Power conversion device, refrigeration cycle device, and air conditioner

Abstract

The power conversion device (100) includes: a reactor (5); a rectifier circuit (6) having: a first bridge arm (30) having switching elements (1, 2) connected in series; and a second bridge arm (32) connected in parallel with the first bridge arm (30) and having switching elements (3, 4) connected in series; and a smoothing capacitor (7) for smoothing the output voltage of the rectifier circuit (6). In addition, the power conversion device (100) includes: an inverter (8) for converting a DC voltage smoothed by the smoothing capacitor (7) into a driving voltage for driving a motor (52) and applying the driving voltage to the motor (52); a voltage detection unit (11) for detecting the DC voltage; and a control unit (10) for controlling the operation of the rectifier circuit (6) and the inverter (8). The control unit (10) controls the operation of the switching elements (1, 2) based on the detected values ​​of the induced voltage and the DC voltage caused by the motor (52).

Description

Technical Field

[0001] The present disclosure relates to a power conversion device including a diode bridge-less (DBL) rectifier circuit, a refrigeration cycle device including the power conversion device, and an air conditioner equipped with the refrigeration cycle device. Background Art

[0002] As a prior art related to power conversion devices equipped with DBL rectifier circuits, the technology described in Patent Document 1 below is available. Patent Document 1 discloses a technique for implementing synchronous rectification, wherein a switching element connected to the positive electrode of a smoothing capacitor is turned on for at least a portion of the time that current flows through a bridge circuit, while switching elements not included in the current path are maintained in the off state. The technique is described as enabling highly efficient power conversion.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-7326

[0004] However, the synchronous rectification described in Patent Document 1 does not consider the impact of motor induced voltage on efficiency when the load is a motor. In the high-speed range where the motor rotates at high speeds, the motor induced voltage increases, increasing the motor current and impacting efficiency. Therefore, there is room for improvement in motor efficiency in this high-speed range. Summary of the Invention

[0005] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to obtain a power conversion device capable of further improving the efficiency of a motor in a high-speed rotation range.

[0006] In order to solve the above-mentioned problems and achieve the purpose, the power conversion device disclosed in the present invention includes: a reactor; and a rectifier circuit, the rectifier circuit including: a first bridge arm, in which a first upper arm element and a first lower arm element are connected in series; and a second bridge arm, which is connected in parallel with the first bridge arm and in which a second upper arm element and a second lower arm element are connected in series. In the rectifier circuit, a power supply voltage output from an AC power supply is applied between the connection point between the first upper arm element and the first lower arm element, and the connection point between the second upper arm element and the second lower arm element via the reactor. In addition, the power conversion device includes: a smoothing capacitor, which smoothes the output voltage of the rectifier circuit; and an inverter, which converts the DC voltage smoothed by the smoothing capacitor into a drive voltage for driving a motor and applies the voltage to the motor. Furthermore, the power conversion device includes a first voltage detection unit for detecting the DC voltage, and a control unit for controlling the operation of the rectifier circuit and the inverter. The control unit controls the operations of the first upper arm element and the first lower arm element based on the detected values ​​of the induced voltage and the DC voltage caused by the motor.

[0007] According to the power conversion device of the present disclosure, it is possible to achieve further improvement in the efficiency of the motor in the high-speed rotation range. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a diagram showing a configuration example of a power conversion device according to the first embodiment.

[0009] Figure 2 This is a diagram schematically showing the current-loss characteristics of a general metal oxide semiconductor field effect transistor (MOSFET).

[0010] Figure 3 This is a diagram showing one of the switching patterns related to the basic operation of the rectifier circuit in the first embodiment.

[0011] Figure 4 This is another diagram showing the switching pattern related to the basic operation of the rectifier circuit in the first embodiment.

[0012] Figure 5 This is a diagram showing a first path of current flowing through the rectifier circuit according to the first embodiment.

[0013] Figure 6 This is a diagram showing a second path of current flowing through the rectifier circuit according to the first embodiment.

[0014] Figure 7 This is a diagram showing a third path of current flowing through the rectifier circuit according to the first embodiment.

[0015] Figure 8 This is a diagram showing a fourth path of current flowing through the rectifier circuit according to the first embodiment.

[0016] Figure 9 This is a flowchart for explaining the operation of the main parts in the first embodiment.

[0017] Figure 10 This is a timing chart for explaining the operation of the main parts in the first embodiment.

[0018] Figure 11 This is a diagram showing a configuration example of a power conversion device according to a modification of the first embodiment.

[0019] Figure 12 This is a diagram showing a configuration example of a power conversion device according to a second embodiment.

[0020] Figure 13 This is a diagram showing a switching pattern related to the basic operation of the rectifier circuit and the short-circuit circuit in the second embodiment.

[0021] Figure 14 This is a diagram showing a fifth path of current flowing through the rectifier circuit or the short-circuit circuit in the second embodiment.

[0022] Figure 15 This is a diagram showing a sixth path of current flowing through the rectifier circuit or the short-circuit circuit in the second embodiment.

[0023] Figure 16 This is a diagram showing a seventh path of current flowing through the rectifier circuit or the short-circuit circuit in the second embodiment.

[0024] Figure 17 This is a diagram showing an eighth path of current flowing through the rectifier circuit or the short-circuit circuit in the second embodiment.

[0025] Figure 18 This is a timing chart for explaining the operation of the main parts in the second embodiment.

[0026] Figure 19 This figure shows the configuration of a power conversion device having a boosting function as a comparative example.

[0027] Figure 20 It is a diagram showing a configuration example of a refrigeration cycle device according to a third embodiment. DETAILED DESCRIPTION

[0028] Implementation method 1.

[0029] Figure 1 FIG. 1 is a diagram showing a configuration example of a power conversion device 100 according to Embodiment 1. Figure 1 As shown, the power conversion device 100 according to the first embodiment includes a reactor 5, a rectifier circuit 6, a smoothing capacitor 7, an inverter 8, a control unit 10, voltage detection units 11 and 13, a current detection unit 12, and a gate circuit unit 14. In the following description, the voltage detection unit 11 may be referred to as a "first voltage detection unit," and the voltage detection unit 13 may be referred to as a "second voltage detection unit."

[0030] Power conversion device 100 applies an AC voltage to motor 52 to drive motor 52. AC power supply 50 applies a power supply voltage Vs to power conversion device 100. Motor 52 is used as a drive unit to drive a load (not shown). An example of a load is a compressor. Compressors are installed in the refrigeration cycle of air conditioners, refrigerators, or freezers.

[0031] A typical rectifier circuit has a structure consisting of four diodes connected in a bridge. In contrast, the rectifier circuit 6 of the first embodiment is a DBL rectifier circuit. A DBL rectifier circuit has a structure consisting of four switching elements connected in a bridge. That is, in a DBL rectifier circuit, each of the four diodes is replaced by a switching element.

[0032] Rectifier circuit 6 includes a first bridge arm 30 and a second bridge arm 32 connected in parallel with first bridge arm 30. First bridge arm 30 includes switching element 1 as a first upper arm element and switching element 2 as a first lower arm element. Switching element 1 and switching element 2 are connected in series. Second bridge arm 32 includes switching element 3 as a second upper arm element and switching element 4 as a second lower arm element. Switching element 3 and switching element 4 are connected in series. The first and second upper arm elements are connected to the positive electrode of smoothing capacitor 7, and the first and second lower arm elements are connected to the negative electrode of smoothing capacitor 7.

[0033] exist Figure 1 In the figure, a diode is connected in parallel to each of the switching elements 1, 2, 3, and 4. An example of the switching elements 1, 2, 3, and 4 is the MOSFET shown in the figure. When MOSFETs are used for the switching elements 1, 2, 3, and 4, parasitic diodes exist within the elements. Therefore, when MOSFETs are used, parasitic diodes are used, thereby omitting the parallel-connected diodes.

[0034] Unlike unidirectional devices like diodes, which allow current to flow in only one direction, MOSFETs are generally bidirectional devices that allow current to flow in both directions. In other words, if a charge is supplied to the MOSFET's gate to turn it on, current can also flow in the opposite direction. The opposite direction mentioned here refers to the direction opposite to the current flowing through the parasitic diode built into the MOSFET.

[0035] One end of the reactor 5 is connected to one side of the AC power supply 50, and the other end of the reactor 5 is connected to the connection point 34 of the switching elements 1 and 2. The connection point 36 of the switching elements 3 and 4 is connected to the other side of the AC power supply 50. Figure 1 In a configuration in which reactor 5 is connected to the other side of AC power source 50, reactor 5 can be divided into two, and the two divided reactors 5 can be connected to both one side and the other side of AC power source 50. In either configuration, in rectifier circuit 6, the AC voltage output by AC power source 50, namely, power supply voltage Vs, is applied between connection point 34 and connection point 36 via reactor 5. Connection points 34 and 36 constitute the input terminals of rectifier circuit 6.

[0036] A smoothing capacitor 7 is connected between output terminals of the rectifier circuit 6. The rectifier circuit 6 rectifies a power supply voltage Vs applied from an AC power supply 50 via a reactor 5 and converts the voltage into a DC voltage.

[0037] The smoothing capacitor 7 is charged by the output of the rectifier circuit 6. The smoothing capacitor 7 smoothes the output voltage of the rectifier circuit 6. An inverter 8 is connected to both ends of the smoothing capacitor 7. The inverter 8 converts the DC voltage Vdc smoothed by the smoothing capacitor 7 into a drive voltage for driving the motor 52 and applies the voltage to the motor 52.

[0038] The motor 52 includes a rotation sensor 54. The rotation sensor 54 detects the position or speed of a rotating member (not shown) of the motor 52. The detection value of the rotation sensor 54 is input to the control unit 10. The control unit 10 calculates the rotation speed of the motor 52 based on the detection value of the rotation sensor 54.

[0039] The voltage detector 13 detects the power supply voltage Vs. The voltage detector 11 detects the DC voltage Vdc smoothed by the smoothing capacitor 7. The DC voltage Vdc is also the input voltage to the inverter 8. The detected values ​​of the power supply voltage Vs and the DC voltage Vdc are input to the control unit 10.

[0040] The current detection unit 12 detects the primary current Is flowing to the input side of the rectifier circuit 6. The primary current Is is also the reactor current flowing to the reactor 5. The detected value of the primary current Is is input to the control unit 10. Figure 1 In the example, the detector of the current detection unit 12 is arranged in the electrical wiring on one side of the AC power supply 50, but the present invention is not limited to this. The detector of the current detection unit 12 may be arranged in the electrical wiring on the other side of the AC power supply 50.

[0041] The control unit 10 generates a control signal for controlling conduction of the switching elements 1 , 2 , 3 , and 4 based on the detected values ​​of the power supply voltage Vs, the primary current Is, the DC voltage Vdc, and the rotation speed of the motor 52 , and outputs the control signal to the gate circuit unit 14 .

[0042] Based on the control signal output from the control unit 10, the gate circuit unit 14 generates and outputs gate signals Q1, Q2, Q3, and Q4 for driving the switching elements 1, 2, 3, and 4. Gate signal Q1 is a signal that controls the conduction state of switching element 1 from on to off, or from off to on. Gate signal Q2 is a signal that controls the conduction state of switching element 2 from on to off, or from off to on. Gate signal Q3 is a signal that controls the conduction state of switching element 3 from on to off, or from off to on. Gate signal Q4 is a signal that controls the conduction state of switching element 4 from on to off, or from off to on.

[0043] When driving the switching elements 1, 2, 3, and 4, the gate signals Q1, Q2, Q3, and Q4 are converted to and outputted at voltage levels capable of driving the switching elements 1, 2, 3, and 4. The gate circuit unit 14 can be implemented using a level shift circuit or the like.

[0044] The control unit 10 includes a processor 10a and a memory 10b. The processor 10a is a computing unit such as a microprocessor, microcomputer, CPU (Central Processing Unit), or DSP (Digital Signal Processor). The memory 10b is a nonvolatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), or EEPROM (registered trademark) (Electrically Erasable Programmable Read-Only Memory).

[0045] Memory 10b stores programs that execute the functions of control unit 10. Processor 10a transmits and receives necessary information via an interface including an analog-to-digital converter and a digital-to-analog converter (not shown). Processor 10a executes the programs stored in memory 10b to perform the necessary processing. Calculation results from processor 10a are stored in memory 10b.

[0046] Figure 2 This is a diagram schematically showing the current-loss characteristics of a typical MOSFET. Figure 2 Indicates the loss characteristics of the diode and the loss characteristics of the MOSFET when it is turned on. Figure 2 As shown, in region A, where the current is smaller than current value I0, the diode loss is greater than the switching element loss. Conversely, in region B, where the current is larger than current value I0, the diode loss is smaller than the switching element loss. By utilizing these characteristics, the device can operate efficiently by using synchronous rectification, which turns on the switching element connected in antiparallel to the diode at the timing when the primary current Is flows through the diode.

[0047] Next, refer to Figure 3 and Figure 4 The basic operation of the power conversion device 100 according to the first embodiment will be described with reference to the accompanying drawings. Figure 3 This is a diagram showing one of the switching patterns related to the basic operation of the rectifier circuit 6 in the first embodiment. Figure 4 This is another diagram showing the switching pattern related to the basic operation of the rectifier circuit 6 in the first embodiment. Figure 3 and Figure 4 The horizontal axis represents time. Figure 3 and Figure 4 In each of the figures, the operating waveforms of the power supply voltage Vs, primary current Is, gate signal Q1, gate signal Q2, gate signal Q3, and gate signal Q4 are shown in order from the top. The polarity of the power supply voltage Vs is referred to as "positive polarity" when the power supply voltage Vs takes a positive value, and as "negative polarity" when the power supply voltage Vs takes a negative value.

[0048] exist Figure 3 In this example, when the power supply voltage Vs is positive, the switching element 4 is controlled to be on while current is flowing through the parallel-connected diode. In other words, when the power supply voltage Vs is positive, the switching element 4 is controlled to be on when current is flowing through the parallel-connected diode, and is controlled to be off when current is not flowing through the parallel-connected diode. This operation is the aforementioned synchronous rectification.

[0049] When the power supply voltage Vs is negative, the switching element 3 is controlled to be on while current is flowing through the parallel-connected diode. In other words, when the power supply voltage Vs is negative, the switching element 3 is controlled to be on when current is flowing through the parallel-connected diode, and is controlled to be off when current is not flowing through the parallel-connected diode. This operation is also synchronous rectification.

[0050] In addition, Figure 3 In the example, when the power supply voltage Vs is positive, switching element 2 is controlled to be on at the same time as switching element 4 is controlled to be on. At this time, a primary current Is flows through rectifier circuit 6 via the AC power supply 50, reactor 5, switching element 2, switching element 4, and AC power supply 50. This action, in which primary current Is flows without passing through smoothing capacitor 7, is called a "power supply short circuit."

[0051] The power supply short-circuiting operation accumulates energy in the reactor 5. The subsequent synchronous rectification operation then releases the energy accumulated in the reactor 5 to the smoothing capacitor 7. This boosts the voltage of the smoothing capacitor 7, namely the DC voltage Vdc.

[0052] Furthermore, when the power supply is short-circuited, the switching element 1 is controlled to be off. This is to prevent the charge stored in the smoothing capacitor 7 from flowing through the switching elements 1 and 2. Figure 3 , the power supply short circuit is performed twice, but the present invention is not limited thereto. The power supply short circuit may be performed only once, or three or more times, or a plurality of times or less.

[0053] When the power supply voltage Vs is positive, after switching element 2 is switched on and off once or more, normal synchronous rectification is resumed. Specifically, switching element 1 is switched on while switching element 4 is switched on. Furthermore, switching element 1, the upper arm element, and switching element 4, the lower arm element, are positioned diagonally opposite each other.

[0054] When the power supply voltage Vs is negative, the switch element 1 is controlled to be turned on at the same time as the switch element 3 is controlled to be turned on. At this time, the primary current Is flows through the AC power supply 50, the switch element 3, the switch element 1, the reactor 5, and the AC power supply 50 in the rectifier circuit 6. This operation is also a power supply short-circuit operation in which the primary current Is flows without passing through the smoothing capacitor 7. During this short-circuit, the switch element 2 is controlled to be turned off. This is to prevent the charge stored in the smoothing capacitor 7 from flowing through the switch elements 1 and 2. Although the same as shown in FIG. Figure 3 In the positive half cycle, the power supply short-circuit is similarly performed twice in the example, but the power supply short-circuit may be performed once, three times or more, or multiple times or less.

[0055] Furthermore, when the power supply voltage Vs is negative, after switching element 1 is switched on once or more, normal synchronous rectification is resumed. Specifically, switching element 2 is switched on while switching element 3 is switched on. Furthermore, switching element 2, the lower arm element, and switching element 3, the upper arm element, are positioned diagonally opposite each other.

[0056] Next, explain Figure 4 First, the switching element 4 is controlled to be on during the period when the power supply voltage Vs is positive, and is controlled to be off during the period when the power supply voltage Vs is negative. Furthermore, the switching element 3 is controlled to be off during the period when the power supply voltage Vs is positive, and is controlled to be on during the period when the power supply voltage Vs is negative.

[0057] When the power supply voltage Vs is positive, switching element 2 is controlled to be on at the same time that switching element 4 is controlled to be on. This operation is called a power short-circuit operation. After the power short-circuit operation, switching element 2 is controlled to be off, and switching element 1 is controlled to be on. This operation is called a synchronous rectification operation. Subsequently, switching elements 1 and 2 are alternately turned on and off, and the power short-circuit operation and synchronous rectification operation are repeated alternately.

[0058] When the power supply voltage Vs is negative, switching element 1 is controlled to be on at the same time that switching element 3 is controlled to be on. This operation is a power short-circuit operation. After the power short-circuit operation, switching element 1 is controlled to be off, and switching element 2 is controlled to be on. This operation is a synchronous rectification operation. Subsequently, switching elements 1 and 2 are alternately turned on and off, and the power short-circuit operation and synchronous rectification operation are repeated alternately.

[0059] Through the above operation, the DC voltage Vdc is boosted to a voltage exceeding the power supply voltage Vs. In addition, since the primary current Is flows throughout the entire half cycle of the power supply voltage Vs, the power factor is improved.

[0060] Figure 3 and Figure 4 The difference in the operation of is whether the switching control is implemented throughout the entire region of one cycle of the power supply voltage Vs. Figure 4 The action is called "global switch". Figure 3 The action is called "partial switching". In addition, focusing on the difference in switching speed, Figure 4 The action is called "high-speed switching". Figure 3 The action is called "slow switching".

[0061] In order to obtain a large step-up ratio, Figure 4 On the other hand, in order to reduce the switching loss, Figure 3 Therefore, if the motor 52 is switched to the Figure 3 Actions and Figure 4 The operation can increase the variable width of the DC voltage Vdc and improve the efficiency.

[0062] Next, the operation of the main portion of the power conversion device 100 according to Embodiment 1 will be described. Furthermore, before describing the operation of the main portion, the path of the primary current Is flowing through the rectifier circuit 6 according to Embodiment 1 will be described.

[0063] Figure 5 : is a diagram showing a first path of current flowing in the rectifier circuit 6 of the first embodiment. Figure 5 The current path shown is defined as "current path (1)". Figure 5 Figure 2 shows the current path for synchronous rectification when power supply voltage Vs is positive. Switching elements 1 and 4 are on, while switching elements 2 and 3 are off. In this state, current flows through AC power supply 50, reactor 5, switching element 1, inverter 8, switching element 4, and AC power supply 50.

[0064] Figure 6: is a diagram showing a second path of current flowing in the rectifier circuit 6 of the first embodiment. Figure 6 The current path shown is defined as "current path (2)". Figure 6 Figure 2 shows the current path for a power supply short circuit when power supply voltage Vs is positive. Switching elements 2 and 4 are on, while switching elements 1 and 3 are off. In this state, current flows through AC power supply 50, reactor 5, switching element 2, switching element 4, and AC power supply 50.

[0065] Figure 7 : is a diagram showing a third path of current flowing in the rectifier circuit 6 of the first embodiment. Figure 7 The current path shown is defined as "current path (3)". Figure 7 Figure 2 shows the current path for synchronous rectification when the power supply voltage Vs is negative. Switching elements 2 and 3 are on, and switching elements 1 and 4 are off. In this state, current flows through AC power supply 50, switching element 3, inverter 8, switching element 2, reactor 5, and AC power supply 50.

[0066] Figure 8 : is a diagram showing a fourth path of current flowing in the rectifier circuit 6 of the first embodiment. Figure 8 The current path shown is defined as "current path (4)". Figure 8 Figure 2 shows the current path for a power supply short circuit when power supply voltage Vs is negative. Switching elements 1 and 3 are on, and switching elements 2 and 4 are off. In this state, current flows through AC power supply 50, switching element 3, switching element 1, reactor 5, and AC power supply 50.

[0067] Figure 9 This is a flowchart for explaining the operation of the main parts in embodiment 1. First, the control unit 10 calculates the current rotation speed of the motor 52 based on the detection value of the rotation sensor 54 (step S101). Next, the control unit 10 calculates the induced voltage sensed by the motor 52 based on the current rotation speed and the induced voltage constant (step S102). The larger the induced voltage constant, the larger the induced voltage. In addition, the faster the rotation speed, the larger the induced voltage. In addition, the induced voltage constant is one of the parameters that records the characteristics of the motor used. Data related to the motor constant including the induced voltage constant is stored in the memory 10b in the control unit 10.

[0068] In parallel with step S101, the control unit 10 checks the current DC voltage detection value (step S103). The control unit 10 compares the induced voltage with the DC voltage (step S104). If the induced voltage is lower than the DC voltage (step S104, No), the process returns to the beginning and repeats steps S101 and S103. On the other hand, if the induced voltage exceeds the DC voltage (step S104, Yes), the DC voltage is boosted (step S105). After step S105, the process returns to the beginning and repeats steps S101 and S103.

[0069] In step S104 , the determination is “No” if the induced voltage is equal to the DC voltage, but it may be determined as “Yes.” That is, it may be determined as either “Yes” or “No” if the induced voltage is equal to the DC voltage.

[0070] Figure 10 This is a time chart for explaining the operation of the main parts in Implementation 1. Figure 10 In accordance with Figure 9 The main part of the action waveform when the flowchart is in action. Specifically, Figure 10 In the figure, the operating waveforms of the power supply voltage Vs, primary current Is, DC voltage Vdc and induced voltage Vm, zero-crossing signal Zc, gate signal Q1, gate signal Q2, gate signal Q3, and gate signal Q4 are shown in order from the top. The horizontal axis represents time. Regarding DC voltage Vdc and induced voltage Vm, DC voltage Vdc is represented by a solid line, and induced voltage Vm is represented by a dashed-dotted line.

[0071] The zero-crossing signal Zc is a signal generated inside the control unit 10 based on the detected value of the power supply voltage Vs. Figure 10 The diagram shows a "High" output when the power supply voltage Vs is positive and a "Low" output when the power supply voltage Vs is negative, but the present invention is not limited to this. The zero-crossing signal Zc may also be a signal that outputs a "Low" output when the power supply voltage Vs is positive and a "High" output when the power supply voltage Vs is negative.

[0072] As described above, when the power supply voltage Vs is positive, that is, when the zero-crossing signal Zc is High, the gate signal Q4 is turned on, corresponding to the timing of the flow of the primary current Is. Conversely, when the power supply voltage Vs is negative, that is, when the zero-crossing signal Zc is Low, the gate signal Q3 is turned on, corresponding to the timing of the flow of the primary current Is.

[0073] Here, in Figure 10In the operation waveform, during the period T1 when the gate signal Q4 is turned on, the DC voltage Vdc is greater than the induced voltage Vm. Therefore, the boost operation is not performed, and the current flows in the current path (1) defined above. Figure 10 In the figure, it is marked as "(1)". The other current paths are marked in the same way below.

[0074] Furthermore, during the period T2 when the gate signal Q3 is on, the DC voltage Vdc is also larger than the induced voltage Vm. Therefore, the voltage step-up operation is not performed, and the current flows in the current path (3) defined above.

[0075] On the other hand, in the next cycle of the power supply voltage Vs, there is a period during which the induced voltage Vm is greater than the DC voltage Vdc. Therefore, during period T3 when the gate signal Q4 is on, the current flow in current path (1) and the current flow in current path (2) are repeated. Furthermore, during period T4 when the gate signal Q3 is on, the current flow in current path (3) and the current flow in current path (4) are repeated. That is, synchronous rectification and boosting operations are repeated during periods T3 and T4.

[0076] Furthermore, during periods T3 and T4, the synchronous rectification and boost operations can be switched without changing the switching operation of gate signals Q3 and Q4, which perform synchronous rectification. In other words, during periods T3 and T4, the synchronous rectification and boost operations can be switched without intervening a period during which the switching operation is stopped.

[0077] When the rotation speed of motor 52 increases, the induced voltage Vm of motor 52 increases. Consequently, under the same load conditions, the current flowing through motor 52, i.e., the motor current, increases, increasing losses in motor 52. In contrast, in the control of Embodiment 1, when the induced voltage Vm of motor 52 exceeds DC voltage Vdc, the synchronous rectification is switched to a boost operation to boost DC voltage Vdc. This suppresses increases in motor current. This further improves the efficiency of motor 52 in the high-speed rotation range.

[0078] Furthermore, in the control of Embodiment 1, since synchronous rectification and boost operations can be switched without intervening a switching stop period during which switching control is not performed, the switching between synchronous rectification and boost operations can be performed quickly. This can suppress the increase in losses associated with the boost operation.

[0079] In addition, Figure 1 In the embodiment, the motor 52 is provided with the rotation sensor 54, but the present invention is not limited to this structure. Figure 11 That's how it's constructed. Figure 11FIG. 1 is a diagram showing a configuration example of a power conversion device 100A according to a modified example of the first embodiment. Figure 11 As shown, the motor 52 may include an induced voltage detector 56, and the detection value of the induced voltage detector 56 may be input to the control unit 10 of the power conversion device 100A. The induced voltage detector 56 directly detects the induced voltage induced by the winding (not shown) of the motor 52.

[0080] The detection value of the induced voltage detector 56 is input to the control unit 10. Figure 11 In the case of the power conversion device 100A shown in FIG. 1 , the induced voltage does not need to be calculated, so the calculation can be omitted. Figure 9 The processing of steps S101 and S102 in the flowchart.

[0081] In addition, Figure 11 Although three detectors are shown in the middle figure, at least one detector is sufficient.

[0082] In addition, Figure 1 and Figure 11 In the structure, the switching elements 1, 2, 3, and 4, the rectifier elements constituting the rectifier circuit 6, and the switching elements constituting the inverter 8 are typically formed using semiconductor elements made of silicon-based materials, but are not limited to this. Among these semiconductor elements, the switching elements 1, 2, 3, and 4, the rectifier elements constituting the rectifier circuit 6, and the switching elements constituting the inverter 8 may also be formed using wide band gap (WBG) semiconductors such as silicon carbide, gallium nitride, gallium oxide, or diamond.

[0083] Generally, WBG semiconductors have lower losses than silicon semiconductors. Therefore, using WBG semiconductors to form these semiconductor elements can create even lower-loss devices. Furthermore, WBG semiconductors have a higher withstand voltage than silicon semiconductors. This increases the withstand voltage and permissible current density of semiconductor elements, allowing for miniaturization of semiconductor modules incorporating semiconductor switching elements. Furthermore, because WBG semiconductors have high heat resistance, the heat dissipation unit used to dissipate heat generated in the semiconductor module can be miniaturized, simplifying the heat dissipation structure used to dissipate heat generated in the semiconductor module.

[0084] As described above, the power conversion device according to Embodiment 1 includes a reactor and a rectifier circuit that applies a power supply voltage output from an AC power supply via the reactor. The rectifier circuit includes: a first arm having a first upper arm element and a first lower arm element connected in series; and a second arm connected in parallel with the first arm and having a second upper arm element and a second lower arm element connected in series. The control unit detects the DC voltage smoothed by the smoothing capacitor that smoothes the output voltage of the rectifier circuit, and controls the operation of the first upper arm element and the first lower arm element based on the detected value of the DC voltage and the induced voltage caused by the motor. This further improves the efficiency of the motor in the high-speed rotation range where the motor induced voltage increases. In addition, the second upper arm element and the second lower arm element are elements that are controlled to be turned on when current flows to the diodes connected in parallel with them, and are controlled to be turned off when current does not flow to the diodes.

[0085] In the above control, when the induced voltage is lower than the detected DC voltage value, the first upper and lower arm elements are alternately turned on and off every half-cycle of the power supply voltage. Furthermore, when the induced voltage changes from being lower than the detected DC voltage value to being higher than the detected DC voltage value, the first upper and lower arm elements are alternately turned on and off within the same half-cycle regardless of the polarity of the power supply voltage. This control allows for rapid switching between synchronous rectification and boost operations, thus minimizing the increase in losses associated with the boost operation.

[0086] Implementation method 2.

[0087] Figure 12 FIG. 1 is a diagram showing a configuration example of a power conversion device 100B according to Embodiment 2. In the power conversion device 100B according to Embodiment 2, Figure 1 In the configuration of the power conversion device 100 according to the first embodiment shown, a short-circuit circuit 17 is provided between the reactor 5 and the rectifier circuit 6. The short-circuit circuit 17 includes a short-circuit switch element 16 and a diode bridge 15 connected in parallel with the short-circuit switch element 16. The short-circuit circuit 17 performs a power supply short-circuit operation to short-circuit the power supply voltage Vs applied via the reactor 5 by turning on the short-circuit switch element 16. Figure 12 In the embodiment, gate circuit unit 14 is replaced by gate circuit unit 14B. In addition to gate signals Q1, Q2, Q3, and Q4, gate circuit unit 14B also generates and outputs gate signal Q5 for driving short-circuit switch element 16. Other configurations are identical or equivalent to those in embodiment 1, and identical or equivalent components are denoted by the same reference numerals, and repeated descriptions are omitted.

[0088] Figure 13This is a diagram showing a switching pattern of basic operations of the rectifier circuit 6 and the short-circuit circuit 17 in the second embodiment. Figure 13 The horizontal axis represents time. Figure 13 In the vertical axis direction, the operation waveforms of the power supply voltage Vs, the primary current Is, the gate signal Q5, the gate signal Q1, the gate signal Q2, the gate signal Q3 and the gate signal Q4 are shown in order from the upper side.

[0089] exist Figure 13 In this example, when the power supply voltage Vs is positive, switching elements 1 and 4 are controlled to be on while current is flowing through the parallel-connected diodes. Furthermore, when the power supply voltage Vs is negative, switching elements 2 and 3 are controlled to be on while current is flowing through the parallel-connected diodes. This operation constitutes the aforementioned synchronous rectification.

[0090] When the DC voltage Vdc needs to be boosted, Figure 13 As shown, gate signal Q5 is controlled to be on, turning short-circuiting switch element 16 on. At this point, current flows through short-circuiting circuit 17, along a path that passes through AC power supply 50, reactor 5, diode bridge 15, short-circuiting switch element 16, diode bridge 15, and AC power supply 50. Consequently, energy is accumulated in reactor 5. Subsequently, when short-circuiting switch element 16 becomes non-conductive, the energy accumulated in reactor 5 is released into smoothing capacitor 7 via rectifier circuit 6. This boosts the DC voltage Vdc across smoothing capacitor 7.

[0091] In addition, Figure 13 2 shows an example in which the power supply short circuit is performed twice every half cycle of the power supply voltage Vs, but the present invention is not limited thereto. The power supply short circuit may be performed only once, three times or more, or multiple times or less.

[0092] Next, the operation of the main portion of the power conversion device 100B according to Embodiment 2 will be described. Before describing the operation of the main portion, the path of the current flowing through the rectifier circuit 6 or the short-circuit circuit 17 according to Embodiment 2 will be described.

[0093] Figure 14 : is a diagram showing a fifth path of current flowing through the rectifier circuit 6 or the short-circuit circuit 17 in the second embodiment. Figure 14 The current path shown is defined as "current path (5)". Figure 14 shows the current path for synchronous rectification when power supply voltage Vs is positive. Switching elements 1 and 4 are on, switching elements 2 and 3 are off, and short-circuit switching element 16 is off. In this state, current flows through AC power supply 50, reactor 5, switching element 1, inverter 8, switching element 4, and AC power supply 50.

[0094] Figure 15 : is a diagram showing the sixth path of the current flowing through the rectifier circuit 6 or the short-circuit circuit 17 in the second embodiment. Figure 15 The current path shown is defined as "current path (6)". Figure 15 shows the current path for a power supply short circuit when power supply voltage Vs is positive. Switching elements 1 and 4 are on, switching elements 2 and 3 are off, and short-circuiting switching element 16 is on. In this state, current flows through AC power supply 50, reactor 5, diode bridge 15, short-circuiting switching element 16, diode bridge 15, and AC power supply 50.

[0095] Figure 16 : is a diagram showing a seventh path of current flowing through the rectifier circuit 6 or the short-circuit circuit 17 in the second embodiment. Figure 16 The current path shown is defined as "current path (7)". Figure 16 shows the current path for synchronous rectification when power supply voltage Vs is negative. Switching elements 2 and 3 are on, switching elements 1 and 4 are off, and short-circuit switching element 16 is off. In this state, current flows through AC power supply 50, switching element 3, inverter 8, switching element 2, reactor 5, and AC power supply 50.

[0096] Figure 17 : is a diagram showing the eighth path of the current flowing through the rectifier circuit 6 or the short-circuit circuit 17 in the second embodiment. Figure 17 The current path shown is defined as "current path (8)". Figure 17 shows the current path for a power supply short circuit when power supply voltage Vs is negative. Switching elements 2 and 3 are on, switching elements 1 and 4 are off, and short-circuiting switching element 16 is on. In this state, current flows through AC power supply 50, diode bridge 15, short-circuiting switching element 16, diode bridge 15, reactor 5, and AC power supply 50.

[0097] Figure 18 This is a time chart for explaining the operation of the main parts in Implementation 2. Figure 18 In accordance with Figure 9 The main part of the action waveform when the flowchart is in action. Specifically, Figure 18 In the figure, the operating waveforms of the power supply voltage Vs, primary current Is, DC voltage Vdc and induced voltage Vm, zero-crossing signal Zc, gate signal Q5, gate signal Q1, gate signal Q2, gate signal Q3, and gate signal Q4 are shown in order from the top. The horizontal axis represents time. Regarding DC voltage Vdc and induced voltage Vm, DC voltage Vdc is represented by a solid line, and induced voltage Vm is represented by a dashed-dotted line.

[0098] Here, in Figure 18 In the operation waveform, during the period T5 when the gate signal Q4 is turned on, the DC voltage Vdc is larger than the induced voltage Vm. Therefore, the boost operation is not performed, and the current flows in the current path (5) defined above.

[0099] Furthermore, during the period T6 when the gate signal Q3 is on, the DC voltage Vdc is also larger than the induced voltage Vm. Therefore, the voltage step-up operation is not performed, and the current flows in the current path (7) defined above.

[0100] On the other hand, in the next cycle of the power supply voltage Vs, there is a period during which the induced voltage Vm is greater than the DC voltage Vdc. Therefore, during period T7 when the gate signal Q4 is on, the current flow in the current path (5) and the current flow in the current path (6) are repeated. Furthermore, during period T8 when the gate signal Q3 is on, the current flow in the current path (7) and the current flow in the current path (8) are repeated. That is, during periods T7 and T8, the synchronous rectification and boosting operations are repeated.

[0101] Furthermore, during periods T7 and T8, the synchronous rectification and boost operations are switched without changing the switching operation of gate signals Q1, Q2, Q3, and Q4, which perform synchronous rectification. In other words, during periods T7 and T8, the synchronous rectification and boost operations can be switched without intervening a switching stop period.

[0102] When the rotation speed of motor 52 increases, the induced voltage Vm of motor 52 increases. Consequently, under the same load conditions, the current flowing through motor 52, i.e., the motor current, increases, increasing losses in motor 52. In contrast, in the control of Embodiment 2, when the induced voltage Vm of motor 52 exceeds DC voltage Vdc, the synchronous rectification is switched to a boost operation to boost DC voltage Vdc, thereby suppressing increases in the motor current. This further improves the efficiency of motor 52 in the high-speed rotation range.

[0103] Furthermore, in the control of the second embodiment, the synchronous rectification and boost operations can be seamlessly switched simply by controlling the short-circuit switching element 16, without changing the synchronous rectification switching pattern in the rectifier circuit 6. This simplifies the control during the boost operation compared to the first embodiment.

[0104] In the configuration of the second embodiment, the circuits for synchronous rectification and the circuits for boosting are dispersed, which can reduce the amount of heat generated in each switching element compared to the first embodiment.

[0105] In the circuit configurations of Embodiments 1 and 2, the reactor 5 is disposed on the input side of the rectifier circuit 6. In addition to these configurations, a configuration in which the reactor 5 is disposed on the output side of the rectifier circuit 6 is also known. Figure 19 Indicate one example. Figure 19 This diagram shows the configuration of a power conversion device 100C having a boosting function as a comparative example.

[0106] In the power conversion device 100C of the comparative example, Figure 1 In the configuration of the power conversion device 100 according to the first embodiment shown, the reactor 5 is arranged on the output side of the rectifier circuit 6, and a boost circuit 20 is arranged between the reactor 5 and the smoothing capacitor 7. The boost circuit 20 includes a switching element 22 connected in parallel with the smoothing capacitor 7, and a diode 21 connected in a direction to prevent the charge stored in the smoothing capacitor 7 from flowing into the rectifier circuit 6. Figure 19 In FIG. 1 , gate circuit unit 14 is replaced by gate circuit unit 14C. Gate circuit unit 14C generates and outputs gate signal Q6 for driving switching element 22 in addition to gate signals Q1 , Q2 , Q3 , and Q4 .

[0107] By turning on switching element 22, boost circuit 20 performs a short-circuiting operation, short-circuiting the output voltage of rectifier circuit 6 applied via reactor 5. This short-circuiting operation accumulates energy in reactor 5. Subsequently, by turning switching element 22 off, the energy accumulated in reactor 5 is released to smoothing capacitor 7. This boosts the DC voltage Vdc across smoothing capacitor 7.

[0108] exist Figure 19 In the structure shown in FIG. 1 , all the power supplied to the inverter 8 passes through the diode 21. In contrast, in the structures of the first and second embodiments, there is no element corresponding to the diode 21. Therefore, according to the power conversion devices 100, 100A, and 100B of the first and second embodiments, it is possible to compare Figure 19 The power conversion device 100C shown is used to reduce the loss caused by semiconductor elements.

[0109] As described above, the power conversion device of embodiment 2 includes: a reactor; a rectifier circuit to which a power supply voltage output from an AC power supply is applied via the reactor; and a short-circuit circuit disposed between the reactor and the rectifier circuit, which short-circuits the power supply voltage via the reactor when switched on. The rectifier circuit includes: a first arm having a first upper arm element and a first lower arm element connected in series; and a second arm connected in parallel with the first arm and having a second upper arm element and a second lower arm element connected in series. The control unit detects a DC voltage smoothed by a smoothing capacitor that smoothes the output voltage of the rectifier circuit, and controls the operation of the short-circuit circuit based on the detected DC voltage and the induced voltage caused by the motor. This further improves the efficiency of the motor in the high-speed rotation range where the motor induced voltage increases. The first and second upper arm elements, and the first and second lower arm elements are controlled to be turned on when current flows through the diodes connected in parallel therewith, and are controlled to be turned off when current does not flow through the diodes.

[0110] In the above control, when the induced voltage is smaller than the detected DC voltage value, the short-circuit circuit is controlled to be open. When the induced voltage is larger than the detected DC voltage value, the short-circuit circuit is controlled to be open and closed. Thus, in Embodiment 2, switching between synchronous rectification and boost operation can be performed solely by controlling the short-circuit circuit. This simplifies the control during boost operation compared to Embodiment 1.

[0111] Implementation method 3.

[0112] Figure 20 This is a diagram showing a configuration example of a refrigeration cycle apparatus 200 according to Embodiment 3. Figure 20 Refrigeration cycle device 200 according to Embodiment 3 includes the power conversion device 100 described in Embodiment 1. Refrigeration cycle device 200 includes a refrigeration cycle 150, in which a compressor 41 including a motor 52, a four-way valve 42, an outdoor heat exchanger 43, an expansion valve 44, and an indoor heat exchanger 45 are installed via refrigerant piping 46. Motor 52 is driven by inverter 8. Alternatively, refrigeration cycle device 200 may include the power conversion device 100A described in Embodiment 1 or the power conversion device 100B described in Embodiment 2.

[0113] The compressor 41 includes a compression mechanism 47 for compressing the refrigerant and a motor 52 for operating the compression mechanism 47. This constitutes a refrigeration cycle 150 that circulates the refrigerant from the compressor 41 between the outdoor heat exchanger 43 and the indoor heat exchanger 45 to perform cooling and heating. Figure 20 The refrigeration cycle 150 shown can be applied to, for example, an air conditioner.

[0114] The refrigeration cycle device 200 of Embodiment 3 includes the power conversion device 100 described in Embodiment 1. As described above, the power conversion device 100 of Embodiment 1 can further improve the efficiency of the motor in the high-speed rotation range. Therefore, when the refrigeration cycle device 200 of Embodiment 3 is applied to, for example, an air conditioner, the efficiency of these products can be further improved compared to conventional systems.

[0115] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, the embodiments may be combined with each other, and part of the configuration may be omitted or modified without departing from the spirit of the invention.

[0116] Description of reference numerals:

[0117] 1, 2, 3, 4, 22…switching element; 5…reactor; 6…rectifier circuit; 7…smoothing capacitor; 8…inverter; 10…control unit; 10a…processor; 10b…memory; 11, 13…voltage detection unit; 12…current detection unit; 14, 14B, 14C…gate circuit unit; 15…diode bridge; 16…short-circuit switching element; 17…short-circuit circuit; 20…boost circuit; 21…diode; 30…first bridge arm; 32 …Second bridge arm; 34, 36…Connection point; 41…Compressor; 42…Four-way valve; 43…Outdoor heat exchanger; 44…Expansion valve; 45…Indoor heat exchanger; 46…Refrigerant piping; 47…Compression mechanism; 50…AC power supply; 52…Motor; 54…Rotation sensor; 56…Induction voltage detector; 100, 100A, 100B, 100C…Power conversion device; 150…Refrigeration cycle; 200…Refrigeration cycle device.

Claims

1. A power conversion device, characterized in that: have: Reactors; A rectifier circuit comprising: a first bridge arm having a first upper arm element and a first lower arm element connected in series; and a second bridge arm connected in parallel with the first bridge arm and having a second upper arm element and a second lower arm element connected in series, wherein a power supply voltage output from an AC power supply is applied between a connection point between the first upper arm element and the first lower arm element and a connection point between the second upper arm element and the second lower arm element via the reactor; a smoothing capacitor for smoothing the output voltage of the rectifier circuit; an inverter that converts the DC voltage smoothed by the smoothing capacitor into a drive voltage for driving a motor and applies the drive voltage to the motor; a first voltage detection unit configured to detect the DC voltage; a current detection unit configured to detect a primary current flowing to an input side of the rectifier circuit; a second voltage detection unit for detecting the power supply voltage, and a control unit that controls the operation of the rectifier circuit and the inverter, The control unit controls the operation of the first upper arm element and the first lower arm element based on the induced voltage caused by the motor and the detected value of the DC voltage. The second upper arm element and the second lower arm element are controlled to be turned on when current flows to the diodes connected in parallel therewith, and are controlled to be turned off when current does not flow to the diodes. When the induced voltage is smaller than the detected value of the DC voltage, The first upper arm element and the first lower arm element are alternately controlled to be on and off every half cycle of the power supply voltage. When the induced voltage is greater than the detected value of the DC voltage, Regardless of the polarity of the power supply voltage, the first upper arm element and the first lower arm element are alternately controlled to be on and off in a half cycle of the same polarity.

2. The power conversion device according to claim 1, wherein: The upper and lower arm elements in the first arm and the second arm are formed of wide-bandgap semiconductors.

3. The power conversion device according to claim 2, characterized in that The wide bandgap semiconductor is silicon carbide, gallium nitride, gallium oxide or diamond.

4. A power conversion device, characterized in that: have: Reactors; A rectifier circuit comprising: a first bridge arm having a first upper arm element and a first lower arm element connected in series; and a second bridge arm connected in parallel with the first bridge arm and having a second upper arm element and a second lower arm element connected in series, wherein a power supply voltage output from an AC power supply is applied between a connection point between the first upper arm element and the first lower arm element and a connection point between the second upper arm element and the second lower arm element via the reactor; a short-circuit circuit disposed between the reactor and the rectifier circuit, configured to short-circuit the power supply voltage via the reactor by a switching operation; a smoothing capacitor for smoothing the output voltage of the rectifier circuit; an inverter that converts the DC voltage smoothed by the smoothing capacitor into a drive voltage for driving a motor and applies the drive voltage to the motor; a first voltage detection unit configured to detect the DC voltage; a current detection unit configured to detect a primary current flowing to an input side of the rectifier circuit; a second voltage detection unit configured to detect the power supply voltage; as well as a control unit that controls the operations of the rectifier circuit, the inverter, and the short-circuit circuit; The control unit controls the operation of the short-circuit circuit based on the induced voltage caused by the motor and the detected value of the DC voltage. The first upper arm element and the second upper arm element, and the first lower arm element and the second lower arm element are controlled to be turned on when current flows to the diodes connected in parallel thereto, respectively, and are controlled to be turned off when current does not flow to the diodes. When the induced voltage is smaller than the detected value of the DC voltage, The short circuit is controlled to be open, When the induced voltage is greater than the detected value of the DC voltage, The short circuit is controlled to be on and off.

5. The power conversion device according to claim 4, characterized in that The upper and lower arm elements in the first arm and the second arm are formed of wide-bandgap semiconductors.

6. The power conversion device according to claim 5, characterized in that The wide bandgap semiconductor is silicon carbide, gallium nitride, gallium oxide or diamond.

7. A refrigeration cycle device, characterized in that: have: The power conversion device according to any one of claims 1 to 6; and A compressor equipped with the motor.

8. An air conditioner, characterized in that: A refrigeration cycle device according to claim 7 is provided.

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