calculations by the processor 91 can be stored in the memory 92.

[0059] As described above, according to the first embodiment, the power conversion device 1 sequentially variably controls the SW frequency fsw of the SW element 142 included in the boost circuit 140 of the AC-DC converter 100 based on a specified mathematical formula within a range between a set upper limit and a set lower limit, and changes the average SW frequency, which is the average value of the SW frequency fsw, in accordance with the operating state of the load 2 or the operating environment of the load 2. This makes it possible for the power conversion device 1 to change the loss or heat generation load of the components in accordance with the load current, bus voltage, and component states.

[0060] Embodiment 2. Fig. 9 is a diagram illustrating the control operation of the power conversion device 1 according to embodiment 2. The horizontal axis of Fig. 9 represents time. The upper part of Fig. 9 shows the waveform of one cycle of the power supply voltage, the center part of Fig. 9 shows the waveform of the change in the control gain in the control system 420, and the lower part of Fig. 3 shows the waveform of the SW frequency fsw.

[0061] The power conversion device 1 according to the second embodiment changes the gain values ​​of the control gains so as to follow the change in the SW frequency fsw in a similar manner, as shown in Fig. 9. The control gains related to the processing here are the voltage control proportional gain Kvp, the voltage control integral gain Kvi, the current control proportional gain Kip, and the current control integral gain Kii shown in the control system 420 in Fig. 2. Specifically, the gain values ​​of the control gains are changed in the following procedure.

[0062] The control unit 400 changes the current control proportional gain Kip, or both the current control proportional gain Kip and the voltage control proportional gain Kvp, among the control gains, based on the following equation (2) in response to a change in the SW frequency fsw.

[0063]

[0064] In the above equation (2), fsw_base is the reference SW frequency fsw, fsw_new is the calculated SW frequency fsw, Kbase is the control gain corresponding to the reference SW frequency fsw_base, and Knew is the control gain corresponding to the calculated SW frequency fsw_new.

[0065] Further, the current response angular frequency ωi, which is the angular frequency due to the control response of the current control, and the voltage response angular frequency ωv, which is the angular frequency due to the control response of the voltage control, are expressed by the following equations (3) and (4).

[0066]

[0067] The current response angular frequency ωi and the voltage response angular frequency ωv need to be separated by at least a factor of 5. Therefore, when only the current control proportional gain Kip is changed based on the SW frequency fsw, if the current response angular frequency ωi is less than or equal to 5 times the voltage response angular frequency ωv, the voltage control proportional gain Kvp is also changed based on the SW frequency fsw.

[0068] Generally, the break point angular frequency ωpi of a PI controller can be expressed by the following equation (5) using a proportional gain Kp and an integral gain Ki.

[0069]

[0070] Furthermore, the break point angular frequency ωpii of the PI controller for current control and the current response angular frequency ωi must be separated by at least five times, and the break point angular frequency ωpiv of the PI controller for voltage control and the voltage response angular frequency ωv must be separated by at least five times. Therefore, when changing the proportional gain Kip, if the break point angular frequency ωpii of the PI controller is less than or equal to five times the current response angular frequency ωi, the integral gain Ki is adjusted. When changing the proportional gain Kvp, if the break point angular frequency ωpiv of the PI controller is less than or equal to five times the voltage response angular frequency ωv, the integral gain Kvi is adjusted.

[0071] 10 is a diagram showing simulation results used to explain the effects of the power conversion device 1 according to the second embodiment. In FIG. 10, the first row shows the waveform of the power supply current Is, the second row shows the waveform of the power supply voltage vac in solid lines, and the waveform of the bus voltage Vdc in dashed lines. The third row shows the waveform of the SW frequency fsw, and the fourth row shows the waveform of the control gain. The left waveforms in the first to third rows are waveforms obtained when the control gain is fixed, and the right waveforms in the first to third rows are waveforms obtained when the control gain is varied. In the waveform obtained when the control gain is varied, the gain value of the control gain is changed to follow changes in the SW frequency fsw, as shown in FIG. 9.

[0072] As shown in the first waveform, when the control gain is fixed, pulsation appears in the waveform of the power supply current Is. In contrast, when the gain value of the control gain is changed so as to follow changes in the SW frequency fsw, the pulsation that appeared when the gain value of the control gain was fixed is eliminated or reduced. This is thought to be because the operation of the control system 420 is stabilized by changing the gain value of the control gain so as to follow changes in the SW frequency fsw.

[0073] As described above, according to the second embodiment, the power conversion device 1 includes the control unit 400 that performs control calculations to control the SW of the SW element 142, and the control unit 400 changes the control gain of the control system 420 built in the control unit 400 in accordance with changes in the average SW frequency. This allows the power conversion device 1 to enjoy the effects of the first embodiment and to operate the control system 420 stably even if the SW frequency fsw changes.

[0074] Third Embodiment Fig. 11 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to a third embodiment. The refrigeration cycle-applied device 900 according to the third embodiment includes the power conversion device 1 described in the first embodiment. The refrigeration cycle-applied device 900 according to the third embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 11, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0075] 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.

[0076] Inside the compressor 315, a compression mechanism 904 that compresses the refrigerant and a motor 314 that operates the compression mechanism 904 are provided.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 1 Power conversion device, 2 Load, 3 Motor drive device, 91 Processor, 92 Memory, 100 AC-DC converter, 110 AC power supply, 130 Rectifier circuit, 132 Rectifier element, 140 Boost circuit, 141 Reactor, 142, 312 SW element, 143 Freewheel diode, 144 Boost diode, 210 Capacitor, 212, 214 Electrical wiring, 310 Inverter, 314 Motor, 315 Compressor, 400 Control unit, 401, 404 Adder / subtractor, 402, 405 PI controller, 403 Current command generator, 406 Duty ratio calculator, 407 SW signal generator, 420 Control system, 501, 502 Voltage detector, 503 Current detector, 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. an AC-DC converter having a reactor and a switching element operable while changing a switching frequency, rectifying and boosting a power supply voltage applied from an AC power supply to convert it into a DC voltage, and applying the converted DC voltage to a load; The switching frequency is sequentially variably controlled within a range between a set upper limit value and a set lower limit value based on the following formula (1): An average switching frequency, which is an average value of the switching frequencies, is changed according to the operating state or the operating environment of the load. Power conversion device. [Equation 1] where Bref is the command value of the magnetic flux density of the reactor, N is the number of turns of the reactor winding, Ae is the effective cross-sectional area of ​​the reactor's magnetic core, vac is the power supply voltage, Vdc is the bus voltage which is the voltage value of the DC voltage, and fsw is the switching frequency.

2. The average switching frequency is changed in accordance with the load current, which is the current flowing through the load. The power conversion device according to claim 1 .

3. When the average switching frequency is changed in accordance with the load current, either one or both of the upper limit value and the lower limit value is changed. The power conversion device according to claim 2 .

4. When the load current decreases, either one or both of the upper limit value and the lower limit value is increased; When the load current increases, either one or both of the upper limit value and the lower limit value is reduced. The power conversion device according to claim 3 .

5. Changing the average switching frequency in response to the bus voltage The power conversion device according to claim 1 .

6. When the average switching frequency is changed according to the bus voltage, either one or both of the upper limit value and the lower limit value is changed. The power conversion device according to claim 5 .

7. When the bus voltage increases, the upper limit value is increased, or the lower limit value is decreased, or the upper limit value is increased and the lower limit value is decreased; When the bus voltage drops, the upper limit value is lowered, or the lower limit value is raised, or the upper limit value is lowered and the lower limit value is raised. The power conversion device according to claim 6.

8. the AC-DC converter includes a boost diode; The average switching frequency is changed in accordance with a reactor temperature, which is the temperature of the reactor, a switching element temperature, which is the temperature of the switching element, and a diode temperature, which is the temperature of the boost diode. The power conversion device according to claim 1 .

9. When suppressing an increase in the reactor temperature with priority over an increase in the switching element temperature and an increase in the diode temperature, either one or both of the upper limit value and the lower limit value are increased; When suppressing an increase in the switching element temperature or the diode temperature with priority over an increase in the reactor temperature, one or both of the upper limit value and the lower limit value are reduced. The power conversion device according to claim 8.

10. The average switching frequency is changed depending on the deterioration state of the switching element and the reactor. The power conversion device according to claim 1 .

11. When the degree of deterioration of the reactor is higher than the degree of deterioration of the switching element, either one or both of the upper limit value and the lower limit value is increased, When the degree of deterioration of the switching element is higher than the degree of deterioration of the reactor, either one or both of the upper limit value and the lower limit value are reduced. The power conversion device according to claim 10.

12. a control unit that performs control calculations to control the switching of the switching element; The control unit changes a control gain of a control system established in the control unit in response to a change in the average switching frequency. The power conversion device according to claim 1 .

13. The control gain is calculated using the following formula (2) with respect to the control gain of the reference switching frequency: The power converter according to claim 12. [Equation 2] Here, fsw_base indicates a reference switching frequency, fsw_new indicates a calculated switching frequency, Kbase indicates a reference switching control gain, and Knew indicates a calculated control gain of the switching frequency.

14. A motor drive device comprising the power conversion device according to any one of claims 1 to 13.

15. A refrigeration cycle device comprising the power conversion device according to any one of claims 1 to 13.

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