JP2014220954A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that allows preventing resonance of an input current.SOLUTION: A power conversion device includes a capacitor connected to an input side, a switching element, a smoothing capacitor connected to an output side, and a control section controlling the switching element, and converts an AC voltage inputted from an AC power supply into a DC voltage by causing the control section to on/off control the switching element. The power conversion device also includes: a sensor circuit obtaining at least one of an AC voltage value and an AC current value inputted from the AC power supply; and a current-resonance detection section detecting whether an AC current of the AC power supply resonates by using data of a sensor value obtained from the sensor circuit. When the current-resonance detection section determines that the AC current resonates, the control section changes control parameters and controls the switching element.

Description

  The present invention relates to a resonance suppression control method for a power conversion device, and more particularly to a resonance suppression method for suppressing resonance due to a capacitor component of an input unit of a power conversion device and an inductance component of a power supply system line input to the power conversion device. is there.

  For example, AC / DC power converters (ACDC converters) as power converters are used in various power electronics products. The ACDC converter switches an AC voltage to generate a DC voltage, but switching noise is included in the AC voltage of the ACDC converter at that time, which adversely affects devices other than the ACDC converter. For this reason, a capacitor is often installed at the input stage of the ACDC converter in order to eliminate noise.

  The circuit configuration of the power conversion device 3 and the external power supply 4 from the system is shown in FIG. Generally, in order to satisfy the noise standard, the power converter 3 is connected to the input side with a noise removing capacitor 2 for the purpose of noise removal.

  By the way, between the external power supply 4 and the power conversion device 3 from the system, there are actually impedance components such as a pole transformer, a low voltage distribution line, a lead-in line, and an indoor electric wiring as shown in FIG. In addition, the above impedance component has a different constant depending on each household. Since this impedance component is usually an inductance component, an equivalent circuit is as shown in FIG.

  When converting from an AC voltage to a DC voltage using the power conversion device 3, as a general control method, for example, there is a method of performing PWM modulation by comparing a voltage (or current) command value with a triangular wave carrier. At this time, due to LC resonance caused by the inductance component 5 of the system and the noise removing capacitor 2 shown in FIG. 19, if there is a disturbance from the system or a harmonic component of the input current near the resonance frequency, the component is amplified. The gain near the resonance frequency as the control system of the entire system of the power conversion device 3 is amplified.

  If this resonance frequency is sufficiently lower than the control frequency or switching frequency of the power converter 3, there is a phase margin, so that it is easy to suppress resonance. In addition, when the resonance frequency is sufficiently higher than the switching frequency of the power converter, there is no phase margin, but the gain is small, so that the input current does not resonate. However, when the gain near the resonance frequency increases and the phase margin becomes zero, the input current resonates and it becomes difficult to suppress.

Conventionally, as a method for suppressing such LC resonance, a technique disclosed in Patent Document 1 is known. This is because the control unit of the power conversion device has a first proportional element that multiplies the deviation signal between the set voltage command value and the capacitor voltage Vc of the LC filter by Kp1 · C, and the output of this proportional element and the capacitor current. A band-pass filter having a second proportional element for multiplying the deviation signal from Ic by Kp 2 · L and a pseudo-differential element for canceling the transfer function of the LC filter is provided, and a control amount and voltage command obtained from the band-pass filter The value V ^* is added to generate a voltage command value V2 ^*, and the generated voltage command value V2 ^* is applied to the LC filter unit.

JP 2012-39827 A

However, the problem handled by the above-described conventional resonance suppression method is only considered for resonance suppression when the switching frequency and the LC resonance frequency are close. When the LC resonance as described above occurs in the frequency response characteristics of the power converter, the gain near the LC resonance frequency increases. At this time, if the phase margin near the resonance frequency becomes zero, resonance cannot be suppressed. Further, when performing power conversion control, there is a time lag such as filtering, sampling delay, calculation processing, etc., until each sensor value is acquired and control calculated based on the acquired value is executed. For this reason, the control amount Vc ^* actually calculated from the control amount Vc necessary for resonance suppression and the sensor value becomes Vc ≠ Vc ^* depending on the frequency component due to filter characteristics, sampling delay, etc. May not be. In order to solve the above problems, an IC or microcomputer that is driven at a sufficiently high frequency with respect to the LC resonance frequency is usually required, but this increases the cost.

  The present invention has been made to solve the above problems, and suppresses resonance of the input current even when LC resonance occurs at a frequency where the phase of the control loop of the entire system exceeds 180 °. An object of the present invention is to provide a power conversion device that can be used.

  The present invention includes a capacitor connected to the input side, a switching element, a smoothing capacitor connected to the output side, and a control unit for controlling the switching element, and an AC voltage input from an AC power source is controlled by the control unit. In the power conversion apparatus that converts the switching element into a DC voltage by controlling on / off of the switching element, the power conversion apparatus includes a sensor circuit that acquires at least one of an AC voltage value and an AC current value input from an AC power source, and a sensor circuit A current resonance detection unit that detects whether or not the AC current of the AC power supply is resonating using the acquired sensor value data, and when the current resonance detection unit determines that the AC current is resonating, The control unit controls the switching element by changing a control parameter.

  According to the present invention, as described above, the power conversion device of the present invention does not require a special circuit, and exhibits the effect that the resonance of the input current can be suppressed by adjusting the control parameter of the control unit.

1 is a block circuit diagram showing a schematic configuration of an entire system from an AC power supply including a power conversion device according to Embodiment 1 of the present invention to a load. It is a figure which shows the current pathway of the whole system from AC power supply including the power converter device by Embodiment 1 of this invention to load. In the power converter device by Embodiment 1 of this invention, it is a figure which shows the image which controls an input electric current to the electric current target value of the power factor 1. FIG. It is a diagram explaining the principle of operation of the power converter device by Embodiment 1 of this invention. It is a control block diagram for demonstrating operation | movement of the power converter device by Embodiment 1 of this invention. It is a figure which shows the actual alternating current waveform by the ideal alternating current waveform controlled by the general power converter device, and the time lag of a control part. It is a figure by the time lag of the control part of a common power converter device. It is a diagram explaining the processing time from the sensor value acquisition start of a general power converter to the control execution start. It is a Bode diagram when there is no resonance frequency of the whole system of a general power converter. It is a Bode diagram when there is a resonance frequency of the whole system of a general power converter. It is a diagram which shows an input current waveform and a target current waveform when the input current of a general power converter is resonating. It is a diagram for demonstrating operation | movement of the current resonance detection part of the power converter device by Embodiment 1 of this invention. It is a Bode diagram for demonstrating operation | movement of the power converter device by Embodiment 1 of this invention. It is a diagram for demonstrating the time transition of the process of the control part of the power converter device by Embodiment 1 of this invention. It is a flowchart which shows the control algorithm of the power converter device by Embodiment 1 of this invention. It is a Bode diagram for demonstrating operation | movement of the power converter device by Embodiment 2 of this invention. It is a block diagram including the system of the input side to which the power converter device by this invention is applied. It is a figure explaining the system | strain on the input side to which the power converter device by this invention is applied. It is a block diagram which shows the whole system to which the power converter device by this invention is applied.

Embodiment 1 FIG.
Hereinafter, the power conversion device according to the first embodiment of the present invention will be described. 1 is a block circuit diagram showing a schematic configuration of an entire system from an external power supply to a load including a power conversion device according to Embodiment 1 of the present invention. As shown in FIG. 1, an AC voltage power source 1 (hereinafter simply referred to as an AC power source 1) as an AC input power source is connected from an external power source 4 to a power conversion device 3 via a system inductance component 5. A noise removing capacitor 2 is connected to the input side of the power conversion device 3, and a diode bridge 6 and a reactor 7 as a current limiting circuit are sequentially connected to the subsequent stage. The switching element 11 and the rectifier diode 9 are connected to the subsequent stage of the reactor 7, and the positive electrode of the smoothing capacitor 8 in the output stage is connected to the cathode side of the rectifier diode 9. The other end of the switching element 11 opposite to the one on the reactor 7 side is connected to the negative electrode of the smoothing capacitor 8.

  An AC voltage detection circuit 31 (SV1) that acquires an input voltage value from the AC power supply 1 is connected in parallel with the AC power supply 1, and an AC current detection circuit 32 (SI1) that acquires an input current value from the AC power supply 1 Is provided. Further, a smoothing capacitor voltage detection circuit 33 (SV2) is provided in parallel with the smoothing capacitor 8.

  The control unit 12 performs on / off control of the switching element 11 by the control line 40. In addition, the control unit 12 receives the voltage value or current value as a sensor value from the sensor circuit such as the AC voltage detection circuit 31, the AC current detection circuit 32, and the smoothing capacitor voltage detection circuit 33 by the signal lines 41a, 41b, and 41c. Get as. Moreover, the power converter device 3 includes a current resonance detection unit 13 that detects that the alternating current is resonating. The current resonance detection unit 13 inputs data of at least one sensor value of each sensor value acquired from the sensor circuit by the control unit 12 from the signal line 42a, and the control current resonates based on the input sensor value data. And the determination result is notified to the control unit 12 through the signal line 42b.

ここで、Vacは交流電圧検出回路３１（ＳＶ１）において測定される入力電圧、Vdcは電力変換装置３の出力電圧、V_Lはリアクトル７にかかる電圧である。 Here, the operation principle of the power conversion device according to Embodiment 1 will be described. The power conversion device 3 in FIG. 1 passes through the current paths shown in FIG. 2 by turning on and off the switching element 11. The relationship between the voltages in each current path shown in FIG. 2 can be expressed by Expression (1). The duty _ON in the equation represents the duty ratio of the switching element (ON ratio, 0 to 1).

Here, Vac is an input voltage measured in the AC voltage detection circuit 31 (SV1), Vdc is an output voltage of the power converter 3, and V _L is a voltage applied to the reactor 7.

ここで、ｅ：誘導起電力、ｉ：電流、Ｌ：インダクタンス Here, the voltage V _L (corresponding to the induced electromotive force) applied to the reactor 7 for the input current to follow the input current target value of the power factor 1 can be obtained from the equation (2) which is a relational expression of inductance. . Thus, the duty ratio when switching the switching element 11 is controlled so as to apply _VL to the reactor 7 to control the input current. This image is shown in FIG.

Where e: induced electromotive force, i: current, L: inductance

The power converter 3 operates as a chopper circuit that boosts the voltage (= Vac−V _L ) applied to the previous stage of the switching element 11 to Vdc. If the switching off-duty is duty _OFF (= 1-duty _ON ), the step-up ratio at this time can be obtained from the following equation (3).

That is, the on-duty duty _ON can be calculated as in Expression (4) by determining the off-duty when switching the switching element 11 from Expression (3). By operating with this on-duty duty _ON , the input current is controlled.

FIG. 3 shows an image for controlling the input current to a current target value with a power factor of 1. Further, a diagram for explaining the operation principle is shown in FIG. 4A shows the input voltage Vac, the input current target value Iac ^* , and the output voltage Vdc, FIG. 4B shows the on / off state of the switching element 11, and FIG. 4C shows the voltage applied to the reactor 7. V _L , FIG. 4 (d) shows the input current Iac. An input voltage Vac is applied to the reactor 7 when the switching element 11 is operated and the switching element 11 is on, and (input voltage Vac−output voltage Vdc) is applied when the switching element 11 is off. When voltage is applied to reactor 7, input current Iac flows according to equation (2). As shown in FIG. 4D, the input current Iac increases when the switching element 11 is switched on and decreases when the switching element 11 is off.

Next, FIG. 5 shows a control calculation block diagram of the power conversion device 3 of the first embodiment. That is, the control unit 12 adds a predetermined control gain to the deviation signal between the target value Iac ^* of the alternating current and the measured alternating current value Iac (PI in FIG. 5), and the target of the voltage V _L to be applied to the reactor 7. Find the value. Thereafter, the duty of the switching element is calculated by the equations (3) and (4). According to the control calculation block of FIG. 5, the alternating current Iac of the alternating current power source 1 can be controlled to a desired current waveform. Here, a mechanism in which an alternating current resonates by the noise removing capacitor 2 of the power conversion device 3 and the inductance component 5 of the system will be described. First, according to the control block diagram of FIG. 5, the alternating current is controlled so as to follow the alternating voltage (following the current target value of power factor 1). However, as shown in FIG. 6, in practice, a delay due to arithmetic processing, a filter circuit, and the like occurs after the sensor value is acquired until the control is executed. For this reason, as shown in FIG. 7, the AC current to be controlled follows the AC voltage of the AC power supply 1 with a slight delay.

  When an ideally controlled alternating current waveform is FFTed, in addition to the frequency of the alternating current power supply 1, there are a frequency component of a control frequency, a switching frequency, and a frequency component of a harmonic of the control frequency and the switching frequency. However, in practice, the AC current waveform is slightly delayed (or slightly shifted) from the AC voltage waveform, and therefore, harmonic components of the AC power supply are generated in addition to the above frequency components. If this harmonic component is amplified by LC resonance, it may oscillate and become uncontrollable.

  In general, as illustrated in FIG. 8, the control unit 12 acquires each sensor value before performing current control, and performs arithmetic processing using the acquired AD value. For this reason, a delay of Ts occurs between each current / voltage value of the power conversion device 3 and the sensor value subjected to AD sampling at the time when the control execution is started. For this reason, the gain of the frequency characteristic of the power converter 3 drops from a certain frequency band as shown in FIG.

  Next, when LC resonance with the inductance component 5 of the system occurs, the Bode diagram of the power converter 3 increases the gain near the resonance frequency as shown in FIG. At this time, if there is no phase margin in the frequency band where the gain has increased, the AC current will resonate, and in the worst case, the AC current may be damaged by the overcurrent of the AC current. FIG. 11 shows an image of a current waveform in which alternating current resonates. The above is the mechanism by which alternating current resonates.

式（５）により求めた電流波形の共振周波数が所定の範囲内（f_1TH＜f＜f_2TH）であると、電流共振検出手段は次のステップに移行する。 Next, a resonance detection method of the current resonance detection unit 13 of the power conversion device 3 will be described. The current resonance detection unit 13 obtains a difference between the sensor value Iac of the alternating current during operation of the power conversion device 3 and the target value Iac ^* of the control unit 12, and detects zero crossing. The time T from the zero cross detection to the next zero cross detection is measured, and the resonance frequency of the alternating current is obtained by the equation (5).

When the resonance frequency of the current waveform obtained by the equation (5) is within a predetermined range (f _1TH <f <f _2TH ), the current resonance detecting means moves to the next step.

計算した結果、ΔIacの値が所定の閾値I_THより大きい場合、電流共振検出部１３は交流電流が共振したと判定する。以上の、交流電流のセンサ値Iacと制御部１２の目標値Iac^*との差のゼロクロス、およびピーク値のイメージを図１２に示す。 In the next step, the peak value ΔIac of the difference between the sensor value Iac of the alternating current and the target value Iac ^* is calculated by the equation (6).

As a result of the calculation, when the value of ΔIac is larger than the predetermined threshold value I _TH , the current resonance detector 13 determines that the alternating current has resonated. FIG. 12 shows an image of the zero crossing and peak value of the difference between the sensor value Iac of the alternating current and the target value Iac ^* of the control unit 12 described above.

  In the above description, the example in which resonance is determined using the sensor value Iac of the AC current detection circuit 32 has been described. However, even if the sensor value of the AC voltage detection circuit 31, that is, the AC voltage value, is used, the resonance similarly occurs. Can be determined. When resonance occurs, not only the current but also the input of the power conversion device 3, that is, the voltage at both ends of the noise removal capacitor becomes a waveform in which the resonance waveform is superimposed. Therefore, for example, from the difference between the ideal AC voltage waveform when no resonance has occurred and the sensor value of the AC voltage detection circuit 31, the zero cross and peak values are obtained in the same manner as in the case of the current described above. Can be determined.

  Next, a control method of the control unit 12 when the current resonance detection unit 13 determines that the alternating current has resonated will be described. As described above, since there is a delay from when the sensor value is acquired to when control is actually started, a harmonic component of the alternating current is generated, and the frequency characteristic of the power conversion device 3 is from a certain band. Gain falls. When the time from the start of sensor value acquisition to the execution of control based on the acquired sensor value is shortened, the level of the harmonic component decreases, and the level of the resonance peak due to LC resonance also decreases. Further, the frequency characteristic of the power conversion device 3 moves to the high frequency side in order to follow the frequency characteristic to a higher frequency band. For this reason, the phase margin becomes zero due to the LC resonance, so that the phase margin is provided even in the band where the AC current resonance has occurred, and the resonance of the AC current does not occur. This is shown in FIG. The Bode diagram before shortening the time until the control based on the acquired sensor value is started after the thin solid line in FIG. 13 starts acquiring the sensor value, and the control is executed after the thick solid line starts acquiring the sensor value. It is a Bode diagram after shortening time to do.

  FIG. 14 shows the time transition of the processing of the control unit before changing the time from the start of acquiring the sensor value to executing the control (Ts) and after changing and shortening (Ts ′). As shown in FIG. 14, before changing, the sensor value acquisition is started by shifting processing other than the calculation processing for controlling based on the sampling of the sensor value and the acquired sensor value to another timing. It is possible to shorten the time until the control based on the sensor value acquired from the above is executed.

FIG. 15 is a flowchart showing a resonance suppression control algorithm. First, in step S10, the current resonance detection unit 13 obtains a difference Iac−Iac ^* between the sensor value Iac of the alternating current during operation of the power conversion device 3 and the target value Iac ^* of the control unit 12, and detects a zero cross. Next, in step S20, a time T from the zero cross detection to the next zero cross detection is measured to obtain the resonance frequency of the alternating current, and in step S30, it is determined whether or not the resonance frequency is within a predetermined range. . If it is determined in step S30 that the resonance frequency is within the predetermined range, the process proceeds to step S40. On the other hand, if it is determined in step S30 that the resonance frequency is outside the predetermined range, the resonance determination is terminated. In step S40, the peak value ΔIac of the difference Iac−Iac ^* between the sensor value Iac of the alternating current and the target value Iac ^* is calculated. Next, in step S50, it is determined whether or not ΔIac is greater than a predetermined threshold value Ith. If it is determined in step S50 that ΔIac is greater than the predetermined threshold value Ith, the current resonance detector 13 determines in step S60 that the alternating current is resonating. When the current resonance detection unit 13 determines that the alternating current is resonating, the control unit 12 changes the reading timing of each sensor value in step S70.

  In the above embodiment, the sensor reading timing is changed when resonance occurs, and the time from sensor reading to control execution is shortened. However, the present invention is not limited to this. The time from sensor reading to control execution may be shortened by increasing the frequency itself.

Embodiment 2
Hereinafter, a power converter according to Embodiment 2 of the present invention will be described. In the first embodiment, the sensor reading timing is changed as a resonance suppression method. However, since the processing capability of the microcomputer is limited, there is a limit to the movement of the frequency characteristics to the high frequency side. For this reason, even if the reading timing of the sensor is changed, if the gain of the power conversion device 3 exceeds 0 dB and the phase is −180 ° or less due to an increase in gain near the resonance frequency, the alternating current resonates. May end up.

  In such a case, if the current resonance detection unit 13 determines that the alternating current is resonating, the control unit 12 decreases the control gain, which is the PI term in FIG. As a result, as shown in FIG. 16, the gain of the frequency characteristic of the power conversion device 3 decreases, the increase in gain due to LC resonance decreases, and the alternating current resonates even if the phase is −180 ° or less and there is no phase margin. To prevent that.

  In the above description, the resonance is suppressed by lowering the control gain when resonance occurs. However, the present invention is not limited to this. For example, the input power can be reduced by suppressing the output power of the power converter when the resonance occurs. The gain may be suppressed by reducing the current.

  If it is determined that the alternating current is resonating, first, the sensor reading timing is changed as in the first embodiment, and the resonance continues even if the sensor reading timing is changed to the limit of the capability of the microcomputer or IC. In this case, the control gain may be lowered or the output power of the power conversion device may be suppressed as in the second embodiment.

  In the second embodiment, even if the ability of the microcomputer or IC is not high, an effect that the resonance of the alternating current can be suppressed is obtained.

  As described above, as described in the first and second embodiments, according to the present invention, when the current resonance detection unit 13 determines that the alternating current is resonating, the control unit 12 starts the sensor value acquisition start. The control parameters such as the time until the start of control execution, the control frequency, and the gain are changed to suppress the resonance of the alternating current.

Embodiment 3
Hereinafter, a power converter according to Embodiment 3 of the present invention will be described. In Embodiment 3, when the current resonance detection unit 13 of the control unit 12 determines that the alternating current is resonating, the operation itself of the power conversion device 3 is stopped as a fail-safe function. In particular, it is effective to stop the operation of the power conversion device 3 when resonance continues even if the resonance suppression measures of the first and second embodiments are taken.

  In each of the above embodiments, the current resonance determination method of the current resonance detector 13 determines whether or not the resonance of the alternating current is generated based on the difference between the sensor value and the target value. It is not limited to. For example, the sensor value data of the AC current detection circuit 32 and the AC voltage detection circuit 31 may be taken and subjected to FFT conversion, and it may be determined that resonance occurs when a spectrum in a predetermined frequency band exceeds a predetermined threshold.

  In addition, although the power converter device of each said embodiment is set as the structure which used the diode bridge for the input stage, it is not restricted to this, For example, a semi-bridge structure may be sufficient.

  In addition, although the power converter device of each said embodiment demonstrated the step-up circuit, it is not restricted to this, For example, a step-down circuit may be sufficient.

1 AC power supply, 2 noise removing capacitor, 3 power converter,
4 external power supply, 5 system inductance components, 6 diode bridge, 7 reactor, 8 smoothing capacitor, 9 rectifier diode, 10 load, 11 switching element, 12 control unit, 13 current resonance detection unit, 31 AC voltage detection circuit, 32 AC Current detection circuit, 33 smoothing capacitor voltage detection circuit, 40 control line, 41a to 41c signal line, 42a to 42b signal line

As the power converter, for example, AC-DC power converter (ACDC converter) is used in various power electronics products. The ACDC converter switches an AC voltage to generate a DC voltage, but switching noise is included in the AC voltage of the ACDC converter at that time, which adversely affects devices other than the ACDC converter. For this reason, a capacitor is often installed at the input stage of the ACDC converter in order to eliminate noise.

The present invention includes a capacitor connected to the input side, a switching element, a smoothing capacitor connected to the output side, and a control unit for controlling the switching element, and an AC voltage input from an AC power source is controlled by the control unit. In the power conversion apparatus that converts the switching element into a DC voltage by controlling on / off of the switching element, the power conversion apparatus includes a sensor circuit that acquires at least one of an AC voltage value and an AC current value input from an AC power source, and a sensor circuit. A current resonance detection unit that detects whether or not the AC current of the AC power supply is resonating using the acquired sensor value data, and when the current resonance detection unit determines that the AC current is resonating, control unit, the sensor value acquisition start by the sensor circuit, the time to control the switching element based on the acquired sensor value, By transferring the processing other than processing to control based on the sampling and acquired sensor value capacitors values from the sensor value acquisition start timing other than the timing to control the switching element, controls the switching element is shortened To do.

According to the present invention, as described above, the power conversion device of the present invention does not require a special circuit, and has the effect of suppressing the resonance of the input current by changing the control process of the control unit.

Claims (10)

A capacitor connected to the input side; a switching element; a smoothing capacitor connected to the output side; and a control unit that controls the switching element, wherein the control unit receives the AC voltage input from an AC power source. In a power conversion device that converts to a DC voltage by on-off control of a switching element,
The power converter includes a sensor circuit that acquires at least one of an AC voltage value and an AC current value input from an AC power source, and the AC current of the AC power source resonates using sensor value data acquired from the sensor circuit. A power resonance detecting unit that detects whether or not the power resonance is detected, and the control unit controls the switching element by changing a control parameter based on a determination result of the current resonance detecting unit. apparatus.   When the current resonance detection unit determines that the alternating current is resonating, the control unit starts the sensor value acquisition by the sensor circuit and controls the switching element based on the acquired sensor value. The power conversion device according to claim 1, wherein the time is changed.   When the current resonance detection unit determines that the alternating current is resonating, the control unit starts the sensor value acquisition by the sensor circuit and controls the switching element based on the acquired sensor value. The power conversion device according to claim 2, wherein the time is shortened.   The power conversion device according to claim 2, wherein when the current resonance detection unit determines that the alternating current is resonating, the control unit increases the control frequency. The control unit is configured to calculate a duty of the switching element by adding a predetermined control gain to a deviation signal between the target value Iac ^* of the alternating current and the measured alternating current value Iac, and the current resonance detecting unit However, when it is determined that the alternating current is resonating, the control gain is reduced.   2. The power conversion device according to claim 1, wherein when the current resonance detection unit determines that the alternating current is resonating, the control unit controls the switching element to suppress output power. .   The power conversion device according to claim 1, wherein when the current resonance detection unit determines that the alternating current is resonating, the control unit stops the operation of the switching element. The current resonance detection unit measures a time interval at which the alternating current target value Iac ^* and the alternating current value Iac cross each other, obtains a resonance frequency of the alternating current from the measured time, and the resonance frequency is a predetermined value. If it exists in a frequency range, it will determine with alternating current resonating, The power converter device of any one of Claims 1-7 characterized by the above-mentioned. The current resonance detection unit determines that the alternating current is resonating when a difference between the target value Iac ^* of the alternating current and the alternating current value Iac exceeds a predetermined threshold. 8. The power conversion device according to 8.   The current resonance detection unit performs FFT conversion on the alternating current value acquired from the sensor circuit, and determines that the alternating current is resonating when a current spectrum value in a predetermined frequency band exceeds a predetermined threshold. The power converter according to any one of claims 1 to 7, wherein

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