Power conversion device

Abstract

Provided are: a rectifier circuit (4) connected to an AC power source (1) and rectifying an input voltage from the AC power source (1); a bridge arm circuit (5) connected to the rectifier circuit (4) and having an upper bridge arm composed of a plurality of semiconductor elements (51, 52) connected in series and a lower bridge arm composed of a plurality of semiconductor elements (53, 54) connected in series, the upper bridge arm and the lower bridge arm being connected in series, the plurality of semiconductor elements (53, 54) of at least the lower bridge arm being switching elements; a balancing resistor (6) connected in parallel to the semiconductor elements (51-54) of the bridge arm circuit (5); at least one charge-discharge capacitor (7) connected between a connection point of the semiconductor elements (51, 52) of the upper bridge arm and a connection point of the semiconductor elements (53, 54) of the lower bridge arm; a smoothing capacitor (8) connected to an output of the bridge arm circuit (5); and a surge prevention circuit (2) provided between the AC power source (1) and the bridge arm circuit (5) and provided with a current-limiting resistor (21).

Description

Technical Field

[0001] This application relates to a power conversion device. Background Technology

[0002] As a circuit method for high-efficiency power converters, it is known to utilize the charging and discharging of capacitors to output multi-level DC power. However, multi-level converters suffer from the problem that low-voltage components cannot be used because the voltage applied to each semiconductor element during unstable conditions is less than half of the DC bus voltage.

[0003] To address this problem, a power conversion device comprising the following components has been disclosed (e.g., Patent Document 1): a reactor connected to a DC power supply on the input side; a switching element; a charging and discharging capacitor that is charged and discharged by switching the switching element on and off; a diode that provides a charging and discharging path; a balancing resistor connected in parallel with each switching element and diode; and a capacitor for output voltage smoothing.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2014-33553 Summary of the Invention

[0005] The problem the invention aims to solve

[0006] In the power conversion device of Patent Document 1, overvoltage can be suppressed in the stopped state, but there is a problem of applying overvoltage to semiconductor elements during the initial charging when the power is turned on.

[0007] This application discloses a technology for solving the problems described above, with the aim of providing a power conversion device that can suppress overvoltage during initial charging, operation, and shutdown when the power is turned on.

[0008] Solution for solving the problem

[0009] The power conversion device disclosed in this application includes: a rectifier circuit connected to an AC power source for rectifying an input voltage from the AC power source; a bridge arm circuit connected to the rectifier circuit, having an upper bridge arm composed of multiple semiconductor elements connected in series and a lower bridge arm composed of multiple semiconductor elements connected in series, the upper and lower bridge arms being connected in series, and at least the multiple semiconductor elements of the lower bridge arm being switching elements; a balancing resistor connected in parallel with the semiconductor elements of the bridge arm circuit; at least one charge / discharge capacitor connected between the connection point of the semiconductor elements of the upper bridge arm and the connection point of the semiconductor elements of the lower bridge arm; a smoothing capacitor connected to the output of the bridge arm circuit; and an impulse prevention circuit disposed between the AC power source and the bridge arm circuit, having a current limiting resistor.

[0010] The effects of the invention

[0011] According to the power conversion device disclosed in this application, overvoltage can be suppressed during the initial charging, operating, and stopping states when the power is turned on. Attached Figure Description

[0012] Figure 1 This is a basic structural diagram of the power conversion device involved in Implementation Method 1.

[0013] Figure 2 This is a circuit diagram of the power conversion device involved in Implementation Method 1.

[0014] Figure 3 This is the operating waveform during the initial charging of a comparative example of the power conversion device according to Embodiment 1.

[0015] Figure 4 This is the operating waveform during the initial charging of a comparative example of the power conversion device according to Embodiment 1.

[0016] Figure 5 It is the voltage waveform of the smoothing capacitor during the initial charging of the power conversion device according to Embodiment 1 with respect to the change of the current limiting resistor.

[0017] Figure 6 It refers to the voltage waveform of the smoothing capacitor during initial charging, relative to the change in capacitance of the smoothing capacitor in the power conversion device according to Embodiment 1.

[0018] Figure 7 It is the voltage waveform of the smoothing capacitor during initial charging of the power conversion device according to Embodiment 1 with respect to the change of the balancing resistor.

[0019] Figure 8 It is the voltage waveform of the smoothed capacitor during the initial charging of the power conversion device according to Embodiment 1, relative to the change in capacitance of the charging and discharging capacitor.

[0020] Figure 9 It is the operating waveform of the power conversion device according to Embodiment 1 during initial charging with respect to the change in the overvoltage level index.

[0021] Figure 10 It is the operating waveform of the power conversion device according to Embodiment 1 during initial charging with respect to the change in the overvoltage level index.

[0022] Figure 11 It is the operating waveform of the power conversion device according to Embodiment 1 during initial charging with respect to the change in the overvoltage level index.

[0023] Figure 12It is the operating waveform of the power conversion device according to Embodiment 1 during initial charging with respect to the change in the overvoltage level index.

[0024] Figure 13 It is a graph that plots the maximum voltage applied to the semiconductor switching element of the power conversion device according to Embodiment 1 with respect to the change of the overvoltage level index.

[0025] Figure 14 This is a circuit diagram of the power conversion device involved in Embodiment 2.

[0026] Figure 15 This is a circuit structure diagram of another method 1 of the power conversion device involved in Embodiment 2.

[0027] Figure 16 This is a circuit structure diagram of another method 2 of the power conversion device involved in Embodiment 2.

[0028] Figure 17 This is a circuit diagram of the power conversion device involved in Embodiment 3.

[0029] Figure 18 This is a circuit diagram of another embodiment of the power conversion device involved in Implementation 3.

[0030] Figure 19 It is the operating waveform of the power conversion device according to Embodiment 3 during initial charging with respect to the change in the overvoltage level index.

[0031] Figure 20 It is the operating waveform of the power conversion device according to Embodiment 3 during initial charging with respect to the change in the overvoltage level index.

[0032] Figure 21 It is the operating waveform of the power conversion device according to Embodiment 3 during initial charging with respect to the change in the overvoltage level index.

[0033] Figure 22 It is the operating waveform of the power conversion device according to Embodiment 3 during initial charging with respect to the change in the overvoltage level index.

[0034] Figure 23 It is a graph that plots the maximum voltage applied to the semiconductor switching element in relation to the change in the overvoltage level index of the power conversion device according to Embodiment 3.

[0035] Figure 24 This is a circuit diagram of the power conversion device involved in Embodiment 4.

[0036] Figure 25This is a graph comparing the initial charging characteristics of the charging and discharging capacitors of the power conversion device according to Embodiment 4 in the 3-resistor mode and the 4-resistor mode.

[0037] Figure 26 This is a circuit diagram of the power conversion device involved in Embodiment 5.

[0038] Figure 27 The graph is a chart showing the maximum voltage applied to the semiconductor switching element of the power conversion device according to Embodiment 5 with respect to the change in the overvoltage level index.

[0039] Figure 28 This is a block diagram of an example hardware structure of a controller for a power conversion device.

[0040] (Explanation of reference numerals in the attached diagram)

[0041] 1: AC power supply; 1a: Single-phase AC power supply; 1b: Three-phase AC power supply; 2: Surge protection circuit; 21: Current limiting resistor; 22: Switch; 3: Reactor; 4: Rectifier circuit; 4a: Diode rectifier circuit with only one branch; 4b, 4c: Bridge rectifier circuit; 41, 42: Diodes; 5, 5a, 5b, 5c: Bridge arm circuit; 51, 52, 53, 54, 56, 57: Semiconductor switching elements; 51a, 52a: Diodes; 6, 6a, 6b, 6c: Balancing resistors; 61, 62, 63, 64, 65, 66, 67: Balancing resistors; 7, 7a: Charging and discharging capacitors; 8: Smoothing capacitors; 9: Controller; 10: Load; 100, 200, 201, 202, 300, 301, 400, 500, 1000: Power conversion devices; 2000: Processor; 2001: Storage device. Detailed Implementation

[0042] Implementation method 1.

[0043] Embodiment 1 relates to a power conversion device comprising: a diode rectifier circuit with only one branch for rectifying an input voltage from a single-phase AC power supply; a bridge arm circuit having an upper bridge arm and a lower bridge arm having two semiconductor switching elements connected in series; a balancing resistor connected in parallel with each semiconductor switching element of the bridge arm circuit; a charge / discharge capacitor connected between the connection points of the semiconductor switching elements of the upper bridge arm and the connection points of the semiconductor switching elements of the lower bridge arm; a smoothing capacitor connected to the output of the bridge arm circuit; an inrush prevention circuit having a current limiting resistor between the single-phase AC power supply and the diode rectifier circuit with only one branch; and a reactor.

[0044] The following describes the structure and operation of the power conversion device involved in Embodiment 1, based on the basic structural diagram of the power conversion device. Figure 1 The circuit structure diagram of the power conversion device is as follows: Figure 2 The operating waveform of the comparative example during initial charging is... Figure 3 , Figure 4 The voltage waveform of a smooth capacitor during initial charging, relative to the change in the current-limiting resistor. Figure 5 The voltage waveform of the smoothing capacitor during its initial charging, relative to the change in capacitance of the smoothing capacitor. Figure 6 The voltage waveform of the smoothing capacitor during initial charging, relative to the change in the balancing resistance. Figure 7 The voltage waveform during the initial charging of a capacitor is smoothed relative to the change in capacitance during charging and discharging. Figure 8 The initial charging waveform relative to the change in the overvoltage level index. Figures 9-12 And a graph showing the maximum voltage applied to the semiconductor switching element relative to the change in the overvoltage level index. Figure 13 Please provide an explanation.

[0045] Based on Figure 2 Before describing the structure of the power conversion device 100 in Embodiment 1, based on Figure 1 This describes the basic structure that is used in power conversion devices in both Embodiment 1 and Embodiment 2 and thereafter.

[0046] The power conversion device 1000 takes AC power 1 as input and includes an impulse prevention circuit 2 (including a current limiting resistor), a rectifier circuit 4, a bridge arm circuit 5, a balancing resistor 6, a charging and discharging capacitor 7, a smoothing capacitor 8, and a load 10 connected to the output.

[0047] Here, rectifier circuit 4 converts the AC power supply 1 from AC to DC. Bridge arm circuit 5 has an upper bridge arm and a lower bridge arm composed of series circuits of semiconductor elements.

[0048] The balancing resistor 6 is connected in parallel with the semiconductor element of the bridge arm circuit 5. Specific connection methods are described in each embodiment. At least one charge / discharge capacitor 7 is connected between the connection point of the semiconductor element in the upper bridge arm and the connection point of the semiconductor element in the lower bridge arm.

[0049] A smoothing capacitor 8 is connected to the output of the bridge arm circuit 5, and a load 10 is connected to the smoothing capacitor 8.

[0050] Here, semiconductor elements include semiconductor switching elements and diodes.

[0051] Furthermore, regarding the location of the impact prevention circuit 2, when the AC power supply 1 is a three-phase AC power supply, it is set to be located after the rectifier circuit 4.

[0052] Typically, in power conversion devices, a reactor is installed on the input side, and a controller is required to drive the bridge arm circuit. However, this is not directly related to the purpose of this application, namely, "to provide a power conversion device capable of suppressing overvoltage during the initial charging, operating, and stopping states of the power converter when the power is turned on." Figure 1 Except for the basic structure.

[0053] Furthermore, although AC power supply 1 and load 10 are not constituent elements of power conversion device 1000, they are closely related, and therefore will be described without distinction.

[0054] Next, the explanation Figure 2 The structure of the power conversion device 100 shown is illustrated.

[0055] The power conversion device 100 takes a single-phase AC power supply 1a as input and includes an impulse prevention circuit 2 comprising a current limiting resistor 21 and a switch 22, a reactor 3, a diode rectifier circuit 4a with only one branch including diodes 41 and 42, a bridge arm circuit 5a having a series circuit of semiconductor switching elements 51 and 52 in the upper bridge arm and a series circuit of semiconductor switching elements 53 and 54 in the lower bridge arm, a balancing resistor 6a having resistors 61, 62, 63, and 64, a charging / discharging capacitor 7, and a smoothing capacitor 8. A load 10 is connected to the output. Furthermore, the power conversion device 100 includes a controller 9 for driving the bridge arm circuit 5a.

[0056] Will as Figure 2 The rectifier circuit with only one branch (only one end of single-phase AC) consisting of two diodes 41 and 42, as shown, is described as a diode rectifier circuit 4a with only one branch. For single-phase AC as described in the following embodiments, it is described as a bridge rectifier circuit 4b consisting of four diodes, and for three-phase AC, it is described as a bridge rectifier circuit 4c consisting of six diodes.

[0057] Regarding the balancing resistor, it is generally referred to as balancing resistor 6a, and in specific cases, it is referred to as balancing resistor 61.

[0058] In a diode rectifier circuit 4a with only one branch, the connection point between the anode of diode 41 and the cathode of diode 42 is connected to one end of a single-phase AC power supply 1a via reactor 3. The connection point between the upper and lower arms of bridge arm circuit 5a is connected to the other end of the single-phase AC power supply 1a. In the same diode rectifier circuit 4a, the cathode of diode 41 is connected to the positive side of the DC bus of bridge arm circuit 5a, and the anode of diode 42 is connected to the negative side of the DC bus of bridge arm circuit 5a.

[0059] Balancing resistors 61-64 are connected in parallel with semiconductor switching elements 51-54, respectively. Charging / discharging capacitor 7 is connected in parallel with the series circuit of semiconductor switching elements 52 and 53, i.e., in parallel with the series circuit of balancing resistors 62 and 63. Smoothing capacitor 8 is connected to the output of bridge arm circuit 5a, and load 10 is connected to this output.

[0060] Regarding the current-limiting resistor 21, it can be replaced by a PTC (Positive Temperature Coefficient) thermistor or an NTC (Negative Temperature Coefficient) thermistor. Regarding the semiconductor switching elements 51 to 54, they are described as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), but they can also be replaced by IGBTs (Insulated-Gate Bipolar Transistors). Alternatively, they can be constructed from semiconductor switching elements made of new materials such as SiC and GaN.

[0061] In the power conversion device 100, switch 22 is turned off during the initial charging operation. At the point when the initial charging operation is completed (details will be explained later), switch 22 is turned on to bypass the current limiting resistor 21. Then, a drive signal from controller 9 is used to operate semiconductor switching elements 51-54.

[0062] By appropriately controlling the switching of semiconductor switching elements 51-54 using a drive signal from controller 9, the power supply current can be made sinusoidal and the power factor approximately 1. Furthermore, the charging / discharging capacitor 7 and the smoothing capacitor 8 can be controlled to arbitrary voltage values.

[0063] In particular, by setting the voltage of the charging / discharging capacitor 7 to half the voltage of the smoothing capacitor 8, a 3-level output can be achieved. By setting the output to 3 levels, compared to a typical 2-level power converter, the inductance of the reactor 3 can be reduced, and the losses during the switching operation of the semiconductor switching elements 51-54 can be reduced.

[0064] When the same resistance values ​​are applied to the balancing resistors 61, 62, 63, and 64, the overvoltage suppression effect is high. Here, the average value of the resistances of the balancing resistors 61, 62, 63, and 64 is set as Rf.

[0065] Furthermore, the resistance value of the current limiting resistor 21 is set to R0, the electrostatic capacitance of the charge / discharge capacitor 7 is set to Cf, and the electrostatic capacitance of the smoothing capacitor 8 is set to C0.

[0066] Furthermore, in the following descriptions, unless otherwise specified, the "average value Rf of the resistances of balancing resistors 61, 62, 63, and 64" will be recorded as "the resistance value Rf of the balancing resistors".

[0067] In addition, the unit of resistance is Ω and the unit of capacitance is μF for calculation.

[0068] Here, it is explained Figure 2 The power conversion device 100 shown is in normal operation. Figure 2 In the power conversion device 100 shown, the operation is switched according to whether the AC voltage output from the AC power source 1 is positive or negative.

[0069] When the AC voltage output from AC power supply 1 is positive, the semiconductor switching elements 51 and 52 of the upper bridge arm are switched on and off. This switches the path of current flowing through the charging / discharging capacitor 7 to charge it, the path of current flowing through the charging / discharging capacitor 7 to discharge it, and the path of current not flowing through the charging / discharging capacitor 7. Through this switching, the input voltage from AC power supply 1 is boosted and output to the smoothing capacitor 8.

[0070] Furthermore, when the AC voltage output from AC power supply 1 is negative, the semiconductor switching elements 53 and 54 of the lower bridge arm are switched on and off. As a result, the previously described path is switched, and the input voltage from AC power supply 1 is boosted and output to the smoothing capacitor 8.

[0071] Furthermore, actions in normal situations are not limited to those described above.

[0072] Next, regarding the initial charging action of the charging / discharging capacitor 7 and the smoothing capacitor 8 when the power is turned on, based on... Figures 3 to 13 Please provide an explanation.

[0073] First, let's explain the initial charging operation of the comparative example. Regarding the circuit constants, let the resistance value of the current limiting resistor be R0 = 10Ω, the resistance value of the balancing resistor be Rf = 100kΩ, the electrostatic capacitance of the smoothing capacitor 8 be C0 = 1000μF, and the electrostatic capacitance of the charging and discharging capacitor 7 be Cf = 10μF.

[0074] Figure 3 , Figure 4 The waveform shown is the initial charging action waveform when the power is turned on. The waveform shown is the action waveform when the power is turned on at time 0.

[0075] Figure 3This is the overall waveform. F3a is the power supply voltage of AC power supply 1, F3b is the voltage of smoothing capacitor 8 (solid line) and charging / discharging capacitor 7 (dashed line), F3c is the voltage across semiconductor switching element 51, and F3d is the voltage across semiconductor switching element 54.

[0076] also, Figure 3 The actual waveforms of F3a, F3c, and F3d are denser and indistinguishable as sine waves, but in Figure 3 The waveforms are sparse for ease of understanding.

[0077] Figure 4 It's an amplified waveform, obtained by amplifying the action immediately after the power is switched on. Corresponding to... Figure 3 F3a to F3d. Specifically, F4a is the power supply voltage of AC power supply 1, F4b is the voltage of smoothing capacitor 8 (solid line) and charging / discharging capacitor 7 (dashed line), F4c is the voltage across semiconductor switching element 51, and F4d is the voltage across semiconductor switching element 54.

[0078] After the power is turned on, the smoothing capacitor 8 is charged immediately, but the charging / discharging capacitor 7 is not charged immediately. The voltage difference between the smoothing capacitor 8 and the charging / discharging capacitor 7 is applied to the semiconductor switching elements 51 and 54.

[0079] When the power is switched on, the applied voltage may overshoot, creating a period of overvoltage. If this occurs, semiconductor switching elements cannot be constructed with low voltage withstand capability, resulting in a structure that is detrimental to efficiency and cost reduction.

[0080] To address the overvoltage issue, it is necessary to slow down the charging time of the smoothing capacitor 8 or speed up the charging time of the charging and discharging capacitor 7 to suppress voltage overshoot.

[0081] Here, we will explain a method for suppressing overvoltage during the initial charging process.

[0082] The charging speed of the smoothing capacitor 8 can be expressed by the coefficient K0 of equation (1), which is the product of R0 and C0.

[0083] K0=R0*C0 (1)

[0084] If the coefficient K0 increases, the charging time will be longer; if the coefficient K0 decreases, the charging time will be shorter. Figure 5 The results show a comparison of the charging waveforms of the smoothing capacitor 8 when the resistance values ​​R0 = 10Ω (solid line), R0 = 30Ω (dashed line), and R0 = 50Ω (single-dot dashed line) are set as current limiting resistors.

[0085] Regarding the circuit constants other than the resistance value R0 of the current limiting resistor, they are the same constants under the three conditions. Let the resistance value of the balancing resistor be Rf = 100kΩ, the electrostatic capacitance of the smoothing capacitor 8 be C0 = 1000μF, and the electrostatic capacitance of the charging and discharging capacitor 7 be Cf = 10μF.

[0086] If the resistance value R0 of the current limiting resistor is increased, K0 will increase, and therefore the charging time of the smoothing capacitor 8 will be longer.

[0087] In addition, increasing the electrostatic capacitance C0 of the smoothing capacitor 8 can also slow down the charging time. Figure 6 The results show a comparison of the charging waveforms of the smoothing capacitor 8 when the electrostatic capacitance C0 = 1000uF (solid line), C0 = 3000uF (dashed line), and C0 = 5000uF (single-dot dashed line).

[0088] Regarding the circuit constants other than the electrostatic capacitance C0 of the smoothing capacitor 8, they are the same constants under all three conditions. Assume the resistance of the current-limiting resistor is R0 = 10Ω, the resistance of the balancing resistor is Rf = 100kΩ, and the electrostatic capacitance of the charging / discharging capacitor 7 is Cf = 10μF. When the electrostatic capacitance C0 of the smoothing capacitor 8 increases, the coefficient K0 also increases; therefore, it can be concluded that the charging time of the smoothing capacitor 8 becomes longer.

[0089] If the coefficient K0 is the same, the charging time will be the same even if the resistance value R0 of the current limiting resistor and the electrostatic capacitance C0 of the smoothing capacitor 8 are different.

[0090] Furthermore, the charging speed of the charging and discharging capacitor 7 can be expressed by the coefficient Kf of equation (2), which is the product of the resistance value Rf, which is used as a balancing resistor, and the electrostatic capacitance Cf of the charging and discharging capacitor 7.

[0091] Kf=Rf*Cf (2)

[0092] If the coefficient Kf increases, the charging time will be longer; if the coefficient Kf decreases, the charging time will be shorter.

[0093] Figure 7 The results show a comparison of the charging waveforms of capacitor 7 when the resistance values ​​set as balancing resistors are Rf = 10kΩ (solid line), Rf = 30kΩ (dashed line), and Rf = 50kΩ (single-dot dashed line).

[0094] Regarding the circuit constants other than the resistance value of the balancing resistor, they are the same constants under the three conditions. Let the resistance value of the current limiting resistor be R0 = 10Ω, the electrostatic capacitance of the smoothing capacitor 8 be C0 = 1000μF, and the electrostatic capacitance of the charging and discharging capacitor 7 be Cf = 10μF.

[0095] If the resistance value Rf of the balancing resistor is increased, the coefficient Kf will increase, and therefore the charging time will be longer.

[0096] In addition, it is important to note that if the resistance value Rf of the balancing resistor is made too small, although the charging time will be shorter, the loss of the balancing resistor will be greater.

[0097] In addition, increasing the electrostatic capacitance Cf of the charging / discharging capacitor 7 can also slow down the charging time. Figure 8 The results show a comparison of the charging waveforms of capacitor 7 when the electrostatic capacitance Cf = 10uF, Cf = 30uF, and Cf = 50uF are set as charging and discharging capacitor 7.

[0098] Regarding the circuit constants other than the electrostatic capacitance of the charging and discharging capacitor 7, they are the same constants under the three conditions. Let the resistance value of the current limiting resistor be R0 = 10Ω, the resistance value of the balancing resistor be Rf = 10kΩ, and the electrostatic capacitance of the smoothing capacitor 8 be C0 = 1000μF.

[0099] When the electrostatic capacitance Cf of the charging and discharging capacitor 7 is increased, the coefficient Kf also increases, so it can be seen that the charging time becomes longer.

[0100] If the coefficient Kf has the same value, then even if the resistance value Rf of the balancing resistor and the electrostatic capacitance Cf of the charging and discharging capacitor 7 are different, the charging time will be the same.

[0101] By increasing or decreasing the coefficient K0, the charging speed of the smoothing capacitor 8 can be controlled; by increasing or decreasing the coefficient Kf, the charging speed of the charging and discharging capacitor 7 can be controlled.

[0102] As explained above, in the circuit structure of the power conversion device 100 of this embodiment 1, it is effective to reduce the coefficient Kf and increase the coefficient K0 in order to suppress the overvoltage applied to the semiconductor switching elements 51 to 54 during initial charging.

[0103] Here, the index of the degree of overvoltage can be represented by the coefficient Km in equation (3).

[0104] Km=Kf / K0 (3)

[0105] The coefficient Km, which serves as an indicator of the degree of overvoltage, can represent the balance between the charging time of the smoothing capacitor 8 and the charging / discharging capacitor 7. The smaller the coefficient Km, the better the overshoot during the initial charging of the charging / discharging capacitor 7 can be suppressed.

[0106] Figures 9-12The figure shows the charging characteristics of the smoothing capacitor 8 and the charging / discharging capacitor 7 when the coefficients are set to Km = 100 (comparative example), Km = 20, Km = 7.5, and Km = 3.

[0107] Figure 9 Corresponding to coefficient Km = 100, Figure 10 Corresponding to coefficient Km = 20, Figure 11 This corresponds to the coefficient Km = 7.5. Figure 12 This corresponds to the coefficient Km = 3.

[0108] exist Figures 9-12 In the diagram, the solid lines of F9a (F10a, F11a, F12a) represent the voltage of the smoothing capacitor 8, and the dashed lines represent the voltage of the charging and discharging capacitor 7.

[0109] exist Figures 9-12 In this context, F9b (F10b, F11b, F12b) represents the voltage difference between the voltage of the smoothing capacitor 8 and the voltage of the charging / discharging capacitor 7. This voltage difference is applied to the semiconductor switching elements 51 and 54.

[0110] Regarding voltages exceeding 300V when the coefficient Km = 100 in the comparative example, reducing the coefficient Km results in suppressing overshoot voltage.

[0111] The peak value of the AC voltage of the single-phase AC power supply 1a in this embodiment 1 is 374V. Therefore, the convergence value of the voltage of the smoothing capacitor 8 is 374V, and the convergence value of the voltage of the charging and discharging capacitor 7 is 187V.

[0112] With a coefficient Km = 20, the peak value of the voltage applied to the semiconductor switching element becomes 280V, and the overshoot of the voltage applied to the semiconductor switching element is reduced to 280 / 187 = 1.5 times. By suppressing the peak value of the voltage applied to the semiconductor switching element, the effectiveness of the power conversion device 100 of Embodiment 1 can be confirmed.

[0113] Furthermore, by reducing the coefficient Km to 7.5, the peak value of the voltage applied to the semiconductor switching element becomes 234V, and the overshoot is reduced to 234 / 187 = 1.25 times, which further confirms the effectiveness of the power conversion device 100 of Embodiment 1.

[0114] Furthermore, by reducing the coefficient to Km = 3, it is almost impossible to detect overshoot of the voltage applied to the semiconductor switching element, thus maximizing the effect of the power conversion device 100 of Embodiment 1.

[0115] In the above analysis, the resistance value R0 of the current limiting resistor is increased in order to reduce the coefficient Km, thereby slowing down the charging speed of the smoothing capacitor 8 and suppressing the overshoot of the voltage applied by the semiconductor switching element.

[0116] However, by reducing the resistance value Rf of the balancing resistor to speed up the charging and discharging of the capacitor 7, it is also possible to suppress overshoot of the voltage applied by the semiconductor switching element.

[0117] Additionally, the charging time can be adjusted by changing the electrostatic capacitance C0 of the smoothing capacitor 8 and the electrostatic capacitance Cf of the charge / discharge capacitor 7. However, the capacitor capacitance affects the operation of the converter itself, and capacitors are more expensive components compared to resistors, therefore their selection has less flexibility.

[0118] If we graph the coefficient Km and the peak value of the voltage applied to the semiconductor switching element, we get Figure 13 The relationship shown.

[0119] exist Figure 13 In the figure, the horizontal axis represents the coefficient Km, and the vertical axis represents the maximum voltage [V] across the semiconductor switching element.

[0120] Clearly, the smaller the coefficient Km, the better the peak voltage can be suppressed.

[0121] When the balancing resistors 61, 62, 63, and 64 are set to the same resistance value, the effect of the power conversion device 100 in Embodiment 1 is increased. However, even if the resistance values ​​of the balancing resistors deviate by 10% or 20%, the effect can still be fully obtained.

[0122] In the power conversion device of Embodiment 1, the semiconductor switching elements 51 and 54 are suppressed from becoming overvoltage during initial charging.

[0123] In the power conversion device 100 of Embodiment 1, overvoltage can be suppressed during initial charging, and semiconductor switching elements can be constructed using components with lower voltage ratings. Therefore, the suppression cost increases, and high-efficiency semiconductor switching elements can be selected, enabling the construction of a more efficient power converter.

[0124] As described above, the power conversion device of Embodiment 1 includes: a diode rectifier circuit with only one branch for rectifying the input voltage from a single-phase AC power supply; a bridge arm circuit having an upper bridge arm and a lower bridge arm with two semiconductor switching elements connected in series; a balancing resistor connected in parallel with each semiconductor switching element of the bridge arm circuit; a charge / discharge capacitor connected between the connection points of the semiconductor switching elements of the upper bridge arm and the connection points of the semiconductor switching elements of the lower bridge arm; a smoothing capacitor connected to the output of the bridge arm circuit; an impulse prevention circuit having a current limiting resistor between the single-phase AC power supply and the diode rectifier circuit with only one branch; and a reactor.

[0125] Therefore, the power conversion device of Embodiment 1 can suppress overvoltage during the initial charging, operation, and shutdown states when the power is turned on.

[0126] Implementation method 2.

[0127] The power conversion device in Embodiment 2 is configured to have a bridge rectifier circuit instead of a diode rectifier circuit with only one branch.

[0128] Regarding the structure and operation of the power conversion device involved in Implementation Method 2, based on the structural diagram of the power conversion device, i.e. Figure 14 And other circuit structure diagrams, i.e. Figure 15 , Figure 16 The explanation will focus on the differences from Implementation Method 1.

[0129] In Implementation Method 2 Figures 14-16 In this document, the same symbols are added to the parts that are the same as or equivalent to those in Implementation 1.

[0130] In addition, to distinguish them from Embodiment 1, they are designated as power conversion devices 200, 201, and 202.

[0131] The difference between Embodiment 2 and Embodiment 1 is that the diode rectifier circuit 4a with only one branch and two diodes is replaced with a bridge rectifier circuit 4b with four diodes. AC to DC conversion is achieved by using the bridge rectifier circuit 4b. Therefore, the connections between the single-phase AC power supply 1a, the bridge rectifier circuit 4b, and the bridge arm circuit 5a are changed.

[0132] The power conversion device 200 takes a single-phase AC power supply 1a as input and includes an impulse prevention circuit 2 (including a current limiting resistor 21 and a switch 22), a reactor 3, a bridge rectifier circuit 4b, a bridge arm circuit 5a (with a series circuit of semiconductor switching elements 51 and 52 in the upper bridge arm and a series circuit of semiconductor switching elements 53 and 54 in the lower bridge arm), a balancing resistor 6a (with resistors 61, 62, 63, and 64), a charging / discharging capacitor 7, and a smoothing capacitor 8), and a load 10 connected to the output. Furthermore, the power conversion device 200 includes a controller 9 for driving the bridge arm circuit 5a.

[0133] A single-phase AC power supply 1a is connected to the input of the bridge rectifier circuit 4b via a reactor 3. The output of the bridge rectifier circuit 4b is connected in parallel with the lower arm of the bridge arm circuit 5a, which is composed of a series circuit of semiconductor switching elements 53 and 54.

[0134] The connections of the bridge arm circuit 5a, balancing resistors 61 to 64, charging / discharging capacitor 7, and smoothing capacitor 8 are the same as in embodiment 1, so the description is omitted.

[0135] In Implementation Method 2 Figure 14In the structure, the charging characteristics of the smoothing capacitor 8 and the charging / discharging capacitor 7 are the same as those in Embodiment 1, so the functions and operations described in Embodiment 1 can be applied.

[0136] In addition, as a result of Figure 14 The circuit method obtained by modifying the circuit structure, in Figure 15 and Figure 16 The circuit configuration shown is the same as that of the power conversion device 200 in Embodiment 2 in terms of function and operation.

[0137] The power conversion device 201 is as follows Figure 15 The structure is formed by replacing semiconductor switching elements 51 and 52 with diodes 51a and 52a as shown.

[0138] In embodiment 2, by using the bridge rectifier circuit 4b, even if the semiconductor switching elements 51 and 52 are not semiconductor switching elements, it is possible to perform [interaction / operation]. Figure 14 The power conversion device 200 operates in the same way.

[0139] It has the following advantages: compared with the case composed of semiconductor switching elements 51 and 52, the case composed of diodes 51a and 52a can be constructed at a lower cost.

[0140] In addition, the power conversion device 202 is as follows Figure 16 As shown, the surge protection circuit 2 and the reactor 3 are moved to the output side of the bridge rectifier circuit 4b. Even with this circuit configuration, the function and operation remain unchanged compared to the power conversion devices 200 and 201.

[0141] In the power conversion device 200 of Embodiment 2, it is possible to suppress the semiconductor switching element 51 (diode 51a) and semiconductor switching element 54 from becoming overvoltage during initial charging.

[0142] In the power conversion device 200 of Embodiment 2, overvoltage can be suppressed during initial charging, and semiconductor switching elements can be constructed using components with lower voltage ratings. Therefore, the suppression cost increases, high-efficiency components can be selected, and a higher-efficiency power converter can be constructed.

[0143] As explained above, the power conversion device of Embodiment 2 is configured to have a bridge rectifier circuit instead of a diode rectifier circuit with only one branch.

[0144] Therefore, the power conversion device of Embodiment 2 can suppress overvoltage during the initial charging, operation, and stop states when the power is turned on.

[0145] Implementation method 3.

[0146] The power conversion device of Implementation Method 3 uses a three-phase AC power supply as the AC power source.

[0147] Regarding the structure and operation of the power conversion device involved in Implementation Method 3, based on the circuit structure diagram of the power conversion device, i.e. Figure 17 Other circuit structure diagrams, i.e. Figure 18 The initial charging waveform relative to the change in the overvoltage level index. Figures 19-22 And a graph showing the maximum voltage applied to the semiconductor switching element relative to the change in the overvoltage level index. Figure 23 The explanation will focus on the differences from implementation methods 1 and 2.

[0148] In implementation method 3 Figure 17 , Figure 18 In this document, the same symbols are added to the parts that are the same as or equivalent to those in embodiments 1 and 2.

[0149] In addition, to distinguish them from embodiments 1 and 2, they are designated as power conversion devices 300 and 301.

[0150] The difference between Embodiment 3 and Embodiment 2 is that the single-phase AC power supply is changed to a three-phase AC power supply. This is achieved by using a bridge rectifier circuit 4c with six diodes to convert the three-phase AC to DC. Therefore, the connections of the three-phase AC power supply 1b, the surge protection circuit 2, the reactor 3, the bridge rectifier circuit 4c, and the bridge arm circuit 5a are changed.

[0151] The power conversion device 300 takes a three-phase AC power supply 1b as input and includes a bridge rectifier circuit 4c, an impulse prevention circuit 2 with a current limiting resistor 21 and a switch 22, a reactor 3, a bridge arm circuit 5a with a series circuit of semiconductor switching elements 51 and 52 in the upper bridge arm and a series circuit of semiconductor switching elements 53 and 54 in the lower bridge arm, a balancing resistor 6a with resistors 61, 62, 63, and 64, a charging and discharging capacitor 7, and a smoothing capacitor 8. A load 10 is connected to the output. Furthermore, the power conversion device 300 includes a controller 9 for driving the bridge arm circuit 5a.

[0152] The three-phase AC power supply 1b is converted into DC by a bridge rectifier circuit 4c, and then connected in parallel with the lower arm of the bridge arm circuit 5a, which is composed of a series circuit of semiconductor switching elements 53 and 54, via an impulse prevention circuit 2 and a reactor 3.

[0153] The connections of the bridge arm circuit 5a, balancing resistors 61-64, charging / discharging capacitor 7, and smoothing capacitor 8 are the same as in embodiments 1 and 2, so the description is omitted.

[0154] Figure 18This describes the circuit structure of a power conversion device 301, which is another embodiment of the power conversion device 300. As explained in Embodiment 2, a bridge rectifier circuit 4c is used to convert AC to DC, thus allowing the semiconductor switching elements 51, 51 in the upper arm of the bridge arm circuit 5a to be replaced with diodes 51a, 52a. As the bridge arm circuit 5b, the power conversion device 301 functions and operates the same as the power conversion device 300.

[0155] In implementation method 3, the power supply is changed from single-phase AC power supply to three-phase AC power supply, so the charging speed of smoothing capacitor 8 and charging / discharging capacitor 7 are different.

[0156] If a three-phase AC power supply is used, the average DC voltage at the output of the bridge rectifier circuit 4c increases compared to a single-phase AC power supply. Therefore, the charging time of the smoothing capacitor 8 increases. Consequently, the value of the effective coefficient Km changes compared to Embodiment 1 and Embodiment 2.

[0157] Figures 19-22 The figure shows the charging characteristics of the smoothing capacitor 8 and the charging / discharging capacitor 7 when the coefficients are set to Km = 100 (comparative example), Km = 10, Km = 3.7, and Km = 1.5.

[0158] Figure 19 Corresponding to coefficient Km = 100, Figure 20 Corresponding to coefficient Km = 10, Figure 21 Corresponding to coefficient Km = 3.7, Figure 22 This corresponds to the coefficient Km = 1.5.

[0159] exist Figures 19-22 In the diagram, the solid lines of F19a (F20a, F21a, F22a) represent the voltage of the smoothing capacitor 8, and the dashed lines represent the voltage of the charging and discharging capacitor 7.

[0160] exist Figures 19-22 In the diagram, F19b (F20b, F21b, F22b) represents the voltage difference between the voltage of the smoothing capacitor 8 and the voltage of the charging / discharging capacitor 7. This voltage difference is applied to the semiconductor switching element 51 (diode 51a) and the semiconductor switching element 54.

[0161] Regarding voltages exceeding 300V when the coefficient Km = 100 in the comparative example, reducing the coefficient Km results in suppressing overshoot voltage.

[0162] In Implementation Method 3, the peak value of the AC voltage of the three-phase AC power supply is 374V. Therefore, the convergence value of the voltage of the smoothing capacitor 8 is 374V, and the convergence value of the voltage of the charging and discharging capacitor 7 is 187V.

[0163] With a coefficient Km = 10, the peak voltage of the charging / discharging capacitor 7 becomes 280V, and the overshoot of the voltage applied to the semiconductor switching element is reduced to 280 / 187 = 1.5 times. By suppressing the peak voltage applied to the semiconductor switching element, the effectiveness of the power conversion device 300 of Embodiment 3 can be confirmed.

[0164] Furthermore, by reducing the coefficient Km to 3.7, the peak value of the voltage applied to the semiconductor switching element becomes 234V, and the voltage overshoot is reduced to 234 / 187 = 1.25 times, which further confirms the effectiveness of the power conversion device 300 of Embodiment 3.

[0165] Furthermore, by reducing the coefficient Km to 1.5, it is almost impossible to detect overshoot of the voltage applied to the semiconductor switching element, thus maximizing the effect of the power conversion device 300 of Embodiment 3.

[0166] If we graph the coefficient Km and the peak value of the voltage applied to the semiconductor switching element, we get Figure 23 The relationship shown.

[0167] exist Figure 23 In the figure, the horizontal axis represents the coefficient Km, and the vertical axis represents the maximum voltage [V] across the semiconductor switching element.

[0168] Clearly, the smaller the coefficient Km, the better the peak voltage can be suppressed. It can be seen that if the coefficient Km is set to 1 / 2 compared with embodiment 1, the same effect as embodiment 1 is obtained.

[0169] In the power conversion device of embodiment 3, the semiconductor switching element 51 (diode 51a) and semiconductor switching element 54 are prevented from becoming overvoltage during initial charging.

[0170] In the power conversion device 300 of embodiment 3, overvoltage can be suppressed during initial charging, and semiconductor switching elements can be constructed using components with lower voltage ratings. Therefore, the suppression cost increases, high-efficiency components can be selected, and a higher-efficiency power converter can be constructed.

[0171] As explained above, the power conversion device of Embodiment 3 uses a three-phase AC power supply as the AC power source.

[0172] Therefore, the power conversion device of embodiment 3 can suppress overvoltage during the initial charging, operation, and stop states when the power is turned on.

[0173] Implementation method 4.

[0174] The power conversion device in Implementation 4 is formed by changing the balancing resistor to a 3-resistor configuration.

[0175] Regarding the structure and operation of the power conversion device involved in Implementation Method 4, based on the circuit structure diagram of the power conversion device, i.e. Figure 24 The figure also compares the initial charging characteristics of the charging and discharging capacitors in the 3-resistor and 4-resistor configurations of power conversion devices. Figure 25 The explanation will focus on the differences from Implementation Method 1.

[0176] In implementation method 4 Figure 24 In this document, the same symbols are added to the parts that are the same as or equivalent to those in Implementation 1.

[0177] In addition, to distinguish it from Embodiment 1, it is designated as a power conversion device 400.

[0178] In Embodiment 4, the difference from Embodiment 1 is that the balancing resistors are changed from a 4-resistor configuration to a 3-resistor configuration. Specifically, the four balancing resistors 61 to 64 are changed to three balancing resistors 61, 64, and 65.

[0179] The power conversion device 400 takes a single-phase AC power supply 1a as input and includes an impulse prevention circuit 2 comprising a current limiting resistor 21 and a switch 22, a reactor 3, a diode rectifier circuit 4a with only one branch, a bridge arm circuit 5a having a series circuit of semiconductor switching elements 51 and 52 in the upper bridge arm and a series circuit of semiconductor switching elements 53 and 54 in the lower bridge arm, a balancing resistor 6b having balancing resistors 61, 64, and 65, a charging / discharging capacitor 7, a smoothing capacitor 8, and a load 10 connected to the output. Furthermore, the power conversion device 400 includes a controller 9 for driving the bridge arm circuit 5a.

[0180] Explain the connection of bridge arm circuit 5a, balancing resistor 6b, and charging / discharging capacitor 7.

[0181] A balancing resistor 61 is connected in parallel with semiconductor switching element 51, and a balancing resistor 64 is connected in parallel with semiconductor switching element 54. A balancing resistor 65 is connected in parallel with the series circuit of semiconductor switching elements 52 and 53.

[0182] The charging and discharging capacitor 7 is connected in parallel with the series circuit of semiconductor switching elements 52 and 53 and the balancing resistor 65.

[0183] The connection of the single-phase AC power supply 1a, the surge protection circuit 2, the reactor 3, the diode rectifier circuit 4a with only one branch, and the bridge arm circuit 5a is the same as in implementation method 1, so the description is omitted.

[0184] Furthermore, when it is necessary to distinguish between balancing resistors 61, 64 and 65, balancing resistors 61 and 64 are recorded as individual balancing resistors, and balancing resistor 65 is recorded as a shared balancing resistor.

[0185] In the power conversion device 400 of embodiment 4, which changes the balancing resistor to a 3-resistor configuration, overshoot of the applied voltage to the semiconductor switching element can be suppressed when the coefficient Km is set to a small value.

[0186] Based on the relationship between the values ​​of balancing resistors 61, 64 and 65, the difference between the voltage of the charging / discharging capacitor 7 and the voltage of the smoothing capacitor 8 changes.

[0187] It is speculated that if the value of the balancing resistor 65 is set to twice the value of the balancing resistors 61 and 64, the voltage of the charging and discharging capacitor 7 will become half the voltage of the smoothing capacitor 8.

[0188] Figure 25 The results show the resistance values ​​set as current limiting resistor R0 = 10Ω, balancing resistor Rf = 10kΩ, electrostatic capacitance of charge / discharge capacitor 7 Cf = 10uF, electrostatic capacitance of smoothing capacitor 8 C0 = 1000μF, and the convergence value of voltage of charge / discharge capacitor 7 was investigated.

[0189] exist Figure 25 In the diagram, the solid line corresponds to the 4-resistor configuration, and the dashed line corresponds to the 3-resistor configuration.

[0190] The convergence value of the voltage of the charge / discharge capacitor 7, which is 187V when the balancing resistor is 4, rises to 210V when the balancing resistor is 3. This is due to the charging of the charge / discharge capacitor 7 from the AC power supply side. Furthermore, Figure 25 The curve (solid line) for the 4-resistor method and Figure 8 The curve for 10μF (solid line) is the same.

[0191] If you want to set the voltage of the charging / discharging capacitor 7 to be half that of the smoothing capacitor, and if you set the value of the balancing resistor 65 to be about 1.5 times that of the balancing resistors 61 and 64, then the voltage of the charging / discharging capacitor 7 will become half that of the voltage of the smoothing capacitor 8.

[0192] However, under such a configuration, if the AC power supply is cut off due to a circuit breaker or the like, the voltage of the charging / discharging capacitor 7 will not be half the voltage of the smoothing capacitor 8.

[0193] Therefore, in applications where both power-on and power-off conditions need to be considered, the overvoltage suppression effect is higher when using a 4-resistor configuration with 4 balancing resistors as in Embodiments 1 to 3.

[0194] In the structure of the power conversion device in embodiments 2 and 3, the balancing resistor can also be changed from a 4-resistor configuration to a 3-resistor configuration.

[0195] In the case where a three-phase AC power supply is used in Embodiment 3, if it is desired to set the voltage of the charging / discharging capacitor 7 to 1 / 2 of the voltage of the smoothing capacitor 8, if the value of the balancing resistor 65 is set to approximately 1.1 times that of the balancing resistors 61 and 64, then the voltage of the charging / discharging capacitor 7 becomes 1 / 2 of the voltage of the smoothing capacitor 8.

[0196] In Embodiment 4, the power conversion device 400 sets the value of the balancing resistor 65 to twice that of the balancing resistors 61 and 64. Although the reduction effect on the peak voltage applied to the semiconductor switching elements 51 and 54 is smaller compared to the power conversion device of Embodiment 1 with the 4-resistor method, the peak voltage can still be suppressed. Therefore, it is possible to prevent the semiconductor switching elements 51 and 54 from becoming overvoltage during initial charging.

[0197] The power conversion device 400 of embodiment 4 can suppress overvoltage during initial charging, and the semiconductor switching element can be constructed from components with lower voltage tolerance. Therefore, the suppression cost increases, high-efficiency components can be selected, and a higher-efficiency power converter can be constructed.

[0198] Furthermore, in the power conversion device 400 of embodiment 4, the number of balancing resistors that can be configured is 3, so the power conversion device can be configured at a lower cost.

[0199] As explained above, the power conversion device in Embodiment 4 is formed by changing the balancing resistor to a 3-resistor configuration.

[0200] Therefore, the power conversion device of embodiment 4 can suppress overvoltage during the initial charging, operation, and stop states when the power is turned on.

[0201] Implementation method 5.

[0202] The power conversion device in embodiment 5 is formed by connecting three semiconductor switching elements of the upper and lower bridge arms in series in the bridge arm circuit.

[0203] Regarding the structure and operation of the power conversion device involved in Implementation Method 5, based on the structural diagram of the power conversion device, i.e. Figure 26 And a graph showing the maximum voltage applied to the semiconductor switching element relative to the change in the overvoltage level index. Figure 27 The explanation will focus on the differences from Implementation Method 1.

[0204] In implementation method 5 Figure 26 In this document, the same symbols are added to the parts that are the same as or equivalent to those in Implementation 1.

[0205] In addition, to distinguish it from Embodiment 1, it is designated as a power conversion device 500.

[0206] In embodiment 5, the difference from embodiment 1 is that the number of series semiconductor switches in the upper and lower arms of the bridge arm circuit 5c is set to three each. With this structural change, the number of balancing resistors and charging / discharging capacitors is also increased.

[0207] The power conversion device 500 takes a single-phase AC power supply 1a as input and includes an impulse prevention circuit 2 (including a current limiting resistor 21 and a switch 22), a reactor 3, a diode rectifier circuit 4a with only one branch, a bridge arm circuit 5c (with a series circuit of semiconductor switching elements 56, 51, and 52 in the upper bridge arm and a series circuit of semiconductor switching elements 53, 54, and 57 in the lower bridge arm), a balancing resistor 6c (with resistors 66, 61, 62, 63, 64, and 67), charging and discharging capacitors 7 and 7a, a smoothing capacitor 8, and a load 10 connected to the output. Furthermore, the power conversion device 500 includes a controller 9 for driving the bridge arm circuit 5c.

[0208] Explain the connection of bridge arm circuit 5c, balancing resistor 6c, and charging / discharging capacitors 7 and 7a.

[0209] For the upper bridge arm, balancing resistors 66, 61, and 62 are connected in parallel with semiconductor switching elements 56, 51, and 52, respectively. For the lower bridge arm, balancing resistors 63, 64, and 67 are connected in parallel with semiconductor switching elements 53, 54, and 57, respectively.

[0210] The charging and discharging capacitor 7 is connected in parallel with the series circuit of semiconductor switching elements 52 and 53, i.e., the series circuit of balancing resistors 62 and 63.

[0211] The charging and discharging capacitor 7a is connected in parallel with the series circuit of semiconductor switching elements 51, 52, 53, and 54, i.e., the series circuit of balancing resistors 61, 62, 63, and 64.

[0212] The connection of the single-phase AC power supply 1a, the surge protection circuit 2, the reactor 3, the diode rectifier circuit with only one branch 4a, and the bridge arm circuit 5c is basically the same as in embodiment 1, so the description is omitted.

[0213] In the power conversion device 500 of Embodiment 5, when the balance of the charging time of the smoothing capacitor 8 and the charging / discharging capacitors 7, 7a is disrupted, an overvoltage is applied to the semiconductor switching elements. When the balance is disrupted, the semiconductor switching elements most susceptible to overvoltage are the uppermost semiconductor switching element 56 of the upper bridge arm and the lowermost semiconductor switching element 57 of the lower bridge arm. The voltage difference between the smoothing capacitor 8 and the charging / discharging capacitor 7a is applied to the semiconductor switching elements 56, 57. It is necessary to suppress this voltage overshoot.

[0214] When the same resistance values ​​are applied to the balancing resistors 66, 61, 62, 63, 64, and 67, the overvoltage suppression effect is high. Here, the average value of the resistances of the balancing resistors 66, 61, 62, 63, 64, and 67 is set as Rf.

[0215] It is also possible to set the electrostatic capacitance of the charging / discharging capacitor 7 and the charging / discharging capacitor 7a to different values, but here they are set to the same value, Cf. Furthermore, the resistance value of the current limiting resistor 21 is set to R0, and the electrostatic capacitance of the smoothing capacitor is set to C0.

[0216] The coefficients Kf, K0, and Km can be defined using the same method as in Implementation Method 1.

[0217] Figure 27 The graph shows a coefficient Km, which is an indicator of the degree of overvoltage, and the maximum voltage applied to the semiconductor switching elements 56 and 57.

[0218] exist Figure 27 In the figure, the horizontal axis represents the coefficient Km, and the vertical axis represents the maximum voltage [V] across the semiconductor switching element.

[0219] exist Figure 27 In the diagram, the solid line represents the case where the upper and lower bridge arms of the power conversion device 500 in Embodiment 5 consist of three semiconductor switching elements connected in series. The dashed line represents the case where the upper and lower bridge arms of the power conversion device 100 in Embodiment 1 consist of two semiconductor switching elements connected in series.

[0220] The coefficient Km remains the same until it reaches approximately 3. However, in the case of 3 semiconductor switching elements connected in series, the voltage applied to the switching element becomes 1 / 3 of the voltage of the smoothing capacitor 8. Therefore, if the coefficient Km is further reduced, voltage overshoot is suppressed.

[0221] The above explains the implementation method 1. Figure 1 The circuit structure is configured such that the upper and lower bridge arms are three semiconductor switching elements connected in series. Regarding the circuit structures of embodiments 2 and 3, i.e. Figures 14-16 , Figure 17 , Figure 18 The circuit structure can also be set as three semiconductor switching elements connected in series.

[0222] Furthermore, when a bridge rectifier circuit 4b or 4c is used for the rectifier circuit 4, the power conversion device 201 of Embodiment 2 can be used as described. Figure 15 ), 202 Figure 16 ), Power conversion device 301 of embodiment 3 ( Figure 18 That is, the semiconductor switching element of the upper bridge arm is changed to a diode.

[0223] Even with a reduced balancing resistance as in embodiment 4, it is possible to increase the number of semiconductor switching elements connected in series. In this case, Figure 26 In this case, by replacing balancing resistors 62 and 63 with one balancing resistor, the number of balancing resistors can be reduced to five.

[0224] In addition, while embodiment 5 describes the case where the semiconductor switching elements of the upper and lower bridge arms are connected in series in sets of three, it is also possible to connect the semiconductor switching elements of the upper and lower bridge arms in series in sets of four or five.

[0225] In the power conversion device 500 of embodiment 5, even when the number of series connections of the semiconductor switching elements of the upper and lower bridge arms is increased, overvoltage applied to the semiconductor switching elements during initial charging is suppressed.

[0226] In the power conversion device 500 of embodiment 5, overvoltage can be suppressed during initial charging, and semiconductor switching elements can be constructed using components with lower voltage tolerance. Therefore, the suppression cost increases, and high-efficiency semiconductor switching elements can be selected, enabling the construction of a more efficient power conversion device.

[0227] As explained above, the power conversion device of Embodiment 5 is formed by connecting three semiconductor switching elements of the upper and lower bridge arms in series in the bridge arm circuit.

[0228] Therefore, the power conversion device of embodiment 5 can suppress overvoltage during the initial charging, operation, and stop states when the power is turned on.

[0229] Here, Figure 28 An example of the hardware of the controller 9 of the power conversion device is shown. For example... Figure 28 As shown, it consists of a processor 2000 and a storage device 2001. Although not shown, the storage device includes volatile storage devices such as random access memory and non-volatile auxiliary storage devices such as flash memory.

[0230] Alternatively, a hard disk can be provided as an auxiliary storage device instead of flash memory. The processor 2000 executes the program input from the storage device 2001. In this case, the program is input from the auxiliary storage device to the processor 2000 via a volatile storage device. Furthermore, the processor 2000 can either output data such as calculation results to the volatile storage device of the storage device 2001, or save data in the auxiliary storage device via the volatile storage device.

[0231] This application describes various exemplary embodiments and examples, but the various features, methods and functions described in one or more embodiments are not limited to the application of a specific embodiment and can be applied to the embodiment alone or in various combinations.

[0232] Therefore, numerous variations not illustrated are conceivable within the scope of the technology disclosed in this application. These include variations of at least one constituent element, additions, omissions, and extraction of at least one constituent element combined with constituent elements of other embodiments.

Claims

1. A power conversion device, comprising: A rectifier circuit, connected to an AC power source, rectifies the input voltage from the AC power source; A bridge arm circuit, connected to the rectifier circuit, has an upper bridge arm composed of a plurality of semiconductor elements connected in series and a lower bridge arm composed of a plurality of semiconductor elements connected in series, the upper bridge arm and the lower bridge arm being connected in series, and at least the plurality of semiconductor elements in the lower bridge arm being switching elements. A balancing resistor is connected in parallel with the semiconductor element of the bridge arm circuit; At least one charge / discharge capacitor is connected between the connection point of the semiconductor element in the upper bridge arm and the connection point of the semiconductor element in the lower bridge arm; A smoothing capacitor is connected to the output of the bridge arm circuit; as well as An impact prevention circuit, disposed between the AC power supply and the bridge arm circuit, includes a current limiting resistor. When the charging speed of the charging and discharging capacitor is set to a coefficient Kf and the charging speed of the smoothing capacitor is set to a coefficient K0, Km is represented by Kf / K0. In order to suppress the overvoltage applied to the semiconductor element when the power is turned on, Km is set to be less than 100.

2. The power conversion device according to claim 1, wherein, The value of Kf is obtained by multiplying the average resistance value of the balancing resistor by the capacitance value of the charging / discharging capacitor, and the value of K0 is obtained by multiplying the resistance value of the current limiting resistor by the capacitance value of the smoothing capacitor.

3. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a single-phase AC power supply. The rectifier circuit is a diode rectifier circuit with only one branch. The balancing resistor is connected in parallel with each of the semiconductor elements of the bridge arm circuit.

4. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a single-phase AC power supply. The rectifier circuit is a bridge rectifier circuit. The balancing resistor is connected in parallel with each of the semiconductor elements of the bridge arm circuit.

5. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a single-phase AC power supply. The rectifier circuit is a diode rectifier circuit with only one branch. The balancing resistor includes: A common balancing resistor is connected in parallel with the semiconductor element at the bottom of the upper bridge arm and the semiconductor element at the top of the lower bridge arm; and Individual balancing resistors are connected in parallel with each semiconductor element of the upper bridge arm and each semiconductor element of the lower bridge arm, excluding the semiconductor element connected to the common balancing resistor.

6. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a single-phase AC power supply. The rectifier circuit is a bridge rectifier circuit. The balancing resistor includes: A common balancing resistor is connected in parallel with the semiconductor element at the bottom of the upper bridge arm and the semiconductor element at the top of the lower bridge arm; and Individual balancing resistors are connected in parallel with each semiconductor element of the upper bridge arm and each semiconductor element of the lower bridge arm, excluding the semiconductor element connected to the common balancing resistor.

7. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a three-phase AC power supply. The rectifier circuit is a bridge rectifier circuit. The balancing resistor is connected in parallel with each of the semiconductor elements of the bridge arm circuit.

8. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a three-phase AC power supply. The rectifier circuit is a bridge rectifier circuit. The balancing resistor includes: A common balancing resistor is connected in parallel with the semiconductor element at the bottom of the upper bridge arm and the semiconductor element at the top of the lower bridge arm; and Individual balancing resistors are connected in parallel with each semiconductor element of the upper bridge arm and each semiconductor element of the lower bridge arm, excluding the semiconductor element connected to the common balancing resistor.

9. The power conversion device according to claim 3 or 4, wherein, The Km is set to a constant below 20.

10. The power conversion device according to claim 7, wherein, The Km is set to a constant below 10.

11. The power conversion device according to claim 1 or 2, wherein, The AC power supply is a single-phase AC power supply. The rectifier circuit is a diode rectifier circuit with two diodes connected in series. One end of the single-phase AC power supply is connected to the junction of the two diodes. The other end of the single-phase AC power supply is connected to the connection point between the upper bridge arm and the lower bridge arm of the bridge arm circuit.

12. The power conversion device according to claim 1 or 2, wherein, The Km is set to a constant such that the voltage applied to the semiconductor element when the power is turned on does not exceed the withstand voltage of the semiconductor element.

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