JP2014217199A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that allows further accurately measuring a switching frequency corresponding to a resonant frequency and setting the switching frequency.SOLUTION: A power conversion device 1 includes: a current-resonance full-bridge converter 4 switching-controlled on the basis of a preset switching frequency; switching-frequency setting means 18 for measuring the switching frequency that reaches the maximum power conversion efficiency by changing the switching frequency when a predetermined condition is met and resetting the switching frequency; and an input/output-power suppressing and controlling means 20 for limiting input/output power. The switching-frequency setting means is configured so that the switching frequency is reset only when a state in which the input/output power is limited by the input/output-power suppressing and controlling means 20 continues over a predetermined time.

Description

  The present invention relates to a power conversion device that can be suitably used as a power conditioner for a fuel cell power generation system.

  As a DC / DC converter built in a power conditioner that converts DC power output from a fuel cell into AC power linked to a commercial power system and outputs it in a fuel cell power generation system, it is one of the most efficient types of isolated converters. Current resonant full-bridge converters are often used.

  An example of the current resonance full bridge converter is disclosed in Patent Document 1 below. In this conventional converter, a resonant capacitor is connected in series with a high-frequency transformer, and zero current switching is performed by driving the switching elements constituting the high-frequency bridge inverter at a constant switching frequency that matches the resonance frequency of current resonance. As a result, switching loss and noise are reduced to achieve higher efficiency.

JP 2011-72137 A

  However, transformer leakage inductance and resonant capacitor capacitance may deviate from the design value due to variations in transformer manufacturing, aging of the transformer and resonant capacitor, temperature conditions, etc. As a result, zero current switching cannot be performed accurately. In this case, there is a problem in that power conversion efficiency is reduced due to an increase in switching loss and switching noise occurs.

  Also in the above-mentioned Patent Document 1, in paragraph No. 0061, if the circuit constant varies due to individual differences of circuit elements, the resonance frequency may also vary. Therefore, the switching frequency of the booster circuit is not fixedly determined in advance. It is mentioned that it is preferable to adopt a configuration in which the switching frequency is automatically corrected in a state where the grid-connected inverter device is actually operated. Further, in paragraph numbers 0063 to 0064, as an example of a configuration for automatically correcting the switching frequency, the boost control unit is provided with efficiency calculating means for calculating the power conversion efficiency in the booster circuit and the inverter circuit, and the conversion efficiency is maximized. A configuration in which the switching frequency is adjusted by the boost control unit is disclosed. Specifically, the input power detection means of the booster circuit and the output power detection means of the inverter circuit are provided, and the efficiency calculation means calculates the conversion efficiency from the ratio of the detection power of the output power detection means to the detection power of the input power detection means. calculate. The step-up control unit changes the switching frequency of the step-up circuit within a predetermined range, and sets the frequency at which the conversion efficiency calculated by the efficiency calculating means is maximized as a new switching frequency.

  However, even when the grid-connected inverter device is operating, the household load may fluctuate, which may cause fluctuations in the input / output power. There is a problem in that the frequency cannot be accurately grasped, and a new switching frequency thus set may deviate from the resonance frequency. Such a problem is not suggested in Patent Document 1.

  Therefore, an object of the present invention is to provide a power conversion device that can more accurately measure and set a switching frequency that matches a resonance frequency.

  In order to achieve the above object, the present invention takes the following technical means.

  That is, the present invention includes a current resonance bridge converter that performs switching control based on a preset switching frequency, a switching frequency setting unit that resets the switching frequency when a predetermined condition is satisfied, and input / output power. In the power conversion apparatus including the input / output power suppression control means for limiting the input / output power, the switching frequency setting means continues the input / output power restriction by the input / output power suppression control means for a predetermined time. The switching frequency is reset only when the switching frequency is set (Claim 1).

  According to the power conversion device of the present invention, the switching frequency setting means switches the switching frequency based on the actual measurement value of the current resonance frequency of the current resonance bridge converter or the maximum input / output power conversion efficiency of the power conversion device. By resetting the frequency, switching loss and noise generation in the current resonance bridge converter can be reduced. The input / output power suppression control means limits the input power to the rated power, limits the output power to the rated output, and controls the input current so as not to exceed the upper limit current value transmitted from the control unit of the fuel cell. By limiting the input / output power to be limited, it is possible to prevent the deterioration of the fuel cell stack and the electrical breakdown of the components of the current resonance bridge converter. Furthermore, when the state where the input / output power is limited continues for a predetermined time, it is often the case that a certain amount of power load is continuously used, and after that the fixed time is Since it is expected that the power load will continue to be used, performing switching frequency resetting in such a condition will cause the switching frequency to exactly match the actual current resonance frequency, further reducing switching loss and noise. Reduction can be achieved.

  The present invention also provides a current resonance bridge converter that boosts input DC power from a DC power supply, and converts the DC power boosted by the converter into low-frequency AC power that is connected to the system power and outputs the power to the system. A low-frequency inverter, an input current sensor and an input voltage sensor provided on the input side of the current resonance bridge converter, an output current sensor and an output voltage sensor provided on the output side of the low-frequency inverter, and a control unit. The current resonance bridge converter includes a bridge inverter that converts input DC power into high-frequency AC power by a switching operation of a switching element and outputs the bridge inverter, and a primary side connected to the output side of the bridge inverter. A transformer and a current resonant capacitor connected in series to the primary side or secondary side of the transformer. And a rectifier circuit connected to the secondary side of the transformer, and the control unit inputs and outputs based on detection values of the input current sensor, the input voltage sensor, the output current sensor, and the output voltage sensor. Efficiency calculating means for calculating power conversion efficiency; switching frequency setting means for setting a switching frequency; converter control means for controlling the switching element based on the switching frequency set by the switching frequency setting means; Inverter control means for controlling a frequency inverter, wherein the converter control means and / or the inverter control means includes: an input current detected by the input current sensor; an output current detected by the output current sensor; and the input current sensor The input current to be detected and the input voltage to be detected by the input voltage sensor And input / output power based on at least one of the output power calculated based on the input power calculated based on the output current detected by the output current sensor and the output voltage detected by the output voltage sensor. The switching frequency setting means changes the switching frequency within a predetermined range when the predetermined condition is satisfied, and the calculation result of the efficiency calculation means at a plurality of frequency points is provided. In the power converter that resets the switching frequency based on the switching frequency setting means, when the input / output power restriction is performed by the input / output power suppression control function for a predetermined time The switching frequency is reset only in the above-described manner. Claim 2).

  According to the power conversion device of the present invention, in addition to the operation and effect of the power conversion device according to claim 1, the power consumption of the power load connected to the system is limited output power (for example, by the input / output power suppression control function) If the input / output power of the power converter exceeds the rated input / output power of the power converter or the output power of the power converter according to the allowable output current value of the fuel cell) The shortage will be covered by grid power. By resetting the switching frequency in such a state, even if the power consumption of the power load fluctuates somewhat, the fluctuation is absorbed as an increase / decrease in the power consumption of the system power, and the input / output of the power conversion device Since the power stably operates at a predetermined power, it is possible to search for a frequency point at which the power conversion efficiency is maximized more accurately.

  Further, the switching frequency setting means resets the switching frequency when the input / output power is not limited by the input / output power suppression control function while changing the switching frequency within a predetermined range. It is preferable to cancel the setting (claim 3). According to this, when the power consumption of the power load is greatly reduced during the search for the optimal frequency, and the input / output power is no longer restricted, the resetting of the switching frequency is stopped and the previous setting was made. By maintaining the switching frequency, a value greatly deviating from the resonance frequency can be prevented from being set by the switching frequency setting means.

  In the power conversion device of the present invention, it is preferable that the switching frequency setting means is configured not to reset the switching frequency until a predetermined period has elapsed since the previous resetting. . While the switching frequency is fluctuated within a predetermined range for resetting the switching frequency, the conversion efficiency is reduced and noise is generated. According to the above configuration, the switching frequency is frequently reset. To avoid this, for example, to cope with aging degradation of the step-up transformer and current resonance capacitor, the switching frequency is reset when the input / output power is stable after 30 days or more after the previous resetting. It can be configured as follows.

  As described above, according to the power conversion device of the first aspect of the present invention, the switching frequency setting means allows the switching frequency based on the actual measurement value of the current resonance frequency of the current resonance bridge converter, By resetting the switching frequency at which the input / output power conversion efficiency is maximized, switching loss and noise generation in the current resonance bridge converter can be reduced. The input / output power suppression control means limits the input power to the rated power, limits the output power to the rated output, and controls the input current so as not to exceed the upper limit current value transmitted from the control unit of the fuel cell. By limiting the input / output power to be limited, it is possible to prevent the deterioration of the fuel cell stack and the electrical breakdown of the components of the current resonance bridge converter. Furthermore, when the state where the input / output power is limited continues for a predetermined time, it is often the case that a certain amount of power load is continuously used, and after that the fixed time is Since it is expected that the power load will continue to be used, performing switching frequency resetting in such a condition will cause the switching frequency to exactly match the actual current resonance frequency, further reducing switching loss and noise. Reduction can be achieved.

  In the power conversion device according to claim 2 of the present invention, the power consumption of the power load connected to the system is limited output power by the input / output power suppression control function (for example, the rated input / output power and fuel of the power conversion device). If the output power of the power converter according to the battery's allowable output current value is exceeded, the input / output power of the power converter is limited to the specified power by the input / output power suppression control function, and the shortage is the grid power. Be covered. By resetting the switching frequency in such a state, even if the power consumption of the power load fluctuates somewhat, the fluctuation is absorbed as an increase / decrease in the power consumption of the system power, and the input / output of the power conversion device Since the power stably operates at a predetermined power, it is possible to search for a frequency point at which the power conversion efficiency is maximized more accurately.

  According to the power conversion device of the third aspect of the present invention, when the input / output power is not limited due to the power consumption of the power load being greatly reduced during the search for the optimum frequency, the switching frequency is reduced. By canceling the resetting and maintaining the previously set switching frequency, a value greatly deviating from the resonance frequency can be prevented from being set by the switching frequency setting means.

  Further, according to the power conversion device of claim 4 of the present invention, while changing the switching frequency within a predetermined range for resetting the switching frequency, the conversion efficiency is reduced and the generation of noise is induced. However, according to the above configuration, more than 30 days have passed since the previous resetting in order to avoid frequent resetting of the switching frequency, for example, to cope with aging degradation of the step-up transformer and the current resonance capacitor. It can be configured to reset the switching frequency when the input / output power later becomes stable.

1 is a schematic circuit diagram of a fuel cell power generation system using a power conversion device according to an embodiment of the present invention. It is a control flowchart of switching frequency setting.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a fuel cell power generation system using a power conditioner 1 as a power converter according to an embodiment of the present invention. The fuel cell power generation system includes a fuel cell 2 serving as a power source, The power conditioner 1 is mainly composed of a power conditioner 1 that converts DC power output from the fuel cell 2 into low-frequency AC power that is connected to commercial grid power and outputs it to the grid 3.

  As the fuel cell 2, a conventionally known appropriate type such as a solid oxide fuel cell (SOFC) or a polymer electrolyte fuel cell (PEFC) can be adopted.

  The power conditioner 1 includes a current resonance full-bridge converter 4 that constitutes a boosting circuit that boosts a DC voltage output from the fuel cell 2 to a voltage necessary for grid connection with commercial power, and the converter 4 outputs The DC power is converted into AC power connected to the low frequency commercial system power and output to the system 3 through the filter circuit 21, and switching of the switching elements constituting the converter 4 and the inverter 5 is performed. Control unit 6 for controlling the operation, input voltage sensor 7 and input current sensor 8 as input power detection means provided on the input side of converter 4, and output power detection means provided on the output side of converter 4 An output voltage sensor 9 and an output current sensor 10 are provided. In the present embodiment, the output voltage sensor 9 and the output current sensor 10 are provided on the output side of the converter 4 and on the output side of the inverter 5.

  The current resonance full-bridge converter 4 includes a high-frequency full-bridge inverter 11 that converts input DC power from the fuel cell 2 into high-frequency AC power by switching operations of switching elements Q1 to Q4 such as MOSFETs and IGBTs, and the full-bridge inverter 11 A step-up high-frequency transformer 12 whose primary side is connected to the output side, a current resonance capacitor 13 composed of a film capacitor connected in series to the primary side of the transformer 12, and a diode bridge connected to the secondary side of the transformer 12 A rectifier circuit 14, a smoothing capacitor 15 (DC link capacitor) provided on the output side of the rectifier circuit 14, and a smoothing capacitor 16 provided on the input side of the full bridge inverter 11. The current resonance capacitor 13 can also be provided on the secondary side of the transformer 12.

  The full-bridge inverter 11 of the present embodiment is formed by four-bridge connection of four switching elements Q1 to Q4, and the control unit 6 alternately performs high-frequency switching between the set of switching elements Q1 and Q4 and the set of switching elements Q2 and Q3. As a result, the input DC power is converted into high-frequency AC power and output to the primary side of the transformer 12. The switching frequency of each switching element Q1 to Q4 is set in advance so as to coincide with the current resonance frequency determined by the constants of the current resonance capacitor 13, the transformer 12, and the smoothing capacitor 15. In the present embodiment, the switching frequency as a design value is 60 kHz.

  The control unit 6 is mainly composed of a microcomputer, and inputs and outputs based on the output voltage value and output current value detected by the output power detection means and the input voltage value and input current value detected by the input power detection means. Efficiency calculating means 17 for calculating the power conversion efficiency, switching frequency setting means 18 for setting the switching frequency, and switching elements Q1 to Q1 constituting the full bridge inverter 11 based on the switching frequency set by the switching frequency setting means 18 Converter control means 19 that performs drive control of Q4 and inverter control means 20 that performs drive control of a switching element (not shown) of a bridge circuit that constitutes the low-frequency inverter 5 are provided. Each means may be realized by a program executed by a microcomputer, or may be realized by a dedicated circuit or a driver IC provided separately from the microcomputer.

  The efficiency calculating means 17 calculates the input power value as the product of the input voltage detected by the input voltage sensor 7 and the input current detected by the input current sensor 8, and the output voltage and output current sensor detected by the output voltage sensor 9. Based on the output current detected by 10, the active power component of the AC output power can be calculated as the output power value. The ratio of the output power value to the calculated input power value is calculated in real time as the power conversion efficiency.

  The mode of switching control by the converter control unit 19 and the inverter control unit 20 can be conventionally known. In particular, in this embodiment, the converter control unit 19 is stored in the storage unit of the switching frequency setting unit 18. With reference to the switching frequency, a drive pulse based on the frequency is output to each of the switching elements Q1 to Q4. It is only necessary to perform control based on the set switching frequency, and it is not necessary that the frequency of the drive pulse exactly matches the set switching frequency, and dead time control is performed as is well known in the art. In addition, phase shift PWM control may be performed. Furthermore, input / output power suppression control may be performed in the converter 4 by PWM control.

  The inverter control means 20 also performs active power control and reactive power control based on the input power detected by the input power detection means and the output power detected by the output power detection means as conventionally known. In particular, in this embodiment, the input / output power suppression control is performed so that the upper limit of the input current value of the power conditioner 1 becomes a predetermined current value. That is, when the SOFC cell stack is adopted as the fuel cell module, the fuel cell module is generally operated in a state where the power generation output is kept constant near the rated output. Since the thermal balance is maintained and the reaction temperature of the SOFC is maintained at a constant temperature, the power generation efficiency is optimal. Therefore, the control unit of the fuel cell 2 sets a minimum value (for example, 1A) as the command current value when starting the fuel cell 2, and sets a current value (for example, 7A) corresponding to the rated output as the command current upper limit value. Above, gradually increase the command current value until the rated output is obtained, that is, until the current of the generated power reaches the command current upper limit value, and then keep the command current value constant near the command current upper limit value. It is configured. Then, the current command current value is constantly output from the control unit of the fuel cell 2 to the control unit 6 of the power conditioner 1 so that the power conditioner 1 does not make an excessive power request, and the inverter control means 20 Based on the command current value, an upper limit (for example, 6.9 A) of the input current value of the power conditioner 1 is set so as to approach the command current value and not exceed the command current value. The inverter control means 20 controls the low frequency inverter 5 by the feedback control based on it. Thus, in the present embodiment, the inverter control means 20 constitutes the input / output power suppression control means, and by performing the output control by the inverter 5 in this way, the current resonance full bridge converter at the set switching frequency. 4 can be switched, and switching loss and noise can be reduced by zero current switching.

  The switching frequency setting means 18 for setting the switching frequency includes a storage means for storing the switching frequency and an update program for rewriting the switching frequency stored in the storage means. The update program is executed when a predetermined switching frequency resetting condition is satisfied, and the update program is gradually changed within a predetermined frequency range including the current resonance frequency in the current resonance bridge converter 4 at the time of design. The power conversion efficiency is measured by the efficiency calculation means at each frequency point, and the frequency at which the power conversion efficiency becomes maximum after scanning the entire frequency range is reset as the switching frequency in the storage means.

  An example of the control flow for resetting the switching frequency by the switching frequency setting means 18 is shown in FIG. In this embodiment, first, in step S1, it is determined whether or not the state where the input power is in the vicinity of 700 W continues for one minute as the switching frequency resetting condition. This corresponds to the fact that the output voltage of the fuel cell is approximately 100 V and the current value corresponding to the rated output is 7 A, so that the fuel cell is in the rated output state and the input current is reduced by the inverter control means 20. This is a condition for indirectly determining that the state is restricted so as not to rise. Instead of determining that the input power is in the vicinity of 700 W, the switching frequency setting means 18 refers to various control values used by the inverter control means 20 for control, and the current inverter control means 20 outputs It is also possible to directly determine whether or not the power is limited. Whether or not it continues for 1 minute is determined, for example, by measuring the instantaneous input power every second to several seconds, and if the instantaneous input power measured intermittently for 60 seconds is near 700 W, the condition is met It can be. The vicinity of 700 W includes a margin of about 10%.

  Next, in order to change the switching frequency within a range of ± 5 kHz including 60 kHz as a design value, first, the switching frequency is changed to the minimum value of 55 kHz. Note that the variable range of the frequency is different for each system, and the variable range can be designed for each system. The switching frequency of the switching elements Q1 to Q4 becomes 55 kHz in response to the drive pulses of the switching elements Q1 to Q4 by the converter control means 19 by changing the switching frequency. Since the input / output power is temporarily unstable due to such a change in the switching frequency, a predetermined interval is provided in step S3, and the apparatus waits for 1 second, for example.

  Next, in step S4, it is determined again whether the input power remains in the vicinity of 700W. This is because, when the input power is greatly reduced due to a large decrease in power consumption of the power load during the execution of the control flow of FIG. This is because the input / output power fluctuates greatly and the frequency point at which the maximum conversion efficiency is achieved cannot be measured accurately. Here, when it is detected that the input power has greatly decreased from 700 W, the reset control so far is temporarily interrupted, and the process returns to step S1 and waits for another one minute in the vicinity of 700 W.

  Next, in step S5, the power conversion efficiency at the current frequency point is calculated by the efficiency calculating unit 17 and stored in a predetermined storage unit. The power conversion efficiency is preferably calculated as an average value for a predetermined time (for example, 10 seconds).

  Next, the switching frequency is increased by 1 kHz (step S6), and the above steps S3 to S6 are repeated until the switching frequency reaches a maximum of 65 kHz. As a result, since the power conversion efficiency for each frequency point is stored in the storage means, all the power conversion efficiencies measured in step S8 are compared, and the frequency corresponding to the maximum power conversion efficiency is intermediate. Set as maximum efficiency frequency.

  Next, in order to search for the optimum switching frequency with higher accuracy, in step S9, the switching frequency is set to the intermediate maximum efficiency frequency −0.5 kHz, and the same as step S3 to step S7, but the frequency increment. Is set to 0.1 kHz and is repeated until the intermediate maximum efficiency frequency +0.5 kHz (steps S10 to S14).

  Thereafter, all the measured power conversion efficiencies are compared (step S15), and the frequency corresponding to the maximum power conversion efficiency is reset as the switching frequency (step S16).

  After this resetting is performed, it waits until 30 days have passed (step S17), and when 30 days have passed, it returns to step S1.

  According to the power conditioner 1 according to the present embodiment described above, when the fuel cell 2 is in the rated output state in the configuration in which the input / output power control of the inverter 5 is performed so as not to exceed the rated output current of the fuel cell 2. By causing the inverter control means 20 to perform the input / output power suppression control, the switching frequency of the current resonance full bridge converter 4 by the converter control means 19 can be fixed, and the switching frequency setting means can optimize the switching frequency. By setting to, switching loss and noise in high frequency switching of the converter 4 can be reduced. Further, the power conversion efficiency is measured while changing the frequency by setting the execution timing of the resetting of the switching frequency by the switching frequency setting means when the fuel cell 2 is in a stable state at the rated output state. The accuracy can be ensured, and the optimum switching frequency can be set more accurately.

  The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate. For example, the present invention can be applied to a power conditioner for a solar cell. Further, the power conversion device of the present invention can be realized as a DC / DC converter that does not include a low-frequency inverter. In this case, the input / output power suppression control means is provided on the output side of the current resonance bridge converter. An output suppression circuit may be used, or the control means of the current resonance bridge converter may perform PWM control of the drive pulse width of the switching elements Q1 to Q4 so as to suppress the output power of the converter. Even in such a case, by setting the driving pulse frequency (switching frequency) to an optimum value, it is possible to obtain a relatively good efficiency and to suppress the generation of noise as much as possible. In addition, the current resonance bridge converter of the present invention can be configured by a current resonance half bridge converter instead of the current resonance full bridge converter 4 of the above embodiment.

1 Power conditioner (power converter)
2 Fuel cell (DC power supply)
3 systems 4 Current resonance full bridge converter (Current resonance bridge converter)
5 Low Frequency Inverter 6 Control Unit 7 Input Voltage Sensor 8 Input Current Sensor 9 Output Voltage Sensor 10 Output Current Sensor 11 Full Bridge Inverter (Bridge Inverter)
12 Transformer 13 Current resonance capacitor 14 Rectifier circuit 17 Efficiency calculation means 18 Switching frequency setting means 19 Converter control means 20 Inverter control means (input / output power suppression control means)

Claims (4)

A current resonance bridge converter in which switching control is performed based on a preset switching frequency, switching frequency setting means for resetting the switching frequency when a predetermined condition is satisfied, and input / output power for limiting input / output power In a power converter comprising a suppression control means,
The switching frequency setting means resets the switching frequency only when the state where the input / output power restriction is performed by the input / output power suppression control means continues for a predetermined time. It is comprised, The power converter device characterized by the above-mentioned. A current resonance bridge converter that boosts input DC power from a DC power source, a low-frequency inverter that converts DC power boosted by the converter into low-frequency AC power that is connected to the system power and outputs the power to the system, and An electric power conversion device including an input current sensor and an input voltage sensor provided on an input side of a current resonance bridge converter, an output current sensor and an output voltage sensor provided on an output side of the low frequency inverter, and a control unit. The current resonance bridge converter includes a bridge inverter that converts input DC power into high-frequency AC power by a switching operation of a switching element, outputs a transformer, a transformer having a primary side connected to the output side of the bridge inverter, A current resonant capacitor connected in series to the primary side or the secondary side; A rectifier circuit connected to the secondary side of the power supply, and the control unit converts the input / output power conversion efficiency based on the detected values of the input current sensor, the input voltage sensor, the output current sensor, and the output voltage sensor. Efficiency calculating means for calculating, switching frequency setting means for setting the switching frequency, converter control means for controlling the switching element based on the switching frequency set by the switching frequency setting means, and controlling the low frequency inverter The inverter control means, and the converter control means and / or the inverter control means includes an input current detected by the input current sensor, an output current detected by the output current sensor, and an input current detected by the input current sensor. And the input voltage detected by the input voltage sensor. Input / output for limiting input / output power based on at least one of input power and output power detected by the output current sensor and output voltage detected by the output voltage sensor A power suppression control function, wherein the switching frequency setting means changes the switching frequency within a predetermined range when a predetermined condition is satisfied, and sets the switching frequency based on the calculation results of the efficiency calculation means at a plurality of frequency points. In the power converter to be reset,
The switching frequency setting means resets the switching frequency only when the state in which the input / output power restriction is performed by the input / output power suppression control function continues for a predetermined time. It is comprised, The power converter device characterized by the above-mentioned.   3. The power conversion device according to claim 2, wherein the switching frequency setting means is in a state where input / output power is not restricted by the input / output power suppression control function while changing the switching frequency within a predetermined range. When it becomes, the power converter which stops resetting of the said switching frequency.   4. The power conversion device according to claim 1, wherein the switching frequency setting means is configured not to reset the switching frequency until a predetermined period has elapsed since the previous resetting. A power conversion device.

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